Monitoring the Cardiac Surgical Patient - Chapter 4 Flashcards
1
Q
What information does the pulse pressure provide?
A
fluid status and valvular competence
2
Q
What is the disadvantage of the three-electrode system?
A
It cannot monitor the anterior wall and only one pair of electrodes can be selected for monitoring at one time.
3
Q
What is the recommendation for ECG monitoring for cardiac surgical anesthesia?
A
A five-electrode surface ECG monitor be used in the diagnostic mode, with a frequency response of 0.05 to 100Hz. Ideally, this monitor should be able to display at least two leads simultaneously. Typically leads V5 and II are monitored.
4
Q
What systolic pressure variation (SPV) is highly predictive of hypovolemia?
A
SPV > 15 mmHg
5
Q
What precaution should be taken with the placement of the five-electrode system?
A
All leads should be protected with waterproof tape
6
Q
What is a “pop” test?
A
It is a square wave method to estimate both the natrual frequency and the damping coefficient of a system
7
Q
What does the PCWP catheter measure?
A
A direct estimate of LA filling pressure.
An indirect estimate of LV filling pressure.
8
Q
How does an optimally or critically damped system appear after a flush during the “pop” test?
A
A critically damped system will settle to baseline after only one or two oscillations and will reproduce systolic pressures accurately.
9
Q
What is the disadvantage of the five-electrode system?
A
The V5 electrode will interfere with a left thoracotomy incision
10
Q
What is the correlation between CO and area under the curve (AUC)?
A
Inversely proportional
11
Q
What is the recommendation for temperature monitoring during cardiac surgery?
A
Monitor temperature at two sites: a cord site and shell site
12
Q
How does increasing the temperature of thermodilution injectate affect CO measurement?
A
1 degree of increase in the temperature overestimates CO by 3%.
13
Q
Name the two most preferred routes to the CVP insertion.
A
The right IJV is the most preferred, followed by left subclavian vein
14
Q
What are some of the limitations in measuring CO by thermodilution?
A
Inaccurate temp: Blood clot over thermistor tip
Invalid CO: Shunts (LV + RV outputs unequal)
invalid CO: Tricuspid Regurg (recirculation of thermal signal)
15
Q
What are the three positive deflections and two negative deflections in CVP tracings?
A
- Positive deflections: a, c, and v waves
- Negative deflections x and y descents
16
Q
How is thermodilution done?
A
inject fixed volume, 10 ml, (of room temp or iced D5W) into CVP port at end-expiration + measure resulting change in blood temp at distal thermistor (average of 3 measures)
17
Q
What diuretic is used in CPB prime to ensure adequate urine output?
A
Mannitol
18
Q
Can a PAC be placed in a patient with LBBB?
A
LBBB is a relative contraindication. Should PAC be warranted, an external pacing should be immediately available d/t the risk of RBBB.
19
Q
What are bipolar leads and unipolar leads in the augmented three-electrode system?
A
Bipolar leads: I, II, III
Unipolar leads: AVR, AVF, AVL
20
Q
What are some of the contraindications for PAC placement?
A
- significant tricuspid/pulmonary stenosis, endocarditis or mechanical prosthetic valve replacement
- Presence of a right-sided mass (tumor/thrombosis)
- LBBB (relative contraindication) - PAC placement may can cause RBBB. (Have temporary pacemaker ready.)
21
Q
How does an underdamped system appear after a flush during the “pop” test and how does it affect blood pressure monitoring?
A
An underdamped system will continue to oscillate for a prolonged time. In terms of pressure monitoring, this translates to an overestimation of systolic BP and an underestimation of diastolic BP.
22
Q
Will NIBP work during CPB?
A
No. Pulsatile blood flow is absent
23
Q
What is a concern for brachial artery catheterization?
A
Compromised flow distal to catheter placement. It is a secondary option or is not utilized in non-heparinized surgical procedures.
24
Q
What are the leads in the three-electrode system and their augmented leads and what do each lead help detect?
