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4.4.3 Indications for PAC Use
PAC is clinically indicated for assessment of these main variables and their response
to therapeutic interventions during a wide range of different disease entities:
• Loading status, mainly including right heart failure, pulmonary dysfunction, pul-
monary hypertension, severe left ventricular failure needing extra treatments like
intra-aortic balloon pump, or shock (septic, cardiogenic, or non-cardiogenic)
• Main hemodynamic parameters of the right heart and the lung, including pulmo-
nary artery pressure (PAP), pulmonary artery occlusion pressure (PAOP), pul-
monary vascular resistance (PVR), and mixed venous oxygen saturation (SvO
2
)
• Monitoring and assessment of cardiac output (CO)
However, risks and benefits of PAC insertion should be assessed before its utili-
zation. Often in low- to moderate-risk cardiac patients, the risks outweigh the ben-
efits, and it is not recommended to use PAC as a “routine” monitoring in such
cardiac surgery patients, especially if there is not enough experience and sufficient
skill in insertion of PAC and interpretation of its data. In other words, like many
other diagnostic devices and technologies, “appropriate patient, sufficient skill in
PAC insertion and data analysis, and, finally, appropriate setting” should be present
before utilization of PAC.
4.4.4 Contraindications of PAC
These are usually due to anatomical causes and include:
• Tricuspid valve stenosis
• Pulmonary valve stenosis
• Previous mechanical prosthesis in any of the two above valves
• Current endocarditis in any of the two above valves
• Tumor and/or mass in right atrium or right ventricle
• Thrombosis in right atrium or right ventricle
• Tetralogy of Fallot due to the potential hyper-reaction of the pulmonary artery in
such patients to mechanical stimuli causing spasm and cyanotic spells
• Current underlying severe arrhythmia mandating full preparedness to treat any
hemodynamic derangement
• Newly inserted pacemakers which could lead to displacement of the pacemaker
wire
• Contraindications to insertion of CVC (see the previous section)
4.4.5 Technical Considerations for PAC Insertion
The basic principles for PAC insertion are in essence similar to CVC insertion;
however, a few more points should be considered which are discussed here:
• The most preferred approach is right internal jugular vein, while subclavian and
femoral veins are not routinely used especially for cardiac surgery patients.
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• Guiding the catheter through its path in order to reach to pulmonary artery is
used by three ways: the curve of the wave on monitor and its trend, fluoroscopic
assessment of catheter tip, and electrocardiography (ECG)-guided approach;
however, in intensive care unit, usually the curve of the wave is used for catheter
insertion and controlled by chest X-ray.
• Changing the patient position to a head-down and right lateral tilt helps the tip of
the PAC to progress from right atrium (RA) to right ventricle (RV) and pulmo-
nary artery (PA).
• An introducer sheath is inserted first, which is mainly like a CVC; this sheath is
the conduit for passage of PAC and lets us move PAC back and forth; however,
it is a relatively large-bore CVC, nearly 8.5–9 F, and so mandates vigorous cau-
tion during its insertion.
• The catheter is 110 cm length and usually 7–8 F. having length markers at 10 cm
intervals for accurate and careful back-and-forth movements of the catheter.
• There is a sterile plastic cover on the catheter; this plastic cover should be
attached firmly to the distal head of the introducer sheath to prevent contamina-
tion, though it is not fully protective and mandates strict adherence to infection
prevention methods and, more importantly, avoidance of unnecessary back-and-
forth movements.
• Before passing the catheter tip through the introducer sheath and advancing it to
the right heart, zeroing of the catheter with the monitoring system at the level of
the right atrium should be done while the patient is at supine position; also, the
tip of PAC should be raised about 30 cm, and the pressure should be checked
with the monitor which equals 22 mm Hg.
• PAC has usually 4–5 lumens for the following purposes (demonstrated in
Fig. 4.4):
1. Distal lumen near the tip of catheter for measurement of pulmonary artery
pressure.
2. A balloon located 4–5 cm proximal to the tip of catheter and 1.5 mL volume
which should be filled for “flow-directed movement of the catheter”; its related
lumen should be attached to a specific 2
mL syringe, and the balloon should be
checked for symmetrical filling before insertion of PAC; also, the balloon should
not be filled when PAC tip is in wedge position to prevent unwanted injuries in
lung tissue and pulmonary arterial branches.
3. The most proximal lumen opening nearly 30 cm proximal to the tip of catheter
used for measurement of central venous pressure or RA pressure.
