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Respiratory pulse oximetry plethysmographic waveform amplitude correlates with arterial pulse pressure variations


Arterial pulse pressure (PP) respiratory variation is a good predictor of fluid responsiveness in ventilated patients. Recently, it has been shown that variation in PP may correlate with variation in pulse oximetry plethysmographic (POP) waveform amplitude, as they both depend on the stroke volume. We designed a prospective study to evaluate the correlation between respiratory arterial PP variation and POP waveform amplitude variations in ventilated patients and the influence of acute lung injury (ALI) in this relationship.


Sixty patients were included in the study. Thirty-nine (65%) had diagnosis of ALI and 21 (35%) had normal gas exchange, defined as a relation of PaO2 to FiO2 (P/F) below and above 300, respectively. Respiratory variation in arterial PP and POP waveform amplitude were recorded simultaneously on a beat-to-beat basis, and mean values of two measures for each parameter were compared for correlation and agreement.


Respiratory variation in POP waveform amplitude could accurately predict variation in arterial PP with a sensibility of 83.3%, specificity of 85.7%, positive predictive value (PPV) of 71.4 and negative predictive value (NPV) of 92.3. The area under the ROC curve was 0.88 (0.79–0.97) with a best cutoff value of 14% to predict a variation in arterial PP of 13%. The kappa index of agreement was 0.65 (P < 0.001). Eighteen (30%) patients had variations in arterial PP above 13%, and 21 (35%) showed variations in POP waveform amplitude above 14%. In patients without ALI (P/F > 300) the sensibility was 100%, specificity was 93.3%, NPV was 100% and PPV was 80%. In the group with ALI (P/F < 300) the kappa index measure of agreement was 0.55, and in the group without ALI the kappa index was 0.85. PEEP levels were not different between the groups.


Respiratory variation in arterial PP above 13% can be accurately predicted by a variation in POP waveform amplitude of 14% with good correlation and agreement. Our results confirm the findings of a recent trial and suggest that the correlation is even stronger when ALI is absent. These findings raise potential clinical applications of respiratory variation in POP waveform amplitude for haemodynamic management of patients without an arterial catheter.

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Penna, G., Kalichsztein, M., Nobre, G. et al. Respiratory pulse oximetry plethysmographic waveform amplitude correlates with arterial pulse pressure variations. Crit Care 11 (Suppl 2), P310 (2007).

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