Medical problems

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8

Medical problems

Introduction

General surgical operations are now performed on patients who are older, more frail and with significant and often multiple (medical) co-morbidities, so it becomes even more important to appreciate and consider these ‘medical’ conditions. Rates of deaths and complications after abdominal surgery have been the subject of a report by the Royal College of Surgeons of England (at: www.rcseng.ac.uk/publications/docs/higher-risk-surgical-patient). A high-risk patient is defined as one whose estimated risk of mortality is greater than 5%, and includes any patient over the age of 65 years undergoing major gastrointestinal or vascular surgery, and any patient over 50 years with diabetes mellitus or renal impairment. Recommendations include preoperative risk assessment with a tailored management plan directed by consultant surgeons and anaesthetists, and rapid identification and treatment of postoperative infection.

‘Medical’ disorders appear in surgical practice in four main ways:

• A pre-existing medical condition may precipitate a surgical admission because of exacerbation, progression or complications of the condition: for example, foot problems in diabetes

• A pre-existing medical condition may be made worse by operation. In chronic obstructive pulmonary disease, for example, general anaesthesia and postoperative sputum retention may precipitate life-threatening pneumonia

• A surgical condition may be complicated by an unrelated medical disorder. For example, a patient with rheumatoid arthritis on steroid therapy is vulnerable to impaired healing and recurrent infection

• An occult condition can become manifest under the stress of anaesthesia and operation. For example, perioperative or postoperative myocardial infarction can be caused by occult ischaemic heart disease

Cardiac and cerebrovascular disease

Emergency surgery in patients with cardiac disease is about four times more likely to result in death than the same operation done electively. Thus, preoperative assessment is vitally important in emergency patients so any cardiac condition can be recognised and stabilised, electrolyte imbalances corrected and appropriate anaesthesia, surgical technique, monitoring and aftercare employed to minimise risk.

1 Ischaemic heart disease

The clinical manifestations of ischaemic heart disease are:

Asymptomatic coronary artery disease may progress to infarction under anaesthetic and surgical stresses, including laryngoscopy and endotracheal intubation, pain, hypoxia, rapid blood loss, anaemia, hypotension, hypocarbia and fluid overload. For major operations, general anaesthesia and spinal anaesthesia carry similar risks. Local anaesthesia, when practicable, is much safer.

Clinical problems

a: Stable angina and myocardial infarction more than three months previously There is usually little increased risk during operation and exercise tolerance is by far the most important indicator of the patient’s ability to tolerate anaesthesia and surgery. This can be assessed in the history (remembering that exercise tolerance may be limited by mobility problems rather than cardiorespiratory problems). Formal assessment on a treadmill may be helpful, and occasionally coronary angiography is required to fully assess cardiac risk.

In general, all cardiac medication should be continued perioperatively. Nitrates, which dilate the coronary arteries and reduce preload and left ventricular work, may reduce cardiac ischaemia during general anaesthesia and should not be stopped in the perioperative period. A transdermal nitrate patch is a useful alternative to tablets or sprays. Beta-adrenergic blockers, which reduce cardiac work and oxygen demand, should be continued unless non-ischaemic cardiac failure develops. Most patients will be taking aspirin (and some clopidogrel in addition), and the risks of bleeding have to be weighed against the risks of stopping anti-platelet treatment.

b: Acute coronary syndrome (ACS) This is a term applied to a spectrum of conditions from unstable angina to non-ST-elevation myocardial infarction (NSTEMI) to ST-elevation myocardial infarction (STEMI). Acute coronary syndrome associated with surgery usually occurs during the first few days after operation, particularly on the second to fourth postoperative nights, rather than during the operation. Typical chest pain is not always a feature and postoperative ACS may present ‘silently’ (i.e. painlessly) with otherwise unexplained hypotension, cardiac failure, arrhythmias or cardiac arrest, particularly in patients with diabetes. Diagnosis is made on the basis of at least two of the following: appropriate symptoms (particularly typical cardiac ischaemic pain); a significant rise in a cardiac biomarker, usually troponin; and ECG changes consistent with ischaemia (dynamic changes including ST depression, T-wave flattening or inversion) or infarction (ST elevation). It is always helpful to have a preoperative ECG for comparison which should be performed on all patients over 50 years of age and any with cardiac symptoms or signs.

Troponin is a very specific marker of myocardial damage, but be aware that this damage may result from conditions other than ischaemia or infarction due to coronary artery disease, e.g. sepsis, hypotension or heart failure, and therefore the management may differ from that of ACS.

The medical treatment of ACS includes aspirin, clopidogrel (for anti-platelet activity) and fractionated heparin (given subcutaneously). These drugs adversely effect clotting in the perioperative period and the ‘harm/benefit’ balance requires negotiation between cardiology and surgical teams. Other treatments such as nitrate and beta-adrenergic receptor blockade are less likely to have adverse ‘surgical’ effects. ST-elevation myocardial infarction is ideally treated by emergency primary revascularisation but this depends on the ‘surgical’ stability of the patient, and on how close the nearest coronary intervention centre is. Thrombolysis is an option, but the potential salvage of myocardium has to be weighed against the serious risk of major haemorrhage.

