Change in energy expenditure normalized to fat free mass during general anesthesia in elderly and young adults.

Fat free mass will be measured using foot to foot bioimpedance analysis followed by standard preoperative investigations. The six minute walk test will be explained to each patient and separate consent will be obtained. The 6MWT is a simple practical test that measures the distance a patient can walk in six minutes on a flat hard surface reflecting submaximal functional capacity. It involves global physiological responses and allows for self paced walking making it suitable for assessing daily functional capacity. On the day of surgery standard monitors will be applied and anesthesia will be induced and maintained with propofol fentanyl and vecuronium. An endotracheal tube 7 or 8 mm ID will be used and mechanical ventilation will be set based on predicted body weight and endtidal CO2 between 35 and 40 mmHg. Minute ventilation will be calculated using the Holliday Segar formula. Depth of anesthesia during intubation will be maintained using propofol. Intraoperative monitoring will include temperature and low flow anesthesia of 500 mL per min will be initiated with sevoflurane to reach a minimum alveolar concentration of 0.8 supported by propofol until the desired MAC is achieved. Alarm limits will be set for ventilatory parameters. The following variables will be recorded every five minutes until the end of surgery namely MV temperature heart rate systolic blood pressure mean arterial pressure diastolic blood pressure end tidal oxygen fraction of inspired oxygen and EtCO2. Postoperatively patients will be observed in the post anesthesia care unit for at least one hour with rescue analgesia administered as 0.5 mcg per kg fentanyl if needed. Intraoperative opioid consumption blood loss and fluid requirements will be documented. Relevant time points such as post induction incision and end of surgery will be noted. Energy expenditure will be calculated using Weirs equation.