The effects of positive end-expiratory pressure and end-inspiratory pause on dead space and alveolar ventilation in mechanically ventilated dogs.

OBJECTIVE

To evaluate the effect of 5 cmHO positive end-expiratory pressure (PEEP) and end-inspiratory pause (EIP) on airway dead space (V) and its resultant effects on alveolar tidal volume (V) and physiological dead space-to-tidal volume ratio (V/V) in dorsally recumbent anesthetized dogs.

STUDY DESIGN

Prospective, controlled clinical study.

ANIMALS

Healthy adult dogs (n = 20, > 20 kg) undergoing elective surgery.

METHODS

Dogs were mechanically ventilated across three 5 minute phases: 1) without PEEP (PEEP); 2) with 5 cmHO PEEP (PEEP); and 3) with PEEP plus an EIP (30% of inspiratory time) (PEEP+EIP), allowing 15 minutes of stabilization between phases. During each phase, expired CO tension and tidal volume (V) were measured using volumetric capnography, and arterial blood gases assessed. V, V and V/V were calculated offline and compared between phases using mixed-effect linear models. Data are presented as mean ± standard deviation (95% confidence interval) and indexed to the predicted ideal body mass when appropriate.

RESULTS

The V was 16.8 ± 1.7 (16.3-17.19) mL kg. PEEP significantly increased V [7.9 ± 1.6 (7.1-8.6) to 8.4 ± 1.8 (7.6-9.3) mL kg; p = 0.001] and V/V [0.52 ± 0.1 (0.49-0.55)% to 0.55 ± 0.1 (0.52-0.59)%; p = 0.001]. PEEP decreased V [8.9 ± 0.8 (8.6-9.4) to 8.3 ± 0.8 (7.9-8.7) mL kg; p = 0.001]. EIP reversed these changes, decreasing V back to baseline [7.8 ± 1.6 (7.1-8.6) mL kg], resulting in V/V and V returning to baseline values. Arterial PaCO remained stable across phases.

CONCLUSIONS AND CLINICAL RELEVANCE

Although PEEP increased V and decreased V, the addition of a 30% EIP mitigated these effects, suggesting that incorporating an EIP may be an effective strategy to optimize dead space and ventilation in dogs receiving mechanical ventilation with PEEP.