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Vol. 40. Issue 10.
Pages 459-462 (October 2004)
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Vol. 40. Issue 10.
Pages 459-462 (October 2004)
Original Articles
DOI: 10.1016/S1579-2129(06)60356-X
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Altitude, the Ratio of PaO2 to Fraction of Inspired Oxygen, and Shunt: Impact on the Assessment of Acute Lung Injury
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J.R. Pérez-Padilla
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perezpad@servidor.unam.mx

Correspondence: Dr. J.R. Pérez-Padilla. Departamento de Fisiología Pulmonar y Clínica de Sueño. Instituto Nacional de Enfermedades Respiratorias. Tlalpan 4502. México DF. México
Departamento de Fisiología Pulmonar and Clínica de Sueño, Instituto Nacional de Enfermedades Respiratorias, México DF, Mexico
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The ratio of PaO2 to the fraction of inspired oxygen (PaO2/FIO2) is commonly used to determine the severity of acute lung injury and acute respiratory distress syndrome (ARDS). The research presented here used computational models of the lung to analyze the effect of altitude on the PaO2/FIO2 ratio and pulmonary shunt.

At a given shunt, the PaO2/FIO2 ratio is lower at higher altitudes. Therefore, when evaluating for ARDS based on a PaO2/FIO2 ratio of <200 mm Hg, patients residing at high altitudes will have less shunt and, presumably, less severe lung injury than patients at sea level.

This should be taken into consideration when comparing patients from different altitudes. Shunt should more often be measured directly or be estimated assuming a constant arteriovenous oxygen content difference.

Key Words:
Shunt
Oxygenation index
Ratio PaO2 to fraction of inspired oxygen (FIO2),
PaO2/FIO2
Acute respiratory distress syndrome (ARDS)
Altitude

El cociente presión arterial de oxígeno/fracción inspiratoria de oxígeno (PaO2/FiO2) se utiliza comúnmente para definir el grado de lesión pulmonar y el síndrome de insuficiencia respiratoria progresiva del adulto. En el presente trabajo se analizan las modificaciones que experimenta el índice con la altura sobre el nivel del mar y con los cortocircuitos en modelos computacionales de pulmón.

El cociente PaO2/FiO2 disminuye con la altura sobre el nivel del mar al mismo cortocircuito. Por lo tanto, los pacientes que residen a alturas considerables sobre el nivel del mar tienen un cortocircuito menor y presumiblemente un grado de daño pulmonar menor que los residentes al nivel del mar en el momento de cumplir el criterio de síndrome de insuficiencia respiratoria progresiva del adulto con un cociente PaO2/FiO2 de 200 Torr.

Esta variación debe tomarse en cuenta para la comparación de pacientes cuando provienen de alturas diferentes e indica que se ha de utilizar más frecuentemente la medición directa del cortocircuito o bien el cortocircuito calculado, asumiendo una diferencia arteriovenosa del contenido de oxígeno constante.

Palabras clave:
Cortocircuito
Índices de oxigenación
PaO2/FiO2
Síndrome de insuficiencia respiratoria progresiva del adulto (SIR-PA)
Altitud
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Copyright © 2004. Sociedad Española de Neumología y Cirugía Torácica (SEPAR)
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