When used as a primary or supplemental technique, various authors have reported an increase in heart rate with the intraosseous injection of epinephrine- and levonordefrin-containing anesthetic solutions.1–6 The increase in heart rate has ranged from 8 to 32 beats/min. As demonstrated by a number of studies,1–6 the patient usually perceives the increase in heart rate.

In previous studies,1–6 the local anesthetic solution was administered intraosseously over a 1- to 2-minute period using a conventional syringe. The Wand/CompuDent local anesthetic system has been developed to deliver a controlled amount of anesthetic solution at a precise and controlled rate. The slow rate of anesthetic solution administration with the Wand takes 4 minutes and 45 seconds to deliver 1.4 mL of anesthetic solution.

Clinically, it would be advantageous to reduce or eliminate the increase in heart rate using epinephrine-containing solutions with the intraosseous injection. We propose that a slow rate of anesthetic solution deposition may potentially reduce the increase in heart rate. Therefore, the purpose of this prospective, randomized, single-blinded, crossover study was to compare the effect on heart rate of delivering an intraosseous injection of 1.4 mL of 2% lidocaine with 1 : 100,000 epinephrine using 2 rates and 2 methods of solution deposition.

Methods

Sixty-one adult subjects participated in this study. The subjects were in good health and were not taking any medications that would alter their perception of pain. The Ohio State University Human Subjects Review Committee approved the study and written informed consent was obtained from each subject.

The 61 blinded subjects randomly received 3 sets of intraosseous injections using: the Wand local anesthetic system at a deposition rate of 45 seconds (fast injection); the Wand local anesthetic system at a deposition rate of 4 minutes and 45 seconds (slow injection); and a conventional syringe at a deposition rate of 4 minutes and 45 seconds (slow injection), in 3 separate appointments spaced at least 3 weeks apart, in a crossover design.

For all intraosseous injections, 1.4 mL of 2% lidocaine with 1 : 100,000 epinephrine (Xylocaine, Astra Zeneca LP, York, Pa) was administered. With the crossover design, there were 183 total intraosseous injections administered and each subject served as his/her own control. Ninety-three injections were administered on the right side, and 90 injections were administered on the left side. The same side randomly chosen for the first intraosseous injections was used again for the second and third intraosseous injections.

Before the experiment, the 3 methods of intraosseous injections were randomly assigned 6-digit numbers from a random number table. Each subject was randomly assigned to each of the 3 methods of injection to determine which intraosseous injection was to be administered at each appointment. Only the random numbers were recorded on the data collection sheets to further blind the experiment.

To monitor heart rate (pulse rate), the subjects were connected to a pulse oximeter (Criticare Systems Inc, Waukesha, Wis) by means of a sensor attached to the nail of the forefinger. No audible beeping noise was emitted from the pulse oximeter. Through use of an automated printout, heart rate was recorded during baseline, during the infiltration/perforation, and during anesthetic solution deposition. For purposes of data analysis, readings were grouped into 3 time periods. Period One was the average of readings taken at 2-minute intervals for 8 minutes prior to anesthetic injection (baseline). Period Two was the average of readings taken at 1-minute intervals for 8 minutes during infiltration and intraosseous perforation. Period Three was the average of readings taken at 15-second intervals during anesthetic solution deposition. Trained assistants performed the monitoring of the pulse oximeter. The first molar was pulp tested during the experiment to ensure that the intraosseous injections were successful. The intraosseous injection with the Stabident system (Fairfax Dental Inc, Miami, Fla) was given in the following manner. With the subjects in a reclining position, the area of perforation was determined by the horizontal line from the buccal gingival margins of the first and second molars and a vertical line that passed through the interdental papilla on the distal aspect of the first molar. A point approximately 2 mm below the intersection of these lines was selected as the perforation site if the site was in attached gingiva. If this point was in alveolar mucosa, the perforation site was moved just above the junction of the attached gingiva and alveolar mucosa. An infiltration injection of 0.6 mL of 2% lidocaine with 1 : 100,000 epinephrine was administered through a 30-gauge needle attached to an aspirating syringe in the muccobuccal fold apical to the predetermined perforation site. Prior to the infiltration, topical anesthetic (20% benzocaine, Patterson Dental Supply Inc, St Paul, Minn) was placed on a cotton tip applicator and applied to the infiltration site for 1 minute. Five minutes after the infiltration, pressure was applied at the predetermined perforation site with an explorer. If the subject felt pain (22 of 183 injections), an additional 0.3 mL of 2% lidocaine with 1 : 100,000 epinephrine was administered. The same site was retested and all subjects were successfully anesthetized.

