The pin index safety system prevents wrong cylinder attachment on the yoke of an anaesthesia machine. Which pin positions correspond to a nitrous oxide cylinder?
- A Pins 1 and 5
- B Pins 2 and 6
- C Pins 3 and 5 ✓
- D Pins 4 and 6
Correct answer: C. Pins 3 and 5
Explanation
Nitrous oxide cylinders carry the pin index combination of holes at positions 3 and 5, which matches only the N2O yoke. Oxygen uses pins 2 and 5, carbon dioxide uses pins 1 and 6, and entonox uses pin 7 alone. This asymmetric coding makes it physically impossible to connect a cylinder to the wrong gas pipeline inlet, a standard equipment safety fact asked repeatedly in Indian postgraduate examinations.
Reference: Morgan and Mikhail's Clinical Anesthesiology, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.