Study protocol and pilot results of an observational cohort study evaluating effect of red blood cell transfusion on oxygenation and mitochondrial oxygen tension in critically ill patients with anaemia: the INsufficient Oxygenation in the Intensive Care Unit (INOX ICU-2) study

Mitochondrial oxygen tension in critically ill patients receiving red blood cell transfusions: a multicenter observational cohort study

PURPOSE

Currently, there is no marker of efficacy of red blood cell (RBC) transfusion. This study describes the impact of RBC transfusion on mitochondrial oxygen tension (mitoPO2) and mitochondrial oxygen consumption (mitoVO2) in critically ill patients with anemia.

METHODS

Critically ill patients with a hemoglobin concentration < 10 g/dL, for whom a single RBC unit had been ordered, were included. MitoPO2 was measured with the COMET device immediately before RBC transfusion, 0.5 h, 1 h, 3 h, and 24 h after RBC transfusion. MitoVO2 was calculated from dynamic mitoPO2 measurements during cessation of local oxygen supply.

RESULTS

Sixty-three patients participated, median age 64.0 (interquartile range (IQR) 52.3-72.8) years, median hemoglobin concentration before transfusion 7.4 (IQR 7.1-7.7) g/dL. Median mitoPO2 values were 55.0 (IQR 49.6-63.0) mmHg before RBC transfusion, 51.0 (IQR 41.5-61.2) directly after and 67.3 (IQR 41.6-83.7) at 24 h after RBC transfusion. Median mitoVO2 values were 3.3 (IQR 2.1-5.9) mmHg/s before RBC transfusion, 3.7 (IQR 2.0-5.1) mmHg/s directly after, and 3.1 (IQR 2.5-4.8) mmHg/s 24 h after RBC transfusion. In the higher Hb concentration group (> 7 g/dL), we saw a dissociation of the effect of RBC transfusion on mitoPO2 versus on mitoVO2 values. MitoPO2 and mitoVO2 values were not associated with commonly used parameters of tissue perfusion and oxygenation.

CONCLUSION

RBC transfusion did not alter mitoPO2 and mitoVO2 in critically ill patients with anemia. MitoPO2 and mitoVO2 values were not notably associated with Hb concentrations, parameters of severity of illness and markers of tissue perfusion or oxygenation. Given the high baseline value, it cannot be excluded nor confirmed whether RBC can improve low mitoPO2. Trial registration number NCT03092297 (registered 27 March 2017).

Description of mitochondrial oxygen tension and its variability in healthy volunteers

OBJECTIVES

Describing mitochondrial oxygenation (mitoPO2) and its within- and between-subject variability over time after 5-aminolevulinic acid (ALA) plaster application in healthy volunteers.

DESIGN

Prospective cohort study.

SETTING

Measurements were performed in Leiden University Medical Center, the Netherlands.

PARTICIPANTS

Healthy volunteers enrolled from July to September 2020.

INTERVENTIONS

Two ALA plasters were placed parasternal left and right, with a 3-hour time interval, to examine the influence of the calendar time on the value of mitoPO2. We measured mitoPO2 at 4, 5, 7, 10, 28, and 31 hours after ALA plaster 1 application, and at 4, 5, 7, 25, and 28 hours after ALA plaster 2 application.

PRIMARY AND SECONDARY OUTCOME MEASURES

At each time point, five mitoPO2 measurements were performed. Within-subject variability was defined as the standard deviation (SD) of the mean of five measurements per timepoint of a study participant. The between-subject variability was the SD of the mean mitoPO2 value of the study population per timepoint.

RESULTS

In 16 completed inclusions, median mitoPO2 values and within-subject variability were relatively similar over time at all time points for both plasters. An increase in overall between-subject variability was seen after 25 hours ALA plaster time (19.6 mm Hg vs 23.9 mm Hg after respectively 10 and 25 hours ALA plaster time).

CONCLUSIONS

The mitoPO2 values and within-subject variability remained relatively stable over time in healthy volunteers. An increase in between-subject variability was seen after 25 hours ALA plaster time warranting replacement of the ALA plaster one day after its application.

TRIAL REGISTRATION

ClinicalTrials.gov with trial number NCT04626661.