The perforator was pushed through the gingiva until the perforator contacted bone. Holding the drill at a 90° angle to the bone, the handpiece was activated in a series of short bursts, using light pressure, until a breakthrough feeling was observed or until 2 to 5 seconds elapsed. The handpiece was continuously activated while the perforator was within bone to prevent lodging or breakage that might have occurred if the perforator was allowed to stop rotating.

For the Wand injections, a cartridge of 2% lidocaine with 1 : 100,000 epinephrine was placed into the unit's handpiece assembly and placed into the cartridge holder with a quarter turn in a counterclockwise direction. A 26-gauge ⅜ inch Luer-Lok needle was attached to the end of the sterile plastic Wand tubing. The majority of the Wand plastic handle was removed to shorten the length for ease of placement in the perforator opening. The foot pedal was depressed once to activate the purge cycle which removed air from the tubing. A sterile silicone stopper was placed on the needle and pushed to the hub to prevent backflow of anesthetic solution during the injection. The needle was bent at the hub to a 45° angle to allow for easier insertion.

For the conventional syringe injection, 0.4 mL of anesthetic solution was withdrawn from a cartridge of 2% lidocaine with 1 : 100,000 epinephrine using a 1-mL tuberculin syringe and sterile technique. The cartridge was then placed in a standard aspirating syringe. A 27-gauge ½ inch needle was attached to the syringe and the needle was bent to a 45° angle to allow for easier insertion.

The slow Wand intraosseous injection was administered as follows. The subject was blindfolded and informed the injection would take almost 5 minutes and that they would hear chimes during the injection. The needle was fully inserted into the perforation opening. The Wand unit was activated at a slow rate of 1.4 mL per 4 minutes and 45 seconds by partially depressing the foot pedal for 8 seconds. By removing the foot from the foot pedal, the Wand automatically activated the cruise control which continued to deliver the solution at the slow rate. Approximately 1 drop of anesthetic solution was delivered every other second on the slow setting. Visually monitoring the green lights on the unit and audibly monitoring the corresponding chimes determined when deposition of solution was complete. The investigator had direct vision of the needle, and if minor leakage of anesthetic solution was observed, the needle was repositioned until no leakage occurred. A total of 1.4 mL of anesthetic solution was delivered because solution was lost during the initial purge of the Wand assembly and there was some anesthetic solution remaining in the tubing and cartridge at the completion of the injection.

The fast Wand intraosseous injection was given as follows. The subject was blindfolded and informed the injection would take almost 5 minutes and that they would hear chimes during the injection. The injection was the same as above except the Wand unit was activated at the fast rate (45 seconds) by fully depressing the foot pedal, and the Wand handpiece assembly was held in place for 4 minutes and 45 seconds.

The conventional syringe injection was administered as follows. The subject was blindfolded and informed the injection would take almost 5 minutes and that they would hear chimes during the injection. The needle was fully inserted into the perforation opening. In order to mimic a slow Wand injection, the plunger of the syringe was very slowly depressed to deposit the anesthetic solution over a period of 4 minutes and 45 seconds. Wand units were activated at the beginning of the syringe injection. Visually monitoring the green lights on the unit and audibly monitoring the corresponding chimes determined when deposition of solution was complete.

The blinding of the slow and fast Wand and syringe injections was accomplished by one, blindfolding all subjects at all appointments. Two, during the conventional syringe injection, 2 Wand units were activated so the subject would hear both slow and fast rate chimes in the background. Three, during the slow and fast Wand injections, a conventional loaded syringe was placed on the instrument tray so the subject would see both the Wand unit and syringe at the start of the appointment. Four, during the slow and fast Wand injections, a standard syringe emptied of anesthetic solution was placed on the instrument tray before the blindfold was removed. At 2 minutes after deposition of anesthetic solution for all intraosseous injections, subjects were asked “Did your heart feel as if it were beating faster?” All intraosseous injections were given by one operator (LS).

Comparisons between the heart rate for the 3 intraosseous injections were analyzed using a repeated-measures ANOVA with a Tukey-Kramer post hoc test. With a nondirectional alpha risk of .05 and a power of 80%, a sample size of 60 subjects was required to demonstrate a difference of ± 30% in heart rate increase between the injections. Subjective responses to heart rate increases between groups were analyzed using logistic regression and chi-square analysis. Comparisons were considered significant at P < .05.

