Hyperventilation increases muscle protein synthesis in critically ill trauma patients

Background. Critically ill trauma patients are often in negative nitrogen b alance and demonstrate advanced muscle protein wasting, which is in part du e to a decrease in muscle protein synthesis. Previous studies have been per formed on the relationship between pH and protein metabolism. Some evidence suggests that alkalosis might enhance protein synthesis. The purpose of th e present study is to determine whether protein synthesis is increased in t rauma patients who have a respiratory alkalosis from hyperventilation. Methods. Trauma patients in the intensive care unit (n = 8) who were treate d with hyperventilation for elevated intracranial pressures were enrolled. Muscle protein synthesis rates were determined in vivo using the flooding m ethod with L-[H-2(5)]phenylalanine. Measurements were performed twice on ea ch patient within a 36-h period, first during hyperventilation and then aft er hyperventilation was discontinued. Hemoglobin oxygen saturation was main tained above 95% for all measurements. Results. Protein synthesis in muscle was 1.38 +/- 11%/day during hyperventi lation (pH 7.50 +/- 0.02, pCO(2) 27.3 +/- 1.0 mm Hg) and 0.93 +/- 0.15%/day after respiratory parameters were normalized (pH 7.39 +/- 0.01, pCO(2) 39. 4 +/- 1.5 mm Hg). The synthesis rate was significantly higher (P < 0.01, pa ired t test), 0.46 +/- 0.13%/day (32.6%), at the time of hyperventilation. Conclusion. Muscle protein synthesis is elevated during hyperventilation in critically ill patients with traumatic brain injury. We believe this preli minary study provides data that warrant confirmation in larger clinical stu dies. It suggests that this ventilatory therapeutic strategy may have a rol e in mitigating the negative nitrogen balance and muscle protein wasting th at can impair the recovery of these patients. (C) 2000 Academic Press.