Essential Notes for MRCS - Book 2(A)

Assessing LV function
Echocardiography: provides an estimate of ejection fraction and can assess valvular structure and
regions of ventricular wall akinesis suggestive of previous ischaemic damage.

Combined cardiopulmonary testing (CPET): this is a programmed exercise test on a cycle or treadmill
with measurement of inspired and expired gases. It assesses peak oxygen consumption and anaerobic
threshold and provides an objective measurement of functional capacity.

Always bear in mind that a patient may need his or her cardiac condition optimised by a cardiologist.
This may require pharmacological measures such as β–blockers, statins or ACE inhibitors, all of which
have been shown to improve surgical outcomes in different groups of patients. It may be necessary to
arrange angioplasty, coronary artery bypass graft (CABG) or valvular surgery before other elective
procedures are attempted.

Intraoperative considerations for patients with cardiac disease

Cardiac effects of general anaesthesia (GA) include:
Systemic vascular resistance decreases (induction decreases arterial pressure by 20–30%) • Tracheal
intubation decreases BP by 20–30 mmHg
Causes myocardial depression (IV agents less than inhaled agents) • Cardiac irritability increases
(increased sensitivity to the catecholamines released in response to surgery predisposes to arrhythmia)

Cardiac effects of regional anaesthesia include:
Vasodilatation (blocks sympathetic outflow)
May be combined with GA for pain control

Ischaemic heart disease

Preoperative considerations

Known risk factors must be identified in the history (eg smoking, hypertension, hyperlipidaemia, diabetes,
including a positive family history). A careful examination of the heart and lungs must be performed.
Remember that ischaemia may be silent.



New York Heart Association (NYHA) classification
Grade 1 No limitation on ordinary physical activity Grade 2 Slight limitation on physical activity;
ordinary activity results in palpitations, dyspnoea or angina Grade 3 Marked limitation of physical
activity; less than ordinary activity results in palpitations, dyspnoea or angina Grade 4 Inability to
carry out any physical activity without discomfort; symptoms may be present at rest

A recent myocardial infarction (MI) dramatically increases the risk of re-infarction in the perioperative
period, ie 80% in the first 3 weeks, 25–40% in the first 3 months and 10–15% in 3–6 months. After 6
months the risk drops to 5% and is normally the minimum time period that is an acceptable risk for an
elective procedure. Obviously the risk must be balanced against any potential benefit of a surgical
procedure.

Hypertension



Causes of hypertension
Essential hypertension
Pain
Anxiety (eg white-coat hypertension)
Fluid overload
Hypoxia and hypercapnia

If the diastolic blood pressure is >110 mmHg then elective procedures should be discussed with the
anaesthetist and possibly postponed until better control can be achieved. After appropriate pain relief
take three separate BP readings, separated by a period of at least 1 hour, to help exclude anxiety or
discomfort as a cause.

Newly diagnosed hypertension must be assessed for possible reversible aetiological factors (eg renal
disease, endocrine diseases such as phaeochromocytoma, pregnancy, the OCP and coarctation of the
aorta).

Chronic (long-standing) hypertension puts the patient at increased risk of cardiovascular disease,
cerebrovascular events and renal impairment. These patients are also at higher risk of hypertensive
crises. These conditions need to be excluded or optimised, if possible, before an elective surgical
procedure. LVH (whether clinically, radiologically or electrocardiographically detected) is directly
related to myocardial ischaemia. Poorly controlled hypertension in the immediate pre-op period
predisposes the patient to perioperative cardiac morbidity and must be avoided.

Valvular disease

Patients with valvular disease are susceptible to endocarditis if they become septic. Prophylactic
antibiotics are important. They may also be on long-term anticoagulation.

Aortic stenosis

Associated with a 13% risk of perioperative death (risk increases with increasing stenosis to 50% for
patients with critical aortic stenosis). Symptomatic aortic stenosis (AS) produces syncope, dyspnoea and
angina. On examination there may be an ejection systolic murmur (radiates to the carotids), a soft or
absent second heart sound, and pulsus parvus. The valve needs assessing with echocardiography (valve
area <1 cm2 or gradient of >50 mmHg indicates critical AS).

Mitral stenosis

May predispose to pulmonary hypertension and right cardiac failure. Clinically look for mitral facies,
diastolic murmur and atrial fibrillation (AF) (increased pressure chronically enlarges the left atrium).
Must be given prophylactic antibiotics for invasive procedures. Minimise fluid overload and changes in
cardiac rate.

Arrhythmias

Atrial fibrillation

Common arrhythmia giving an irregularly irregular beat. Due to short-circuiting of the electrical impulses
of the atria resulting in disorganised muscle contraction. Causes reduced efficiency of the atria to pump-
prime the ventricles.



Common causes of atrial fibrillation
Acute causes
Fluid overload
Sepsis (especially chest)
Ischaemic event
Alcohol
Pulmonary embolism (PE)
Dehydration
Thyrotoxicosis
Chronic causes
Ischaemic or valvular disease



Questions to ask yourself about each case of AF
Is it reversible?
Acute: may be reversible (consider ways to reduce or remove causes listed above) • Chronic: rarely
reversible (eg irreversibly dilated atria, ischaemic disease)
Is the rate compromising cardiac output?
Indication of the need for and the speed of intervention; consider oral medication (eg digoxin) vs IV
medication (eg amiodarone) vs DC cardioversion
Does the patient need anticoagulating?
AF predisposes to thrombotic events (blood in the auricles of the atria moves sluggishly and forms clots
which are then expelled into the systemic circulation – commonly causing a cerebrovascular accident
[CVA])

Pacemakers and implanted ventricular defibrillators

Problems during the surgical period include:
Interactions with diathermy current: electrical interference with device (eg causing resetting, rate increases
or inhibition); current travelling down wires and causing myocardial burn
Effect of anaesthetic agents on pacing and sensing thresholds • Problems with rate control devices; may not
allow physiological responses (eg tachycardia)



Ask yourself the following questions about the device
Reason for insertion?
Continuous or demand model?
If continuous, is it working optimally (ie is the ECG showing captured beats – large electrical spike

seen before each ventricular contraction)?

Patients should have the pacemaker evaluated by cardiology before and after surgery because they will
be able to assess and advise on any changes required to the settings.

Always use bipolar diathermy if possible and check for deleterious effects. Unipolar diathermy current
may pass down pacing wires, causing cardiac burns so advice should be sought from the cardiologist if
unipolar diathermy is thought to be necessary.

Cardiac failure

Due to acute or chronic ischaemic or valvular disease
Exercise tolerance is a good indictor of cardiac reserve; ask: • How far can you walk?
• Can you manage a flight of stairs without getting short of breath?
Morbidity and mortality increase proportionally to severity of congestive cardiac failure (CCF) • Ask for a
cardiology review in order to optimise fully (eg ACE inhibitors, diuretics) before surgery

Care with fluid management in the perioperative period is essential – remember that these patients may
require their regular diuretics.

2.3 Preoperative management of respiratory disease



In a nutshell ...

Respiratory disease commonly includes chronic pulmonary obstructive disease (COPD), asthma, cystic
fibrosis, bronchiectasis and infections

Optimise any reversible component of the condition and avoid surgery during infective exacerbations of
the disease • Encourage smoking cessation (even if just for 24 hours preoperatively)
Note that patients with respiratory disease may be on regular long-term steroids.

