Arterial carboxyhaemoglobin levels in children admitted to PICU: a retrospective observational study

Abstract

While carbon monoxide (CO) is considered toxic, low levels of endogenously produced CO are protective against cellular injury induced by oxidative stress. Carboxyhaemoglobin (COHb) levels have been associated with outcomes in critically ill adults. We aimed to describe the distribution of carboxyhaemoglobin in critically ill children and the relationship of these levels with clinical outcomes. This retrospective observational study was conducted at a large tertiary paediatric intensive care unit (PICU). We included all children admitted to the PICU over a two-year period who underwent arterial blood gas analysis. We measured the following: Population and age-related differences in COHb distribution; (ii) Change in COHb over the first week of admission using a multi-level linear regression analysis; (ii) Uni- and multivariable relationships between COHb and length of ventilation and PICU survival. Arterial COHb levels were available for 559/2029 admissions. The median COHb level was 1.20% (IQR 1.00-1.60%). Younger children had significantly higher COHb levels (p-value <2 x 10-16). Maximum Carboxyhaemoglobin was associated with survival 1.67 (95% CI 1.01-2.57, p-value=0.02) and length of ventilation (odds ratio 5.20, 95% CI 3.07-7.30, p-value 1.8 x 10-6) following multi-variable analysis. First measured and minimum COHb values were weakly associated with length of ventilation, but not survival. In conclusion, children have increased COHb levels in critical illness, which are greater in younger children. Higher COHb levels are associated with longer length of ventilation and death in PICU. This is likely to reflect increased oxidative stress.

Retrospective evaluation of carboxyhemoglobin and methemoglobin levels in dogs and cats with respiratory disease

“…A higher maximum COHb was also associated with an increased duration of mechanical ventilation. It was postulated that the higher COHb was a marker of increased oxidative stress in this patient population 14 . A study in infants determined that the development of late‐onset sepsis was associated with higher COHb and that COHb decreased when blood cultures were negative.…”

“…Thus, increased CO production can be associated with inflammatory conditions 8 . The exploration of COHb as a prognostic indicator for patients with respiratory disease has yielded mixed results 2,9–15 …”

“…These hypotheses were based on the preponderance of evidence in human medicine suggesting that a higher COHb is associated with a lower disease severity. 2,9–15 …”

“…8 The exploration of COHb as a prognostic indicator for patients with respiratory disease has yielded mixed results. 2,[9][10][11][12][13][14][15] Methemoglobin (MetHb) results when 1 or more of the iron ions in hemoglobin are oxidized from the ferrous to the ferric state, preventing hemoglobin from binding oxygen. While a small amount of MetHb may form following the unloading of oxygen to tissues, most endogenous MetHb forms when NO interacts with hemoglobin.…”

COVID-19 morbidity and mortality caused by endogenous carbon monoxide poisoning, with recommendations for testing and treatment

“…We suspect mechanical ventilation and hyperoxygenation treatments are keeping free CO levels in the lungs of COVID-19 patients artificially low, while raising the level in blood and other organs where free CO is more harmful. Critically, studies show arterial COHb rises with each additional day patients are on mechanical ventilators and the level correlates with mortality [Chawla 2019]. In addition, the partial pressure of their arterial oxygen keeps falling as their arterial free CO and COHb keep rising [Ascha 2018].…”