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Background and aims Bone marrow aspiration and/or biopsy (BMAB), performed under local anaesthesia in adults, is a common and often painful procedure. Anxiety is known to intensify pain during the procedure. Nitrous oxide (N2O), known for its sedative and analgesic benefit in various short medical procedures and labour pain, could be advantageous also for pain relief during bone marrow examination. N2O acts rapidly and is eliminated in a couple of minutes once the inhalation is stopped, and occasional side effects (e.g. dizziness and nausea) are mild. The aim of this study was to compare the analgesic effects of inhaled 50% mixture of nitrous oxide and oxygen to 50% oxygen during bone marrow examination. Methods In this randomized, controlled, patient and observer blinded study patients received either 50% mixture of nitrous oxide and oxygen or 50% mixture of oxygen in air during bone marrow examination, in addition to local analgesia. Both patient groups comprised 35 adult patients. Pre-procedural anxiety and procedural pain were rated on the Numeral Rating Scale (NRS 0‒10). Cognitive function was measured before and 30 min after the procedure. Possible side effects were recorded. A telephone interview was performed 24 h later. Results There were no statistically significant differences in pain scores of the procedural steps (median NRS ranging 3.0‒4.0) between the study groups. High pain scores of 8‒10 comprised 0% vs. 8.6% of the scores during infiltration, 2.9% vs. 5.7% during puncture, 11.4% vs. 14.3% during aspiration and 2.9% vs. 2.9% during biopsy in N2O and 50% O2 groups, respectively (NS). Pre-procedural anxiety (median NRS 3.5 in both groups), measured in the outpatient clinic just prior to procedure, correlated with pain intensity during bone marrow aspiration (P = 0.045). There were no significant differences between side effects. During the BMAB four patients (3 in N2O group, 1 in 50% O2 group) reported dizziness and one patient in the N2O group reported nausea. Gas inhalation did not affect the cognitive function of the participants. In both groups the majority (>80%) of the patients was satisfied with the inhalation technique. During the 24 h interview, most of the participants were pain free and they did not report any serious adverse effects. Conclusions In spite of similar moderate to strong procedural pain in both groups and no benefit of N2O, most patients were satisfied with the inhalational techniques. We assume that the bedside presence of an anaesthesiologist and the distraction caused by the inhalational arrangements introduced positive context-sensitive therapeutic effect independent of the gas used. Pre-procedural anxiety predicted pain associated with bone marrow aspiration. Implications Inhaled 50% nitrous oxide was not an effective analgesic during bone marrow examination in our unselected outpatient population. Further studies should concentrate on its use with patients predicted to be at increased risk of suffering intense pain during the procedure, such as very anxious patients or those who have a painful history of previous bone marrow examinations.

Background and purpose Local infiltration anaesthesia is frequently painful due to low pH of the used anaesthetics, such as lidocaine. Usually pH of the solution is near 4.0, which causes tissue irritation and excitation of the pain mediating nerve endings. Warming and buffering the local anaesthetic solution have been shown to reduce the patient’s experience of pain and unpleasantness during infiltration. Buffering reduces the dissociation of the local anaesthetic molecule and may enhance the anaesthetic’s entrance into nerve cells. In this randomized placebo-controlled trial warmed and buffered lidocaine with adrenaline was compared to room temperature unbuffered lidocaine with adrenaline infiltrated before bone marrow aspiration and/or biopsy (BMAB). The aim was to find out to what extent warming and buffering would diminish pain during infiltration and whether this would be reflected in less pain also during subsequent steps of the BMAB procedure. Methods One hundred patients scheduled to undergo BMAB were interviewed regarding subjective experiences from previous medical procedures, current chronic and temporary medications, and their present state of anxiety before the BMAB procedure. They received local anaesthetic infiltration of lidocaine prior to BMAB. The solution used was either warmed lidocaine 20 mg/ml with adrenaline buffered with sodium bicarbonate 75 mg/ml (warmed and buffered group, 50 patients, pH approximately 7.3, 32°C) or unbuffered lidocaine 20 mg/ml with adrenaline mixed with NaCl 0.9% solution (control group, 50 patients, pH approximately 3.7, room temperature). The lidocaine concentration was similar in both groups. The bone marrow sampling needle was inserted 2 min after local anaesthetic infiltration. The grade of preprocedural anxiety, and pain sensations during the BMAB, both rated on NRS (numeral rating scale, 0–10) were compared between the groups. Results In comparison with the use of an unbuffered solution at room temperature warmed and buffered lidocaine with adrenaline caused less pain during infiltration (median NRS 4.0 vs. 2.0, P < 0.002) but it did not make performing the other phases of BMAB any less painful. As expected, painful experiences from previous medical, other than BMAB, or dental procedures and anxiety were associated with local anaesthetic infiltration pain during BMAB. Patients’ own pain or anxiolytic medication did not lessen pain during BMAB. Conclusions By warming and buffering the lidocaine solution containing adrenaline it is possible to make the pain during infiltration less intense. Unfortunately, such benefit was not detected during the following steps of BMAB, initiated 2 min later. Preprocedural anxiety made procedural pain more intense including that of the local anaesthetic infiltration. Implications Warming and buffering the local anaesthetic prior to its administration is an effective and simple way of diminishing pain during infiltration. This benefit seems to be underutilized in the BMAB procedure. However, warming and buffering are not sufficient enough to diminish pain during bone marrow sampling and thus additional pain alleviating methods should be used, particularly in patients showing preprocedural anxiety.