A
I, aVL: lateral ischemia
II: inferior ischemia; dysrhythmias (maximal P wave and QRS height)
III, aVF: inferior ischemia
aVR: Not monitored
25
If a subclavian cannulation is unsuccessful, what action must be taken prior to an attempt on the contralateral side?
CXR must be taken to confirm there is no pneumothorax on the unsuccessful side.
26
What is a shell compartment?
It represents the majority of the body (muscle, fat, bone), which receives a smaller proportion of the blood flow.
27
When is endotracheal leads used and what does it help to monitor?
For pediatric population to detect atrial dysrhythmias
28
What is the contraindication for femoral artery catheterization?
Prior vascular surgery involving the femoral arteries or a skin infection of the groin
29
What is the formula and normal value for systemic vascular resistance (SVR)?
Formula: 80 x (MAP - CVP) / CO
Normal value: 700 - 1600 dyne/s/cm5
30
What voltage does the ECG generate?
0.5mV - 2mV at the skin surface. (Very weak)
31
What do a, c, v waves reflect?
a wave - atrial contraction
c wave - the bulging of blood against the tricuspid valve during systole
v wave - atrial filling
32
What does SvO2 indirectly indicate?
SvO2 is an indirect indicator of CO if O2 sat, VO2, and Hgb remain constant
33
Describe the a, c, v waves in correlation with ECG.
a wave - P wave
c wave - QRS
v wave - after the T-wave
34
What is the main source of ECG artifact?
The loss of integrity of the insulation on leads and connecting cables
35
What does PulseCO SPV + SV predict?
1. Predicts SV in response to volume after cardiac surgery + in ICU
2. Similar estimates of preload v. echo during hemorrhage
3. Helpful in dx of hypovolemia after blast injury
36
What does the PA catheter measure?
RV function, pulmonary vascular resistance (PVR), and left atrial filling pressure (CO, PAP, PCWP, CVP to estimate LV filling volume)
37
What method is used to measure CO by PAC?
Thermodilution with cold injectate by inject fixed volume, 10 ml, (of room temp or iced D5W) into CVP port at end-expiration + measure resulting change in blood temp at distal thermistor.
CO is inversely proportional to the area under the curve.
38
Where should the tip of the PAC be placed in order to accurately measure CO?
The tip of the catheter must be in the PA and not "wedged."
39
How does myocardia ischemia affect PA pressure or PCWP?
MI increases PCWP and PA pressure d/t decreased ventricular compliance
40
What is the normal value for mixed venous oxygen saturation (SVO2)?
75%
41
What is the formula and normal value for pulmonary vascular resistance (PVR)?
Formula: 80 x (PAM - PCWP) / CO
Normal value: 20 - 130 dyne/s/cm5
42
What are some of the causes for a large v wave?
mitral regurgitation, myocardial ischemia, ventricular pacing, PVCs
43
What is the unipolar lead in the five-electrode system?
Precordial unipolar lead (Left precordial V5 or right precordial V4R)
44
What are the four mandatory ASA standards of monitoring and what means are available for the monitoring of those four standards?
I. Qualified personnel
II. Oxygenation: SaO2, FiO2
III. Ventilation: ETCO2, stethoscope, disconnect alarm
IV. Circulation: BP, pulse, ECG
45
What is macro shock?
Current \>1 mA, which is the perception threshold
46
What is a modified three-electrode system?
It is a three-electrode system with different locations of the lead placement
47
What can a narrow pulse pressure on the arterial waveform indicate?
pericardial tamponade and hypovolemia
48
What are the differences among aortic, femoral and dorsalis pedis arterial pressure waveform?
1. Aortic: round waveform, prominent dicrotic notch at the upper part of the descending wave
2. Femoral: delay in pulse transmission (higher systolic pressure) and slurring
3. Dorsalis pedis: loss of dicrotic notch, second wave
49
Name four complications of a radial artery line placement?
1. vasospastic disease
2. prolonged shock
3. high-dose vasopressors
4. prolonged cannulation
50
What are the indications for an ECG?
