Enhancement of Analgesic Effect by Combination of Non-Noxious Stimulation and Noxious Stimulation in Humans.

The aim of the this study was to investigate the combined effects of heterosegmental non-noxious and noxious stimulation on electrically induced tooth pain. The late component of somatosensory-evoked potentials (SEP), induced by electrical tooth stimulation and pain intensity, were examined under electrical stimulation to forearms. Noxious, non-noxious, and combined non-noxious and noxious electrical stimulation were applied to median nerves on the forearms. Four experimental sessions (ie, control session, combined non-noxious and noxious stimulation session, non-noxious stimulation session, and noxious stimulation session were performed for each subject at each 10-minute interval for 30 minutes. The amplitudes of the SEP and VAS scores in the combined stimulation session decreased significantly compared with those in the control session and the reduction rates were 51.1% (13.4 µV) and 41.0% (23.5 mm), respectively. These results show that the combined stimulation has a more potent analgesic effect than that of either the non-noxious or the noxious stimulation. It is suggested that a potent analgesia was produced by an activated central mechanism, including endogenous opioid and descending pain inhibitory systems due to combined non-noxious and noxious stimulation.

Heterotopic CO2 laser stimulation inhibits tooth-related somatosensory evoked potentials.

BACKGROUND: The diffuse noxious inhibitory control (DNIC) effect is the neurophysiological basis for the phenomenon that heterotopic "pain inhibits pain" in remote areas of the body. The effect of DNIC is mediated by spino-bulbo-spinal loops and a final postsynaptic inhibitory mechanism. The DNIC effect depends on intensity, duration, quality, and application site of conditioning stimulation and stimulated nerve fiber-type. DNIC induced by CO(2) laser conditioning stimulation has, however, not yet been investigated, and the present study was designed to examine this. METHODS: As the indicator of test stimulation, the late component of somatosensory evoked potentials (SEPs) induced by electrical tooth stimulation and pain intensity were examined under CO(2) laser conditioning stimulation. As the conditioning stimuli, CO(2) laser energy (lambda = 10.6 microm, spot size Ø = 2 mm) was applied to the dorsum of the left hand. RESULTS: The maximum reductions in SEP amplitude and pain intensity evaluated using a visual analog scale were 34.7% and 28.7%, respectively during CO(2) laser conditioning stimulation. No aftereffect was observed. CONCLUSION: The present study revealed that CO(2) laser radiation attenuated the late component of SEPs induced by electrical tooth stimulation, triggering the DNIC effect but with no aftereffect.

New method for postoperative pain relief using a combination of noxious and non-noxious stimuli after impacted wisdom tooth extraction.

Although in clinical dentistry the major method used for pain relief is oral administration of analgesics, alternative methods are available, such as transcutaneous electrical nerve stimulation (TENS), acupuncture, vibration and conditioned pain modulation (CPM), formerly termed diffuse noxious inhibitory control. The aim of the present study was to investigate the combined effects of non-noxious (TENS) and noxious (CPM) stimuli on postoperative pain after extraction of an impacted wisdom tooth. The study involved 44 patients who were scheduled to undergo impacted wisdom tooth extraction. The patients were randomly allocated into four groups: noxious stimuli, non-noxious stimuli, combined noxious and non-noxious stimuli, and a sham group. On the day after tooth extraction, stimulation procedures for pain relief were performed and changes in the level of perceived pain were scored using a visual analog scale (VAS). The combination of non-noxious and noxious stimuli decreased the VAS scores by 63.7%, indicating a more potent analgesic effect than that in the non-noxious, noxious, and sham groups. This method of analgesia using a combination of non-noxious and noxious stimuli can be applied to patients who are unable to tolerate analgesics, such as those with allergy, hypersensitivity or digestive disorders, and those who are pregnant.

Occurrence of intermittent Wolff-Parkinson-White syndrome during intravenous sedation.

