Physiological effects of high-flow nasal cannula therapy in preterm infants

Abstract

ObjectiveHigh-flow nasal cannula (HFNC) therapy is increasingly used in preterm infants despite a paucity of physiological studies. We aimed to investigate the effects of HFNC on respiratory physiology.Study designA prospective randomised crossover study was performed enrolling clinically stable preterm infants receiving either HFNC or nasal continuous positive airway pressure (nCPAP). Infants in three current weight groups were studied: <1000 g, 1000–1500 g and >1500 g. Infants were randomised to either first receive HFNC flows 8–2 L/min and then nCPAP 6 cm H2O or nCPAP first and then HFNC flows 8–2 L/min. Nasopharyngeal end-expiratory airway pressure (pEEP), tidal volume, dead space washout by nasopharyngeal end-expiratory CO2 (pEECO2), oxygen saturation and vital signs were measured.ResultsA total of 44 preterm infants, birth weights 500–1900 g, were studied. Increasing flows from 2 to 8 L/min significantly increased pEEP (mean 2.3–6.1 cm H2O) and reduced pEECO2 (mean 2.3%–0.9%). Tidal volume and transcutaneous CO2 were unchanged. Significant differences were seen between pEEP generated in open and closed mouth states across all HFNC flows (difference 0.6–2.3 cm H2O). Infants weighing <1000 g received higher pEEP at the same HFNC flow than infants weighing >1000 g. Variability of pEEP generated at HFNC flows of 6–8 L/min was greater than nCPAP (2.4–13.5 vs 3.5–9.9 cm H2O).ConclusionsHFNC therapy produces clinically significant pEEP with large variability at higher flow rates. Highest pressures were observed in infants weighing <1000 g. Flow, weight and mouth position are all important determinants of pressures generated. Reductions in pEECO2 support HFNC’s role in dead space washout.

Gas flow in preterm infants treated with bubble CPAP: an observational study

“…Several studies have already indicated overlapping actions by demonstrating that nHF can generate some distending pressure similar to CPAP. [13][14][15][16][17][18] The main differences between the two systems are that the desired pressure is set by the clinician during bubble CPAP, whereas with nHF the clinician does not set, and is not aware of, the delivered pressure. In both systems, the device set pressure and the delivered prong pressure is likely to be higher than the pressure transmitted into the airway.…”

“…10,11 The postulated mechanisms of action of nHF include reduction of dead space through the washout of nasopharyngeal carbon dioxide produced by the "high" gas flows, and the generation of a distending pressure. 5,[12][13][14][15][16][17][18] It is suggested that CPAP exerts its effects primarily through generation of distending pressure, and nHF by the high gas flow into the airway. We postulate there may be overlap between the mechanisms of action of the two modes.…”

“…We postulate there may be overlap between the mechanisms of action of the two modes. 5,19 Studies, including a recent randomised crossover study by Liew et al, have demonstrated that nHF produces some distending pressure, [13][14][15][16][17][18][19] but no studies have measured the gas flow delivered into the nose by CPAP systems. This study measured the gas flow into the nose and the CPAP pressure at the nasal prongs in preterm infants receiving bubble CPAP.…”

2019 Year in Review: Neonatal Respiratory Support

“…Degree of leak around the nares, mouth open or closed, degree of spontaneous breathing, and flow settings have important effects on the degree of pressure generation and therefore on support. 21,22 Liew et al 23 conducted a prospective randomized crossover study to assess the effects of HFNC on respiratory physiology. Among 44 infants whose birthweight was < 2,000 g, increasing flows from 2 to 8 L/min led to a mean increase in end-expiratory pressure of 2.3-6.1 cm H 2 O as measured with nasopharyngeal airway pressure monitoring.…”

Implementation of a protocol‐based strategy for weaning nasal high flow therapy in preterm infants

“…The advantages of nHFT include ease of use, less nasal trauma, and improved patient comfort compared to nasal continuous positive airway pressure (nCPAP) 3,4 . Physiological effects of nHFT include improved alveolar ventilation by reducing dead space ventilation, generation of end‐expiratory airway pressure, improved oxygenation, lowering respiratory rate, 5 reduction in patient work of breathing 6 . Evidence from two recent systematic reviews has concluded that nHFT has shown “non‐inferiority” 7 or “similar rates” 8 for success compared to nCPAP in preterm infants greater than 28 weeks gestation postextubation.…”