Preparation for anaesthesia
Recognition of general medical and specific anaesthetic risk factors facilitates the implementation of pre-emptive measures and improves patient safety. Early assessment, liaison with the anaesthetist and appropriate investigations avoid unnecessary delays. In any case, the anaesthetist who is to be present during the operation should assess the patient preoperatively and participate in the preparation for surgery.
Preoperative evaluation and management
Investigation of the general condition of the patient before surgery should be specific according to the general history and clinical signs. Investigations in fit people are unnecessary and uneconomic, but indicated tests should be performed as early as possible, preferably before admission. Routine haematological and biochemical screens, with electrocardiography and chest radiography, are prudent investigations in elderly people receiving general anaesthesia for all but minor surgery. The saving of a serum sample for transfusion cross-match, a check for hepatitis antigen and a sickle-cell screen, if indicated, should not be forgotten.
Uncontrolled hypertension and angina, dysrhythmias and cardiac failure are common reasons for postponement of elective procedures. Correction of hypertension and ischaemic heart disease is essential and needs to be continued through the operative period, even though the patient may be unable to take oral drugs. Fast atrial fibrillation needs to be controlled before anaesthesia. Symptomatic disorders of sinoatrial conduction require pacemaker insertion before anaesthesia, as do all cases of either Mobitz type 2 second-degree block or third-degree heart block. In an emergency, transvenous temporary pacing wires or external pacing can be used. Modern variable-rate demand pacemakers may require resetting to fixed rate mode, but are generally stable during anaesthesia. However, a cardiological opinion should be sought, bipolar diathermy employed if possible and the.diathermy plate should be positioned so that the current does not cross the heart or pacemaker wires.
Recent myocardial infarction is a strong contraindication to elective anaesthesia. There is a significant mortality from anaesthesia within 3 months of infarction, and elective procedures should ideally be delayed until at least 6 months have elapsed.
Patients with valvular disease will need corrective treatment of any preoperative infections, and appropriate perioperative prophylactic antibiotic cover, to avoid subacute bacterial endocarditis.
Patients with cardiac disease need careful preoperative evaluation. Much can be derived from a detailed history including exercise tolerance and drug history. Echocardiography has enabled noninvasive assessment of cardiac function. Any electrolyte abnormality (especially hypokalaemia) or anaemia should be corrected and the circulatory volume should be maintained at normal level. Perioperatively, the presence of an adequate urine output is a useful indicator of adequacy of the circulating volume.
Operative procedures create an increased demand for oxygen due to pain, surgical stress and temperature loss. Patients with cardiac disease may need a period of elective postoperative mechanical pulmonary ventilation after surgery, until the period of raised oxygen consumption has passed. The careful anaesthetist and surgeon plan such care before surgery.
Thoracic surgical procedures demand specific preoperative tests of respiratory function including spirometry and blood gas analysis. In general surgical practice, respiratory infection and asthma are the common problems needing treatment before anaesthesia. In chronic respiratory failure, careful attention should be given to perioperative physiotherapy, early mobilisation and treatment of infection. Measurement of oxygen saturation and blood gas tensions preoperatively give a very useful guide to future values on recovery. The need for postoperative ventilatory support should be anticipated. Regional anaesthesia as appropriate is advantageous in respiratory disease. Upper abdominal and thoracic procedures are unsuited to regional anaesthesia alone, as positive pressure ventilation under general anesthesia is necessary.
Aspiration of gastric contents carries a high risk of acid pneumonitis, pneumonia and death. Regurgitation in the presence of a hiatus hernia, or from ‘the full stomach’, may result from emergency (nonstarved) cases, bowel obstruction or paralytic ileus and indicates mandatory precautions during anaesthesia. A rapid sequence induction is conducted, in which the patient is ‘preoxygenated’ and cricoid pressure is applied from loss of consciousness until the lungs are protected by tracheal intubation. Bowel obstruction requires preoperative nasogastric aspiration and careful correction of fluid and electrolyte balance before anaesthesia is induced.
H2-receptor blocking agents such as ranitidine are administered if there is an increased risk of regurgitation, ideally at least 2 hours preoperatively.
Anaesthesia in the presence of jaundice carries a high risk of renal damage. The anaesthetist should ensure that no hypovolaemia occurs and that a good urine output is present before induction, by the preoperative infusion of intravenous crystalloid solutions. A diuretic agent should only be used if the circulating volume is first assessed to be adequate.
Familial porphyria and hyperpyrexia are hereditary metabolic disorders associated with high anaesthetic risks. Phaeochromocytoma is also associated with severe anaesthetic complications. The presence of these disorders requires highly specific preanaesthetic planning. Diabetes and adrenal suppression from steroid therapy are also common metabolic disorders which complicate anaesthesia.
Non insulin-dependent diabetic patients on diet and oral hypoglycemic agents will need blood sugar measurement during anaesthesia. An intravenous infusion of glucose may be required if the long-acting hypoglycemic effects persist even if the agent was omitted on the day of surgery.
