Hemodynamic responses to different modes of mechanical ventilation in dogs with normal and acid aspirated lungs.

Hemodynamic function during spontaneous breathing (SB), IMV, IPPV, continuous positive airway pressure with 10 torr PEEP (CPAP10), IMV with 10 torr PEEP (IMV10), and continuous positive pressure ventilation with 10 torr PEEP (CPPV10) were studied in 13 normovolemic anesthetized dogs. Hemodynamic function was also studied during each type of ventilation after inducing acid aspiration with 0.1 molar HCl, 5 ml/kg, in these animals. In normal dogs, hemodynamic function during IMV and IPPV did not differ significantly from that observed in spontaneously breathing dogs. CPAP10 had no effect on the hemodynamic function. IMV10 decreased cardiac index, increased arterial-mixed venous O2 content difference (avDO2) compared to SB and decreased stroke index compared to SB, IMV, and CPAP10. CPPV10 significantly decreased cardiac and stroke indicies compared to SB, IMV, IPPV and CPAP10, and increased avDO2 compared to SB. After acid aspiration, IMV did not affect the hemodynamic function, but IPPV caused a significant decrease in stroke index compared to SB. Again, CPAP10 had no significant effect on the hemodynamic function. IMV10 decreased cardiac index and increased systemic vascular resistance compared to SB and decreased stroke index compared to SB and IMV. CPPV10 increased pulmonary vascular resistance and avDO2 compared to SB, decreased cardiac index compared to SB and IMV, decreased stroke index compared to SB, IMV, and CPAP10 and increased systemic vascular resistance compared to SB, IMV, IPPV, and CPAP10. Comparing percentage change of cardiac and stroke indices before and after aspiration indicated that the decrease in lung compliance caused by acid aspiration did not prevent the hemodynamic effects of different types of ventilation. Among different types of mechanical ventilation with PEEP, CPAP10 caused the least cardiovascular depression.