Cardiac Output Monitoring: Believe the Patient copertina

Cardiac Output Monitoring: Believe the Patient

Cardiac Output Monitoring: Believe the Patient

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Day one after mitral valve surgery. The monitor says the cardiac index is a healthy three point two. The lactate is six, the feet are cold and the urine has stopped. One of those numbers is lying — and it isn't the lactate. This episode is cardiac output monitoring, for the exam and for the bedside: how each device works, the physiology underneath, when we actually use them, and where each one misleads you. We start with first principles: cardiac output as heart rate times stroke volume, the exam definitions of preload, afterload and contractility, and why a normal blood pressure can hide a failing pump. Then the Fick principle, what a central venous saturation can and can't tell you, and how to diagnose a low-output state by looking at the whole patient rather than one number. Then the devices, one by one. The pulmonary artery catheter — Stewart–Hamilton thermodilution, the continuous thermal-filament version, floating one by the waveforms, complications, the evidence from ESCAPE and PAC-Man, and why it's still the only monitor that shows you the right heart and the pulmonary circulation directly. PiCCO and LiDCO, and their volumetric extras. Uncalibrated pulse contour monitors, and the arrhythmias, valve leaks, vasoplegia and balloon pumps that break them. Stroke volume and pulse pressure variation, and why an open chest and a failing right ventricle make them unreliable. The oesophageal Doppler — the four assumptions behind its number. Echo, which gives you not just the number but the reason. Bioimpedance, and why it never caught on. And what the console really tells you on ECMO, a BiVAD or an implanted LVAD. We finish with a quick-fire quiz, so you can test yourself on the lot. Chapters (00:00) Cold open — one of these numbers is lying(00:50) The physiology: stroke volume, pressure and flow(01:50) The Fick principle and venous saturations(02:55) Diagnosing low output at the bedside(03:55) The pulmonary artery catheter and thermodilution(05:55) Floating a PA catheter by the waveforms(07:25) Complications and the evidence(09:05) Transpulmonary thermodilution — PiCCO(10:20) Lithium dilution — LiDCO(10:55) Uncalibrated pulse contour monitors(12:00) Stroke volume and pulse pressure variation(12:55) The oesophageal Doppler and its assumptions(15:30) Echo: the number and the reason(16:20) Bioimpedance and bioreactance(16:55) Flow on ECMO, BiVADs and LVADs(17:35) Putting it together(18:05) Quick-fire quiz Key takeaways Cardiac output = heart rate × stroke volume; mean arterial pressure = cardiac output × SVR — so a normal pressure says nothing about which one is holding it upCentral venous saturation is not truly mixed venous, and it can mislead in both directions — low for reasons other than output, and high when the tissues can't extract oxygenDiagnose low output from the whole patient: symptoms, signs, end-organ function, lactate and acidosisThe PA catheter is the reference standard (Stewart–Hamilton thermodilution); continuous versions use a thermal filament and lag behind sudden changeKnow the waveforms — RA 0–8, RV 15–30/0–8, PA 15–30/4–12, wedge ~12 mmHg; never leave the balloon wedged; beware existing left bundle branch blockESCAPE and PAC-Man showed no routine survival benefit — use it where the numbers will change what you doPiCCO adds global end-diastolic volume and extravascular lung water, but needs regular recalibration; any thermodilution is unreliable on ECMOUncalibrated pulse contour is good for trends, poor in AF, aortic regurgitation, vasoplegia, a damped line or a balloon pumpSVV/PPV above ~12–13% predicts fluid responsiveness only in a fully ventilated, closed-chest patient in sinus rhythmOesophageal Doppler assumes a nomogram aortic area, a fixed 70:30 split, the right vessel at a sensible angle, and laminar flow; normal FTc 330–360 msEcho stroke volume = LVOT area × VTI — the diameter is squared, so small errors grow; its real value is telling you why the output is lowOn ECMO or a BiVAD the console shows circuit flow only; an LVAD estimates flow from power and speed References / further reading Binanay C et al. Evaluation study of congestive heart failure and pulmonary artery catheterization effectiveness: the ESCAPE trial. JAMA 2005; 294: 1625–33Harvey S et al. Assessment of the clinical effectiveness of pulmonary artery catheters in management of patients in intensive care (PAC-Man): a randomised controlled trial. Lancet 2005; 366: 472–7Marik PE et al. Dynamic changes in arterial waveform derived variables and fluid responsiveness in mechanically ventilated patients: a systematic review of the literature. Crit Care Med 2009; 37: 2642–7Cecconi M et al. Consensus on circulatory shock and hemodynamic monitoring. Task force of the European Society of Intensive Care Medicine. Intensive Care Med 2014; 40: 1795–815Teboul JL et al. Less invasive hemodynamic monitoring in critically ill patients. Intensive Care Med 2016...
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