2 Chronic heart failure (CHF)

This is a complex clinical syndrome with symptoms and signs resulting from impairment of the heart as a pump due to structural or functional abnormalities. The severity of heart failure correlates poorly with objective measurements of heart function (such as ejection fraction), such that up to 50% of patients presenting with symptoms and signs of heart failure will have ‘preserved ejection fraction’ (previously called ‘diastolic heart failure’). Assessment of severity is based on clinical features, particularly when exercise tolerance is limited (New York Heart Association classification). Patients with renal impairment or electrolyte abnormalities have a poorer prognosis and tend to decompensate more readily with operative stress.

Most patients will be taking diuretics, an angiotensin converting enzyme (ACE) inhibitor and a beta-blocker as first line treatment, and nitrates and digoxin if the condition is more severe, and these treatments should be continued if possible.

Patients with CHF should be optimised before major surgery, but there is still an increased mortality of up to 5%. The causes, symptoms and signs of cardiac failure are shown in Figure 8.1.

Clinical problems

Preoperative assessment of cardiac failure

Chest X-ray may demonstrate cardiomegaly and there may be signs of pulmonary oedema including upper lobe diversion, hilar congestion, septal Kerley B lines and pleural effusions (see Fig. 8.1). ECG may show an arrhythmia, myocardial ischaemia, ventricular hypertrophy, left bundle branch block or loss of R waves.

Left ventricular function can be assessed by echocardiography and documented more precisely by radionuclide studies using multiple gated acquisition (MUGA), but the best assessment is a clinical one based on exercise tolerance. Measurement of blood urea and electrolytes is important as baseline and also indication of severity of the condition.

If there is any doubt about the fitness of a patient for operation, a cardiological opinion should be sought.

3 Cardiac arrhythmias

Clinical problems

a: Atrial fibrillation (Fig. 8.2) Pre-existing (preoperative) atrial fibrillation is usually secondary to ischaemic heart disease but may be caused by mitral valve disease or thyrotoxicosis. Atrial fibrillation with a controlled ventricular rate (i.e. a pulse rate of less than 90 beats per minute at rest) causes minimal extra risk. An uncontrolled ventricular rate may cause perioperative heart failure. Atrial fibrillation (even with a controlled ventricular response) increases the risk of arterial embolism from any thrombus present in the left atrium. Adequate control of ventricular rate should be achieved before operation with beta-blocker and digoxin, occasionally supplemented with verapamil or amiodarone. Digoxin can be given intravenously if rapid control is necessary but potassium levels need to be monitored closely as digoxin given in the presence of hypokalaemia can lead to further arrhythmias. If the patient is anticoagulated with warfarin, there is a small risk of excessive bleeding at operation; stabilising the international normalised ratio (INR) between 1.5 and 2.5 may be the safest option. Another alternative is to stop warfarin and change to heparin.

Acute onset of AF postoperatively may be due to a major surgical (e.g. anastomotic leakage after bowel resection) or medical (e.g. pneumonia) complication (Fig. 8.2). If the onset of atrial arrhythmia (particularly atrial fibrillation) is associated with right bundle branch block on the ECG, this suggests a diagnosis of pulmonary embolism.

b: Bradycardia Bradycardia is common in young fit athletic patients and is not a problem. In patients taking beta-blockers or digoxin, if the apex rate is below 60 beats per minute, that day’s dose should be omitted and the regular dose reviewed.

Bradycardia may be caused by complete heart block, which should be easily diagnosed on the ECG. This may require urgent temporary transvenous pacing, particularly when there is significant haemodynamic compromise.

If a patient has a cardiac pacemaker, it is important to know the reason for its insertion: is the patient pacemaker-dependent, has the pacemaker been checked recently, what type of pacemaker has been inserted? Surgical diathermy, particularly monopolar diathermy, can interfere with the pacemaker if the current flows close to the heart. Ideally, bipolar diathermy should be used if diathermy is required. In addition a strong magnet should be available; if placed over the pacemaker this will return the rate to 100 beats/min.

4 Hypertension

About one in four patients coming to surgery is either hypertensive or is receiving antihypertensive therapy. Most have ‘essential’ hypertension, but causes such as renal artery stenosis and phaeochromocytoma must be considered in patients presenting with raised blood pressure which has not been appropriately investigated. (For other causes see Fig. 8.3.) Undiagnosed renal artery stenosis puts the patient at risk of severe acute kidney injury if there is an episode of hypotension, and phaeochromocytoma of potentially fatal hypertensive crisis.

Clinical problems

5 Cerebrovascular disease

A patient has cerebrovascular disease if there is a history of stroke or transient ischaemic attacks (TIAs). Cerebral atherosclerosis may render the blood flow to the brain precarious, with an increased risk of perioperative stroke from hypoxia, hypotension or increased blood viscosity resulting from dehydration.

Patients with ischaemic heart disease or peripheral vascular disease should also be assumed to have cerebrovascular disease and, as a minimum, the carotid arteries should be auscultated for bruits. In high-risk patients, or if a carotid bruit is present, a duplex Doppler examination of the carotid arteries should be performed, and patients with a stenosis greater than 70% considered for carotid endarterectomy before the planned operation if conditions permit. The anaesthetist should be warned of any signs or symptoms suggestive of carotid artery disease so that special care can be taken to avoid hypotension during surgery.

After a stroke, operation should be avoided for at least 2 months if practicable. This is because autoregulation of cerebral blood pressure becomes disrupted, so that cerebral arterial pressure becomes directly related to systemic arterial pressure. Brain perfusion thus loses the buffering effect of autoregulation on peaks and troughs of blood pressure that tend to occur during anaesthesia and surgery. If operation cannot be delayed, it is important to prevent hypertension and hypotension in the perioperative period.

