Early hearing testing of still critically ill neonates

To use a newly applied hearing screening technique for early measurement in neonatal intensive care unit (NICU) patients to learn more about the high incidence of hearing loss in this population.

An automated, portable infant hearing screener that measures the auditory brain-stem response at the bedside was used at the NICU of the Hospital Nacional de Niños, San Jose, Costa Rica. Patients were evaluated early, even if they were on a ventilator. The screener tested with a 40-dB hearing level click stimulus to each ear over a bandwidth of 750 to 3000 Hz.

During a 15-month period, 92 newborns underwent 226 auditory brain-stem response tests (range, one to six tests; mean, 2 1/2 tests). Before discharge from the NICU or death, each infant was successfully screened. Of 72 infants discharged from the hospital alive, 68 passed bilaterally and four failed bilaterally, a 6% failure rate. Of 20 infants who died, 15 failed bilaterally, a 75% failure rate. Persistent bilateral failure of the test was detectable from each infant's first test and showed an association (chi-square, P<.001) with death. The overall bilateral failure rate was 21%.

Simple bedside auditory brain-stem response screening of all NICU infants was consistently possible regardless of clinical status, the early onset of hearing loss suggests that NICU treatment was not ototoxic and the unexpectedly high overall bilateral test failure rate resulted from the inclusion of patients who would have died untested if conventional testing had been done.