influence of naloxone on relief of acute oro-facial pain by transcutaneous electrical nerve...
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Pain, 24 (1986) 323-329
Influence of Naloxone on Relief of Acute &o-Facial Pain by Transcutaneous Electrical Nerve
Stimulation (TENS) or Vibration
P. Hansson *, A. Ekblom *, M. Thomsson ** and B. Fjellner *** * Department of Physiology II, Karolinska Institutet, S-104 01 Stockholm, ** Department of Oral Surgery,
Siidersjukhuset, S-IO0 64 Stockholm, and *** Department of Dermatoiop, Karolinska Sjukhuset, S-l 04 Of Stockholm (Swede@
(Received 17 June 1985, revised received 14 August 1985, accepted 23 August 1985)
Twenty-eight patients suffering acute pain following operative removal of im- pacted third molars took part in the present study. In 20 patients who reported pain reduction exceeding 25% of the initial pain intensity during vibratory stimulation (100 Hz) or TENS (2 or 100 Hz), only 1 patient (given 2 Hz TENS) reported pain increase after injection of 0.8 mg naloxone (i.v.). In 8 patients, not treated with afferent stimulation, 2 experienced increase in pain intensity after naloxone injec- tion. The results show that pain relief using TENS or vibration is not influenced by naloxone.
Transcutaneous electrical nerve stimulation (TENS) (211 and, to some extent, vibratory stimulation  are presently in use for pain relief. The mechanisms of action for pain relief by these modes of afferent stimulation are largely unknown. Experimental evidence [8,12,20,27] has been produced, indicating that activity set up in large myelinated fibres by afferent stimulation might interact with pain transmit- ting pathways. Furthermore, the contribution of an opioid-dependent mechanism to obtain pain relief by TENS  and acupuncture stimulation [3,19,25] has been proposed. In these studies naloxone, an opioid antagonist, has been used as a tool to study the involvement of opioid systems in pain relief induced by afferent stimula- tion. Studying chronic pain patients, Sjolund and collaborators [6,28,29] have
0304-3959/86/%03.50 0 1986 Elsevier Science Publishers B.V. (Biomedical Division)
reported evidence supporting an opioid link in pain relief obtained using low frequency (train stimulation) TENS.
In the present investigation we have further studied the effect of naloxone on pain relief induced by TENS and vibratory stimulation in opiate-naive subjects with postoperative oro-facial pain. The effect of naloxone on clinical pain perception was also studied.
Subjects Twenty-eight patients, aged 18-39 years (16 females and 12 males), were from a
clinic for oral surgery and had suffered postoperative pain (subjective pain intensity not varying more than + 10% during the last 2 h) for 3-24 h (1 patient for 6 days). All patients had an impacted third molar surgically removed by one of the authors (M.T.), and in none of the patients were the gingival incisions made in front of the first premolar to avoid interference with cross-innervation from the contralateral side of the mouth. Local anaesthesia, i.e., 3.5 ml Xylocain@ (20 mg/ml) containing Adrenaline (12.5 pg/ml) (Astra Lakemedel AB) was given before surgery. No premeditation was used and none of the patients had experienced oro-facial pain for at least 2 weeks prior to surgery. No analgesics were allowed before the trials. The patients were told that they might experience pain relief, no change, or aggravation of pain during stimulation. They were also informed that two substances, commonly used in the clinic, were to be administered to further investigate their reaction to stimulation. No hints were given concerning their normal indications. Every effort was made to avoid suggestion. All patients were assured that they could stop the stimulation and withdraw from the trial at any time. All subjects were tested between 13.00 and 17.00 h.
Puin assessment Before the start of stimulation the patients were asked to rate their pain intensity
by using a 5-graded verbal scale - light, light-moderate, moderate, moderate-severe or severe pain. Patients with different pain ratings prior to stimulation were about evenly distributed on basis of this scale. The subjects also rated their pain intensity before and after the stimulation period using a visual analogue scale (VAS), and continuously during the trial using a device with a graphic rating scale (GRS) consisting of a lever attached to a potentiometer in contact with an ink-writer, which was out of sight of the patient. For further technical description see Ottoson et al.  and Hansson and Ekblom . The results obtained with the two scales used (VAS. continuous GRS) were consistent. The results were evaluated from the recordings with the GRS.