There are few other measures likely to reduce cerebrovascular complications in patients with cerebrovascular disease, although there is an argument for prescribing low-dose aspirin (75 mg daily) to inhibit platelet aggregation. The surgeon needs to be involved in any decision to stop or start aspirin; in any case, this needs to be stopped at least a week before major surgery to reduce the risk of excessive bleeding.

6 Valvular heart disease

The common valvular abnormalities are mitral regurgitation, aortic stenosis and aortic regurgitation. Any of these may dangerously alter cardiovascular dynamics, but stenotic lesions are more serious than regurgitant ones, as the cardiac output tends to be fixed.

Under perioperative stress, valvular disease may precipitate acute myocardial ischaemia, hypotension, cardiac failure, arrhythmias or thromboembolism. Valvular heart disease also predisposes to infective endocarditis.

Aortic stenosis

Aortic stenosis is potentially the most serious valvular disorder in a surgical patient because it limits the cardiac output and reduces blood flow to the coronary arteries. Indeed, the patient may already be functioning close to the limit with almost no reserve. Perioperative hypotension and tachycardia can be life-threatening in such cases. Aortic ‘sclerosis’ produces a similar ejection systolic murmur and is caused by fixed, rigid valve leaflets, usually with systolic hypertension. The perioperative risk is that of the hypertension and arterial disease.

In a patient with an ejection systolic murmur, any associated cardiac symptoms may help identify the murmur as pathological, e.g. a history of syncope, angina or shortness of breath on exertion. Note, however, that any systolic murmur is difficult to categorise clinically, particularly in the elderly, and an echocardiogram must be performed to identify the valvular cause and offer an assessment of severity. A specialist cardiology assessment may also be required.

Clinical signs of aortic stenosis are:

If aortic stenosis is suspected, an echocardiogram will confirm the diagnosis and aid assessment of severity by measuring the aortic valve area, the gradient across the valve and an estimate of left ventricular systolic function.

Non-urgent surgery may be best delayed until after operative intervention to the aortic valve. This may now be carried out percutaneously in frail or elderly patients in whom previously the risk of valve replacement was prohibitive.

Symptomatic valvular disease is potentially dangerous and requires full preoperative assessment and treatment. Major valvular heart disease may be discovered in recent immigrants from developing countries where rheumatic heart disease is prevalent. Patients with valvular heart disease require cardiac monitoring during operation and usually intensive care afterwards.

Patients with mechanical valves are usually maintained on permanent warfarin anticoagulation and it is important to maintain this to prevent valve thrombosis, a potentially fatal condition. Patients with bioprosthetic valves (pig valves) do not usually require anticoagulation.

It should be remembered that warfarin is intended to minimise intravascular thrombosis and does not affect the extrinsic thrombotic mechanisms. For many operations it is safe to continue warfarin therapy as long as the INR is maintained in the lower therapeutic range (INR 1.5–2.5). For major surgery where much bleeding is anticipated, some surgeons prefer to stop warfarin 2 days before operation and substitute subcutaneous heparin or an intravenous infusion. For patients with mitral valve prostheses where the risk of thrombosis is high, full heparinisation must be carefully maintained throughout the perioperative period. However, heparin anticoagulation is more brittle than warfarin and carries a greater risk of over-anticoagulation and potential haemorrhage. For other patients, heparin can be stopped 12 hours before operation and restarted once the danger of bleeding is over. The advantage of heparin over warfarin is that its effects can be quickly reversed by stopping the infusion or with protamine if bleeding is excessive. However, rapid reversal may precipitate thrombosis.

In all cases it is advisable to involve the haematologist in discussion for advice on management, and in anticipation of specific treatment.

Infective endocarditis and indications for antibiotic prophylaxis

Valvular disease, and in particular prosthetic replacement valves, carry a risk of infective endocarditis. When blood is forced under pressure through a narrow orifice, laminar flow is disrupted and eddy currents predispose to local thrombus formation and deposition of circulating bacteria. The vegetations of infective endocarditis thus form on the low-pressure side of the jet of blood passing through a damaged valve or a ventricular septal defect. The left side of the heart is more susceptible than the right because of the higher pressures and greater potential for turbulence.

Streptococcus viridans is the most common causative organism of infective endocarditis. Other bacteria, such as coliforms or fungi, e.g. Candida, may also be responsible. Many types of operation and some invasive investigations cause transient bacteraemia. Although the incidence of infective endocarditis following such procedures is small, the consequences can be catastrophic. The efficacy of prophylactic antibiotics is not absolutely proven, but they are all that is available. The relative risks associated with various cardiac and valvular lesions are summarised in Figure 8.4. The procedures most likely to cause bacteraemia are also shown in Figure 8.4.

The choice of prophylactic antibiotics and the dose regimen depend on the anticipated organisms, the operative procedure and local protocols.

Respiratory diseases

Respiratory complications (mainly atelectasis and pneumonia) occur in as many as 15% of surgical patients and are the leading cause of postoperative mortality in the elderly. The risk of a respiratory complication increases with the increasing duration of anaesthetic and is amplified by pre-existing respiratory disease such as chronic obstructive pulmonary disease, asthma or bronchiectasis. Other important factors include smoking, cardiac failure, obesity, old age and general debility. Good postoperative pain relief allows the patient to breathe deeply and cough, which, along with effective physiotherapy, helps reduce the risk of respiratory complications.

