AMNIOTIC
FLUID SHAKE TEST
The shake test is a qualitative measurement of the
amount of pulmonary surfactant contained in the amniotic fluid. It is quick and
inexpensive. It is a bedside test of lung maturity. In an obstetric emergency,
an immediate decision about delivery can be made. The advantages of this test
over the others are that a physician, technician or must can perform it and the
test are highly reliable as
¨ It
evaluates the ability of pulmonary surfactant to generate a stable foam in the
presence of ethanol.
¨ Ethanol,
a nonfoaming competitive surfactant, eliminates the contributions of protein,
bile salts and salts of free fatty acids to the formation of a stable foam.
¨ At
an ethanol concentration of 47.5 percent, stable bubbles that foam after
shaking are due to amniotic fluid lecithin.
¨ Positive
tests, a complete ring of bubbles at the meniscus with a 1:2 dilution of
amniotic fluid, are rarely associated with neonatal RDS.
¨ It
is a screening test that gives useful information if mature.
Reference
Values
Normal
Positive: persistence of a foam ring for 15 minutes
after shaking (at an amniotic fluid – alcohol dilution of 1:2) indicates lung
maturity.
Procedure:
1. Test
is based on the ability of amniotic fluid surfactant to form a complete ring of
bubbles on the surface of the amniotic fluid in the presence of 95% ethanol.
2. Place
a mixture of 95% ethanol and amniotic fluid in an appropriate container and
shake for 15 seconds. A commercial kit is also available.
Clinical
implications:
1. If
a complete ring of foam forms and persists for 15 minutes the test is positive.
2. If
no ring of bubbles forms, the test is negative.
3. The
test has a high false – negative rate but a low false – positive rate. The L/S
ratio must be >4:1 for this test to be positive.
Interfering
Factors
1. Blood
or meconium contamination can alter results.
2. Contamination
of glassware or reagents can alter test results.
Interventions
Pretest
patient care
1. Obtain
informed consent.
2. Explain
the procedure and the reason foe testing.
3. Use
sterile techniques.
Posttest
patient care
1. Interpret
test outcome counsel appropriately.
2. Provide
counseling if test is negative.
3. Provide
future treatment modalities.
