In: Anesthesia22 Nov 2009
A batch of 2-mL 2% plain lidocaine and a pack of 2% lidocaine containing 1:80,000 epinephrine were supplied by the manufacturer (AstraZeneca, King’s Langley, Herts, UK). The cartridges were identical except for an individual label on each cartridge that contained an identifying code number. The pH of a sample of each solution from the same batch numbers was measured on an electronic pH meter (Corning, Sudbury, Suffolk, UK).
Twenty-four healthy young adults (14 men, 10 women) between the ages of 20 and 24 volunteered for this trial after it was approved by the local ethics committee. A power analysis dictated that a sample size of 24 adults provided a 90% chance of detecting a 10-mm difference in the visual analogue scales (VAS) at the 1% level. It was predicted that not all volunteers would have their data entered into the trial and that a level of significance of 5% was acceptable. The power analysis dictated that at the 5% level, there was a 90% chance of detecting a 10-mm difference in the VAS if 17 volunteers were included and an 80% chance of detecting this difference if half the volunteers were included.
Each volunteer received 4 injections at 1 trial visit. The injections were as follows:
• Injection 1: 1.0 mL of solution injected over 30 seconds following aspiration into the buccal sulcus in the first premolar region on the right-hand side.
• Injection 2: 1.0 mL of solution injected over 30 seconds following aspiration into the buccal sulcus in the first premolar region on the left-hand side.
• Injection 3: 0.2 mL of solution injected over 10 seconds following aspiration into the palatal mucosa distal to the second premolar on the right-hand side.
• Injection 4: 0.2 mL of solution injected over 10 seconds following aspiration into the palatal mucosa distal to the second premolar on the left-hand side.
The same operator, who was blinded to the identity of the solutions, gave all the injections. Thirty-gauge short needles and aspirating syringes were used throughout. No topical anesthetic was applied before injection. The allocation of the cartridges was such that each solution was injected at 1 of each pair of injections. The order in which the solutions were administered was randomized. The solutions used for injections 1 and 3 were determined independently by 2 tosses of a coin (with injections 2 and 4 receiving the other solution).
Immediately after each local anesthetic administration, the volunteer recorded injection discomfort on a continuous 100-mm VAS with endpoints “no pain” and “unbearable pain.” Because the sensitivity of acute pain trials is dependent on the production of moderate pain, data were entered into the study only if one or both scores in the pair (ie, a pair of buccal or a pair of palatal scores) were at least 30 mm on the VAS. This score isregarded as representing moderate pain. Pairs of injections where both entries were less than 30 mm were rejected.
In order to compare the pain scores between the sexes, both buccal VAS scores for the 12 individuals included were added to provide a total buccal pain score for each volunteer (maximum possible score = 200). Similarly, a total palatal pain score was determined for each of the 17 individuals included in the palatal injection comparison.
Differences between solutions and order effects were analyzed using Student’s paired t test. Sex differences were compared with Student’s unpaired t test. Differences were considered significant when P < .05.
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