RE4: Chapter 16: Clinical Monitoring I Flashcards
What is the overall incidence of perioperative ischemia in patients with CAD scheduled for cardiac or noncardiac surgeries?
Ranges from 20% - 80%
What fraction of patients scheduled for noncardiac surgery have risk factors for CAD?
What is the major cardiac morbidity after significant vascular surgery?
1/3 and postop MI is 3x as frequent in pts with ischemia!
Prolonged stress-induced ischemia (ST-segment depression)
What is the ST-segment trending monitors average sensitivity/specificity in determining myocardial ischemia?
74% sensitivity
73% specificity
What two chest leads have been shown to exhibit the greatest shift in ST junction and must be accounted for in applying diagnostic criteria for MI?
V2 and V3
Define PR segment.
The PR segment extends from the end of the P wave to the start of ventricular depolarization (appearance of a Q wave)
What point intersects the PR segment?
Isoelectric point or isoelectric reference
Define ST junction.
The ST junction is the point at which the QRS complex ends and the ST segment begins.
SYNONYMOUS WITH THE J POINT!
What is the point between the S wave and ST segment?
J point or ST point
What method of measurement most accurately assesses ST-segment deviation values?
Measuring the degree of ST-segment depression or elevation AT THE J-POINT.
How do you measure ST deviation?
By measuring the horizontal distance i.e. 60ms (1.5mm) or 80ms (2mm) from the J point on the ST segment relative to the iso line.
If 60ms distance from J-point is preferred with tachycardia, what could 80ms from the J-point measurement lead to?
ST-point that intersects a T wave instead of the ST-segment. This would reflect a FALSE significant shift in the ST -segment, suggesting myocardial injury (false positive) or masking a significant ST-segment depression (false negative)
Which has a greater specificity (fewer false positives), horizontal/downsloping depressed ST segment or an upsloping depressing ST segment?
A horizontal or downsloping depressed ST segment has greater specificity than an upsloping depressed ST segment
A common technique for setting ST measurement points involves adjustments of what two or three variables?
Two variables: Iso point and ST point
Three variables: Iso point, J point and ST point
True or False - The precordial leads should be placed via palpating of the costae, not by gross visual estimation of an intercostal space
True
Without a preoperative 12-lead, what leads best monitor for ST-segment elevation or depression?
V3, V4, V5, limb lead III, and aVF (in this order of preference)
What lead is recommended for assessment of narrow QRS complex rhythm?
Lead II
What are the preferred ECG leads to monitor the pt?
V3 and III
What is a MAC1(L)?
Modified chest lead MAC1(L) is a modified augmented chest lead V1
This modified chest lead is configured using limb lead aVL and has been shown to have a diagnostic accuracy similar to true chest lead V1.
What is the gold standard for distinguishing between premature ventricular ectopy and premature aberrantly conducted beats?
MAC1(L) (based on the His-bundle recordings)
Where should the following leads be placed? RA LA LL RL
RA-over the outer right clavicle
LA-over the outer left clavicle
LL-near the left iliac crest or midway between the costal margin and left iliac crest, anterior axillary line
RL-at any convenient location on the body
Where should the following leads be placed? V1 V2 V3 V4 V5 V6 V7 V8 V9 V3R V4R
V1-4th intercostal space right of sternal border
*V2-4th intercostal space left of sternal border
*V3-equal distance between V2 and V4
*V4-Midclavicular line at the 5th intercostal space
V5-Horizontal to V4 on the anterior axillary line or midway between V4 and V6
V6-horizontal to V5 on the mid axillary line
V7-horizontal to V6 on the posterior axillary line
V8-horizontal to V7 below the left scapula
V9-horizontal to V8 at the left paravertebral border
V3R-placed right side of chest wall in mirror image to V3
V4R-placed right side of chest wall in mirror image to V4
*V2, V3 and V4 are precordial leads
What variables should be accounted for when monitoring pts at risk for ischemic events?
Lead placement, ECG lead selection, gain setting, frequency bandwidth
What should the gain of the ECG monitor be set to?
1cm/mV
What should the frequency bandwidth be set to?
Diagnostic mode: 0.05 - 100Hz
OR
Filter mode w/low-end bandwidth intact: 0.05 - 30Hz or 40Hz
When should the diagnostic mode of an ECG monitor be used?
