Warmed and buffered lidocaine for pain relief during bone marrow aspiration and biopsy. A randomized and controlled trial.

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.