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: (i) 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; (iii) 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 (OR 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 may reflect increased oxidative stress in these children.
Highlights
Exogenous carbon monoxide (CO) has long been considered toxic due to competitive inhibition of haemoglobin oxygen binding
Observational study, we aimed to 1) evaluate the distribution of arterial COHb in children admitted to a medical paediatric intensive care unit; 2) describe the trajectory of arterial COHb levels over the first 7 days of admission; 3) seek associations between arterial COHb and ICU outcomes: given the low rate of mortality on paediatric ICU, we sought associations between COHb and length of ventilated stay
Lower maximum COHb values, had lower risk adjusted mortality (Fig 5). In this single centre retrospective observational study, we describe the distribution of arterial COHb in children admitted to ICU
Summary
Exogenous carbon monoxide (CO) has long been considered toxic due to competitive inhibition of haemoglobin oxygen binding. Endogenous CO is increasingly being associated with beneficial physiological effects [1]. Heme is oxidised to produce CO, free iron and biliverdin, a reaction catalysed by heme oxygenase (HO). Of the three known isoforms of HO, HO-1 is highly induced by oxidative stress, it acts to limit damage from the oxidant heme [2].
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