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

Abstract

Objective: High-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 design: A 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.

Results: A 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).

Conclusions: HFNC 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.

Keywords: high flow nasal cannula oxygen; neonatology; physiology; respiratory.

Figure 1

Study flow chart and pathway. Detailed study design and procedures including inclusion, exclusion and exit criteria. CPAP, continuous positive airway pressure; FiO2, oxygen concentration; HFNC, high-flow nasal annula; LPM, litres per minute; NIV, non-invasive ventilation; SpO2, oxygen saturation;TOSCA, transcutaneous CO2.

Figure 2

Scatter plot of relationship between nasopharyngeal end-expiratory positive pressure (pEEP) and weight-adjusted flow rate. Figure demonstrates large variability of pEEP measured above 6 L/min/kg, with some pEEP measured up to 8–13 cm H₂O.