Gas conditioning during helmet noninvasive ventilation: effect on comfort, gas exchange, inspiratory effort, transpulmonary pressure and patient–ventilator interaction

Abstract

Background There is growing interest towards the use of helmet noninvasive ventilation (NIV) for the management of acute hypoxemic respiratory failure. Gas conditioning through heat and moisture exchangers (HME) or heated humidifiers (HHs) is needed during facemask NIV to provide a minimum level of humidity in the inspired gas (15 mg H2O/L). The optimal gas conditioning strategy during helmet NIV remains to be established. Methods Twenty patients with acute hypoxemic respiratory failure (PaO2/FiO2 < 300 mmHg) underwent consecutive 1-h periods of helmet NIV (PEEP 12 cmH2O, pressure support 12 cmH2O) with four humidification settings, applied in a random order: double-tube circuit with HHs and temperature set at 34 °C (HH34) and 37 °C (HH37); Y-piece circuit with HME; double-tube circuit with no humidification (NoH). Temperature and humidity of inhaled gas were measured through a capacitive hygrometer. Arterial blood gases, discomfort and dyspnea through visual analog scales (VAS), esophageal pressure swings (ΔPES) and simplified pressure–time product (PTPES), dynamic transpulmonary driving pressure (ΔPL) and asynchrony index were measured in each step. Results Median [IqR] absolute humidity, temperature and VAS discomfort were significantly lower during NoH vs. HME, HH34 and HH37: absolute humidity (mgH2O/L) 16 [12–19] vs. 28 [23–31] vs. 28 [24–31] vs. 33 [29–38], p < 0.001; temperature (°C) 29 [28–30] vs. 30 [29–31] vs. 31 [29–32] vs 32. [31–33], p < 0.001; VAS discomfort 4 [2–6] vs. 6 [2–7] vs. 7 [4–8] vs. 8 [4–10], p = 0.03. VAS discomfort increased with higher absolute humidity (p < 0.01) and temperature (p = 0.007). Higher VAS discomfort was associated with increased VAS dyspnea (p = 0.001). Arterial blood gases, respiratory rate, ΔPES, PTPES and ΔPL were similar in all conditions. Overall asynchrony index was similar in all steps, but autotriggering rate was lower during NoH and HME (p = 0.03). Conclusions During 1-h sessions of helmet NIV in patients with hypoxemic respiratory failure, a double-tube circuit with no humidification allowed adequate conditioning of inspired gas, optimized comfort and improved patient–ventilator interaction. Use of HHs or HME in this setting resulted in increased discomfort due to excessive heat and humidity in the interface, which was associated with more intense dyspnea. Trail Registration Registered on clinicaltrials.gov (NCT02875379) on August 23rd, 2016.

The Effects of Sequential Ventilation Therapy on Blood Gas Indexes, Pulmonary Function Indexes, Clinical Efficacy, and Safety in Patients with Severe Cor Pulmonale

“…By observing the ventilation time of the two groups, it was shown that the invasive ventilation time and total ventilation time of the study group were significantly shorter than those of the control group, indicating that sequential ventilation therapy could reduce the time of tracheal intubation, thereby reducing the invasive ventilation time [ 10 ]. In addition, the comparison of blood gas indexes at different time periods before and after treatment showed that the PH changes of the two groups were consistent and had no significant difference after treatment, indicating that both treatment methods could better maintain PH stability [ 11 ]. After different treatments, the blood oxygen value of the two groups increased, while the blood carbon dioxide value decreased, and the improvement of PaCO 2 and PaO 2 in the study group was significantly better than that in the control group.…”

Non-invasive ventilation for acute hypoxemic respiratory failure, including COVID-19

“…In one recent study, a double-tube circuit with no humidification allowed adequate conditioning of inspired gas, optimal comfort, and improved patient–ventilator interaction. [ 74 ] The use of heated humidifiers or HME in this setting resulted in increased discomfort due to excessive heat and humidity in the interface, which was associated with more intense dyspnea. [ 74 ] Humidification may be necessary when fresh gas flows >40 L/min are applied.…”

“…[ 74 ] The use of heated humidifiers or HME in this setting resulted in increased discomfort due to excessive heat and humidity in the interface, which was associated with more intense dyspnea. [ 74 ] Humidification may be necessary when fresh gas flows >40 L/min are applied. [ 75 ]…”

Helmet noninvasive support for acute hypoxemic respiratory failure: rationale, mechanism of action and bedside application

“…Preliminary data seem to show that no humidification is needed during helmet NIV if the total system’s minute ventilation does not exceed a threshold of around 40 L/min, which is the case for hypoxemic patients treated with helmet NIV. A double-tube circuit without any humidification reduces discomfort and provides sufficient conditioning of the inspired gas, without any effect on inspiratory effort and work of breathing [ 69 ].…”