OASIS

Question 1

What is the incidence of OASIS?

Multip?
Primip?

Answer 1

2.9%

Question 2

What are the classifications of OASIS?

Answer 2

First-degree tear: Injury to perineal skin and/or vaginal mucosa.

Second-degree tear: Injury to perineum involving perineal muscles but not involving the anal
sphincter.

Third-degree tear: Injury to perineum involving the anal sphincter complex:
Grade 3a tear: Less than 50% of external anal sphincter (EAS) thickness torn.
Grade 3b tear: More than 50% of EAS thickness torn.
Grade 3c tear: Both EAS and internal anal sphincter (IAS) torn.

Fourth-degree tear: Injury to perineum involving the anal sphincter complex (EAS and IAS) and anorectal mucosa.

Question 3

How is the anorectal mucosa sutured?

Answer 3

Interupted 3/0 vicryl

Question 4

How is the IAS sutured?

Answer 4

If identifiable close it separately.
Interrupted or mattress 3/0 PDS.
Not overlapping fashion.

Question 5

How is the EAS sutured?

Answer 5

Overlapping or end-to-end closure has comparable outcomes (cochrane).
Interrupted mattress suture in 3/0 PDS.

Question 6

What is a rectal button hole tear?

Answer 6

Anal sphincter complex remains intact but higher tear including the rectal mucosa.
It is by definition NOT a 4th degree tear.

Question 7

Risk factors for OASIS.

Answer 7

Asian ethnicity
Nulliparity
BW >4kg
shoulder dystocia
OP position
Prolonged 2nd stage
Instrumental delivery
- particularly forceps (with epis OR 1.3, without epis OR 6.5)
Previous OASIS (OR 5.5, 5-7% women)

Question 8

What are the evidence based interventions to prevent OASIS?

Answer 8

• No evidence for prophylactic episiotomy - evidence conflicting
• Strong evidence for episiotomy if instrumental required
• Episiotomy at 60% angle
• Hands-on controlled delivery of the head
• Warm compresses during second stage (50% reduction in cochrane review)
• Antenatal perineal massage - reduces episiotomy and need for suturing in nullips only. No effect on OASIS.

Question 9

What is the % occult OASIS?

Answer 9

33%

Question 10

What is the post-operative care for OASIS?

Answer 10

• broad-spectrum antibiotics
• postoperative laxatives - Bulking agents should not be given routinely with laxatives.
• Women should be advised that physiotherapy following repair of OASIS could be beneficial.
• reviewed at a convenient time (usually 6–12 weeks postpartum). Where possible, review should be by clinicians with a special interest in OASIS.
• If a woman is experiencing incontinence or pain at follow-up, referral to a specialist gynaecologist or colorectal surgeon should be considered.

Question 11

What investigations can check for occult or persistent OASIS?

Answer 11

endoanal ultrasonography

anal manometry

Question 12

What % women are asymptomatic 12 months after OASIS repair?

Answer 12

60-80%

Question 13

What is the advice for future deliveries after OASIS?

Answer 13

All women who sustained OASIS in a previous pregnancy should be counselled about the mode of delivery and this should be clearly documented in the notes.

Risk of OASIS after previous is 5-7%. And 17% women will experience worsening faecal symptoms after second vaginal birth.

Evidence for prophylactic episiotomy is conflicting and therefore an episiotomy should only be performed if clinically indicated.

All women who have abnormal endo-anal ultrasonography and/or manometry should be offered elective caesarean birth.