Chronic obstructive pulmonary disease and asthma

COPD is pathologically distinct, but frequently coexists with bronchospasm. It may be difficult to
determine the importance of each condition in an individual. Generalised airflow obstruction is the
dominant feature of both diseases.

History and examination of patients with COPD/asthma

Questions should be directed at:
Patient’s exercise tolerance (eg walking distance on the flat) • Any recent deterioration resulting in
hospital admission
Previous admission to ITU for ventilation
Need for home oxygen, and present medical therapy (eg need for steroids) • Current smoking habit, or
when smoking was stopped
Changes on examination (eg are they consistent with chronic lung disease/focal infective exacerbations)

Investigation of COPD and asthma

Assess baseline levels with lung function tests:
Forced expiratory volume in 1 s/forced vital capacity (FEV1/FVC) ratio (if <50% the risk of postop
respiratory failure is increased)
Arterial blood gases (ABGs) confirming CO2 retention in pure chronic bronchitis • Sputum cultures and
sensitivity in the presence of a productive cough • Chest radiograph

Management of COPD and asthma

Give preoperative salbutamol (nebulisers)
Must treat any reversible component (eg infective exacerbations) • Consider regional anaesthesia for body
surface/lower extremity surgery • Intraoperative nitrous oxide can rupture bullae, leading to a tension
pneumothorax, so use opiates in doses that are not associated with pronounced respiratory depression
Ensure humidification of inspired gases
Postoperatively, offer advice about smoking; provide chest physiotherapy; administer continuous positive
airway pressure (CPAP) in an HDU setting; provide adequate pain relief allowing deep breathing and
early mobilisation; nurse in an upright position in bed, monitoring oxygen saturation

Hypoxia in the perioperative setting is most commonly due to inadequate ventilation or respiratory
depression with opiates rather than loss of hypoxic drive due to prolonged high-concentration oxygen
therapy. However, the latter should always be borne in mind when dealing with patients with chronic
respiratory disease.

Tuberculosis

Many patients have evidence of old TB disease or previous anti-TB surgery on chest radiography. This is
not usually a problem, but the resulting lung change and reduced respiratory capacity may need
consideration.

Active TB should be considered in recent immigrants from areas where TB is endemic, and in
immunosuppressed and HIV patients. They may require preoperative chest radiography, sputum culture,
Mantoux testing (if they haven’t had previous BCG) and treatment if appropriate.

Bronchiectasis and cystic fibrosis

Preoperative sputum culture and ABG are needed to act as baseline information. Input from respiratory
physicians is advisable.

Active physiotherapy, bronchodilators and treatment of residual infections are required before elective
surgery. Postoperative physiotherapy at least three times per day is essential.

Smoking

Short-term effects of smoking

Nicotine increases myocardial oxygen demand

Carbon monoxide reduces oxygen delivery by binding to haemoglobin • Carboxyhaemoglobin levels fall if
stopped before 12 h pre-surgery • High carboxyhaemoglobin can give false pulse oximetry readings •
Airway irritability and secretions are increased

Long-term effects of smoking

Reduces immune function, increases mucus secretion
Reduces clearance and causes chronic airway disease (cessation needs to be longer than 6–8 weeks to
bring about an improvement) • Increased risk of ischaemic heart disease

Intraoperative considerations in patients with respiratory disease

Site and size of incision

Upper abdominal incisions result in an inability to breathe deeply (basal atelectasis) or to cough (retained
secretions), and have a higher incidence of respiratory complications compared with lower abdominal
incisions (30% vs 3%). In patients with known respiratory disease, think about the optimal incision site
(eg transverse rather than midline).

Analgesia

Optimise analgesia using a combination of local and regional techniques to allow deep breaths and
coughing as required. Remember local infiltration intraoperatively. Infiltration of local anaesthesia (LA),
eg Chirocaine, into the rectus sheath is helpful in upper midline incisions in those with compromised
respiratory function.

Anaesthetic agents

Anaesthetic agents have the following effects:
Reduce muscle tone and thus functional residual capacity
Increase airway resistance and reduce lung compliance
Cause atelectasis in dependent zones of the lung, resulting in pulmonary vascular shunting • Increase
ventilatory dead space

2.4 Preoperative management of endocrine disease



In a nutshell ...

Diabetes mellitus
Thyroid problems
Parathyroid problems

Preoperative management of diabetes mellitus

Perioperative management of diabetes mellitus
Avoid hypoglycaemia (especially under anaesthesia – risk of cerebral damage) • Avoid hyperglycaemia
(osmotic diuresis and dehydration)
Supply enough insulin (prevent ketoacidosis)
Be aware of increased risks of postoperative complications (infective, arteriopathic, etc)

Reasons for good glycaemic control

Prevention of ketosis and acidaemia
Prevention of electrolyte abnormalities and volume depletion secondary to osmotic diuresis • Impaired
wound strength and wound healing when plasma glucose concentration is >11 mmol/l • Hyperglycaemia
interferes with leucocyte chemotaxis, opsonisation and phagocytosis, and so leads to an impaired immune
response • Avoidance of hypoglycaemia in an anaesthetised patient

Preoperative precautions in patients with diabetes

Full pre-op history and examination (diabetes is associated with increased risk of IHD, hypertension,
peripheral vascular disease [PVD], autonomic and peripheral neuropathy, renovascular disease and renal
failure, impaired vision, susceptibility to gastric reflux and delayed gastric emptying) • Check U&Es
ECG
Confirm adequate glycaemic control (see below)

Perioperative precautions in patients with diabetes

Place first on operating list (reduces period of starvation and risk of hypoglycaemia) • Protect pressure
areas (especially with PVD and neuropathy)
At risk of increased infection and arteriopathic disease (renal, cardiac, neurological, peripheral)
postoperatively • Involve patients themselves in the management of their diabetes during this period; they
are usually very knowledgeable and have managed their disease for a long time


Assessment of pre-op control of diabetes
Daily glucose measurements from the patient’s diary
HbA1c measurement (assesses glycaemic control over the last 8 weeks by measuring levels of glycation
of haemoglobin) • Good control <6.5% (<48 mmol/mol)
Adequate control 6.5–8.0% (48–64 mmol/mol)
Poor control >8.0% (>64 mmol/mol)
The normal HbA1c reference range for a non-diabetic patient is 4.0–6.0% (20–42 mmol/mol)

Management of diabetes

Management of type 2 diabetes mellitus
Optimise control preoperatively and continue normal oral hypoglycaemic control until the morning of
surgery (except chlorpropamide and metformin, which may need to be reduced or stopped 48 hours in

advance – can predispose to lactic acidosis). Postoperatively monitor BM regularly and institute a sliding
scale of intravenous insulin if the patient is unable to tolerate an oral diet immediately. Restart patients
back on their normal oral hypoglycaemic regimen as soon as an enteral diet is recommenced.

Management of type 1 diabetes mellitus
Achieve good pre-op control and admit the patient the night before surgery. Monitor the patient’s BM
from admission, and commence the patient on a sliding scale of insulin on the morning of surgery. Restart
regular insulin once the patient is eating and drinking normally and observe closely for sepsis. Only
discharge the patient once his or her control is within recognised limits because the insulin requirements
may well increase transiently after a stressful stimulus such as surgery.

