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Performance of Invasive Mode in Different Heated Humidification Systems With High-Flow Nasal Cannula

BACKGROUND: Oxygen therapy via high-flow nasal cannula generates physiologic changes that impact ventilatory variables of patients. However, we know that there are detrimental effects on airway mucosa related to inhalation of gases. The objective of this study was to evaluate the performance in terms of absolute humidity, relative humidity, and temperature of different brands of heated humidifiers and circuits in the invasive mode during the use of high-flow oxygen therapy in flows between 30 and 100 L/min. METHODS: A prospective observational study conducted at the Sanatorio Anchorena equipment analysis laboratory; September 5 to October 20, 2019. RESULTS: A statistically significant interaction was found among the programmed flows and the different combinations of devices and circuits for the delivery of absolute humidity (P < .001). An effect of flow on delivered absolute humidity was found, regardless of the equipment and circuit combination (P < .001). However, in the invasive mode, the combination of the Fisher&Paykel MR850 heated humidifier with the Medtronic-Dar circuit, the Intersurgical circuit, and the AquaVENT circuit always reached or achieved absolute humidity values > 33 mg/L, even at flows up to 100 L/min. The combination of the Flexicare FL9000 heated humidifier with the Fisher&Paykel RT202 circuit, the Fisher&Paykel Evaqua 2 circuit, the Flexicare circuit, the AquaVENT circuit, and the GGM circuit achieved similar results. The mean (SD) of absolute humidity delivered in the invasive mode (36.2 ± 5.9 mg/L) was higher compared with the noninvasive mode (26.8 ± 7.2 mg/L) (P < .001), regardless of circuit and programmed flows. CONCLUSIONS: When heated humidifiers were used in the invasive mode for high-flow oxygen therapy, absolute humidity depended not only on the heated humidifiers and the combination of circuits but also on the programmed flow, especially at flows > 50 L/min. Moreover, the heated humidifiers exhibited different behaviors, in some cases inefficient, in delivering adequate humidification. However, some equipment improved performance when set to the invasive mode.