Effects of non-invasive respiratory supports on inspiratory effort in moderate-severe COVID-19 patients. A randomized physiological study

Abstract

Rationale and objective: Various forms of Non-invasive respiratory support (NRS) have been used during COVID-19, to treat Hypoxemic Acute Respiratory Failure (HARF), but it has been suggested that the occurrence of strenuous inspiratory efforts may cause Self Induced Lung Injury(P-SILI). The aim of this investigation was to record esophageal pressure, when starting NRS application, so as to better understand the potential risk of the patients in terms of P-SILI and ventilator induced lung injury (VILI).

Methods and measurements: 21 patients with early de-novo respiratory failure due to COVID-19, underwent three 30 min trials applied in random order: high-flow nasal cannula (HFNC), continuous positive airway pressure (CPAP), and non-invasive ventilation (NIV). After each trial, standard oxygen therapy was reinstituted using a Venturi mask (VM). 15 patients accepted a nasogastric tube placement. Esophageal Pressure (ΔPes) and dynamic transpulmonary driving pressure (ΔPLDyn), together with the breathing pattern using a bioelectrical impedance monitor were recorded. Arterial blood gases were collected in all patients.

Main results: No statistically significant differences in breathing pattern and PaCO₂ were found. PaO₂/FiO₂ ratio improved significantly during NIV and CPAP vs VM. NIV was the only NRS to reduce significantly ΔPes vs. VM (-10,2 ±5 cmH20 vs -3,9 ±3,4). No differences were found in ΔPLDyn between NRS (10,2±5; 9,9±3,8; 7,6±4,3; 8,8±3,6 during VM, HFNC, CPAP and NIV respectively). Minute ventilation (Ve) was directly dependent on the patient's inspiratory effort, irrespective of the NRS applied. 14% of patients were intubated, none of them showing a reduction in ΔPes during NRS.

Conclusions: In the early phase of HARF due to COVID-19, the inspiratory effort may not be markedly elevated and the application of NIV and CPAP ameliorates oxygenation vs VM. NIV was superior in reducing ΔPes, maintaining ΔPLDyn within a range of potential safety.

Keywords: COVID 19; Hypoxemic acute respiratory failure; Non invasive respiratory supports.

Fig. 1

Flowchart for patients. (ER=Emergency Room; n.= number; NRS= non invasive respiratory support).

Fig. 2

Effects of different non-invasive respiratory supports on breathing pattern, ventilation, and comfort; (twenty-one patient). (HFNC= high flow nasal cannula; CPAP= continuous positive airway pressure; NIV= non-invasive mechanical ventilation; RR =Respiratory Rate; Ve= minute ventilation. VTi = inspiratory tidal volume; PBW=Predicted body weight; VAS= Visual Analogue Score).

Fig. 3

Effects of different non-invasive respiratory supports on gas exchange and respiratory mechanics (fifteen patients). (HFNC= high flow nasal cannula; CPAP= continuous positive airway pressure; NIV= non-invasive mechanical ventilation; PaFiO₂ = PaO₂/FiO₂ ratio; ΔPes = tidal change in oesophageal pressure, ΔPL_Dyn = Dynamic tidal change in transpulmonary pressure).

Fig. 4

Upper part: correlation analysis between minute ventilation and ΔPes (inspiratory effort). Lower pan: correlation analysis between minute ventilation and ΔPL_Cym. (HFNC; High flow nasal cannula, CPAP; continuous positive airway pressure, NIV; non invasive mechanical ventilation. Ve= minute ventilation, ΔPes = tidal change in oesophageal pressure. ΔPL_Dym = Dynamic tidal change in transpulmonary pressure).