Except for minor surgery, an intravenous infusion of glucose with soluble insulin is likely to be necessary with close monitoring and control of blood sugar levels. Insulin-dependent diabetes always needs preoperative conversion to control with rapidly acting soluble insulin by intravenous infusion on the operative day, and this is continued until the patient has recovered from the operation. In practice, for maintenance of blood sugar levels, it is best to keep a constant infusion of 5—10 per cent glucose with potassium supplementation through a separate intravenous channel at about 2 litres/24 hours. Soluble short-acting insulin is given continuously by intravenous syringe pump, with the rate indicated by frequent (1—4-hourly) measurement of blood glucose concentration. The plasma potassium level needs careful control. The circulating volume should be manipulated independently via a separate infusion of normal saline, blood or colloid. In this way a steady control of blood glucose concentration can be easily achieved by an experienced nurse. Patients who are receiving corticosteroids or who have received them in the past 2 months require supplemention with hydrocortisone during and after surgery to avoid adrenal insufficiency (Addisonian crisis).
Whether iatrogenic (including therapeutic) or pathological in origin, coagulation disorders need careful assessment before surgery with a coagulation screen, or clotting factor and platelet measurements. In acquired disorders, such as disseminated intravascular coagulation, fresh frozen plasma or cryoprecipitate and platelets may be given to the patient by the anaesthetist perioperatively to control haemorrhage. Patients receiving therapeutic warfarin need to cease treatment several days preoperatively and have prothrombin time (PT) measurement until the International Normalised Ratio (INR) falls to about 1.5 from the therapeutic range of 2.0—4.2. At an INR of 1.5,surgical haemostasis should be achieved. Vitamin K can be used to hasten the reversal of warfarin but it is a long-acting agent and can cause weeks of resistance to warfarin after surgery, so it is better to avoid it. When the risk of thrombosis and embolism is high, an intravenous infusion of heparin can be used to replace warfarin. The heparin can be stopped or reversed with protamine for the period of surgery. Rapid control of heparin activity is easy, but it is not so with warfarin.
In cerebral disease and trauma, hypoxia, hypercarbia and respiratory obstruction raise intracranial pressure and can cause cerebral damage. In the presence of deteriorating consciousness, management of the airway and ventilation is of prime importance, and especially so in traumatic injury in which early endotracheal intubation and pulmonary ventilation should precede supine positioning for computed tomography (CT) of the brain. Particular care of the neck during intubation is necessary if a cervical fracture is suspected. Skull traction and awake intubation under local anaesthesia are sometimes used.
Anticonvulsant drugs must be continued during surgery on epileptic patients, and this may necessitate using intravenous administration.
In peripheral neuropathies and myopathies, the need for prolonged periods of postoperative ventilation should be anticipated.
Anaesthesia and psychiatric disease
General, rather than regional, anaesthesia is usually necessary. Tricyclic antidepressants and monoamine oxidase inhibitor drugs potentiate sympathomimetic agents so adrenaline and cocaine must be avoided. Pethidine can also cause hypertension with these drugs. Other narcotic analgesic agents can be used but caution is necessary as their side effects can be potentiated, especially with monoamine oxidase inhibitors.
Starvation before surgery
Standard practice for many years has been 6 hours’ abstinence from food and 4 hours’ abstinence from fluids. Recently, there has been a shift to permit clear, nonfizzy fluids up to 2 hours preoperatively. These rules apply whenever loss of protective laryngeal reflexes may pertain, as during regional anaesthesia and sedation. Small children are usually given a glucose drink about 4hours preoperatively to prevent perioperative hypoglycaemia.
Consent for surgery and anaesthesia
Informed consent should be obtained by the surgical team, preferably the operating surgeon, before any sedation is given, but the anaesthetist should still explain anaesthetic procedures, especially regional and spinal techniques, and discuss potential sequelae.
Preoperative drugs and treatment
Preoperative sedative and analgesic medication is becoming much less common. Heavy sedative, antiemetic, antitussive, amnesic medication was previously used for the relatively unpleasant inductions of anaesthesia with pungent inhalational agents. Except for patients who are already in pain, opioid analgesic agents are generally first given during induction of anaesthesia, administered intravenously for rapid onset of action prior to surgery. For reduction of anxiety, oral short-acting benzodiazepines are now more commonly used 1—2 hours preoperatively, especially for children. Oral trimeprazine is also still popular for children.
For the increasing numbers of day-case procedures, preoperative sedation is avoided so as to promote rapid emergence from anaesthesia and mobilisation.
The anticholinergic agents, atropine, glycopyrronium and hyoscine, are used to reduce respiratory and oral secretions. They are not essential with modern anaesthetic agents, but still useful for airway surgery and endoscopy. Atropine and glycopyrronium also protect against vagal dysrhythmias, for which administration at induction is just as effective, and can cause alertness and tachycardia. Hyoscine is pleasantly sedative without the cardiac effects of atropine, but it can cause excessive sedation in infants or the elderly.
Antithrombotic prophylaxis is usually initiated preoperatively in major surgery, commonly by subcutaneous heparin injection. Particular attention must be given to higher risk patients such as women taking contraceptive and hormone replacement drugs, and those undergoing pelvic, hip, knee and cancer surgery. Low dose progesterone preparations may be effectively covered by subcutaneous heparin, but other less commonly prescribed forms of contraceptive hormone treatment may need to be stopped 1 month before major surgery.
Preoperative chest physiotherapy, possibly with bronchodilator treatment, may be indicated.
If indicated, prophylactic antibiotic agents are given by the anaesthetist in concert with the surgeon, either with the premedication or intravenously at induction of anaesthesia.
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