During a laparoscopic cholecystectomy exhaled CO2 is 6%, but inhaled CO2 is 1%. Which explanation could NOT account for rebreathing CO2?

During a laparoscopic cholecystectomy exhaled CO2 is 6%, but inhaled CO2 is 1%. Which explanation could NOT account for rebreathing CO2?

• A. Channeling through soda lime
• B. Faulty expiratory valve
• C. Exhausted soda lime
• D. Absorption of CO2 through peritoneum

Answer: (D)

The situation points to rebreathing of CO2 in the breathing circuit. When CO2-rich gas is rebreathed, you see higher end-tidal CO2 and also some CO2 present in the inspired gas, which happens if the circle system isn’t removing CO2 properly or if expired gas is slipping back into the inspiratory limb. Problems like channeling through the soda lime (gas bypassing the absorber), a exhausted or ineffective soda lime, or a faulty expiratory valve can all allow exhaled CO2 to be inhaled again, explaining the 6% end-tidal CO2 with 1% inspired CO2. Absorption of CO2 through the peritoneum, while it raises the patient’s overall CO2 load (central, arterial, and end-tidal CO2), does not contaminate the inspired gas in the anesthesia circuit. It increases CO2 transfer from blood to the lungs and back, but it doesn’t cause CO2 to appear in the fresh gas being delivered to the patient. So peritoneal absorption cannot account for the observed rebreathing pattern in the circuit.

The situation points to rebreathing of CO2 in the breathing circuit. When CO2-rich gas is rebreathed, you see higher end-tidal CO2 and also some CO2 present in the inspired gas, which happens if the circle system isn’t removing CO2 properly or if expired gas is slipping back into the inspiratory limb. Problems like channeling through the soda lime (gas bypassing the absorber), a exhausted or ineffective soda lime, or a faulty expiratory valve can all allow exhaled CO2 to be inhaled again, explaining the 6% end-tidal CO2 with 1% inspired CO2.

Absorption of CO2 through the peritoneum, while it raises the patient’s overall CO2 load (central, arterial, and end-tidal CO2), does not contaminate the inspired gas in the anesthesia circuit. It increases CO2 transfer from blood to the lungs and back, but it doesn’t cause CO2 to appear in the fresh gas being delivered to the patient. So peritoneal absorption cannot account for the observed rebreathing pattern in the circuit.