Patients with intermittent Wolff-Parkinson-White (WPW) syndrome, defined as intermittent loss of the delta waves, can show occasional conduction through the accessory pathway. WPW syndrome often causes paroxysmal supraventricular tachycardia or atrial fibrillation. However, it may be difficult to identify the abnormalities preoperatively because of their only intermittent occurrence. We report a case in which exogenously administered epinephrine and an autonomic imbalance may have precipitated the abrupt occurrence and disappearance of the delta waves.

Pentazocine transport by square-wave AC iontophoresis with an adjusted duty cycle.

So far, pentazocine iontophoresis has never been studied, although pentazocine is widely used in pain management. The purpose of this study was to determine whether pentazocine transportation through a cellophane membrane could be enhanced using square-wave alternating current (AC) iontophoresis with an adjusted duty cycle and dependence on the voltage and the duty cycle. Voltages of 10, 25 and 40 V with duty cycles of 50%, 51%, 52%, 53%, 54% and 55% were applied for 60 minutes at a high frequency of 1 MHz to diffusion cells on both sides of a cellophane membrane. The donor compartment was filled with a solution containing pentazocine. Square-wave AC iontophoresis with an adjusted duty cycle enhanced pentazocine transportation at higher voltages and duty cycles. These results suggested that the direct current (DC) component of the square-wave AC played an important role in enhancing pentazocine transportation despite changes in polarity at very high frequency of 1 MHz. The higher voltages and duty cycles induced a pH change. The practical electrical conditions that could be applied clinically were 25 V with a 54% duty cycle or 40 V with a 53% duty cycle.

Heterotopic ischemic pain attenuates somatosensory evoked potentials induced by electrical tooth stimulation: diffuse noxious inhibitory controls in the trigeminal nerve territory.

The purpose of this study was to determine whether the late component of somatosensory evoked potentials (SEP) induced by electrical tooth stimulation and pain intensity are inhibited by heterotopic ischemic stimulation. The tourniquet pressure with 50 mmHg greater than the individual's systolic pressure was applied to the left upper arm for 10 min as ischemic conditioning stimulation. The late component of SEP and visual analogue scale (VAS) were recorded at 4 times and both were significantly decreased when ischemic conditioning stimulation was applied. The maximum reductions in SEP amplitude and the VAS value were 26.1% and 21.2%, respectively, during ischemic conditioning stimulation. After-effect was observed 5 min after removal of the conditioning stimulation. The present study revealed that heterotopic ischemic stimulation attenuated the late component of SEP induced by electrical tooth stimulation, triggering diffuse noxious inhibitory controls (DNIC) and after-effects in the trigeminal nerve territory. It was also suggested that the DNIC effect differs, depending on the intensity, kind, and quality of the test and conditioning stimuli.

Postoperative hyperthermia of unknown origin treated with dantrolene sodium.

An 11-year-old girl was scheduled for alveolar cleft bone grafting with an iliac bone under general anesthesia. Anesthesia was performed with 70% nitrous oxide, 30% oxygen, and propofol. On the first and second postoperative day, persistent hyperthermia was observed. Because the administration of diclofenac sodium had not been effective for the hyperthermia, dantrolene sodium was given. Her body temperature gradually dropped and returned to normal level on the fifth postoperative day. The hyperthermia in the present case might have been caused by a rapidly elevated muscle metabolism in response to pain and stress after the propofol anesthesia. The oral administration of dantrolene sodium successfully lowered the patient's high body temperature.

A new method of recording somatosensory evoked potentials by randomized electrical tooth stimulation with 6 levels of intensity.

