Impact of initial respiratory compliance in ventilated patients with acute respiratory distress syndrome related to COVID-19

Potential for the lung recruitment and the risk of lung overdistension during 21 days of mechanical ventilation in patients with COVID-19 after noninvasive ventilation failure: the COVID-VENT observational trial

Background

Data on the lung respiratory mechanics and gas exchange in the time course of COVID-19-associated respiratory failure is limited. This study aimed to explore respiratory mechanics and gas exchange, the lung recruitability and risk of overdistension during the time course of mechanical ventilation.

Methods

This was a prospective observational study in critically ill mechanically ventilated patients (n = 116) with COVID-19 admitted into Intensive Care Units of Sechenov University. The primary endpoints were: «optimum» positive end-expiratory pressure (PEEP) level balanced between the lowest driving pressure and the highest SpO₂ and number of patients with recruitable lung on Days 1 and 7 of mechanical ventilation. We measured driving pressure at different levels of PEEP (14, 12, 10 and 8 cmH₂O) with preset tidal volume, and with the increase of tidal volume by 100 ml and 200 ml at preset PEEP level, and calculated static respiratory system compliance (C_RS), PaO₂/FiO₂, alveolar dead space and ventilatory ratio on Days 1, 3, 5, 7, 10, 14 and 21.

Results

The «optimum» PEEP levels on Day 1 were 11.0 (10.0–12.8) cmH₂O and 10.0 (9.0–12.0) cmH₂O on Day 7. Positive response to recruitment was observed on Day 1 in 27.6% and on Day 7 in 9.2% of patients. PEEP increase from 10 to 14 cmH₂O and VT increase by 100 and 200 ml led to a significant decrease in C_RS from Day 1 to Day 14 (p < 0.05). Ventilatory ratio was 2.2 (1.7–2,7) in non-survivors and in 1.9 (1.6–2.6) survivors on Day 1 and decreased on Day 7 in survivors only (p < 0.01). PaO₂/FiO₂ was 105.5 (76.2–141.7) mmHg in non-survivors on Day 1 and 136.6 (106.7–160.8) in survivors (p = 0.002). In survivors, PaO₂/FiO₂ rose on Day 3 (p = 0.008) and then between Days 7 and 10 (p = 0.046).

Conclusion

Lung recruitability was low in COVID-19 and decreased during the course of the disease, but lung overdistension occurred at «intermediate» PEEP and VT levels. In survivors gas exchange improvements after Day 7 mismatched C_RS.

Trial registration

ClinicalTrials.gov, NCT04445961. Registered 24 June 2020—Retrospectively registered.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12871-022-01600-0.

Non-pharmacological treatments for COVID-19: current status and consensus

Purpose

COVID-19 is a disease caused by SARS-CoV-2 (coronavirus type 2 of the severe acute respiratory syndrome), isolated in China, in December 2019. The strategy currently used by physicians is to control disease and to treat symptoms, including non-pharmacological treatments, as there is still no specific treatment for COVID-19. Thus, the aim of this article is to carry out a systematic review about non-pharmacological treatments used for COVID-19, addressing current status and consensus found in the literature.

Methods

Three databases were consulted for evidence referring to the drugs indicated for COVID-19 (Cochrane Central, MEDLINE and Embase). The following terms and combinations were used: ((“2019-nCoV” OR 2019nCoV OR nCoV2019 OR “nCoV-2019” OR “COVID-19” OR COVID19 OR “HCoV-19” OR HCoV19 OR CoV OR “2019 novel*” OR Ncov OR “n-cov” OR “SARS-CoV-2” OR “SARSCoV-2” OR “SARSCoV2” OR “SARSCoV2” OR SARSCov19 OR “SARS-Cov19” OR “SARS-Cov-19”) OR “severe acute respiratory syndrome*” OR ((corona* OR corono*) AND (virus* OR viral* OR virinae*)) AND ((“lung injury”) OR (“ventilation use”) OR (“respiratory injuries” OR prone)) AND (treatment)) NOT Drugs NOT medicines NOT antivirals.

