Alternative Methods to Determine Optimum Mean Arterial Blood Pressure After Cardiac Arrest using Cerebral Oximetry
CCCF ePoster library. Bhate T. Oct 27, 2015; 114772; P58 Disclosure(s): Dr. Griesdale is supported by the VGH & UBC Hospital Foundation Best of HealthFund.
Dr. Tahara Bhate
Dr. Tahara Bhate
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Abstract
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P58


Topic: Basic/Translational Science


Alternative Methods to Determine Optimum Mean Arterial Blood Pressure After Cardiac Arrest using Cerebral Oximetry



Tahara Bhate, J. Bitman, M. Sekhon, D. Griesdale

Dept of Medicine, Division of Critical Care, Vancouver General Hospital, University of British Columbia, Vancouver, Canada | Dept of Medicine, Division of Critical Care, Vancouver General Hospital, University of British Columbia, Vancouver, Canada | Dept of Medicine, Division of Critical Care, Vancouver General Hospital, University of British Columbia, Vancouver, Canada | Dept of Medicine, Division of Critical Care, Vancouver General Hospital, University of British Columbia, Vancouver, Canada

Introduction:

In hypoxic ischemic brain injury (HIBI), the effective zone of cerebral autoregulation becomes narrowed and right-shifted. Optimizing mean arterial pressures to maintain adequate cerebral perfusion may be required in this population. The zone of autoregulation can be identified by examining how fluctuations in mean arterial pressure result in changes in regional cerebral saturation of oxygen (rSO2)(1). The correlational coefficient between MAP and rSO2 is termed the cerebral oximeter index (COx) and varies between -1 and +1. Positive values indicate impaired autoregulation with near zero or negative values indicating intact autoregulation. There are several reported methods to identify the zone of autoregulation and optimal mean arterial pressure (MAPOpt) including: intersection of two regression lines(2) and the MAP value with the most negative COx (nadir) when there is a trend of increasing COx away from this nadir(3). ICM+® brain monitoring software (Division of Neurosurgery, Cambridge UK) will plot a fitted curve to determine the optimal MAP. This would avoid the limitations of interpretation and spurious data points with the nadir COx method.



Objectives: The goal of this project was to determine the bias and limits of agreement comparing the nadir COx method (nadir COx) vs. the fitted curve (fitted COx). In addition, we developed manual rules (manual COx) that can be used in absence of a fitted curve. We additionally sought to compare the bias and limits of agreement between the manual COx and fitted COx rules.

Methods: Invasive MAP and rSO2 (INVOS®, Covidian, Ireland) were captured into ICM+® each 6 seconds for 20 patients admitted to the ICU after cardiac arrest. COx values were plotted against MAP for each patient in 6 hour periods for 24-72 hours(n=119). Investigators developed manual COx rules to determine MAPOpt from cerebral oximetry data. These were validated by assessing inter-observer agreement between 3 observers on a subset of the data (n=36). Using the full dataset, we then compared both the nadir COx and manual COx methods to the fitted COx values obtained using ICM+®. Results were compared using percent agreement with 5 mmHg, intraclass correlational coefficient (ICC), and Bland-Altman plots.

Results:

Consistent results were obtained with the manual COx method, with 89% overall agreement within 5mmHg between the 3 observers, and an ICC of 0.96 (95%CI 0.93-0.98). All 3 methods varied in the percentage of data that was interpretable, from 53.8% (nadir COx) to 85.7% (fitted COx). When compared to the fitted COx, the manual COx method performed superior to the nadir COx method (Figure 1). A MAPopt within 5mmHg of that calculated the fitted COx method was obtained for 61.3 and 85.7% of the data for nadir COx and manual COx methods, respectively. The ICC for the nadir COx method was 0.788 (95%CI 0.661-0.869), compared to 0.921 for the manual COx (95%CI 0.877-0.95). In addition, a Bland-Altman plot demonstrated a mean difference in values between the nadir COx and fitted COx of -2.17mmHg (95%CI -3.90, -0.43), compared to 0.46mmHg (95%CI -0.46, 1.37) between the manual COx and fitted COx methods.



Conclusion: The nadir COx method does not provide a good approximation of the more sophisticated analysis provided by ICM+®. Determination of MAPOpt in future should be done where possible with computer based analysis, using either ICM+® or other analogous software; if manual data interpretation is required, the manual COx method offers a superior alternative to current practice.

References: (1) Ameloot K, Meex I, Genbrugge C, Jans F, Boer W, Verhaert D, et al. Hemodynamic targets during therapeutic hypothermia after cardiac arrest: A prospective observational study. Resuscitation 2015;91:56–62.
(2) Brady KM, Lee JK, Kibler KK, Easley RB, Koehler RC, Shaffner DH, et al. Continuous Measurement of Autoregulation by Spontaneous Fluctuations in Cerebral Perfusion Pressure Comparison of 3 methods. Stroke 2008;39:2531–7.

(3)Lee JK, Brady KM, Chung S-E, Jennings JM, Whitaker EE, Aganga D, et al. A pilot study of cerebrovascular reactivity autoregulation after pediatric cardiac arrest. Resuscitation 2014; 85:1387-1393
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