Respiratory changes in arterial pulse pressure and fluid responsiveness in spontaneously breathing patients

Introduction

We investigated whether the respiratory changes in arterial pulse pressure (ΔPP), an accurate indicator during mechanical ventilation (MV), and in arterial systolic pressure (ΔPS), easy to calculate, could predict fluid responsiveness in spontaneously breathing patients. The respiratory changes in intrathoracic pressure during spontaneous breathing, reversed compared with MV, could be insufficient to modify loading conditions of ventricles. We thus also tested those indicators during a forced respiratory cycle.

Methods

We prospectively studied 32 spontaneously breathing ICU patients (mean age: 61 ± 13 years) with clinical signs justifying volume expansion (VE). Hemodynamic measurements were performed during quiet respiration and during a forced respiratory effort (f) at baseline and immediately after a 500 ml 6% hydroxyethylstarch VE. Patients were then separated into responders (R) (increase in stroke volume [SV] assessed by transthoracic echocardiography = 15% after VE) and nonresponders (NR).

Results

Before VE, ΔPP (13 ± 5% vs 7 ± 3%, P = 0.003) and ΔPS (10 ± 4% vs 6 ± 3%, P = 0.002) were higher in R (n = 19) than in NR (n = 13). Receiver operating characteristic (ROC) curve analysis showed that the forced respiratory effort did not sensitize the method (ΔPP f = 0.72 ± 0.09 vs ΔPP = 0.82 ± 0.08, P = 0.048 and ΔPS f = 0.69 ± 0.10 vs ΔPS = 0.82 ± 0.08, P = 0.045). No statistical difference was observed between ΔPP and ΔPS ROC curves areas (0.81 ± 0.08 vs 0.82 ± 0.08, P = 0.888). Using a threshold ΔPP baseline value of 12%, R and NR were discriminated with 93% of specificity and 63% of sensitivity. No relation was observed between ΔPP and ΔPS baseline value and the increase of stoke volume during VE (r = 0.5, P = 0.058 for ΔPP).

Conclusion

In spontaneous breathing patients, ΔPP = 12% predicts an increase in SV with high probability (92%) without prejudging the importance of this increase. On the contrary, ΔPP <12% does not allow one to predict fluid responsiveness.