Dental somatosensory evoked potentials (SEPs) corresponding to the stimulus intensity levels were recorded at 6 different levels of intensity presented in a randomized order. The relationships between the amplitude of the late SEP component with latency between 150 and 300 msec and each stimulus intensity level were also compared in conditions of randomized intensity and constant intensity. The amplitude of the late component increased significantly with the increased stimulus intensity both in the randomized and constant intensity stimulation. The amplitude of the late component in the randomized stimulation with a 1-sec interstimulus interval (ISI) increased in the same manner as that in the constant intensity condition with a 1-sec ISI. The randomized stimulation with the prolonged ISI increased the amplitude of the late component. The latency of the late positive component significantly increased with the randomized stimulation with a 3-sec ISI. This phenomenon might be attributable to the psychological contamination. SEP recording in the randomized dental stimulation with a 1-sec ISI may have applications in neuropharmacological research or physiological research on pain and evaluation of the effects of analgesics, anesthetics, acupuncture and transcutaneous electrical nerve stimulation (TENS).

An experimental system for a heterotopic pain stimulation study in humans.

So far heterotopic pain stimulation study has been performed in humans. Many studies have examined changes in subjective pain threshold and nociceptive somatic reflex. However, there are few studies using somatosensory evoked potentials (SEPs) for heterotopic pain stimulation study. Here we describe a new experimental system for a heterotopic pain stimulation study in humans. This system consists of three subsystems including the electrical test stimulation for teeth, the recording of SEP induced by electrical tooth stimulation and conditioning nerve stimulation. The preliminary experiment performed in eight healthy subjects indicated that the electrical test stimulation subsystem with the SEP recording subsystem is also very well indicated for subjective and objective pain evaluation, including VAS estimation and the amplitude of the SEP late component induced by electrical tooth stimulation. Under the experimental system in the present study, electrical median nerve stimulation as conditioning stimulation significantly decreased both the SEP amplitude induced by electrical tooth simulation and subjective pain expressed by the VAS. These results revealed that our experimental system works well and it is very suitable and useful for the study of the pain mechanism under heterotopic stimulation in humans.

Long-term pain control in trigeminal neuralgia with local anesthetics using an indwelling catheter in the mandibular nerve.

OBJECTIVE: The authors sought to determine the usefulness of long-term continuous trigeminal nerve block with local anesthetics using an indwelling catheter in a patient with trigeminal neuralgia. DESIGN: The study design included pain control in a patient with trigeminal neuralgia until the time of neurosurgical operation. SETTING: The study was conducted in the Dental Hospital of Tokyo Medical and Dental University. PATIENT: The patient was a 78-year-old woman with trigeminal neuralgia in the right maxillary region. Her pain could not be controlled by carbamazepine and was unbearable. INTERVENTION: The authors estimated the patient's pain intensity, quality, and locality using a visual analog scale to determine the effectiveness of continuous nerve block. OUTCOME MEASURES: Visual analog scores were measured during treatment. The treatment term was divided into three periods according to the difference of the catheter location and injection protocol (premandibular nerve block, infuser injection, and patient-controlled analgesia [PCA] pump injection). The authors also examined the patient's general condition and blood concentration of drugs. RESULTS: The visual analog values were 44.8 +/- 3.6, 26.7 +/- 3.5, and 11.9 +/- 3.1 mm in each period, respectively. The value in the PCA pump infusion period was significantly lower than that in the other periods. No side effects of the local anesthetics were observed on the patient's systemic condition. CONCLUSIONS: The authors controlled trigeminal neuralgia pain by blocking the mandibular nerve with local anesthetics administered through an indwelling catheter. Because the continuous nerve block with local anesthetics is reversible and only mildly toxic, this method is beneficial for pain control in patients with trigeminal neuralgia scheduled to undergo microvascular decompression.

Comparison of topical anesthesia of 20% benzocaine and 60% lidocaine gel.

OBJECTIVE: The purpose of this study was to determine the efficacies of 2 topical anesthetics commonly used in dentistry. STUDY DESIGN: The alveolar mucosa of the upper incisor apices of 20 healthy male volunteers was applied for 20 minutes with either 20% benzocaine gel or nothing as a control. The second part of experiment was done with 60% lidocaine gel and vehicle as control. Three methods of stimulation were given, and the pain rating score and visual analog scale were measured after each stimulation. RESULTS: Twenty percent benzocaine did not significantly alter pain perception as measured by the pain rating score and visual analog scale with these 3 methods of stimulation. In contrast, 60% lidocaine significantly reduced pain perception according to these measurements. We conclude that 60% lidocaine gel is effective for topical anesthesia before infiltration anesthesia.

