ANAL SPHINCTER INJURIES (OASIS) AT DELIVERY
Background: Anal incontinence severely impairs quality of life. It affects 4 to 19 % of women and is statistically related to number of vaginal deliveries. It is grossly underreported and most patients that do seek help are referred to gastroenterologists or colorectal surgeons. Incidence of recognized sphincter injuries at time of delivery is 1 to 2 %. However studies with anal ultrasound showed incidence of anal sphincter injuries at 28 to 41 %. Depending on the degree of injury symptoms range from partial to complete inability to control passing of winds, liquid or solid stools. About three thirds of patients are asymp- tomatic in puerperium, however half of them are at risk of developing anal incontinence in later life. Hypoestrogenisem, additional perineal trauma during consequent deliveries and sphincter atrophy can unmask anal sphincter damage years later.
Timely recognition and treatment are vital for good long term results and quality of life, if possible immediately after delivery. Good knowledge of perineal anatomy, recognition of risk factors, intense search and appropriate treatment and follow-up are essential to management of anal sphincter injuries. All secondary sphincter repair is less effective.
Content: Updated overview of current opinion and guidelines on anal sphincter injuries are pre- sented. Anal sphincter is composed of external anal sphincter (EAS) and internal anal sphincter (IAS). Striated EAS is divided into three parts – subcutaneous, superficial, deep, and con- nected to puborectalis muscle posteriorly. Smooth-muscled IAS is a continuation of a cir- cular smooth-muscle layer of rectum. In between there is a thin longitudinal muscle layer. IAS constitutes 70 % of resting tone and is under constant contraction. EAS contributes to 30 % of resting tone and almost all pressure during active contraction. EAS injury leads to insufficient contraction after rectal sampling and filling which causes urgency – patient can feel the pressure but cannot hold bowel contents for long. IAS injury leads to complete inability to control passing of bowel contents.
Perineal tears are classified to four degrees depending on tear depth. With first degree tear only vaginal mucosa is torn, second degree perineal muscles are damaged, third degree describes any tearing of anal sphincter and fourth of rectal mucosa. New guidelines recom- mend further classification of 3rd degree tears:
3a = < 50 % EAS ruptured 3b = > 50 % EAS ruptured 3c = IAS rupture Ultrasound with anal plug is nowadays considered to be the golden standard for diagnosis and follow-up of anal sphincter injuries. Entire length of anal sphincter muscle is shown from U shaped puborectalis muscle to anus. IAS appears as hypo-echoic homogenous circle around rectal mucosa, while EAS appears as outer hyper- echoic heterogenous circle. Dur- ing voluntary contraction distance between ruptured ends of EAS enlarges. 3D ultrasound shows promising results but is not yet standardized. Anal sphincter manometry, pudendal nerve latency and EMG of anal sphincter also contribute valuable information on anal sphincter function and injuries.
Risk factors are: fetal weight over 3500g, forceps delivery (but not vacuum extraction) occipito-posterior presentation, shoulder dystocia, prolonged second stage of delivery, median episiotomy, previous anorectal surgery and maternal age over 35 years at first delivery are described as risk factors. Caesarean section prevents anal sphincter injuries. Studies show that restrictive use of mediolateral episiotomy in comparison to spontaneous delivery prevents anal sphincter injuries.
Rectal examination prior to suturing perineal tears is essential for timely recognition of anal sphincter injuries. EAS appears more read while IAS smooth muscle has a lighter colour (white meat). Sphincter continuity can be palpated between index finger and thumb (pill-rolling motion) and voluntary contraction felt. Immediately after delivery voluntary contraction can be diminished or absent due to temporary loss of sensation or epidural analgesia.
Studies currently show better results with overlap comparing to end-to-end technique for sphincter repair. Further randomised controlled trial will give final answers on the sub- ject. Application of wide-spectrum antibiotics, continued oraly for 5 to 7 days is recommended. No specific diet is needed, patients are advised to take lactulose 15 ml per day for 7 to 10 days and defecate regularly. Application of Foley catheter for 24 hours and NSARs are also recommended. Follow up with anal ultrasound and manometry after 3 to 6 months in perineal clinic is mandatory.
Conclusions: Anal sphincter ruptures during vaginal delivery often remain unrecognised, which can later lead to fecal incontinence and impaired quality of life. Timely recognition and proper treatment are vital to good healing results.
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