33. OBSTETRIC HAEMORRHAGE

Obstetric haemorrhage can occur before birth (antepartum) or after birth (post partum). Causes of antepartum haemorrhage include placenta praevia, placental abruption and uterine rupture. Causes of post partum haemorrhage include uterine atony, retained placenta, placenta accreta and birth trauma.

Obstetric haemorrhage can cause maternal death. The anaesthetist must carefully assess the degree of blood loss and attempt to resuscitate the patient before anaesthesia. Blood loss may be external and also internal (concealed).

The anaesthetist must also be aware of the physiological changes of pregnancy that will affect the anaesthetic. Obstetric patients are at a greater risk of aspiration and difficult intubation.

Placenta Praevia

Placenta praevia occurs when the placenta lies near the internal opening of the uterus (internal os). The risk of this occurring in a normal pregnancy is 0.25% and the incidence increases if the patient has had a previous caesarean section.

The patient may complain of painless bleeding. The diagnosis is made with ultrasound. One third of women who have vaginal bleeding in late pregnancy will have placenta praevia.

Ultrasound can also show how much of the internal os is covered by the placenta. With mild placenta praevia the placenta is low in the uterus but does not reach the internal os or just reaches the edge of the internal os and the mother may delivery vaginally. With severe placenta praevia the placenta covers the internal os and the mother needs a caesarean section because the foetus will compress the placenta with vaginal delivery, obstructing its blood supply and causing maternal haemorrhage.

Traditionally, general anaesthesia has been used for caesarean section for placenta praevia. However, for elective, low risk placenta praevia spinal anaesthesia may be used. For emergency caesarean section and high-risk placenta praevia, it is safer to use general anaesthesia. It is difficult to manage an awake patient and treat severe haemorrhage at the same time.

All patients with placenta praevia must have two large size intravenous cannulas and blood available because the surgeon may need to cut though the placenta to deliver the baby. The anaesthetist must try to treat any hypovolaemia before giving the anaesthesia. In severe haemorrhage the dose of thiopentone must be reduced (usually less than 100 mg). Ketamine (0.5 to 1.0 mg/kg) may be a good choice for induction of anaesthesia.

The placenta can invade the wall of the uterus (placenta accreta, placenta increta and placenta percreta). This occurs in 0.04% of all pregnancies and in 5 to 9% of mothers with placenta praevia. The risk is greater in women with placenta praevia who have had a previous caesarean section. In patients with placenta percreta and accreta massive blood loss can occur (2000 to 5000 ml). About 20% of these patients will develop coagulopathies. At least 30% will need a caesarean hysterectomy to stop the bleeding.

Placental Abruption

Placental abruption (abrupto placentae) is bleeding behind the placenta causing partial separation of the placenta from the uterine wall. 

It usually causes painful frequent uterine contractions and vaginal bleeding. Placental abruption is more common in women who have had several pregnancies, abdominal trauma during pregnancy, have an abnormal uterus or who have had a previous placental abruption. It can be mild, moderate or severe.

The amount of blood loss from the vagina is less than the total amount of blood loss, as some blood will remain behind the placenta (concealed haemorrhage). As much as 4000 ml of blood can be in the uterus.

The anaesthetist must perform a careful examination to estimate the total blood loss. 10% of patients will develop disseminated intravascular coagulopathy (DIC) with low amounts of fibrinogen, platelets and factors V and V11. If possible, all patients should have their coagulation tested. A bedside test of coagulation is to place 5 ml of blood into a glass test tube, shake gently and allow to stand. A coagulation defect is present if a clot does not form within 6 minutes.

The anaesthetic management of placental abruption depends on the severity of haemorrhage and the health of the mother and foetus. If the abruption is severe, the anaesthetist must use general anaesthesia with rapid sequence induction. Hypovolaemia and abnormal coagulation make spinal or epidural anaesthesia dangerous.

Uterine Rupture

Management requires treatment of severe haemorrhage, emergency laparotomy and may require caesarean hysterectomy.

Retained Placenta

Retained placenta is when all or part of the placenta fails to deliver. It happens in 1% of all vaginal deliveries. Haemorrhage occurs because the uterus cannot contract. If there has been a lot of bleeding and the patient shows signs and symptoms of hypovolaemia, spinal or epidural anaesthesia may not be suitable and may cause severe hypotension. General anaesthesia must be performed with a rapid sequence induction to prevent aspiration of gastric contents.

Uterine Atony

Uterine atony occurs in 2 to 5% of all vaginal deliveries. It ranges from mild to severe. A completely atonic uterus can bleed 2 litres of blood in less than 5 minutes. The anaesthetist must treat the blood loss, give intravenous oxytocin and monitor the patient. The obstetrician can try to treat the atonic uterus by massage of the uterus, placing packs in the uterus and giving ergot or prostaglandin f2a. The anaesthetist must be aware that prostaglandin f2a can cause bronchospasm, hypotension and hypertension. Oxytocin is a vasodilator and must be given slowly and carefully if the mother is hypovolaemic. If the patient continues to bleed she may need an emergency laparotomy for hysterectomy or ligation of the internal iliac arteries.

ECTOPIC PREGNANCY

Patients with ectopic pregnancy may have severe blood loss. The anaesthetist must assess the amount of blood loss and attempt to treat the hypovolaemia before surgery.