ANAEMIA

Severe anaemia interferes with the body’s oxygen transport system by reducing the amount of oxygen that can be carried by the blood as oxyhaemoglobin. This means that, to supply the tissues with adequate amounts of oxygen, the heart must pump more blood. This results in the tachycardia, flow murmurs and heart failure sometimes found in severely anaemic patients.

If a severely anaemic patient is to be subjected to surgery, which may cause blood loss, and to anaesthesia, which may interfere with oxygen transport by the blood, all possible steps must be taken to correct the anaemia preoperatively. If time is limited, it may be possible to do this only by transfusion, after consideration of the possible benefits and risks.

There is no absolute haemoglobin concentration below which a patient is “unfit for anaesthesia”.

The decision to anaesthetize a patient depends on the circumstances and on the urgency of the need for surgery. Ideally, of course, every patient should have a haemoglobin level “normal” for the community from which he or she comes. However, a patient with a ruptured ectopic pregnancy cannot be sent away with iron tablets or even wait for a preoperative blood transfusion. As a rough guide, most anaesthetists prefer not to anaesthetize a patient whose haemoglobin level is below 8 g/dl if the need for surgery is not urgent, especially if serious blood loss is expected.

Remember that “anaemia” is not a complete diagnosis and may indicate that the patient has another pathological condition that has so far gone undetected. Possibilities include sickle-cell disease, chronic gastrointestinal bleeding from hookworm infection or a duodenal ulcer. The cause of “incidental” anaemia may be far more in need of treatment than the condition requiring surgery. It is therefore important to investigate anaemic patients properly and not to regard anaemia as a “nuisance” for the anaesthetist or to assume that it is necessarily due to parasitic infection.

Emergency surgery

An anaemic patient with an urgent need for surgery has a lower oxygen-carrying capacity of the blood than normal. Avoid drugs and techniques that may worsen the situation by lowering the cardiac output (such as deep halothane anaesthesia) or by allowing respiration to become depressed. Ether and ketamine do not depress cardiac output or respiration significantly.

Oxygen supplementation is desirable for anaemic patients. Blood lost must be replaced with blood, or the haemoglobin concentration will fall further. Ensure that the patient does not become hypoxic during or after the operation.

See also The Clinical Use of Blood (WHO, 2001).

HYPERTENSION

Elective surgery

Elective anaesthesia and surgery are contraindicated in any patient with sustained hypertension and blood pressure greater than 180 mmHg (24.0 kPa) systolic or 110 mmHg (14.7 kPa) diastolic. This degree of hypertension will be associated with clinical signs of left ventricular hypertrophy on chest X-rays and electrocardiograms, retinal abnormality and, possibly, renal damage.

Patients whose hypertension has been reasonably well controlled can be safely anaesthetized. It is important not to discontinue any regular treatment with antihypertensive drugs or the patient’s blood pressure may go out of control. After a full assessment of the patient, including obtaining a chest X-ray and an electrocardiogram and measuring serum electrolyte concentrations (especially if the patient is taking diuretic drugs), you may carefully use any suitable anaesthetic technique, with the exception of administering ketamine, which tends to raise the blood pressure. If the patient is receiving treatment with beta blockers, the treatment should be continued, but remember that the patient will be unable to compensate for blood loss with a tachycardia, so special attention is needed.

If an elective operation is postponed to allow hypertension to be treated, the patient should normally be allowed a period of 4–6 weeks to stabilize before returning for surgery. It is not safe simply to start antihypertensive drugs the day before an operation.

Emergency surgery

In an emergency, the same principles apply to the management of a hypertensive patient as to a patient who has had a recent myocardial infarction. Consider a conduction anaesthetic technique and make every attempt to avoid hypotension, which can precipitate a cerebrovascular accident or myocardial infarction. Severely hypertensive patients whose need for surgery is not urgent should be referred.

RESPIRATORY DISEASES

Tuberculosis is a multisystem disease whose respiratory and other effects may present problems for the anaesthetist. There are, firstly, the problems of anaesthetizing a patient with a severe systemic illness, who may have nutritional problems and abnormal fluid losses from fever combined with a poor oral intake of fluid and water and a high metabolic rate requiring a greater supply of oxygen than normal.

