2016, Number 4
Rev Invest Clin 2016; 68 (4)
Classifying Acute Respiratory Distress Syndrome Severity: Correcting the Arterial Oxygen Partial Pressure to Fractional Inspired Oxygen at Altitude
Pérez-Padilla R, Hernández-Cárdenas CM, Lugo-Goytia G
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Language: English
References: 4
Page: 169-170
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In the well-known Berlin definition of acute respiratory distress syndrome (ARDS), there is a recommended adjustment for arterial oxygen partial pressure to fractional inspired oxygen (PaO2/FIO2) at altitude, but without a reference as to how it was derived. At the same shunt, PaO2/FIO2 decreases with altitude, impairing a proper comparison of individuals with similar lung damage if they reside at different altitudes and if the shunt is not directly measured, as is the case in most patients. It is then very important in multicenter studies to correct the PaO2/FIO2 by altitude or barometric pressure (i.e. raise the value of PaO2/FIO2 obtained at altitude), but unfortunately, the adjustment is not a simple function of altitude or barometric pressure. The correction suggested by the working group does the opposite of what is needed because it requests a multiplication by a fraction: barometric pressure (Pbar)/760. If, instead of multiplying by Pbar/760, we divide by the ratio (to set, for example, varying limits for ARDS severity at different altitudes), the resulting PaO2/FIO2 is closer to that expected at sea level for lower shunts (and high PaO2/FIO2), but overcorrects at higher shunts and of course does not take into account changes in PaO2/FIO2 due to modifications of FIO2. Our aim was to develop an equation able to take into account the impact of altitude on PaO2/FIO2 so that patients from different altitudes could be compared at a more homogeneous degree of lung damage.REFERENCES