Effect of end-inspiratory pause on airway and physiological dead space in anesthetized horses.

OBJECTIVE

To evaluate the impact of a 30% end-inspiratory pause (EIP) on alveolar tidal volume (V), airway (V) and physiological (V) dead spaces in mechanically ventilated horses using volumetric capnography, and to evaluate the effect of EIP on carbon dioxide (CO) elimination per breath (Vcobr), PaCO and the ratio of PaO-to-fractional inspired oxygen (PaO:FiO).

STUDY DESIGN

Prospective research study.

ANIMALS

A group of eight healthy research horses undergoing laparotomy.

METHODS

Anesthetized horses were mechanically ventilated as follows: 6 breaths minute, tidal volume (V) 13 mL kg, inspiratory-to-expiratory time ratio 1:2, positive end-expiratory pressure 5 cmHO and EIP 0%. Vcobr and expired tidal volume (V) of 10 consecutive breaths were recorded 30 minutes after induction, after adding 30% EIP and upon EIP removal to construct volumetric capnograms. A stabilization period of 15 minutes was allowed between phases. Data were analyzed using a mixed-effect linear model. Significance was set at p < 0.05.

RESULTS

The EIP decreased V from 6.6 (6.1-6.7) to 5.5 (5.3-6.1) mL kg (p < 0.001) and increased V from 7.7 ± 0.7 to 8.6 ± 0.6 mL kg (p = 0.002) without changing the V. The V to V ratio decreased from 51.0% to 45.5% (p < 0.001) with EIP. The EIP also increased PaO:FiO from 393.3 ± 160.7 to 450.5 ± 182.5 mmHg (52.5 ± 21.4 to 60.0 ± 24.3 kPa; p < 0.001) and Vcobr from 0.49 (0.45-0.50) to 0.59 (0.45-0.61) mL kg (p = 0.008) without reducing PaCO.

CONCLUSIONS AND CLINICAL RELEVANCE

The EIP improved oxygenation and reduced V and V, without reductions in PaCO. Future studies should evaluate the impact of different EIP in healthy and pathological equine populations under anesthesia.