Tidal volume needed/kg in extremely low premature infants is inversely proportional to birth weight.

What is it about?

When using volume-targeted ventilation, smaller babies need a larger tidal volume per kilogram to account for the dead space of the flow sensor. We performed an observational study to determine the tidal volume needed for normocapnea in a cohort of extremely low birth weight infant. We showed that the tidal volume needed to achieve appropriate tidal volume was around 6ml/kg in babies of around 400-500g, compared to 5ml/kg in infants of 700-800g. The reason for this is that the dead space of the flow sensor (approx. 0.7ml) becomes proportionally larger in the smallest infants and thus a slightly larger tidal volume is needed. The absolute tidal volume is only slightly greater than the sum of anatomical and instrumental dead space, indicating that there is some mixing of fresh gas and dead space gas.

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Why is it important?

Choosing the correct tidal volume is the key to successful application of volume-targeted ventilation. Many practitioners mistakenly think that smaller tidal volumes are appropriate for small babies and that error often leads to "failure" of volume-targeted ventilation.