Synopsis
Identify and classify obstetric anal sphincter injury accurately, organise skilled repair, and support bowel function, wound recovery and future birth counselling.
- Grade 3a involves less than half the external anal sphincter thickness; 3b involves more than half.
- Grade 3c includes both external and internal sphincter injury; fourth degree also involves anorectal mucosa.
- A rectal buttonhole with an intact sphincter complex is a distinct injury, not a fourth-degree tear.
- When uncertain about third-degree extent, classify to the higher grade and seek senior help.
- Repair is normally performed in theatre by a trained clinician under regional or general anaesthesia.
- Use end-to-end repair for partial external sphincter tears; full-thickness tears may use end-to-end or overlap.
- Provide broad-spectrum antibiotics, a stool-softening laxative and appropriate pain relief after repair.
- Arrange specialist review at approximately six to twelve weeks, with earlier assessment for symptoms or wound concerns.
Key red flags
Uncertain sphincter integrity or rectal mucosal involvement requires experienced assessment before routine suturing.
Persistent severe pain, fever, offensive discharge or a separating wound needs urgent review; wound breakdown requires same-day maternity assessment.
New faecal urgency, incontinence, inability to control flatus or stool passing vaginally must be actively assessed rather than dismissed as normal recovery.
Investigation priorities
Define the injured layers before planning appropriate repair.
Management branches
A tear may involve the sphincter complex or anorectal mucosa.
- Explain the need for a detailed examination and ensure effective analgesia before assessing the full extent of injury.
- Classify and document the tear, including internal sphincter involvement and any mucosal defect, and ask for senior help when uncertain.
- Arrange repair by an appropriately trained clinician or supervised trainee, normally in theatre under regional or general anaesthesia.
- If bleeding is excessive, control it temporarily as appropriate and expedite theatre while assessing the need for haemorrhage resuscitation.
Key medicines
Lactulose after sphincter repairA usual adult starting regimen is 15 mL orally twice daily, adjusted to produce soft formed stools; RCOG recommends stool-softening treatment for about 10 days after repair.Reduce the dose if stools become loose or diarrhoea occurs. Avoid routine combination with a bulking agent after OASI; check for suspected obstruction and seek review for significant abdominal pain or persistent bowel difficulty.
Broad-spectrum antibioticsAdminister the locally specified OASI regimen at repair and postoperatively as directed; drug, route, dose and duration depend on allergy, operative findings, renal function and the protocol.A national recommendation for broad-spectrum cover does not identify one mandatory UK regimen. Document doses and stop date, and reassess clinically if infection develops rather than simply extending prophylaxis.