Caudal block is a relatively simple, inexpensive and widely used anesthesia technique. However, the success rate and complications of adult caudal anesthesia have rarely been reported. Surgical procedures for hemorrhoids and other minor anorectal disorders account for a large proportion of elective ambulatory surgeries. The short in-hospital period made it difficult to collect postoperative information from these patients. This study was a single-center, large-sample, prospective, investigator-blinded trial designed to investigate the efficacy, complications and related risk factors for complications of caudal block in adult anorectal surgery. Complete follow-up was performed by three anesthesiologists, and complete postoperative follow-up data were obtained for 973 patients, which greatly improved the integrity of the results of this study.
However, in contrast with pediatric surgery, caudal block is not preferred in adult surgery. One of the reasons might be that adult caudal block sometimes cannot provide satisfactory anesthesia[16-18]. There can be technical difficulty, mainly due to the inconspicuous anatomical markings of fistulas in adults and possible anatomical variations[19, 20]. As research progresses, assistive technologies to improve the success rate of caudal block have been developed, such as ultrasound guidance and preoperative magnetic resonance examination. In this study, the results showed that the caudal block efficacy resulted in unexpectedly high satisfaction (95.38%). This may be related to the following two factors. First, all caudal block procedures were performed by experienced and skillful attending anesthesiologists. Second, caudal block was very suitable for these anorectal surgeries. A recent clinical randomized study also confirmed this view, the maximal resting anal pressure (MRP) and maximal squeezing anal pressure (MSP) were measured by anorectal manometry before and after caudal block, and caudal block could significantly decrease both pressures.
Another limitation of caudal block in adults might be the potential complications. The research on complications of caudal block in children was very widely[24, 25]. but there were few reports in adults. Several complications, such as LAST and TNS, have been reported. Therefore, we focused on complications related to caudal anesthesia in adults. Our results showed that the incidence of complications related to caudal block in anorectal surgery was not as high as expected. A reported study of a large sample of 5083 patients found an incidence of complications of adult epidural anesthesia of approximately 1.34. The incidence of complications of adult caudal block in our study is acceptable compared with that reported in other research. Meanwhile, we found that except for 3 cases of LAST, there were no malignant adverse events, such as serious cardiac events, severe respiratory depression/acute respiratory failure or total spinal anesthesia, throughout the process. Meanwhile, the 3 patients with LAST all recovered by nonoperative management without any sequelae. Therefore, our results indicate that caudal block in adult anorectal surgery is a safe anesthesia method when undertaken by experienced anesthesiologists.
It is worth noting that we recorded some complications of caudal block, including LAST, TNS, CES and localized pain at the caudal insertion site.
LAST is one of the most serious complications of caudal block. Such events range across a continuum from mild subjective prodromal symptoms to seizure, cardiac arrest, and/or death. Three cases of severe LAST were recorded. The clinical manifestations included dizziness, flushing, dysphoria and involuntary muscle twitches. Fortunately, all three patients had a good prognosis after treatment with sedation and respiratory support, and no sequelae were recorded. Therefore, it is particularly important to observe the patient after injection and to immediately discover and deal with LAST. We observed an incidence of LAST in caudal block of 0.31%, while the incidence of complications of epidural anesthesia is 0.01%[27, 28], there was a lower probability of spinal anesthesia at our hospital. The independent risk factor for this complication was “multiple punctures”. The abundant anatomical blood supply to the soft tissue of the sacrococcygeal region might be one reason for this complication. Meanwhile, caudal anesthesia requiring a single large-dose injection of local anesthetics may be another reason. Recent studies have reported that large amounts of absorbed local anesthetic are stored in skeletal muscle, suggesting that both adult and pediatric patients with low muscle mass are at a higher risk for LAST[29, 30]. Current guidelines recommend that haemodynamic deterioration caused by LAST should be treated by Intralipid® 20% as first-line therapy along with epinephrine/adrenaline for cardiopulmonary resuscitation until circulation is restored or extracorporeal membrane oxygenation has been installed. To prevent LAST, ultrasound guidance might be a wise choice. A meta-analysis showed that ultrasound reduced the incidence of vascular puncture associated with PNB compared with peripheral nerve stimulation. We will confirm this in future studies. It might be better to make patients awake to get instant feedback on paraesthesias, pain, or symptoms of local anaesthetic systemic toxicity during the whole anesthesia procedure. Meanwhile it was reported that the Risk of LAST has nothing to do with the type of anesthetic.