Efficacy of anterior and middle superior alveolar (AMSA) anesthesia using a new injection system: the Wand.

OBJECTIVE: This study examined the effect of anterior and middle superior alveolar (AMSA) field block of maxillary nerves using a new local anesthetic system--the Wand. METHOD AND MATERIALS: Twenty healthy volunteers aged 23 to 44 years were used in the study. Either side of the maxillary teeth was randomly selected for AMSA injection; the other side was left as a control. For each side, 1.8 mL of 2% lidocaine solution with 1/80,000 epinephrine was injected by the Wand on a point that bisects the maxillary first and second premolars and is midway between the crest of the free gingival margin and the midpalatine suture. Pain rating score (PRS) and visual analogue scale (VAS) were applied for measurement of puncture, insertion, and injection pain. Electric pulp stimulation was given to each maxillary tooth every 10 minutes for 1 hour after the injection in order to find out the specific tooth on which AMSA injection was effective. RESULTS: During needle insertion, 14 out of 20 subjects answered moderate pain and VAS showed 27.3 mm (mean). During injection, 11 of 20 revealed no pain and the mean of VAS was 14.5 mm. No one claimed severe pain by PRS. Electric pulp stimulation indicated that lateral incisors, canines, and first and second premolars were more anesthetized than central incisors and first molars. CONCLUSION: AMSA injection using the Wand method seems to avoid severe injection pain and seems to be very effective for pulpal anesthesia at lateral incisors, canines, and premolars.

Allergic reaction to epinephrine preparation in 2% lidocaine: two case reports.

We report 2 cases of hypersensitivity to an epinephrine preparation in local anesthetics which were found by skin tests for local anesthetics. Both patients had uncomfortable episodes to local anesthetics at dental treatment. In both cases, the skin tests showed positive reactions to 2% lidocaine with 1:80,000 epinephrine. Furthermore drug lymphocyte stimulation test revealed positive reaction to epinephrine hydrochloride, epinephrine bitartrate in case 1, whereas in case 2, the drug lymphocyte stimulation test showed positive response to epinephrine bitartrate. Attention should be paid to exogenous epinephrine preparations that have the potential to induce hypersensitivity during dental treatment.

[Incident and accident reports in Tokyo Medical and Dental University Dental Hospital (FY 2001-2002)].

In 2002, the Dental Hospital of Tokyo Medical and Dental University set up a working group for risk management. This working group analyzed 225 incident and accident reports submitted to the hospital in 2001 and 2002. Each report was analyzed with regard to "type," "place," "reporter," "severity," and "cause" in order to diagnose hospital safety and prevent future incidents and accidents. The cause of incidents and accidents was analyzed using the SHEL model, where S stands for Software, H for Hardware, E for Environment, and L for Liveware. The severity of the consequence was classified into 6 levels, where level 0 = "error not applied," level 1 = "not affected," level 2 = "watch and see or additional test," level 3 = "treatment," level 4 = "aftereffect," and level 5 = "death." The incidents and accidents judged to have potentially high risk were given a score of "+H," irrespective of the level. The results of the analyses revealed that most of the incidents and accidents happened in "wards," "operation rooms," and "oral surgery clinics." This is probably because the incident and accident reporting system is well established by nurses working in these clinics. Additional analysis revealed that most of the reports were written and submitted by nurses. The frequencies of "treatment procedure," "misuse of dental instruments," "mis-prescription," "falling down" and "needlestick" related incidents and accidents were the highest and were caused mainly by L and S. There were only 3 accidents above level 4, however, less severe cases were given a score of +H due to the high potential risk involved.

Lidocaine transport through a cellophane membrane by alternating current iontophoresis with a duty cycle.

