The title is how I sometimes refer to HFNC, but one could ask whether that is all there is to high flow, is it just another way to deliver CPAP, but with no control, or knowledge, of the pressure delivered?
A new study examined the lung mechanics in infants receiving CPAP and HFNC, and they tried to match the actual distending pressure achieved between the groups. (Lavizzari A, Respiratory mechanics during NCPAP and HHHFNC at equal distending pressures. Archives of Disease in Childhood – Fetal and Neonatal Edition. 2014). In a randomized cross-over study of 20 preterm infants with mild RDS, babies received 2,4, or 6 cmH2O of CPAP or 2,4, or 6 L/min. They then measured the retropharyngeal pressure and compared lung mechanics between periods of CPAP and periods of HFNC which achieved matching pressures.
Not too surprisingly pressures achieved during HFNC were very variable. 5 of the babies did not achieve a pressure of more than 2 cmH2O even with 6 liters per minute. only 5 babies got up to 6 cmH2O, so the comparisons were done at 2 and 4 cmH2O. There were basically no differences found. Although all the inspiratory work of breathing estimates were a little higher with HFNC than with CPAP.
The babies had very low oxygen requirements, and fairly good lung compliance, I guess it is possible that the results might have been different with subjects that had stiffer lungs; but this study does suggest that HFNC is indeed a ‘poor man’s CPAP’, with CPAP actually delivered often being less than 2 cmH2O but, when CPAP is generated, the physiological effects are similar to traditional CPAP. Again suggesting that the only real benefit of HFNC is comfort.
Or is it? Another small cross-over trial evaluated comfort using the EDIN scale during 24 hours periods with either CPAP (at 4 to 5 cmH2O) or HFNC (at 5 or 6 L/min) in 20 preterm infants with mild respiratory distress. (Klingenberg C, et al. Patient comfort during treatment with heated humidified high flow nasal cannulae versus nasal continuous positive airway pressure: a randomised cross-over trial. Archives of Disease in Childhood – Fetal and Neonatal Edition. 2013). No difference in the discomfort scores was found. A nice aspect of this study was that the authors asked parents how they felt about the therapies, the parents clearly preferred the HFNC, they thought their child was more satisfied, they could do more in the care of the baby, and they had improved interaction with them.
Finally another small cross-over study compared pressures achieved with 2 different HFNC systems (Collins CL, et al . Comparison of the pharyngeal pressure provided by two heated, humidified high-flow nasal cannulae devices in premature infants. Journal of Paediatrics and Child Health. 2013). Basically, at the same flow the pressures were the same. And again, very variable, at the highest flows they tested, 7 and 8 L/minute, the pressures were a bit lower with the Fisher-Paykell device, probably because of the pressure limiting valve. At 8 liters per minute the average pressure was between 4 and 5 with each device, but the standard deviation was 2.2, meaning that 95% of the time the pressures were between 0 and about 9 (if they were truly normally distributed, which is unlikely to be exactly true). So poor man’s CPAP, with unreliable pressures, no apparent physiologic advantage, a possibility of having very high or very low distending pressures, but parents prefer it, and there is less nasal trauma. Clinical outcomes are not any worse, and babies who are failing on HFNC (which is likely to be sometimes due to them not actually getting any pressure) can often be rescued with CPAP.
Based on our experience (Klingenberg et al , Thanks for the citation!) I believe that nasal HFNC should not be looked upon as an alternative, but rather as supplemental tool in the management of mild RDS in premature newborns. In our unit, most premature babies with RDS will start treatment on n-CPAP, and switch to HFNC when stable on low FiO2. Treatment failure is easily recognized and the baby can be but back on n-CPAP again. (This may apply to BPD patients as well.)
I think this is a better approach in CPAP-weaning, compared to CPAP –pausing. However, we may experiences that the perceived better acceptance of HFCN may lead to a longer treatment period as doctors, nurses, parents (and babies?) are not so eager in stopping respiratory support compared to on n-CPAP. Thus it remains to be seen if HFNC actually decrease costs for the “poor man”.
Couldn’t agree more. As a result of 2 recent trials we no longer do the ‘CPAP pausing’ thing, but we seem to be entering a phase where rather than going from CPAP to spontaneous breathing, everyone has to transition for a period of high flow cannulae, and then to wean flows down.
I think we have to be careful, because it seems to families and caregivers so much more comfortable, there is a reluctance to wean, and some kids who could probably be looking after themselves (although with tachypnea and maybe some retractions) stay on high for cannulae for a long time. Too long a time