Perioperative Anesthetic Management in Morbidly Obese Patients

Abstract

SUMMARY besity is a major health problem including an increased risk for coronary artery disease (CAD), hypertension (HTN), diabetes mellitus (DM), gallbladder disease, dyslipidemia, degenerative joint disease, obstructive sleep apnea (OSA), socioeconomic and psychological impairment. Clinically, obesity is best expressed in terms of BMI = body weight (kg) / height (m2). Extreme obesity is a BMI more than 40 kg/m2, and morbid obesity is BMI more than 55 kg/m2. Obesity is a complex and multifactorial disease. Genetic, ethnic and socioeconomic factors may contribute. Medical disorders such as Cushing's disease or hypothyroidism may predispose to obesity. Corticosteroids, antidepressants and certain other drugs may lead to weight gain. Morbid obesity is associated with reduction in functional residual capacity (FRC), expiratory reserve volume (ERV) and total lung capacity (TLC). These changes have been attributed to mass loading and splinting of the diaphragm. Obstructive sleep apnea (OSA) is a recurrent apnea that leads to hypoxemia, hypercapnia and pulmonary and systemic vasoconstriction. It is present in approximately 5% of extremely obese patients. Recurrent hypoxemia leads to secondary polycythemia and is associated with an increased risk of ischemic heart disease and cerebrovascular disease, O Summary 126 while hypoxic pulmonary vasoconstriction leads to right ventricular failure. Cardiovascular system dominates morbidity and mortality in obesity and manifests itself in the form of ischemic heart disease, hypertension and cardiac failure. Hypoxia, hypercapnia, electrolyte disturbance caused by diuretic therapy and coronary artery disease may precipitate arrhythmia in obese patients. Morbidly obese patients frequently experience gastroesophageal reflux disease due to increased intra-abdominal pressure; also these patients may develop type II diabetes mellitus and can be resistant to insulin. Early degenerative arthritic changes of the weight bearing joints, including the knees, hips, and spine have been reported in obese patients. Obesity is also a risk factor for deep venous thrombosis, venous stasis ulcers, and pulmonary embolism. Proper adjusting of the doses of different drug groups is an important issue which requires full understanding of the pharmacodynamics and pharmacokinetics of each drug. Most anesthetic agents are metabolized in different way if compared with non-obese persons; for example, volatile anesthetic agents are metabolized to a greater extent by morbidly obese patients than by non-obese patients and this leads to concern about toxicity. Summary 127 Great care should be taken in the preoperative assessment. Careful history, clinical examination and investigations should be played more towards cardiovascular diseases, pulmonary functions as well as endocrinal abnormalities including thyroid function and diabetes mellitus. Anesthetic management of obese patients should take into consideration the specific problems associated with obesity and optimize them before surgery. Antibiotics, anxiolytics, analgesia, and prophylaxis against both aspiration pneumonitis and DVT should be addressed during premedication. Intraoperative considerations include proper positioning of morbidly obese patients also protection of pressure areas because pressure sores and neural injuries are more common in this group, especially if they are diabetic. Proper monitoring of these high risk patients with full routine monitors, specially, capnometry and pulse oximetry should be done. General anesthesia is better as regard ventilation which should be controlled. However, a combined method of epidural (good for postoperative pain relief) and general anesthesia is the best procedure in the anesthetic management in morbidly obese patients. The most important complications that may face the obese patients postoperatively include respiratory problems