Effectiveness of nasal highflow in hypercapnic COPD patients is flow and leakage dependent

Abstract

BackgroundNasal Highflow (NHF) delivers a humidified and heated airflow via nasal prongs. Current data provide evidence for efficacy of NHF in patients with hypoxemic respiratory failure. Preliminary data suggest that NHF may decrease hypercapnia in hypercapnic respiratory failure. The aim of this study was to evaluate the mechanism of NHF mediated PCO2 reduction in patients with chronic obstructive pulmonary disease (COPD).MethodsIn 36 hypercapnic COPD patients (PCO2 > 45 mmHg), hypercapnia was evaluated by capillary gas sampling 1 h after NHF breathing under four conditions A to D with different flow rates and different degrees of leakage (A = 20 L/min, low leakage, two prongs, both inside; B = 40 L/min, low leakage, two prongs, both inside; C = 40 L/min, high leakage, two prongs, one outside and open; D = 40 L/min, high leakage, two prongs, one outside and closed). Under identical conditions, mean airway pressure was measured in the hypopharynx of 10 COPD patients.ResultsHypercapnia significantly decreased in all patients. In patients with capillary PCO2 > 55 mmHg (n = 26), PCO2 additionally decreased significantly by increased leakage and/or flow rate in comparison to lower leakage/ flow rate conditions (A = 94.2 ± 8.2%; B = 93.5 ± 4.4%; C = 90.5 ± 7.2%; D = 86.8 ± 3.8%). The highest mean airway pressure was observed in patients breathing under condition B (2.3 ± 1.6 mbar; p < 0.05).ConclusionsThis study demonstrates effective PCO2 reduction with NHF therapy in stable hypercapnic COPD patients. This effect does not correlate with an increase in mean airway pressure but with increased leakage and airflow, indicating airway wash out and reduction of functional dead space as important mechanisms of NHF therapy. These results may be useful when considering NHF treatment in hypercapnic COPD patients.Trial registrationClinical Trials: NCT02504814; First posted July 22, 2015.

High-Flow Nasal Cannula: A Promising Oxygen Therapy for Patients with Severe Bronchial Asthma Complicated with Respiratory Failure

“…However, we believe that the main reason is that HFNC effectiveness is flow-and leakage-dependent. at we found no CO 2 reduction in asthmatic patients may be explained by findings reported by Braunlich et al in COPD patients [31]. e latter study demonstrated that effective PCO 2 reduction by HFNC therapy does not correlate with mean airway pressure increase, but with elevated leakage and airflow.…”

Comparison of high flow nasal cannula with noninvasive ventilation in chronic obstructive pulmonary disease patients with hypercapnia in preventing postextubation respiratory failure: A pilot randomized controlled trial

“…Thus, the role of HFNC in weaning COPD with hypercapnia is still unclear. Physiological studies reported that the high velocity of the gas could rinse the dead space of the upper airway and reduce carbon dioxide rebreathing (Biselli et al, 2018), to improve alveolar ventilation in COPD, which ultimately improves dyspnea and arterial blood gases (ABGs; Braunlich, Mauersberger, & Wirtz, 2018;McKinstry et al, 2018;Pisani et al, 2017). In the retrospective comparison of HFNC to NIV in postextubation patients by Yoo et al (2016), a subgroup analysis of partial pressure of PaCO 2 >45 mmHg patients showed that reintubation rate and ICU mortality did not differ significantly.…”

Non‐invasive ventilation or high‐flow oxygen therapy: When to choose one over the other?

“…Surprisingly, pCO 2 reduced to normal values, despite a decrease in minute volume suggesting it was most likely achieved by washout of the respiratory tract and functional reduction in dead space . In another physiological study of 36 stable COPD patients, the washout effect was correlated with increased leakage and airflow . A randomized cross‐over study (long‐term oxygen therapy versus HFOT at 30 L/min with room air) confirmed that HFOT reduced CO 2 rebreathing, and also showed that it increased tidal volume and improved breathing pattern with a reduction of respiratory rate without any change in minute ventilation .…”

“…Ventilatory support is the main physiological effect expected from treatment during a COPD exacerbation. HFOT contributes to reduced respiratory efforts by the PEEP effect and by the reduction of functional dead space through washout in the upper airways contributing to partial pressure of CO 2 (pCO 2 ) reduction . Increased tidal volume and decreased respiratory rate are other physiological effects of HFOT favouring a reduction in the work of breathing in acute hypercapnic respiratory failure …”