Oxygen cost of breathing in patients with emphysema or chronic bronchitis in acute respiratory failure.

This study compared the oxygen cost of breathing (VO2 resp) in 19 patients with severe chronic obstructive pulmonary disease intubated for acute respiratory failure. Ten patients showed radiologic (X-ray and/or computed tomographic scan) evidence of emphysema. The remaining ones were considered as having chronic bronchitis. Measurements were made just before extubation. Despite similar expiratory airflow obstruction, patients with emphysema exhibited significantly higher VO2 resp than patients with chronic bronchitis (109 +/- 61 versus 42 +/- 26 ml/min/m2, respectively; p < 0.006). Moreover, emphysema was associated with nutritional depletion assessed through decreases in body mass index (emphysema: 17.9 +/- 3.5 kg/m2; chronic bronchitis: 28.8 +/- 8.2 kg/m2; p < 0.005). This seemed to affect somatic stores (significant decreases in arm muscular circumference and triceps skin-fold thickness, whereas visceral stores were preserved (no decreases in serum albumin, serum prealbumin, and retinol binding protein). Malnutrition appeared to be the consequence of a hypermetabolic state of the respiratory muscles, with a significant negative correlation between VO2 resp and body mass index, arm muscular circumference, and triceps skinfold thickness (p < 0.05). Total oxygen consumption normalized for body surface was similar in the two groups. Thus, in emphysematous patients, the oxygen available for tissues other than respiratory muscles was significantly reduced (emphysema: 124 +/- 51 ml/min/m2; chronic bronchitis: 207 +/- 78 ml/min/m2; p < 0.02). This could explain nutritional differences observed between patients with emphysema and those with chronic bronchitis.