Morbidly obese patients are at increased risk of intra-operative haemodynamic instability, which may necessitate intensive monitoring. Non-invasive monitoring is increasingly used to measure cardiac output; however, it is unknown whether the weight-based algorithm utilised in these devices is applicable to patients with morbid obesity. We compared the level of agreement and trending ability of non-invasive cardiac output measurements (Nexfin ) with the gold-standard thermodilution technique in 30 morbidly obese patients undergoing laparoscopic surgery. Bland-Altman analysis revealed a mean (SD) bias of 0.60 (1.62) l.min (limits of agreement -2.67 to 3.86 l.min ) and the precision error was 46%. Polar plot analysis resulted in an angular bias of 2.61°, radial limits of agreement of -60.08° to 49.82° and angular concordance rate was 77%. Both agreement and trending were outside the Critchley criteria for the comparison of cardiac output devices with a gold-standard. Nexfin has an unacceptable level of agreement compared with thermodilution for cardiac output measurement in morbidly obese patients.

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.

Peripheral intravenous (IV) catheters can break off while still in the patient, with possible detrimental effects such as upstream migration to the heart. These catheters have probably been damaged by the needle during a difficult insertion. A peripheral IV catheter was removed in a 90 year old patient and only half of the catheter was retrieved. By using ultrasound examination the remaining part of the IV catheter was identified, and retrieved surgically, before it could migrate towards the heart. This case report suggests that ultrasound should not only be used for difficult placement of a peripheral IV catheter, but can also be used when removal is complicated.

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