A prospective multicentre observational study to quantify nocturnal light exposure in intensive care

Background

Disrupted circadian rhythms can have a major effect on human physiology and healthcare outcomes, with proven increases in ICU morbidity, mortality and length of stay.

Methods

We performed a multicentre observational study to study the nocturnal lux exposure of patients in 3 intensive care units.

Results

The median light intensity recorded was 1 lux over the 6-hour recording period; however, this is deceptive as it hides short periods of high lux. When looked at in shorter time segments of 30 minutes, there were significant periods of lux higher than a crude median, especially in higher acuity patients. There was a positive correlation between acuity (as estimated by SOFA score) and maximum lux (R = 0.479, p = .0001), median lux (R = 0.35, p = .006) and cumulative lux (R = 0.55, p = .000001). There was no relationship between neighbouring patient acuity and lux.

Conclusions

Clinicians should practice vigilance at night to provide optimal environmental conditions for patients to minimise potential harm.

Body mass index and clinical outcome of severe COVID-19 patients with acute hypoxic respiratory failure: Unravelling the “obesity paradox” phenomenon

Background and aims

Although obesity have been generally shown to be an independent risk factor for poor outcomes in COVID-19 infection, some studies demonstrate a paradoxical protective effect (“obesity paradox”). This study examines the influence of obesity categories on clinical outcomes of severe COVID-19 patients admitted to an intensive care unit with acute hypoxic respiratory failure requiring either non-invasive or invasive mechanical ventilation.

Methods

This is a single centre, retrospective study of consecutive COVID-19 patients admitted to the intensive care unit between 03/2020 to 03/2021. Patients were grouped according to the NICE Body Mass Index (BMI) category. Admission variables including age, sex, comorbidities, and ICU severity indices (APACHE-II, SOFA and PaO2/FiO2) were collected. Data were compared between BMI groups for outcomes such as need for invasive mechanical ventilation (IMV), renal replacement therapy (RRT) and 28-day and overall hospital mortality.

Results

340 patients were identified and of those 333 patients had their BMI documented. Just over half of patients (53%) had obesity. Those with extreme obesity (obesity groups II and III) were younger with fewer comorbidities, but were more hypoxaemic at presentation, than the healthy BMI group. Although non-significant, obesity groups II and III paradoxically showed a lower in-hospital mortality than the healthy weight group. However, adjusted (age, sex, APACHE-II and CCI) competing risk regression analysis showed three-times higher mortality in obese category I (sub-distribution hazard ratio = 3.32 (95% CI 1.30–8.46), p = 0.01) and a trend to higher mortality across all obesity groups compared to the healthy weight group.

Conclusions

In this cohort, those with obesity were at higher risk of mortality after adjustment for confounders. We did not identify an “obesity paradox” in this cohort. The obesity paradox may be explained by confounding factors such as younger age, fewer comorbidities, and less severe organ failures. The impact of obesity on indicators of morbidity including likelihood of requirement for organ support measures was not conclusively demonstrated and requires further scrutiny.

Dynamic blood oxygen indices in mechanically ventilated COVID-19 patients with acute hypoxic respiratory failure: A cohort study

Background

Acute hypoxic respiratory failure (AHRF) is a hallmark of severe COVID-19 pneumonia and often requires supplementary oxygen therapy. Critically ill COVID-19 patients may require invasive mechanical ventilation, which carries significant morbidity and mortality. Understanding of the relationship between dynamic changes in blood oxygen indices and clinical variables is lacking. We evaluated the changes in blood oxygen indices–PaO2, PaO2/FiO2 ratio, oxygen content (CaO2) and oxygen extraction ratio (O2ER) in COVID-19 patients through the first 30-days of intensive care unit admission and explored relationships with clinical outcomes.

Methods and findings

We performed a retrospective observational cohort study of all adult COVID-19 patients in a single institution requiring invasive mechanical ventilation between March 2020 and March 2021. We collected baseline characteristics, clinical outcomes and blood oxygen indices. 36,383 blood gas data points were analysed from 184 patients over 30-days. Median participant age was 59.5 (IQR 51.0, 67.0), BMI 30.0 (IQR 25.2, 35.5) and the majority were men (62.5%) of white ethnicity (70.1%). Median duration of mechanical ventilation was 15-days (IQR 8, 25). Hospital survival at 30-days was 72.3%. Non-survivors exhibited significantly lower PaO2 throughout intensive care unit admission: day one to day 30 averaged mean difference -0.52 kPa (95% CI: -0.59 to -0.46, p<0.01). Non-survivors exhibited a significantly lower PaO2/FiO2 ratio with an increased separation over time: day one to day 30 averaged mean difference -5.64 (95% CI: -5.85 to -5.43, p<0.01). While all patients had sub-physiological CaO2, non-survivors exhibited significantly higher values. Non-survivors also exhibited significantly lower oxygen extraction ratio with an averaged mean difference of -0.08 (95% CI: -0.09 to -0.07, p<0.01) across day one to day 30.

Conclusions

As a novel cause of acute hypoxic respiratory failure, COVID-19 offers a unique opportunity to study a homogenous cohort of patients with hypoxaemia. In mechanically ventilated adult COVID-19 patients, blood oxygen indices are abnormal with substantial divergence in PaO2/FiO2 ratio and oxygen extraction ratio between survivors and non-survivors. Despite having higher CaO2 values, non-survivors appear to extract less oxygen implying impaired oxygen utilisation. Further exploratory studies are warranted to evaluate and improve oxygen extraction which may help to improve outcomes in severe hypoxaemic mechanically ventilated COVID-19 patients.

Combinatorial analysis of the structural requirements of the Escherichia coli hemolysin signal sequence

We have investigated the substrate specificity of the Escherichia coli hemolysin transporter system. Translocation of hemolysin is dependent on a C-terminal signal sequence located within the last 60 amino acids of this protein. Previous comparative studies of the signal sequence have revealed a conserved helix(alpha1)-linker-helix(alpha2) motif, suggesting that secondary structure is important for transport. In this study, we generated three random libraries in the alpha1, linker, and alpha2 regions, as well as an alpha1-amphiphilic helical library to identify features buried within the structural motif that contribute to transport. Combinatorial variants were generated by altering the primary sequence of specific regions, and correlation between the genotype and phenotype of the mutant populations allowed us to objectively identify any functional features involved. It was found that the alpha1-amphiphilic helix and the linker are both important for function. To our surprise, the second helix of the conserved structural motif was not essential for transport. The finding that a predicted amphiphilic helix and hydrophobicity, rather than primary sequence, contribute to transport in the alpha1 region allows us to speculate on the mechanism of multiple substrate recognition. This may have implications for understanding the broad substrate specificity common among other ATP-binding cassette transporters.