Clinical problems

a Chronic obstructive pulmonary disease (COPD)

COPD (smoking-related lung disease—chronic bronchitis and emphysema) is common and strongly predisposes to postoperative respiratory complications, particularly bronchopneumonia, lobar collapse and pneumothorax. There is often a degree of reversible bronchoconstriction, and this can be assessed before operation by measuring peak expiratory flow before and after bronchodilator treatment. Many patients will already have had spirometry and vitalography in family practice or in specialist hospital COPD services and their treatment optimised. Otherwise preoperative assessment by the hospital ‘chest team’ will help bring the patient into optimum health. The forced expiratory volume in 1 second (FEV1) is perhaps the single most useful assessment of severity of chronic lung disease.

Other chronic lung diseases include bronchiectasis, pneumoconiosis, pulmonary fibrosis, sarcoidosis and pulmonary tuberculosis.

d Asthma

Asthma is common in children and adolescents but may occur later in life, particularly as a component of COPD. The main elements of asthma are airway hyper-reactivity (with constriction), bronchial wall oedema, excessive mucus production and airway plugging. All these factors predispose to atelectasis, infection and hypoxia.

Asthmatic problems can be exacerbated by the following factors associated with general anaesthesia and surgery:

In patients with asthma, the usual medication should be continued in the perioperative period, given via a nebuliser if necessary. Operations should be postponed during acute exacerbations.

Perioperative management of respiratory disease and high-risk patients

The following measures will maximise respiratory function and reduce the risk of postoperative complications:

• Preoperative physiotherapy—helps prevent postoperative chest complications. Physiotherapy should include teaching the patient breathing exercises and correct posture

• Drug therapy—adjust to achieve optimum respiratory function. Theophyllines may be added in patients with asthma, and nebulised bronchodilator drugs (such as salbutamol) may improve the reversible component of COPD and help to prevent a perioperative exacerbation of asthma. Adequate hydration reduces the risk of retained secretions which might cause airways obstruction. Prophylactic antibiotics are not recommended for COPD

• Encouragement of smokers to quit—should be started at the time of booking for elective surgery

• Alternative methods of anaesthesia—local, regional or spinal—should be considered for patients with chronic respiratory disorders, but are not necessarily the best solution. With the use of newer anaesthetic drugs and techniques, patients may be better off with endotracheal intubation and ventilation using short-acting muscle relaxants. These techniques allow good bronchial toilet at the end of operation. Certain abdominal operations are technically more difficult under spinal anaesthesia, for example if a patient with chest trouble coughs persistently during the procedure; general anaesthesia avoids this

• Early postoperative physiotherapy—aims to enhance deep breathing, coughing and general mobility, reducing the incidence of respiratory complications

Gastrointestinal disorders

The main gastrointestinal conditions giving rise to complications in surgical patients are malnutrition, dental problems, peptic ulcer disease, gastro-oesophageal reflux and inflammatory bowel disease. Previous abdominal surgery may also complicate inpatient treatment.

Malnutrition

Many surgical patients are malnourished because of reduced food intake, malabsorption and changes in metabolism (in trauma, burns and sepsis). Studies have shown that 50% of patients undergoing gastrointestinal surgery are mildly malnourished and 30% are moderately or severely malnourished. The severity of malnourishment proportionately increases postoperative morbidity and mortality. For example, severely malnourished patients experience eight times the rate of complications and three times the expected mortality following gastrointestinal surgery. Wound healing is delayed, immune resistance is impaired and muscles are weakened.

Peptic ulcer disease

Peptic ulcer disease may be a surgical problem in its own right, but patients admitted for other reasons may have an active peptic ulcer exacerbated by hospital stresses. These include serious illness and trauma, operations, and drugs such as aspirin, NSAIDs and corticosteroids. The result may be a sudden catastrophic haemorrhage (presenting as haematemesis or melaena), or occasionally perforation. Bleeding may also result from acute stress ulceration in the seriously ill patient. Note that stress ulceration is distinct from chronic peptic ulcer disease.

Patients with known peptic ulcer disease or strongly suggestive symptoms should receive perioperative prophylaxis with proton pump inhibitors. NSAIDs and irritant oral drugs should be avoided.

Previous gastrectomy may have a number of long-term side-effects. These include anaemia (deficiency of iron, vitamin B12 and occasionally folate) and, rarely, osteomalacia. A full blood count should be included in the preoperative assessment of these patients.

Hepatic disorders

Pre-existing liver disease may have important consequences in the surgical patient and generally increases postoperative morbidity and mortality. A history of jaundice must be evaluated as it may be a clue to serious risks for both patient and medical staff.

Clinical problems

a History of jaundice

A past history of jaundice raises the possibility that the patient may be a carrier of hepatitis B or C and this can readily be transmitted to health care staff. The main danger is from needle-stick injuries.