Used when ST-segment analysis is a priority during an anesthetic
What does a PA catheter allow for assessment of?
LV filling pressures, right sided CO, calculation of PVR and SVR
What is essential for accurate interpretation from central lines?
Normal distances, pressures and waveform morphology for CVP, RV, PA and PAOP recordings.
What are normal distances to the junction of the vena cava and RA from various distal anatomic sites? Subclavian RIJ LIJ Femoral vein R median basilic vein L median basilic vein
Subclavian: 10cm RIJ:15cm LIJ: 20cm Femoral vein: 40cm R median basilic vein: 40cm L median basilic vein: 50cm
What is the distance from the RIJ to distal cardiac and pulmonary structures? Junction venae cavae and RA RA RV PA PAWP
Junction venae cavae and RA: 15cm RA: 15-25cm RV: 25-35cm PA: 35-45cm PAWP: 40-50cm
What are normal (absolute values) for intracardiac and pulmonary pressures? MRAP RV PA S/D MPAP PAOP MLAP LVEDP
MRAP: 5mmHg RV: 25/5mmHg PA S/D: 25/10mmHg MPAP: 15mmHg PAOP: 10mmHg MLAP: 8mmHg LVEDP: 8mmHg
What waves will be seen on a CVP tracing when the tip of the catheter lies above the junction of the vena cava and the RA?
a, c, v waves
What produces am a wave?
Contraction of the RA
What produces a c wave?
Closure of the tricuspid valve
What produces a v wave?
Passive filling of the RA (which encompasses a portion of RV systole)
How does the waveform change when the PAC is advanced further through the right intraventricular cavity?
Brisk upstroke (isovolumetric contraction and rapid ejection [RV systole]) and steep downslope (reduced ejection and isovolumetric relaxation [RV systole and diastole])
Why should the PAC w/balloon inflated be in the RV for as short a time as possible?
To reduce incidence of ventricular ectopy or development of a conduction defect (BBB)
What does RVEDP estimate?
RVEDP is used to estimate RVED volume (RVEDV) which approximates RV preload.
What does the CVP port estimate?
RV end-diastolic pressure (EDP)
What does the distal tip of the PAC estimate?
RV systolic pressure via PA systolic reading
How does the waveform change when the PAC is in the PA?
Diastolic pressure is acutely INCREASED with little change in the systolic pressure
What produces the upstroke of the PA waveform?
Opening of the pulmonic valve, followed by RV ejection
What produces the downstroke and dicrotic notch of the PA waveform?
Sudden closure of the pulmonic valve leaflets (beginning of diastole)
How does the PAOP waveform differ from the CVP one?
What produces the a, c, and v wave?
Pressure values are HIGHER.
a wave is produced by LA systole
c wave is produced by closure of the mitral value
v wave is produced by filling of LA and upward displacement of mitral valve during LV systole
What are the labels for the negative waveforms that follow the a, c, and v waves?
What do they represent?
The descents that follow the a, c, and v waves are labeled as x, x1, and y
x descent - start of atrial diastole
x1 descent - downward pulling of the septum during ventricular systole
y descent - opening of the tricuspid valve
How does the PA pressure waveforms correspond to the ECG?
a wave follows depolarization of the atria (P wave)
c and v waves occur at the beginning of ventricular depolarization (QRS complex)
v wave may not appear until shortly after the T wave
What can alter the shape of a waves?
A fib, junctional rhythms, and PVCs
What can ventricular pacing cause on a PAC waveform?
The presence of cannon a waves and the loss of a waves
What can valvular defects cause on the PAC waveform?
An increase in the amplitude of the v wave secondary to the regurgitation
What can significant tricuspid regurg and mitral regurg cause the CVP or PAOP recording to mimic?
Tricuspid regurg = CVP recording to mimic RV tracing
Mitral regurg = PAOP recording to appear as a PA tracing
What can assist in making the diagnosis so whether the PA catheter recording is PA or PAOP?
SVO2
SVO2 will be elevated (>77%) if catheter is in the wedged position (assuming it’s not in a region that is atelectatic; which would produce a false negative result (normal or low SVO2))
Why should you NOT flush a wedged catheter?
