JJM MEDICAL COLLEGE DAVANGERE DEPARTMENT OF ANAESTHESIOLOGY<br />SEMINAR ON<br />Blood pressure , ECG , Central venous pressure<br /> CHAIRPERSON PRESENTED BY<br /> DR.RAVISHANKAR . R B DR.RAVIVARMA.D<br /> PROFESSOR PG IN ANAESTHESIA<br /> DEPT OF ANAESTHESIA<br />
1. Indirectbp measurement2. Directbp measurement3. Intra operative ECG4. Central venous pressure<br />
“ Not everything that counts can be counted. And not everything that can be counted counts.” - Albert Einstein<br /> adapted from THE ICU BOOK by PAUL MARINO<br />
“Of all the procedures done in clinical medicine that have important consequences, measurement of blood pressure is likely the one that is done most haphazardly” – kaplan,M.D<br />adapted from THE ICU BOOK by PAUL MARINO<br />
White coat effect – this is not important for anaesthetists</li></li></ul><li>Influence of bladder size<br /><ul><li>The length of the bladder should be at least 80% of the circumference of the upper arm and the width of the bladder should be at least 40% of the upper arm circumference
If the bladder is too small for the size of the arm, the pressure measurements will be falsely elevated
A cuff that is larger than needed will not produce spurious pressure recordings</li></ul>Am J Cardiol1989;63:983-985<br />
“It is what we think we know already that often prevents us from learning”<br /> - Claude Bernard<br />
The sounds<br /><ul><li>The first korotkoff sound corresponds to the systolic pressure but the value is lower than IBP
The disappearance fifth korotkoff sound corresponds to the diastolic pressure but the value is higher than IBP</li></li></ul><li>Problems with human ear<br /><ul><li>Best hearing frequency- 200 to 4000 Htz
Lowest hearing frequency – 16 Htz</li></ul>“ A situation exists where the human ear being used to measure BP is, at best, basically deaf to some sound it should be detecting”<br />adapted from Am J Cardiol 1989;63:983-985<br />
Some habits cannot be changed<br /><ul><li>The bell of the stethoscope is a low frequency transducer
The diaphragm is designed to detect high frequency sounds
Since korotkoff sound is in the lower frequency BELL should be used for BP measurement</li></ul>Recommendations for blood pressure measurement. Circulation 2005;111:697-716<br />
SBP decreases by 8 mm<br /> DBP increases by 5 mm<br /> SBP increases by 8 mm<br /> DBP decreases by 5 mm<br />
Deflation rate<br /><ul><li>Recommended rate is 2 to 3 mm per sec
In case of slow heart rate it is 1 mm per pulse
When the rate is greater than 3 mm per sec</li></ul>Systolic is underestimated and diastolic is over estimated <br />
“Shock”ing truth<br /><ul><li>Korotkoff sounds are generated by blood flow
low flow states can diminish theintensity of these sounds.
When this occurs, the sounds may not be heard at first and this will result in falsely low recordings for the systolic bloodpressure.</li></ul>Cohn JN. Blood pressure measurement in shock. JAMA 1967; 119:118.<br />
Oscillometric method<br /><ul><li>The oscillometric method uses the principle of plethysmography
When an inflated cuff is placed over an artery, the pulsatilepressure changes in the artery will be transmitted to the inflated cuff, producing similar changes in cuff pressure.
The periodic changes in cuff pressure are then processed electronically to derive a value for the mean, systolic, and diastolic blood pressures.</li></li></ul><li>The accuracy of oscillometric blood pressure measurements is disturbingly low.<br />J clinMonit1990;6:284–298<br />
Belief ?<br /><ul><li>The distinction between pressure and flow is important to recognize because there is a tendency to equate pressure and flow in certain situations
It is most evident in the popularity of pressor or vasoconstrictor agents in the management of clinical shock.
In this setting, an increase in blood pressure is often assumed to indicate an increase in systemic blood flow</li></li></ul><li><ul><li>Ejection of the stroke volume from the heart is accompanied by a pressure wave and a flow wave.
When vascular impedance (i.e., compliance and resistance) is increased the velocity of the flow wave is decreased.
Thus when vascular impedance is abnormal, the arterial pressure is not a reliable index of blood flow.</li></li></ul><li>Direct measurement<br />
“Mean”arterial pressure<br /> 1. The mean pressure is the true driving pressure for peripheral blood flow.<br /> 2. The mean pressure does not change as the pressure waveform moves distally<br /><ul><li>Heart rates faster than 60 beats/minute, which are common in critically ill patients, lead to errors in the estimated mean arterial pressure.</li></li></ul><li>Systolic amplification <br /><ul><li>The increase in systolic pressure in peripheral arteries is the result of pressure waves that are reflected back from the periphery .
These reflected waves originate from vascular bifurcations and from narrowed blood vessels.
Amplification of the systolic pressure is particularly prominent when the arteries are noncompliant, causing reflected waves to bounce back faster</li></li></ul><li>transducer<br />
Resonant Systems<br /><ul><li>Vascular pressures are recorded by fluid-filled plastic tubes that connect the arterial catheters to the pressure transducers.
This fluid-filled system can oscillate spontaneously, and the oscillations can distort the arterial pressure waveform
Prognostic value of routine preoperative ECG<br />“ Due to improvement in accuracy of clinical cardiac risk factors to identify patients who are at increased risk of peri operative cardiac events, the routine use of ECG in all patients is of questionable value”<br />noordzij et al: Am J Cardiol 2006;97:1103-1106<br />
<ul><li>The magnitude and extent of Q waves provide a crude estimateof LVEF and are a predictor of long-term mortality.
Although the optimal time interval between obtaining a 12-leadECG and elective surgery is unknown, general consensus suggeststhat an ECG within 30 days of surgery is adequate for thosewith stable disease in whom a preoperative ECG is indicated.</li></li></ul><li>Electrographic monitoring systems<br /><ul><li>All electrocardiographic monitors use filters to narrow the signal bandwidth in an attempt to reduce environmental artifacts and improve signal quality
Most modern electrocardiographic monitors allow the operator a choice of several bandwidths. </li></ul> (1) a diagnostic mode with a bandwidth of 0.05 to 130 Hz <br /> (2) a monitoring mode with a bandwidth of 0.5 to 40 Hz <br /> (3) a filter mode with a bandwidth of 0.5 to 20 Hz.<br />
Criteria for Acute Myocardial Ischemia<br /><ul><li>1 mm (0.1 mV) or more of horizontal or down-sloping ST-segment depression
rapidly up-slopingST segment that is also depressed less than 1.5 mm is considered normal
T-wave changes not accompanied by significant ST-segment displacement rarely signify myocardial ischemia</li></li></ul><li>The best lead<br /><ul><li>When two leads can be monitored simultaneously, lead II is the best compliment to lead V5 because it significantly improves the sensitivity for ischemia and usually reveals the p wave for dysrhythmia diagnosis</li></li></ul><li>Different “avatars” <br />
There are two methods of CVP monitoring<br /><ul><li>manometer system: enables intermittent readings and is less accurate than the transducer system
transducer system : enables continuous readings which are displayed on a monitor.</li></li></ul><li>Body Position<br /><ul><li>The zero reference point for venous pressures in the thorax is a point on the external thorax where the fourth intercostal space intersects the mid- axillary line
It corresponds to the position of the right and left atrium when the patient is in the supine position.
It is not a valid reference point in the lateral position</li></li></ul><li>End-Expiration ?<br /> Intravascular pressures should be measured at the end of expiration, when they are equivalent to the transmural pressure<br /> in PEEPwhts the problem ?<br />