Predictive value of frc and respiratory compliance on pulmonary gas exchange induced by high frequency jet ventilation in humans

Abstract

Summary: To determine if functional residual capacity (FRC), compliance of the respiratory system (C), or underlying pulmonary disease are predictive for the efficacy of high frequency jet ventilation (HFJV) on pulmonary gas exchange, we investigated six adult patients within 4 h of abdominal surgery and six patients with severe adult respiratory distress syndrome. Gas exchange during intermittent positive pressure ventilation (IPPV) was compared with that during HFJV at frequencies of 100 b.p.m. (HFJV100) and 200 b.p.m. (HFJV200), resulting in a minute ventilation of about 400 ml kg-1 with both ventilatory frequencies, and in both groups of patients. Baseline FRC and C were measured during IPPV with the multiple-breath nitrogen washout method and from expiratory pressure-volume curves, respectively. Changes in the alveolar-arterial oxygen difference (PAO2-PaO2): FlO2 ratio induced by HFJV correlated negatively with C (HFJV100: r = -0.78, P <0.005; HFJV200: r = -0.84, P < 0.005); that is, greater oxygenation was obtained in patients with a better compliance. Similarly, changes in arterial partial pressure of carbon dioxide (Paco2) induced by HFJV correlated negatively with C (HFJV100: r = -0.77, P < 0.001; HFJV200: r = -0.61, P < 0.05). In contrast, there was no significant correlation between FRC measured during IPPV and changes in (PAO2-PaO2): FlO2 ratio or Paco2 induced by HFJV, as these changes were influenced more by the patient's pulmonary disease than by baseline FRC. These results should be interpreted in the context of different underlying pathophysiological mechanisms reducing FRC in both groups of patients. © 1990 British Journal of Anaesthesia.