Digital block is widely used in the emergency department (ED) for procedures on fingers. These procedures include suturing lacerations, suturing partially or completely amputated fingertips, incision and drainage of abscesses, reducing a fracture and blocking painful stings. Nerve block is superior to local infiltration because the latter requires a large dose in a relatively small area to achieve good anaesthesia. In addition, local infiltration can distort the tissue, particularly in areas requiring precise anatomical alignment. There are many local anaesthetics in use—either alone or in combination with other agents—which aim to achieve both a fast onset of action and prolonged duration of action. The most common of these are lidocaine (1–2%) and bupivacaine (0.25–0.5%). The former has a faster onset of action and the latter has a longer duration of anaesthesia.1 Several trials have mixed both drugs together or with other agents to shorten their onset of action or increase the duration of anaesthesia (eg, clonidine, epinephrine and ketorolac).1^–3

Lidocaine is mixed commercially with epinephrine for nerve blocks to increase the duration of action. This makes its anaesthetic properties comparable to those of bupivacaine. However, an old dogma that the use of this mixture in digital blocks will lead to necrosis and ischaemia has resulted in this mixture being avoided in digital blocks. After reviewing the literature we could not find evidence that the use of this mixture caused ischaemia. In contrast, we found several studies suggesting that it is a safe combination in selected patients.4^–8

From the literature comparing bupivacaine and lidocaine,9 10 we found that infiltration of bupivacaine and lidocaine may last for up to 6 h and 2 h, respectively. In another study, 2% lidocaine with epinephrine produced digital anaesthesia for an average of 10.4 h.1 This means that long procedures may need repeated doses of lidocaine, which may not be the case for bupivacaine. In one study by Valvano and Leffler,10 the pain of injection with bupivacaine alone was compared with that of bupivacaine + lidocaine. Although this study observed no difference in the pain of injection, the observed findings could be due to the presence of bupivacaine in both anaesthetics. We did not find any other study comparing the pain of injection of the local anaesthetics, but this characteristic may be the most important one for any local anaesthetic. If lidocaine + epinephrine produces a duration of action comparable to that of bupivacaine, the main reason for not using it is the pain of the injection. The two anaesthetics used in this study are already available in most EDs. The results of this trial may change the practice without adding a new agent. This is a cost-effective change in favour of patient care that is possible in any ED. The results of this clinical trial will help to determine which of these two available local anaesthetics achieves a fast onset and long duration of action while producing the least amount of pain in an ED setting. Such an agent will also determine the most appropriate time to start a painful procedure after the block, and it will also provide both a longer duration of anaesthesia in the post-procedure period and sufficient time for the operator to finish the procedure without reinjecting the local anaesthetic.

In this study we compared bupivacaine with lidocaine + epinephrine for use as a digital block in healthy volunteers. Our aim was to discover if there is a difference in the pain of injection between the two drugs. The time of onset and duration of action of the two anaesthetics were also recorded and compared. Differences in the pain of injection for these two anaesthetics have not been investigated, so we selected this variable to be our primary outcome.

METHODS

Design

This was a randomised double-blind prospective self-controlled study in a group of healthy volunteers. Each participant was randomly assigned to receive either lidocaine (1%) + epinephrine 1:100 000 in the right hand and bupivacaine (0.5%) in the left hand, or lidocaine (1%) + epinephrine 1:100 000 in the left hand and bupivacaine (0.5%) in the right hand. Randomisation tables were used, and an independent assistant prepared the syringes with the drugs and labelled them with an ID number and right or left, according to the randomisation. The assistant was independent of the recruitment process to ensure concealment of the randomisation process and blinding of the medication. The volunteers and the physician conducting the block and recording the outcomes were blind to which drug was administered to which hand.

Setting

This study was conducted in the department of emergency medicine of King Faisal Specialist Hospital and Research Center (KFSHRC), a tertiary care centre.

Participants

The participants were volunteers who were recruited by advertising brochures distributed in KFSHRC, other hospitals and universities. All volunteers were screened to ensure that they met the following inclusion criteria: >18 years of age; no history of cardiovascular or liver disease; not diabetic and no history of peripheral vascular disease; not on any current medication; no analgesia within the last 48 h; no previous procedures conducted on either hand; no previous condition of the hand (eg, Reynaud’s disease); and no known allergies. None of the volunteers were members of the staff, under the supervision of any of the investigators or related to any of the investigators.

Interventions

Each participant was given both a verbal and written description of the procedure (fig 1) and all signed a written consent form on the day of the procedure. Participants were not aware of the type of anaesthetic administered to each hand. A pain visual analogue scale (VAS) chart was explained to the participants. The third (middle) finger of both hands was used. We adopted the dorsal approach, one of the techniques described by Reichman and Tolson.11 All the used syringes were labelled as described above, delivered on the day of the procedure, kept at the same temperature and administered by the same physician using the same sequence and technique. The needle size (3.75 cm, 25 G), speed of injection (1 ml over 15 s), anaesthetic temperature (room temperature) and site of injection (web space at 2, 4, 8 and 10 o’clock in relation to the bone, 1 ml in each site) were kept constant for all participants in order to control for their effects.

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Figure 1

Study flow diagram.

