FEATURE ANAESTHESIA


The anaesthesia personnel


encounters these obese individuals in the operating room for a wide range of surgeries either planned or an emergency and are faced with challenges of obesity per se as well as their co- morbidities. The challenges faced by the anaesthetist are real and likely to increase in the forthcoming years. These patients seek medical help


for weight loss, weight maintenance as well as reduction in various risk factors. Medical management includes behavioural and lifestyle medication including a dietary and exercise program as well as pharmotherapy. A lot of obese individuals are on medical management for their obesity related co-morbidities. Bariatric surgeries are becoming


one of the most common surgeries encountered these days. A thorough understanding of obesity


pathophysiology and organ system changes help providing adequate care in the operating room as well as in the postoperative care area. These patients present with a myriad of medical problems ranging from diabetes mellitus, hypertension, obstructive sleep apnoea, cardiorespiratory dysfunction and potentially difficult airways. An early preoperative assessment helps identify these problems and plan the intra-operative management as well as postoperative care.


OBSTRUCTIVE SLEEP APNEA This is defined as complete cessation of airflow for 10 seconds or more occurring at least 4-5 times per hour with a fall in oxygen saturation of at least 4%. Obstructive sleep hypopnea is defined as partial reduction of airflow of at least 50%, lasting for at least 10 seconds, occurring 15 times or more in an hour, along with a drop in saturation of 4%. These results are recorded in the form of an apnea/hypopnea index (AHI). The severity of obstructive sleep apnea/hypopnea syndrome (OSAHS) is defined arbitrarily, but a recent recommendation for classification of the disease is as follows:  Mild disease - AHI of 5-15 events/hr  Moderate disease - AHI of 15-30 events/hr  Severe disease - AHI < 30 events/hr


These patients are prone to


developing systemic and pulmonary hypertension, cardiac arrythmias and also left ventricular hypertrophy, therefore treatment is strongly recommended for OSA. Treatment depends upon the severity of OSA and consists of application of a continuous positive airway pressure (CPAP) or a bilevel positive pressure might be necessary. A baseline arterial blood gases is helpful in determining the baseline carbon dioxide retention and provides guidelines for perioperative oxygen administration, helps in weaning and deciding course of ventilator management.


CARDIOVASCULAR SYSTEM These morbidly obese patients have varying degrees of cardiorespiratory dysfunctions, they are prone to developing a term coined as “Obesity Cardiomyopathy” which results due to long standing obesity with high BMI of 40 or greater, resulting in left and right sided ventricular hypertrophies resulting in


«These patients can present with breathlessness, fatigue syncope-signs of pulmonary hypertension and cardiac failure»


cardiac failure. These patients can present with breathlessness, fatigue syncope- signs of pulmonary hypertension and cardiac failure of raised JVP, pulmonary crackles, hepatomegaly and peripheral edema. An electrocardiogram may show right ventricular hypertrophy and right axis deviation. Echocardiography depicts dilated cardiomyopathy and grades of pulmonary hypertension. Severe OSA should alert one to the possibility of pulmonary hypertension and right- ventricular failure and prompt an echocardiographic evaluation. Intravenous access, peripheral as well


as central, need to be assessed during the preoperative visit, the possibility of invasive monitoring should be discussed with the patient. If needed dopler should be used to cite these vessels. Pulmonary pathophysiology has


substantial changes in obesity. The chest wall and lung compliance reduces while airway resistance increases, the respiratory musculature is weakened. The ERV is inversely proportional to the BMI. In supine position there is basal alveolar collapse resulting in atelectasis. These regions are well perfused but under ventilated resulting in ventilation- perfusion mismatch and resultant arterial hypoxemia. ERV, FRV, TLC and FEV1 can reduce from 20-80% of predicted values. Patients with severe OHS may develop in ‘Pickwikian syndrome’ being hypersomnolent, plethoric, cyanotic, dypsneic due to chronic hypoxia and hypercapnia, pulmonary hypertension and right heart failures. Non-alcoholic Steatohepatitis


(NASH), with or without liver dysfunction, is commonly associated with obesity. Preoperative liver function tests must be carried out. The effect of NASH on the clearance of anaesthetic drugs has not been extensively studied. Renal blood flow is increased along


with increased glomerular filtration rate (GFR) in obesity, leading to increased renal clearance of drugs. Diabetes is one of the most commonly


presenting endocrine disorders in these obese patients. Glucose levels fasting and postprandial are noted. Insulin levels are done fasting as well as post prandial, C-peptide and glycosylated haemoglobin evaluated pre and post surgery. Diabetic neuropathies are common and silent infacts are common in uncontrolled diabetics.


DEEP VEIN THROMBOSIS This needs special mention, as obesity is a major risk factor for deep vein thrombosis and pulmonary embolism. Various studies have shown that older patients, history of smoking, previous history of DVT/ PE are prone to developing PE following bariatric surgery. Many factors impact the choice of anticoagulation used for venous thromboembolism prophylaxis. Although current anticoagulants such as unfractionated and low molecular weight heparins and vitamin K antagonists are effective for the prevention and treatment of thrombosis, they have several limitations. New anticoagulants have been developed that selectively inhibit thrombin or factor Xa, and have predictable dose- 


Arab Health Issue 4 2011 21


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