High flow oxygen therapy combines several physiological effects: Oxygenation, PEEP, an increase in the end-expiratory lung volume (EELV), a lower respiratory rate (RR), a decrease in intrinsic PEEP and work of breathing, lower PaCO2, and improved humidification and comfort (1, 2). The optimal flow setting depends on the indications and the desired physiological effect.
Oxygenation, PEEP, the increase in EELV and the decrease in RR, intrinsic PEEP and work of breathing are all flow-dependent, which means we need to use the highest flow accepted by the patient to optimize the treatment (3, 4, 5, 6). The decrease in PaCO2 and minute ventilation is achieved at 30 l/min and does not change at a higher flow (3). There is no data about using the flow setting to optimize humidification.
Initial settings and adjustments
Flow: The initial setting is 60 l/min. If the patient complains of discomfort, the flow can be decreased down to a minimum of 30 l/min. Any discomfort is usually due to the velocity of gas rather than the flow itself, and can be eased by using a large-bore cannula. For patients suffering from acute respiratory failure with increased respiratory drive, the flow can be increased to more than 60 l/min.
Temperature: In order to optimize the humidification effect, the temperature should be maintained at 37°C.
Oxygen: Oxygen is adjusted to maintain SpO2 within target ranges of 92%-96% for most patients and 88%-92% for patients with chronic respiratory disease (7, 8).
- Mauri T, Turrini C, Eronia N, Grasselli G, Volta CA, et al. Physiologic Effects of High-Flow Nasal Cannula in Acute Hypoxemic Respiratory Failure. Am J Respir Crit Care Med. 2017 May 1;195(9):1207-1215 (abstract).
- Goligher EC, Slutsky AS. Not Just Oxygen? Mechanisms of Benefit from High-Flow Nasal Cannula in Hypoxemic Respiratory Failure. Am J Respir Crit Care Med. 2017 May 1;195(9):1128-1131.
- Mauri T, Alban L, Turrini C, Cambiaghi B, Carlesso E, Taccone P, et al. Optimum support by high-flow nasal cannula in acute hypoxemic respiratory failure: effects of increasing flow rates. Intensive Care Med. 2017 Jul 31 [Epub ahead of print] (abstract).
- Parke RL, Bloch A, McGuinness SP. Effect of Very-High-Flow Nasal Therapy on Airway Pressure and End-Expiratory Lung Impedance in Healthy Volunteers. Respir Care. 2015 Oct;60(10):1397-403.
- Pisani L, Fasano L, Corcione N, Comellini V, Musti MA, Brandao M, et al. Change in pulmonary mechanics and the effect on breathing pattern of high flow oxygen therapy in stable hypercapnic COPD. Thorax. 2017 Apr;72(4):373-375 (abstract).
- Luo JC, Lu MS, Zhao ZH, Jiang W, Xu B, Weng L, et al. Positive End-Expiratory Pressure Effect of 3 High-Flow Nasal Cannula Devices. Respir Care. 2017 Jul;62(7):888-895 (abstract).
- O'Driscoll BR, Howard LS, Davison AG; British Thoracic Society. BTS guideline for emergency oxygen use in adult patients. Thorax 2008;63:vi1-68.
- Beasley R, Chien J, Douglas J, Eastlake L, Farah C, King G, et al. Thoracic Society of Australia and New Zealand oxygen guidelines for acute oxygen use in adults: 'Swimming between the flags'. Respirology 2015;20:1182-91.
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