Monitoring of mitochondrial oxygen tension in the operating theatre: An observational study with the novel COMET® monitor

INTRODUCTION

The newly introduced Cellular Oxygen METabolism (COMET®) monitor enables the measurement of mitochondrial oxygen tension (mitoPO2) using the protoporphyrin IX triplet state lifetime technique (PpIX-TSLT). This study aims to investigate the feasibility and applicability of the COMET® measurements in the operating theatre and study the behavior of the new parameter mitoPO2 during stable operating conditions.

METHODS

In this observational study mitochondrial oxygenation was measured in 20 patients during neurosurgical procedures using the COMET® device. Tissue oxygenation and local blood flow were measured by the Oxygen to See (O2C). Primary outcomes included mitoPO2, skin temperature, mean arterial blood pressure, local blood flow and tissue oxygenation.

RESULTS

All patients remained hemodynamically stable during surgery. Mean baseline mitoPO2 was 60 ± 19 mmHg (mean ± SD) and mean mitoPO2 remained between 40-60 mmHg during surgery, but tended to decrease over time in line with increasing skin temperature.

CONCLUSION

This study presents the feasibility of mitochondrial oxygenation measurements as measured by the COMET® monitor in the operating theatre and shows the parameter mitoPO2 to behave in a stable and predictable way in the absence of notable hemodynamic alterations. The results provide a solid base for further research into the added value of mitochondrial oxygenation measurements in the perioperative trajectory.

Severe bleeding in the ICU

PURPOSE OF REVIEW

Severe bleeding events, which require blood transfusions, are a challenge faced by many critical care physicians on a daily basis. Current transfusion guidelines generally recommend rather strict transfusion thresholds and strategies, which can appear opposing to a patient in need for urgent transfusion at first sight. Moreover, applied guidelines are lacking evidence and specificity for the typical ICU patient population and its comorbidities. Transfusion decisions, which are pivotal for clinical outcome, are often unsatisfactorily based on hemoglobin levels only.

RECENT FINDINGS

Recent publications generally support previous studies that a strict transfusion regimen is superior to a liberal one for the majority of cases. Newly developed and easily feasible techniques are currently in clinical trials and have the potential to become a valuable supplementation to hemoglobin-guided decision-making. In addition to the choice of the ideal transfusion strategy, physiological status and comorbidities were found to have a major impact on the outcome of severe bleedings in the ICU.

SUMMARY

The body of evidence for ICU-specific transfusion guidelines is scarce. Critical care physicians should properly evaluate their patient's comorbidities and consider extended point-of-care testing for transfusion decisions in indistinct anemic situations. A strict transfusion strategy should, however, be applied whenever possible.

Mitochondrial Oxygen Monitoring During Surgical Repair of Congenital Diaphragmatic Hernia or Esophageal Atresia: A Feasibility Study

Current monitoring techniques in neonates lack sensitivity for hypoxia at cellular level. The recent introduction of the non-invasive Cellular Oxygen METabolism (COMET) monitor enables measuring in vivo mitochondrial oxygen tension (mitoPO2), based on oxygen-dependent quenching of delayed fluorescence of 5-aminolevulinic acid (ALA)-enhanced protoporphyrin IX. The aim is to determine the feasibility and safety of non-invasive mitoPO2 monitoring in surgical newborns. MitoPO2 measurements were conducted in a tertiary pediatric center during surgical repair of congenital diaphragmatic hernia or esophageal atresia. Intraoperative mitoPO2 monitoring was performed with a COMET monitor in 11 congenital diaphragmatic hernia and four esophageal atresia neonates with the median age at surgery being 2 days (IQR 1.25-5.75). Measurements were done at the skin and oxygen-dependent delayed fluorescence was measurable after at least 4 h application of an ALA plaster. Pathophysiological disturbances led to perturbations in mitoPO2 and were not observed with standard monitoring modalities. The technique did not cause damage to the skin, and seemed safe in this respect in all patients, and in 12 cases intraoperative monitoring was successfully completed. Some external and potentially preventable factors-the measurement site being exposed to the disinfectant chlorohexidine, purple skin marker, or infrared light-seemed responsible for the inability to detect an adequate delayed fluorescence signal. In conclusion, this is the first study showing it is possible to measure mitoPO2 in neonates and that the cutaneous administration of ALA to neonates in the described situation can be safely applied. Preliminary data suggests that mitoPO2 in neonates responds to perturbations in physiological status.