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Click Test for RDS
Targeted Early Rescue Surfactant in Ventilated Preterm Infants Using the Click Test. Osborn DA, Jeffery HE, Bredemeyer SL, et al. Pediatrics 2000; 106 (3): e30.
This study was done to determine whether the click test, a rapid bedside test of surfactant function, results in earlier and more appropriate surfactant administration in ventilated preterm infants than does usual early rescue treatment. 126 ventilated preterm infants were randomized to have their need for surfactant therapy determined by the click test or by the usual clinical and xray criteria. The treatment group had the click test performed on tracheal aspirate as soon as possible after admission, and if negative or equivocal (surfactant deficient), surfactant was given. The control group had surfactant given as soon as possible after the clinical diagnosis of RDS was made. In infants < 28 weeks gestation, use of the click test resulted in significantly earlier surfactant therapy (median time: 50 min vs 159 min), and in a reduction in the number of infants receiving surfactant (48% vs 79%). In infants 28 - 36 weeks gestation, no differences between groups were noted. Neonatal morbidity and mortality was similar in both groups.
Comment. The frequent use of antenatal steroids in preterm labor has significantly reduced the incidence and severity of RDS in premature infants. Consequently, we are seeing a larger proportion of premature babies who may require respiratory support for reasons other than surfactant deficiency (ie apnea, wet lungs, infection), and who will not benefit from surfactant replacement therapy. The investigators in this study used the click test to determine which premature infants were likely to benefit from surfactant replacement. When done on tracheal aspirates from ventilated infants < 28 weeks gestation, the use of this test may result in significant cost savings by reducing the percentage of babies needing surfactant treatment.
The click test is a rapid test for surfactant function. When performed on tracheal aspirates, it has been reported to be 93% sensitive and 100% specific for surfactant deficiency when compared to clinical and radiographic diagnoses of RDS. The test appears to be much more complicated than the usual bedside tests run in our NICUs. It involves adding 0.2 cc of tracheal aspirate with an equal volume of 95% ethanol in a test tube, mixing in a vortex mixer for 15 seconds, pipetting bubbles from the surface and suspending them over air-free water in the well of a glass slide, then observing for 2 minutes at 10-40x magnification with a microscope and counting the number of bubbles that "click". I suspect that most of our hospitals would find it difficult to maintain adequate quality control when running this as a bedside test to determine the appropriateness of a clinical therapy.
Andrew B. Kairalla MD