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

Diego A Portela; Stuart R McKenzie; Raiane A Moura; Margaret Gonzalez; Pablo A Donati; Ignacio Sandez; Joaquin Araos; Ludovica Chiavaccini; Elizabeth A Maxwell; Pablo E Otero

doi:10.1016/j.vaa.2025.08.038

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

Vet Anaesth Analg. 2025 Nov-Dec;52(6):771-778. doi: 10.1016/j.vaa.2025.08.038. Epub 2025 Aug 20.

Affiliations

¹ Department of Comparative, Diagnostic, and Population Medicine, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA. Electronic address: dportela@ufl.edu.
² Department of Comparative, Diagnostic, and Population Medicine, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA.
³ Department of Anesthesiology and Pain Management, Facultad de Ciencias Veterinarias, Universidad de Buenos Aires, Buenos Aires, Argentina.
⁴ Hospital Veterinario Vetsia, Anaesthesia service, Leganés, Madrid, Spain.
⁵ College of Veterinary Medicine, Cornell University, Department of Clinical Sciences, Ithaca, NY, USA.
⁶ Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA.

PMID: 40925835
DOI: 10.1016/j.vaa.2025.08.038

Abstract

Objective: To evaluate the effect of 5 cmH₂O positive end-expiratory pressure (PEEP) and end-inspiratory pause (EIP) on airway dead space (V_Daw) and its resultant effects on alveolar tidal volume (V_Talv) and physiological dead space-to-tidal volume ratio (V_D/V_T) 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_OFF); 2) with 5 cmH₂O PEEP (PEEP_ON); and 3) with PEEP_ON plus an EIP (30% of inspiratory time) (PEEP_ON+EIP), allowing 15 minutes of stabilization between phases. During each phase, expired CO₂ tension and tidal volume (V_T) were measured using volumetric capnography, and arterial blood gases assessed. V_Daw, V_Talv and V_D/V_T 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_T was 16.8 ± 1.7 (16.3-17.19) mL kg^-1. PEEP_ON significantly increased V_Daw [7.9 ± 1.6 (7.1-8.6) to 8.4 ± 1.8 (7.6-9.3) mL kg^-1; p = 0.001] and V_D/V_T [0.52 ± 0.1 (0.49-0.55)% to 0.55 ± 0.1 (0.52-0.59)%; p = 0.001]. PEEP_ON decreased V_Talv [8.9 ± 0.8 (8.6-9.4) to 8.3 ± 0.8 (7.9-8.7) mL kg^-1; p = 0.001]. EIP reversed these changes, decreasing V_Daw back to baseline [7.8 ± 1.6 (7.1-8.6) mL kg^-1], resulting in V_D/V_T and V_Talv returning to baseline values. Arterial PaCO₂ remained stable across phases.

Conclusions and clinical relevance: Although PEEP increased V_Daw and decreased V_Talv, 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.

Keywords: PEEP; airway dead space; end-inspiratory pause; physiological dead space; volumetric capnography.

MeSH terms

Animals
Dogs / physiology
Female
Male
Positive-Pressure Respiration* / veterinary
Prospective Studies
Pulmonary Alveoli* / physiology
Respiration, Artificial* / veterinary
Respiratory Dead Space* / physiology
Tidal Volume