Diagnosis of dysrhythmias, ischemia, conduction defects, electrolyte disturbances, and monitor effect of cardioplegia during aortic cross-clamp
51
Which type of central line cannulation carries the highest risk for pneumothorax?
Subclavian
52
What is Seldinger method used for?
To place a central venous line
53
What type of cardiac surgical patients is CVP monitoring indicated?
All cardiac surgical patients
54
Which type of the electrode cardiogram is preferred for cardiac surgical patients?
The five-electrode system
55
Which alternate site for a central line is the least preferred?
External jugular vein
56
How many leads can be monitored with the five-electrode system and what are those leads?
Seven: (I, II, III, aVL, aVF, aVR, plus one precordial unipolar leads, V5 or V4R)
57
Name six complications of IJ central line placement.
1. Pnemothorax/hemothorax
2. Air embolism
3. Arrhythmias
4. Carotid artery puncture/cannulation
5. Chylothorax
6. Infection
58
How can mixed venous oxygen saturation (SVO2) be measured?
With PAC or by venous blood gas
59
Which side does the central line cannulation risks the laceration of the thoracic duct?
left side
60
What are some of the relative contraindications for IJ central line placement?
1. Presence of carotid disease
2. Recent cannulation of the IJV
3. Contralateral diaphragmatic dysfunction
4. Thyromegaly or prior neck surgery
61
Describe the damping coefficent of an underdamped, optimal and overdamped system.
underdamped: 0.2 - 0.4
optimal: 0.4 - 0.6
overdamped: 0.6 - 0.8
62
What are the advantages of the five-electrode system?
1. Seven different leads can be monitored simultaneously.
2. Anterior, lateral, and inferior (except for the posterior) wall can be monitored for ischemia.
63
What is a common non-cardiac complication of CPB?
Acute renal failure (2.5% to 31%)
64
What are the five indications for an arterial line?
1. Rapid moment to moment BP changes
2. Frequent blood sampling
3. Circulatory therapies: bypass, IABP, vasoactive drugs, deliberate hypotensionn
4. Failure of indirect BP: burns, morbid obesity
5. Pulse contour analysis: SPV, SV
65
What is the goal of glucose level during CPB and how often should blood glucose be measured
Under 200 mg/dL and every 30-60mins
66
When is noninvasive methods for measuring blood pressure (BP) indicated for monitoring hemodynamic parameters during a cardiac surgical procedure?
NIBP monitoring should only be used until an arterial catheter is placed and as a back-up monitor after arterial catheter placement.
67
Where is the reference point of CVP transducer?
Right atrium
68
How is damping coefficient calculated?
The damping coefficient is calculated by measuring the amplitude ratio of two successive peaks after a flush
69
What are epicardial electrodes also know as?
Atrio-Ventricular (AV) pacing wires
70
What factors affect CVP?
Circulating blood volume (fluid status), venous tone, and RV function
71
What is a "underdamped" waveform and how is it manifested?
The rate of dissipation of the energy of a pressure wave is slower than expected and will display a sharper and higher waveform.
72
How can stroke volume be monitored from the arterial waveform?
SV can be estimated from the area under the aortic pressure wave from the onset of systole to the dicrotic notch
73
What is the advantage of the modified three-electrode system?
Modified three-electrode system can be used to maximize P wave height for the diagnosis of atrial dysrhythmias or to increase the sensitivity of the three-lead ECG for the detection of anterior myocardial ischemia. It can monitor anterior, lateral and inferior wall but not simultaneously.
74
What is the advantage of brachial arterial line over the radial arterial line? Disadvantage?
Advantage: Minimzes arterial occlusion (bent wrist will not affect the pressure monitoring)
Disadvantage: Collateral circulation not as good as the hand. Greater risk for thrombosis
75
What is used to monitor adequate heparin effect in CPB?
Activated clotting time
76
What are some of the reasons for the placement of epicardial electrodes?
1. Before weaning the patient from CPB or before sternal closure.
2. Allow AV pacing in the post bypass period.
3. Record atrial and/or ventricular epicardial ECGs.
4. Most useful in the postoperative diagnosis of complex conduction problems and dysrhythmias.
77
What is the risk involved in axillary artery catheterization?
