We know that infants with SVT can respond to ice water on their face. But why does this work? And what's the best way to achieve success?

A mini-thread on SVT and ice

Disclaimer: video is not strictly an infant



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This is the diving reflex- hold your breath + your face is in water: leading to bradycardia, apnoea, + incr peripheral vascular resistance. Incr PVR preserves O2 consumption where it’s needed while reducing it where it isn’t. Bradycardia reduces the work of the heart

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It works because of the thermoreceptors in your skin which are abundant in your hands, feet, and face. They cause vasoconstriction (to preserve heat) and this increases vagal tone. This causes reflex bradycardia.

https://emj.bmj.com/content/emermed/29/8/611.full.pdf

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Additionally when you dive into cold water you take a deep breath in. This increase in intrathoracic pressure causes baroreceptor stimulation (in the carotid bodies and the aortic arch) causing an increase in vagal tone (just like a valsalva).

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How do we elicit the diving reflex in infants? Many people submerge the infant's head in a bucket of ice water. Actually ice to the face hasn’t been shown to be any less effective than full dunking (ice in a bag or a cloth). It's also more practical



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One case report showed cold burn injuries in a 4 day old baby: so be sensible. 10°C is fine; <5°C can stimulate pain fibres + cause a sympathetic response (which isn't what you want); >20°C doesn't cause a vagal response).

10-15 secs is adequate in infants (Smith, 2012)

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Lewis et al (2017) showed that ice to the face was one of the most successful vagal manouevres (effective in 36%). But know that around a number of infants (20-50%) will likely need adenosine, but that’s another thread….

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