In this study, we recorded one case of CES. The patient suffered reduced perineal sensation, altered bladder function leading to painless urinary retention, and loss of anal tone. CES has five characteristic features: bilateral neurogenic sciatica, reduced perineal sensation, altered bladder function leading to pain, reduced urinary retention, loss of anal tone and loss of sexual function. It is usually caused by caudal nerve stimulation, infection, inflammation or tumors. The patient suffered elicited paresthesiae during the puncture procedure. Unfortunately, we failed to perform magnetic resonance imaging (MRI) to rule out possible spinal cord hematoma or infection. Stimulation caused by puncture might be the most likely reason for this complication in this case. However, CES is a severe nerve complication, but the majority of patients who suffer this complication usually recover within 2 weeks of treatment with steroids or without any treatment. In this case, all symptoms began to resolve on the ninth day and completely recovered on the 14th day after surgery with steroid therapy. This event indicates that elicited paresthesiae during the puncture procedure is a strong sign of nerve stimulation with the potential for CES. Switching to general anesthesia and providing steroid therapy are wise management choices. MRI might also help to diagnose changes in the spinal cord.
In this study, 3 patients suffered TNS, with symptoms of pain in the lower back and/or buttocks with or without radiating pain into one or both legs. All the symptoms resolved in 3 days without any treatment. All kinds of intraspinal anesthesia, including spinal, epidural and caudal anesthesia, could cause TNS. In the 1990s, TNS were first reported as clinical signs of mild, temporary neurologic dysfunction independent from the kind or concentration of local anesthetic, such as lidocaine, bupivacaine, mepivacaine or ropivacaine. Meanwhile, TNS have also been reported in both spinal and epidural anesthesia[35-40]. The mechanism of TNS is still a mystery, but no connections to neurological pathology have been suggested in the literature. The administration of a nonsteroidal anti-inflammatory drug has been suggested to produce significant relief from symptoms and might be a significant factor in reducing patient anxiety.
Localized pain at the caudal insertion site
We innovatively included another complication in this study. Surprisingly, we found that 34 patients suffered postoperative pain after caudal block, the incidence of which (3.08%) was higher than that of any other complication. These similar complications could occur during any intraspinal anesthesia procedure, including the establishment of epidural and spinal anesthesia. Few previous studies have included this in the scope of caudal block-relevant complications. However, this complication was often present during clinical follow-up. A number of patients considered it the most unacceptable aspect of caudal block. However, the pain in most patients was not severe and usually disappeared without therapy in 48 hours. However, it is still the main patient complaint after surgery, and thus merits attention. Then, we analyzed the independent risk factors for this complication to develop a strategy for reducing its incidence. Our results suggest that multiple attempts to locate the caudal space and the use of lidocaine may be closely related to the occurrence of this complication. It is easy to understand that multiple punctures can aggravate the skin and soft tissue damage at the puncture site and thus increases the likelihood of pain around the puncture site after surgery. Ultrasound guidance might be a feasible method to reduce the number of punctures[42, 43].
To avoid interfering with the clinical behavior of the attending anesthesiologist, we did not specify a concentration of local anesthetic for use in caudal block. We also failed to record some objective numerical data to further evaluate the block efficiency, such as the MRP and MSP. However, these limitations did not affect the results of the study, as our research is focused on the safety and efficacy of sacral anesthesia and does not involve the comparison of these data.