SINCE the introduction of oral opioids for clinical use, the management of cancer pain has become easier. However, we sometimes encounter patients in whom it is difficult to manage pain using only opioids and other analgesics. In such cases, neurolytic agents have been used in celiac plexus blocks for abdominal pain and in subarachnoid blocks for pain in the trunk or in the extremities. 1
Saddle block with phenol in glycerin is extremely effective for perineal cancer pain, but most clinicians hesitate to employ it because of the incidence of irreversible, undesirable side effects and difficulty in controlling its use.
High concentrations of tetracaine have been reported to control the pain related to severe postherpetic neuralgia. 2Although high concentrations of tetracaine are cytotoxic, side effects induced by this preparation may be less persistent than those induced by phenol. In the present study, we investigated the effectiveness and the side effects of saddle block using 10–20 % tetracaine for perineal pain due to recurrent rectal cancer.
In the present study, saddle blocks were performed in eight patients: six men and two women between the ages of 54 and 81 yr. All reported perineal pain due to the local recurrence of rectal cancer after surgery (Miles operation). Although they were medicated with oral morphine sulphate and with additional drugs such as nonsteroidal antiinflammatory drugs, all rated their pain as more than 70 mm on a 100-mm visual analog scale. Following the administration of a routine caudal anesthetic to confirm that the pain could be relieved to some extent by blocking only the sacral nerve area, saddle blocks with 10–20% tetracaine were performed. Informed consent was obtained from all patients after giving each a detailed explanation of the procedure, including a warning about the possible risks of persistent nerve injury, which might result in urinary incontinence.
Unless catheters were already in place (following the original surgery), a bladder catheter was inserted before the block. Saddle block was performed with the patient in a modified sitting position. A lateral position support was fixed to the operating table, and the patients were instructed to sit sideways on the operating table, with their backs against a support. The block was performed while the support was tilted back 10°. A subarachnoid puncture was made with a 25-gauge Quincke needle (70 mm; TOP, Tokyo, Japan) between L5 and S1. After confirming the reflux of cerebrospinal fluid, 0.3–0.65 ml of a 10 or 20% solution of tetracaine (40–130 mg) in 20% glucose (60–130 mg) was slowly injected (over 90–120 s). §The patients were kept in a sitting position for 4 h after injection and then at rest in bed until the next morning.
Effectiveness was evaluated 24 h and 7 days after the block using a 10-point scale, on which 10 was defined as the pain before the initial block, and 0 was defined as the complete disappearance of pain. The block was repeated if pain relief was inadequate or if the pain recurred. Follow-up investigation was conducted to assess long-term effectiveness. Patients in whom a urinary catheter was placed just before the block was performed were given instructions on how to avoid urinary retention, and the catheter was withdrawn if possible.
The results of saddle block and each patient's clinical course are shown in table 1. Neurologic status and occurrence of dysuria are shown in table 2. In all patients, dermatomal sensory block in the sacral area was achieved.
In patient 1, anesthesia was obtained between areas S2 and S5 after the first injection (using 0.4 ml tetracaine, 10%). The patient did not report any pain before his death 3 months later, even though the tumor grew so large that it was exposed in the perineal area.
In patient 2, anesthesia was obtained below S3 after the first block, but a second block was performed 1 month later due to continued pain. Following the second block, the patient's pain score decreased to 2 on the 10-point scale (anesthesia at S2 and S3). The degree of pain remained virtually unchanged until his death 6 months later, although lower abdominal pain had to be treated with morphine and some additional drugs.
Adequate pain relief could not be achieved after the first block in patient 3. The second block, performed 1 week later, resulted in almost complete relief of perineal pain. No analgesics were required for 9 months after the second procedure. Although the patient then reported lower abdominal pain, perineal pain remained slight until the patient died 1 yr later.
In patient 4, effective pain relief was maintained for 6 months after the first block. A second block, performed 7 months after the first, resulted in anesthesia at S2 and below. However, the pain did not subside completely. The patient reported pain at the bottom of the perineal region.
Patients 5 and 6, who received only a single block, reported no perineal pain before they died.
Patient 7 reported no perineal pain after the first block until his death 4 months later. In this patient, an epidural catheter was also placed to control pain caused by the tumor's invasion of the sciatic nerve. Although perineal pain gradually recurred 4 months after the first block in patient 8, it remained within a tolerable range. This patient died 5 months after the first block.
In three patients (2–4), a bladder catheter was placed immediately prior to each block (permanent catheters were already in place in the remaining patients). Two of the catheters were removed within 1 week after the block. Micturition ceased in patients 3 and 4 (both women) after the block. Although a slight leakage occurred after withdrawal of the catheter, the amount of residual urine was decreased to zero by periodically compressing the lower abdomen to induce urination. Patient 2 began urinary training 3 days after the block. The catheter was withdrawn once but was reinserted later at the patient's request when a slight leakage occurred.