The purpose of this study was to determine whether lidocaine can be efficiently transported across a cellophane membrane using a square-wave alternating current (AC) with an adjusted duty cycle. Three voltages at 1 kHz with 6 duty cycles were applied for 60 min to the diffusion cells on both sides of the cellophane membrane. The donor chamber was filled with 1% lidocaine hydrochloride solution. The transport of lidocaine was enhanced in a voltage-, and duty cycle-dependent manner. These findings indicate that voltage and the direct current (DC) component of the square-wave AC play important roles in generating the driving force necessary for lidocaine delivery. Additionally, the periodic polarity alteration could reduce the electrode polarization. The higher voltages and duty cycles induced a pH change. The practical electrical conditions which are preferable for clinical application were 10 V with a 70% duty cycle or 20 V with a 60% duty cycle.

Diffuse noxious inhibitory controls triggered by heterotopic CO2 laser conditioning stimulation decreased the SEP amplitudes induced by electrical tooth stimulation with different intensity at an equally inhibitory rate.

The purpose of this study was to investigate (1) whether selective Adelta-fiber stimulation with CO(2) laser produces a diffuse noxious inhibitory controls (DNIC) effect in the trigeminal nerve territory; and (2) whether the DNIC effect differs depending on test stimulus intensities under constant conditioning stimuli. To examine whether the CO(2) laser radiation on the dorsum of the hand selectively stimulates Adelta-fibers, laser evoked potentials (LEP) were recorded. The mean peak latency of LEP was 381.4 ms. The findings revealed that the CO(2) laser selectively stimulated Adelta-fibers. Electrical tooth stimuli with 3 levels of intensities (1.2, 1.4, 1.6 times the pain threshold) were applied to subjects as test stimulation in randomized order, with a CO(2) laser stimulus of 18 mJ/mm(2) applied to the dorsum of the hand for 4 min as the noxious conditioning stimulus. Somatosensory evoked potentials (SEP) induced by electrical tooth stimulation were recorded and tooth pain intensity was evaluated using a visual analogue scale (VAS). The amplitudes of the SEP late component and VAS values were significantly decreased only during the conditioning stimuli without aftereffect. The inhibitory rates of the amplitudes ranged from 31.3% to 34.6% and the VAS values from 29.0% to 31.2%. There were no significant differences in their inhibitory rates between the 3 test stimulus intensities. The result indicated that selective Adelta-fiber stimulation with the CO(2) laser produces a DNIC effect in the trigeminal nerve territory and suggested that the DNIC effect does not depend on the intensity of the test stimuli.

General anesthesia for dental treatment in a Williams syndrome patient with severe aortic and pulmonary valve stenosis: suspected episode of postoperatively malignant hyperthermia.

A 28-month-old boy (height, 76 cm; weight, 9.4 kg) diagnosed as having Williams syndrome presented for dental care. We report a case of postoperatively suspected malignant hyperthermia after the administration of general anesthesia for dental treatment in this patient with severe supravalvular aortic stenosis and pulmonary artery hypoplasia. Anesthesia was maintained through the inhalation of nitrous oxide and sevoflurane with oxygen. The patient was hemodynamically stable and no other abnormalities were observed. After the completion of the dental treatment, he was transferred to the pediatric ward. On arrival at the ward, the patient's core temperature increased to 39.5 degrees C and tachypnea (RR, 30 breaths/min) was observed. The SPO2 during inhalation was slightly low (92%-93%). Serum biochemistry revealed an elevated CK level (1345 U/L) but no other abnormal findings. Twelve hours after the dental treatment, the patient's core temperature fell to 37.4 degrees C. After hospitalization for 4 days, the patient was discharged in good condition. In the present case, general anesthesia was employed for dental treatment despite severe supravalvular aortic stenosis and peripheral pulmonary artery hypoplasia, because conventional dental therapy was very difficult as a result of the patient's mental retardation and hyperkinesia. The present case suggests that the use of volatile agents that could trigger malignant hyperthermia should be avoided wherever possible.

