Difference between arterial and end-tidal carbon dioxide pressures during laparoscopy in paediatric patients

Purpose: To assess the effect of pneumoperitoneum on P(a-ET)CO₂ gradient in children. Methods: Sixty one ASA I and II children (10.7 ± 3.0 yr, 38.4 ± 14.2 kg, mean ± SD), scheduled for visceral or urological laparoscopic procedures, were studied. They were anaesthetized, intubated, paralysed and their lungs ventilated with constant ventilator settings to obtain P(ET)CO₂ values between 4.3 and 4.8 kPa. Intra-abdominal pressure was maintained between 8 and 14 mmHg. The following measurements were performed at steady state, before the pneumoperitoneum (T₁) and 15 min later (T₂): heart rate, systolic and diastolic arterial pressure; peak airway and intra-abdominal pressure; P(a)CO2 corrected for the patient's temperature; P(ET)CO₂ drawn between the micropore filter and the ventilator tubes, corrected for BTPS conditions; P((a-ET))CO₂. Values between -1.0 and +1.0 mmHg were considered nil; patient position (horizontal or head-down tilt): all patients were horizontal at T₁. Results: Arterial pressure, heart rate and peak airway pressure increased at T₂: P(a)CO₂ and P(ET)CO₂ increased by 14%. The incidence of negative gradients increased from 54 to 67% although mean P((a-ET))CO₂ remained clinically unchanged. No difference was found in P((a-ET))CO₂ were [-5.6; +3.2] at T₁ and [-8.8; + 4.8] at T₂. Conclusion: P(ET)CO₂ often overestimates P(a)CO₂ during laparoscopy in children, by up to 8.8 mmHg. Arterial blood gas analysis should be performed during long procedures to avoid hyperventilation.