4. The 4th lumen having a thermistor for measurement of cardiac output using ther-
modilution method.
5. Often the 5th lumen being used for assessment of mixed venous blood oxygen
saturation (SvO2).
When advancing PAC through introducer sheath from the right internal jugular
approach, we should have different related curve patterns at related distance inter-
vals, i.e., for CVP (10–15 cm), RA pressure (15–25 cm), RV pressure (30–35 cm),
PA pressure (40–45 cm), and wedge pressure (45–55 cm) as described below and
demonstrated in Fig. 4.5:
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Fig. 4.4 PAC ingredients: note the tip of the balloon in three subsequent figures to be inflated; the
3rd figure demonstrates a filled balloon in large view
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1. Central venous pressure curve, demonstrating the tip of the catheter being located
in central veins and/or RA, for CVP at 10–15 cm and for RA pressure at about
15–25 cm.
2. The catheter tip passes through the tricuspid valve to go to the right ventricle
(RV); a significant increase in systolic deflection is seen, and the diastolic deflec-
tion does not change so much; this part of the curve belongs to RV when PAC tip
goes in as much as 30–35 cm.
30
Pressure Right atrium
Right ventricle
Pulmonary artery
Pulmonary artery wedge
20
10
0
mmHg
1
A
LA
Balloon
4
LV
2
3
Fig. 4.5 A schematic presentation of the PAC course and its related pressure waveforms in car-
diac chambers, pulmonary artery, and main left pulmonary artery
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3. With catheter progress through the pulmonary valve to reach the entry of pulmo-
nary artery (PA), a dicrotic notch is seen in the point just after the peak of systole,
while the bottom of the pressure wave curve increases suddenly showing the
diastolic pressure of PA which is higher than the diastole of RV and resembles
the wave contour of the systemic arterial pressure; of course in a smaller scale;
so PA pressure appears when PAC tip goes in about 40–45 cm.
4. Catheter progression as much as about 5 cm causes another new pattern in wave
contour which would be nearly at 45–55 cm from PAC tip; here, there would be
another change in the wave contour which indicates pulmonary artery wedge
pressure (PAWP) or pulmonary artery occluding pressure (PAOP) which could
usually be demonstrated on the monitor screen play after PAC balloon dilatation
leading to wedge location of the tip of catheter; of course, PAC tip should not
stay in wedge position for more than a few minutes to prevent unwanted compli-
cations like rupture of the pulmonary arterial branches or segmental necrosis of
lung tissue; frequent withdrawal of PAC as much as 3–5 cm prevents PAC tip
lodging, hence preventing such problems.
5. If these curves are not seen in the above length intervals, there is a real chance of
catheter coiling, a dangerous complication of PAC discussed in the next para-
graph; for prevention of such an event, strictly following the curves is a useful
preventive strategy.
4.4.6 Complications of PAC
In 2003, the American Society of Anesthesiologists’ task force on PAC (2003)
stated that “overall deaths attributable to PAC are 0.02–1.5%” and also classified
PAC complications in three main categories:
1. PAC complications due to complications of CVC, i.e., “arterial puncture, postop-
erative neuropathy (pain and sensation deficit), air embolism (air in blood ves-
sels), and pneumothorax (air outside the lungs), reported in less than 3.6 %.”
2. The complications mainly related to the mechanical effects of the catheter itself,
i.e., “severe dysrhythmias, right bundle branch block, and complete heart block,
seen in 0.3–3.8 %.”
3. The complications related to persisting catheter in place, i.e., “rupture of the
pulmonary artery and its attributed death, infarction of the pulmonary tissue,
catheter-related sepsis, positive catheter tip culture, valvular/endocardial vegeta-
tion, thrombophlebitis, mural thrombosis, and thrombosis of the veins, i.e., clots
in vein, occurring between 0.03 and 3 %.”
Sufficient skill, enough experience, and having a high index of suspicion and
vigilance in detection of any complication may help the clinician prevent these
potentially deadly complications or diagnose them as early as possible. The follow-
ing comments should be remembered regarding the complications of PAC:
• Atrial or ventricular arrhythmia, often in the form of ventricular premature con-
tractions, is seen during catheter passage from RV; these arrhythmias are usually
benign; head-up and right lateral position might decrease the incidence of this
complication.
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• PAC could lead to right bundle branch block (RBBB); so in patients with under-
lying left bundle branch block (LBBB), complete atrioventricular block (AV
block) would be possible; though not frequent, it could be lethal.