Results

A total of 28 articles were selected. These articles adopted one or more treatment methods for patients with severe cases of COVID-19, i.e., oxygen therapy, prone position, inhaled nitric oxide, intravenous infusion, passive immunotherapy, mesenchymal stem cells (MSC).

Conclusion

There is still no specific treatment approved for patients with COVID-19. The available evidence is not able yet to indicate the benefits or harms of non-pharmacological treatments, but some studies show that some treatments can play an important role in relation to COVID-19. The current consensus among researchers is that several studies using a randomized clinical trial should be carried out to provide evidence of safety and efficacy of the proposed treatments.

Impact of Airway Humidification Strategy in Mechanically Ventilated COVID-19 Patients

BACKGROUND

Humidification of inspiratory gases is mandatory in all mechanically ventilated patients in ICUs, either with heated humidifiers (HHs) or with heat and moisture exchangers (HMEs). In patients with COVID-19, the choice of the humidification device may have relevant impact on patients' management as demonstrated in recent studies. We reported data from 2 ICUs using either HME or HH.

METHODS

Data from patients with COVID-19 requiring invasive mechanical ventilation during the first wave in 2 ICUs in Québec City were reviewed. In one ICU, HMEs were used, whereas heated-wire HHs were used in the other ICU. We compared ventilator settings and arterial blood gases at day one after adjustment of ventilator settings. Episodes of endotracheal tube occlusions (ETOs) or subocclusions and a strategy to limit the risk of under-humidification were reported. On a bench test, we measured humidity with psychrometry with HH at different ambient temperature and evaluated the relation with heater plate temperature.

RESULTS

We reported data from 20 subjects positive for SARS-Cov-2, including 6 in the ICU using HME and 14 in the ICU using HH. In the HME group, P_aCO2 was higher (48 vs 42 mm Hg) despite higher minute ventilation (171 vs 145 mL/kg/min predicted body weight [PBW]). We also reported 3 ETOs occurring in the ICU using HH. The hygrometric bench study reported a strong correlation between heater plate temperatures of the HH and humidity delivered. After implementation of measures to avoid under-humidification, including heater plate temperature monitoring, no more ETOs occurred.

CONCLUSIONS

The choice of the humidification device used in subjects with COVID-19 had a relevant impact on ventilation efficiency (increased CO₂ removal with lower dead space) and on complications related to low humidity, including ETOs that may be present with heated-wire HHs when used with high ambient temperatures.

Positive end-expiratory pressure in COVID-19 acute respiratory distress syndrome: the heterogeneous effects

BACKGROUND

We hypothesized that as CARDS may present different pathophysiological features than classic ARDS, the application of high levels of end-expiratory pressure is questionable. Our first aim was to investigate the effects of 5-15 cmH2O of PEEP on partitioned respiratory mechanics, gas exchange and dead space; secondly, we investigated whether respiratory system compliance and severity of hypoxemia could affect the response to PEEP on partitioned respiratory mechanics, gas exchange and dead space, dividing the population according to the median value of respiratory system compliance and oxygenation. Thirdly, we explored the effects of an additional PEEP selected according to the Empirical PEEP-FiO2 table of the EPVent-2 study on partitioned respiratory mechanics and gas exchange in a subgroup of patients.

METHODS

Sixty-one paralyzed mechanically ventilated patients with a confirmed diagnosis of SARS-CoV-2 were enrolled (age 60 [54-67] years, PaO2/FiO2 113 [79-158] mmHg and PEEP 10 [10-10] cmH2O). Keeping constant tidal volume, respiratory rate and oxygen fraction, two PEEP levels (5 and 15 cmH2O) were selected. In a subgroup of patients an additional PEEP level was applied according to an Empirical PEEP-FiO2 table (empirical PEEP). At each PEEP level gas exchange, partitioned lung mechanics and hemodynamic were collected.

