Research Paper|Articles in Press

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

Published:March 21, 2023DOI:



      To evaluate the impact of a 30% end-inspiratory pause (EIP) on alveolar tidal volume (VTalv), airway (VDaw) and physiological (VDphys) dead spaces in mechanically ventilated horses using volumetric capnography, and to evaluate the effect of EIP on carbon dioxide (CO2) elimination per breath (Vco2br–1), PaCO2, and the ratio of PaO2-to-fractional inspired oxygen (PaO2:FiO2).

      Study design

      Prospective research study.


      A group of eight healthy research horses undergoing laparotomy.


      Anesthetized horses were mechanically ventilated as follows: 6 breaths minute–1, tidal volume (VT) 13 mL kg–1, inspiratory-to-expiratory time ratio 1:2, positive end-expiratory pressure 5 cmH2O and EIP 0%. Vco2br–1 and expired tidal volume (VTE) 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.


      The EIP decreased VDaw from 6.6 (6.1–6.7) to 5.5 (5.3–6.1) mL kg–1 (p < 0.001) and increased VTalv from 7.7 ± 0.7 to 8.6 ± 0.6 mL kg–1 (p = 0.002) without changing the VTE. The VDphys to VTE ratio decreased from 51.0% to 45.5% (p < 0.001) with EIP. The EIP also increased PaO2:FiO2 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 Vco2br–1 from 0.49 (0.45–0.50) to 0.59 (0.45–0.61) mL kg–1 (p = 0.008) without reducing PaCO2.

      Conclusions and clinical relevance

      The EIP improved oxygenation and reduced VDaw and VDphys, without reductions in PaCO2. Future studies should evaluate the impact of different EIP in healthy and pathological equine populations under anesthesia.


