05 Aug 12

Less-invasive approaches to perioperative haemodynamic optimization

Posted in Monitoring at 9:28 by Laci

By M Geisen, A Rhodes, M Cecconi

Curr Opin Crit Care 2012;18:377-384

A number of less-invasive haemodynamic monitoring devices have been introduced in recent years, largely replacing the pulmonary artery catheter (PAC) as a standard monitoring tool. Apart from tracking cardiac output (CO), these monitors provide additional haemodynamic parameters. The aim of this article is to review the most widely used less-invasive monitoring modalities, their technical characteristics and limitations regarding their clinical performance.

Recent findings
The utilization of CO monitoring in the perioperative setting has been shown to be associated with improved outcomes if integrated into a haemodynamic optimization strategy. These findings provide the basis of recent recommendations for perioperative monitoring.

Summary
An array of monitoring modalities have been introduced that can reliably track CO in the perioperative setting and make the PAC dispensable in most clinical situations. In order to be used safely and efficiently, knowledge regarding the inherent monitoring techniques and their limitations, their clinical validity and the utility of the parameters provided is crucial.

04 Nov 11

Arterial waveform analysis for the anaesthesiologist: past, present and future concepts

Posted in Monitoring at 0:47 by Laci

By R Thiele and M Durieux

Anesth Analg 2011;113:766-776

Qualitative arterial waveform analysis has been in existence for millennia; quantitative arterial waveform analysis techniques, which can be traced back to Euler’s work in the 18th century, have not been widely used by anesthesiologists and other clinicians. This is likely attributable, in part, to the widespread use of the sphygmomanometer, which allows the practitioner to assess arterial blood pressure without having to develop a sense for the higher-order characteristics of the arterial waveform. The 20-year delay in the development of devices that measure these traits is a testament to the primitiveness of our appreciation for this information. The shape of the peripheral arterial pressure waveform may indeed contain information useful to the anesthesiologist and intensivist. The maximal slope of the peripheral arterial pressure tracing seems to be related to left ventricular contractility, although the relationship may be confounded by other hemodynamic variables. The area under the peripheral arterial pressure tracing is related to stroke volume when loading conditions are stable; this finding has been used in the development of several continuous cardiac output monitors. Pulse wave velocity may be related to vascular impedance and could potentially improve the accuracy of waveform-based stroke volume estimates. Estimates of central arterial pressures (e.g., aortic) can be produced from peripheral (e.g., brachial, radial) tracings using a Generalized Transfer Function, and are incorporated into the algorithms of several continuous cardiac output monitors.

02 Nov 11

The impact of phenylephrine, ephedrine and increased preload on third-generation Vigileo-FloTrac and Esophageal Doppler Cardiac Output measurements

Posted in Fluid management, Inotropic support, Monitoring at 0:40 by Laci

By  L Meng, N Phuong Tran, B Alexander, K Laning, G Chen, Z Kain and M Cannesson

Anesth Analg 2011;113: 751-757

Cardiac output (CO) monitoring based on pulse contour analysis (Vigileo-FloTrac) has the potential to be used for goal-directed fluid therapy in the perioperative setting. However, factors such as vasopressor usage may impact Vigileo-FloTrac’s reliability in tracking CO changes. We tested third-generation Vigileo-FloTrac system’s ability to accurately measure the changes in CO induced by vasopressor administration and increased preload in comparison with esophageal Doppler measurements.

Methods
In 33 anesthetized patients, CO was monitored simultaneously by the third-generation Vigileo-FloTrac and esophageal Doppler. Hemodynamic challenges included phenylephrine (to increase vasomotor tone), ephedrine (to increase myocardial contractility and heart rate), and whole-body tilting (to increase preload). Measurements were performed before and after each intervention.

Results
Overall, 176 pairs of CO measurements were obtained. The difference between paired pulse contour and Doppler measurements of CO was 0.14 ± 2.13 L/min (mean ± SD), and the percentage error (2 SD of the difference divided by the mean CO of the reference method) was 66%. The trending ability of pulse contour versus Doppler was 23% (concordance, the percentage of the total number of data points that are in 1 of the 2 quadrants of agreement) after phenylephrine treatment, 69% (concordance) after ephedrine treatment, and 96% (concordance) after whole-body tilting.

Conclusions
The pulse contour method of measuring CO, as implemented in the third-generation Vigileo-FloTrac device, accurately tracks changes in CO when preload changes. However, the pulse contour method does not accurately track changes in CO induced with phenylephrine and ephedrine.

16 Nov 09

Accuracy of AccuChek glucose measurement in intensive care patients

Posted in Glycemic control, Monitoring at 4:00 by Laci

By I Meynaar, M van Spreuwel, P Tangkau, L Dawson, S Visser, L Rijks, T Vlieland

Crit Care Med 2009; 37:2691-2696

To evaluate the accuracy of the AccuChek Inform point-of-care glucose measurement device as compared with central laboratory glucose measurement.

Design

Prospective, observational study.

Setting

A ten-bed mixed closed format intensive care unit in a 500-bed general hospital. The unit has a computerized insulin protocol aiming for 81 to 135 mg/dL.

Patients

All intensive care unit patients were eligible.

Interventions

None.

Measurements and main results

Paired samples (AccuChek glucose in whole blood calibrated to give whole blood results and central laboratory glucose in serum) were taken simultaneously. In 32 critically ill patients, we obtained the following information: mean ± standard deviation age 71.6 ± 11.9 yrs; mean Acute Physiology and Chronic Health Evaluation II score at admission 17.8 ± 6.7; 239 paired samples were taken from arterial catheters. Mean AccuChek whole blood glucose was 126 ± 36 mg/dL (7.0 ± 2.0 mmol/L); mean central laboratory serum glucose was 137 ± 38 mg/dL (7.6 ± 2.1 mmol/L). Mean difference was 11 mg/dL (0.61 mmol/L) (8%) (95% Confidence Interval = 9-13 mg/dL, p < .001). ISO 15197 guideline requires 95% of point-of-care measurements to be within 15 mg/dL margins with reference <75 mg/dL or within 20% if reference is higher. In total, 216 (90.4%) of AccuChek measurements were within ISO 15197 margins. Because AccuChek was calibrated to give whole blood results, we calculated a correction factor of 1.086 from the two mean values to correct whole blood AccuChek into serum-like results. This is almost the same as the correction factor of 1.080 given by Roche Diagnostics. By multiplying AccuChek whole blood results with 1.086, 225 (94.1%) of results were within the ISO 15197 margins. Hematocrit did not influence AccuChek results in the 0.20 to 0.44 range. Beyond this range, there were not enough data to draw conclusions.

Conclusions

In critically ill patients, the accuracy of AccuChek glucose measurement calibrated to give serum-like results with blood samples derived from arterial catheters is acceptable but falls short by about 1% of complying with the ISO 15197 guideline.

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