THE SURFACTANT TEST

INDICATIONS (1) There should be a legitimate reason for induction, but not one which is so strong that you would induce the patient anyway, such as severe gestational hypertension (21.3). Indications include an elective Caesarean section with uncertain dates, suspected growth retardation (23.14), and diabetes (in which the surfactant test is somewhat unreliable, 21.2). (2) If you are able to use ultrasound to localize the placenta, and find that it is in the way of the needle, reassess the need for the test. In practice little harm results from going through it. If however she is Rhesus-negative, putting a needle through the placenta increases the risk of rhesus immunization. (3) She must have a mobile presenting part, showing that she has enough liquor to aspirate. If there is not enough liquor, he is probably mature enough anyway.

ASPIRATION Take a sterile 10 ml syringe and a long 1mm diameter needle. If she is very obese, you may need an extra long one. Have a second syringe ready in case the first sample is blood-stained. Ask her to empty her bladder, so that you don’t aspirate her urine. There is no need for LA. Prepare the skin over her lower abdomen, preferably with iodine. Lay her supine. The lowest part of the baby is usually his head: feel it, lift it up out of her pelvis as far as you can, and then hold it there with your left hand. This will allow liquor to swirl around it, and fill her lower segment.

While retracting the baby’s head upwards, plunge the needle attached to the syringe into her uterus at right angles to the plane of her lower segment, as near to his head as is reasonable, remembering that you don’t want to hit it. Remember also that the commonest complication is rupture of her membranes due to inserting the needle too low, too close to her cervix.

Alternatively, aspirate at the level of her umbilicus on the side of the baby’s limbs. You need to be able to feel the position clearly. There is usually a good pool of liquor there. Injuring the baby is very unusual.

However, it is safer to be guided by ultrasound. Withdraw 5–10 ml of fluid. Record it as being clear, or blood-stained (indicating a traumatic tap), and the vernix in it as being absent, scanty, or plentiful. If you fail, try once more and then give up.

EQUIPMENT You need: (1) 1 ml of clear liquor, uncontaminated by meconium or blood. Only the faintest blood-staining is acceptable. If you cannot avoid blood contamination, centrifuge the liquor hard for 5 mins and test the supernatant. (2) 95% alcohol. (3) Some completely clean glass test-tubes with an internal diameter 8–14mm. (4) ‘Parafilm’ to cover the tubes. If you don’t have this, use new corks or rubber stoppers. If you don’t have these either, a very carefully washed, and even more carefully rinsed, finger is probably better than a used cork or stopper.

METHOD Take exactly 0.5 ml of liquor, 0.5 ml of saline, and 1 ml of alcohol (this mixes a 1:2 dilution of amniotic fluid with an equal volume of alcohol). Shake the mixture vigorously for exactly 15 secs. Then don’t move the tube. Wait 15 mins before examining it in a good light against a dark background.

At a dilution of 1:2 as above a score of 1 or more means that his lungs are mature.

CAUTION! (1) Avoid contamination with anything greasy. (2) Meconium produces a false positive result, so don’t do the test if there is meconium in the fluid. (3) Don’t shake the tubes a second time.

DIFFICULTIES WITH THE SURFACTANT TEST

If you ASPIRATE NOTHING, has your needle entered the amniotic sac? Try again, pushing the needle a little deeper.

If you ASPIRATE BLOOD, it may be fetal or maternal blood. Check the fetal heart half-hourly for 4 hours. If it rises steadily, he is bleeding. Do a Caesarean section immediately.

If her UTERUS BECOMES HARD, and there are other signs of placental abruption, she is bleeding behind her placenta (20.11).