Previous studies have demonstrated the contributing risk factors of postoperative urinary retention, including age, pre-existing neurologic abnormalities, bladder volume on entry to the post-anesthesia care unit, surgical procedure, length of surgery, intraoperative aggressive fluid administration, postoperative pain, and need for postoperative analgesia, or postoperative opioid use.[4, 10] The mechanism of postsurgical urinary retention is still not clear. There are some probable causes, including anxiety, anal distention, bladder distention caused by fluid hydration during surgery, irritation or blockade of pelvic nerves, and reflex inhibition of the urinary bladder detrusor muscle arising from pain.[11, 12]
There are numerous steps reported to prevent postsurgical urinary retention, including the use of parasympathomimetic agents, alpha-adrenergic blockers and anxiolytic agents, restriction of perioperative fluid intake, avoidance of anal packing, use of sitz baths, local anesthesia, short-acting anesthesia, and outpatient surgery.[13-15]
Increased fluid intake might cause overdistension of the bladder and dysfunction of the detrusor muscle. Some studies showed that fluid restriction can prevent postoperative urinary retention effectively.[5, 15, 16] In 2006, Toyonaga et al. reported that a significant increase in postoperative urinary retention was noted in patients with IV fluids in excess of 1000 mL, and perioperative fluid restriction was recommended for prevention. However, fluid restriction with preoperative patient preparation, including nothing by mouth and the use of laxatives, can cause thirst and discomfort in patients. That is why we aimed to determine whether fluid restriction after SH is necessary.
Unlike previous research, our study demonstrated that patients in the non-fluid-restriction group did not have higher urinary retention rates than the fluid-restriction group, although 22 of the 50 patients had external hemorrhoids excised (Table 2). Moreover, the patients in the non-fluid-restriction group patients were significantly older and more likely to exhibit postoperative urinary retention. This might be explained by the lower pain produced by the SH procedure and adequate pain relief after the surgery. In addition, postoperative pain can lead to urinary retention through inhibition of the micturition reflex via increased sympathetic nervous system activity. We found here that fluid restriction itself did not cause pain in patients who underwent hemorrhoidopexy at any time after the operation (Fig. 2), or increase the use of analgesic drugs (three patients in the non-fluid-restriction group and five in the fluid-restriction group; p = 0.702; Table 2). Although overdistension of the bladder is a known risk factor for urinary retention, it did not appear to cause this in our study.
Unexpectedly—as shown in Figure 3—there was no statistically significant difference in the average time to first urination between the two groups (700.04 ± 455.03 min in the non-fluid-restriction group and 737.16 ± 426.32 min in the fluid-restriction group; p = 0.669). This probably arose because all of our patients received intravenous anesthesia so the use of perioperative intravenous fluid was inevitable. Although the perioperative intravenous fluid volumes (218 ± 87.66 mL in EG and 212 ± 89.30 mL in CG), with some oral intake, when combined with irritation from the anal wound, were enough to trigger urination. Therefore, fluid restriction had no effect on delaying urination in these patients.
Although spinal anesthesia with the patient in a prone jackknife position with detailed history taking by the anesthesiologist is thought to enable airway patency, all of our patients were subjected to intravenous anesthesia plus local anesthesia safely. Spinal anesthesia can dull bladder sensations and inhibit the voiding reflex. This could also explain why our patients had lower urinary retention rates after the operation.
In terms of postoperative complications, there were two cases of delayed bleeding, and both of them were in the non-fluid-restriction group. According to previous studies, such bleeding occurs either immediately or 4–10 days after surgery.[19, 20] Delayed bleeding in our two cases occurred at 10 and 14 days after surgery, but we consider that it had no link with fluid restriction. Nisar et al. published a meta-analysis on 15 prospective randomized trials, and reported that the hemorrhoidopexy: hemorrhoidectomy ratio of postoperative rectal bleeding was 2.3 to 1. In addition, in both of our cases with this complication we used a PPH stapler, which has been reported to lead to more postoperative bleeding than the EEA device.
Although this was a prospective, double-blinded, randomized controlled trial, the strength of this study was limited by the small sample size and because it was a single-center experience. The low numbers of recruited patients might lead to low power analysis in this study. Further multiple-center trials are needed to test the validity of our findings.