The optimal PEEP after alveolar recruitment maneuver assessed by electrical impedance tomography in healthy horses

Abstract

BackgroundElectrical impedance tomography (EIT) has been an essential tool for assessing pulmonary ventilation in several situations, such as the alveolar recruitment maneuver (ARM) in PEEP titration to maintain the lungs open after atelectasis reversion. In the same way as in humans and dogs, in horses, this tool has been widely used to assess pulmonary aeration undergoing anesthesia, mechanical ventilation, recruitment maneuver, standing horses, or specific procedures.ObjectivesThe present study aimed to evaluate the distribution of regional ventilation during ARM based on lung monitoring assessment by EIT, with a focus on better recruitment associated with less or no overdistention.MethodsFourteen horses of 306 ± 21 kg undergoing isoflurane anesthesia in dorsal recumbency were used. The animals were mechanically ventilated with a tidal volume of 14 ml kg−1 and a respiratory rate of 7–9. An alveolar recruitment maneuver was instituted, increasing the PEEP by five cmH2O every 5 min until 32 cmH2O and decreasing it by five cmH2O every 5 min to 7 cmH2O. At each step of PEEP, arterial blood samples were collected for blood gas analysis, EIT images, hemodynamic, and respiratory mechanics.ResultsAssociated with the CoV-DV increase, there was a significant decrease in the DSS during the ARM and a significant increase in the NSS when PEEP was applied above 12 cmH2O compared to baseline. The ComplROI showed a significant increase in the dependent area and a significant decrease in the non-dependent area during ARM, and both were compared to their baseline values. The driving pressure decreased significantly during the ARM, and Cst, PaO2, and PaO2/FiO2 ratio increased significantly. The VD/VT decreased significantly at DEPEEP17 and DEPEEP12. There was an HR increase at INPEEP27, INPEEP 32, and DEPEEP17 (p < 0.0001; p < 0.0001; and p < 0.05, respectively), those values being above the normal reference range for the species. The SAP, MAP, DAP, CI, and DO2I significantly decreased INPEEP32 (p < 0.05).ConclusionThe ARM by PEEP titration applied in the present study showed better ventilation distribution associated with better aeration in the dependent lung areas, with minimal overdistention between PEEP 17 and 12 cmH2O decreasing step. Those changes were also followed by improvements in static and regional compliance associated with increased oxygenation and pulmonary ventilation. ARM promoted a transitory decrease in arterial blood pressure and depression in CI with a concomitant drop in oxygen delivery, which should be best investigated before its routine use in clinical cases.

Flow-controlled expiration ventilation using a piston ventilator: effects of expiration time and speed on respiratory and pulmonary mechanics with focus on hysteresis and compliance in healthy horses

“…15 The use of PEEP is believed to reduce atelectotrauma, 15,28 and it has been shown in multiple equine studies to improve V/Q mismatching and oxygenation. [10][11][12][13][14]29 However, studies have shown deleterious effects of PEEP, including pulmonary damage and cardiovascular compromise, and the optimal PEEP setting is dependent on species, context, and concurrent pathophysiologic processes. 16,30 It can be particularly challenging in situations with inhomogeneous lung pathology, such as the horse in dorsal recumbency or in a patient with acute respiratory distress syndrome (ARDS), to titrate ventilatory strategy and minimize further lung pathology.…”

Assessment of Magnetic Resonance Imaging Artefacts Caused by Equine Anaesthesia Equipment: A Cadaver Study

“…Previous studies have demonstrated that the degree of alveolar collapse can be reduced by application of an alveolar recruitment manoeuvre (ARM) and continuous PEEP [16,27,28]. An alternative approach consists of an ARM provided by stepwise incremental and decremental peak inspiratory pressure (PIP) and PEEP, which has been found to be amongst the most effective methods to redistribute ventilation and improve oxygenation [29,30]. Additional strategies involve the use of continuous CPAP, which also proved effective in redistributing ventilation to the dependent lung regions, thereby decreasing ventilation/perfusion mismatch [23].…”

Persistent hypoxaemia and pulmonary oedema in a horse anaesthetised for emergency exploratory laparotomy

“…[21][22][23] However, high values of PIP in patients with atelectasis have been associated with an increased risk of hypoxaemia, 5 presumably related to volutrauma 11 due to overexpansion of a reduced number of open alveoli. As the initial PIP in this case was already greater than 30 mmHg (>3.9 kPa), the first attempt to improve oxygenation and respiratory mechanics was conservative and consisted of an increase in T v and inspiratory time 22,[24][25][26] and by the addition of PEEP.…”