• Pulmonary artery injuries might cause lethal pulmonary artery perforation or
rupture mandating emergent surgery or stenting of the rupture; late pulmonary
artery false aneurysm is also reported.
• Pulmonary infarction due to catheter dislodgement in segmental or bronchial
pulmonary arterial branches is another potential complication.
• Right ventricle rupture, a highly morbid complication needing extreme vigilance
for prevention, once occurred, rigorous and prompt surgical treatment in the first
minutes is mandatory.
• Endobronchial hemorrhage is a highly morbid complication especially in patients
receiving anticoagulants.
• Catheter coiling due to excessive and repetitive back-and-forth movements of the
catheter, which might even mandate surgical catheter removal.
• Catheter tip balloon rupture.
• Catheter tip entrapment is RV trabeculae leading to mechanical injury of RV
wall, if the balloon is not filled.
• Tricuspid or pulmonary valve mechanical injuries if the catheter is withdrawn with-
out deflation of the catheter tip balloon (Taylor and Tiede 1952; Swan et al. 1970;
Swan and Ganz 1974, 1975, 1979; Elliott et al. 1979; Kelly et al. 1981; Sise et al.
1981; Hardy et al. 1983; Mohr et al. 1987; Matthay and Chatterjee 1988; Durbin
1990; Himpe 1990; Ikeda et al. 1991; Urschel and Myerowitz 1993; Westenskow
and Silva 1993; Shevde et al. 1994; Zarshenas and Sparschu 1994; Poelaert et al.
1995; Sumita et al. 1995; Connors et al. 1996; Mueller et al. 1998; Rhodes et al.
2002; Cotter et al. 2003; Gibson and Francis 2003; Masugata et al. 2003; Richard
et al. 2003; Sandham et al. 2003; Yu et al. 2003; Domino et al. 2004; Monnet et al.
2004; Uzun et al. 2004; Binanay et al. 2005; Harvey et al. 2005; Oransky et al. 2005;
Shah et al. 2005; Stevens et al. 2005; Summerhill and Baram 2005; Swan 2005;
Harvey et
al. 2006; Heresi et al. 2006; Lavine and Lavine 2006; Vender 2006;
Wheeler et al. 2006; Williams and Frenneaux 2006; Akima et al. 2007; Bussieres
2007; Leibowitz and Oropello 2007; Mielniczuk et al. 2007; Pirracchio et al. 2007;
Frazier and Skinner 2008; Langesaeter et al. 2008; Mathews and Singh 2008; Vincent
et al. 2008; de Waal et al. 2009; Katsikis et al. 2009; Ramaswamykanive and Bihari
2009; Renner et al. 2009; Schramm et al. 2009; Hida et al. 2010; Nossaman et al.
2010; Reuter et al. 2010; Takada et al. 2010; Zuffi et al. 2010; Alhashemi et al. 2011;
Barmparas et al. 2011; Gurgel and do Nascimento 2011; Hessel and Apostolidou
2011; Richard et al. 2011; Schwann et al. 2011; Trof et al. 2011; Trzebicki et al.
2011; Booth et al. 2012; Godoy et al. 2012; Gologorsky et al. 2012; Pipanmekaporn
et al. 2012; Truijen et al. 2012; Kalra et al. 2013; Rajaram et al. 2013; Satler 2013).
4.5 Cardiac Output Monitoring
Cardiac output monitoring is performed using a number of invasive and noninvasive
approaches. Also, it is a very determining issue in cardiovascular monitoring, espe-
cially in critical patients including cardiac surgery patients. A brief discussion of the
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currently used methods for cardiac output assessment is presented here, though the
interested reader could find detailed discussion in the related textbooks. Also, a
great number of clinical and laboratory studies have been performed on this topic
due to the importance of this variable especially in critically ill patients to define the
benefits and weaknesses of each method.
4.5.1 Fick Principle
Fick principle was described in 1870 by the German physiologist and physicist Adolf
Eugen Fick, who developed this principle to be used for a number of applications
including direct cardiac output measurement. The Fick principle assumes that the
amount of oxygen taken up by the lungs (i.e., O
2
consumption) is taken up from the
air, entirely transferred through the lungs and transported in blood flow (circulation).
Based on this fact, we use the Fick principle and calculate how much oxygen is taken
from the air and is then transported to the tissues by pulmonary circulation.
