FEATURE ANAESTHESIA
«Obesity is a major risk factor for deep vein thrombosis and pulmonary embolism»
TBW in males and 70% in females. LBW is approximately 20-30% of the IBW. The physiological changes associated
with obesity lead to alterations in distribution, binding, and elimination of many drugs. Highly lipophilic substances such as barbiturates and benzodiazepines show significant increase in volume of distribution (Vd) in the obese in comparison to the normal weight individuals. Less lipophilic compounds have little or no change in distribution (Vd) with obesity. Cardiac failure and reduced liver
blood flow may slow elimination of drugs by liver. Cisatracurium is the muscle relaxant of choice due to its hoffman degradation. Rocuronium administration is based on IBW. The dose of SCH is based on TBW and ideal intubating conditions are obtained using 1mg/ kg doses. With regards to inhalation anaesthetics desflurane is the preferred agent of choice due to its fast onset and rapid elimination. Desflurane does not affect the liver or renal functions and has minimal toxicity. Use of sevoflurane might lead to increased serum inorganic fluoride ions concentration, best avoided in renal impairment. Most anesthetic agents are dosed according to the IBW and titrated as per requirements. Normal blood volume in a healthy
adult is 70ml/kg. In obese individuals the blood volume decreases with increasing BMI. Total body water is also decreased, almost 40-50% of the total body water. Long duration of surgical times as well as inability to calculate insensible losses might lead to subsequent hypovolaemia. Patients might require 4-5 litres of fluid for a 2-3 hours operative time for adequate rehydration. CVP and PA lines might be necessary in a few cases.
EXTUBATION OF THE OBESE PATIENT All obese patients should be extubated when fully awake and having attained adequate muscle power. Obesity tends to have a higher incidence of difficult
intubation. Ensure patients having a difficult airway can be extubated over an Aintree catheter or using the baileys manoeuvre. As a general rule, re- intubations presents additional challenges compared to the initial, first attempt, elective intubation. Here, patients are likely to be more hypoxic, hypercapneic, having more secretions, vomiting and aggressiveness. The necessary time would be shortened and the equipment not readily available. Any difficult extubation is potentially a reintubation. And any reintubation is a challenge which should be looked out for and managed. OSA patients tends to be a difficult mask ventilation a difficult intubation and a increased arterial desaturations. The risk of obstruction following extubation has reported to be increased in patients with OSA with an incidence of life threatening post-extubation obstruction in 7/135 patients. Nasal or oral CPAP and BiPAP
should be readily available for use in the postoperative period. For those with a difficult airway and a strong history of obstructive sleep apnea, the patients are recovered more gradually, transferred to the post-anesthesia care unit (PACU) and awakened with their head end elevated at 45 degrees.
REGIONAL ANAESTHESIA It is technically more demanding and challenging due to difficulty in citing
anatomical landmarks. Special equipment may be required such as long needles and use of dopplers for citing the space. Thoracic epidurals have shown to improve postoperative pulmonary functions by decreasing oxygen consumption and allowing reduction in pulmonary complications and also decreasing as well as preventing incidences of DVT. Caring for the obese still remains a challenge despite the availability of newer techniques and drugs. ■
AH Arab Health Issue 4 2011 23
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