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

Direct Use of Clinical Tolerance Limits for Assessing the Degree of Agreement between Two Methods of Measuring Blood Pressure

A large number of new methods of measuring blood pressure (BP) have recently emerged with advances in technology. Different methods of measuring BP generally provide varying readings compared with one another. Clinicians must decide how to respond to these variations and how to assess the degree of agreement. Clinical agreement between two quantitative measurements on a group of subjects is generally assessed with the Bland-Altman method. This method requires a comparison of Bland-Altman limits with the prespecified clinical tolerance limits. This review describes an alternative simple and robust method that directly uses clinical tolerance limits for assessing agreement without calculating Bland-Altman limits. The many advantages of this method are illustrated with the help of real-life examples of BP measurements.

Comparison of oscillometric, non-invasive and invasive arterial pressure monitoring in patients undergoing laparoscopic bariatric surgery – a secondary analysis of a prospective observational study

Background

Oscillometric, non-invasive blood pressure measurement (NIBP) is the first choice of blood pressure monitoring in the majority of low and moderate risk surgeries. In patients with morbid obesity, however, it is subject to several limitations. The aim was to compare arterial pressure monitoring by NIBP and a non-invasive finger-cuff technology (Nexfin®) with the gold-standard invasive arterial pressure (IAP).

Methods

In this secondary analysis of a prospective observational, single centre cohort study, systolic (SAP), diastolic (DAP) and mean arterial pressure (MAP) were measured at 16 defined perioperative time points including posture changes, fluid bolus administration and pneumoperitoneum (PP) in patients undergoing laparoscopic bariatric surgery. Absolute arterial pressures by NIBP, Nexfin® and IAP were compared using correlation and Bland Altman analyses. Interchangeability was defined by a mean difference ≤ 5 mmHg (SD ≤8 mmHg). Percentage error (PE) was calculated as an additional statistical estimate. For hemodynamic trending, concordance rates were analysed according to the Critchley criterion.

Results

Sixty patients (mean body mass index of 49.2 kg/m²) were enrolled and data from 56 finally analysed. Pooled blood pressure values of all time points showed a significant positive correlation for both NIPB and Nexfin® versus IAP. Pooled PE for NIBP versus IAP was 37% (SAP), 35% (DAP) and 30% (MAP), for Nexfin versus IAP 23% (SAP), 26% (DAP) and 22% (MAP). Correlation of MAP was best and PE lowest before induction of anesthesia for NIBP versus IAP (r = 0.72; PE 24%) and after intraoperative fluid bolus administration for Nexfin® versus IAP (r = 0.88; PE: 17.2%). Concordance of MAP trending was 90% (SAP 85%, DAP 89%) for NIBP and 91% (SAP 90%, DAP 86%) for Nexfin®. MAP trending was best during intraoperative ATP positioning for NIBP (97%) and at induction of anesthesia for Nexfin® (97%).

Conclusion

As compared with IAP, interchangeability of absolute pressure values could neither be shown for NIBP nor Nexfin®, however, NIBP showed poorer overall correlation and precision. Overall trending ability was generally high with Nexfin® surpassing NIBP. Nexfin® may likely render individualized decision-making in the management of different hemodynamic stresses during laparoscopic bariatric surgery, particularly where NIBP cannot be reliably established.

Trial registration

The non-interventional, observational study was registered retrospectively at (NCT03184285) on June 12, 2017.

Intraoperative Monitoring of the Obese Patient Undergoing Surgery: A Narrative Review

With the increasing prevalence of obesity in the population, anaesthetists must confidently manage both the pathophysiological and technical challenges presented in bariatric and non-bariatric surgery. The intraoperative period represents an important opportunity to optimise and mitigate risk. However, there is little formal guidance on what intraoperative monitoring techniques should be used in this population. This narrative review collates the existing evidence for intraoperative monitoring devices in the obese patients. Although a number of non-invasive blood pressure monitors have been tested, an invasive arterial line remains the most reliable monitor if accurate, continuous monitoring is required. Goal-directed fluid therapy is recommended by clinical practice guidelines, but the methods tested to assess this had guarded applicability to the obese population. Transcutaneous carbon dioxide (CO₂) monitoring may offer additional benefit to standard capnography in this population. Individually titrated positive end expiratory pressure (PEEP) and recruitment manoeuvres improved intraoperative mechanics but yielded no benefit in the immediate postoperative period. Depth of anaesthesia monitoring appears to be beneficial in the perioperative period regarding recovery times and complications. Objective confirmation of reversal of neuromuscular blockade continues to be a central tenet of anaesthesia practice, particularly relevant to this group who have been characterised as an "at risk" extubation group. Where deep neuromuscular blockade is used, continuous neuromuscular blockade is suggested. Both obesity and the intraoperative context represent somewhat unstable search terms, as the clinical implications of the obesity phenotype are not uniform, and the type and urgency of surgery have significant impact on the intraoperative setting. This renders the generation of summary conclusions around what intraoperative monitoring techniques are suitable in this population highly challenging.