So, if we calculate the amount of oxygen transferred from the air to the lungs, we
could assume it as the amount of oxygen transported from the lungs to the tissues; hence,
we could consider “consumed oxygen” instead of “transported oxygen” to calculate
“cardiac output.” In other words, we can simply express Fick principle as follows:
O uptakebythe lungs Oconsumptionbytotal body VO
22 2
() ()
==
We could calculate arterial oxygen content (CaO
2
) and venous oxygen content
(CvO
2
) and then subtract them (CaO
2
− CvO
2
); finally, we multiply the result in
cardiac output (CO); so we will have the Fick formula:
VO CO CaOCvO
22
2
=.
×
()
−
And then we resolve the above formula for cardiac output:
CO VO CaOCvO
222
=/ .−
()
Although the Fick principle seems basically simple and is still considered as the
most accurate method of cardiac output measurement, in clinical practice, its calcu-
lation is very difficult and mandates sophisticated technical procedures, being used
more commonly in experimental labs than the clinical setting.
Other less sophisticated and more practical methods have been developed based
on Fick principle with some modifications in practice. One of these is the “partial
carbon dioxide rebreathing” method which uses carbon dioxide instead of O
2
for
calculations discussed here.
4.5.2 Indicator Dilution Techniques
Today, mainly two indicators are used for calculation of cardiac output in the clini-
cal setting and include lithium and cold water; these methods use an indicator
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(thermal or chemical) and calculate its passage time and/or passage dilution model
after passing downstream the blood flow circulation; based on the technical method
of measurement, the cardiac output measurement techniques are classified as fol-
lows (Table 4.2):
4.5.2.1 Techniques Using Cold Water and Its Temperature Change
• Thermodilution using PAC (PAC-TD) with application of a bolus of cold water
and measurement of cardiac output based on this injection. Thermodilution
method is usually done using a pulmonary artery catheter (i.e., PAC-TD) and is
considered the gold standard for cardiac output monitoring, though the technique
needs many points to be considered and is also invasive and relatively expensive
and needs experience and enough training. Although PAC-TD method has been
defined as the superior method for cardiac output assessment, there are studies
considering its accuracy and invasiveness, so suggesting other methods includ-
ing less invasive thermodilution methods, pulse contour cardiac output assess-
ment methods, respiratory-based estimates, esophageal Doppler monitoring, and
flow probe and transcutaneous Doppler for cardiac output monitoring.
• Continuous thermodilution using PAC (continuous thermodilution with PAC)
• Transpulmonary Thermodilution: Conventional thermodilution method man-
dates using a PAC with a thermistor in its tip; this system has a thermistor inside
the CVC and calculates the variables using the curve of arterial line (usually
from femoral, axillary, or brachial arteries); so, in this system, a bolus dose of
cold water is injected in right atrium, and at the same time, the temperature fluc-
tuations are recorded in the next seconds, measured using a central arterial line.
CO is calculated based on these temperature changes to decrease measurements
errors, usually three different measurements are done and the average CO is
calculated. Also, the measurements are done in 3–10 min to have more accurate
data. The “PiCCO” system (Pulsion Medical Systems, Munich, Germany) uses
this technology and estimates these variables: “CO, cardiac output”; “ITBV,
intra-thoracic blood volume”; “GEDV, global end-diastolic volume”; and
“EVLW, extravascular lung water”; the use of transpulmonary thermodilution at
bedside is relatively easy; GEDV is a good index of ventricular preload.
Table 4.2 Commonly used cardiac output monitoring devices
Techniques using cold water and its temperature change including:
Thermodilution using PAC (PAC-TD) with application of a bolus of cold water and
measurement of cardiac output based on this injection
Continuous thermodilution using PAC (continuous thermodilution with PAC)
Transpulmonary bolus thermodilution (often using a CVC and an arterial catheter like
femoral or radial arterial catheters)
Transpulmonary lithium indicator dilution
Partial carbon dioxide (CO
2
) rebreathing
Esophageal Doppler
Pulse contour analysis
Bioimpedance and bioreactance
Ultrasonic cardiac output monitor
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4.5.2.2 Transpulmonary Lithium Indicator Dilution
This invasive method involves using a bolus dose of isotonic lithium chloride (150–
300 mmol LiCl; 1–2 mL) which is injected inside the right atrium (often through a
central venous catheter); then, the arterial concentration of lithium is calculated by
the machine. The lithium dose does not have any clinical significant effect.