Preoperative management of thyroid problems

For more details of thyroid physiology, pathology and management, see the chapter on Endocrine Surgery
in Book 2. Problems associated with thyroid disease include:
Local effects: eg large thyroid goitre can cause vocal fold palsy (recurrent laryngeal nerve damage),
airway compromise (dyspnoea and stridor), laryngeal deviation and difficult intubation
Hormonal effects: problems arise in patients with poorly controlled hypothyroidism or hyperthyroidism
undergoing major emergency procedures (see Endocrine Surgery in Book 2)

Hyperthyroidism

This should be controlled before surgery:
Propylthiouracil decreases hormone synthesis (but increases vascularity) • Potassium iodide reduces gland
vascularity
Propanolol reduces systemic side effects of thyroxine

Increased risks associated with lack of pre-op preparation:
Cardiac: tachycardia, labile BP, arrhythmia
‘Thyroid crisis’ can be precipitated by surgery. This is a syndrome of excessive and uncontrolled thyroxine
release which may result in hyperthermia, life-threatening cardiac arrhythmia, metabolic acidosis, nausea,
vomiting and diarrhoea, mania and coma

Hypothyroidism

Hypothyroidism reduces physiological responses:
Low cardiac output and increased incidence of coronary artery disease (hyperlipidaemia) • Blood loss
poorly tolerated
Respiratory centre less responsive to changes in O2 and CO2 partial pressures • Sensitive to opiate
analgesia

Hypothyroidism carries increased risks of:
Myocardial ischaemia
Hypotension
Hypothermia
Hypoventilation

Hypoglycaemia
Hyponatraemia
Acidosis

Preoperative management of parathyroid problems

For more details of parathyroid physiology, pathology and management, see Chapter 4, Endocrine surgery,
Book 2.

Hyperparathyroidism

Primary hyperparathyroidism is due to a secretory parathyroid adenoma • Secondary hyperparathyroidism
is parathyroid hyperplasia due to chronic hyperstimulation • Tertiary hyperparathyroidism is autonomous
hypersecretion


Problems in hyperparathyroidism
Increased calcium levels; decreased phosphate levels.
Increased risks of:
Renal impairment (needs careful rehydration and fluid balance, monitoring of catheter and central
venous pressure [CVP] line) • Urinary calcium excretion (which may be enhanced by judicious use of
diuretics) • Hypertension
Hypercalcaemic crisis (may occur in elderly people or in those with malignant disease)

Hypoparathyroidism


Problems in hypoparathyroidism
Decreased calcium levels; increased phosphate levels.
Increased risks of:
Stridor
Convulsions
Decreased cardiac output
Manage with careful IV calcium replacement.

2.5 Preoperative management of neurological disease



In a nutshell ...

Epilepsy
Cerebrovascular disease
Parkinson’s disease

Preoperative management of epilepsy

Aim to avoid seizures in the perioperative period by minimising disruption to the maintenance regimen of
medication:
Avoid disturbances of gastrointestinal (GI) function (affects medication absorption and electrolyte balance
• Give usual medications up to the point of surgery
Replace oral medications with parenteral formulations if required • Neurology advice may be required for
patients whose epilepsy is hard to control

Preoperative management of cerebrovascular disease

Avoid changes in BP (hypo-/hypertension) and manage fluids carefully because patients with arteriopathy
have a relatively rigid vascular system
Continue anticoagulants in the form of heparin unless contraindicated • Position neck to avoid syncope
Examine and carefully document preoperative and early postoperative neurological status • Delay elective
surgery if there has been a recent CVA (risk of subsequent CVA increased 20-fold if surgery is performed
in <6 weeks; aim to wait for 6 months)
Indications for carotid endarterectomy (see Chapter 9, Vascular Surgery in Book 2)

Preoperative management of Parkinson’s disease

Parkinson’s disease is due to reduced dopaminergic activity in the substantia nigra (may be degenerative,
drug-induced, post-traumatic). Typical symptoms include tremor, postural instability, rigidity and
dyskinesia.

Perioperative issues include:
Compromised respiratory function
Urinary retention
Confusion, depression, hallucinations
Difficulties with speech and communication



Preoperative medications and Parkinson’s disease
Patients with Parkinson’s disease are often on multiple medications and this must be managed carefully.
They are at risk of drug interactions. Timing of medications must be optimised to allow the best control
of the condition during waking hours (‘on’ and ‘off’ periods) because symptoms occur rapidly if doses
of regular medications are missed. Consider individual special needs when arranging analgesia (eg
may not cope with patient-controlled analgesia). Domperidone is a good antiemetic because it does not
have significant antipyramidal effects.

2.6 Preoperative management of liver disease



In a nutshell ...

Patients with cirrhosis and liver disease do badly and have a high mortality rate with elective surgery.
Problems to anticipate include:

Bleeding due to coagulopathy
Encephalopathy
Increased risk of infection
Increased risk of renal failure
Hypoglycaemia
Acid–base and electrolyte imbalances
Underlying cause (eg malignancy, alcohol abuse and withdrawal)

Distinguish between biliary obstruction (cholestatic jaundice) and chronic decompensated liver failure
(hepatocellular jaundice), and manage the patient accordingly.

Preoperative management of patients with jaundice

Fluid balance

Hypoalbuminaemia and fluid overload are common in jaundiced patients and lead to
pulmonary/peripheral oedema as well as ascites. There may be sodium retention and hypokalaemia due to
secondary hyperaldosteronism, which may be further complicated by the use of spironolactone or other
diuretics.

Acid–base balance

A combined metabolic and respiratory alkalosis may occur. This will cause the oxygen dissociation curve
to shift to the left and decrease oxygen delivery to the tissues.

Clotting

Due to a decrease in vitamin K absorption in cholestatic jaundice, there is reduced synthesis of factors II,
VII, IX and X, and there may also be a thrombocytopenia if there is portal hypertension (due to
hypersplenism).

Hepatorenal syndrome

Renal failure may be precipitated by hypovolaemia. Hepatorenal syndrome has a very poor prognosis.

Drug metabolism

Many drugs, including anaesthetic agents, undergo metabolism by the liver and may therefore have a
prolonged duration of action. Hypoalbuminaemia impairs drug binding and metabolism and may lead to
elevated serum levels.

