Pulmonary gas exchange in anaesthetised horses mechanically ventilated with oxygen or a helium/oxygen mixture.

The research aims to compare the effects of different levels of inspired fraction of oxygen (FiO2) on the lungs of horses under anaesthesia. The findings show that administering a helium/oxygen (He/O2) gas mixture with low FiO2 preserves lung function better than pure oxygen.

Study Design

• The study was conducted on thirty healthy adult horses, which were sedated using specific dosages of acepromazine, detomidine, and xylazine.
• General anaesthesia was administered to the horses using some 5% guaifenesin to effect, diazepam, and ketamine, and was maintained with isoflurane.
• After induction, the horses were split into two groups. One group (Group HX) was ventilated mechanically with a He/O2 gas mixtures at gradually increasing levels of FiO2. This was achieved by blending O2 with Heliox (containing 70% He and 30% O2).
• The second group (Group O) was immediately ventilated with 100% O2.

Methodology

• After 20 minutes of ventilation at each level of FiO2 in Group HX and 60 minutes in Group O, levels of PaO2 and PaCO2 were measured.
• From these measurements, the alveolar to arterial PO2 gradient (P(A-a)O2) was calculated, which measures the efficiency of gas exchange in the lungs.
• The data was analysed using robust categorical regression with clustering on individual horses, setting statistical significance at P < 0.05.

Results

• The results of the study showed that inhaling the He/O2 mixture with a FiO2 of 0.25-0.30 ensured adequate oxygenation of the blood, and was associated with a smaller P(A-a)O2 gradient than inhaling pure O2.
• In Group HX, as the FiO2 level increased, the PaO2 and P(A-a)O2 also increased significantly.
• Group O, which was ventilated with 100% O2, had significantly lower levels of PaO2 and higher levels of P(A-a)O2 compared to Group HX at a FiO2 > 0.90.

Conclusions

• The findings suggest that administering a He/O2 gas mixture with a lower FiO2 can preserve lung function more effectively than ventilation with pure oxygen in anesthetised horses.
• The researchers proposed that a stepwise increase of FiO2 using a He/O2 gas mixture could potentially be more advantageous in terms of pulmonary gas exchange compared to an immediate exposure to 100% O2.