Skeletal muscle perfusion during prolonged 2.03% end-tidal isoflurane-O2 anesthesia in isocapnic ponies.

This study examines how the administration of particular anesthesia, isoflurane O2, impacts the blood flow in skeletal muscles of ponies during prolonged periods. It was found that the anesthesia significantly reduced skeletal muscle blood flow and was also associated with loss of oxygen from the arterial blood.

Introduction

• The research investigates the effects of 1.55 minimum alveolar concentration isoflurane O2 anesthesia, or 2.03% end-tidal isoflurane, on the blood flow in skeletal muscles of ponies in different body positions over different periods of anesthesia time.
• The experiment involved six healthy isocapnic ponies that were put in right lateral recumbency on a nonpadded hardwood floor.

Methodology

• Blood flow was monitored in the up-positioned (nondependent) and down-positioned (dependent) skeletal muscles at the 60, 120, and 180-minute marks.
• This was achieved by injecting 15-micron diameter radionuclide-labeled microspheres into the left ventricle of the heart.
• The results were then compared with data collected from ponies in their conscious state.

Results

• The administration of isoflurane anesthesia led to a dramatic drop in cardiac output and systemic pressure. However, the total peripheral resistance did not show any significant change.
• In specific muscles, namely the triceps brachii, gluteus medius, biceps femoris, and vastus lateralis of both sides, notable reductions in blood flow were observed during anesthesia.
• In the case of the masseter muscles, the perfusion values remained relatively consistent across the three hours of anesthesia.
• Four of the ponies developed severe edema of the dependent masseter muscle. A pony without masseter edema showed signs of forelimb lameness after anesthesia, and two of the ponies with masseter edema showed generalized hind limb weakness post anesthesia.
• Nonetheless, there were no significant differences in blood flow between the up-and down-positioned muscles.
• Overall, it was clear that the application of isoflurane-O2 anesthesia in ponies led to a significant decrease in skeletal muscle blood flow.

Conclusion

• This study suggests that during isoflurane anesthesia, there is a marked decrease in equine skeletal muscle perfusion, and it may be accompanied by an increased oxygen loss from the arterial blood through a process known as the countercurrent O2 exchange that happens between large arterioles and venules.
• These findings can be important for veterinary anesthesiologists to consider when administering anesthesia and planning recovery protocols for equine surgery.