Local problems in the lung – the production of sputum, chronic cough and haemoptysis – may lead to segmental or lobar collapse, resulting in inadequate ventilation and oxygenation. Tracheal tubes may quickly become blocked with secretions, so frequent suction may be necessary. In sick patients who cannot cough effectively, a nasotracheal tube may be left in place after surgery or a tracheostomy performed to allow for aspiration of secretions.

Contamination of anaesthetic equipment with infected secretions must also be considered. If you have to anaesthetize a patient with tuberculosis, use either a disposable tracheal tube, which you can then throw away, or a red rubber tube which, after thorough cleaning with soap and water, can be autoclaved. The patient’s breathing valve and anaesthetic tubing will also need to be sterilized. Black antistatic breathing hose can be autoclaved. It is unlikely that the self-inflating bag (SIB) in a draw-over system will be contaminated but, if you sterilize an SIB, be careful, as many of these are damaged by autoclaving. If you use a Magill breathing system on a Boyle’s machine, the whole system should be autoclaved, as the patient can breathe directly into the bag. If you cannot see how to overcome contamination problems with inhalational anaesthesia, use ketamine or a conduction technique instead.

ASTHMA AND CHRONIC BRONCHITIS

Elective surgery

For elective anaesthesia and surgery in a patient with a history of asthma, the asthmatic condition should be under control and the patient should have had no recent infections or severe wheezing attacks. If the patient takes drugs regularly, treatment must not be discontinued. Special inquiry must be made about any former use of steroids, systemically or by inhaler. Any patient who has previously been admitted to hospital for an asthmatic attack should be referred for assessment.

The patient with chronic bronchitis has some degree of irreversible airway obstruction. In taking a history, you should ask about exercise tolerance, smoking and sputum production. The patient must be told to give up smoking completely at least four weeks before the operation. Simple clinical tests of lung function may be valuable; healthy people can blow out a lighted match 20 cm from the mouth without pursing their lips and can count aloud in a normal voice from 1 to 40 without pausing to draw breath. The nature of the operation is of great importance; elective surgery on the upper abdomen is contraindicated, since respiratory failure in the postoperative period is likely. Patients needing such surgery must be referred to a hospital where their lungs can be ventilated artificially for 1–2 days postoperatively if necessary.

Conduction anaesthesia combined with intravenous sedation with small doses of diazepam may be a better choice of technique than conduction anaesthesia alone or general anaesthesia. If general anaesthesia is necessary, premedication with an antihistamine such as promethazine, together with 100 mg of hydrocortisone, is advisable. It is important to avoid laryngoscopy and intubation during light anaesthesia, as this is likely to lead to severe bronchospasm. Ketamine is quite suitable for intravenous induction because of its bronchodilator properties.

For short procedures:

Ether and halothane are both good bronchodilators, but ether has the advantage that, should bronchospasm develop, epinephrine (0.5 mg subcutaneously) can safely be given. This would be very dangerous with halothane which sensitizes the heart to the dysrhythmic effects of catecholamines. Aminophylline (up to 250 mg for an adult by slow intravenous injection) can be used as an alternative to epinephrine if bronchospasm develops; it is compatible with any inhalational agent.

At the end of any procedure that includes tracheal intubation, extubate with the patient in the lateral position and still deeply anaesthetized; the laryngeal stimulation might otherwise again provoke intense bronchospasm.

Emergency surgery

For emergency surgery, use a technique with intubation and IPPV with added oxygen. Postoperatively, give oxygen at not more than 1 litre/minute via a nasal catheter. Be careful with opiates, as the patient may be unusually sensitive to respiratory depression.

DIABETES

When a diabetic patient needs surgery, it is important to remember that he or she is more likely to be harmed by neglect of the long term complications of diabetes than from the short term control of blood glucose levels. Make a full preoperative assessment, looking especially for symptoms and signs of peripheral vascular, cerebrovascular and coronary disease, all of which are common in patients with diabetes, as is chronic renal failure.

Elective surgery

The diabetic patient who needs elective surgery is not difficult to handle. In the short term, the only major theoretical risk is that undetected hypoglycaemia might occur during anaesthesia. Most general anaesthetics, including ether, halothane and ketamine, cause a small and harmless rise in the blood sugar concentration and are therefore safe to use. Thiopental and nitrous oxide have little effect on the blood sugar concentration; no anaesthetic causes blood sugar to fall.