Cerebral embolus of air or debris
78
Name three factors that invalidate cardiac output measurement by thermodilution.
1. blood clot over the thermister tip
2. Shunts: LV + RV outputs unequal
3. Tricuspid regurgitation: recirculation of thermal signal
79
What is the normal systolic pressure variation?
Down ~ 5 mm Hg due to decreased venous return
80
What can a widened pulse pressure on the arterial waveform indicate?
worsening aortic valvular insufficiency or hypovolemia
81
Distinguish the four different waveforms of PAC
RA pressure waveform: small with a, c, v waves
RV pressure waveform: Increased systolic wave
PA pressure waveform: diastolic pressure increases
PCWP waveform: smaller waveform, similar to RA
82
What is the most common complication associated with PAC insertion?
Dysrhythmias
83
What part of the arterial waveform correlates with the systemic resistance?
the position of the dicrotic notch
84
What is "overdamped" waveform and how is it manifested?
The rate of dissipation of the energy of a pressure wave is faster than expected and will display a rounder and lower waveform.
85
What is the contraindication for radial artery catheterization?
Inadequate collateral flow to the hand
86
What happens to the body when the temperature falls below 32C?
The myocardium is irritable and subject to complex arrhythmias, esp ventricular tachycardia and fibrillation. Coagulation is inhibited.
87
What does CVP provide an estimate of?
Intravascular blood volume
RV preload
88
What is a pulse pressure?
The difference between systolic and diastolic pressures
89
What are the hallmarks of LV failure in a central line monitoring?
Simultaneous readings of high PA pressure and wedge pressure in the presence of systemic hypotension and low CO
90
What is an adequate activated clotting time?
\> 400s
91
What does Somatosensory evoked potentials (SSEPs) help monitor?
The integrity of the spinal cord
92
How does an overdamped system appear after a flush during the "pop" test and how does it affect blood pressure monitoring?
An overdamped system will not oscillate at all but will settle to baseline slowly, thus underestimating systolic and overestimating diastolic pressures.
93
What does the esophageal leads monitor?
atrial dysrhythmia and posterior wall ischemia
94
What is systolic pressure variation (SPV)?
Difference between maximal + minimal values of systolic BP during PPV
95
Simultaneous analysis of what two leads in the five-electrode system can identify 90% of ischmeic episodes?
If leads II and V5 are analyzed simultaneously
96
Name four factors that can increase SVO2.
1. Wedged PAC
2. Low VO2: hypothermia, general anesthesia, NMB
3. Unable to extract O2: Carbon monoxide poisoning
4. High CO: burns, sepsis, L to R shunt, AV fistulas
97
What does the core temperature represent?
The temperature of the vital organs.
98
What can a high or low dicrotic notch position indicate?
high dicrotic notch - high vascular resistance;
low dicrotic notch - low vascular resistance
99
Name three complications of double cannulation of RIJ.
vein avulsion, catheter entanglement, catheter fracture
100
What is micro shock?
Crrent \<1 mA, which requires a means to bypass skin resistance in order to cause hazard
101
Where is IJV located in relation to the carotid artery?
Anterolateral to carotid
102
Name four factors that can decrease SVO2.
1. decreased CO: MI, CHF, hypovolemia
2. decreased Hgb: bleeding, shock
3. decreased SaO2: hypoxia, respiratory distress
4. increased VO2: fever, agitation, thyrotoxic, shivering
103
What are the limitations of TEE?
1. Diseases near the descending aorta
2. airway interferes with TEE signal
104
How should IJV catheter be introduced into the vessel?
From medial to lateral, caudad.
105
What is a catheter "whip?"
A phenonmenon in which the motion of the catheter tip itself produces a noticeable pressure swing. More common with PAC or LV catheters.
106
What is the practical gold standard for evaluating CO?
PAC
107
What are the leads of the modified three-electrode system and what do each lead help to monitor?
