Cardiovascular function, pulmonary gas exchange and tissue oxygenation in isoflurane-anesthetized, mechanically ventilated Beagle dogs with four levels of positive end-expiratory pressure.

OBJECTIVES

To compare pulmonary gas exchange, tissue oxygenation and cardiovascular effects of four levels of end-expiratory pressure: no positive end-expiratory pressure (ZEEP), positive end-expiratory pressure (PEEP) of maximal respiratory system compliance (PEEPmaxC), PEEPmaxC + 2 cmHO (PEEPmaxC), PEEPmaxC + 4 cmHO (PEEPmaxC), in isoflurane-anesthetized dogs.

STUDY DESIGN

Prospective randomized crossover study.

ANIMALS

A total of seven healthy male Beagle dogs, aged 1 year and weighing 10.2 ± 0.7 kg (mean ± standard deviation).

METHODS

The dogs were administered acepromazine and anesthesia was induced with propofol and maintained with isoflurane. Ventilation was controlled for 4 hours with ZEEP, PEEPmaxC, PEEPmaxC or PEEPmaxC. Cardiovascular, pulmonary gas exchange and tissue oxygenation data were evaluated at 5, 60, 120, 180 and 240 minutes of ventilation and compared using a mixed-model anova followed by Bonferroni test. p < 0.05 was considered significant.

RESULTS

Cardiac index (CI) and mean arterial pressure (MAP) were lower in all PEEP treatments at 5 minutes when compared with ZEEP. CI persisted lower throughout the 4 hours only in PEEPmaxC with the lowest CI at 5 minutes (2.15 ± 0.70 versus 3.45 ± 0.94 L minute m). At 180 and 240 minutes, MAP was lower in PEEPmaxC than in PEEPmaxC, with the lowest value at 180 minutes (58 ± 7 versus 67 ± 7 mmHg). Oxygen delivery index (DOI) was lower in PEEPmaxC than in ZEEP at 5, 60, 120 and 180 minutes. Venous admixture was not different among treatments.

CONCLUSION AND CLINICAL RELEVANCE

The use of PEEP caused a transient decrease in MAP and CI in lung-healthy dogs anesthetized with isoflurane, which improved after 60 minutes of ventilation in all levels of PEEP except PEEPmaxC. A clinically significant improvement in arterial oxygenation and DOI was not observed with PEEPmaxC and PEEPmaxC in comparison with ZEEP, whereas PEEPmaxC decreased DOI.