A 55-year-old woman with severe primary pulmonary hypertension and right ventricular dysfunction presents for laparotomy. Why is nitrous oxide best avoided in this patient?

• A It increases pulmonary vascular resistance and can precipitate acute right heart failure ✓
• B It inhibits methionine synthase, worsening right ventricular function
• C It causes bronchoconstriction that elevates pulmonary artery pressures
• D It potentiates neuromuscular blockade, delaying weaning from ventilation

Explanation

Nitrous oxide activates sympathetic outflow and can cause pulmonary vasoconstriction, raising pulmonary vascular resistance, an effect particularly hazardous in pre-existing pulmonary hypertension where it may precipitate acute right ventricular failure. Its inhibition of methionine synthase causes haematological and neurological toxicity only with prolonged exposure, not acute haemodynamic collapse. N2O is not a bronchoconstrictor and does not potentiate neuromuscular blockade.

Reference: Miller's Anesthesia, 9th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.