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        • Aboab J.
        • Niklason L.
        • Uttman L.
        • et al.
        CO2 elimination at varying inspiratory pause in acute lung injury.
        Clin Physiol Funct Imaging. 2007; 27: 2-6
        • Aguirre-Bermeo H.
        • Morán I.
        • Bottiroli M.
        • et al.
        End-inspiratory pause prolongation in acute respiratory distress syndrome patients: effects on gas exchange and mechanics.
        Ann Intensive Care. 2016; 6: 81
        • Ambrósio A.M.
        • Ida K.K.
        • Souto M.T.
        • et al.
        Effects of positive end-expiratory pressure titration on gas exchange, respiratory mechanics and hemodynamics in anesthetized horses.
        Vet Anaesth Analg. 2013; 40: 564-572
        • Auckburally A.
        • Nyman G.
        Review of hypoxaemia in anaesthetized horses: predisposing factors, consequences and management.
        Vet Anaesth Analg. 2017; 44: 397-408
        • Böhm S.H.
        • Maisch S.
        • von Sandersleben A.
        • et al.
        The effects of lung recruitment on the Phase III slope of volumetric capnography in morbidly obese patients.
        Anesth Analg. 2009; 109: 151-159
        • Campbell E.J.M.
        • Nunn J.F.
        • Peckett B.W.
        A comparison of artificial ventilation and spontaneous respiration with particular reference to ventilation–blood flow relationships.
        Br J Anaesth. 1958; 30: 166-175
        • Cumming G.
        • Crank J.
        • Horsfield K.
        • Parker I.
        Gaseous diffusion in the airways of the human lung.
        Respir Physiol. 1966; 1: 58-74
        • Devaquet J.
        • Jonson B.
        • Niklason L.
        • et al.
        Effects of inspiratory pause on CO2 elimination and arterial PCO2 in acute lung injury.
        J Appl Phys. 2008; 105: 1944-1949
        • Dreyfuss D.
        • Saumon G.
        Role of tidal volume, FCR, and end-inspiratory volume in the development of pulmonary edema following mechanical ventilation.
        Am Rev Respir Dis. 1993; 148: 1194-1203
        • Fletcher R.
        • Jonson B.
        Deadspace and the single breath test for carbon dioxide during anaesthesia and artificial ventilation. Effects of tidal volume and frequency of respiration.
        Br J Anaesth. 1984; 56: 109-119
        • Fletcher R.
        • Jonson B.
        • Cumming G.
        • Brew J.
        The concept of deadspace with special reference to the single breath test for carbon dioxide.
        Br J Anaesth. 1981; 53: 77-88
        • Fuleihan S.F.
        • Wilson R.S.
        • Pontoppidan H.
        Effect of mechanical ventilation with end-inspiratory pause on blood-gas exchange.
        Anesth Analg. 1976; 55: 122-130
        • Gogniat E.
        • Ducrey M.
        • Dianti J.
        • et al.
        Dead space analysis at different levels of positive end-expiratory pressure in acute respiratory distress syndrome patients.
        J Crit Care. 2018; 45: 231-238
        • Hopster K.
        • Wogatzki A.
        • Geburek F.
        • et al.
        Effects of positive end-expiratory pressure titration on intestinal oxygenation and perfusion in isoflurane anaesthetised horses.
        Equine Vet J. 2016; 49: 250-256
        • Hopster K.
        • Jacobson B.
        • Hopster-Iversen C.
        • et al.
        Histopathological changes and mRNA expression in lungs of horses after inhalation anaesthesia with different ventilation strategies.
        Res Vet Sci. 2016; 107: 8-15
        • Iman R.L.
        • Conover W.J.
        The use of the rank transform in regression.
        Technometrics. 1979; 21: 499-509
        • Küls N.
        • Braun C.
        • Moens Y.
        The use of positive end-expiratory pressure (PEEP) and alveolar recruitment manoeuvre (ARM) in equine anaesthesia – a review.
        Pferdeheilkunde Equine Medicine. 2016; 32: 436-442
        • López-Herrera D.
        • Matta M.D.L.
        Influence of the end inspiratory pause on respiratory mechanics and tidal gas distribution of surgical patients ventilated under a tailored open lung approach strategy: A randomised, crossover trial.
        Anaesth Crit Care Pain Med. 2022; 41101038
        • Mosing M.
        • Böhm S.H.
        • Rasis A.
        • et al.
        Physiologic factors influencing the arterial-to-end-tidal CO2 difference and the alveolar dead space fraction in spontaneously breathing anesthetised horses.
        Front Vet Sci. 2018; 5: 58
        • Motta-Ribeiro G.C.
        • Melo M.F.V.
        • Jandre F.C.
        A simplified 4-parameter model of volumetric capnograms improves calculations of airway dead space and slope of Phase III.
        J Clin Monit Comput. 2020; 34: 1265-1274
        • Paiva M.
        Computation of the boundary conditions for diffusion in the human lung.
        Comput Biomed Res. 1972; 5: 585-595
        • Pascoe P.J.
        • McDonell W.N.
        • Trim C.M.
        • Gorder J.V.
        Mortality rates and associated factors in equine colic operations - a retrospective study of 341 operations.
        Can Vet J. 1983; 24: 76-85
        • Schramel J.P.
        • Wimmer K.
        • Ambrisko T.D.
        • Moens Y.P.
        A novel flow partition device for spirometry during large animal anaesthesia.
        Vet Anaesth Analg. 2014; 41: 191-195
        • Swanson C.R.
        • Muir III, W.W.
        Dobutamine-induced augmentation of cardiac output does not enhance respiratory gas exchange in anesthetized recumbent healthy horses.
        Am J Vet Res. 1986; 47: 1573-1576
        • Tusman G.
        • Scandurra A.
        • Böhm S.H.
        • et al.
        Model fitting of volumetric capnograms improves calculations of airway dead space and slope of phase III.
        J Clin Monit Comput. 2009; 23: 197-206
        • Tusman G.
        • Gogniat E.
        • Madorno M.
        • et al.
        Effect of PEEP on dead space in an experimental model of ARDS.
        Respir Care. 2019; 65: 11-20
        • Uttman L.
        • Jonson B.
        A prolonged postinspiratory pause enhances CO2 elimination by reducing airway dead space.
        Clin Physiol Funct Imaging. 2003; 23: 252-256
        • West J.B.
        Structure and function—how the architecture of the lung subserves its function.
        in: Respiratory Physiology: The Essentials. 9th edn. Lippincott Williams & Wilkins, USA2012: 1-11
        • Wolff G.
        • Brunner J.X.
        • Weibel W.
        • et al.
        Anatomical and series dead space volume: concept and measurement in clinical praxis.
        Appl Cardiopulm Pathophysiol. 1989; 2: 299-307