Most previously jaundiced patients will have suffered acute infective hepatitis (hepatitis A) and this poses no risk to staff because the infective agent does not cause a chronic carrier state. In contrast, lifetime chronic hepatitis develops in 5–10% of those infected with hepatitis B virus (HBV) and in 80% of those infected with HCV. These diseases should be suspected if the illness associated with the previous jaundice was prolonged or serious. Jaundice contracted in developing countries should be regarded with suspicion because hepatitis B and C are often endemic. Hepatitis C causes a high long-term rate of cirrhosis, although it often develops slowly over many years. Hepatitis B and C are also common among men who have sex with men and intravenous drug abusers who share syringes. The history should include questions to determine whether the patient falls into a high-risk group. Clinical examination should include a search for intravenous injection sites characteristic of drug abuse. In high-risk patients, screening for hepatitis B surface antigen (HBsAg) and hepatitis C antibody should be performed (see Ch. 3).

c The patient with known hepatitis

Patients with any form of hepatitis, whether viral or alcoholic, tolerate general anaesthesia and surgery badly and there is a definite mortality risk. Surgery should be avoided unless essential. If alcoholism is suspected, a CAGE questionnaire (Box 8.1) should be completed. Positive answers to two or more of the four questions suggest a drinking problem.

Box 8.1   CAGE questionnaire for assessing possible alcoholism

An elevated serum gamma glutaryl transpeptidase level and mean corpuscular red cell volume (MCV) are fairly good indicators of excessive alcohol intake.

d The patient with known cirrhosis

Patients with cirrhosis have a high risk of perioperative morbidity and mortality. The main factors are:

The main postoperative complications of cirrhosis are excessive bleeding, defective wound healing, hepatocellular decompensation leading to encephalopathy, and susceptibility to infection.

Excessive bleeding results from several factors:

Portal hypertension may initially be discovered because of ascites or splenomegaly or an acute upper gastrointestinal haemorrhage from oesophageal varices, gastroduodenal ulcers, Mallory–Weiss tears or gastric erosions. If a patient with known oesophageal varices requires an operation, preoperative endoscopic assessment is important and sclerotherapy or banding may be appropriate.

Preoperative assessment and management

Preoperative blood tests for patients with liver disease are listed in Box 8.2. If the prothrombin ratio is prolonged, intravenous vitamin K injections are given for several days before operation. If this fails to correct the abnormal clotting (as in severe hepatocellular impairment), it is important to liaise with a haematologist who may recommend perioperative administration of fresh-frozen plasma or prothrombin complex concentrate (e.g. Octaplex or Beriplex), containing factors II, VII, IX, X, protein C and protein S. If the patient is thrombocytopenic, platelet transfusion may also be required.

Box 8.2   Preoperative blood tests for patients with liver disease

Renal disorders

Renal impairment is commonly encountered in general surgical patients. There is impaired homeostasis of fluid and electrolytes and reduced excretion of nitrogenous compounds. The risk of perioperative complications increases with the degree of renal impairment. Patients fall into two groups: mild and severe chronic renal failure (CRF). Acute renal failure (acute kidney injury) is usually a postoperative complication, often with several contributory causes including hypovolaemia, and is described in Chapter 12. Patients with pre-existing renal disease are particularly vulnerable to progress to acute renal failure (‘acute-on-chronic renal failure’).

Clinical problems

a Mild/moderate chronic renal failure (CKD stage 1–3, eGFR > 30 ml/min)

This is common in the elderly and often associated with hypertension and diabetes. The main management problems in surgical patients are:

• Impaired excretion of drugs—drugs handled by the kidney must be given in smaller doses or less frequently, as documented in official drug formularies. In practice, digoxin and gentamicin pose the main problems

• Fluid and electrolyte homeostasis—only becomes a problem if fluid balance is not monitored carefully in the perioperative period. Monitoring should include regular checks of plasma urea, electrolytes and creatinine, especially if the patient is receiving diuretic therapy

• Reduction in renal reserve—even a small increase in plasma creatinine implies a significant reduction in renal reserve. For example, major reconstructive surgery to the abdominal aorta in a patient with mild renal impairment may interfere with renal function because of aortic cross-clamping near the renal arteries. This is exacerbated by transient hypotension caused by blood loss. The lack of renal reserve in these patients may then progress to acute renal failure

b Severe chronic renal failure (CKD stage 4–5, eGFR < 30 ml/min)

These patients are usually under the care of specialist physicians who should be involved in perioperative management. Patients may be receiving regular haemodialysis or ambulatory peritoneal dialysis; in such patients, surgery may be for renal transplantation (see Fig. 8.5).

Case History

The main perioperative problems of severe CRF are:

• Fluid overload—caused by impaired glomerular filtration and may require correction with large doses of diuretics, fluid restriction and haemofiltration if necessary

• Regulation of plasma osmolality—this is disordered in patients with severe CRF who are particularly vulnerable to hypo- and hypernatraemia. Care must be taken that the sodium content of intravenous fluids is appropriate

• Hyperkalaemia—this is a particular risk in advanced CRF. Patients with lesser degrees of CRF are vulnerable to an increase in potassium load (due to transfusion, tissue damage or hypoxia) or changes in glomerular filtration rate (caused by cardiac failure or hypotension). Hyperkalaemia may cause cardiac arrest and susceptibility to this may be assessed by monitoring the ECG. To minimise this risk, the preoperative plasma potassium level should be stabilised below 5.0 mmol/L, but in chronic hyperkalaemia a plasma potassium up to 6.5 mmol/L rarely causes problems.

