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Updated: Apr 19, 2026
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Published on: July 18, 2025
Retrospective Study on Liberation in Dogs Undergoing Mechanical Ventilation for Longer Than 24 Hours
Abigail E McNally1, Thomas D Greensmith1, Stefano Cortellini1
1Department of Clinical Science and Services, The Royal Veterinary College, University of London, North Mymms, Hertfordshire, UK.
Objective:
To describe liberation in a population of dogs undergoing ≥24 h of mechanical ventilation (MV) and to assess for differences between successful and unsuccessful liberation attempts as well as adherence to criteria for veterinary and human readiness to discontinue MV.
Design:
Retrospective study.
Setting:
University teaching hospital.
Animals:
Forty-seven client-owned dogs undergoing ≥24 h of MV.
Measurements And Main Results:
Medical records were retrospectively reviewed; signalment, underlying disease, indications for MV, and survival to discharge were recorded. Data were collected up to 2 h before discontinuation of MV, noting ventilator settings and physiologic and blood gas variables. Twenty-four of 47 (51.1%) cases undergoing MV were successfully liberated; of these, 22 (91.7%) dogs survived to discharge. Dogs were successfully liberated using various modes of ventilation, including assist control (15/24 [62.5%]), synchronized intermittent mandatory ventilation (8/24 [33.3%]), and pressure support ventilation (1/24 [4.2%]). Forty-eight attempts at liberation occurred in 30 dogs. Of these, 24 of 48 (50%) were successful. Only end-tidal carbon dioxide (ETCO2) was different between successful and unsuccessful liberation attempts, being higher in unsuccessful attempts (35 ± 6.8 vs. 43.7 ± 5.5 mm Hg; p < 0.0001). Sufficient information was available to assess adherence to veterinary liberation criteria in 31-36 liberation attempts, depending on the criterion. Liberation success did not differ between dogs that met the criteria and those that did not. Of dogs with complete data that were successfully liberated, 55% (10/18) did not meet current veterinary criteria to undergo a spontaneous breathing trial (SBT). The prevailing reason for failing to meet the veterinary criteria was cardiovascular instability (8/10), often due to vasopressor use (n = 7).
Conclusions:
Most successfully liberated cases did not fulfill the veterinary criteria for readiness to undergo an SBT. Dogs should not necessarily be precluded from undergoing an SBT or liberation attempt if they are receiving vasopressors but meet the remaining criteria.
