[Pain prevention with fixed 50% nitrous oxide-oxygen mixture during bone-marrow biopsy]

During bone-marrow biopsy, one third of patients score their pain as moderate or severe. Combination of analgesic and hypnotic is effective at reducing pain, but prolonged medical surveillance is necessary. The objective of the study was to assess the effectiveness and ease of use of the equimolar nitrous oxide-oxygen mixture (nitrous oxide), a short acting analgesic with little sedative effect, during bone-marrow biopsy.

As part of a non-controlled prospective observational study, patients undergoing a bone-marrow biopsy received nitrous oxide as an adjuvant to local anaesthesia. Facemask was self-maintained. A questionnaire was given after completion of the procedure to assess the pain (with a numerical-rating scale [RS] ranging from 0 to 10) as the main criterion and the ease of the procedure, the tolerance, and satisfaction, as secondary criteria. The physician noted adverse reactions.

Nineteen women and 21 men were included. The median age was 51 years. Ninety percent of patients felt slight pain, less than 5 out of 10 on the RS. Only one patient had difficulty in keeping the mask. A patient experienced nausea and four presented a fleeting euphoria noticed by the physician. Ninety-five of patients wished to use nitrous oxide again should further bone-marrow examinations be necessary.

Nitrous oxide is an effective analgesic when performing bone-marrow biopsies. Ten percent of patients feel a moderate to severe pain instead of one third. Despite some mild side effects, there is a very good appreciation by patients. Since this study, the authors routinely use nitrous oxide.