Assessment of fluid unresponsiveness guided by lung ultrasound in abdominal surgery: a prospective cohort study

Abstract

A fluid challenge can generate an infraclinical interstitial syndrome that may be detected by the appearance of B-lines by lung ultrasound. Our objective was to evaluate the appearance of B-lines as a diagnostic marker of preload unresponsiveness and postoperative complications in the operating theater. We conducted a prospective, bicentric, observational study. Adult patients undergoing abdominal surgery were included. Stroke volume (SV) was determined before and after a fluid challenge with 250 mL crystalloids (Delta-SV) using esophageal Doppler monitoring. Responders were defined by an increase of Delta-SV > 10% after fluid challenge. B-lines were collected at four bilateral predefined zones (right and left anterior and lateral). Delta-B-line was defined as the number of newly appearing B-lines after a fluid challenge. Postoperative pulmonary complications were prospectively recorded according to European guidelines. In total, 197 patients were analyzed. After a first fluid challenge, 67% of patients were responders and 33% were non-responders. Delta-B-line was significantly higher in non-responders than responders [4 (2-7) vs 1 (0-3), p < 0.0001]. Delta-B-line was able to diagnose fluid non-responders with an area under the curve of 0.74 (95% CI 0.67-0.80, p < 0.0001). The best threshold was two B-lines with a sensitivity of 80% and a specificity of 57%. The final Delta-B-line could predict postoperative pulmonary complications with an area under the curve of 0.74 (95% CI 0.67-0.80, p = 0.0004). Delta-B-line of two or more detected in four lung ultrasound zones can be considered to be a marker of preload unresponsiveness after a fluid challenge in abdominal surgery.The objectives and procedures of the study were registered at Clinicaltrials.gov (NCT03502460; Principal investigator: Stéphane BAR, date of registration: April 18, 2018).

Figure 1

(A) Pleural line (vertical arrows indicate the bat sign, with ribs and pleural line). One A-line at the standardized location (horizontal arrows). (B) B-lines. 6 B-lines visible between two ribs in short-axis. (C) BLUE-points. The BLUE-protocol uses three points per lung. Two hands are applied this way, against the clavicule. Two points are anterior, the upper-BLUE-point (middle of upper hand, that is, roughly, second intercostal space between parasternal and anterior axillary line) and the lower-BLUE-point (middle of lower palm). One point, continuing transversally the lower BLUE-point as «posterior as possible, is the posterolateral alveolar pleural syndrome-point» (PLAPS-point). Note that the PLAPS-point seems rather cranial, but is in actual fact just a bit above the diaphragm usually. (D) The lateral point. For adapting the approach to the perioperative setting with its constraints in this study, we took a clinically accessible lateral point located transversally between lower BLUE-point and PLAPS-point, and longitudinally between anterior and posterior axillary line. Note that, if a theoretical point is not accessible for any reason, device or other, the BLUE-points are flexible up to a large tolerance (indicated by the areas in the cartouche).

Figure 2

Study protocol.

Figure 3

Flow chart of the study.

Figure 4

Analysis of the Delta-SV value according to the Delta-B-line. n = the number of datapoints for each value of the Delta-B-line. *p < 0.05 for the comparison to the Delta-SV for 0 Delta-B-line. Figure generated from MedCalc Statistical Software version 19.7 (MedCalc Software Ltd, Ostend, Belgium; https://www.medcalc.org; 2021).