Accuracy of different oxygenation indices in estimating intrapulmonary shunting at increasing infusion rates of dobutamine in horses under general anaesthesia.

This research analyzed the correlation between different oxygenation indices and venous admixture (Qs/Qt) in sedated horses under varied dobutamine infusion rates, and found that F-shunt demonstrated a stronger correlation over other oxygen indices, irrespective of the dobutamine dose.

Introduction and Research Design

• The purpose of this study was to investigate the connection between various oxygenation indices and venous admixture (Qs/Qt) in horses that were sedated, with differing dobutamine infusion rates.
• Six female horses were sedated with acepromazine, xylazine, diazepam, ketamine, and isoflurane, then were intubated and mechanically ventilated with 100% O2.
• A Swan-Ganz catheter was inserted in the left jugular vein and advanced to the pulmonary artery. The horses were administered varied standardised doses of dobutamine.

Procedure and Measurements

• Arterial and mixed venous blood were sampled eight times at predetermined intervals for each horse.
• Haemoglobin (Hb) concentrations in arterial and venous blood and O2 saturation, arterial oxygen partial pressure (PaO2), venous oxygen partial pressure (PvO2), and barometric pressure were recorded.
• Arterial (CaO2), mixed venous (CvO2), and capillary (Cc’O2) oxygen contents were computed using standard formulae.

Data Analysis

• The correlations between F-shunt, PaO2/FiO2, PaO2/PAO2, P[A - a]O2, and P[A - a]O2/PaO2 were examined through linear regression analysis.
• The coefficient of determination (r(2)) was used to evaluate the goodness-of-fit for each computed formula.
• The Bland-Altman test was used to analyse the agreement between Qs/Qt and F-shunt.

Findings

• All tested oxygen tension-related indices had weak correlations (r(2) < 0.2) with Qs/Qt.
• F-shunt showed a stronger correlation (r(2) = 0.73) and had substantial agreement with Qs/Qt, independent of the dobutamine infusion rate.
• The study concluded that F-shunt had a better correlation with venous admixture (Qs/Qt) than other oxygen indices in anaesthetised horses with different dobutamine infusion rates.