D-FAB-POUR Trial: Dexmedetomidine vs Fentanyl as Adjuvants to Bupivacaine on Postoperative Urinary Retention

Spinal anaesthesia is a common and effective method used to manage pain during lower limb surgeries. It allows patients to remain awake and comfortable while providing excellent pain control. To make spinal anaesthesia last longer and provide better pain relief, certain medications called adjuvants are added to the main anaesthetic drug, bupivacaine. Two commonly used adjuvants are fentanyl, an opioid, and dexmedetomidine, a medication that works on the body's alpha-2 receptors to provide sedation and pain relief.

However, a known side effect of spinal anaesthesia especially when combined with certain adjuvants is postoperative urinary retention (POUR). This condition occurs when a patient is unable to urinate normally after surgery. POUR can be uncomfortable, may delay recovery, and often requires insertion of a urinary catheter, which can increase the risk of infection and hospital stay.

This clinical trial, called the D-FAB POUR Trial, is designed to find out which of these two adjuvants dexmedetomidine or fentanyl is more likely to cause or prevent POUR when used with bupivacaine in patients undergoing elective lower limb surgery.

The study will involve 190 adult patients. Each participant will receive spinal anaesthesia with bupivacaine and be randomly assigned to also receive either dexmedetomidine or fentanyl. Neither the patients nor the doctors will know which medication is given in a process known as double-blinding to ensure fairness and eliminate bias.

The researchers will monitor the ability of patients to urinate at the third and sixth hours after surgery, using ultrasound to measure bladder volume. If the patient is unable to pass urine and the bladder is overly full, temporary or longer-term catheterisation may be needed. These outcomes will help determine how each drug affects bladder function.

In addition to urinary outcomes, the study will also look at side effects like nausea, vomiting, itching, changes in blood pressure or heart rate, sedation level, and how much extra pain relief the patient needs after surgery.

The goal of this research is to help doctors choose the best adjuvant to use in spinal anaesthesia, one that provides effective pain control without increasing the risk of urinary problems. The findings may lead to improved safety, comfort, and recovery for patients undergoing lower limb operations.

Inclusion criteria

• Adults aged 18 to 60 years
• Scheduled for elective lower limb surgery under spinal anesthesia
• Classified as American Society of Anesthesiologists (ASA) physical status II or III
• Minimum height of 150 cm (to ensure uniform drug volume)
• Able to understand the study procedures and provide written informed consent (in English or Nepali)

Exclusion criteria

• Contraindications to spinal anesthesia (e.g., coagulopathy, infection at injection site, hemodynamic instability)
• Known allergy or hypersensitivity to bupivacaine, fentanyl, or dexmedetomidine
• Chronic pain conditions or long-term opioid use
• Neurological, Cardiac, Renal, or uncontrolled diabetic conditions
• Current treatment for prostatic pathology or use of alpha-2 blockers
• Presence of a Foley's catheter preoperatively
• Estimated surgical duration: >2.5 hours
• Inability or unwillingness to provide informed consent