Effect of adjusting PaO2/FiO2 ratio and oxygenation index in critically ill children at altitude >2600 meters above sea level: observational study

BACKGROUND: Oxygenation disorders are a very frequent cause of hospitalization in intensive care. Their diagnosis and classification are essential to assess their severity and thus determine management strategies. The objective of this study was to analyze the effect of high altitude on the interpretation of invasive measures of oxygenation in children undergoing invasive mechanical ventilation, according to the traditional PaO2/FiO2 ratio adjustment equation, according to altitude. This is a cross-sectional observational study of arterial blood gas. Data analyzed included critically ill children between 1 month to 18 years, during 1 year (2017-2018), at an altitude of 2630 m.a.s.l.METHODS: The variables of interest were: arterial blood gas parameters, mean airway pressure taken from ventilatory monitoring at the time of taking arterial blood gases. The PaO2/FiO2 ratio was adjusted according to the criteria of altitude above sea level according to: PaO2/FiO2, × (barometric pressure/760).RESULTS: In 645 arterial blood gas samples from patients who had invasive mechanical ventilation, it was observed that with the traditional PaO2/FiO2 ratio fitting equation, for PaO2/FiO2 ratio index values of 100, 200 and 300 would be equivalent to a high altitude adjusted PF index of: 73 (sensitivity 93%; specificity 100%), 145 (sensitivity 93.8%; specificity 96%) and 219 (sensitivity 79%; specificity 96%), respectively.CONCLUSIONS: The oxygenation metrics used in this study adjusted for high altitude modify the different cut-off points for the prediction of the PaO2/FiO2 ratio. Prospective studies are needed to validate in a larger sample the results found in this study.