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CVP AND FLUID RESPONSIVENESS JAMES RUDGE SIMON LAING

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CVP Where measured Usually measured in the SVC and represents the filling pressure of the right atrium Theory CVP should reflect R sided filling pressure Increasing this > greater SV &CO > increased MAP Cardiac output = stroke volume x heart rate MABP = cardiac output x total peripheral resistance

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VODCAST SLIDE PRELOAD STROKE VOLUME FRANK-STARLING MECHANISM STROKE VOLUME FORCE-TENSION MECHANISM AFTERLOAD 1.Increased contractility (inotropy) 2.Decreased afterload 1.Increased contractility 2.Increased preload

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WHY RELEVANT Fluid resuscitation remains the treatment for shock, hypoperfusion and hypotension BUT – if fluid does not increase SV, it serves no benefit and may be harmful Part of EGDT (? debunked by process and arise) Surviving Sepsis Campaign: after 30ml/kg fluid challenge CVP should be maintained >8mmHg for non-ventilated patients 12-15mmHg for MV patients (to overcome PEEP) Achieved by repeated fluid challenge in addition to maintenance fluids

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THE PAPER Marik, Paul E., and Rodrigo Cavallazzi. "Does the central venous pressure predict fluid responsiveness? An updated meta-analysis and a plea for some common sense*." Critical care medicine 41.7 (2013): 1774-1781

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PAPER Meta-analysis of 43 studies involving adult humans. 2105 fluid responsiveness maneuvers 1802 patients in total Studies were largely in ventilated patients: 22 in ICU patients: 4 cardiac surgery patients 20 in operating room patients: 13 cardiac surgery patients 1 healthy volunteer study

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PAPER A meta-analysis reviewing all relevant clinical trials that investigated the ability of CVP to predict fluid responsiveness defined as an increase in CO or SV following a preload challenge, usually a volume challenge or passive leg raising (PLR) maneuver. Study selection: Only those reporting the correlation coeeficient or AUC between CVP and CO following either PLR, fluid challenge, or PEEP challenge

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THE PAPER Mean CVP Responders: 8.2 (+/- 2.3) Non-responders:9.5 (+/- 2.2) Summary AUC: 33 studies Overall:0.56 (95% CI 0.54-0.58) Summary Correlation coefficient between baseline CVP and delta SVI/CI 20 studies Overall:0.18 (95% CI, 0.1–0.25) 50:50 chance of CVP predicting fluid responsiveness – toss a coin Either very low, or low correlation

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AUC ROC CURVES Good explanation: http://ebp.uga.edu/courses/Chapter%204%20-%20Diagnosis%20I/8%20-%20ROC%20curves.html http://ebp.uga.edu/courses/Chapter%204%20-%20Diagnosis%20I/8%20-%20ROC%20curves.html 1 - SPECIFICITY SENSITIVITY In a perfect test: Begin at 0, ascend vertically to upper left corner, traverse vertically to upper right corner I.e. 100% sensitive and 100% specific The AUC would be 100% or 1.0 A diagonal line from point 0 to upper right corner would have AUC of 50%, or 0.5 This is no better than tossing a coin, 50:50 AUC = 0.5 AUC = 1

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AUC ROC CURVES Sensitivity = true positives Specificity = True negatives As the sensitivity of a test goes up, the specificity usually goes down In the example below, the lower the cutoff for cancer, the higher the percentage of identified cancers (sensitivity) This means more false positives occur, lowering specificity We accept a this because it is better to have more cancer scares than more cancer misses

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CORRELATION COEFFICIENTS PERFECT POSITIVE CORRELATION (R) = 1 PERFECT NEGATIVE CORRELATION (R) = -1 No correlation (r) = 0 Correlation = strength of association between variables Does not inform about cause and effect

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CORRELATION COEFFICIENTS r values: 0.0-0.2 = very low, probably meaningless 0.2-0.4 = low, consider further investigation 0.4-0.6 = reasonable correlation 0.6-0.8 = high correlation 0.8-1.0 = very high, ?bias/errors

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