Other complications of jaundice

Hypoglycaemia may occur due to depleted glycogen stores
Wound failure and infection are increased in the jaundiced patient • Risk of infectivity to surgeon and
hospital personnel if infective hepatitis (patients require hepatitis screen if considered high-risk)

Preoperative management of cholestatic jaundice

If possible relieve jaundice before surgery (eg an endoscopically performed sphincterotomy to drain
common bile duct stones) • Keep the patient well hydrated in an attempt to avoid hepatorenal syndrome •
Check the prothrombin time and administer vitamin K 10 mg IV daily (maximum effect after three doses)
or fresh frozen plasma within 2 hours of a surgical procedure
In the presence of biliary obstruction/anticipated manipulation of the biliary tree administer prophylactic
antibiotics to avoid cholangitis

Preoperative management of chronic liver failure

Fluid and electrolyte management (note that even if there is a low serum sodium these patients have a high
total sodium due to secondary aldosteronism, so additional sodium load in fluids should be avoided)
Management of ascites (consider drainage if gross or refractory ascites, or risk of spontaneous bacterial
peritonitis) • Prevention of encephalopathy (restricted nitrogen, regular lactulose, sedative avoidance,
prophylactic antibiotics such as metronidazole) • Management of coagulopathy (vitamin K and fresh
frozen plasma) • Nutritional support (plus vitamin supplementation)


CHILD’S CLASSIFICATION OF THE SEVERITY OF CHRONIC LIVER DISEASE

Preoperative management of alcohol withdrawal

Dangerous
May cause confusion and aggression
Symptoms often occur at night
Predicting patients who will suffer from withdrawal allows prescription of a sensible prophylactic
regimen (eg reducing dose of chlordiazepoxide from four times per day down to zero over 7–10 days)
rather than acute management with large doses of sedatives, which can be dangerous.

2.7 Preoperative management of renal failure

Renal failure may be acute or chronic. Details of the causes, physiology and management of renal failure
can be found in the Chapter 3.
Patients in established renal failure pose specific problems in perioperative care. Fluid and electrolyte

balance may be deranged and drug/metabolite excretion disturbed. Severe uraemia can directly affect the
cardiovascular, pulmonary, haematological, immunological and central nervous systems. Avoid
nephrotoxic drugs in those with borderline or impaired renal function.



Classification of renal failure
Prerenal, eg haemorrhage (blood); burns (plasma); vomiting (crystalloid) • Renal, eg diabetes;

glomerulonephritis • Postrenal, eg retroperitoneal fibrosis (medially deviated ureters); benign
prostatic hyperplasia (with chronic retention); pelvic malignancies

Preoperative problems in patients with renal failure

Complications encountered preoperatively in patients with established renal failure may include:
Fluid overload, oedema
Hypoalbuminaemia (nephrotic syndrome)
Electrolyte abnormalities (hyperkalaemia, hyponatraemia)
Metabolic acidosis
Higher incidence of arterial disease (ischaemic heart disease and PVD), diabetes and hypertension •
Susceptibility to infection (uraemia suppresses the immune system)

Preoperative management of established renal failure involves:
Dialysis before surgery with regular monitoring of fluid/electrolyte balance • Reduce doses of drugs
excreted by the kidney (eg morphine)
Involvement of the renal team



Note that, when establishing IV access in a patient with severe end-stage renal failure, avoid potential
arteriovenous fistula sites (eg cephalic vein). Veins on the hands can be used.

2.8 Preoperative management of rheumatoid disease

Rheumatoid disease encompasses a range of disorders from joint arthritis to connective tissue diseases
and vasculitis.

Rheumatoid arthritis (RA) is a common relapsing and remitting autoimmune condition resulting in
progressive joint swelling and deformity (see Chapter 9, Orthopaedic Surgery). Prevalence is about 3%
in females and 1% in males.



Increased risks at time of surgery for RA patients
Cardiac: increased risk of valve disease (valvular inflammation occurs as part of the disease and can
damage mitral and tricuspid valves).
Anaemia: of chronic disease.
Respiratory disease: patients often have pleural nodules, pulmonary fibrosis and effusions which may
compromise reserve.
Peripheral neuropathy: be careful of pressure areas.
Renal impairment: may be due to nephritis or medication.
Skin: poor wound healing due to underlying disease and steroid use.

C-spine: 15% of RA patients have atlantoaxial instability of the C-spine which may be associated with
pathological fracture of the odontoid peg, and which predisposes them to atlantoaxial subluxation
(horizontal/vertical); this risk is increased during anaesthesia. Subluxation can result in:
Medullary compression and sudden death
Spinal cord compression (acute/chronic); causes difficulty with clumsy hands, stiff legs, gait, balance •
Occipitocervical pain
Patients with neurological symptoms and signs (including tingling of hands or feet) or those with
persistent neck pain should have a preoperative C-spine radiograph.

2.9 Preoperative assessment and management of nutritional status
In a nutshell ...

Nutritional depletion pre- and post-surgery increases morbidity and mortality. Malnutrition may be due
to:
Decreased intake
Increasingly catabolic states
Impaired digestion or absorption of nutrients
Nutritional support improves outcome and follows a hierarchy:
Oral supplementation
Enteral tube feeding
Parenteral nutrition


Body mass index (BMI)
BMI is calculated with the formula below (note that dry weight should be calculated, so exclude extra
fluid weight due to ascites, renal failure, etc).
BMI = weight (kg)/height2 (m2) Body habitus is classified on the basis of BMI as follows:

<16

Severely malnourished
<19

Malnourished
20–27

Normal
27–30

Overweight
30–35

Obese
35–40 Morbidly obese (if also demonstrates comorbidities)

>40–50

Morbidly obese }
50–60 Super-obese }

60–70 Super-super-obese }

Ultra-obese
>70 { These are predominantly

{ American definitions

Information about nutritional status may also be determined by:
Degree of recent weight loss (>5% mild; 10% moderate; >15% severe) • Percentage of expected body
weight (<85% moderate; <75% severe) • Physical measurements: mid-arm muscle or triceps skinfold
thickness • Serum albumin levels

Note that albumin is also a negative acute phase protein, the levels of which fall in sepsis and
inflammation. Therefore it is not an absolute marker for nutritional status; however, a rising albumin is the
most useful as a measure of recovery.

Nutritional requirements Protein (g/kg per day)

Daily nutritional requirements are shown in the table.


DAILY NUTRITIONAL REQUIREMENTS

kcal/kg per day

25 0.8

Baseline

30–35 1.3–2.0

Catabolic states

40–45 1.5–2.5

Hypercatabolic states


Figure 1.1 B ody mas s inde x

Also required are the following micronutrients:
Electrolytes: sodium, potassium, calcium, chloride, magnesium, phosphate, fluoride • Vitamins: A, B
series, C, D, E, K
Trace minerals: copper, iodine, iron, manganese, selenium, zinc

Malnutrition

Malnutrition is starvation that induces a low-grade inflammatory state, which causes tissue wasting and
impaired organ function. Many patients (especially those with chronic disorders, malignancy and
dementia) may be suffering from malnutrition. Surgery may induce anorexia and temporary intestinal
failure, exacerbating the problem. The postoperative catabolic state and the stress (inhibition of the
normal ketotic response) can cause muscle metabolism and weaken the patient.

Malnutrition in hospital patients is common:
Up to 40% of surgical patients are nutritionally depleted on admission • Up to 60% may become
nutritionally depleted during admission

Malnutrition has prognostic implications for increased postop complications:
Poor wound healing and dehiscence
Immunocompromise leading to infection (chest and wound)
Organ failure


Causes of malnutrition in the surgical patient
Decreased intake
Symptoms such as loss of appetite, nausea, vomiting
Conditions such as alcoholism
Inability to feed oneself (trauma, stroke, dementia)
Disease of the mouth, pharynx, or oesophagus
Primary pathology (eg dysphagia due to tumour)
Opportunistic infection (eg with Candida spp.)

