Applied Evidence

Obstetric anal sphincter injury: How to avoid, how to repair: A literature review

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Observational data conflict as to whether mediolateral episiotomy contributes to, or protects against, obstetric anal sphincter injury—although the burden of evidence favors it as a risk factor that should be avoided when possible.16,23,33 An angle of mediolateral incision cut closer to 45 degrees from the midline has been associated with less obstetric anal sphincter injury than incisions cut at closer angles to the midline.34

Repairing sphincter injury

Detecting injury in labor

With any severe perineal laceration, closely inspect the external and, if exposed, internal anal sphincter and perform a rectal exam, particularly for women with numerous risk factors (although no good evidence supports the role of the rectal exam in diagnosing obstetric anal sphincter injury). Colorectal surgeons have advocated the use of a muscle stimulator to assist in identifying the ends of the external sphincter, but this has not become common practice.35

Immediate vs delayed repair

It is standard practice to repair a damaged anal sphincter immediately or soon after delivery. However, given that a repair should be well done, and since a short delay does not appear to adversely affect healing, be prepared to wait for assistance for up to 24 hours rather than risk a suboptimal repair.36

Better training is needed

Even among trained obstetricians and obgyn residents, 64% have reported no training or unsatisfactory training in management of obstetric anal sphincter injury; 94% of physicians felt inadequately prepared at the time of their first independent repair of the anal sphincter.37,38 To improve your repair skills in a workshop setting, consult the following sources— in the US, or in UK.

Analgesia and setting

Adequate analgesia is an essential element in a good repair. Complete relaxation of the anesthetized anal sphincter complex facilitates bringing torn ends of the sphincter together without tension.39 Though theoretically this can be attained with local anesthetic infiltration, RCOG recommends that regional or general anesthesia be considered to provide complete analgesia.37 It is further recommended that repair of the anal sphincter occur in an operating room, given the degree of contamination present in the labor room after delivery and the devastating effects of an infected repair (SOR: C).40

Repair technique

There are 2 commonly used methods of external anal sphincter repair: one, the traditionally taught end-to-end approximation of the cut ends, and the other, overlapping the cut ends of the external sphincter and suturing through the overlapped portions (FIGURE 2).36 Though an RCT from 2000 noted no significant difference in outcomes between these methods,41 other authors have suggested that an overlapping technique is preferred, and it remains the method most often used by colorectal surgeons in elective, secondary anal sphincter repairs.36,39,42

A Cochrane review of which technique is better has been registered in the Clinical Trials Database. General agreement is that closure using interrupted sutures of a monofilament material, such as 2-0 polydioxanone sulfate (PDS), is the preferred closure method for the external sphincter (SOR: C).36,40 It is recommended that a damaged internal sphincter be repaired with a running continuous suture of a material such as 2-0 polyglactin 910 (Vicryl) (SOR: C).36

2 methods of anal sphincter repair

Two commonly used methods of external anal sphincter repair are end-to-end approximate of the cut ends (top), and overlapping the cut ends and suturing through the overlapped portions (bottom). (Adapted from Leeman et al, Am Fam Physician 2003.33) ILLUSTRATION BY RICH LaROCCO

Immediate post-repair management

Use a stool softener

It had long been thought that constipation following obstetric anal sphincter injury allowed the sphincter to heal more effectively. However, new evidence from RCTs shows that using a laxative instead of a constipating regimen is more helpful in the immediate postpartum phase.43 Toward this end, use a stool softener, such as lactulose, for 3 to 10 days postpartum for women with obstetric anal sphincter injury.40

Should you prescribe an antibiotic?

Given the devastating effects of post-repair infection, most authorities consider it prudent to prescribe a course of broad-spectrum antibiotics, possibly including metronidazole (SOR: C)37,40 A Cochrane review is registered to further examine this issue. A separate Cochrane review of the use of antibiotics for instrument vaginal delivery concluded that quality data were insufficient to make any recommendations.44

Refer for physical therapy

Some authorities consider an early referral to physical therapy for pelvic floor exercises helpful in the immediate post-partum for all patients with obstetric anal sphincter injury (SOR: C).45


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