The Influence of the Ventilatory Pattern on Ventilation, Circulation and Oxygen Transport during Continuous Positive‐Pressure Ventilation <i>An Experimental Study</i>

Abstract

In IPPV, the ventilatory pattern produced by the ventilator and the lung systems is known to influence pulmonary and cardiovascular functions. In this study on dogs the ventilatory pattern of a conventional respirator (Siemens‐Elema Servo Ventilator 900=SV‐900) constituted the norm for comparison with that produced by a system for volume‐controlled HFPPV. The experimental conditions were kept identical (pentobarbital anaesthesia and normoventilation, i.e. arterial P CO2 =40 mm Hg, pH=7.4 and constant F IO2 of the inspired air). At comparable alveolar ventilation the intratracheal peak and mean pressures were always higher during ventilation with SV‐900 than during HFPPV. The calculated alveolar oxygen partial pressure (P AO2 ) was almost identical with the two systems. The differences in arterial P CO2 and P O2 between SV‐900 and HFPPV were negligible when 30% O 2 was used. The total peripheral resistance (TPR) was lower during ventilation with HFPPV, and although the cardiac output (CO) and stroke volume (SV) were greater during HFPPV, calculations of the tension‐time index (TTI) revealed no differences between the two ventilator systems. With 30% O 2 the alveolo‐arterial P O2 difference (A‐aD O2 ) was smaller, the oxygen flux (OF) greater and the venous admixture lower during ventilation with HFPPV. The lower TPR during ventilation with HFPPV in association with a higher cardiac output and improved tissue perfusion indicates that the ventilatory pattern in volume‐controlled HFPPV interferes less with the cardiovascular functions. Thus, HFPPV appears able to give better myocardial and circulatory efficiency.