Treating hypoxemic patients with SARS-COV-2 pneumonia: Back to applied physiology

Temporal Changes in the Oxyhemoglobin Dissociation Curve of Critically Ill COVID-19 Patients

Critical COVID-19 is a life-threatening disease characterized by severe hypoxemia with complex pathophysiological mechanisms that are not yet completely understood. A pathological shift in the oxyhemoglobin curve (ODC) was previously described through the analysis of p50, intended as the oxygen tension at which hemoglobin is saturated by oxygen at 50%. The aim of this study was to analyze Hb-O₂ affinity features over time in a cohort of critically ill COVID-19 patients, through the analysis of ODC p50 behavior. A retrospective analysis was performed; through multiple arterial blood gas (ABG) analyses, each p50 was calculated and normalized according to PaCO₂, pH and temperature; patients' p50 evolution over time was reported, comparing the first 3 days (early p50s) with the last 3 days (late p50s) of ICU stay. A total of 3514 ABG analyses of 32 consecutive patients were analyzed. The majority of patients presented a left shift over time (p = 0.03). A difference between early p50s and late p50s was found (20.63 ± 2.1 vs. 18.68 ± 3.3 mmHg, p = 0.03); median p50 of deceased patients showed more right shifts than those of alive patients (24.1 vs. 18.45 mmHg, p = 0.01). One-way ANOVA revealed a p50 variance greater in the early p50s (σ² = 8.6) than in the late p50s (σ² = 3.84), associated with a reduction over time (p < 0.001). Comparing the Hb-O₂ affinity in critically ill COVID-19 patients between ICU admission and ICU discharge, a temporal shift in the ODC was observed.

Admission criteria in critically ill COVID-19 patients: A physiology-based approach

Introduction

The COVID-19 pandemic required careful management of intensive care unit (ICU) admissions, to reduce ICU overload while facing limitations in resources. We implemented a standardized, physiology-based, ICU admission criteria and analyzed the mortality rate of patients refused from the ICU.

Materials and methods

In this retrospective observational study, COVID-19 patients proposed for ICU admission were consecutively analyzed; Do-Not-Resuscitate patients were excluded. Patients presenting an oxygen peripheral saturation (SpO₂) lower than 85% and/or dyspnea and/or mental confusion resulted eligible for ICU admission; patients not presenting these criteria remained in the ward with an intensive monitoring protocol. Primary outcome was both groups’ survival rate. Secondary outcome was a sub analysis correlating SpO₂ cutoff with ICU admission.

Results

From March 2020 to January 2021, 1623 patients were admitted to our Center; 208 DNR patients were excluded; 97 patients were evaluated. The ICU-admitted group (n = 63) mortality rate resulted 15.9% at 28 days and 27% at 40 days; the ICU-refused group (n = 34) mortality rate resulted 0% at both intervals (p < 0.001). With a SpO₂ cut-off of 85%, a significant correlation was found (p = 0.009), but with a 92% a cut-off there was no correlation with ICU admission (p = 0.26). A similar correlation was also found with dyspnea (p = 0.0002).

Conclusion

In COVID-19 patients, standardized ICU admission criteria appeared to safely reduce ICU overload. In the absence of dyspnea and/or confusion, a SpO₂ cutoff up to 85% for ICU admission was not burdened by negative outcomes. In a pandemic context, the SpO₂ cutoff of 92%, as a threshold for ICU admission, needs critical re-evaluation.

Standardizing PaO2 for PaCO2 in P/F ratio predicts in-hospital mortality in acute respiratory failure due to Covid-19: A pilot prospective study

INTRODUCTION

Up to fifteen percent of patients with novel pandemic coronavirus disease (Covid-19) have acute respiratory failure (ARF). Ratio between arterial partial pressure of oxygen (PaO2) and fraction of inspired oxygen (FiO2), P/F, is currently used as a marker of ARF severity in Covid-19. P/F does not reflect the respiratory efforts made by patients to maintain arterial blood oxygenation, such as tachypnea and hyperpnea, leading to hypocapnia. Standard PaO2, the value of PaO2 adjusted for arterial partial pressure of carbon dioxide (PaCO2) of the subject, better reflects the pathophysiology of hypoxemic ARF. We hypothesized that the ratio between standard PaO2 over FiO2 (STP/F) better predicts Covid-19 ARF severity compared to P/F.

