Nasal high flow therapy: a novel treatment rather than a more expensive oxygen device

Abstract

Nasal high flow is a promising novel oxygen delivery device, whose mechanisms of action offer some beneficial effects over conventional oxygen systems. The administration of a high flow of heated and humidified gas mixture promotes higher and more stable inspiratory oxygen fraction values, decreases anatomical dead space and generates a positive airway pressure that can reduce the work of breathing and enhance patient comfort and tolerance. Nasal high flow has been used as a prophylactic tool or as a treatment device mostly in patients with acute hypoxaemic respiratory failure, with the majority of studies showing positive results. Recently, its clinical indications have been expanded to post-extubated patients in intensive care or following surgery, for pre- and peri-oxygenation during intubation, during bronchoscopy, in immunocompromised patients and in patients with "do not intubate" status. In the present review, we differentiate studies that suggest an advantage (benefit) from other studies that do not suggest an advantage (no benefit) compared to conventional oxygen devices or noninvasive ventilation, and propose an algorithm in cases of nasal high flow application in patients with acute hypoxaemic respiratory failure of almost any cause.

FIGURE 1

Recommended algorithm for high-flow nasal cannula use in acute hypoxaemic respiratory failure in immunocompetent or immunocompromised patients. ^#: arterial oxygen tension (P_aO2)/inspiratory oxygen fraction (F_iO2) <300 (patients with arterial carbon dioxide tension (P_aCO2) >45 mmHg and pH <7.35 are excluded); ^¶: systolic arterial blood pressure <90 mmHg despite adequate fluid administration; ⁺: the rationale for change in nasal high flow (NHF) settings are as follows. 1) Flow rate could be adjusted downwards by 5–10 L·min⁻¹ per 1–2 h if none of the negative prognostic factors are present. However, if targets of arterial oxygen saturation measured by pulse oximetry (S_pO2) and respiratory rate are not achieved, while the flow rate is <60 L·min⁻¹, increase of flow rate by 5–10 L·min⁻¹ is preferred to raising F_iO2; 2) increase in F_iO2 causes increases in P_aO2 and S_pO2; 3) temperature can be set at 37°C or lower (31–34°C), based on the patient's comfort; ^§: haemodynamic instability is defined by heart rate >140 beats·min⁻¹ or change >20% from baseline and/or systolic arterial blood pressure >180 mmHg, <90 mmHg or decrease >40 mmHg from baseline. MV: mechanical ventilation; SOT: standard oxygen treatment.