Arterial to end-tidal CO₂ gradients during isocapnic hyperventilation

Area of Science:

• Anesthesiology
• Respiratory Physiology

Background:

• Isocapnic hyperventilation (ICHV) is used to manage elevated inspired CO2 (PICO2).
• The impact of ICHV on arterial PCO2 (PaCO2) during rising PICO2 is not well-documented.

Purpose of the Study:

• To investigate whether maintaining end-expired CO2 (PETCO2) with ICHV during increased PICO2 also maintains PaCO2.
• To assess the PaCO2-PETCO2 gradient under varying PICO2 levels during robot-assisted surgery.

Main Methods:

• 12 patients undergoing robot-assisted radical prostatectomy or cystectomy were studied.
• Inspired CO2 was increased sequentially, with ventilation adjusted to maintain target PETCO2.
• Arterial-to-end-expired CO2 gradients (Pa-ETCO2) were measured at each PICO2 level.

Main Results:

• PETCO2 was successfully maintained within the target range for most PICO2 levels up to 1.5%.
• Pa-ETCO2 gradients remained stable throughout the study.
• Higher PICO2 levels (≥2%) presented challenges in maintaining target PETCO2.

Conclusions:

• ICHV can effectively maintain PETCO2 and stable Pa-ETCO2 gradients during modest increases in PICO2 during anesthesia.
• Increased ventilation can compensate for moderate PICO2 rises without affecting PaCO2-PETCO2 gradients.
• Airway pressures may limit the efficacy of ICHV at higher PICO2 levels, warranting further investigation.