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
1 Ischaemic heart disease
The clinical manifestations of ischaemic heart disease are:
• Chronic stable exertional angina; previous myocardial infarction
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.
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.
2 Chronic heart failure (CHF)
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.
Fig. 8.1 The causes, symptoms and signs of cardiac failure
The chest X-ray is of a 60-year-old woman with a history of ischaemic heart disease. The signs indicate congestive heart failure. Note: some of these changes are subtle and do not reproduce well in illustrations
Clinical problems
a: CHF before operation Surgery should be postponed until treatment has been optimised and the clinical condition stabilised. Hasty preoperative diuretic therapy is dangerous because it may provoke intravascular volume depletion, hypotension and electrolyte abnormalities. Patients taking diuretics (and often ACE inhibitors or angiotensin receptor antagonists in addition) may have abnormalities such as:
• Hypokalaemia (usually due to potassium-losing diuretics prescribed without potassium supplements)
• Raised plasma urea and creatinine with hyperkalaemia (particularly if taking an ACE inhibitor and spironolactone)—the urea is often raised to a greater extent than creatinine indicating intravascular volume depletion
b: Decompensated heart failure developing during or after operation This problem results from poor tolerance of intravenous fluids, unaccustomed supine posture, myocardial infarction or ischaemia in the perioperative period, or arrhythmias (particularly atrial fibrillation) induced by the stresses of surgery and anaesthesia. Prompt and vigorous diuretic therapy with intravenous furosemide and nitrate is required to prevent worsening cardiac failure, hypoxia, renal failure or other potentially lethal complications. In addition, treatment of any precipitating factors should be instituted such as reducing cardiac stress by giving good pain relief. Postoperative cardiac failure is best managed in an intensive care unit, using a central venous pressure (CVP) line to guide fluid replacement.
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.
3 Cardiac arrhythmias
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.
c: Other arrhythmias Bifascicular block, in which conduction is impaired down two of the three main fascicles (right bundle plus anterior or posterior divisions of the left bundle, manifest by right bundle branch block and left axis deviation on the ECG), may progress to complete heart block (and low cardiac output) under anaesthesia. For these patients, a prophylactic temporary transvenous pacemaker should be considered before operation.
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
a: Mild-to-moderate essential hypertension Patients with a systolic pressure of less than 180 mmHg and a diastolic less than 110 mmHg are at minimal risk of cardiac complications unless there is some other cardiovascular disease. Sometimes, anxiety about the operation contributes to the hypertension. A labile blood pressure or systolic hypertension at any time may, however, indicate widespread atherosclerosis.
b: Treated hypertension Most common antihypertensive drugs are ‘cardioprotective’ and should not be stopped prior to general anaesthesia. Despite the patient being ‘nil by mouth’ in the immediate preoperative period, the normal dose of oral antihypertensive drugs should usually be given with a small amount of water. Sudden withdrawal of antihypertensive drugs may cause rebound hypertension. Withdrawal of beta-blockers may trigger autonomic hyperactivity and lability of blood pressure. Postural hypotension may occur after operation, especially if there is dehydration.
c: Severe or poorly controlled hypertension If the diastolic BP is > 110 mmHg, then treatment needs to be instituted and any non-urgent operative procedure delayed. During anaesthesia the untreated hypertensive patient has a very labile BP and is at high risk of perioperative myocardial infarction, cardiac failure or stroke.
6 Valvular heart disease
Aortic stenosis
Clinical signs of aortic stenosis are:
• Slow rising upstroke of the carotid pulse
• A harsh ejection systolic murmur radiating into the neck
• Hyperdynamic apex beat indicating left ventricular hypertrophy. (Note: the apex beat is only displaced laterally if aortic stenosis coexists with aortic regurgitation or is complicated by cardiac failure)
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.
Infective endocarditis and indications for antibiotic prophylaxis
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.
