Effect of body position on the redistribution of regional lung aeration during invasive and non-invasive ventilation of COVID-19 patients.

Severe COVID-19-related acute respiratory distress syndrome (C-ARDS) requires mechanical ventilation. While this intervention is often performed in the prone position to improve oxygenation, the underlying mechanisms responsible for the improvement in respiratory function during invasive ventilation and awake prone positioning in C-ARDS have not yet been elucidated. In this prospective observational trial, we evaluated the respiratory function of C-ARDS patients while in the supine and prone positions during invasive (n = 13) or non-invasive ventilation (n = 15). The primary endpoint was the positional change in lung regional aeration, assessed with electrical impedance tomography. Secondary endpoints included parameters of ventilation and oxygenation, volumetric capnography, respiratory system mechanics and intrapulmonary shunt fraction. In comparison to the supine position, the prone position significantly increased ventilation distribution in dorsal lung zones for patients under invasive ventilation (53.3 ± 18.3% vs. 43.8 ± 12.3%, percentage of dorsal lung aeration ± standard deviation in prone and supine positions, respectively; p = 0.014); whereas, regional aeration in both positions did not change during non-invasive ventilation (36.4 ± 11.4% vs. 33.7 ± 10.1%; p = 0.43). Prone positioning significantly improved the oxygenation both during invasive and non-invasive ventilation. For invasively ventilated patients reduced intrapulmonary shunt fraction, ventilation dead space and respiratory resistance were observed in the prone position. Oxygenation is improved during non-invasive and invasive ventilation with prone positioning in patients with C-ARDS. Different mechanisms may underly this benefit during these two ventilation modalities, driven by improved distribution of lung regional aeration, intrapulmonary shunt fraction and ventilation-perfusion matching. However, the differences in the severity of C-ARDS may have biased the sensitivity of electrical impedance tomography when comparing positional changes between the protocol groups.Trial registration: ClinicalTrials.gov (NCT04359407) and Registered 24 April 2020, https://clinicaltrials.gov/ct2/show/NCT04359407 .

Hypophosphatemia on ICU Admission Is Associated with an Increased Length of Stay in the ICU and Time under Mechanical Ventilation.

Hypophosphatemia is frequently observed in the ICU and is associated with several impairments such as respiratory failure or infections. We hypothesized that hypophosphatemia on ICU admission is associated with a prolonged duration of mechanical ventilation and ICU length of stay (LOS), particularly in COVID-19 patients. This cross-sectional study analyzed data from 1226 patients hospitalized in the ICU of the Geneva University Hospitals from August 2020 to April 2021. Patients were categorized as having hypophosphatemia (phosphatemia ≤ 0.8 mmol/L) or non-hypophosphatemia (phosphatemia > 0.8 mmol/L) on ICU admission. Linear regressions were performed to investigate the association between hypophosphatemia on ICU admission and ICU LOS and duration of mechanical ventilation. Overall, 250 (20%) patients presented hypophosphatemia on ICU admission. In the univariable analysis, hypophosphatemic patients had longer ICU LOS than non-hypophosphatemic patients, 7.4 days (±10.4) versus 5.6 days (±8.3), (p < 0.01). Hypophosphatemia on ICU admission was associated with a prolonged duration of mechanical ventilation, 7.4 days (±11.2) versus 5.6 days (±8.9), (p < 0.01). These associations were confirmed in the multivariable analysis (p < 0.01). In the subgroup of COVID-19 patients, a significant association between hypophosphatemia and ICU LOS and duration of mechanical ventilation was also observed. In conclusion, hypophosphatemia on ICU admission is associated with a longer ICU LOS and time under mechanical ventilation, both in the general ICU population and in COVID-19 patients.