key: cord-0892756-y4olqb52
authors: Chiappero, Chiara; Misseri, Giovanni; Mattei, Alessio; Ippolito, Mariachiara; Albera, Carlo; Pivetta, Emanuele; Cortegiani, Andrea; Gregoretti, Cesare
title: EFFECTIVENESS AND SAFETY OF A NEW HELMET CPAP CONFIGURATION ALLOWING TIDAL VOLUME MONITORING IN PATIENTS WITH COVID-19
date: 2021-07-09
journal: Pulmonology
DOI: 10.1016/j.pulmoe.2021.06.012
sha: de2ba955298eab29a431e48cf60760814d755537
doc_id: 892756
cord_uid: y4olqb52

Background: High generated tidal volumes (V(t)) have been correlated with higher risk of self-induced lung injury and worse clinical outcome. This study aimed to evaluate the effectiveness and safety of a new helmet continuous positive airway pressure delivered (h-CPAP) configuration allowing V(t) monitoring in patients affected by COVID-19. Methods: This prospective observational study was performed in the respiratory intermediate care unit of University Hospital in Turin, Italy, between March 24th, and June 15th, 2020. Included patients were treated with CPAP via a single-limb intentional leak configuration by a turbine-driven ventilator, provided with a dedicated patch. Effectiveness and safety of the configuration and healthcare workers safety were the outcomes of the study. Main findings: Thirty-five patients were included in this study. Median age was 67 years (IQR 57-76 years), and 30 patients (85.7%) were men. Median value of overall leaks (intentional plus unintentional) was 68 L/min (IQR 63-75). Reliability of V(t) measurements was 100%. An out of scale of V(t) (above 50% compared to the previous values) was never recorded. Six patients (17.1%) needed more than two helmet replacements, due to leak test >10 l/min. Arm oedema and skin breakdowns were reported in sixteen (45.7%) and seven (20%) patients respectively. Among the 63 healthcare workers involved in the care of COVID-19 patients during the study only one was positive at RT-PCR nasopharyngeal swab testing. Conclusions: The use of h-CPAP for treating COVID-19 in this configuration allowed for reliable V(t) monitoring. Further studies evaluating this configuration in larger patients’ cohorts are needed.

As of March 2021, almost 117 million confirmed cases of coronavirus diseases 110 have been reported, including more than 2.5 million deaths 1 . SARS-111

CoV-2 is responsible for acute respiratory failure (ARF) in nearly 20% of cases 2 , 112 often leading to endotracheal intubation and admission to intensive care units (ICUs) . The use of NRS 5,7 may pose an additional risk of infection for healthcare 119 workers. Helmet CPAP (h-CPAP) 8-14 may reduce aerosolization and provide better 120 comfort for patients [8] [9] [10] 15 , in comparison with face masks. In patients receiving NRS, 121 high tidal volumes have been correlated with large diaphragmatic swings, higher risk 122 of self-induced lung injury 16 , and worse clinical outcomes 17 . Thus, the measurement 123 of tidal volume (V t ) may be clinically important to minimize the risk of self-induced 124 lung injury and help clinicians recognize a patient's respiratory drive or respiratory 125 compliance worsening. So far, h-CPAP did not allow measurement of V t due to its 126 intrinsic mechanical properties 18, 19 . Recently, a new configuration of h-CPAP 127 delivered using a turbine driven ventilator with a single-limb intentional leak 128 configuration has been described 18 . This configuration, provided with dedicated 129 software, has allowed for an accurate estimation of V t , intentional and unintentional 130 leaks 18 . This study aimed to clinically evaluate the effectiveness and the safety of 131 this h-CPAP configuration 18 allowing V t monitoring in patients with COVID-19 related 132 ARF in a RICU setting. 133

The study was conducted after the approval of the Ethics Committee of the 136 study center (CORACLE Registry -"Città della Salute e della Scienza di Torino" 137 University Hospital, ID number 0031285, date 24 March 2020), in accordance with 138 the Helsinki Declaration and written informed consent were collected from all patients 139 or legal representatives. We adhered to the STROBE statement (Strengthening the 140 reporting of observational studies in Epidemiology) (see the STROBE checklist in the 141

This prospective single-centre observational study was performed in the RICU 144 of "Città della Salute e della Scienza di Torino" University Hospital, Turin, Italy, 145 between March 24 th , and June 15 th , 2020. 146

