Effects of hypercapnia on endocrine and metabolic responses to anaesthesia in ponies.

The research investigates the effects of high carbon dioxide levels (hypercapnia) on the endocrine and metabolic responses in ponies under anaesthesia. It suggests hypercapnia may positively impact blood flow and does not significantly change the stress response.

Introduction and Methodology

• This study aims to explore the metabolic and endocrine effects of hypercapnia in ponies. Hypercapnia is a condition characterized by abnormally elevated carbon dioxide (CO2) levels in the blood.
• Halothane, an inhalational anaesthetic, was used in six ponies. Neuro-muscular blockade and controlled ventilation were employed to manage the anaesthesia.
• Each pony was anaesthetized twice. In one session, hypercapnia was induced for a 40-minute period (10kPa CO2 level in the blood), while in the other session, normocapnia, the normal level of CO2 (5.3kPa), was maintained throughout two hours of anaesthesia.

Measurements and Observations

• Routine cardiovascular monitoring was performed during the experiment. Blood samples were also taken for testing various parameters, including cortisol, insulin, glucose, lactate, muscle and liver enzymes, and total protein.
• The study observed that anaesthesia led to hypotension (low blood pressure) and lactic acidemia (excess lactic acid in the blood).
• The adverse effects like low blood pressure and lactic acidemia were slightly less severe during the state of hypercapnia.
• It was also noticed that high blood sugar levels or hyperglycemia was more marked during hypercapnia.
• Cortisol, an important stress hormone, exhibited similar increases in both hypercapnia and normocapnia sessions, suggesting that hypercapnia did not significantly impact the stress response of the ponies.

Conclusive Analysis

• The minor changes in insulin levels hinted at a trend towards a decrease but not a major one.
• Other variables related to muscle and liver enzymes, and total protein saw no significant changes.
• In conclusion, it was inferred that 40 minutes of hypercapnia during halothane anaesthesia in ponies resulted in potentially better perfusion (blood flow) and did not markedly alter the stress response in the ponies.