• Metabolic acidosis—this tends to develop in chronic renal failure but it is usually compensated by respiratory alkalosis. This compensation is disrupted by general anaesthesia and also by additional metabolic acidosis resulting from tissue ischaemia or hypoxia

• Chronic normochromic normocytic anaemia—this results from decreased erythropoietin production by the kidney. Cardiovascular function is usually well adapted to this anaemia and preoperative transfusion is unnecessary. If the haemoglobin concentration is substantially below 10 g/dl, the patient is usually treated with erythropoietin

Diabetes mellitus

Severe hypoglycaemia and hyperglycaemia are life-threatening conditions. The blood glucose levels of a surgical patient with diabetes need to be closely monitored and treated.

Patients with diabetes are at special risk from general anaesthesia and surgery for the following reasons:

• Some complications of diabetes are associated with a higher perioperative risk. These are summarised in Box 8.3

Box 8.3   Specific perioperative problems in patients with diabetes

• Stress (including surgery, trauma and infections) causes increased production of catabolic hormones which oppose the action of insulin (see Ch. 2), making diabetic control more difficult

• General anaesthesia, surgery, deprivation of oral intake and postoperative vomiting disrupt the delicate balance between dietary intake, exercise (energy utilisation) and diabetic therapy

• Diabetic ketoacidosis is a cause of elevated leucocyte count and raised amylase level, which may be confusing in the diagnosis of patients presenting with an acute abdomen. Indeed, ketoacidosis may sometimes present with abdominal pain

• There is a greater risk of hospital-acquired infection, which may be elusive as a cause of deterioration

• Episodes of cardiac ischaemia and infarction may be painless

• There may be reduced renal reserve or more overt evidence of renal impairment

Clinical problems

Preoperative assessment in patients undergoing major surgery should include evaluation of current diabetic control by serial blood glucose and glycosylated haemoglobin measurements. Potential cardiovascular and renal complications should be assessed by performing an ECG (with Valsalva manoeuvre to look for autonomic neuropathy) and measuring plasma urea and electrolytes.

Perioperative management aims to maintain blood glucose between 4 and 10 mmol/L, but hypoglycaemia must be avoided. Above 13 mmol/L, the risk of ketoacidosis or a hyperosmolar non-ketotic state is unacceptable unless surgery is critically urgent. Surgery in the presence of ketoacidosis has a high mortality and should be avoided if possible until the acidosis is under control, i.e. until bicarbonate is greater than 20 or pH > 7.3.

For the purposes of perioperative management, patients with diabetes fall into three groups: those who are insulin dependent, those taking oral hypoglycaemic medication and those who are diet controlled. These are general guidelines—there are usually local guidelines and readily available clinical advice (often led by specialist nurse teams).

a Insulin-dependent diabetes

Insulin-dependent diabetics depend for their metabolism on administered insulin. If the blood glucose level is low, insulin is not withheld but glucose infusion is increased. The general principles of perioperative management are:

A typical management protocol is given in Box 8.4 and a recommended insulin infusion regimen (a ‘sliding scale’) in Box 8.5. The key is to adjust the insulin dose hourly according to blood glucose results.

Box 8.4   Perioperative management of insulin-dependent diabetes

Box 8.5   Perioperative management of diabetics using insulin infusion

b Diabetics controlled on oral hypoglycaemic drugs

Many patients are receiving short-acting sulphonylureas such as glipizide. Metformin should be discontinued because of the risk of lactic acidosis. If glycaemic control is difficult then an insulin regimen should be used as above.

On the morning of the operation, the patient is starved in the usual manner and the short-acting sulphonylurea omitted to be reintroduced when oral intake is resumed. Blood glucose should be monitored regularly (at least 4-hourly). If glucose rises above 13 mmol/L, it can be controlled by small subcutaneous doses of short-acting insulin, e.g. 6 units of soluble insulin. If a major operation is planned or if postoperative ‘nil by mouth’ is likely to be prolonged, it is best to use insulin and glucose infusions as for insulin-dependent diabetes.

Thyroid disease

Thyrotoxicosis (Fig. 8.6)

Thyroid or non-thyroid surgery for a patient with uncontrolled thyrotoxicosis carries a risk of thyrotoxic crisis and this carries a high mortality. Thus any patient with features of thyrotoxicosis should have thyroid function tests (TSH and fT4) included in the preoperative assessment.

Case History

In surgery for hyperthyroidism, the patient should be rendered euthyroid before operation using antithyroid drugs (propylthiouracil can be useful as it blocks peripheral conversion of T4 to the active T3) and non-selective beta-blocking drugs.

Hypothyroidism

Patients with untreated hypothyroidism are at moderately increased risk when undergoing surgery. They are more sensitive to CNS depressants, have a decreased cardiovascular reserve, and are also susceptible to electrolyte disorders (particularly water retention). Severe infection, especially accompanied by trauma, a cold environment or depressant drugs, may precipitate myxoedema coma which, though very rare, is often fatal.

If there is clinical suspicion of hypothyroidism, operation should be postponed and thyroid function checked by measuring free thyroxine (fT4) and thyroid stimulating hormone (TSH) levels. If hypothyroidism is diagnosed, oral replacement therapy is commenced, but it may take several weeks to achieve the euthyroid state. If surgery must be performed urgently, it is usually best to proceed with the operation and begin oral treatment later.

