The Trend of Arterial Carboxyhemoglobin in Non-smokers as a Prognostic Tool in Severe COVID-19 Patients: A Single-Centre Prospective Study

Abstract

Introduction Carboxyhemoglobinemia is characterised by decreased oxygen delivery to tissues. In severe and critical coronavirus disease 2019 (COVID-19) illness with hypoxia, this can herald a grave and protracted course of illness. Patients with COVID-19 experience respiratory impairment, lowering the pace at which carbon monoxide (CO) is eliminated and raising the likelihood of carboxyhemoglobinemia. We set out to explore early arterial carboxyhemoglobin (COHb) and COVID-19 patient outcomes in non-smokers and its potential as a predictive tool for mortality. Methods Forty-five patients, non-smokers with severe/critical severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection requiring admission in a North Indian 1200-bedded tertiary care hospital, were recruited prospectively from October 2020 to March 2021. Arterial COHb% was evaluated with arterial blood gases using an analyser, which were taken at the time of admission and then every alternate day for the first 10 days. Carboxyhemoglobinemia was defined as COHb% more than 1%. The primary outcome was defined as the patient's hospital outcome (survivor/non-survivor). Results Of the total 45 subjects, 51.1% (n=23) survived. Patients developed carboxyhemoglobinemia with an incidence of 51% during the course of their hospital stay. The mean ± SD of COHb% on admission was 1.0 ± 0.58 and 1.03 ± 0.8 in non-survivors and survivors, respectively (p=0.870). Maximal individual values of 5.3% and 6.1% were seen in survivors and non-survivors, respectively. On serial COHb measurement, non-survivors had significantly higher COHb% on days 6 and 10. No co-relation of COHb% with inflammatory markers was noted. Conclusion Arterial COHb levels in non-survivors were significantly higher than in survivors on days 6 and 10. Our study did not show a prognostic value of serial COHb measurement in patients with severe COVID-19. To establish COHb as a predictive marker in severely ill COVID-19 patients, additional research is required.

Keywords: arterial blood gas; carboxyhemoglobin; covid-19; mortality; prognosis; trend.

Figure 1. STROBE flow diagram depicting patient enrolment.

STROBE: Strengthening the Reporting of Observational Studies in Epidemiology

Figure 2. Trend analysis of mean COHb% between non-survivors and survivors over 10 days of admission. Error bars represent 95%CI. Significance was noted on day 6 and day 10 ( p< 0.05)

COHb: carboxyhemoglobin; CI: confidence interval

Figure 3. Pearson’s correlation of carboxyhemoglobin on admission with IL-6 (r = -0.005, p= 0.972).

COHb: carboxyhemoglobin; IL-6: interleukin 6

Figure 4. Pearson’s correlation of carboxyhemoglobin on admission with LDH (r = 0.025, p= 0.870).

COHb: carboxyhemoglobin; LDH: lactate dehydrogenase

Figure 5. Pearson’s correlation of carboxyhemoglobin on admission with D-dimer (r = 0.168, p= 0.269).

COHb: carboxyhemoglobin

Figure 6. Pearson’s correlation of carboxyhemoglobin on admission with NLR (r =0.187, p= 0.219).

NLR: neutrophil-to-lymphocyte ratio; COHb: carboxyhemoglobin