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

Butorphanol with oxygen insufflation corrects etorphine-induced hypoxaemia in chemically immobilized white rhinoceros (Ceratotherium simum)

Background

Opioid-induced immobilization is associated with severe respiratory depression in the white rhinoceros. We evaluated the efficacy of butorphanol and oxygen insufflation in alleviating opioid-induced respiratory depression in eight boma-managed rhinoceros.

Results

Chemical immobilization with etorphine, azaperone and hyaluronidase, as per standard procedure for the white rhinoceros, caused severe respiratory depression with hypoxaemia (P_aO₂ = 27 ± 7 mmHg [mean ± SD]), hypercapnia (P_aCO₂ = 82 ± 6 mmHg) and acidosis (pH =7.26 ± 0.02) in the control trial at 5 min. Compared to pre-intervention values, butorphanol administration (without oxygen) improved the P_aO₂ (60 ± 3 mmHg, F_(3,21) =151.9, p <0.001), P_aCO₂ (67 ± 4 mmHg, F_(3,21) =22.57, p <0.001) and pH (7.31 ± 0.06, F_(3,21) =27.60, p <0.001), while oxygen insufflation alone exacerbated the hypercapnia (123 ± 20 mmHg, F_(3,21) =50.13, p <0.001) and acidosis (7.12 ± 0.07, F_(3,21) =110.6, p <0.001). Surprisingly, butorphanol combined with oxygen fully corrected the opioid-induced hypoxaemia (P_aO₂ = 155 ± 53 mmHg) and reduced the hypercapnia over the whole immobilization period (p <0.05, areas under the curves) compared to the control trial. However, this intervention (butorphanol + oxygen) did not have any effect on the arterial pH.

Conclusions

Oxygen insufflation combined with a single intravenous dose of butorphanol improved the immobilization quality of boma-managed white rhinoceros by correcting the opioid-induced hypoxaemia, but did not completely reverse all components of respiratory depression. The efficacy of this intervention in reducing respiratory depression in field-captured animals remains to be determined.

Effects of oxygen insufflation rate, respiratory rate, and tidal volume on fraction of inspired oxygen in cadaveric canine heads attached to a lung model

OBJECTIVE

To assess the effects of oxygen insufflation rate, respiratory rate, and tidal volume on fraction of inspired oxygen (Fio2) in cadaveric canine heads attached to a lung model.

SAMPLE

16 heads of canine cadavers.

PROCEDURES

Each cadaver head was instrumented with a nasal insufflation catheter through which oxygen was delivered. The trachea was attached to a sample collection port connected by means of corrugated tubing to a lung model. Eight treatment combinations that varied in respiratory rate (10 or 20 breaths/min), tidal volume (10 or 15 mL/kg), and oxygen insufflation rate (50 or 100 mL/kg/min) were applied to each head in a replicated Latin square design. Gas samples were manually collected, and inspired oxygen concentrations were analyzed. The Fio2 and end-tidal CO2 concentration were determined and compared among sample groups.

RESULTS

Estimated least squares mean Fio2 for various treatment combinations ranged from 32.2% to 60.6%. The Fio2 was significantly increased at the higher insufflation rate (estimated marginal least squares mean, 48.7% vs 38.6% for 100 and 50 mL/kg/min, respectively), lower respiratory rate (48.9% vs 38.3% for 10 and 20 breaths/min, respectively), and smaller tidal volume (46.8% vs 40.0% for 10 and 15 mL/kg, respectively).

CONCLUSIONS AND CLINICAL RELEVANCE

-Fio2 in the model was affected by oxygen insufflation rate, respiratory rate, and tidal volume. This information may potentially help clinicians interpret results of blood gas analysis and manage canine patients receiving oxygen insufflation via a nasal catheter.