Increasingly catabolic state
Due to disease process, eg sepsis, infection and pyrexia (especially if chronic) • Cachexia due to

malignancy (some tumours cause muscle wasting and weight loss out of proportion to their size, eg
oesophageal cancers)
Organ failure (eg renal or hepatic failure)
Major surgery itself (trauma)
Impaired digestion or absorption
Primary disease of the GI tract (eg inflammation, obstruction, fistulae) • Visceral oedema in patients
with protein malnutrition
Ileus
Post-abdominal surgery
Intra-abdominal sepsis
Electrolyte imbalance (eg hypokalaemia, hyponatraemia)

Assessment of malnourished patients

History

Duration of illness
Weight loss
Reduced appetite
Risk factors (eg alcohol, malignancy)
Reduced tissue turgor
Apathy
Weight loss

Investigation

Arm circumference/triceps skinfold thickness
Serum albumin
FBC
Transferrin
Retinol-binding protein

Malnourished patients requiring elective surgery should be considered for preoperative and perioperative
feeding.

Obesity

Obese patients are at increased risk of surgical complications for many reasons.

Surgical risks of obesity

Respiratory
Decreased chest wall compliance, inefficient respiratory muscles and shallow breathing prolong
atelectasis, and increase the risk of pulmonary infections
Oxygen consumption is increased due to metabolic demand from adipose tissue and increased muscular
work of breathing • Increasing obesity causes respiratory impairment and chronic hypoxia, tolerance to
hypercapnia and polycythaemia • Sleep apnoea can result in cardiac failure

Aspiration
Increased gastric volume and high intra-abdominal pressure predispose to gastric aspiration

Wound healing
Poor-quality abdominal musculature predisposes to dehiscence • Increased adipose tissue predisposes to
haematoma formation and subsequent wound infection

Technical problems
Surgery takes longer and is more difficult due to problems of access and obscuring of vital structures by
intra-abdominal fat deposits • Technical problems arise with IV cannulation and subsequent phlebitis

Assessment of obese patients


Obesity increases risks of:
Hyperglycaemia (insulin resistance)
Hypertension and ischaemic heart disease
Gallstones
Osteoarthritis

For elective surgery in obese patients, the pre-op assessment should include:
Measurement of the patient’s BMI
Discussion with anaesthetist (may require specialist)
Referral to a dietitian
Blood glucose estimation and restoration of glycaemic control • Measurement of blood gases (hypoxia and
hypercapnia reflect respiratory impairment), and respiratory function tests (FEV1/FVC) in patients with
obstructive pulmonary disease

Consideration of treatment for obesity before major surgery (eg weight-loss regimen, procedure such as
gastric bypass in morbidly obese individuals).

Nutritional support

Tailored to the protein, calorific, and micronutrient needs of the patient. It follows a hierarchy, using oral
supplementation if possible, enteral tube feeding if oral feeding cannot supply the required nutrients, and
parenteral feeding only if enteral feeding is not possible.

Oral supplementation

Can be used between or instead of meals
Variety available (milk- or fruit-juice-based)
High in protein and calories
Not all contain micronutrients
Examples include Complan

Enteral tube feeding

Enteral feeding is the best route because it preserves GI mucosal integrity. If the patient cannot take
enough nutrients in orally, tube feeding is the next step.

Enteral tube options include:
NG or nasojejunal (NJ) tube (may be fine-bore)
Percutaneous endoscopic gastrostomy (PEG) or jejunostomy (PEJ). This may be useful in patients who

have had facial, laryngeal or oesophageal surgery, and who cannot have an NG tube
Feeding gastrostomies or jejunostomies may be inserted on the ward, under radiological control,
endoscopically or at open surgery

Feeds include:
Polymeric (whole protein, carbohydrate and fat)
Small-molecule (short peptides, free amino acids and elemental fats) • Specific feeds (eg low-sodium
diets in liver failure)
Feed is delivered at a pre-set speed by a pump, and gastric residual volume is checked to assess
absorption • A feed-free period allows gastric pH to fall and is important to control bacterial colonisation
(see also Bacterial translocation in Chapter 3, Postoperative Management and Critical Care)



Complications of enteral feeding tubes
Feeding tube displaced or blocked
Metabolic (hyperglycaemia, micronutrient deficiencies)
Diarrhoea
Aspiration

Parenteral nutrition

This is used only if enteral feeding is not possible or is contraindicated.

Feeding is via venous access, which may be:
Peripheral vein (long line, peripherally inserted central catheter [PICC] line) • Central access (jugular or
subclavian line)
Tunnelled, cuffed or with a subcutaneous port

Sterile feeds are made up either to standard or to individual prescription. Feeding may be cyclical or
continuous.

Catheter complications

Risks of insertion
Thrombosis
Infection

Metabolic complications
Hyperglycaemia
Electrolyte and fluid imbalance
Hepatic dysfunction
Immunocompromise
Metabolic bone disease

Nutritional planning in surgical patients

Preoperative considerations

Dietitian pre-op assessment of high-risk patients
Encourage increased oral intake
Oral supplementation (high-protein and high-calorie drinks, NG/PEG feeding)

Surgical considerations

Think about placement of tubes for enteral feeding (especially PEJ)

Postoperative considerations

Colorectal surgery
Traditionally the postoperative feeding regimen for bowel surgery was a stepwise progression guided by
improving clinical signs (eg passing of flatus) thus: nil by mouth (NBM), sips and small volumes of clear
fluids, soft diet, normal diet. This has changed in recent years, with many surgeons allowing free fluids on
day 1 and diet as tolerated.
Early feeding has been shown to improve early outcome measures even in the presence of a bowel
anastomosis • Chart food intake and monitor daily on ward rounds
Weigh patients regularly
Patients who have had laparoscopic bowel resections are typically eating and drinking on day 2, and fit for
discharge on day 4 or 5

Upper GI surgery
Oesophageal and gastric resections are typically combined with a feeding jejunostomy placed
intraoperatively, so that the patient can resume enteral feeding very soon after surgery. Many surgeons
will then do a water contrast swallow on day 10 of high-risk anastomoses before allowing oral feeding.

2.10 Risk factors for surgery and scoring systems

There are numerous systems in use in the management of surgical patients that attempt to identify and
stratify risk. These commonly include the risk or severity of the underlying condition (eg Ranson’s criteria
for pancreatitis, the Glasgow Coma Scale (GCS) score, the APACHE score in critical care, etc) or a
global indicator of underlying comorbidities such as the ASA grade for anaesthesia.

Increasingly risk assessment has been tailored to combine underlying comorbidity with the type of surgery
proposed. This has lead to a number of different models for predicting risk:


The POSSUM score (Physiological and Operative Severity Score for the enumeration of Morbidity and
Mortality). The POSSUM score uses 12 physiological and 6 surgical variables for its calculation and can
be used pre- and postoperatively to give an initial estimate and calculation of individual risk. There have
been some reports of overprediction of mortality risks which has led to specialty-specific modifications:
• V-POSSUM in elective vascular surgery
• O-POSSUM in oesophagogastric surgery
• CR-POSSUM in colorectal surgery
ACPGBI has produced a number of scoring systems including a mortality model for colorectal cancer
resection • St Mark’s lymph node scoring system for likelihood of lymph node positivity in colorectal
cancer • Adjuvant! Online gives an estimate of reduction in the risk of death from breast cancer in
patients undergoing chemotherapy

SECTION 3

Principles of anaesthesia

Anaesthesia is the rendering of part (local anaesthesia) or all (general anaesthesia) of the body insensitive
to pain or noxious stimuli.

