Do caudal blocks cause complications following hypospadias surgery in children?

Abstract

An article in this month's Anaesthesia compares postoperative surgical complications in children undergoing urethroplasty under general anaesthesia accompanied by a caudal epidural block with general anaesthesia alone 1. The authors reported a higher incidence of postoperative surgical complications in children who received a caudal block, despite the fact that patients in this group had superior postoperative analgesia. Hypospadias is one of the most common congenital defects affecting the male external genitalia, with an estimated incidence of 1 in 250 male newborns. It is characterised by insufficient development of urethral fold and ventral foreskin, resulting in a more proximal urethral opening located on either the distal penile shaft, mid-shaft or proximal shaft. Surgical technique, duration of surgery and type of hypospadias are independent factors for postoperative complications. Fistula formation is the most common complication after primary hypospadias repair, with an incidence of up to 20%. Various factors have been implicated, mainly the classification of the hypospadias (proximal has a higher incidence compared with distal), but also surgical technique; age; penile engorgement; postoperative inflammatory response; and tissue oedema. Kim et al. 1 reported a retrospective review of complications following primary single stage tubularised incised plate hypospadias repair between 2010 and 2014. The authors found a higher incidence of complications in patients who received a caudal block (24.5%), compared with those who received a general anaesthetic only (15.1%) 1. Their study was limited to only one surgical technique. Tubularised incised plate repair is a successful procedure in distal hypospadias, but in proximal hypospadias cases, it is reported to have a high overall complication rate (33%), including a high incidence of postoperative fistula (21%) 2. In patients with a proximal hypospadias, surgeons may choose to perform a two-stage repair, as this has been associated with a lower complication rate (between 2.5% and 6%) 3. The group who received a caudal in Kim et al.'s study had a disproportionately higher number of patients undergoing proximal repair (31, 14.4%) compared with patients in the general anaesthesia group (9, 7.1%). Perhaps understandably, the incidence of complications was higher in patients receiving caudal block, although the fistula rate (12%) was similar in both groups. Kim et al. also reported that 2.3% of the patients who received a caudal block group developed wound problems, compared with none who did not receive a caudal block 1. However, they did not specify the type of problem, which is important as infection may have higher morbidity compared with haematoma or delayed healing. Other significant complications reported by Kim were urethral stricture (6.5% after caudal block group compared with 3.2% without caudal block) and urethral diverticulum (3.7% vs. 0%) 1. Although their study was standardised in terms of one operating surgeon, similar ages of patients and duration of surgery, patients who received a caudal block had a greater proportion of proximal defects. Urethral stricture is usually a complication following more severe proximal defects although causes of urethral diverticulum are multifactorial. As anaesthetists, we rarely link surgical complications to our anaesthetic interventions. The question that arises from this article is whether there is a causal link between the block itself and surgical complications. If there is a link, should caudal blocks be abandoned for this surgical condition, and if they are abandoned, are there superior alternative analgesic techniques we can employ that are not associated with an increased incidence of complications? Sicard and Cathelin first described the technique of caudal epidural analgesia in adults in 1901, independently, but it is in children that the technique has become popular 4. It is probably the most common regional nerve block performed in children, and is generally regarded as a relatively safe and easy technique to perform. It may be used as a sole anaesthetic technique, but is usually combined with general anaesthesia to provide good postoperative analgesia in children undergoing lower abdominal, urological (hypospadias, orchidopexy, circumcision) or lower extremity surgery. The many perceived advantages for caudal block include: reduced surgical stress response; reduced requirement for systemic analgesia, and hence less postoperative nausea, vomiting or respiratory depression. There have been reports of neurotoxicity related to general anaesthesia and there is an increasing awareness of the potential benefit of sole, or adjuvant, regional or neuraxial anaesthesia. However, the developing spinal cord is also vulnerable to drug-related toxicity and further research on the long-term functional outcomes of neuraxial blocks is required 5. The French-language Society of Paediatric Anaesthetists published a multi-centre prospective one-year observational study examining the epidemiology and incidence of complications following regional anaesthesia in 1992, and again in 2006. In both reports, complications were rare (0.09%) 6. Neuraxial block, of which 80% were caudal blocks, resulted in a significantly higher incidence of complications (0.29%, 95% CI 0.21-0.43) compared with peripheral nerve blocks (0.029%, 95% CI 95% 0.03-0.10). The most common complication following a caudal block was dural puncture, whilst in the peripheral nerve block group it was transient arrhythmias. In their report, the authors encouraged clinicians to choose peripheral, rather than central blocks because of their lower incidence of complications. The Paediatric Regional Anaesthesia Network published a multi-centre prospective observational study in the US that included 13,725 regional blocks performed between 2007 and 2010 7. It confirmed the safety of regional anaesthesia in children. The overall incidence of neuraxial complications was 0.7% and a failure rate of 2% in caudal blocks was reported. Similar to the French group, the US Network stated that peripheral nerve blocks were being increasingly used for infants and children in the US, possibly as a result of the increasing use of ultrasound guidance. More specific to caudal blocks, one retrospective analysis of 2088 caudal blocks 8 found the following complications; vessel puncture (1.9%), subcutaneous infiltration (1.5%) and dural puncture (0.2%). Other known complications are infection, haematoma, motor