Disorders of adrenal function

Adrenal insufficiency

The most common cause of adrenal insufficiency is hypothalamo–pituitary–adrenal suppression by long-term corticosteroid therapy. It is occasionally caused by primary adrenal failure (Addison’s disease) or secondary to pituitary dysfunction (due to tumour or surgery). Very rarely, it results from previous adrenalectomy for treatment for a hypersecretion syndrome or bilateral primary adrenal tumours.

In primary or secondary adrenal failure, the patient is usually already taking oral steroid replacement therapy, but the lack of additional adrenal response to the stresses of trauma, surgery or infection may cause acute postoperative cardiovascular collapse with hypotension and shock (Addisonian crisis).

The ‘typical’ abnormal biochemical profile which should raise concern of the possibility of adrenal insufficiency is hyponatraemia, hyperkalaemia and raised blood urea (intravascular volume depletion). However, these abnormalities are neither sensitive nor specific and a short Synacthen test will be diagnostic.

Cushing’s syndrome

Cushing’s syndrome results from excess secretion of cortisol. This may be in response to excess adrenocorticotropic hormone (ACTH) secretion by a pituitary tumour, ectopic ACTH secretion (usually by a malignant tumour) or rarely due to a primary tumour of an adrenal gland. The most common cause of Cushingoid features is long-term steroid therapy for conditions such as polymyalgia rheumatica or asthma. Clinically the patient may be plethoric, ‘moon-faced’, hypertensive, hirsute and obese with abdominal striae and have a characteristic ‘buffalo hump’. The main surgical problems in Cushingoid patients are hypertension, hyperglycaemia, poor wound healing, infection and peptic ulceration. If the condition is due to steroid therapy, there is an additional risk of secondary adrenal insufficiency.

Musculoskeletal and neurological disorders

Musculoskeletal and neurological disorders influence the outcome of surgery in two main ways. First, any condition which hinders mobility predisposes to chest infection, deep venous thrombosis and pulmonary embolism, aspiration pneumonitis and pressure sores. The last is even more likely if there is also sensory impairment due to stroke or diabetic peripheral neuropathy. Second, specific aspects of these disorders must be considered in relation to general anaesthesia, positioning of the patient on the operating table and the use of drugs.

Rheumatoid arthritis

Rheumatoid arthritis poses special problems related to chronic anaemia, drug therapy and spinal complications. (Note that some of these problems are shared by other collagen disorders):

• Normochromic normocytic anaemia—common in chronic inflammatory disorders, including rheumatoid arthritis, although less common now that active inflammation is better controlled with modern drug therapy. The anaemia is refractory to iron therapy and there is no benefit from preoperative transfusion unless haemoglobin concentration is < 8 g/dl, or the patient is symptomatic

• Gastrointestinal disorders—most will be taking NSAIDs, which together with long-term steroid therapy, predispose to peptic ulceration and perforation. Chronic low-grade bleeding from the upper gastrointestinal tract may exacerbate the existing anaemia in these patients. Operative stress may also precipitate acute gastrointestinal haemorrhage. NSAIDs may contribute to kidney injury

• Long-term steroid therapy—may result in adrenal insufficiency under stress

• Other medications—powerful drugs now used include chloroquine, methotrexate, sulfasalazine and cytokine inhibitors. Refer to standard formularies for potential problems

• Odontoid subluxation (Fig. 8.7)—if rheumatoid arthritis involves the atlanto-axial joint, the transverse ligament may be destroyed, allowing the odontoid process to sublux. During general anaesthesia, the protective reflexes are lost. If the neck is hyperextended during intubation, there is a serious risk of injury to the spinal cord by the unrestrained odontoid

Case History

Haematological disorders

Anaemias

Severe anaemia leads to increased perioperative morbidity and mortality. General anaesthesia poses the greatest risk. For elective surgery, the haemoglobin concentration should be above 10 g/dl before operation but long-standing chronic anaemia probably poses little increased risk.

Management depends on the cause of the anaemia. Whether to transfuse before operation depends on the level of anaemia (trigger levels have come down in recent years as a response to the shortage of blood for transfusion; see local guidelines), whether the anaemia is acute, and the expected operative blood loss. Transmission of human immunodeficiency virus (HIV) and other infective agents by transfusion is a very small risk in developed countries where sophisticated screening of donors is usual, but remains a serious risk in countries without such precautions. Transfusion for anaemia can usually be avoided in young, fit patients but elderly or very ill patients with less cardiorespiratory reserve are more likely to need transfusion. Transfusions should be given at least 24 hours before operation to allow fluid balance to stabilise and ensure optimal red cell function. For diagnosed deficiency anaemias, treatment as appropriate with iron, vitamin B12 or folate may be all that is necessary before operation. Treatment with erythropoietin (EPO) for patients with chronic renal failure is expensive but effective.

Polycythaemia

Polycythaemia may be caused by a primary myeloproliferative disorder such as polycythaemia vera or be secondary to chronic cardiac or pulmonary disease or heavy cigarette smoking. There is an increased red cell mass in primary and secondary polycythaemia producing a high haematocrit and increased blood viscosity. In primary polycythaemia, the platelet count may be increased which, paradoxically, is associated with defective haemostasis as well as the risk of thrombosis.

The main complications of polycythaemia vera are haemorrhage and arterial or venous thrombosis. The risk increases once the haematocrit rises above 50%. In general, operation should be postponed to allow treatment by venesection or myelosuppression. If possible, the cardiovascular system should be allowed to stabilise for about a month after treatment. In an emergency, the haematocrit may be reduced by preoperative venesection, restoring the volume by colloid infusion.