Other adverse reactions included transient extensive block after the second procedure in patient 3. In this patient, who remained in a sitting position for 1 h after the block, anesthesia was present at S2 and below (hypesthesia at S1 and below) when the patient returned to the ward. No dyskinesia was seen in the lower limbs at this time, but during the next 2 h, the lower limbs gradually became paralyzed, with anesthesia spreading up to T10. The patient was again placed in the sitting position. A 30° Fowler position was maintained until the next morning, when anesthesia was observed at S2 and below and hypesthesia was observed at S1 and below (17 h after the block). The lower limbs no longer showed dyskinesia.
In patient 4, hypesthesia (moderate sensory deficit) was noted at S1 and below on the right side after the second block. A burn occurred in the calcaneal region due to a hot water bottle, which the patient used to keep her feet warm. No other patients had permanent sensory deficit in the lower extremities.
As the patients did not experience motor block of the lower extremities due to the saddle block, they ambulated without difficulties, with the exception of two patients (5 and 6) who already had some motor dysfunction of the lower extremities owing to cancer invasion. No patients reported symptoms of bowel dysfunction after the block.
In this report, we describe the effectiveness of a saddle block using 10–20% hyperbaric tetracaine in managing perineal pain due to rectal cancer. When we began this series, 10% tetracaine was thought to be effective. However, in patients 2 and 3, the initial block with 10% tetracaine was not satisfactory, and, hence, a second procedure was performed using 20% tetracaine. In patient 4, complete analgesia was achieved using 0.4 ml tetracaine, 20%—the mixture then used for the remaining patients (although we used only 0.3 ml of the drug in one small, elderly patient [patient 5]).
Other investigators have reported on the clinical application of high-concentration tetracaine. Takeda et al. 2reported long-lasting pain relief after subarachnoid blocks using 5–10% tetracaine in patients with postherpetic neuralgia. Gotoh et al. 3performed supraorbital nerve blocks and infraorbital nerve blocks using 4% tetracaine (diluted with 0.5% bupivacaine) for trigeminal neuralgia and obtained long-lasting analgesia. What is not clear is whether such long-lasting analgesia is due to chemical nerve block or to neurotoxicity. It has been known for some time that local anesthetics can cause nerve injury in animals. 4Adams et al. 5reported that the spinal nerve root of rabbits treated with 2% tetracaine showed a superficial band of swollen and granular degenerating axons. Myers et al. 6reported that rat sciatic nerve treated with 1% tetracaine showed significant endoneural edema, Schwann cell injury, and axonal dystrophy. Mateu et al. 7reported on the effects of 0.15% tetracaine in isolated sciatic and optic nerves of the rat. They demonstrated disruption of the myelin sheath. Takenami et al. 8reported that after intrathecal administration of 10 or 20% tetracaine in rats, lesions that were characterized by axonal degeneration appeared in the posterior white matter and the posterior roots.
Based on these reports, it is likely that high concentrations of tetracaine can damage myelin sheaths, Schwann cells, and axons in patients, and that some component of the long-lasting analgesia we observed may be due to a neurolytic effect. However, this was not associated with clinical symptoms such as neuritis, numbness, and motor disturbance. In addition, the recurrence of pain in some patients 3–6 months after blockade suggests that some of the block may be reversible. This may be one advantage of tetracaine compared with a permanent neurolytic agent such as phenol.
The level of blockade increased unexpectedly in patient 3, even though the patient had been kept in a sitting position for more than 60 min after the block was performed. The dosage (0.65 ml tetracaine, 20%) was larger than that used in other patients (0.4 ml), and it may have been too large for the patient (weight, 44 kg; height, 154 cm). Perhaps the patient also should have been kept in a sitting position for a longer period of time, as is done with phenol in glycerin injection. Ultimately, however, the block was limited to below the S2 region, and long-lasting pain relief was achieved even in this patient.
Tetracaine is the only commercially available crystalline local anesthetic agent. This permits the clinician to make solutions of essentially any desired concentration and specific gravity and to do so at the bedside. Conversely, phenol in glycerin is not commercially available, and it must be made in the pharmacy of each hospital. 1In addition, phenol in glycerin has a high viscosity, making it very difficult to inject through smaller needles. This is not a problem with tetracaine solutions.
In conclusion, saddle block using 0.4 ml tetracaine, 20%, in adults is effective and safe in the management of perineal cancer pain. Although the analgesic effect lasted for more than 6 months in our study, it may be reversible, unlike the analgesic effect of phenol. In addition, tetracaine is easier to use than phenol in glycerin. The degree of dysuria observed after the block was acceptable, and discomfort due to the placement of urinary catheters disappeared, even for the patients in whom urinary catheters were already in place.