Administration of saline and naloxone Before start of the experiment all patients were provided with an intravenous line,
on the dorsal or ventral side of the forearm, which was coupled to a catheter. The
catheter was used to avoid direct manipulation of the patient during the injections, thereby minimizing indications that an injection was to be made. Furthermore, all injections of saline and naloxone (naloxone hydrochloride, Nalonee @, Endo Labora- tories) were performed behind a screen in a double-blind hidden fashion. Only the experiment controller knew the nature of the injected substance, i.e., neither the physician in charge of the intravenous procedure (author B.F.) nor the assistant nurse knew what substance was going to be injected. Furthermore, only the nurse was permanently present in the room during the trials. The patients were told to indicate verbally if they felt any injection during the trial.
Afferent stimulation technique Transcutaneous electrical nerve stimulation (TENS). TENS of low and high
frequency were used. The high frequency TENS consisted of pulses of 0.2 msec duration repeated at a rate of lOO/sec. The low frequency TENS consisted of pulses of 0.2 msec duration delivered in 71 Hz trains for 84 msec at a rate of 2 Hz.
In all TENS procedures conducting carbon rubber electrodes, measuring 3.5 cm x 5 cm, were applied to the skin overlying the painful area. Using 2 Hz TENS the intensity was adjusted so that non-painful muscular contractions were induced. TENS at 100 Hz produced a tingling non-painful sensation.
Vibratory stimulation. 100 Hz of vibratory stimulation with an amplitude of 400-800 pm was used. The probe (disc-shaped probe measuring 3 cm in diameter) was connected to an electromechanical vibrator (Briiel and Kjaer 4809) driven by a sine wave generator (Bruel and Kjaer 1047). The vibrator probe, fixed to a stand, was applied to the skin overlying the painful area with a non-painful pressure trying to exert pressure on the underlying bone . The vibratory movement amplitude was measured by a piezo-electric accelerometer (Brtiel and Kjaer 4367) attached to the stimulus probe.
All stimulation periods lasted for 45 min. Recording of the subjective pain intensity was continued for 15 min after termination of stimulation.
Experimental design Patients not receiving afferent stimulation. Eight patients rated their subjective pain
intensity continuously for 90 min using a graphic rating scale (see above). Fifteen minutes after start of pain assessment 4 ml of saline was injected intravenously. Twenty-five minutes after saline injection 4 ml of naloxone (0.2 mg/ml) was injected. Pain assessment was thereafter continued for another 50 min.
Patients receiving afferent stimulation. Out of 32 patients assigned for treatment using TENS or vibratory stimulation 20 patients who reported pain relief of more than 25% of the initial pain intensity were given naloxone. Six patients received 100 Hz TENS, 7 patients received 2 Hz TENS and 7 patients received 100 Hz of vibratory stimulation. When the patients reported at least 25% pain relief during afferent stimulation (after 15 min + 5 min of stimulation), 4 ml of saline was injected. At about 30 min after start of stimulation 4 ml of naloxone (0.2 mg/ml) was injected. The saline injected was merely given in order to find out if a placebo response would be given, if the patient by chance noted the injection. If so, this
would give a hint to what extent confidence could be attributed to the possible effect of naloxone injection if this was felt by the patient. A change in pain intensity of less than 10%. of the length of the GRS from zero to one end of the scale, was considered as a non-significant change in pain intensity.
A finding from the present study was that in spite of warming (to 37C) of the solutions prior to injection, 9 of the patients felt the injection of saline and/or naloxone as a sensation of coldness or, using naloxone, a smarting sensation radiating in the arm and hand. This was associated with a change in subjective pain intensity in only two patients. One patient, receiving saline, reported a significant increase in pain intensity about 3 min after the injection and one patient. receiving naloxone, reported increased pain relief during vibratory stimulation.
Patients not receiving afferent stimulation Six of the 8 subjects reported no change in pain intensity after injection of 0.8 mg
of naloxone. Two patients, however, experienced a significant increase in pain intensity 2-5 min after naloxone injection.
Patients receiving afferent stimulation Only one patient, receiving 2 Hz TENS, experienced a complete inhibition of pain
reduction (within 2 min) after the injection of naloxone, i.e., an increase in pain intensity to the pretreatment level. Interestingly, this was the patient who had suffered pain for 6 days prior to treatment. Furthermore, one patient receiving 100 Hz vibration and who noted the naloxone injection reported a significant increa