Bleeding disorders

Bleeding diatheses such as thrombocytopenia, von Willebrand’s disease (abnormal platelet function and factor VIII deficiency) and haemophilia are occasionally encountered in surgical practice. Most surgical haematological bleeding problems, however, are caused by poorly controlled anticoagulant therapy, liver disease, aspirin therapy and sometimes vitamin K malabsorption. The last occurs in obstructive jaundice and malabsorption syndromes.

A history of abnormal bleeding or factors which may predispose to abnormal bleeding should be sought from every surgical patient as follows:

Recognising and treating a clotting problem before operation is vital because runaway haemorrhage can easily occur, causing clotting factor depletion. At this point, bleeding may be impossible to control even with transfusion of clotting factors.

If a bleeding disorder is suspected, a platelet count and clotting screen must be performed. The latter includes prothrombin time or ratio and activated partial thromboplastin time. If an abnormality is found, assays of individual clotting factors may be needed. Operation should be deferred if possible until the problem is overcome.

Clinical problems of bleeding disorders

Psychiatric disorders

Alcoholism and drug addiction

Alcoholics are prone to cirrhosis, malnutrition and peripheral neuropathies. Drug addicts are at risk of hepatitis, HIV/acquired immunodeficiency syndrome (AIDS) and other infections. Alcohol acutely potentiates general anaesthetic agents, and an inebriated patient needs smaller doses. In contrast, chronic alcohol abuse induces liver enzymes which break down anaesthetic agents. This also increases tolerance to central nervous system depressants and higher doses of anaesthetics are needed. Similarly, larger doses of sedatives are required for gastrointestinal endoscopy. Opiate addiction leads to similar dosage problems.

Problems of drug withdrawal

Withdrawal symptoms may develop unexpectedly after operation if drug or alcohol addiction has been concealed. Alcohol withdrawal is characterised initially by irritability and tremors. Convulsions may develop after 24–48 hours. Full-scale delirium tremens may appear as long as 10 days after alcohol withdrawal. It is characterised by confusion and visual hallucinations accompanied by fever, tachycardia, pallor, vomiting and sweats. Similar symptoms and signs also occur in a range of other postoperative complications and alcohol withdrawal can be overlooked.

Alcoholic cirrhosis may cause episodic hypoglycaemia, the symptoms of which may be confused with those of delirium tremens. Hypoglycaemia should be excluded by measuring blood glucose.

Mild alcohol withdrawal states may be managed with regular oral doses of clomethiazole or benzodiazepines. Parenteral B vitamins are usually given daily. Opiate withdrawal symptoms are broadly similar to those of alcohol. Treatment is usually with a substitute drug such as methadone.

Obesity

Gross obesity carries 2–3 times the risk of perioperative death or morbidity, as outlined in Table 8.1. Whenever possible, weight should be reduced before operation, particularly if it is not urgent. Referral to a dietician may be helpful although self-help groups often provide stronger motivation. Preoperative investigations for obese patients include blood glucose measurement, respiratory function tests and ECG, even if the patient is asymptomatic.

Table 8.1

Surgical complications of obesity

Complication Factors
Cardiopulmonary complications such as cardiac failure and chest infections Predisposing factors are atherosclerosis, increased demands on the cardiovascular system, decreased chest wall compliance, inefficient respiratory muscles and shallow breathing
Wound complications such as infection, dehiscence Poor-quality abdominal wall musculature with fat infiltration. Large ‘dead space’ in which fat predisposes to haematoma formation
Venous thromboembolism—increased risk of deep venous thrombosis and pulmonary embolism Poor peripheral venous return; delayed return to normal mobility
General anaesthesia complications Anatomical problems, e.g. intravenous cannulae difficult to insert and intubation more difficult. Clinical signs of dehydration and hypovolaemia are more difficult to elicit
Physiological problems: metabolic, e.g. altered distribution of drugs
Predisposition to various medical disorders Hypertension, ischaemic heart disease, type 2 diabetes, gallstones, gout
Operative difficulties Operations take longer because of difficult access and obscuring of vital structures by fat. Leads to a higher incidence of anaesthetic and surgical complications, particularly of the wound
Problems of manual handling Weight and size limitations of standard equipment including CT scanners, operating tables, beds
Need for hoists, powered beds
Risks to staff involved in lifting and handling

Chronic drug therapy

Many drugs prescribed for long-term treatment of ‘medical’ conditions can complicate management of the surgical patient. Note that the risk of stopping long-term medication before surgery is often greater than the risk of continuing it throughout. Drugs that should not normally be stopped include anticonvulsants, antiparkinsonian drugs, antipsychotics, anxiolytics, bronchodilators, cardiovascular drugs, glaucoma drugs, immunosuppressants, drugs of dependence and thyroid or antithyroid drugs. The most important of these commonly encountered in practice are summarised in Box 8.6.

Box 8.6   Potentially dangerous drugs in the surgical patient*

• Glucocorticoids

• Antihypertensive and anti-anginal drugs

• Antidepressants

• Oral contraceptives and hormone replacement therapy (HRT)

• Anticoagulants and anti-platelet drugs

• Diuretics

*Note that formularies such as the BNF carry details of drug interactions with anaesthetic agents

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