Detection of blood volume deficits through conjunctival oxygen tension monitoring

Because acute blood loss may produce abnormal tissue perfusion and oxygenation before affecting blood pressure, we measured conjunctival (PcjO2) and arterial (PaO2) oxygen tensions and blood volume in 16 normotensive emergency department patients whose histories were consistent with significant blood loss. All eight patients with measured blood volume less than 85% of normal, as well as two euvolemic patients, had a PcjO2/PaO2 value of 0.57 or less, yielding a sensitivity of 100%, specificity of 75%, and positive predictive value of 80%. Lowering the cutoff point to 0.50 increased specificity and positive predictive value to 100% while reducing sensitivity to 88%. These results demonstrate that the PcjO2/PaO2 ratio is an early, sensitive, and specific indicator of significant blood volume deficit.