METHODS

Aim of this pilot prospectic observational study was to observe differences between STP/F and P/F in predicting outcome failure, defined as need of invasive mechanical ventilation and/or deaths in Covid-19 ARF. Accuracy was calculated using Receiver Operating Characteristics (ROC) analysis and areas under the ROC curve (AUROC) were compared.

RESULTS

349 consecutive subjects admitted to our respiratory wards due to Covid-19 ARF were enrolled. STP/F was accurate to predict mortality and superior to P/F with, respectively, AUROC 0.710 versus 0.688, p = 0.012.Both STP/F and PF were accurate to predict outcome failure (AUROC respectively of 0.747 and 0.742, p = 0.590).

DISCUSSION

This is the first study assessing the role of STP/F in describing severity of ARF in Covid-19. According to results, STP/F is accurate and superior to P/F in predicting in-hospital mortality.

Low PEEP Mechanical Ventilation and PaO2/FiO2 Ratio Evolution in COVID-19 Patients

Invasive mechanical ventilation (IMV) is the standard treatment in critically ill COVID-19 patients with acute severe respiratory distress syndrome (ARDS). When IMV setting is extremely aggressive, especially through the application of high positive-end-expiratory respiration (PEEP) values, lung damage can occur. Until today, in COVID-19 patients, two types of ARDS were identified (L- and H-type); for the L-type, a lower PEEP strategy was supposed to be preferred, but data are still missing. The aim of this study was to evaluate if a clinical management with lower PEEP values in critically ill L-type COVID-19 patients was safe and efficient in comparison to usual standard of care. A retrospective analysis was conducted on consecutive patients with COVID-19 ARDS admitted to the ICU and treated with IMV. Patients were treated with a lower PEEP strategy adapted to BMI: PEEP 10 cmH₂O if BMI < 30 kg m⁻², PEEP 12 cmH₂O if BMI 30–50 kg m⁻², PEEP 15 cmH₂O if BMI > 50 kg m⁻². Primary endpoint was the PaO₂/FiO₂ ratio evolution during the first 3 IMV days; secondary endpoints were to analyze ICU length of stay (LOS) and IMV length. From March 2 to January 15, 2021, 79 patients underwent IMV. Average applied PEEP was 11 ± 2.9 cmH₂O for BMI < 30 kg m⁻² and 16 ± 3.18 cmH₂O for BMI > 30 kg m⁻². During the first 24 h of IMV, patients’ PaO₂/FiO₂ ratio presented an improvement (p<0.001; CI 99%) that continued daily up to 72 h (p<0.001; CI 99%). Median ICU LOS was 15 days (10–28); median duration of IMV was 12 days (8–26). The ICU mortality rate was 31.6%. Lower PEEP strategy treatment in L-type COVID-19 ARDS resulted in a PaO₂/FiO₂ ratio persistent daily improvement during the first 72 h of IMV. A lower PEEP strategy could be beneficial in the first phase of ARDS in critically ill COVID-19 patients.

Rationale for ozone-therapy as an adjuvant therapy in COVID-19: a narrative review

Coronavirus disease 2019 (COVID-19) is the respiratory disease caused by the novel severe acute respiratory syndrome-coronavirus-2 and is characterized by clinical manifestations ranging from mild, flu-like symptoms to severe respiratory insufficiency and multi-organ failure. Patients with more severe symptoms may require intensive care treatments and face a high mortality risk. Also, thrombotic complications such as pulmonary embolisms and disseminated intravascular coagulation are frequent in these patients. Indeed, COVID-19 is characterized by an abnormal inflammatory response resembling a cytokine storm, which is associated to endothelial dysfunction and microvascular complications. To date, no specific treatments are available for COVID-19 and its life-threatening complication. Immunomodulatory drugs, such as hydroxychloroquine and interleukin-6 inhibitors, as well as antithrombotic drugs such as heparin and low molecular weight heparin, are currently being administered with some benefit. Ozone therapy consists in the administration of a mixture of ozone and oxygen, called medical ozone, which has been used for over a century as an unconventional medicine practice for several diseases. Medical ozone rationale in COVID-19 is the possibility of contrasting endothelial dysfunction, modulating the immune response and acting as a virustatic agent. Thus, medical ozone could help to decrease lung inflammation, slow down viral growth, regulate lung circulation and oxygenation and prevent microvascular thrombosis. Ozone-therapy could be considered a feasible, cost-effective and easy to administer adjuvant therapy while waiting for the synthesis of a therapy or the development of the vaccine.