Fluid challenge: tracking changes in cardiac output with blood pressure monitoring (invasive or non-invasive)

To assess whether invasive and non-invasive blood pressure (BP) monitoring allows the identification of patients who have responded to a fluid challenge, i.e., who have increased their cardiac output (CO).

Patients with signs of circulatory failure were prospectively included. Before and after a fluid challenge, CO and the mean of four intra-arterial and oscillometric brachial cuff BP measurements were collected. Fluid responsiveness was defined by an increase in CO ≥10 or ≥15 % in case of regular rhythm or arrhythmia, respectively.

In 130 patients, the correlation between a fluid-induced increase in pulse pressure (Δ_500mlPP) and fluid-induced increase in CO was weak and was similar for invasive and non-invasive measurements of BP: r² = 0.31 and r² = 0.29, respectively (both p < 0.001). For the identification of responders, invasive Δ_500mlPP was associated with an area under the receiver-operating curve (AUC) of 0.82 (0.74–0.88), similar (p = 0.80) to that of non-invasive Δ_500mlPP [AUC of 0.81 (0.73–0.87)]. Outside large gray zones of inconclusive values (5–23 % for invasive Δ_500mlPP and 4–35 % for non-invasive Δ_500mlPP, involving 35 and 48 % of patients, respectively), the detection of responsiveness or unresponsiveness to fluid was reliable. Cardiac arrhythmia did not impair the performance of invasive or non-invasive Δ_500mlPP. Other BP-derived indices did not outperform Δ_500mlPP.

As evidenced by large gray zones, BP-derived indices poorly reflected fluid responsiveness. However, in our deeply sedated population, a high increase in invasive pulse pressure (>23 %) or even in non-invasive pulse pressure (>35 %) reliably detected a response to fluid. In the absence of a marked increase in pulse pressure (<4–5 %), a response to fluid was unlikely.