Underlying any decision to perform surgery is a recognition of the balance between the risk of the procedure and the potential benefits to the patient. All patients undergo a preoperative assessment (history, examination and appropriate investigations) both to review the diagnosis and need for surgery, and to identify any coexisting disease that may increase the likelihood of perioperative complications. In general any concerns regarding coexisting disease or fitness for surgery should be discussed with the anaesthetist who makes the final decision regarding fitness for anaesthesia.
Ischaemic heart disease remains the most important risk factor for patients undergoing surgery. It is vital as part of a preoperative assessment to identify underlying cardiac disease by history, examination and, where appropriate, investigations. An ECG should be performed in any patient with a history suggestive of cardiac disease and in all patients over 50 years of age.
· Following a myocardial infarction the risk of re-infarction is maximal over subsequent 6 weeks, if surgery is performed the re-infarction rate increases dramatically. Elective surgery should be deferred by at least 6 months wherever possible.
· Hypertension should be controlled prior to any elective surgery to reduce the risk of myocardial infarction or stroke. Specialist cardiac advice may be required prior to emergency surgery in severely hypertensive patients.
· Arrhythmias should ideally be corrected prior to surgery. Chronic or complex arrhythmias should be discussed with a cardiologist prior to surgery wherever possible.
· Patients with signs and symptoms of cardiac failure should have their therapy optimised prior to surgery and require special attention to perioperative fluid balance.
· Patients with abnormal or prosthetic heart valves, patent ductus arteriosus or septal defects, and patients with a history of bacterial endocarditis should have prophylactic oral or intravenous antibiotic cover for any surgical procedures.
· The preoperative assessment should identify coexisting respiratory conditions. Patients must be asked about smoking and where possible should be encouraged to stop smoking at least 6 weeks prior to surgery. Although chest X-rays are often performed as part of the routine assessment of preoperative patients, they should not be relied on to identify underlying respiratory diseases. In general, a chest x-ray is not indicated unless there are acute respiratory signs or severe chronic respiratory disease with no film in the last 12 months.
· Patients with chronic obstructive pulmonary disease (COPD) are at significant risk of postoperative respiratory complications. Patients with severe disease may benefit from a preoperative respiratory opinion and formal respiratory function testing. Preoperatively all therapy should be optimised; pre- and postoperative physiotherapy is essential. Postoperative analgesia should allow pain free ventilation and coughing, to maximise ventilation and reduce the risk of postoperative pneumonia.
Patients with diabetes are at increased risk perioperatively both from the diabetes itself (hypoglycaemia and ketoacidosis) and from the complications of diabetes (ischaemic heart disease, vascular insufficiency, renal failure and increased risk of infection).
· Diet-controlled diabetics often require no specific intervention, but should have perioperative blood glucose monitoring.
· Patients on oral hypoglycaemic agents should omit their drugs on the morning of surgery (unless under-going a short day case procedure) and restart when oral diet recommences. Perioperative blood sugar levels should be monitored. In more major surgery, or when patients are to remain nil by mouth for a prolonged period, intravenous dextrose and variable dose intravenous short acting insulin should be considered.
· Insulin-controlled diabetics normally require conversion to intravenous dextrose and variable dose intra-venous short acting insulin prior to surgery. Close monitoring of blood sugar and urine for ketones is essential. Once oral diet is recommenced the patient should convert back to regular subcutaneous insulin therapy.
· Deep vein thrombosis, which may be complicated by pulmonary embolism, is a significant postoperative risk. Risk factors include previous history of thromboembolic disease, specific thrombophilic disorders (protein C deficiency, protein S deficiency, factor V Leiden mutations), smoking, obesity, prolonged post-operative immobility, malignancy and drugs such as the combined oral contraceptive pill. Wherever possible, risk factors should be identified and modified (including stopping the combined oral contraceptive pill 4 weeks prior to major surgery). Specific prophylaxis includes subcutaneous low-molecular-weight heparin injections and compression stockings, which should be considered for at-risk patients.
· Bleeding disorders such as haemophilia, use of anti-coagulant or antiplatelet medication and chronic liver disease may cause perioperative bleeding. Patients with known coagulation factor or vitamin K deficiencies may require perioperative replacement therapy. Anti-coagulant medication may be reduced, changed or stopped depending on the underlying indication for anticoagulation.
Patients with chronic liver disease may have impaired coagulation (vitamin K and coagulation factor deficiencies), altered metabolism of drugs, increased susceptibility to infection and hypoalbuminaemic oedema. Coagulation deficiencies should be corrected prior to surgery and careful fluid balance is essential. The patient’s alcohol intake should be elicited; symptoms of withdrawal from alcohol may occur during a hospital admission.
Pre-existing renal impairment predisposes to the development of acute tubular necrosis. Hypotension should be avoided and urinary output should be monitored so that oliguria can be recognised early and treated.
In patients requiring emergency surgery there may not be enough time to identify and correct all coexistent diseases. It is however essential to identify any cardiac, respiratory, metabolic or endocrine disease, which may affect anaesthesia. An ECG, chest X-ray and where appropriate, arterial blood gas analysis should be obtained without additional delay. Any anaemia, fluid and electrolyte imbalance or cardiac failure should be corrected prior to surgery wherever possible.