Effects of continuous positive airway pressure on respiratory function in sedated foals

Abstract

Objective:To characterize the effects of continuous positive airway pressure (CPAP) delivered by a commercial human CPAP device on respiratory function in foals with pharmacologically induced respiratory suppression.Design: Prospective randomized, cross-over study comparing CPAP with spontaneous respiration and oxygen insufflation. Setting: University veterinary teaching hospital.Animals: Twelve foals born in consecutive seasons from a university teaching herd.Interventions: Foals were randomized to receive 10 minutes of respiratory support by mask oxygen supplementation or CPAP as a first treatment after induction of respiratory depression by intravenous administration of xylazine and fentanyl. Each foal received the alternate treatment after 10 minutes of breathing ambient air, and the procedure was repeated after 48 hours with treatment order reversed. Measurements and main results:The administration of xylazine and fentanyl by bolus or continuous infusion reliably induced reversible respiratory suppression and recumbency. CPAP was associated with comparable increase in PaO 2 relative to mask oxygen supplementation, but with lower respiratory rate, increased oxygen extraction and increased carbon dioxide elimination.Mild increase in PaCO 2 was observed during CPAP and O 2 supplementation. Expiratory time increased and peak expiratory flow decreased during CPAP. Conclusions:Findings of the study suggest that CPAP might represent a method for improved respiratory support compared to O 2 insufflation due to increased respiratory efficiency. Care must be taken in extrapolation of these findings from foals with pharmacologically induced respiratory compromise to foals with clinical respiratory disease, and further investigation is required to better characterize the cause and impact of marginal hypercapnia observed in these studies. K E Y W O R D Sequine critical care, neonatology, quine respiratory physiology, respiratory insufficiency Abbreviations: ABGS, arterial blood gas sample; CI, confidence interval; CPAP, continuous positive airway pressure; FiO 2 , inspired oxygen pressure; PEF, peak expiratory flow; PIF, peak inspiratory flow; Vt, tidal volume.

Bi-level positive airway pressure (biPAP) for non-invasive respiratory support of foals

“…Increased Vt represents a more efficient ventilation strategy than increased RR, as there is increased alveolar ventilation relative to ventilation of airway dead space, and decreased RR is likely to be associated with decreased work of breathing. Increased inspiratory pressure during biPAP was associated with increased PIF, and the adverse effects on PEF observed during CPAP in previous studies (13) were not observed in the current study, presumably due to the lower expiratory pressures during biPAP ventilation. As expected, increased FiO 2 was observed during mask administration of supplementary O 2 and during biPAP, so observed increases in arterial oxygenation likely reflect the steeper diffusion gradient resulting from these changes.…”

“…Previous studies have demonstrated that CPAP is associated with improved respiratory function in a number of veterinary species (9–12). CPAP has recently been shown to improve gas exchange in healthy foals with pharmacologically induced respiratory suppression (13), however hypercapnia was observed in treated foals in this study, and has been observed previously in anaesthetised horses during CPAP (10, 11, 14).…”

“…Increased PaCO 2 was observed in Group 3 foals following respiratory support, including hypercapnia (PaCO 2 > 60 mmHg) following O 2 administration (two foals) or biPAP (one foal). Hypercapnia has been reported in response to O 2 supplementation in human neonates (28) and foals (13, 29), and may be due to reduced respiratory drive, increased metabolic rate, hypoventilation due to sedation or effects of equipment dead space. As noted above, mask administration of supplementary O 2 was associated with the accumulation of CO 2 within equipment dead space (rebreathing) in the current study, but this was not observed during biPAP.…”

“…Blood gas analysis was performed as described for Group 1 foals. Spirometry was performed on standing foals as previously described (Raidal, McKean et al 2019) by application of a large veterinary anaesthesia mask (SurgiVet large canine mask, product number 32393B1; Sound Veterinary Equipment, Rowville, Australia) placed on the foal's muzzle in such a way as to exclude air leaks and to minimise dead space, but not prevent opening of the nares. A respiratory flow head (Respiratory Flow Head 300 L, MLT300L, ADInstruments, Bella Vista, Australia) and gas sampling port were connected to the anaesthesia mask.…”

“…Previous studies have demonstrated that CPAP is associated with improved respiratory function in a number of veterinary species (9)(10)(11)(12). CPAP has recently been shown to improve gas exchange in healthy foals with pharmacologically induced respiratory suppression (13), however hypercapnia was observed in treated foals in this study, and has been observed previously in anaesthetised horses during CPAP (10,11,14). Bi-level positive airway pressure (biPAP) is also recognised for the management of respiratory insufficiency in human neonates, and has recently demonstrated improved treatment outcomes in preterm human neonates in comparison to CPAP (15,16).…”