Physiologic effects of nasopharyngeal administration of supplemental oxygen at various flow rates in healthy neonatal foals

Evaluation of Nasal Oxygen Administration at Various Flow Rates and Concentrations in Conscious, Standing Adult Horses

This study evaluated the effects of various flow rates and fractions of oxygen on arterial blood gas parameters and on the fraction of inspired oxygen (F_IO₂) delivered to the distal trachea. Oxygen was administered to 6 healthy, conscious, standing, adult horses via single nasal cannula positioned within the nasopharynx. Three flow rates (5, 15, 30 L/min) and fractions of oxygen (21, 50, 100%) were delivered for 15 minutes, each in a randomized order. F_IO₂ was measured at the level of the nares and distal trachea. Adverse reactions were not observed with any flow rate. F_IO₂ (nares and trachea) and PaO₂ increased with increasing flow rate and fraction of oxygen (P < .0001). F_IO₂ (trachea) was significantly less than F_IO₂ (nares) at 50% and 100% oxygen at all flow rates (P < .0001). Differences in PaO₂ were not observed between 100% oxygen-5L/min and 50% oxygen-15L/min and or between 100% oxygen-15L/min and 50% oxygen-30L/min. Tracheal F_IO₂ for 100% oxygen-15L/min was increased compared to 50% oxygen-30L/min (P < .0001). Respiratory rate, ETCO₂, PaCO₂, and pH did not differ between treatments. Administration of 50% oxygen via nasal cannula at 15 and 30 L/min effectively increased in PaO₂ and was well tolerated in conscious, standing, healthy horses. While these results can be used guide therapy in hypoxemic horses, evaluation of the administration of 50% oxygen to horses with respiratory disease is warranted.

Intratracheal oxygen administration increases FIO2 and PaO2 compared with intranasal administration in healthy, standing horses

OBJECTIVE

To evaluate the efficacy of 2 different oxygen delivery strategies-intranasal and tracheal insufflation-on the inspired fraction of oxygen (FIO2) in standing horses and to determine the time needed for arterial oxygen partial pressure (PaO2) equilibration.

ANIMALS

6 healthy adult horses.

PROCEDURES

In this blinded, randomized crossover design study, horses were randomly assigned to receive oxygen via nasal cannula (group N) or transcutaneous tracheal catheter (group T). After placement of venous and arterial catheters, FIO2 was measured through a catheter placed into the distal portion of the trachea. After baseline measurements were obtained, horses received oxygen at up to 25 mL/kg/min for 1 hour via either intranasal or intratracheal catheter. The FIO2 and PaO2 were recorded at 5, 10, 15, 20, 25, 30, 45, and 60 minutes during and 5, 10, 15, 20, and 30 minutes after oxygen insufflation. Data were analyzed by use of a 2-way repeated measures ANOVA with Tukey-Kramer post hoc testing for pairwise comparisons (P < 0.05).

RESULTS

During oxygen administration, FIO2 and PaO2 increased significantly when compared with baseline, resulting in significantly higher values for group T (37.7 ± 2.4%; 214.6 ± 18 mm Hg) than for group N (34.3 ± 3.9%; 184.1 ± 11 mm Hg). The equilibration time was less than 10 minutes.

CLINICAL RELEVANCE

Intratracheal oxygen administration resulted in better oxygenation than nasal insufflation and should therefore be considered in standing horses that are experiencing severe respiratory compromise. The equilibration between FIO2 and PaO2 is rapid in adult horses.

Bi-Level Positive Airway Pressure for Non-invasive Respiratory Support of Foals

Respiratory insufficiency and pulmonary health are important considerations in equine neonatal care. As the majority of foals are bred for athletic pursuits, strategies for respiratory support of compromised foals are of particular importance. The administration of supplementary oxygen is readily implemented in equine practice settings, but does not address respiratory insufficiency due to inadequate ventilation and is no longer considered optimal care for hypoxia in critical care settings. Non-invasive ventilatory strategies including continuous or bi-level positive airway pressure are effective in human and veterinary studies, and may offer improved respiratory support in equine clinical practice. The current study was conducted to investigate the use of a commercial bi-level positive airway pressure (BiPAP) ventilator, designed for home care of people with obstructive respiratory conditions, for respiratory support of healthy foals with pharmacologically induced respiratory insufficiency. A two sequence (administration of supplementary oxygen with, or without, BiPAP), two phase, cross-over experimental design was used in a prospective study with six foals. Gas exchange and mechanics of breathing (increased tidal volume, decreased respiratory rate and increased peak inspiratory flow) were improved during BiPAP relative to administration of supplementary oxygen alone or prior studies using continuous positive airway pressure, but modest hypercapnia was observed. Clinical observations, pulse oximetry and monitoring of expired carbon dioxide was of limited benefit in identification of foals responding inappropriately to BiPAP, and improved methods to assess and monitor respiratory function are required in foals.

Update on interstitial pneumonia

Interstitial pneumonias encompass a wide variety of acute and chronic respiratory diseases and include the specific diseases equine multinodular pulmonary fibrosis and acute lung injury and acute respiratory distress. These diseases have been diagnosed in all age groups of horses, and numerous agents have been identified as potential causes of interstitial pneumonia. Despite the varied causes, interstitial pneumonia is uniformly recognized by the severity of respiratory disease and often poor clinical outcome. This article reviews the causal agents that have been associated with the development of interstitial pneumonia in horses. Pathophysiology, clinical diagnosis, and treatment options are discussed.

Field triage of the neonatal foal

The purpose of this article is to provide a quick reference for field triage of the sick neonatal foal. Therefore, information is focused toward diagnostics and treatments that can be performed in the field. When evaluating a weak, recumbent, or lethargic foal on a farm, it is often difficult to make a definitive diagnosis. Therefore, the approach should be to treat what is treatable and prevent what is preventable. In many cases, the goal will be to stabilize a foal before referral to a tertiary care facility where more intensive and continuous treatment can be performed.

Effects of tidal volume, ventilatory frequency, and oxygen insufflation flow on the fraction of inspired oxygen in cadaveric horse heads attached to a lung model

OBJECTIVE

To measure the effects of tidal volume, ventilatory frequency, and oxygen insufflation flow on the fraction of inspired oxygen in cadaveric horse heads attached to a lung model.

SAMPLE

8 heads of equine cadavers.

PROCEDURES

Each cadaveric horse head was intubated with a nasotracheal tube that extended into the proximal portion of the trachea. Oxygen was delivered through an oxygen catheter contained within and extending to the tip of the nasotracheal tube. The trachea was connected to the lung model by use of a spiral-wound hose with a sampling adaptor. Eight treatment combinations involving 2 tidal volumes (5 and 8 L), 2 ventilatory frequencies (6 and 12 mechanical breathes/min), and 2 insufflation rates (10 and 15 L/min) were applied to each head. Hand-drawn inspired gas samples were collected and analyzed for oxygen concentrations.

RESULTS

The fraction of inspired oxygen (measured at mid trachea) ranged from 26.8% to 39.4%. Fraction of inspired oxygen was significantly higher with a smaller tidal volume, lower ventilatory frequency, and higher insufflation rate.

CONCLUSIONS AND CLINICAL RELEVANCE

In the study model, measured fraction of inspired oxygen varied with ventilatory pattern as well as oxygen insufflation rate. Clinically, this information could be beneficial for interpretation of data regarding arterial blood gases and hemoglobin saturation and in making appropriate oxygen insufflation decisions for anesthetized horses that are breathing room air.