A study of the effect of isoflurane anaesthesia on equine skeletal muscle perfusion.

The research discusses the impact of varying concentrations of isoflurane-02 anaesthesia on equine skeletal muscle blood flow and oxygen delivery. The findings suggest that isoflurane anaesthesia, administered using different minimal alveolar concentrations, may interfere with the autonomous regulation of the skeletal muscle’s vascular beds in ponies.

Research Methodology

• The study used seven healthy, normothermic, isocapnoeic ponies who were subject to varying doses of isoflurane-02 anaesthesia. These dosages were 1.1, 1.5, and 1.8 MAC (minimum alveolar concentration).
• Radionuclide labeled microspheres of 15-micron size were injected into the left ventricle of the ponies to determine the muscle blood flow.
• The effect on muscle blood flow during anaesthesia was compared against measurements taken when the ponies were not under the influence of anaesthesia.

Key Findings

• The usage of isoflurane caused a decrease in the ponies’ aortic pressure and resulted in reduced blood flow in the skeletal muscles, including the temporalis, triceps brachii, longissimus dorsi, gluteus medius, biceps femoris, and vastus lateralis.
• The blood flow values were not significantly different from the control value in the masseter, triceps brachii at 1.1 and 1.5 MAC, and longissimus dorsi lumborum at 1.1 MAC anaesthesia.
• No significant changes were found in the vascular resistance of any muscles at any concentration of isoflurane. Similarly, there were no substantial differences in the muscle parameters among the three isoflurane concentrations.
• Except for the masseter muscle, isoflurane anaesthesia decreased skeletal muscle oxygen delivery.

Conclusions

• The researchers concluded that isoflurane might cause interference in the ‘autoregulation’ of the skeletal muscle’s vascular beds, as the vascular resistance was unchanged, despite the reduction in blood flow and oxygen delivery to the muscles in anaesthetised ponies.
• This interference in ‘autoregulation’ suggests a potential implication for how isoflurane anaesthesia is administered in the veterinary world.