Another metaphor that has been applied in such a circumstance is the “black swan” theory (Fig. 1), referring to an amazing event with a significant impact on the course of subsequent events, and often rationalized in hindsight without affirming experimentation to justify the generalization of the experience.1 Of course, universality, and certainly knowledge of cause and effect, cannot be achieved without the latter. Indeed, without experimentation, there is a risk for “ambitious overgeneralization”, for applying what is gleaned from one unique circumstance to others, which may seem similar, but differ in consequential ways, which, at first, might be overlooked. An example of the phenomenon was described by William Silverman as the widespread application of apparently safe, life-saving oxygen therapy, which caused retinopathy of prematurity when applied too broadly and without attention to dose to treat premature infants to reduce mortality and morbidity.2 Another recent example of ambitious overgeneralization could be the application of phototherapy to increasingly smaller, more immature, and more translucent premature infants without a randomized, controlled trial to evaluate its safety and efficacy in such infants. Only recently, because of a trial that focused on the use of phototherapy to protect against bilirubin-induced injury in such infants, in particular, those weighing between 501 and 750 g, was a potential risk of sustained light exposure identified.3

Medical care of the most immature infants, those born at <24 weeks’ gestation and often weighing little more than a pound, provides another case in point. The apparent “threshold of viability” has moved ever earlier in gestation during the past 50 years with the introduction of mechanical ventilation, artificial surfactants, and other technical innovations. Whereas survival after birth at 22 weeks’ gestation was once perceived as a “black swan” event in prior decades, it has now become much more commonplace. The expectation for survival in some parts of the world has rapidly changed. From 2014 to 2019, survival among all infants born at 22 weeks’ gestation in the US Vermont Oxford Network hospitals increased from 6 to 17% of all liveborn infants (and 29% of resuscitated infants). During that time, the rate of resuscitation more than doubled, from 26 to 58%.4 Today, perhaps the rare and generally unexpected survival of a newborn <22 weeks’ gestation could be characterized as a “black swan” event, with occasional case reports of such early survival now showing up in the literature.5 Will such anecdotes of successful resuscitation prompt more general application of resuscitative efforts at this earlier gestational age?

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