block, urinary retention and bowel perforation. It has been well established that a caudal block can cause urinary retention. Metzelder et al. 9 in their prospective study of 60 patients having distal hypospadias repair reported micturition was significantly impaired after caudal block compared with penile block group (15/27 vs. 5/33, respectively, p < 0.05). Shanthanna et al. 10 conducted a meta-analysis of 17 studies and found a high incidence of motor blockade and urinary retention, particularly in two studies which used relatively high concentrations of local anaesthetic. It is evident that the higher the concentration of local anaesthetic used, the more dense the motor block and the higher the incidence of urinary retention. Urinary retention causes distress in children postoperatively, increases use of systemic analgesia, prolongs hospital stay, and reduces parent and surgeon satisfaction. However, other possible causes of urinary retention are hydration status, bladder capacity, psychosocial factors and voiding habits. To ascertain a direct effect of caudal block on urinary retention, an ultrasound scan at 6 or 12 hours after performing a caudal block has been suggested 11. Urethral fistulae cause significant morbidity, and if a relationship with caudal blocks is established, this may well change current practice. Kundra 12, in a randomised double-blind study of caudal block vs. penile block for hypospadias repair, reported that all patients who developed a fistula coincidently had a caudal block (19.2% incidence in the caudal block group). However this study included a relatively low number of patients (54) and did not control for surgical technique. Another single-centre retrospective review of 452 patients undergoing hypospadias repair reported that caudal block was associated with a four-fold increase in postoperative complications, mainly utero-cutaneous fistula and wound dehiscence (See: http://spuonline.org/abstracts/2015/MP4.cgi). In another centre, a retrospective review of 192 patients undergoing hypospadias surgery showed a higher incidence of fistula formation in patients who had caudal block compared with penile block 13. Indeed the risk ratio for surgical complications in patients who underwent caudal block was 3.47 (95% CI 0.99-12.24) compared with a penile nerve block. Conversely, Zaidi et al. 14, in a retrospective study, found no association between caudal block and urethral fistula formation. Kundra 12 also reported a 27% increase from baseline in penile volume at 10 minutes post caudal block, compared with a 2.5% increase in patients who received a penile block. In patients who received a caudal block, there appeared to be a higher incidence of postoperative oedema (measured at 10 minutes) and delayed wound healing. There are many potentially confounding factors in this study. The duration of penile engorgement was not measured due to the application of a wound dressing, and the effect of a caudal block is short-lived, hence the duration of penile oedema may be relatively short. Whether this may directly affect postoperative wound healing cannot be directly postulated. Zaidi et al. 14 discussed the use of epinephrine infiltration. This may cause reduced subcutaneous wound oxygen tension and jeopardise tissue healing. Epinephrine may be used in hypospadias surgery to reduce bleeding, improve surgical visualisation and reduce haematoma formation. However, it also reduces distal perfusion and causes ischaemic reperfusion injury and in the context of a delicate distal structure such as the penis, this may cause significant problems. Catecholamines are also known to negatively affect macrophage function, which plays an important role in wound healing. Conversely, in more proximal hypospadias and complicated repairs, epinephrine may be advantageous to ensure good surgical conditions; excessive bleeding and prolonged operating times are two factors that may increase postoperative fistula formation in hypospadias repair. The penis is supplied by both the dorsal nerve of the penis and the perineal nerve (which supplies the ventral surface and the frenulum). Both nerves arise from the pudendal nerve; hence a block of the dorsal nerve of the penis alone would not be expected to provide complete analgesia for hypospadias surgery, which is largely performed on the ventral surface 15. Caudal block has more recently been compared with peripheral nerve blocks, and there are several studies demonstrating an improved analgesic profile for peripheral nerve blocks because a single caudal injection has a relatively short duration of action even when adjuvants are co-administered. Naja et al. 16 studied 80 children undergoing hypospadias repair and found that a pudendal nerve block resulted in similar intra-operative analgesia compared with a caudal block, but more prolonged postoperative analgesia. They also concluded that pudendal nerve block is safe and, when a peripheral nerve stimulator is used, the success rate was shown to be high. Beyaz 17 compared block of the dorsal nerve of the penis with caudal block in children undergoing circumcision. Postoperative pain scores at six hours were similar, and there were no major complications in both groups. It is difficult to identify a direct causation between caudal block and surgical complications. This may in part be due to potential confounding factors that include the indirect effects of caudal block such as: urinary retention; vasodilatation; hypotension; and more distal sensory and motor block. We suggest that a large prospective randomised controlled trial is needed to assess postoperative surgical outcomes in patients receiving a caudal block for hypospadias surgery, and to evaluate any mechanisms by which caudal blocks may contribute to complications. The control arm of such a trial might be difficult to choose; the experience and ability to perform distal blocks is probably limited in the UK (in our hospital only one of eleven paediatric anaesthetists performs such blocks for hypospadias surgery). Yet, proposing a trial whereby the control arm includes systemic analgesia only, when caudal block has already been shown to be superior for analgesia, might be considered to be unethical. In the meantime, anaesthetists may increasingly choose to perform a peripheral nerve block for hypospadias surgery such as a pudendal nerve block or, more distally, a combined dorsal nerve of the penis and perineal nerve block, not necessarily because of their fear of complications with a caudal block, but because of superior analgesia. No external funding or competing interests declared.