Continuous Positive Airway Pressure During Mechanical and Spontaneous Ventilation Effects on Central Haemodynamics and Oxygen Transport

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Abstract
The effect of continuous positive airway pressure [CPAP] during continuous mechanical (CMV + PEEP [positive end-expiratory pressure]) and spontaneous (CPAP) ventilation on central hemodynamics and systemic O2 transport was studied in 10 male patients who had undergone aortocoronary bypass graft operation 18 h earlier. With the change from CMV + PEEP 5 cmH2O to CPAP 5 cmH2O, cardiac index increased from 2.58 .+-. 0.44 standard error of the mean to 2.88 .+-. 0.19 l/min/m2 (P < 0.005), and systemic O2 transport improved from 8.5 .+-. 0.6 to 9.5 .+-. 1.0 ml/min per kg (P < 0.05). Arterial O2 tension and content did not change, but mixed venous blood O2 tension increased from 3.5 .+-. 0.2 4.2 .+-. 0.2 kPa (P < 0.005), reflecting the increase in cardiac output. Arteriovenous O2 content difference decreased from 4.6 .+-. 0.5 (CMV + PEEP) to 3.6 .+-. 0.2 (CPAP) ml/100 mil (P < 0.05), while total O2 consumption remained unchanged. Mean systemic arterial pressure increased from 10.8 .+-. 0.4 to 11.6 .+-. 0.4 kPa (P < 0.05) and mean pulmonary arterial pressure changed from 2.2 .+-. 0.1 to 2.4 .+-. 0.1 kPa (P < 0.05). Right atrial and pulmonary capillary wedge pressures did not change. In terms of central hemodynamics and tissue O2 supply, CPAP offers a noteworthy alternative weaning method and an alternative to CMV + PEEP in cases where therapy is prolonged and the patient is able to breathe spontaneously.