Pulse-contour derived cardiac output measurements in morbid obesity: influence of actual, ideal and adjusted bodyweight

The non-invasive Nexfin cardiac output (CO) monitor shows a low level of agreement with the gold standard thermodilution method in morbidly obese patients. Here we investigate whether this disagreement is related to excessive bodyweight, and can be improved when bodyweight derivatives are used instead. We performed offline analyses of cardiac output recordings of patient data previously used and partly published in an earlier study by our group. In 30 morbidly obese patients (BMI > 35 kg/m2) undergoing laparoscopic gastric bypass, cardiac output was simultaneously determined with PiCCO thermodilution and Nexfin pulse-contour method. We investigated if agreement of Nexfin-derived CO with thermodilution CO improved when ideal and adjusted—instead of actual- bodyweight were used as input to the Nexfin. Bodyweight correlated with the difference between Nexfin-derived and thermodilution-derived CO (r = −0.56; p = 0.001). Bland Altman analysis of agreement between Nexfin and thermodilution-derived CO revealed a bias of 0.4 ± 1.6 with limits of agreement (LOA) from −2.6 to 3.5 L min when actual bodyweight was used. Bias was −0.6 ± 1.4 and LOA ranged from −3.4 to 2.3 L min when ideal bodyweight was used. With adjusted bodyweight, bias improved to 0.04 ± 1.4 with LOA from −2.8 to 2.9 L min. Our study shows that agreement of the Nexfin-derived with invasive CO measurements in morbidly obese patients is influenced by body weight, suggesting that Nexfin CO measurements in patients with a BMI above 35 kg/m2 should be interpreted with caution. Using adjusted body weight in the Nexfin CO-trek algorithm reduced the bias

Peri-operative Medication Dosing in Adult Obese Elective Surgical Patients: A Systematic Review of Clinical Studies

Background: Despite the increasing numbers of obese patients undergoing elective surgery, there is a lack of evidence-based dosing guidelines for peri-operative medications in obesity. Objective: The objective was to systematically review the dosing and outcomes of peri-operative medications used in obese elective surgical patients. Methods: Medical subject headings and general keywords were used to systematically search multiple databases (PubMed, EMBASE, Cochrane Library and CINAHL). Studies of medications in obese surgical patients were included if they had a non-obese control or comparative dosing scalar group. The National Health and Medical Research Council GRADE tool was used to assess quality of evidence for each drug. Results: Thirty-three studies of six drug classes were identified: anaesthetics (n = 6), muscle relaxants (n = 10), neuromuscular reversal agents (n = 3), analgesics (n = 2), antibiotics (n = 5) and anticoagulants (n = 7). A variety of dose scalars and/or recommendations was observed for various medications. Lean body weight was proposed as a suitable weight scalar for induction of anaesthesia with propofol whereas total body weight for maintenance of anaesthesia with propofol and depolarizing muscle relaxants. Ideal body weight was reported as an appropriate dosing scalar for non-depolarizing muscle relaxants and neuromuscular reversal agents. Both corrected body weight 40% and ideal body weight were reported as suitable weight scalars for post-operative analgesia with morphine. The standard 2-g dose of cefazolin appeared effective in the prevention of surgical site infection. Body mass index stratified dosing of enoxaparin was effective for venous thromboembolism prevention. Conclusion: No drug recommendation achieved an “Excellent” quality of evidence. Limited data suggest that clinicians should consider each individual class of medication when selecting a dose for obese surgical patients. Routine use of fixed-dosing regimens is likely to under- or overdose obese patients thus predisposing them to adverse drug events or treatment failure leading to patient harm