All the consecutive patients admitted to the study center were assessed for 147 eligibility. Inclusion criteria were: age  18 year-old, clinical diagnosis of acute 148 respiratory failure caused by SARS-CoV-2 (confirmed by RT-PCR on rhino-149 pharyngeal swab), PaO 2 :FiO 2 ratio <250 mmHg during an oxygen supplementation 150 trial of at least one hour with a Venturi mask (FiO2>40%) or non-rebreathing mask, 151 with respiratory distress (respiratory rate (RR) >25 breaths/minute, moderate 152 dyspnoea as measured by the BORG [20]) and evidence of bilateral infiltrates at 153 chest X-ray and/or computed tomography (CT). 154

Patients were excluded if they met one or more of the following criteria: need 155 for intermittent positive airway pressure ventilation (NIPPV) for hypercapnic 156 respiratory failure (PaCO 2 >45 mmHg), a former trial of h-CPAP or helmet NIPPV > 157 24 hours in the emergency department or in other settings before RICU admission. 158

Included patients were treated in CPAP mode via a single-limb intentional leak 161 configuration, by a turbine-driven ventilator (Philips V60 or TROLOGY EVO 162

Respironics Ventilator) provided with a dedicated patch. Detailed description of this 163 configuration has been previously published 18, 21 . In this configuration, the helmet 164 expiratory port was capped with a connector having a 6 mm internal diameter hole to 165 provide the intentional leak as previously described 18 (Fig. 1) Intersurgical, Mirandola, Italy) were secured by padded armpit braces and size was 171 chosen according to patient's neck diameter. When available, helmets equipped with 172 an inflatable neck cushion were used to limit the unintentional leak 12 . The helmet 173 ports were provided with High-Efficiency Particulate Air (HEPA) filters to limit 174

Patients included in the study were treated with continuous h-CPAP (24h/24h) 176 for at least 48-72 hours. When tolerated, prone positioning was kept for at least 2 177 hours three times per day 22 . Positive pressure was chosen between 8 and 15 178 cmH2O and FiO 2 set at the lowest possible value to achieve oxygen saturation 179

Patients on h-CPAP who did not show signs of respiratory distress (e.g. RR 181

<25 or use of accessory muscles) and were able to maintain a SpO 2 >94% with a 182

FiO 2 <50% and a PEEP<10 cmH2O underwent a weaning trial in HFNT or Venturi 183 mask. Criteria to consider a patient as successfully weaned from h-CPAP was ability 184 to maintain a PaO 2 :FiO 2 ratio >250 on Venturi mask with a FiO 2 <40% for at least 24 185

A "leak test" (<10 l/min threshold) was periodically performed by closing with a 187 finger (for 5 to 10 seconds) the 6 mm hole of the expiratory port. As the ventilator 188 measured the overall leaks, unintentional leaks coming from the helmet collar were 189 evaluated when intentional leaks (coming from the expiratory port) were excluded 190 after expiratory port closure. At the end of each test, overall leaks were recorded. Patient's treatment safety was evaluated as: 208 rate of adverse events due the helmet (i.e. skin breakdown) 26-28 209 -rate of suffocation or death due to the interface 29 210

Healthcare workers safety was evaluated as: 211 -SARS-CoV-2 infection rate among RICU staff (symptomatic or asymptomatic 212 infection confirmed by RT-PCR test on rhino-pharyngeal swab) during the 213 study period. 214

Secondary endpoints of the study included: 215 -improvement in arterial blood gases (PaO2, PaCO2, PaO2:FiO2); 216 -need for sedation due the interface intolerance (to reach a target RASS 0/-1) 217

-rate of failure (as defined as need to switch to a facial mask) due the interface 218 intolerance 219 -respiratory rate and dyspnoea (according to Borg scale); 220 -rate of intubation not correlated to the interface setup (detailed criteria for 221 intubation are described in Supplementary material B) 222 -death during RICU stay (not correlated to the interface setup). 223 -other adverse events not correlated to the interface setup (e.g. cardiovascular 224 events, pulmonary embolism, acute kidney injury etc.) 225

Arterial blood gas analyses were recorded at admission before starting h-227 CPAP (T0), within 6 hours (T6), and on day 1 (T24) after h-CPAP initiation. Vital 228 parameters (systemic blood pressure -SBP, heart rate -HR, respiratory rate -RR, 229 tidal volume -V t ) were monitored continuously and recorded together with the 230 assessment of the dyspnoea score, as measured by the BORG 20 scale, three times 231 a day until the start of the weaning, then once a day. 232

