Intramuscular Neostigmine for urinary retntion after spinal anesthesia for knee arthroscopy

Postoperative urinary retention (POUR) is a disturbing complication that negatively affects patient experience and necessitates interventions, including urinary catheterization, that increase the cost and prolong hospital stay with added risk of urinary tract injury and infection. Generally, the incidence of POUR ranges from 2 to 80 % according to the patient and procedure and anesthetic risk factors. Patient risk factors includes older age, male gender. Long-duration procedures, herniorrhaphy, anorectal surgery, orthopedic surgeries increase the risk for POUR. Also, spinal anesthesia, the perioperative use of opioids, large volume of intravenous fluid, medications that affects urinary bladder tone like anticholinergics, and b antagonists. Arthroscopic knee intervention under spinal anesthesia was associated with higher rate for POUR, 10-84%, especially when long-acting local anesthetics is mixed with intrathecal opioids. which is reported to range from. Since most of knee arthroscopy is performed as a day-case surgery, POUR can be a distressing complication for both the patient and the hospital team. Intervention for prevention of POUR includes early ambulation, neuromodulation, anti-spasmodic agents, non-steroidal anti-inflammatory drugs, and alpha-adrenergic antagonist. Neostigmine, which is one of the most commonly used drugs in anesthesia, was investigated for prevention of POUR. 8-9 Intramuscular injection of neostigmine is believed to increase detrusor muscle activity by increasing acetyl choline concentration and enhancement of parasympathetic activity involved in bladder emptying.This study evaluates the role of Intramuscular neostigmine in the prevention of POUR in patients undergoing knee arthroscopy under spinal anesthesia (primary variable). Secondary variables will include time to voiding, volume of first voided urine, residual bladder volume after first voiding, the need of urinary catheter insertion, time to sensation of full bladder.