3.1 Local anaesthesia



In a nutshell ...

Local anaesthetic agents work by altering membrane permeability and preventing the passage of nerve
impulses • They can be used in a variety of ways to effect local or regional anaesthesia: • Topical
• Direct infiltration
• Field block
• Ring block
• Individual nerve block
• Plexus block
• Intravenous regional anaesthesia
• Spinal anaesthesia
• Epidural anaesthesia

Use of local anaesthetic agents thus has the advantage of avoiding the risks of general anaesthetic

Mode of action of local anaesthetics

Work by altering membrane permeability to prevent passage of nerve impulses • Stored as acidic salt
solutions (after infiltration the base is released by the relative alkalinity of the tissue – hence LA is
ineffective in acidic conditions such as in infected wounds)
Often used in combination with GA to reduce opiate analgesic and GA requirements • Ideal LA has low
toxicity, high potency, rapid onset and long duration

Local anaesthetic agents

Dosage of local anaesthetic agents:
0.5% = 5 mg/ml
1% = 10 mg/ml
2% = 20 mg/ml, etc

LAs should be used at their lowest concentration and warmed to body temperature to decrease pain on
injection. Adrenaline may be used with LAs to slow systemic absorption and prolong duration of action.

Advantages of local and regional anaesthesia
No systemic use of drugs (reduced side effects compared with a GA) • Good depth of analgesia in local
area only
No requirement for mechanical ventilation:
• Better for patients with chronic respiratory disease • No atelectasis and infection risk
• Less risk of gastric aspiration
May be used together with reduced level of GA (evidence for reduced morbidity and mortality) • May be
continued for postoperative reasons:
• Analgesia (eg epidural for laparotomy)
• Respiratory function (allows deep inspiration and pain-free chest physiotherapy)


DOSAGE AND USES OF LOCAL ANAESTHETIC AGENTS


Note: never use local anaesthetic agents containing adrenaline near end-arteries (eg digits, penis)
because this may result in ischaemic necrosis.


Less cardiac stress during surgery (reduced ST changes seen on ECG) • Reduced postoperative ileus
Reduced incidence of DVT

Complications of local anaesthetics

Drug toxicity can be local or systemic.

Local toxicity

Inflammatory response
Nerve damage from needle or intraneural injection

Systemic toxicity

Allergy
May occur from overdosage, inadvertent IV administration, absorption from highly vascular areas or cuff
failure in Bier’s block • Causes perioral tingling and paraesthesia, anxiety, tinnitus, drowsiness,
unconsciousness, seizures, coma, apnoea, paralysis and cardiovascular collapse (negatively inotropic and
vasodilatation)

Management of toxicity: stop administration of LA, then perform ABC resuscitation – protect airway,
intubate and ventilate if necessary. Give IV fluids and consider inotropic support.

Topical local anaesthetic

This is in the form of a cream or a spray and is used for routine procedures where only superficial
anaesthesia is required, eg:
EMLA cream before cannulation in children
Lidocaine gel before urethral catheterisation
Xylocaine spray before gastroscopy

Infiltration of local anaesthesia

This is used typically for removal of small skin lesions.


Procedure box: Infiltration of local anaesthetic

Check that there are no allergies and no contraindication for using a local anaesthetic agent with
adrenaline • Check the maximum safe dose for the patient and draw up only that amount, checking the
vial yourself • Use a fast-acting agent such as lidocaine

Using an orange or blue needle, first raise a subcutaneous weal along the line of the proposed skin
incision (this will be an ellipse around a skin lesion, for example)

Keeping the needle in the same site as much as possible, inject deeper into the subcutaneous tissue to the
level of the estimated dissection, aspirating before you inject in any area where there may be vessels

If you draw blood, do not inject, because intravenous lidocaine can cause arrhythmias • Wait a few
moments and test the area for sensation with forceps before incision. Remember that even lidocaine
takes 10–20 minutes to take full effect

Use leftover local to infiltrate if the patient reports sensation

3.2 Regional anaesthesia

Field block and ring block

A field block is infiltration of a LA agent in such a way as to effect anaesthesia in the entire surgical field.
This may involve blocking a nerve that supplies the area, eg when performing an inguinal hernia repair
under LA, a surgeon may combine a direct infiltration of local anaesthesia with an injection of LA into the
ilioinguinal nerve above the anterosuperior iliac spine.
A ring block is a type of field block where the area to be blocked is a digit or the penis. An entire finger
or toe can be made completely numb by injecting a millilitre or two of LA just to either side of the
proximal phalanx at the level of the web space. The nerve runs here with the digital artery and vein, so
adrenaline-containing LA agents should never be used for a ring block, because they might render the digit
ischaemic by putting the end-arteries into spasm. A ring block can be used for manipulation of dislocated
fingers, ingrowing toenail procedures and postoperative analgesia after circumcision.

Brachial plexus block

The brachial plexus is formed from the nerve roots C5–T1 which unite to form the main trunks (upper,
middle and lower) that divide into anterior and posterior nerve divisions at the level of the clavicle.
These subdivide into cords as they enter the axilla, and the cords are named according to their position
relative to the second part of the axillary artery (medial, lateral and posterior). The cords subdivide as
the plexus passes through the axilla.
Brachial plexus blocks may be performed at different levels:
Interscalene block (trunks)
Supra-/infraclavicular block (divisions)
Axillary block (cords)
If injected into the fascial covering of the plexus the anaesthetic will track up and down providing a good
block. These blocks are good for postop pain relief because they last for several hours.



Figure 1.2 The brachial ple xus

Figure 1.3 The fe moral ne rve

Femoral block

The femoral nerve arises from L2–4 and passes downwards on the posterior wall in the groove between
the psoas and iliacus muscles. It lies on the iliopsoas as it passes under the inguinal ligament to enter the
thigh, lateral to the vascular bundle and femoral sheath. The femoral nerve then divides in the femoral
triangle and supplies the muscles of the anterior thigh, cutaneous nerves of the anterior thigh and
saphenous nerve.
The femoral nerve lies at a point that is 1 cm lateral to the pulsation of the femoral artery as it exits from
under the inguinal ligament and 2 cm distal to the ligament. Deep infiltration of LA at this point will
produce a femoral block (note: avoid injecting into the femoral vessels). This is suitable for analgesia
covering the anterior thigh, knee and femur.

Sciatic block

The sciatic nerve arises from the lumbosacral nerve roots L4–S3 and exits under the biceps femoris
muscle. It undergoes early organisation into common peroneal and tibial portions, which run together
centrally down the back of the thigh under adductor magnus. They usually divide in the distal third of the
thigh, although this may occur at a higher level in some individuals.



Figure 1.4 The s ciatic ne rve

The sciatic nerve block can be performed by a lateral, anterior or posterior approach, and is suitable for
ankle and foot surgery. The sciatic nerve lies 2 cm lateral to the ischial tuberosity at the level of the
greater trochanter. Sciatic nerve blocks may be of slow onset (up to 60 minutes) so be patient with your
anaesthetist.

