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Obstetric anal sphincter injury: 7 critical questions about care

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When and how you manage an injury determines the patient’s quality of life. Here are 7 issues to consider.



The authors report no financial relationships relevant to this article.

CASE Large baby, extensive tear

A 28-year-old primigravida undergoes a forceps delivery with a midline episiotomy for failure to progress in the second stage of labor. At birth, the infant weighs 4 kg (8.8 lb), and the episiotomy extends to the anal verge. The resident who delivered the child is uncertain whether the anal sphincter is involved in the injury and asks a consultant to examine the perineum.

What should this examination entail?

The obstetrician is rarely culpable when a third- or fourth-degree obstetric anal sphincter injury (OASIS) occurs—but there is little excuse for letting one go undetected.

To minimize the risk of undiagnosed OASIS, a digital anorectal examination is warranted—before any suturing—in every woman who delivers vaginally. This practice can help you avoid missing isolated tears, such as “buttonhole” of the rectal mucosa, which can occur even when the anal sphincter remains intact (FIGURE 1), or a third- or fourth-degree tear that can sometimes be present behind apparently intact perineal skin (FIGURE 2).1

Clinical training of physicians and midwives also needs to improve.

Every labor room should have a protocol for management of anal sphincter injury2; this article describes detection, diagnosis, and management, focusing on seven critical questions.

Only a physician formally trained in primary anal sphincter repair (or under supervision) should repair OASIS.

FIGURE 1 Buttonhole tear

A buttonhole tear of the rectal mucosa (arrow) with an intact external anal sphincter (EAS) demonstrated during a digital rectal examination. SOURCE: Sultan AH3 (used with permission).

FIGURE 2 Injury obscured by intact skin

(A) Intact perineum on visual examination. (B) Anal sphincter trauma detected after rectal examination. SOURCE: Sultan AH, Kettle C1 (used with permission).

1. When (and how) should the torn perineum be examined?

The first requisite is informed consent for vaginal and rectal examination immediately after delivery. Also vital are adequate exposure of the perineum, good lighting, and, if necessary, sufficient analgesia to prevent pain-related restriction of the evaluation. It may be advisable to place the patient in the lithotomy position to improve exposure.

After visual examination of the perineum, part the labia and examine the vagina to establish the full extent of the tear. Always identify the apex of the vaginal laceration.

Next, perform a rectal examination to exclude injury to the anorectal mucosa and anal sphincter.3

Palpation is necessary to confirm OASIS

Insert the index finger into the anal canal and the thumb into the vagina and perform a pill-rolling motion to palpate the anal sphincter. If this technique is inconclusive, ask the woman to contract her anal sphincter with your fingers still in place. When the sphincter is disrupted, you feel a distinct gap anteriorly. If the perineal skin is intact, there may be an absence of puckering on the perianal skin over any underlying defect that may not be evident under regional or general anesthesia.

Because the external anal sphincter (EAS) is in a state of tonic contraction, the sphincter ends will retract when it is disrupted. These ends need to be grasped and retrieved at the time of repair.

Also identify the internal anal sphincter (IAS). It is a circular smooth muscle (FIGURE 3) that is paler in appearance (similar to the flesh of raw fish) than the striated EAS (similar to raw red meat).4 Under normal circumstances, the distal end of the IAS lies a few millimeters proximal to the distal end of the EAS (FIGURE 4). However, if the EAS is relaxed due to regional or general anesthesia, the distal end of the IAS will appear to be at a lower level. If the IAS or anal epithelium is torn, the EAS is, invariably, torn, too.


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