CS5, CM5: anterior ischemia
CB5: Anterior ischemia; dysrhythmia (maximal P wave)
MCL1: Dysrhythmias (maximal P wave and QRS height)
CC5: global ischemia
108
What does the central venous pressure measure?
Direct measurement of the RA pressure and indirect estimate of the LV filling pressures
109
Name the five complications of arterial catheterization.
Ischemia, throbosis, infection, bleeding, false lowering of radial artery pressure imemdiately after CPB
110
What is the formula and normal value for Cardiac Index (CI)?
Formula: CO/BSA
Normal Value: 2-5 - 4.2 L/min/m2
111
Does the rectal temperature reflect core temperature?
No. It reflects the muscle mass temperature.
112
What can distort PCWP's estimation of LV filling pressure?
mitral valvular pathology
MI
LV dysfunction
113
Define monitoring.
Continuous or repeated observation + vigilance in order to maintain homeostasis.
114
How does the arterial systolic pressure measurement change between aortic pressure and radial pressure?
The systolic pressure measured in a radial arterial catheter may be up to 20 to 50 mm Hg higher due to decreased peripheral arterial elastance and wave summation
115
What is the landmark for a central IJ line placement?
Apex of triangle formed by lateral (clavicular) and medial (sternal) head of SCM. Aim needle caudally and laterally toward ipsilateral nipple
116
Describe the patient position during IJ central placement.
Place the patient in a supine position, at least 15 degrees head-down to distend the neck veins and to reduce the risk of air embolism. Turn the head away from the venipuncture site.
117
What can cause a distortion of CVP?
LV dysfunction, decreased LV compliance (MI), PHTN, valvular disease of the mitral valve
118
When is the risk for chylothorax increased with the IJ central line placement?
when the line is placed on the left side
119
How does RV failure affect CVP?
CVP is increased
120
When should CVP be measured during the respiration cycle?
At end-expiration
121
What are some of the reasons for arterial catheterization?
1. small or rapid changes in arterial perfusion pressure may increase patient risk requiring beat-to-beat assessment.
2. wide variation in BP or intravascular volume is anticipated.
3. frequent blood smpling is required.
4. assessment of BP cannot be performed by other methods.
122
What is the ultimate purpose of monitoring?
To evaluate oxygen supply and demand
123
What is the damping coefficient of a pressure waveform?
The rate of dissipation of the energy of a pressure wave
124
What two locations in the five-electrode system can the precordial unipolar lead be placed on and what do each position help to monitor?
1. V5 position, along the anterior axillary line in the 5th intercostal space, to best monitor the LV.
2. Right precordium to monitor the right ventricle (RV; V4R lead)
125
How do high and low SVO2 correlate with DO2 (oxygen delivery) and VO2 (oxygen consumption).
high SVO2: increased delivery or decreased consumption
low SVO2: decreased delivery or increased consumption
126
What is the most common access route for a central line placement?
Right internal jugular
127
What is the disadvantage of the three-electrode system?
It cannot monitor the anterior wall
128
How can contractility influence the arterial waveform?
Contractility can be judged by the rate of pressure rise during systole
129
Name some core temperature sites / methods.
nasopharyngal, tympanic membrane, bladder, esophageal, CPB arterial / venous line temperature, PAC thermistor
130
What is natural frequency or resonant frequency in an intravascular pressure monitoring system?
Refers to the frequency at which a monitoring system itself resonates and amplifies the signal
131
What information can be obtained from arterial tracing?
heart rate and rhythm, pulse pressure, respiratory variation and volume status, and hemodynamic indices (stroke volume, contractility, and vascular resistance)
132
How does the catheter lumen diameter, tubing connection length, system compliance, and the density of fluid contained in the system affect the natrual frequency?
Directly proportional to the catheter lumen; inversely proportional to the square root of the tubing connection length, system compliance and the density of fluid contained in the system
133
What happens to the body when the temperature rises above or equal to 41C?
Significant enzyme desaturation and cell damage can occure
134
What can cause a cannon a wave?
heart block (particularly third degree), PHTN, tricuspid valve stenosis, AV dissociation, RA contraction against a closed tricuspid valve