Bier’s block

This is IV regional anaesthesia, usually into the upper limb.

Technique for Bier’s block

IV access – both arms!
Exsanguinate limb (eg Eschmark bandage)
Apply double-cuff tourniquet (with padding)
Inflate upper cuff to approximately 300 mmHg
Inject approximately 40 ml 0.5% prilocaine IV into isolated arm • Inflate lower cuff (over anaesthetised
segment)
Release upper cuff (reduces cuff pain and acts as safeguard)

Intercostal nerve blocks

Useful for invasive procedures (eg chest drain insertion) and analgesia (eg flail chest or fractured ribs,
breast surgery). The intercostal nerve runs with the vascular bundle under the overhanging edge of the rib.
Feel for the posterior angle of the rib at the posterior axillary line and insert the needle just below the
edge of the rib (‘walk’ the needle off the rib if necessary). Inject local anaesthetic (note: risk of
pneumothorax).

Spinal anaesthesia

Useful for lower abdominal, perineal and lower limb surgery. It is contraindicated in patients who are
anticoagulated or septic, or who have had previous back surgery or aortic stenosis.
Introduce via fine-bore needle into spinal (subarachnoid) space at L1–2 level (by the cauda equina) • Low
dose, low volume, rapid (<5 minutes) onset • Duration 3–4 hours
Mainly used for perioperative pain relief

Complications of spinal anaesthesia

Toxicity
Hypotension (avoid in severe cardiac disease)
Headache, meningism, neurological disturbance
Urinary retention

Epidural anaesthesia

This is introduced via a large-bore needle to feed the catheter into the extradural space (as the needle
passes through the ligamentum flavum there is a change in resistance signifying placement in the correct

location).
Situated at level of nerve roots supplying surgical site (lumbar for pelvic surgery; thoracic for upper
abdominal) • High dose, high volume, delayed (>5 minutes) onset • Duration of continuous infusion: up to
a few days • Can be used for peri- and postop pain relief



Figure 1.5 Spinal anatomy

Complications of epidural anaesthesia

Dural tap
Backache
Infection
Haematoma
Urinary retention

Monitoring the level

Anaesthetic spreads caudally and cranially in both spinals and epidurals.
Level is controlled by:
Initial level of placement
Patient positioning (eg head-down tilt)
Volume and concentration of anaesthetic
Level is described by the dermatome affected:
Nipples T5
Umbilicus T10

Inguinal ligament T12

High block may cause respiratory depression, and impair cough and deep inspiration (respiratory arrest at
C4 level).

Spinal haematoma and abscess

Haematoma may occur on needle insertion and epidural catheter removal • Catheters should not be
removed when the patient is anticoagulated (can be removed 12 hours post low-dose heparin followed by
2 hours delay before any further doses)
Risk of epidural abscess increases if left in situ for >72 hours

3.3 Sedation



In a nutshell ...

Sedation is the administration of drug(s) to alleviate discomfort and distress during diagnostic and
therapeutic interventions, with maintenance of patient responsiveness and protective reflexes. Allows
for rapid recovery and avoids GA. Sedation can be used:
As a premedication anxiolytic
As an amnesiac (eg relocation of dislocated shoulder) • As an adjunct to regional anaesthesia
During invasive interventions such as endoscopy
In critical care (eg to tolerate endotracheal intubation)

Patients must be monitored carefully.
Supplemental oxygen (mask or nasal cannulae)
Cardiovascular: ECG leads and monitor
Respiratory: pulse oximetry
Central nervous system (CNS): responsive and obeying commands

Avoid sedating high-risk patients (eg elderly patients, obese patients, patients with cardiorespiratory
disease). Be prepared for adverse reactions by ensuring the following:
Presence of an assistant
Resuscitation equipment ready and nearby
IV cannula left in for emergencies (NEVER use a butterfly needle to administer sedation) • Drug is titrated
slowly against response (especially if combined with opiate because of increased risks of
cardiorespiratory depression) • Monitor until full consciousness is regained and discharge home with a
responsible adult

3.4 General anaesthesia



In a nutshell ...

General anaesthesia induces
Narcosis (unconsciousness)
Analgesia
Muscle relaxation

It does this in a controlled and reversible manner, so the patient suffers no pain and has no recollection
of the experience, and the surgeon has ideal operating conditions.
Stages of general anaesthesia
Pre-op assessment and preparation
Induction and muscle relaxation
Maintenance and monitoring
Recovery
Postop monitoring and transfer

Preoperative anaesthetic assessment

The anaesthetist will assess the patient fully preoperatively, ideally to assess and try to minimise risks of
general anaesthesia, to counsel the patient and prescribe premedication.



ASA grading (estimation of risk for anaesthesia and surgery)
Class 1 Normal healthy individual
Class 2 Patient with mild systemic disease Class 3 Patient with severe systemic disease that limits
activity but is not incapacitating Class 4 Patient with incapacitating disease that is a constant threat to
life Class 5 Moribund patient not expected to survive, with or without an operation

Premedication

Objectives and functions of premedication:
Anxiolytic effect
Causes sedation and enhancement of hypnotic effect of GA • Causes amnesia
Dries secretions
Antiemetic effect
Increases vagal tone
Modification of gastric contents

Benzodiazepines

These are sedative, anxiolytic and amnesic.
Midazolam
• Induction of anaesthesia
• Sedation during endoscopy and procedures performed under LA • Hypnotic effect
• Used for premed
• Used for treatment of chronic pain
• Is water-soluble, has short duration, gives rapid clear-headed recovery • Dose is 0.05–0.1 mg/kg by
slow IV injection
• May cause over-sedation or respiratory depression • Can be reversed with flumazenil (which may itself

cause seizures) • All patients having midazolam sedation should have IV access, pulse oximetry, ECG
monitoring and resuscitation facilities available, and should not drive or operate machinery for 24 hours
afterwards
Temazepam: 10–20 mg orally 1 hour pre-surgery • Diazepam: oral or IV; longer duration than other
benzodiazepines and more difficult to reverse

Droperidol

A butyrophenone
Antiemetic, neuroleptic, α blocker
Prolonged duration action and ‘locked in’ syndrome may cause problems • Rarely used

Opioids

Analgesic and sedative
Examples are papaveretum (Omnopon) 20 mg IM, morphine 10 mg IM.
Can be reversed with naloxone (Narcan)

Anticholinergics

Competitive acetylcholine antagonists at muscarinic receptors • Dry secretions; prevent reflex bradycardia
Example: IV atropine 300–600 μg pre-induction

Glycopyrronium
Less chronotropic effect than atropine
Doesn’t cross the BBB
200–400 μg IV/IM pre-induction

Hyoscine (scopolamine)
As for atropine but more sedative and antiemetic • May cause bradycardia, confusion, ataxia in elderly
people • 200–600 μg subcutaneously
60 minutes pre-induction

Antacids

These are used to prevent aspiration of gastric contents (causing Mendelson syndrome) in patients at risk
(eg pregnancy, trauma patients [not starved], obese, hiatus hernia), eg:
Cimetidine 400 mg orally 1–2 hours pre-surgery
Ranitidine 50 mg IV or 150 mg orally 1–2 hours pre-surgery • Omeprazole 20 mg orally 12 hours pre-
surgery

