Spinal analgesia is one of the oldest methods of relieving pain in surgical patients. Despite numerous advantages there are a number of disadvantages . Several reports described hearing loss after spinal analgesia [2-5] and it has been suggested that this occurs more often than is generally assumed although the symptoms may be overlooked. The aim of the present study was to determine the degree of vestibulocochlear dysfunction in patients undergoing spinal analgesia for lower abdominal surgery. Two spinal needles (Howard Jones Spinal Needle®; Bignell Surgicals, Sussex, England and Whitacre Spinal Needle®, Becton Dickinson, NJ, USA) were used and compared during a study of auditory function following spinal analgesia.
The study was carried out in 80 patients, aged 20-40 yr, who were American Society of Anesthesiologists physical status I. Males were undergoing inguinal herniorraphy and the females tubectomy. Exclusion criteria included any systemic disorder, any history of hearing disorders, chronic smokers, or inability to co-operate during audiometry. After local Ethics Committee approval, informed consent was obtained from all patients.
The patients were randomly divided into two groups of 40. Group 1 patients received spinal analgesia through a Howard Jones® 22-G needle; those in Group 2 received the same but through a Whitacre® 25-G needle. Audiometry was initially performed one day prior to surgery.
All patients were premedicated with diazepam 0.2 mg kg−1 orally, maximum 10 mg, on the night before surgery and 0.1 mg kg−1 on the morning of surgery. They also received 0.15 mg kg−1 morphine sulphate and 0.5 mg kg−1 promethazine hydrochloride intramuscularly, 45 min prior to surgery. After preloading with at least 500 mL of 0.9% saline, spinal analgesia was administered at the L3,4 interspace using bupivacaine 3.5 mL 0.5% in 8% glucose. Only one dural puncture was allowed in each patient; if an additional puncture was necessary the patient was excluded from the study. The Howard Jones® needle was inserted with the bevel parallel to the longitudinal axis of spinal column, while the Whitacre® needle was inserted with the aperture facing cephalad.
A clinical audiometer (Beltone-2000 Audiometer®; Beltone Electronics Corporation, IL, USA) was used with the system calibrated according to ANSI-1969. Audiometry consisted of pure tone audiometry using the ascending-descending technique performed by an experienced audiometrist and was carried out in the frequency range 250 Hz-8 kHz at octave intervals. The first audiogram was conducted one day before operation, and two further recordings were made on the second and seventh postoperative days.
The degree of hearing impairment was recorded during and following the operation as per the subjective complaints. Patient monitoring consisted of heart rate and systolic arterial pressure at 5-min intervals during the operation. The level of analgesia was estimated by pinprick after 20 min.
Recumbence during first 12 h postoperatively was advised for every patient. On the second postoperative day, auditory function analysis and other cranial nerve examinations were performed by an anaesthesiologist. Audiograms were performed on the second and seventh postoperative days under the same conditions as the preoperative audiogram. The audiometrist and the patient were blind to the size and type of needle used.
All results are presented as means (±SEM). The preoperative audiogram from each patient was compared with the postoperative audiograms for any change in hearing level at each frequency. The mean change in hearing level for both ears was calculated at each frequency. A 'worse side' was defined as the side on which any hearing loss was greater. The results were analyzed for statistical significance using Student's t-test. P < 0.05 was taken to be significant.
The mean age of the patients and the level of analgesia in both groups were comparable. The preoperative blood pressure and the lowest blood pressure recorded intraoperatively in both groups were comparable (Table 1). The incidence of post-dural puncture headache was greater in Group 1 (15 out of 40 patients) compared to Group 2 (two out of 40 patients), the difference was significant (P < 0.01).