Immediately after withdrawing the needle, a stopwatch was started. The volunteer was asked to score the pain of injection on the VAS and the pain sensation was checked every minute at both the radial and ulnar aspects of the middle phalanx using a testing needle. At each time point the participants were asked to point to the degree of pain on the VAS. The time of complete anaesthesia was noted at the point when the participants stated they could no longer feel the pain. The same testing was continued to document the return of sensation, which was noted when participants stated that they started to feel the pain again. A telephone follow-up call was made to all participants 24 h after the end of the procedure.

Main outcome measures

Pain of injection was measured as the primary outcome using a 0–100 mm pain VAS. The time before anaesthesia to pinpricks and the duration of anaesthesia were reported by all volunteers in minutes. All participants were instructed to report any adverse effects such as persistent pain and change in colour or coldness in any of the injected digits during and after the procedure.

Primary data analysis

The statistical test used was the paired t test. Type I error was set at the 0.05 level and the power of the study was set at the 0.80 level. The sample size was calculated as 10 volunteers with an expected variance of 20 mm on the VAS score (a minimum important difference of 20 mm).12 13

The baseline characteristics were summarised separately by treatment group using means and standard deviations to describe continuous variables and frequency counts to describe categorical variables. Differences between the intervention and control groups were tested for significance using the Student t test (two-tailed) for continuous variables and a χ² test for nominal variables. An “intent-to-treat” analysis was used and all statistical tests were two-tailed and performed at the 0.05 significance level.

RESULTS

Twelve healthy volunteers were randomised; their mean age and gender are shown in table 1. The randomisation table resulted in more cases with lidocaine + epinephrine being injected in the right hand than in the left hand. We therefore present the baseline characteristics in table 2 to assess the effect of this possible confounder on our primary and secondary outcomes. Table 2 compares the outcomes of each anaesthetic injected in each side for each outcome; the side of the injection did not appear to have an effect on the outcomes of the injections.

The final outcomes comparing injections of lidocaine (1%) + epinephrine (1:100 000) and bupivacaine (0.5%) are shown in table 3. The median VAS scores for pain of injection were lower for lidocaine + epinephrine than for bupivacaine (26 mm vs 40.5 mm; p<0.05). The median times before anaesthesia to pinprick were similar for both anaesthetics (3.5 min vs 3.3 min; p = 0.84). The median time for return of pinprick sensation was much longer for bupivacaine than for lidocaine + epinephrine (321 min vs 701 min; p<0.05). Follow-up at 24 h was completed for all subjects and no side effects were reported.

DISCUSSION

Lidocaine with epinephrine is widely used in the acute care setting for procedural local anaesthesia because of its fast onset of action;9 many studies have shown it to be safe as a digital block.4^–8 Our study shows that, in addition, it produces less pain at the time of injection. This is an important feature to be considered when selecting an anaesthetic for a painful procedure. Researchers added epinephrine to lidocaine in an attempt to increase the duration of anaesthesia when long anaesthesia was required. This led to the use of bupivacaine (where available) as an alternative choice.1 Our study confirms this finding as a secondary outcome. The significant difference in pain of injection between these two common anaesthetics favours the use of lidocaine with epinephrine. Lidocaine with epinephrine is therefore a better choice when the main goal of the block is the avoidance of pain associated with the procedure or the injury. Moreover, the duration of anaesthesia achieved by lidocaine + epinephrine was 321 (228–463) min, which is sufficient time for any procedure to be accomplished in an emergency room setting. The current underuse of bupivacaine by some physicians has been attributed to different reasons,14 but pain of injection was not thought to be a discouraging feature. Our study shows that pain of injection should be considered when choosing a local anaesthetic for digital block. If a longer duration of anaesthesia is required than that provided by lidocaine + epinephrine, particularly for post-procedural anaesthesia, bupivacaine can be considered while keeping in mind the increased discomfort associated with the injection.

We chose a sample size of 12 to achieve a conclusive result regarding the pain of injection, but not for the time of onset of anaesthesia which was not significantly different between the two anaesthetics studied. This result favours the use of lidocaine + epinephrine, so the time to onset of anaesthesia will not prevent the use of this anaesthetic which, in addition, is a less painful injection.

Because this study compared only the pain of injection of lidocaine + epinephrine and bupivacaine, further studies investigating the pain of injection of other anaesthetics are recommended. Such studies can investigate the impact of the addition of epinephrine to bupivacaine in terms of pain of injection. The use of lidocaine with epinephrine should be used with caution in patients with peripheral vascular diseases such as diabetes, since the safety of this mixture has not been studied in this group of patients.

Limitations of the study

This study was performed on healthy volunteers. The effect of a coexisting painful injury in the same digit on the perception of the pain of an injection or the ability to distinguish between the pain of the two anaesthetics is not clear. We used one concentration of both anaesthetics. Whether different concentrations would change the perception of the pain of injection will need further investigation.

CONCLUSION

Lidocaine (1%) with epinephrine (1:100 000) was significantly less painful during injection and had a shorter duration of action than bupivacaine (0.5%). Despite these differences, both drugs showed a similar onset of action for use in digital nerve block without complications. Despite the shorter duration of action of lidocaine + epinephrine, it is still sufficient for use in emergency room applications.