Can result in vascular damage ranging from minor endobronchial hemorrhage to massive hemoptysis
Is there a correlation between the size of the v wave and degree of regurg?
No
Who can significant tricuspid and mitral regurg be associated with normal CVP and PAOP reading?
Pts with low volume status and compliant atria
When large v waves are detected on a CVP or PAOP tracing, where should estimates of preload be measured?
Just before the upstroke of the v wave (or c wave when present)
What is CVP an estimate of?
RV preload (RVEDP)
What does low CVP correlate with?
Hypovolemia
What can RV values be elevated 2nd to?
Pulm HTN, VSD, pulmonary stenosis, RV failure, constrictive pericarditis, cardiac tamponade
A false high value can also produce a phenomenon known was what?
Catheter whip which is an exaggerated oscillation of the PA tracing. This can occur with excessive catheter coiling if the tip of the PA catheter is near the pulmonic valve or with dilate pulmonary arteries.
What does PAOP and CVP indirectly assess?
ventricular function
To ensure accurate measurement, the mean or diastolic pressure should always be determined at what point?
End-expiration - this is the time when the pleural pressure is approx. equal to atm pressure.
What zone is the goal for placement of PAC?
Zone III
List in order (high to low) pressure in the West Zone III?
(PAP) Pa > Pv > PA (Alveolar)
What factors contribute to the dynamic state of zone III?
Application of PEEP
Significant diuresis
Hemorrhage
Change in patient position
What can cause a giant a wave (“Cannon a waves) on a CVP or PAOP tracing?
Junctional rhythms Complete AV block PVCs Ventricular pacing (asynchronous) Tricuspid or mitral stenosis Diastolic dysfunction Myocardial ischemia Ventricular hypertrophy
What can cause a loss of a waves or only v waves on a CVP or PAOP tracing?
A fib
Ventricular pacing in the setting of asystole
What can cause large v waves on a CVP or PAOP tracing?
Tricuspid or mitral regurgitation
Acute increase in intravascular volume
What can cause elevated CVPs?
RV failure Tricuspid stenosis or regurg Cardiac tamponade Constrictive pericarditis Volume overload Pulmonary HTN Chronic LV failure
What are potential causes of increased PAPs?
LV failure MS or MR L to R shunt ASD or VSD Volume overload Pulmonary HTN "Catheter whip"
What are potential causes of elevated PAOP pressures?
LV failure MS or MR Cardiac tamponade Constrictive pericarditis Volume overload Ischemia
Where circumstances cause PADP to poorly correlate with PAOP?
When PVR is elevated (ex. COPD, HPV, PE, ARDS, hypercarbia)
When HR > 130
Severe mitral or aortic regurg
When lung zone III has changed to zone II or I
What does increases in PVR and HR cause the PADP related to the PAOP?
PADP exceeds PAOP
What does severe regurg and lung zone changes cause PADP related to PAOP?
PADP is less than PAOP
What is PVR and SVR used as an estimate of?
PVR = RV Afterload SVR = LV Afterload
Define afterload.
Defined a systolic wall stress or the impedance the ventricle must overcome to eject its SV
Which has a lower compliance, PVR or SVR?
SVR
What are normal values of PVRI and SVRI?
PVRI: 45 - 225 dynes/sec/cm5/m2
SVRI: 1760 - 2600 dynes/sec/cm5/m2
What is PVRI and how is it calculated?
What formula is PVRI taken from?
PVRI is PVR calculated with CI instead of CO
PVRI = (PAP - PAOP / CI) x 80
This formula is taken from Ohm’s law
How is SVRI calculated?
SVRI = (MAP - RAP or CVP) / CI ) x 80
How is CI calculated?
What are normal values for CO and CI?
CI = CO/BSA
*CI adjusts for variable of height and weight
CO=5-6L/min
CI=2.8-3.6L/min/m2
What is the most common technique used for determining CO?
Thermodilution
What factors can overestimate thermodilution CO values?
Low injectable volumes
Injectate that is too warm
Thrombus on the thermistor of the PAC
Partially wedged PAC
What factors can underestimate the thermodilution CO values?
Excessive injectable volume
Injectate solutions that are too cold
What factors can cause the thermodilution CO values to be unpredictable?
