Ventilator-Induced Signal Interference and the Accuracy of the Pressure Reactivity Index in Acute Brain Injury.

BACKGROUND

The pressure reactivity index (PRx) is a widely used marker of cerebral autoregulation (CA) in patients with acute brain injury (ABI). However, its accuracy may be compromised by mechanical ventilation (MV), which can influence both arterial blood pressure (ABP) and intracranial pressure (ICP).

OBJECTIVE

The objective was to assess how different components of MV, especially recruitment maneuvers (RMs), affect PRx computation and its reliability in reflecting CA.

METHODS

We revisited the theoretical basis of PRx and derived a mathematical expression that quantifies the influence of MV-related interferences on PRx values. The influence of both frequency and amplitude of such interferences was further investigated through in silico experiments. Special attention was given to the effects of a common RM technique.

RESULTS

PRx calculations were found to be stable in the presence of high-frequency signal interference (> 0.2 Hz), consistent with standard respiratory cycles. However, low-frequency perturbations, such as those introduced during RMs, may distort the ABP-ICP relationship and cause PRx to underestimate CA dysfunction.

CONCLUSIONS

While PRx is generally robust against fast ventilatory signals, its interpretation may be significantly affected during low-frequency interventions such as RMs. Clinical teams should consider these limitations when using PRx to guide management, especially during advanced ventilator strategies in patients with ABI.