During in-hospital cardiac arrest, high-quality CPR is ongoing. ETCO2 is being monitored. The ETCO2 reading drops suddenly from 25 mmHg to 8 mmHg after drug administration. Which drug was most likely just given?

• A Amiodarone 300 mg IV
• B Sodium bicarbonate 50 mEq IV
• C Adrenaline 1 mg IV ✓
• D Magnesium sulphate 2 g IV

Explanation

Intravenous adrenaline during CPR causes intense vasoconstriction, which shunts pulmonary blood flow and transiently reduces pulmonary capillary perfusion. Since ETCO2 during CPR reflects pulmonary perfusion (CO2 delivery to the lung), any vasoconstrictor that reduces pulmonary flow will acutely drop ETCO2 even if CPR quality and CO2 production are unchanged. This is a well-recognised phenomenon after IV adrenaline boluses during arrest and should not be interpreted as CPR quality deterioration. Sodium bicarbonate generates CO2 and would transiently increase ETCO2, not decrease it.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.