What anesthesia is recommended for an anal fistulotomy in an infant?

Anesthesia for Anal Fistulotomy in an Infant

General anesthesia is the recommended approach for anal fistulotomy in infants, with caudal block using bupivacaine 0.25% at 1.0 ml/kg providing optimal postoperative pain control.

Induction and Maintenance Strategy

For induction, use intravenous fentanyl 1-2 mcg/kg combined with sevoflurane in oxygen-enriched air. 1 This combination provides adequate anesthesia while maintaining hemodynamic stability in the infant population. Alternative opioids include morphine at 25-100 mcg/kg or sufentanil at 0.5-1 mcg/kg if fentanyl is unavailable. 1

Critical Considerations for Infant Anesthesia

• Avoid rapid intravenous injection (less than 2 minutes) as this has been associated with severe hypotension in neonates and infants, particularly when combined with fentanyl. 2
• Infants less than 44 weeks post-conceptual age have significantly increased risk of postoperative apnea requiring extended monitoring for at least 12 hours. 3, 1
• Maintain normothermia throughout the perioperative period, as infants are particularly vulnerable to hypothermia. 1
• Monitor glucose carefully to prevent hypoglycemia while avoiding hyperglycemia. 1

Regional Anesthesia: The Critical Component

Caudal block is the preferred regional technique and should be performed in all infants undergoing anal fistulotomy unless contraindicated. 1, 4 This approach provides superior postoperative analgesia and dramatically reduces opioid requirements.

Caudal Block Technique

• Use bupivacaine 0.25% at a dose of 1.0 ml/kg (maximum safe dose 2.5 mg/kg). 1
• Consider adding clonidine as an adjunct to prolong block duration. 3, 1
• The caudal approach is technically straightforward and highly effective for perineal procedures. 4

A key advantage of this technique is that it avoids anal sphincter dilatation, which carries risk of iatrogenic fecal incontinence. 4 Stay sutures should be used instead of anal retractors to prevent stretching of the internal anal sphincter. 4

Postoperative Pain Management Algorithm

In the Post-Anesthesia Care Unit (PACU)

• Administer intravenous fentanyl for breakthrough pain, titrated to effect. 3, 1
• Continuous pulse oximetry monitoring is mandatory for 24 hours in infants receiving opioids due to apnea risk. 1

On the Ward

• Rectal paracetamol at a loading dose of 20-40 mg/kg, then 10-15 mg/kg every 6 hours. 1
• NSAIDs are contraindicated in young infants (particularly those under 3 months) due to age-related contraindications. 1
• Transition to oral analgesics as soon as the infant tolerates oral intake. 3

Important Pitfalls to Avoid

Never use manual anal dilatation or aggressive sphincter stretching, as this significantly increases the risk of long-term fecal incontinence. 4 The surgical technique should focus on precise fistulotomy without compromising sphincter integrity.

Avoid midazolam for prolonged sedation in infants. While midazolam can be used cautiously, the FDA warns that prolonged exposure to anesthetic agents in infants may result in neuronal apoptosis and potential long-term cognitive deficits, particularly with exposures longer than 3 hours. 2 The clinical significance remains uncertain, but the window of vulnerability extends through the first several months of life. 2

Surgical Context and Timing

The evidence supports that fistulotomy is more effective than conservative management in infants with persistent fistula-in-ano. 5 While some fistulas may resolve spontaneously (42.9% in one series), those persisting beyond 1-3 months warrant surgical intervention. 6 The procedure can typically be performed as a day case (97% in one series), making it suitable for outpatient surgery with appropriate anesthetic management. 4

Postoperatively, all infants should be discharged on laxative therapy to prevent constipation and reduce strain on the surgical site. 4, 6