Abstract:
Objective To compare the effect of invasive continuous positive airway pressure (CPAP),
pressure-controlled ventilation with positive end expiratory pressure (PCV+PEEP) and
spontaneous breathing (SB) on carbon dioxide removal, blood oxygenation and indicators of
tissue perfusion in healthy anaesthetised dogs.
Study design Prospective randomised crossover study.
Animals Fifteen intact male dogs of various breeds of mean (± standard deviation) age and
weight of 25 (± 19) months and 21.7 (± 9.9) kg, respectively.
Methods Dogs were anaesthetised (buprenorphine, medetomidine, propofol) and
maintained with isoflurane in 50% oxygen-air mixture and kept in right lateral recumbency.
Ventilation treatments (CPAP: 4 cmH2O; PCV+PEEP: 10 cmH2O peak inspiratory pressure, 4
cmH2O positive end-expiratory pressure, respiratory rate of 10 breaths minute-1 and
inspiratory-to-expiratory ratio of 1:2; SB: standard circle circuit, no pressure applied) were
administered to each dog consecutively in random order under the same anaesthetic period
with 5-minute SB washout period between treatments. Arterial and central venous blood
samples for gas analysis were collected at the start (0 minutes) and end (20 minutes) of each
ventilation treatment. Arterial to venous content difference was calculated for each
ventilatory treatment. Other physiological variables and spirometry measures were collected
at 5-minute intervals from start to end for each ventilation treatment. Data was compared
using a general linear mixed model (p < 0.05).
Results Arterial oxygen tension was significantly higher and carbon dioxide tension lower
after PCV+PEEP than CPAP and SB (all: p < 0.001), but no different between CPAP and SB (p =1.000 and p = 0.697 respectively). Central venous oxygen and carbon dioxide tensions were
significantly lower after PCV+PEEP compared to SB and CPAP (all: p < 0.001). The tidal volume
and minute volume were higher during PCV+PEEP than during SB and CPAP (both: p < 0.001).
Arterial-venous oxygen content difference was higher with PCV+PEEP compared to SB and
CPAP (both: p < 0.001).
Conclusion and clinical relevance. An increased tidal volume with PCV+PEEP resulted in
improved arterial oxygenation and carbon dioxide elimination as compared to CPAP and SB.
CPAP resulted in similar oxygenation and ventilation to SB. Increased oxygen extraction
occurred with PCV+PEEP, probably associated with a reduced cardiac output. The clinical
benefit of short-term invasive CPAP over SB in the healthy anaesthetised dog remains
uncertain.
