Hemodynamic monitoring

Editor's Notes

• #2: Understanding the principles and practice of hemodynamic monitoring is essential to the management of critically ill children. This area of medicine not only requires a detailed knowledge of patient physiology and pathophysiology, but demands an understanding of the physical principles that underpin the technology and awareness of the limitations and potential errors of the information gathered.
• #3: The Ideal Monitoring System Physical examination clinical pattern recognition--- level of consciousness,hydration, peripheral edema, respiratory pattern, CRT, toe to core temp, gap, heart rate & rhythm, pulse type, urine output, hepatomegaly, JVP, best clinical practice is most likely to include a combination of clinical skills and noninvasive technologies that will allow the most efficient and least invasive real-time hemodynamic evaluation of the critically ill patient
• #9: Practice– rate, rhythm, ischemia, conduction defects, CO in children hyperkalemia, Post op to detect tachycardia is sinus origin by identifying it high speed 50mm/sec Errors– electrical interference, how to eliminate, heart rate by +nce of R wave & measurement of RR interval, movement artifacts can b minimised by placing lead over bony prominences
• #10: At the bedside, haemodynamic monitoring can be approached in a series of steps aimed at assessing global and regional perfusion
• #14: Pressure is not equal to flow Automated BP devices such as Dinamap (device for indirect noninvasive mean arterial pressure) have reduced the incidence of error associated with the manual technique of measurement. These devices employ the oscillometric method and can measure heart rate as well as SBP, DBP, and mean BP (MBP). The principle is that blood flow through a vessel produces oscillations of the arterial wall, and these are transmitted to an inflatable cuff. Practice– trend analysis, non appropriate for critically ill hemodynamic unstable or on inotropes Errors– AHA width of bladder40% of mid circumference of limb & length is 2 times width Complications--- ulnar nerve palsy
• #15: 1616- harvey anounced that galen was wrong (heart constantly produces blood)
• #16: Complex periodic signals, such as an arterial pressure waveform, can be described mathematically as the sum of a series of simpler waveforms called a Fourier series. Alternatively, the arterial tracing can be thought of as a sum of simpler waveforms, sine waves, and cosine waves. The first harmonic, or fundamental frequency, is equal to the heart rate. The natural frequency of the system is the speed at which the system oscillates once set in motion (also called the resonant frequency) and should be at least 10 times the fundamental frequency. The heart rate in critically ill children is often high, which can cause problems with systolic overshoot, as the harmonic components of the pressure wave approach the resonant frequency of the system. In general, to reproduce a pressure tracing without loss of significant characteristics for clinical use, the measurement system must have an accurate frequency response to approximately 10 times the fundamental frequency (first 10 harmonics). Calibration-- Calibration is a process in which the reading, or output of a device, is adjusted to match a known input value. For example, an electronic pressure transducer may be calibrated against a mercury manometer. If the input to the device is zero, the output should be adjusted so that the reading also is set to zero. This “zeroing” reduces any baseline offset, thus reducing systematic errors in subsequent readings. The system then is calibrated to a nonzero value, for example, 100 mm Hg pressure, and the system gain is adjusted to read this value as well. Zeroing-- The process of eliminating the atmospheric pressure is called vvzeroing,__ and what is essentially being done is opening the  uid column on the measuring device to atmosphere and adjusting the electronics so that atmospheric pressure is the starting value or zero Leveling– eliminates effect of hydrostatic pressure.phlebostatic axis—4th i.c space , vertical line b/w ant & post chest wall Frequency response-- The ability of a measurement system to accurately measure an oscillating signal, such as arterial blood pressure, is dependent upon the system’s frequency response. The system can either overestimate or underestimate the true amplitude of a signal ,overdampning-oscillations dying,underdampning—resonance Impedence--Impedance is the ratio of the change in blood flow along a vessel to the change in the pressure in the vessel. Impedance has both resistive and reactive components .. Only resistance doesnot describe it as also depends on calibre length arrangement of vessels….. When blood is propelled through a vessel at a branch point, a reflected pressure wave back toward the heart increases the impedance of the system. The major sites of wave reflection from vessel branching are from vessels approximately 1 mm in diameter.3 Thus these small vessels contribute significantly to overall impedance.