RESULTS

At 15 cmH2O of PEEP the lung elastance, lung stress and mechanical power were higher compared to 5 cmH2O. The PaO2/FiO2, arterial carbon dioxide and ventilatory ratio increased at 15 cmH2O of PEEP. The arterial-venous oxygen difference and central venous saturation were higher at 15 cmH2O of PEEP. Both the mechanics and gas exchange variables significantly increased although with high heterogeneity. By increasing the PEEP from 5 to 15 cmH2O, the changes in partitioned respiratory mechanics and mechanical power were not related to hypoxemia or respiratory compliance. The empirical PEEP was 18 ± 1 cmH2O. The empirical PEEP significantly increased the PaO2/FiO2 but also driving pressure, lung elastance, lung stress and mechanical power compared to 15 cmH2O of PEEP.

CONCLUSIONS

In COVID-19 ARDS during the early phase the effects of raising PEEP are highly variable and cannot easily be predicted by respiratory system characteristics, because of the heterogeneity of the disease.

Mechanical ventilation parameters in critically ill COVID-19 patients: a scoping review

BACKGROUND

The mortality of critically ill patients with COVID-19 is high, particularly among those receiving mechanical ventilation (MV). Despite the high number of patients treated worldwide, data on respiratory mechanics are currently scarce and the optimal setting of MV remains to be defined. This scoping review aims to provide an overview of available data about respiratory mechanics, gas exchange and MV settings in patients admitted to intensive care units (ICUs) for COVID-19-associated acute respiratory failure, and to identify knowledge gaps.

MAIN TEXT

PubMed, EMBASE, and MEDLINE databases were searched from inception to October 30, 2020 for studies providing at least one ventilatory parameter collected within 24 h from the ICU admission. The quality of the studies was independently assessed using the Newcastle-Ottawa Quality Assessment Form for Cohort Studies. A total of 26 studies were included for a total of 14,075 patients. At ICU admission, positive end expiratory pressure (PEEP) values ranged from 9 to 16.5 cm of water (cmH₂O), suggesting that high levels of PEEP were commonly used for setting MV for these patients. Patients with COVID-19 are severely hypoxemic at ICU admission and show a median ratio of partial pressure of arterial oxygen to fraction of inspired oxygen (PaO₂/FiO₂) ranging from 102 to 198 mmHg. Static respiratory system compliance (Crs) values at ICU admission were highly heterogenous, ranging between 24 and 49 ml/cmH₂O. Prone positioning and neuromuscular blocking agents were widely used, ranging from 17 to 81 and 22 to 88%, respectively; both rates were higher than previously reported in patients with "classical" acute respiratory distress syndrome (ARDS).

CONCLUSIONS

Available data show that, in mechanically ventilated patients with COVID-19, respiratory mechanics and MV settings within 24 h from ICU admission are heterogeneous but similar to those reported for "classical" ARDS. However, to date, complete data regarding mechanical properties of respiratory system, optimal setting of MV and the role of rescue treatments for refractory hypoxemia are still lacking in the medical literature.

Early management of critically ill patients with COVID-19

Coronavirus disease 2019 (COVID-19) is associated with a severe acute respiratory condition requiring respiratory support and mechanical ventilation. Based on the pathophysiology and clinical course of the disease, a therapeutic approach can be adapted. Three phases have been identified, in which different strategies are recommended in a stepwise invasiveness approach. In the second or acute phase, patients are frequently admitted to the ICU for severe pneumonia and hypoxemia with evidence of a proinflammatory and hypercoagulable state. This stage is an opportunity to intervene early in the disease. Medical strategies and mechanical ventilation should be individualized to improve outcomes.

CARDS vs ARDS – implications for respiratory support

Based on a handful of early reports and anecdotal experience, experts hypothesised that severe COVID-19 pneumonia was clinically different from the more classical presentation of the acute respiratory distress syndrome (ARDS), despite fulfilling the Berlin definition. The most striking difference noted was the dissociation of the severity of hypoxaemia and the compliance of the respiratory system (Crs). It was proposed that patients were presenting along a time-related spectrum with two distinct phenotypes at either end. Initially, type ‘L” is characterised by low elastance (high Crs), low lung weight, low right-to-left shunt, and low lung recruitment potential. With time, patients would eventually become type “H” with high elastance (low Crs), high lung weight (oedema), high right-to-left shunt with greater potential for lung recruitment and thus resemble classical ARDS. Subsequently, numerous studies have examined the mechanics and gas exchange of COVID-19 patients and have found no consistent relationships between hypoxaemia, recruitability and compliance. There was no convincing evidence found of a time-related spectrum of disease. In conclusion, despite significant variability, COVID-19 produces a clinical picture largely consistent with classical ARDS. Furthermore, the outcomes using traditional lung protective strategies have been acceptable and do not warrant change at this stage.