Vasovagal syncope with asystole associated with intravenous access.

Two cases of vasovagal syncope (VVS) during venous access are reported. Both patients had a history of fainting episodes and experienced bradycardia with asystole, hypotension, and fainting. Pain and phobic stress during venous access triggered an increase in parasympathetic tone, resulting in bradycardia with asystole and hypotension in both cases. Hypotension and bradycardia likely caused cerebral hypoperfusion, leading to fainting. The intense parasympathetic tone triggered by somatic or emotional stress was likely responsible for directly depressing the sinus node, leading to asystole and bradycardia. Bradycardia with asystole progressing to syncope is a potentially fatal dysrhythmia in patients with cardiovascular disease or older patients with decreased cardiac function. Appropriate treatment for VVS includes the administration of intravenous fluids, vagolytics, ephedrine, and the rapid use of the Trendelenburg position. Intravenous fluids and atropine were used to treat the present patients.

The different effects of intravenous propofol and midazolam sedation on hemodynamic and heart rate variability.

Heart rate (HR) and arterial blood pressure (BP) changes have been reported during conscious sedation with propofol and midazolam. One potential mechanism to explain these changes is that propofol and midazolam affect HR and BP via changes in the cardiac autonomic nervous system. Two specific hypotheses were tested by HR variability analysis: 1) propofol induces predominance of parasympathetic activity, leading to decreased HR and BP, and 2) midazolam induces predominance of sympathetic activity, leading to increased HR and decreased BP. Thirty dental patients were included in a prospective, randomized study. HR, BP, low frequency (LF), high frequency (HF), and entropy were monitored during the awake, sedation, and recovery periods and depth of sedation was assessed using the Observer's Assessment of Alertness/Sedation score. Propofol induced a significant decrease in total power (503 +/- 209 ms(2)/Hz versus 162 +/- 92 ms(2)/Hz) and LF/HF ratio (2.5 +/- 1.2 versus 1.0 +/- 0.4), despite the absence of any change in HR during the sedation period compared with baseline. Midazolam decreased normalized HF (34 +/- 10% versus 10 +/- 4%) but did not significantly change LF/HF ratio (2.3 +/- 1.1 versus 2.2 +/- 1.4) and increased HR in the sedation period. Compared with baseline, propofol was associated with a significant increase in normalized HF in the recovery period (34 +/- 11% versus 44 +/- 12%) and a significant decrease in HR, whereas midazolam was associated with an increase in LF/HF ratio (2.3 +/- 1.1 versus 3.7 +/- 1.8) with no change in HR. These results indicated a dominant parasympathetic effect of propofol and a dominant sympathetic effect of midazolam in both periods. These results should be considered during conscious sedation, especially in patients at risk of cardiovascular complications.

Endotracheal intubation device with a charge couple device camera.

We developed an orotracheal intubation device equipped with a charge couple device (CCD) camera, providing a wide field of vision. We used this device to perform endotracheal intubations in 62 anesthetized patients undergoing dental treatment and oral surgery. The time required to perform an endotracheal intubation with this system was examined. The use of this system is described below. The wand with the CCD camera was inserted into the oropharyngeal cavity. The oropharynx, including the epiglottis and glottis, could be visualized on the monitor screen. The tube introducer was inserted into the trachea through the vocal cords via the side tube of the wand. The wand with the CCD camera was withdrawn, leaving the tube introducer in the trachea. The endotracheal tube was then inserted into the trachea by using the tube introducer as a guide. The time required for the procedure was determined. The mean total time for the procedure was 41.2 s (maximum, 155 s; minimum, 14 s). There were no significant differences in this procedure when the patients were grouped according to the Cormack and Lehane classification. There was no failure to intubate using this system. Because the device can extensively visualize not only the larynx, glottis, and vocal cords, but also the movement of the tube introducer, on the monitor screen via the CCD camera, endotracheal intubation can be easily performed while the vocal cords are visualized on the monitor screen.