A method for producing normocarbia during general anaesthesia for caesarean section

Area of Science:

• Anesthesiology
• Obstetric Anesthesia
• Respiratory Physiology

Background:

• The Bain anesthetic system is used for intermittent positive pressure ventilation during Caesarean sections.
• Maintaining appropriate carbon dioxide levels is crucial for maternal and fetal well-being.

Purpose of the Study:

• To investigate the relationship between fresh gas flow (FGF) and end-tidal carbon dioxide (ETCO2) levels in pregnant patients undergoing Caesarean section using the Bain system.
• To determine the optimal FGF rate for maintaining normocapnia in this patient population.

Main Methods:

• Twenty-six patients undergoing Caesarean section were anesthetized using the Bain system.
• Intermittent positive pressure ventilation was applied.
• End-tidal carbon dioxide tension was measured in relation to varying FGF rates (80 ml/kg/min and 120 ml/kg/min).

Main Results:

• An inverse relationship was observed between maximum ETCO2 tension and FGF rate.
• Significantly lower ETCO2 levels were found at 120 ml/kg/min FGF compared to 80 ml/kg/min.
• Estimated CO2 levels in pregnant patients were higher than reported values for non-pregnant individuals at equivalent FGF rates.

Conclusions:

• A fresh gas flow rate of at least 120 ml/kg/min is required when using the Bain system with positive pressure ventilation to maintain maternal arterial carbon dioxide tension near the normal term value (4.1-4.4 kPa).
• Higher FGF rates are necessary in pregnant patients compared to non-pregnant individuals to achieve normocapnia.