Problems for the anaesthetist in the care of the obese patient

Abstract

THE PUm'OSE OF TInS PaESENTAT~ON is to review the available information regarding obesity and anaesthesia, to give an account of experience with obese patients, and to draw some conclusions regarding the anaesthetic care of this type of individual. The factors that may be involved in the problem facing the anaesthetist are as follows: (a) aetiology, (b) associated medications, (c) nutritional or electrolyte changes, (d) physiological changes, (e) anatomical changes, and (f) concomitant disease.The aetiology of obesity has been reviewed by McCracken; a of the various factors considered, it appears unlikely that many are of significance as far as anaesthesia is concerned. The ordinary obese patient shows no evidence of thyroid or pituitary abnormality, and though conditions such as myxoedema, Cushing's syndrome, Froehlich's syndrome, and insulin producing tumours of the pancreas can all produce a degree of obesity, the associated endocrine disturbances are usually primarily apparent. However, surgery in the obese patient can be associated with unanticipated complications due to hypothyroidism, hypokalemia, or adrenal insufficiency. Another rare syndrome exists in which among other signs obesity is associated with hypotonia, electromyographic studies showing no abnormality. 2Whatever the aetiology of the condition may be, diet and exercise are important factors in the treatment, 3,4 as well as psychotherapy and perhaps surgery. Drugs are often used for their direct effect, or to treat related conditions such as hypertension. At a time when current thinking is much concerned with the interaction of drugs, the effects of thyroid preparations, sedative ,and tranquillizing drugs, and amphetamines are relevant to the anaesthetic situation. Cessation of administration of the latter may even be associated with withdrawal symptoms in the postoperative period. 5 Drugs with a high lipid solubility will form reservoirs in the body of the obese patient during anaesthesia, and even when consciol.:ness and pain responses have returned their effect may modify the action of tranquillizing, anti-emetic, or analgesic drugs given at that time. However, a realization of the potential problems mentioned so far is of little help in dealing with the principal hazards, which are cardiopulinonary in nature. They consist of a decrease in functional residual capacity, the magnitude being a function of the severity of obesity and integrity of the muscles of the thorax and diaphragm. This is exaggerated in the supine and head-down positions. Any initial hypoxia is due to uneven pulmonary perfusion ventilation ratios, and hypercapnia ensues ff there is increased ventilatory impairment. The work of breathing is increased