• #18: 30ml/hr acute rise in pr ---leads to square wave by closure of the valve—a sinusoidal pr wave is formed
• #19: Why measure pressure when needs flow Distal pulse wave amplification Organ blood flow=(art. pr.- venous pr.)/resistance Cvs has 3 types of pr. 1)hemodynamic- by contraction of left ventricle 2)kinetic 3) hydrostatic Pulse pr. Arterial BP –syst. Diastolic & mean Practical information from various BP MAP SAP & DAP--- vascular tone Peripheral pulse pressure ---stroke volume Diff. parts of pulse-upstroke, peak, dicrotic notch & limb, reflection wave(effect on SBP) Diff. wave types– hypovolumia, hyperdynamic pulse(AR, AV fistula, thyrotoxicosis, anemia, sepsis), pulses paradoxus, pulsus alternans(dec myocardial contractility, pulsus bisferiens(hypertrophic cardiomyopathy),pulsus tardus(aortic stenosis)
• #21: Art. Oxyhemoglobin saturation(ABG)—SaO2 Art. Oxyhemoglobin saturation(pulse ox)—SpO2 Both SaO2 & SpO2 – oxy-Hb dissociation curve– SpO2 >95%(PaO2-80-90mmHg) , PaO2 <60 mm Hg– SpO2<90% Lag behind pt. condition av. 4,8or 16 sec It measures & calculates the O2 saturation of Hb in art. Blood not actual O2 content of blood Limitation- motion, low perfusion states Spo2 monitoring--Continuous SpO2 monitoring enables almost immediate detection of even a small reduction in arterial oxygen saturation. However, based on the sigmoid shape of the dissociation curve there is a time delay of the detection of acute oxygenation failure. SpO2 should be maintained >92% in most critically ill patients. The SpO2 signal is often inaccurate in the presence of altered skin perfusion. The inability to measure SpO2 is an indicator of abnormal peripheral perfusion. Lactate metabolism biproduct osf glycolysis. Enden mierhoff—in cytoplasm –2 pyruvate,2 ATP pyruvate –1 atp +lactate or enter into kreb cycle Imp prognostic marker but is not a marker of goal directed resuscitation
• #22: Cvp, urine output, can fail to detect early septic shock, tissue hypoxia—ScVO2 or SVo2 Oxygen content- 2 forms dissolved in plasma <2%, combined with HbSO2-->98% Note-Changes in hemoglobin have a larger impact on arterial oxygenation than changes in PaO2 Hypoxemia (reflected by a decrease in PaO2) has a relatively minor impact on arterial oxygenation if the accompanying change in SaO2 is small. PaO2 influences oxygenation only to the extent that it influences saturation, depending on the position on the oxygen dissociation curve.
• #23: Continuous scvo2 monitoring edwards Imp. As included in surviving sepsis guidelines Study rivers et al. systemic approach vs early goal directed therapy(map, CVP), MAP, CVP SCVO2 Scvo2 in early decompensated congestive heart failure ander et al. –found scvo2 monitoring dec lactates levels
• #24: Problem—need insertion of pulmonary artery catheter
• #25: a decrease in SvO2 of 5% from its normal value (65%-77%) represents a significant fall in DO2 and/or an increase in O2 demand Unfortunately, studies in septic adults have shown that many patients already have a ScVO2 value of> 70% at the start of therapy, although they might still need hemodynamic improvement..
• #26: Preload isDefined as end diastolic myocardial stretch i.e wall tension estimated at bed side as CVP,fluid responsiveness,pulse pr variation,systolic pressure variation Dynamic measures such as PPV, SPV r more accurate in mechanically ventilated pt. Principle behind dynamic measures-swings in intrathoracic pr.
• #28: Site of measurement Normal 5-3mm of Hg, combination of min. rise in CVP & an associated inc. in BP s. Central venous pressure must be considered to be the result of the complex interaction between intravascular volume status, ventricular compliance, and intrathoracic pressure.
• #29: Where to make measurement( top ,bottom or middle)--- base of a wave
• #30: Question wether to give fluid or bolus Patients can be volume limited at CVP values as low as 2 mm Hg (based on sternal angle referenced values), whereas others may respond at CVP values greater than 18 mm Hg Y descent explanation—y descent is due to emptying the atrial volume during early diastole, Hepatojugular reflux– ascending portion --cvp returns to baseline in <10sec.if heart is functioning on flat part– rise is sustained Limitations– very small value so need to filter out all hydrostatic errors , accurate levelling a smaal shift of 1.36cm—1mmHg
• #31: Group A & B techniques r based on physiologic interaction of heart & lung i.e compression of vena cava– dec.venous return--;inc. in RA pr.--RV preload dec.—dec LV output other mechanism postulated to inc. LV SV variation with PPV include the following changes during insp. Caused by inc. transpulmonary pressuresi.e inc. RV afterload--- inc LV preload– dec LV afterload – the end result of these pressure changes is that LV SV inc. while RV SV dec. during PP insp. The delay of pulmonary blood flow transit time results in dec. RV SV translating to dec. LV SV a few heartbeats later i.e usually during expiration. These phasic difference r exaggerated in the setting of hypovolemia---- the underfilled venacava is more collpsible --- the underfilled right atrium is more susceptible to inc. intrathoracic pr. ---these inc. variation in pr. b/w insp. Phase & exp. Phase can b used to identify hypovolemia & volume responsiveness & is the basis of cavallaro group A & B indices , incliding SVV & PPV
• #32: Examines the diff. b/w the SV during the insp. & exp. Phases of ventilation– but required mean to directly or indirectly assess SV ,by eliminating eliminating arterial compliance as a variable
• #34: Distensibility index– barbier & colleagues Viellard & baron ---on SVC collapsability – threshold of 36% sensitivity of 90% specificity of 100%
• #35: Form of reversible volume challenge Volume trnasferred =4.3ml/Kg
• #36: Resp systolic variation test– 3-4 consecutive press. Controlled breaths of inc. peak pressure EEOT- by monnet et al iterrupting mechanical ventilation for 15-20 sec at end of expiration
• #38: The method for sensing the indicator varies according to the injectate and may utilize a thermistor (temperature), densitometry or oximetry (dye), or an ion-selective electrode (lithium charge) The shape of the curve will differ according to where it is measured relative to the site of injection. E.g brief time– peak with short tail—pulmonary artery
• #39: Applied the concept of mass balance to measure blood flow Most technically challenging– but most useful -- as applicable in anatomic shunts & Qs & Qp calculated seperately Best indicator – O2 consumption and CO2 production
• #42: test of choice in critically ill hypotensive patients to identify or exclude a vcardiac_ cause of shock
• #43: Limitations– secretions, movements, sedated & cooperative pt.