Diabetic patients may be classified according to whether their diabetes is controlled with insulin (insulin-dependent diabetes or Type I) or by diet and/or oral hypoglycaemic drugs (non-insulin dependent diabetes or Type II).

Insulin-dependent diabetes

For insulin-dependent patients, ensure that the diabetes is under reasonably good control:

As an alternative, if frequent blood sugar measurements are impossible:

This scheme is simple and will maintain blood glucose levels in most diabetic patients in the range 5–14 mmol/litre. However, make regular checks of blood glucose concentration and change the regimen, if necessary. Note that, if glass infusion bottles are used, the dose of insulin will need to be increased by about 30%, as the glass adsorbs insulin.

Where several patients are due to undergo surgery on a given day, diabetic patients should be first on the list, since this makes the timing and control of their insulin regimen much easier.

Non-insulin dependent diabetes

If the patient’s diabetes is controlled by diet alone, you can normally use an unmodified standard anaesthetic technique suitable for the patient’s condition and the nature of the operation.

Patients with non-insulin dependent diabetes controlled with oral hypoglycaemic drugs should not take their drugs on the morning of anaesthesia. Because certain drugs (notably chlorpropamide) have a very long duration of action, there is some risk of hypoglycaemia, so the blood sugar concentration should be checked every few hours until the patient is able to eat again.

If difficulties arise with these patients, it may be simpler to switch them temporarily to control with insulin, using the glucose plus insulin infusion regimen described above.

Emergency surgery

The diabetic patient requiring emergency surgery is rather different. If the diabetes is out of control, there is danger from both diabetes and the condition requiring surgery. The patient may well have:

In these circumstances, medical resuscitation usually has priority over surgical need, since any kind of anaesthesia attempted before correction of the metabolic upset could rapidly prove fatal.
Resuscitation will require large volumes of saline with potassium supplementation (under careful laboratory control). There is no point in giving much more than 4 International Units of insulin per hour, but levels must be maintained either by hourly intramuscular injections or by continuous intravenous infusion. The patient will need a nasogastric tube and a urinary catheter.

If the need for surgery is urgent, use a conduction anaesthetic technique once the circulating volume has been fully restored. Before a general anaesthetic can be given, the potassium deficit and acidosis must also have been corrected, or life-threatening dysrhythmias are likely. The level of blood sugar is much less important; it is better left on the high side of normal.

OBESITY

Obese patients (who may also be diabetic) face a number of problems when anaesthesia is necessary. Obesity is often associated with hypertension – though with a very fat arm the blood pressure is difficult to measure and may appear high when in fact it is not. Because of the extra body mass, the cardiac output is greater than in a non-obese person; more work is also required during exertion, which places greater stress on the heart. The association of smoking, obesity and hypertension is often a fatal one, with or without anaesthesia.

Because of the mass of fat in the abdomen, diaphragmatic breathing is restricted and the chest wall may also be abnormally rigid because of fatty infiltration. Breathing becomes even more inefficient when the patient is lying down, so IPPV during anaesthesia is recommended, with oxygen enrichment if possible.

Extra technical problems are found in obese patients. A fat neck makes airway control and intubation difficult and excess subcutaneous fat leads to difficulty with venepuncture and conduction anaesthesia. Do not give drugs on a weight basis, as this will result in an overdose. For most drugs given intravenously, a 120 kg patient needs only about 130% of the normal dose for an adult of 60–70 kg. For general anaesthesia in the obese patient, a technique based on tracheal intubation with IPPV using relaxants is recommended.

PREVENTION OF BLOOD-SPREAD INFECTIONS DURING ANAESTHESIA AND SURGERY

Because of the risk of infection, blood transfusion must be used only when medically necessary and when the potential benefits outweigh the risks. The decision to transfuse should be based on both the patient’s condition and the local availability and safety of blood supplies. Where blood supplies are scarce or unsafe, it may be possible to use pre-donation by the patient in elective cases or to use autologous transfusion in emergencies.
Minimize the risk of transmission of infection: