The Metabolic Cost of Breathing in Critical Surgical Patients

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Abstract
Twenty ventilator-dependent patients, 14 male and six female, age 47.9 ± 14, status post polytrauma (14), emergency surgery (three), and coronary artery bypass (three) were evaluated to compare measured energy expenditure (MEE) between the intermittent mandatory ventilation mode (IMV) and assist mode ventilation (AMV) utilizing indirect calorimetry. The MEE was then compared to the predicted basal energy expenditure (PEE) utilizing the Harris-Benedict equation (HBE) and approporiate correction factors dependent on disease and injury status (mean 1.65 ± 0.24). The mean oxygen consumption (V̇O2) (IMV) was 347.5 ± 54.6 ml/min; (V̇O2) (AMV) was 307.1 ± 51.4 ml/min (p < 0.001). The mean MEE (IMV) was 2,380 ± 369 kcal/day; MEE (AMV) was 2,128 ± 342 kcal/day (p < 0.05). The mean predicted energy expenditure (PEE) was 2,731 ± 416 kcal/day. The IMV mode required 11.6% more pulmonary work when compared to AMV (V̇O2 IMV – V̇O2 AMV). The PEE overestimated caloric needs in ventilator-dependent patients by 12.8% on IMV and 22.1% on AMV. The MEE (IMV) required 10.7% more energy than MEE (AMV). Assist mode ventilation resulted in decreased work of breathing and decreased energy expenditure, and the (HBE) inaccurately predicted caloric needs in ventilator dependent patients.

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