Due to the nature of the study, a convenience sample of consecutive patients 233 was included, and no a priori sample size calculation was done. 234

Continuous variables were expressed as median values with interquartile 235 range (IQR), and categorical variables were expressed as proportions. Comparisons 236 between groups were performed for continuous variables using the Wilcoxon rank-237 sum test. Variance analysis (ANOVA) test was used to compare results of repeated 238 measures (T0, T6, T24). Categorical variables were examined using the Fisher's 239 exact test. All statistical analyses were performed using STATA 13.1 (StataCorp, 240

College Station, Tx, USA). 241

Seventy-one patients were admitted to the study centre during the period of 245 study. A total of thirty-five patients (49%) were eligible and all were included in this 246

Baseline characteristics and blood gas analysis of the included patients at 248 admission are showed in Table 1 Reliability of V t measurements was 100%. An out of scale of V t (above 50% 257 compared to the previous values) was never recorded in any patient at any time- reported in Table C .2, Supplementary material C. Table 3 shows respiratory 280 parameters at admission in RICU (T0), after 6 hours (T6), and after 24 hours (T24) 281 since the start of helmet CPAP. Respiratory parameters at the start and at the end of 282 helmet CPAP weaning are shown in Table C .3, Supplementary material C. Our data showed the effectiveness and safety of h-CPAP for patients with 297 COVID-19 related ARF in a RICU setting, using a high-performance turbine-driven 298 ventilator in a single-limb intentional leak new configuration allowing V t monitoring. 299

This is the first clinical study evaluating this new h-CPAP configuration 18 . 300

The measurement of V t was accurate throughout the study period, and no 301 major flaws concerning unintentional leak affected estimates. Accurate V t monitoring 302

is clinically important to minimize the risk of Self-Inflicted Lung Injury (SILI) avoiding 303 the generation of high V t , while limiting unintentional leaks. The helmet may provide 304 better tolerability and fewer unintentional leaks 11,30 than mask interfaces. Indeed, in 305 our study, side effects were mild and did not cause interruption of CPAP treatment in 306 any patient. 307

Median total unintentional and intentional leaks were measured as 68 l/min 308 (IQR 63-75). In a preliminary bench study evaluating this configuration, 18 the amount 309 of only intentional leaks was 43.6 l/min at 10 cmH 2 O and 48.6 l/min at 12 cmH 2 O 310 using a ID 5.5 mm connector. We can speculate that the use of a larger I.D (6 mm) 311

could have led to this result. In six patients (17.1%), more than two replacements of 312 the interface every three hours were needed, due to a "positive leak test" (>10 l/min). 313

Real-time leaks monitoring allowed quick identification of helmet displacements and 314 subsequent repositioning. 315

Although suggested by other authors 31 , active humidification was not used in 316 this study and HEPA filters were positioned on the two helmet ports, limiting the risk 317 of infection related to condensation removal procedures. Mucus plugging never 318 occurred. As turbine-driven ventilators are fed by room air instead of high-pressure 319 dry air, we can speculate that a better natural airway humidification was obtained in 320 the proposed configuration. 321

The ATS / ERS guidelines in 2017 stressed that every trial on the use of NIV 322 must be managed by a team of experts and patients should be closely monitored, in 323 order to avoid any delay in intubation, also in consideration of the increased risk of 324 Our study has several limitations. Firstly, the study did not include a control 336 group and we did not compare our ventilator configuration with others. However, to 337 the best of our knowledge, there are no other commercially available TDVs 338 configurations able to estimate V t in a reliable way. Secondly, although different tools 339 may be used to assess V t non-invasively during h-CPAP, these are not clinically 340 applicable on a long term basis 41 . Finally, our study design was intended as a 341 preliminary evaluation of the effectiveness and safety of the new h-CPAP 342 configuration in a clinical setting. Thus, speculations on the overall efficacy of h-343 CPAP in COVID-19 was outside its scope. 344

The use of h-CPAP for treating COVID-19 related ARF using high-346 performance turbine-driven ventilators in a single-limb intentional leak configuration 347 allowing V t monitoring may be reliable, effective, and safe for both patients and 

Characteristics of and Important Lessons from the 356

COVID-19) Outbreak in China: Summary of a Report of 357 72314 Cases from the Chinese Center for Disease Control and Prevention

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