Results

Sixty-one adult subjects, 26 women and 35 men, age 20 to 39 years with an average age of 26 years, participated.

Maximum mean heart rates for each type of injection for baseline (Time Period One) and during infiltration/perforation (Time Period Two) are presented in Tables 1 and 2. Other than a small, yet statistically significant increased maximum heart rate in the baseline of women with the syringe compared with the fast Wand, there were no significant differences in the first 2 time periods.

Table 1 Maximum Mean Heart Rates (± SD) for Each Type of Injection by Gender During Baseline (Time Period One)

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Table 2 Maximum Mean Heart Rates (± SD) for Each Type of Injection by Gender During Infiltration/Perforation (Time Period Two)

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The subjects' subjective increase in heart rate was significantly higher for the fast Wand solution deposition versus either the slow solution deposition with the Wand or syringe for both men and women (Table 3). There was no significant difference in the subjects' subjective increase in heart rate in the slow Wand versus slow syringe solution deposition.

Table 3 Perceived Heart Rate Increase by Injection Method and Gender Following Anesthetic Solution Deposition (Time Period Three)

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The subjects' objective increase in heart rate was significantly higher for the fast Wand solution deposition versus either the slow solution deposition with the Wand or syringe for both men and women (Table 4). The mean change in heart rate was most dramatic in women and men who experienced an increase of 28 beats/min and 21 beats/min, respectively, in the fast Wand compared with the slow Wand or syringe solution deposition. There was no significant difference between the slow Wand and slow syringe solution deposition (Table 4). The Figure depicts heart rate at 15-second intervals for 4 minutes and 45 seconds for the 3 injection techniques. Significant differences were shown for the fast Wand solution deposition when compared with the slow techniques.

Table 4 Mean Heart Rate Changes and Mean Maximum Heart Rates (± SD) for Each Type of Injection by Gender During Anesthetic Solution Deposition (Time Period Three)

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Discussion

During Period Three, the subjects' objective increase in heart rate was significantly higher for the fast Wand solution deposition versus either the slow solution deposition with the Wand or syringe for both men and women (Table 4). Previous studies1–3,5,6 of the intraosseous injection have reported a mean increase in heart rate of 8 to 32 beats/min when depositing 1.8 mL of 2% lidocaine with 1 : 100,000 epinephrine over a 1- to 2-minute period. Replogle et al1 and Chamberlain et al2 found no significant changes in mean diastolic, mean systolic, or mean arterial blood pressure. In our study, the fast Wand solution deposition increased heart rate by 21 to 28 beats/min and the heart rate returned to the preinjection heart rate within several minutes (Figure). These results are similar to the findings of Replogle et al1 and Guglielmo et al.3 Therefore, the fast Wand solution deposition caused a higher increase in heart rate than a slow solution deposition.

Replogle et al1 felt that the mean increase in heart rate of 28 beats/min, recorded in her study, would not be clinically significant in healthy patients. According to McGowan,7 aerobic conditioning requires greater increases than 28 beats/min. The upper heart rate limit for a 25-year-old person is 195 beats/min, and the recommended range during exercise is 137 to 166 beats/min for a 20-minute period.7 For people age 65 years, the upper limit is 155 beats/min, with an exercise range of 108 to 132 beats/min for a 20-minute period.7 In this study, the highest heart rate was 123 beats/min with the fast injection. For the slow Wand, the highest heart rate was 119 beats/min and was 108 beats/min for the slow syringe. Because we studied a young adult population, the results of this study may not apply to children or the elderly.

The slow Wand and slow syringe solution deposition had significantly lower heart rates than the fast solution deposition (Table 1). Therefore, increasing the time of solution deposition to 4 minutes and 45 seconds reduced heart rates but did not completely eliminate an increase. Ideally, we would like to have a solution deposition rate where the patient does not perceive an increased heart rate. A deposition rate slower than 4 minutes and 45 seconds is currently not achievable with the Wand unit because the rate is predetermined. It would be possible, but difficult, to extend the time of deposition with the conventional syringe. However, a slower solution deposition rate may not be clinically practical. We feel it is advantageous to reduce the heart rate by slowing the solution deposition rate even if it takes 4 minutes and 45 seconds. The intraosseous procedure is more comfortable for the patient because of the reduced heart rate and provides a good success rate. The success rate (obtaining 2 consecutive 80 readings with the pulp tester), as recorded in this study, averaged 97% for the 3 techniques in the first molar (data not presented). If an intraosseous injection is required that does not contain a vasoconstrictor, 3% mepivacaine plain may be used. However, the efficacy of the 3% mepivacaine is less than 2% lidocaine with 1 : 100,000 epinephrine.1,8–10