Before operation, the hearing threshold values were comparable in both groups at all frequencies in both ears. At 250 Hz, both groups showed small but significant changes after operation compared to preoperative values. Also, a significant bilateral reduction in hearing was demonstrated at 4 kHz in Group 1 patients (Table 2). The hearing loss on the 'worse side' was greater in Group 1 than in Group 2 patients, and was significant (P < 0.01). Similar results were obtained from the 'better' ear. Intragroup audiometric analysis showed hearing thresholds between the right and left ears in both groups (Table 3); there were significant differences between right and left ears at 250 Hz (Groups 1 and 2) and at 4 KHz (Group 1 only). Audiometry showed that three of the 40 patients (7.5%) in Group 1 had some hearing impairment. One patient had > 15 dB hearing loss at all frequencies ranging from 250 Hz-4 kHz in both ears, while the other had a unilateral reduction in hearing in the right ear at all frequencies. A third patient had > 15 dB unilateral reduction in hearing at 250, 500, and 1000 Hz frequencies. One patient in Group 2 showed a significant hearing impairment in the postoperative period at 250 Hz (P < 0.05).
The previously reported incidence of vestibulocochlear dysfunction after spinal analgesia varies between 0.2-8% based on the incidence with which patients complained of deafness, i.e. a major hearing deficit [2,6]. The incidence of minor hearing deficits after spinal analgesia varies from 9-93% depending on the type of needle used [3-5]. Hearing deficits are associated with the type of needle tip ; a non-cutting needle is thought to cause less damage to the dural fibres when compared to a cutting needle and hence might reduce the leak of cerebrospinal fluid (CSF) after the procedure. In view of this, we selected two groups of young patients (20-40 yr) who were allocated to receive spinal analgesia either through a cutting (larger size) needle or a non-cutting (finer) needle. This enabled us to separate the two groups of patients maximally with regard to the loss of CSF following the procedure. We wanted to determine any complications (hearing loss, postdural puncture headache) using a wide difference of needle size. Our study only considered single attempts at dural puncture. Post-dural puncture headache was seen in two out of the three patients who had hearing impairment. This reaffirms the relative validity of the 'Mihic concept' . Of three patients who developed hearing impairment, two happened to have post-dural puncture headaches, which were treated conservatively with analgesics, positioning and hydration. The degree of severity of the headache was mild to moderate in all affected patients. The end result of the hearing impairment was that two of the three patients who experienced a hearing loss recovered after 2 weeks, and the third patient recovered after 3 weeks.
The major objection to the studies cited above is that all subjects were elderly (mean age > 65 yr) and undergoing transurethral resection of the prostate . Although absorption of irrigating fluid during this operation produces a syndrome of visual disturbances, tinnitus, vertigo, and deafness the authors denied any biochemical or clinical evidence of its occurrence .
The aetiology of vestibulocochlear dysfunction after spinal analgesia remains unknown. It has been suggested that the decrease in CSF pressure that follows dural puncture is a result of leakage through the dural tear caused by the needle . The decreased pressure may be transmitted, via the cochlear aqueduct, to the perilymph in the inner ear causing endolymphatic hydrops. Endolymphatic hydrops is involved in the pathogenesis of Menière's disease and the initial hearing loss observed in these patients also occurs within the low frequency range and may be unilateral . Alteration in CSF pressure has been shown to induce changes in the perilymphatic pressure in the inner ear. Thus, the difference in CSF leakage is the most likely explanation for the audiometric results we found.
In our study, young patients aged 20-40 yr were studied because the cochlear aqueduct is patent in 80% of such individuals, cf. the elderly . Moreover, the clinical effect of CSF leakage is more evident in young patients as a consequence of a change in needle size/diameter . In most studies, hearing deficits > 10 dB were taken as significant to compensate for subjective and observer errors. It is well-known that these deficits can develop up to, or last until, the eighth postoperative day , so we performed a third audiogram on the seventh postoperative day. One patient showed a progression in hearing loss even on the seventh postoperative day. Other studies have been limited to an audiogram on the second postoperative day [3-5].
Our two groups were similar in age, level of sensory blockade, dose of bupivacaine used, preoperative blood pressure and degree of hypotension. Thus, the most likely explanation for the observed hearing loss is that the size and design of needle might have led to different dural tears causing variable amounts of CSF loss and thereby influence the CSF pressure. Studies involving fresh cadaver dural punctures with different sizes of spinal needle support this explanation . In conclusion, our study suggests that the use of non-cutting type finer gauge needles for spinal analgesia should reduce impairment in hearing after the procedure, compared to the cutting type larger gauge needles.
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