A couple of years ago I wrote an editorial for the Jornal de Pediatria, a Brazilian journal, about extubation failure. (full text available free here). At that time the most promising test fo predicting extubation failure appeared to be some variant of the Spontaneous Breathing Test.
Tests of pulmonary mecahnics or lung volumes have been disappointing as a rule, and test of maximal inspiratory force have also not worked out. A variant of a test where the infant is switched to CPAP for a certain limited duration of time, and the infant then observed seems most useful. But what exactly to observe?
Lorna Gillespie and her colleagues measured minute ventilation during assisted ventilation, then repeated the measure during ETT CPAP for 10 minute, the minute ventilation test, MVT. If the CPAP minute ventilation was less than 50% of that during assisted ventilation then the baby is considered ready for extubation. This is one of the few (or perhaps the only) randomized controlled trials in this area. Infants randomized to have the MVT were extubated earlier than those randomized to be extubated when the clinical team thought they were ready.
The Melbourne group (those guys again!) compared the measuring minute ventilation approach to observing the baby for hypoxia and bradycardia. Most of the babies who were reintubated had a VE ratio more than 0.5, so they would have passed the MVT. The test they devised, the spontaneous breathing test, SBT, requires switching to ETT CPAP for 3 minutes, and observing the baby. “A failed SBT was recorded if the infant had either a bradycardia for more than 15 seconds and/or a fall in SpO2 below 85% despite a 15% increase in FIO2″.
A new study by Sanjay Chawla and coworkers evaluating the SBT has just been published. (Chawla S, Natarajan G, Gelmini M, Kazzi SNJ: Role of spontaneous breathing trial in predicting successful extubation in premature infants. Pediatric Pulmonology 2012:n/a-n/a.) They used an almost identical SBT, except that it lasted 5 minutes, and they do not mention the FiO2 in their definition of hypoxia. Nevertheless they found that an SBT pass was strongly predictive of successful extubation, and failing the SBT was modestly predictive of extubation failure (8 failed the test and of these 5 babies were later extubation failures).
I think this test deserves a modestly sized RCT to see if duration of intubation and lung injury can be improved by using the test, and the number of extubation/intubation episodes can also be decreased. I think the test seems sufficiently predictive that it could be used to encourage earlier extubation if the test is passed, and a serious consideration of delaying extubation if failed, although there are some extubation successes among infants who fail the test, so if everything else is optimal then a trial of extubation might still be worth it. Failing extubation isn’t such a bad thing if you can re-intubate the baby with minimal trauma, using pre-medication.