Use of end-tidal CO2 tension to predict arterial CO2 values in isoflurane-anesthetized equine neonates.

This research examines the correlation between arterial carbon dioxide tension (PaCO2) and end-tidal carbon dioxide tension (PetCO2) in spontaneously breathing equine neonates under isoflurane anesthesia, highlighting an increase in the differences between these values over time likely due to hypoventilation and decreased pulmonary capillary perfusion.

Research Overview

• The study aimed to demonstrate the relationship between end-tidal carbon dioxide tension (PetCO2) and arterial carbon dioxide tension (PaCO2) in anesthetized, spontaneously breathing young horses. This was done to evaluate the accuracy of PetCO2 measurements in predicting arterial carbon dioxide levels during anesthesia, a vital parameter to monitor in anesthetized patients.

Key Findings

• The researchers found that both PetCO2 and PaCO2 values increased with respect to time in anesthetized neonate horses, meaning that the amount of carbon dioxide in the neonate’s blood and exhaled breath increased during the anesthesia period.
• The difference between the values of PetCO2 and PaCO2 also increased over time. This suggests that while end-tidal CO2 tension is a useful indication of arterial CO2 levels early in the anesthesia period (i.e., less than or equal to 60 minutes), it becomes less reliable as anesthesia time increases.
• The study further discovered that the ratio of dead space volume to tidal volume (Vd/Vt), indicating the physiologic dead space in the lung meaning the portion of the lung where gas exchange does not occur, increased with time under isoflurane anesthesia. This increase suggests a decrease in effective pulmonary function, likely contributing to the rising differences between PetCO2 and PaCO2.

Conclusion

• This research provides important insight into the dynamics of carbon dioxide tension in anesthetized equine neonates. The findings indicate that the increased difference in PetCO2 and PaCO2 values over time may be attributable to hypoventilation (reduced breathing depth and/or frequency) and decreased pulmonary capillary perfusion (reduced blood flow in the lungs), both possibly resulting from the physiological side effects of prolonged isoflurane anesthesia.
• These observations could be critical for managing anesthesia in young horses, implying that relying solely on PetCO2 measurements for longer anesthesia periods might not provide an accurate representation of the animal’s arterial carbon dioxide levels, hence other ways of monitoring should also be considered.