R to L VSD
L to R VSD
Tricuspid regurg
What technology allows for continuous venous oximetry to be measured?
Fiberoptic refle tante spectrophotometry through two fiberoptics housed in the PAC
What can a decrease in SVO2 reflect a change in?
Oxygen delivery (presumable via a reduction in CO)
What is a normal SVO2?
65-77%
What factors increase SVO2?
L - R shunts Hypothermia Sepsis Cyanide toxicity A wedged PAC Increased in CO
What factors cause a decrease in SVO2?
Hyperthermia Shivering Seizures Reduced pulmonary transport of O2 Hemorrhage Decreased CO2
What is the difference between SVO2 and SCVO2 measurements?
SCVO2 measures venous O2 saturation from the upper body and head while SVO2 depends of blood flow from the SVC, IVC and coronary sinus.
What is the O2 content and venous O2 saturation in the coronary sinus?
O2 content is approx. 7mL/dL
Venous O2 sat is 35%
Is mixed venous O2 content is greater or less in the IVC than the SVC?
Greater
How often should BP be recorded during anesthesia?
At least once every 5 minutes
How often is BP recommended to be taken during induction of anesthesia?
1 minute intervals because of cardio depressant effects of induction agents
What % should NIBP cuffs have a bladder dimension of the circumference of the extremity?
40%
How do loose cuffs, cuffs positioned below the level of the heart or cuffs that are too small change the BP?
Overestimates the BP
How are the SBP, DBP, and MAP effect when the cuff is placed on the thigh or calf?
SBP is greater than the arm
DBP and MAP are lower than the arm
What sounds are heard through a stethoscope during auscultation of BP?
Korotkoff sounds
What is the formula to compare brachial BP to forearm BP?
Brachial DBP = 25.2 + 0.59 x forearm DBP
If the cuff is placed on the forearm and pt is supine or HOB is elevated 45 degrees, how is BP effected?
Overestimates the proximal brachial BP
What is the gold standard for monitoring BP?
Direct measurement of arterial BP
What are risk factors with placement of an arterial line?
thrombus formation Hematoma Vasospasm Embolization Injury to adjacent nerves/veins Loss of limb secondary to poor collateral circulation Iatrogenic injuries Acute blood loss
Where should an arterial line transducer be zeroed and placed?
At the level of the LA
How is BP reading effected if the transducer is positioned below or above the heart?
Above the heart = decrease in BP
Below the heart = increase in BP
What are indications for invasive BP monitoring?
Potential for acute changes in hemodynamics (aortic aneurysm, carotid endarterectomy, craniotomy)
Pts with poorly controlled BP preoperative
Pts with comorbidities that are at substantial risk for stroke or heart attack
If patients have poor vascular compliance, what can occur on arterial tracing?
Overshoot or “ringing”
BP recordings will overestimate SBP and MAP
What can cause a dampened waveform?
How does this affect the BP estimate?
Flexed wrist or low pressure in device
Underestimates BP recording
What size catheter is typically used for an arterial line?
20-gauge is commonly used (22-gauge is optional)
Needle, bevel pointing upward, is directed at a 45 degree angle towards the palpated pulse. Once blood is seen, the angle of the needle is reduced to approx. 30 degrees and then advanced slightly.
What is TEE?
Transesophageal echocardiography
Noninvasive diagnostic tool for monitoring systolic wall motion abnormalities (SWMA), vascular aneurysms, calculation of EF, ventricular preload, and measuring blood flow within the heart chambers across valves.
What produces ultrasound by vibrating when exposed to electric current to produce US waves for a TEE?
Piezoelectric crystals
What is the frequency of piezoelectric crystals in TEE probes?
3.7 to 7 MHz
What is hypokinesia?
Contraction that is less vigorous than normal (wall thickness is decreased)
What is akinesia?
Absence of wall motion (can be associated with MI)
What is dyskinesia?
Paradoxical movement (outward motion during systole)
*Hallmark of MI and ventricular aneurysm
What is the best single view for routine monitoring of SWMA (myocardial ischemia)?
Short axis at the mid papillary muscle level (standard monitoring view)
This includes segments of the myocardium perfumed by all three coronary arteries.
