Static thoracic compliance as a measurement of pulmonary function in dogs

Thoracic compliance measurements by use of readily available equipment were determined to be practical and safe in dogs. Twenty healthy dogs (age 1 to 16 years, weight 2.3 to 49.5 kg) were anesthesized for routine procedures such as dentistry or neutering. The animals were first hyperventilated to reduce pulmonary atelectasis, to check for leakage at the endotracheal tube cuff, and to induce mild hypocarbia, thus minimizing voluntary respiratory efforts. Total thoracic compliance measurements were calculated as the difference between exhaled volumes at static inspiratory pressures of 15 and 20 cm of H2O, divided by the pressure difference, and expressed as a function of body weight. The procedure was easy, took 5 to 10 minutes, and caused no recognizable ill effects in any of the dogs studied. Mean total thoracic compliance was 42.25 +/- 32 ml/cm of H2O. There was a significant correlation with weight, but no significant relationship was seen between compliance and age, or gender. The mean weight-adjusted total thoracic compliance was 1.85 +/- 0.56 ml/cm of H2O/kg. In studies in a small group of dogs with documented respiratory tract disease, 4 of 7 had a mean compliance greater than 2 SD below the normal range. Thus, this test may become part of the routine workup of any animal being anesthetized for procedures such as bronchoscopy to evaluate respiratory tract disease. Routine monitoring of animals on ventilators could provide early warning of complications such as pneumonia, pleural effusion, or pulmonary edema.