Anesthesia · patient case question
What is the strongest contraindication to nitrous oxide–oxygen sedation for him TODAY?
Patient case: Sedation for an anxious smoker
Patient: Male, 44 years old
Chief Complaint: “I cannot get through an appointment without something to calm me down, and I want to stop smoking.”
Background: Twenty-pack-year smoking history. No cardiac or respiratory diagnosis. He had uneventful nitrous oxide sedation two months ago. He has a history of a single seizure in adolescence, cause never established.
Vital Signs: BP 132/80 mmHg · HR 82 bpm · SpO₂ 96% on air · T 99.4°F
Findings: He attends today with a four-day upper respiratory tract infection and is completely unable to breathe through his nose.
Show answer and explanation
Correct answer: A. His complete nasal obstruction
- A. CORRECT. Nitrous oxide is delivered through a NASAL HOOD. If the patient cannot breathe through the nose the technique simply cannot work, and attempting it risks inadequate sedation and hypoxia. NASAL OBSTRUCTION is an ABSOLUTE contraindication, and an active upper respiratory tract infection is a clear reason to defer. The other respiratory considerations are RELATIVE: COPD, where the hypoxic respiratory drive matters and high inspired oxygen can be hazardous; severe asthma; and pneumonia.
- B. Repeated exposures LESS THAN ONE WEEK apart are a relative contraindication, because nitrous oxide inactivates methionine synthase by oxidising vitamin B12 and repeated close exposure can cause bone marrow suppression. Two months is far outside that window and is irrelevant.
- C. Anxiety is the INDICATION, not a contraindication — mild to moderate apprehension, the frightened child, gagging, and reducing awareness of time are exactly what nitrous oxide is for. Note the twist, though: SEVERE apprehension is a relative contraindication, because a highly anxious patient often cannot tolerate the mask and needs a different technique.
- D. Smoking itself is not a contraindication. The chronic respiratory disease that may accompany it can be.
Note: ABSOLUTE contraindications to memorise: nasal obstruction, complete inability to communicate (disability or language), raised intracranial pressure, use as a substitute for adequate local or general anaesthesia, patient refusal, active or recovering substance abuse, and lack of adequate gas scavenging. RELATIVE: pulmonary disease, respiratory infection, first-trimester pregnancy, psychiatric illness, immunocompromise, multiple sclerosis, blocked middle ear, current cannabis or hallucinogen use, severe apprehension, and repeated exposures under a week apart.