Perioperative non-invasive versus semi-invasive cardiac index monitoring in patients with bariatric surgery - a prospective observational study

Abstract

Background: In morbidly obese patients undergoing laparoscopic bariatric surgery, the combination of obesity-related comorbidities, pneumoperitoneum and extreme posture changes constitutes a high risk of perioperative hemodynamic complications. Thus, an advanced hemodynamic monitoring including continuous cardiac index (CI) assessment is desirable. While invasive catheterization may bear technical difficulties, transesophageal echocardiography is contraindicated due to the surgical procedure. Evidence on the clinical reliability of alternative semi- or non-invasive cardiac monitoring devices is limited. The aim was to compare the non-invasive vascular unloading to a semi-invasive pulse contour analysis reference technique for continuous CI measurements in bariatric surgical patients.

Methods: This prospective observational study included adult patients scheduled for elective, laparoscopic bariatric surgery after obtained institutional ethics approval and written informed consent. CI measurements were performed using the vascular unloading technique (Nexfin®) and semi-invasive reference method (FloTrac™). At 10 defined measurement time points, the influence of clinically indicated body posture changes, passive leg raising, fluid bolus administration and pneumoperitoneum was evaluated pre- and intraoperatively. Correlation, Bland-Altman and concordance analyses were performed.

Results: Sixty patients (mean BMI 49.2 kg/m²) were enrolled into the study and data from 54 patients could be entered in the final analysis. Baseline CI was 3.2 ± 0.9 and 3.3 ± 0.8 l/min/m², respectively. Pooled absolute CI values showed a positive correlation (r_s = 0.76, P < 0.001) and mean bias of of - 0.16 l/min/m² (limits of agreement: - 1.48 to 1.15 l/min/m²) between the two methods. Pooled percentage error was 56.51%, missing the criteria of interchangeability (< 30%). Preoperatively, bias ranged from - 0.33 to 0.08 l/min/m² with wide limits of agreement. Correlation of CI was best (r_s = 0.82, P < 0.001) and percentage error lowest (46.34%) during anesthesia and after fluid bolus administration. Intraoperatively, bias ranged from - 0.34 to - 0.03 l/min/m² with wide limits of agreement. CI measurements correlated best during pneumoperitoneum and after fluid bolus administration (r_s = 0.77, P < 0.001; percentage error 35.95%). Trending ability for all 10 measurement points showed a concordance rate of 85.12%, not reaching the predefined Critchley criterion (> 92%).

Conclusion: Non-invasive as compared to semi-invasive CI measurements did not reach criteria of interchangeability for monitoring absolute and trending values of CI in morbidly obese patients undergoing bariatric surgery.

Trial registration: The study was registered retrospectively on June 12, 2017 with the registration number NCT03184272 .

Keywords: Bariatric surgery; Cardiac output; Finger-cuff; Hemodynamic monitoring; Non-invasive monitoring; Obesity; Vascular unloading technique.

Fig. 1

Study design and measurement time points. In the pre- and intraoperative phase cardiac index measurements with both the non- and semi-invasive monitoring devices were performed at five time points in each phase, at which hemodynamic changes were likely to occur due to clnically necessary steps of anesthesia induction, changes in posture or induction of pneumoperitoneum or fluid bolus administration. ATP: anti-Trendelenburg posture, PLR: passive leg raising, PP: pneumoperitoneum

Fig. 2

Correlation and Bland-Altman analyses of cardiac index measurements between Nexfin® and FloTrac™ for the total data sample. Pooled Spearman correlation analysis with correlation coefficient (r_s) and P value shown in the left diagram. 2 data points lie outside of the axis range for better visualization of the diagram. The right diagram shows Bland-Altman plot of non-invasive (Nexfin®) and semi-invasive (FloTrac™) cardiac index (CI) measurements in l/min/m². Bland-Altman analysis showing the mean difference and 95% limits of agreement for each comparison (bias ±1.96 standard deviation of the difference) as dots. 3 data points lie outside of the axis range for better visualization of the diagram. In addition, the value for the calculated percentage error (PE) is displayed in the diagram

Fig. 3

Four square plot of the concordance for cardiac index trending between Nexfin® and FloTrac™ for the total data sample. Hemodynamic trending interchangeability using a four-quadrant plot representation of the changes in cardiac index (CI) measurements from the total data sample. Data points in the left lower und right upper quadrant depict CI values with the same delta change (in %) – negative or positive. Number of values with changes in CI < 15% were excluded (exclusion zone, number of excluded values and remaining number of CI values). The concordance of the remaining values is also displayed in the diagram. An acceptable trending ability was assumed at a level of concordance > 92%. One data point lies outside the axis range

Fig. 4

Four square plot of the concordance for cardiac index trending in the preoperative phase between Nexfin® and FloTrac™. Hemodynamic trending interchangeability using a four-quadrant plot representation of the changes in cardiac index (CI) measurements from the total data sample. Data points in the left lower und right upper quadrant depict CI values with the same delta change (in %) – negative or positive. Number of values with changes in CI < 15% were excluded (exclusion zone, number of excluded values and remaining number of CI values). The concordance of the remaining values is also displayed in the diagram. Panel a shows trending between baseline, patient awake and anesthesia induction with anti-Trendelenburg position, Panel b anesthesia induction with anti-Trendelenburg position and baseline anesthesia, Panel c baseline anesthesia and passive leg raising and Panel d anesthesia with passive leg raising and fluid bolus administration

Fig. 5

Four square plot of the concordance for cardiac index trending in the intraoperative phase between Nexfin® and FloTrac™. Hemodynamic trending interchangeability using a four-quadrant plot representation of the changes in cardiac index (CI) measurements. Data points of each diagram depict CI values in the left lower und right upper quadrant with the same delta change (in %) – negative or positive. Number of values with changes in CI < 15% were excluded (exclusion zone, number of excluded values and remaining number of CI values). The concordance of the remaining values is also displayed in the diagram. Panel a shows trending between anesthesia with induction of pneumoperitoneum and anti-Trendelenburg posture, Panel b anesthesia with pneumoperitoneum in anti-Trendelenburg posture and anesthesia with pneumoperitoneum in anti-Trendelenburg posture plus fluid bolus administration, Panel c anesthesia with pneumoperitoneum in anti-Trendelenburg posture plus fluid bolus administration and end of pneumoperitoneum and Panel d end of pneumoperitoneum and end of anesthesia in anti-Trendelenburg position