[Treatment recommendations for mechanical ventilation of COVID‑19 patients]

Hintergrund

Aufgrund der Neuartigkeit der COVID‑19-Erkrankung existieren keine evidenzbasierten Empfehlungen für die Beatmung dieser Patienten.

Fragestellung

Darstellung von Parametern, die eine individualisierte lungen- und diaphragmaprotektive Beatmung ermöglichen.

Material und Methode

Selektive Literaturrecherche und Diskussion von Expertenempfehlungen.

Ergebnisse

In der aktuellen Literatur wird der Unterschied des ARDS bei COVID‑19 zum klassischen ARDS beschrieben. Evidenzbasierte Empfehlungen zum Umgang mit dieser Diskrepanz gibt es nicht. In der Vergangenheit wurden bereits Parameter und Ansätze für eine personalisierte Beatmungsstrategie eingeführt und erprobt.

Schlussfolgerungen

Unter Verwendung der dargestellten Parameter ist es möglich, die Beatmung von COVID‑19-Patienten zu individualisieren, um so dem heterogenen klinischen Bild des COVID‑19-ARDS gerecht zu werden.

Respiratory physiology of COVID-19-induced respiratory failure compared to ARDS of other etiologies

BACKGROUND

Whether respiratory physiology of COVID-19-induced respiratory failure is different from acute respiratory distress syndrome (ARDS) of other etiologies is unclear. We conducted a single-center study to describe respiratory mechanics and response to positive end-expiratory pressure (PEEP) in COVID-19 ARDS and to compare COVID-19 patients to matched-control subjects with ARDS from other causes.

METHODS

Thirty consecutive COVID-19 patients admitted to an intensive care unit in Rome, Italy, and fulfilling moderate-to-severe ARDS criteria were enrolled within 24 h from endotracheal intubation. Gas exchange, respiratory mechanics, and ventilatory ratio were measured at PEEP of 15 and 5 cmH2O. A single-breath derecruitment maneuver was performed to assess recruitability. After 1:1 matching based on PaO2/FiO2, FiO2, PEEP, and tidal volume, COVID-19 patients were compared to subjects affected by ARDS of other etiologies who underwent the same procedures in a previous study.

RESULTS

Thirty COVID-19 patients were successfully matched with 30 ARDS from other etiologies. At low PEEP, median [25th-75th percentiles] PaO2/FiO2 in the two groups was 119 mmHg [101-142] and 116 mmHg [87-154]. Average compliance (41 ml/cmH2O [32-52] vs. 36 ml/cmH2O [27-42], p = 0.045) and ventilatory ratio (2.1 [1.7-2.3] vs. 1.6 [1.4-2.1], p = 0.032) were slightly higher in COVID-19 patients. Inter-individual variability (ratio of standard deviation to mean) of compliance was 36% in COVID-19 patients and 31% in other ARDS. In COVID-19 patients, PaO2/FiO2 was linearly correlated with respiratory system compliance (r = 0.52 p = 0.003). High PEEP improved PaO2/FiO2 in both cohorts, but more remarkably in COVID-19 patients (p = 0.005). Recruitability was not different between cohorts (p = 0.39) and was highly inter-individually variable (72% in COVID-19 patients and 64% in ARDS from other causes). In COVID-19 patients, recruitability was independent from oxygenation and respiratory mechanics changes due to PEEP.

CONCLUSIONS

Early after establishment of mechanical ventilation, COVID-19 patients follow ARDS physiology, with compliance reduction related to the degree of hypoxemia, and inter-individually variable respiratory mechanics and recruitability. Physiological differences between ARDS from COVID-19 and other causes appear small.