A Pilot Study on Electrical Impedance Tomography During CPAP Trial in Patients With Severe Acute Respiratory Syndrome Coronavirus 2 Pneumonia: The Bright Side of Non-invasive Ventilation

Abstract

Background: Different severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pneumonia phenotypes were described that match with different lung compliance and level of oxygenation, thus requiring a personalized ventilator setting. The burden of so many patients and the lack of intensive care unit (ICU) beds often force physicians to choose non-invasive ventilation (NIV) as the first approach, even if no consent has still been reached to discriminate whether it is safer to choose straightforward intubation, paralysis, and protective ventilation. Under such conditions, electrical impedance tomography (EIT), a non-invasive bedside tool to monitor lung ventilation and perfusion defects, could be useful to assess the response of patients to NIV and choose rapidly the right ventilatory strategy.Objective: The rationale behind this study is that derecruitment is a more efficient measure of positive end expiratory pressure (PEEP)-dependency of patients than recruitment. We hypothesized that patients who derecruit significantly when PEEP is reduced are the ones that do not need early intubation while small end-expiratory lung volume (ΔEELV) variations after a single step of PEEP de-escalation could be predictive of NIV failure.Materials and Methods: Consecutive patients admitted to ICU with confirmed SARS-CoV-2 pneumonia ventilated in NIV were enrolled. Exclusion criteria were former intubation or NIV lasting > 72 h. A trial of continuos positive airway pressure (CPAP) 12 was applied in every patient for at least 15 min, followed by the second period of CPAP 6, either in the supine or prone position. Besides standard monitoring, ventilation of patients was assessed by EIT, and end-expiratory lung impedance (ΔEELI) (%) was calculated as the difference in EELI between CPAP12 and CPAP6. Tidal volume (Vt), Ve, respiratory rate (RR), and FiO2 were recorded, and ABGs were measured. Data were analyzed offline using the dedicated software. The decision to intubate or continue NIV was in charge of treating physicians, independently from study results. Outcomes of patients in terms of intubation rate and ICU mortality were recorded.Results: We enrolled 10 male patients, with a mean age of 67 years. Six patients (60%) were successfully treated by NIV until ICU discharge (Group S), and four patients failed NIV and were intubated and switched to MV (Group F). All these patients died in ICU. During the supine CPAP decremental trial, all patients experienced an increase in RR and Ve. ΔEELI was < 40% in Group F and > 50% in Group S. In the prone trial, ΔEELI was > 50% in all patients, while RR decreased in Group S and remained unchanged in Group F.Conclusion: ΔEELI < 40% after a single PEEP de-escalation step in supine position seems to be a good predictor of poor recruitment and CPAP failure.

Proning Responder or Not? This Is the Question*

“…SARS-CoV-2 pneumonia outbreak lead rapidly to the evidence that PP could be beneficial in many of these patients, and not only in the intubated ones, so that a new challenge arose, made compelling by the enormous amount of patients requiring hospital admission, that is to persuade both intensivists and nonintensivists to prone their patients inside and outside the ICUs. Actually, a huge amount of literature is being published on PP in awake COVID patients, showing overall encouraging results ( 9 , 10 ), while unexpectedly, less trials focuses on intubated patients, probably because they are equated to “classical” ARDS ones ( 11 ).…”

Expert opinion document: “Electrical impedance tomography: applications from the intensive care unit and beyond”

“…In ARDS patients treated with pressure support ventilation, Mauri et al used EIT to demonstrate a more homogenous distribution of ventilation when the pressure support level was titrated to a physiologic range of P 0.1 [ 21 ]. EIT can also be used to assess the clinical impact of respiratory support with high flow nasal cannula [ 22 ] and identify patients at risk for failure during support with non-invasive ventilation [ 23 ].…”

“…Indeed, duration of NIV use [ 47 , 48 ] and location of application [ 48 ] have been associated with hospital mortality in COVID-19 patients intubated after NIV failure. EIT has been proposed as a tool to assess the response to continuous positive airway pressure (CPAP) and recognize patients at risk for CPAP failure [ 23 ]. In a series of 10 patients admitted to the ICU for COVID-19 pneumonia and supported with CPAP, Rauseo et al performed an EIT-guided decremental PEEP trial from 12 cmH 2 O to 6 cmH 2 O and found that a reduction of EELI smaller than 40% after PEEP de-escalation predicted CPAP failure [ 23 ].…”

“…A lung protective strategy, either during invasive and noninvasive ventilation, should require real-time monitoring of regional lung ventilation to determine the distribution of lung ventilation such as hyperventilation. During the height of the COVID-19 pandemic, Rauseo et al [ 23 ] demonstrated that the number of patients with respiratory failure far exceeded the availability of intensive care unit beds, often prompting physicians to choose non-invasive ventilation as initial therapy. Under such conditions, EIT was identified as a helpful tool to assess the response of patients to NIV and rapidly identify an optimal ventilatory strategy.…”

Imaging the acute respiratory distress syndrome: past, present and future

“…However, the amount of alveolar collapse was variable across COVID-19 studies, in relation to varying ventilatory management, patient morphometry (presence of obesity) and timing of EIT measurements [ 67 ]. Finally, EIT and LUS allowed the demonstration that awake prone positioning induced lung reaeration of dorsolateral lung regions, in conjunction with changes in positive pressure levels, with potentially important effects on patient outcomes [ 68 , 69 ].…”