This method is usually not used in the following:
• Patients below 40 kg (88 lb).
• Patients in the first trimester of pregnancy.
• Patients receiving high doses of neuromuscular blocking agents since they may
interfere with the sensor readings of lithium.
• Caution should be taken in patients under lithium therapy.
After injection of lithium dose, the concentration-time curve of lithium dilution
in the arterial system is drawn by machine, and cardiac output (CO) is often calcu-
lated through a central arterial line and the “Stewart-Hamilton” equation is used to
calculate cardiac output:
CO LiD60AUC 1PCV=/××
()
−
in which:
CO = calculated cardiac output
LiD = lithium dose (mmol) = the amount of injected lithium
AUC = area under curve for concentration-time curve of lithium
PCV = packed cell volume based on hemoglobin concentration calculated as g/dl;
this correction is due to the lack of lithium entry into red blood cells (RBCs)
and white blood cells (WBCs) in its first pass. This method is used in LiDCO
system, LiDCO Group plc, London, UK
4.5.3 Partial Carbon Dioxide (CO
2
) Rebreathing
This method is based on Fick principle; however, instead of calculating oxygen
transport, it calculates cardiac output based on CO
2
transport from tissues to the
lungs and its excretion, which is done based on 3 min rebreathing intervals. In fact,
CO
2
is the marker of choice in this method for calculating cardiac output. For this
purpose, a disposable rebreathing loop is added to the mechanical ventilation cir-
cuit. This rebreathing loop contains three items:
• Air flow measurement device
• Pulse oximeter
• CO
2
infrared light absorption sensor
For this method, we could consider the following modification as “Fick formula
for calculation of cardiac output using CO
2
”:
CO VCOSetCO
22
=/
∆×
∆
()
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in which:
CO = cardiac output
ΔVCO
2
= changes in CO
2
elimination
S = correction index
ΔetCO
2
= changes in partial pressure of end-tidal CO
2
between normal breathing
and CO
2
rebreathing
The rebreathing cycles are used in 3-min intervals to calculate the amount of
change in CO
2
during rebreathing episodes.
The noninvasive cardiac output (NICO) monitor (Novametrix Medical Systems
Inc., Wallingford, CT, USA) uses CO
2
rebreathing technology. The method is appli-
cable to adults above 40 kg. The accuracy of this method is much more acceptable
in ICU and operating room in clinically stable patients under full mechanical venti-
latory support. But in patients with intrapulmonary shunt, the accuracy of this
method is decreased. So the technique mandates full control of respiration through
use of full mechanical ventilatory support, and also, there should not be any intra-
pulmonary shunts.
4.5.4 Esophageal Doppler
The application of this method was first introduced in the 1970s and then developed
in the 1980s; it is usually administered through the “esophageal Doppler monitor-
ing” or simply “EDM” which uses ultrasound for calculation of cardiac output. It is
noninvasive and uses the pulsatile flow through the ascending thoracic aorta for
calculation of cardiac output. The ultrasound transducer is attached to the tip of a
flexible probe; this probe is introduced into the esophagus through the mouth; nasal
passage while not routine is possible. However, the patient should be anesthetized
since its passage is not possible, while the patient is awake. Also, in patients with
esophageal disease, EDM probe should not be used unless extreme caution is
applied to prevent any possible injury; even the least resistance should prevent fur-
ther advancement. Usually a depth of 30–35 cm inside the esophagus is acceptable
(mid-thoracic level). Then transducer often uses pulsed wave Doppler (5 MHz) or
continuous wave Doppler (4 MHz); less frequently, M-mode Doppler is used by
some manufacturers. EDM calculates the cross-sectional area of aorta based on age,
sex, weight, and height according to the machine software. EDM needs some train-
ing before use; about 10–12 probe placements are often enough; however, mainte-
nance of the probe in its place needs care in order to prevent “probe displacement”
out of the esophagus (e.g., during routine ICU nursing care).
The blood passing through the lumen of aorta in each heartbeat is about 70
% of
stroke volume, while 30 % of the stroke volume goes to head and neck arteries and
the coronary vascular bed; so the calculated cardiac output by the machine should
be multiplied by a constant of 1.4 to compensate for cerebral and coronary perfu-
sion; some machines automatically compensate this ratio and demonstrate the final
figure.
The results of CO assessments with EDM are more useful when the trend of
change is considered rather than the punctual readings of CO.
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