Additional medication

Patients may also be given (according to case):
Steroids
Prophylactic antibiotics
Anticoagulants
Immunosuppressants (eg if undergoing transplantation)

Induction of general anaesthesia

This is the administration of drug(s) to render the patient unconscious before commencing surgery. It may
be intravenous or inhalational. The IV route is quicker, but requires IV access, so inhalation induction
may be the method of choice in children, or in people who are needle phobics or difficult to cannulate. IV
induction agents are liquid-soluble, and thus hydrophobic. IV induction agents are also used for
maintenance of anaesthesia, by slow IV infusion.
Thiopental sodium is a commonly used induction agent. It is a barbiturate that appears as a pale-yellow
powder with a bitter taste and a faint smell of garlic. It is given in an alkaline solution (pH 10.8) and so is
irritant if injection occurs outside the vein. It causes a smooth and rapid induction but has a narrow
therapeutic window and overdose may cause cardiorespiratory depression. It is a negative inotrope and
can result in a drop in BP. There is often associated respiratory depression. It sensitises the pharynx and
cannot be used with laryngeal airways
Propofol is more expensive than thiopental but has the advantage of a slight antiemetic effect. It is a phenol
derivative that appears as a white aqueous emulsion, and may cause pain on injection. It gives a rapid
recovery without a ‘hangover’ and has a lower incidence of laryngospasm, which makes it the agent of
choice if using a laryngeal mask. It causes vasodilatation and is a negative inotrope, resulting in a drop in
BP, and therefore it is not recommended for hypovolaemic patients • Etomidate is less myocardial
depressive, so is better used in cardiovascularly unstable patients

Inhalational anaesthetics may also be used for induction and are discussed later in this chapter.

Complications of induction agents

Complications include:
Hypotension
Respiratory depression
Laryngeal spasm
Allergic reactions
Tissue necrosis from perivenous injection

The effects are especially pronounced in hypovolaemic patients.

Contraindications include previous allergy and porphyria. For a discussion of intubation see Chapter 3.

Muscle relaxants

Depolarising muscle relaxants

Depolarising muscle relaxants work by maintaining muscle in a depolarised (or relaxed) state.

The main example is suxamethonium. This has a structure similar to two acetylcholine molecules and
acts in the same way as acetylcholine at the neuromuscular junction. The rate of hydrolysis by plasma
cholinesterase is, however, much slower, so depolarisation is prolonged, resulting in blockade. Its action
cannot therefore be reversed. As it acts on the acetylcholine receptor there is an initial period of muscle
fasciculation that may be painful and distressing to the patient.

It is the most rapid-acting of all the muscle relaxants and is therefore useful when rapid tracheal
intubation is required (crash induction). It has a duration of 2–6 minutes in normal individuals, but some
people have a deficiency of plasma cholinesterase and show a prolonged response (scoline apnoea).

Complications of depolarising muscle relaxants
Muscle pain
Hyperkalaemia
Myoglobinaemia
Bradycardia
Hyper- or hypotension
Malignant hyperpyrexia

Contraindications of depolarising muscle relaxants
Patients prone to hyperkalaemia, especially burns victims • History or family history of malignant
hyperpyrexia • History or family history of bronchospasm

Non-depolarising muscle relaxants

All have a slower onset than suxamethonium, but longer duration. Atracurium or benzylisoquinolinium
provides intermediate duration.
Atracurium undergoes non-enzymatic metabolism independent of hepatic or renal function and thus has a
safety-net advantage for critically ill patients. It does, however, cause significant histamine release in
some people, which can cause cardiovascular problems or redness at the site of injection. Other
benzylisoquinoliniums include cisatracurium and gallamine
Vecuronium is an aminosteroid of intermediate duration. Another aminosteroid is pancuronium • Reversal
agents: neostigmine is used to reverse non-depolarising neuromuscular blockade, but the resulting
muscarinic action may induce a profound bradycardia and it is therefore given with atropine or
glycopyrronium

Factors causing prolonged neuromuscular blockade

Hypothermia
Acidosis
Hyperkalaemia
Increasing age
Concurrent use of suxamethonium
Inhalational anaesthetics

People with myasthenia gravis have a lower number of post-synaptic receptors due to autoantibodies
against them; this makes these patients more sensitive to non-depolarising muscle relaxants, but resistant
to suxamethonium.

Maintenance of general anaesthesia

Inhalational anaesthetics are usually used for maintenance of anaesthesia, after IV induction, but can be
used for induction, eg in children.


Halothane
• A volatile liquid anaesthetic of the halogenated hydrocarbon class • Inhalation is well tolerated and non-
irritant, which means that it rarely causes patients to cough or hold their breath • It is a very potent
anaesthetic • Causes respiratory depression, resulting in the retention of CO2
• It is a negative inotrope, resulting in a decrease in heart rate and BP
• In addition it is a mild general muscle relaxant • Enflurane
• A liquid, halogenated methylethyl ether anaesthetic • Causes respiratory and myocardial depression,
resulting in a decrease in cardiac output and a rise in PaCO2
• Has been shown to cause EEG changes; it is best avoided in epilepsy • Can cause hepatotoxicity and
hyperthermia but less commonly than halothane • Free fluoride ions are a product of metabolism and may
result in the very rare complication of fluoride-induced nephrotoxicity • Isoflurane

• Also a halogenated ether
• The inhaled anaesthetic of choice for most surgical procedures • It is an isomer of enflurane but only an
insignificant amount is metabolised by the patient • Hepatotoxicity is rare and malignant hyperthermia is
as common as with other agents • Respiration is depressed and respiratory tract irritation may occur •
There is a decrease in systemic vascular resistance due to vasodilatation and BP falls. This may result in
an increase in heart rate and rarely in ‘coronary steal’ syndrome
Sevoflurane
• A halogenated ether, volatile liquid anaesthetic • Produces a rapid induction and recovery which means
that postop pain relief must be planned well • Nitrous oxide
• A potent analgesic in concentrations >20%
• Weak anaesthetic properties
• Potentiates the effect of other inhalational anaesthetic agents, allowing a reduction in the dose required •
A mixture of 50% nitrous oxide and oxygen (Entonox) is used for analgesia, especially in obstetrics and
emergency departments • Nitrous oxide will diffuse into any air-containing space • It diffuses more
rapidly than nitrogen, and can lead to distension of the bowel • It must not be used in those who have
recently been diving, exposed to high atmospheric pressures, or who are suspected of having a gas-filled
space (eg pneumothorax or pneumocephalus)
• Avoid prolonged exposure to nitrous oxide as it causes suppression of methionine synthetase, which
leads to myelosuppression and a megaloblastic anaemia

Contraindications to inhalational anaesthetics

Pyrexia after administration of halothane or a history of jaundice is an absolute contraindication to its use.

Similar to all inhalational anaesthetics, apart from nitrous oxide, it is also associated with malignant
hyperthermia.


INTRAVENOUS VS INHALATIONAL INDUCTION OF ANAESTHESIA

Intravenous Inhalational

Advantages Fast-acting

No IV access required

Anticonvulsant and antiemetic Slower reflex depression
properties

Dose titratable Upper oesophageal tone maintained