There was no significant difference in heart rate increases between the slow Wand and slow syringe solution deposition (Table 4). Subjectively, the slow solution deposition with the conventional syringe was difficult because of fatigue in maintaining a constant pressure on the syringe handle. Basically, the pressure on the syringe handle was intermittent without constant pressure. With the Wand unit, the handpiece with needle assembly was held in position during the slow injection without having to control the injection pressure. However, the subjective and objective heart rate increases were similar indicating that the flow rate with the syringe could be regulated similarly to the Wand.

The Figure depicts heart rate at 15-second intervals for 4 minutes and 45 seconds for the 3 methods of intraosseous injections by gender. Approximately 45 seconds after the anesthetic solution deposition began, the heart rate increased for both genders and all 3 injection techniques. However, the fast Wand solution deposition caused a statistically higher rate of increase from 60 seconds to 90 seconds than either of the slow solution deposition rates (Figure). Approximately 120 seconds after solution deposition began, all 3 injection techniques leveled off and continued at a steady level for 285 seconds. Again, the rate of solution deposition affected the increase in heart rate.

With regard to gender and the findings of this study, heart rate was higher for women than for men (Tables 1 through 4). Agelink et al11 and Umetani et al12 found that premenopausal women tend to have a greater resting heart rate than men of the same age. According to Wilmore and Costill,13 the greater heart rate and smaller stroke volume of women are due to the fact that women have smaller bodies, smaller hearts, and smaller blood volume.

The subjects' subjective increase in heart rate was significantly higher for the fast Wand solution deposition (89 to 96%) versus either the slow solution deposition with the Wand or syringe (69 to 77%) for both men and women (Table 3). The increase in percentage of subjective heart rate would seem appropriate because during the fast Wand solution deposition the increase was 28 beats/min for women and 21 beats/min for men. On the other hand, the heart rate increase for the slow injections ranged from 10 beats/min to 12 beats/min during solution deposition. Previous studies have reported a subjective increase in heart rate during solution deposition of 60 to 93% using a 1- to 2-minute deposition time.1,3,14–17 As in agreement with this study, previous authors1,3,6 have found that subjective and objective heart rate increases coincided when using monitoring devices such as a pulse oximeter or an electrocardiogram.

What is the minimum heart rate change necessary for a subject to subjectively perceive an increase? The confounding factor is whether the subject may actually be experiencing a chronotropic or ionotropic effect as reported by Replogle et al.1 Borg and Borg18 developed an exertion scale to relate an individual's personal sense of physical exertion to his/her heart rate. According to this scale, a rating of 6 (resting heart rate of 60 beats/min) means no physical exertion, and light physical exertion is rated a 7 (resting heart rate of 70 beats/min). Therefore, based on the Borg scale, the assumption would be that an individual might require approximately 10 beats/min increase in heart rate to notice a subjective change.

Except for women in the slow syringe group, there were no significant differences between the baseline maximum mean heart rates for the 3 injection techniques (Period One, Table 1). The difference of only 6 beats/min between the slow syringe group and fast Wand group would not be clinically significant. The change may be attributed to individual variations between appointments. Replogle et al1 and Wood et al5 did not find differences in baseline readings between appointments.

There were no significant differences between the infiltration/perforation maximum mean heart rates for the 3 injection techniques (Period Two, Table 2). Because the infiltration/perforation procedure was identical for all 3 appointments, no statistical significance would be expected. The infiltration of 0.6 mL to 0.9 mL of 2% lidocaine with 1 : 100,000 epinephrine did not seem to raise the mean maximum heart rate much above baseline readings (Tables 1 and 2). Because of the small amount of anesthetic solution delivered, it would be unlikely that a significant increase in heart rate would occur. While perforation may cause pain,19 it did not seem to increase heart rate (Table 2).

Conclusion

In conclusion, an intraosseous injection of 1.4 mL of 2% lidocaine with 1 : 100,000 epinephrine with the Wand at a 45-second rate of anesthetic deposition resulted in a significantly higher heart rate (21 to 28 beats/min) when compared with a 4-minute and 45-second anesthetic solution deposition using either the Wand or traditional syringe (10 to 12 beats/min).