monitoring by combining pulse contour analysis and a transpulmonary thermodilution technique to provide a continuous display of PiCCO cardiac index (L/min/m2) and stroke volume (mL/kg).
Calibration of the PiCCO to more accurate transpulmonary thermodilution cardiac output measurements needs to be repeated every 8 hours, or more frequently if the patient is hemodynamically unstable.
Additional data derived from the PiCCO system include:Extravascular lung water index (mL/kg).Global end‐diastolic volume (measure of cardiac preload in mL/m2).Systemic vascular resistance index (dyn·s/cm5/m2).Stroke volume variation (%).
FloTrac™ system (Edwards Lifesciences)
Requires an arterial line.
Uses pulse contour analysis based on an algorithm to provide continuous cardiac output, stroke volume, and stroke volume variation in real time.
Provides an estimate of cardiac output using the standard deviation of the arterial pulse pressure around the mean arterial pressure and a conversion factor.
Calibration is not required.
Pulse power analysis
LiDCO system
Lithium dilution cardiac output (LiDCO) requires a peripheral or central arterial line.
Uses pulse power analysis rather than pulse contour analysis. The algorithm is based on the assumption that the net power change in the system in a heartbeat is the difference between the amount of blood entering the system, the stroke volume, and the amount of blood flowing out peripherally.
Requires calibration using transpulmonary lithium indicator dilution technique via a peripheral venous line. It is not as accurate when the patient is receiving lithium or certain neuromuscular‐blocking agents.
Central lines
CVP is measured via a central line at the level of the right atrium or vena cava. It is equal to the right ventricular end‐diastolic pressure.
CVP can be used to determine preload, the filling pressure of the heart. It has been used to estimate whether a patient is adequately resuscitated as well as helping to assess right ventricular function.Table 11.1 Waveform components.Waveform/descentPhase of cardiac cycleECGMechanical eventA waveEnd diastoleFollows P wavePressure increase due to atrial contractionC waveEarly systoleFollows R wavePressure increase due to tricuspid bulging into the right atriumV waveLate systoleEnd of T wavePressure increase due to systolic filling of the atriumX descentMid systoleDrop in atrial pressure due to atrial relaxationY descentEarly diastoleDrop in atrial pressure due to early ventricular filling
A central line allows for infusion of hypertonic solutions and medications that can damage peripheral veins. It also allows for serial venous blood analysis and venous blood gas (VBG).
Of particular importance, lactate and central venous saturation measurements from VBGs have been used to direct resuscitation efforts.
Normal CVP is 2–8 mmHg.
Common locations
Internal jugular, subclavian vein, femoral vein.
Complications
Rates of up to 15%.
Inadvertent arterial puncture and/or cannulation, pneumothorax, hemothorax, cardiac arrhythmias, venous air embolism, infections.
Waveform components
As the heart beats, a CVP waveform is produced. There are three waves and two descents (Table 11.1 and Figure 11.2).
Controversy regarding the utility of CVP monitoring
Use of CVP to guide fluid management has been heavily debated. CVP is not useful as a static measurement. Trending the CVP can be useful to determine a patient’s response to a fluid challenge.
Useful measurements depend on proper calibration, normal pulmonary resistance, and right heart function.
Pulmonary artery catheter monitoring
Background
Swan and Ganz first described the pulmonary artery catheter (PAC) in 1970 and it was widely used in the 1980s. However, as more trials were published in the 1990s and 2000s, its popularity declined.
Connors et al. published a prospective randomized trial in 1996 finding an increased cost, length of stay, and mortality in critically ill patients with a PAC.
The Fluid and Catheter Treatment Trial compared mortality, ventilator‐free days, and ICU length of stay among patients with acute lung injury and found no significant benefit to PAC in PAC‐directed resuscitation. The use of PAC resulted in no difference in LOS in the ICU or mortality.
Procedure
The PAC requires placement of a balloon‐tipped catheter into the right atrium, across the tricuspid valve, into the right ventricle, and across the pulmonary valve, until it is ‘wedged’ into a pulmonary artery. At each anatomic location different pressure waveform profiles will be seen (Figure 11.3).
Indications
Acute MI with progressive hypotension or suspected mechanical complications.
Acute right ventricular failure.
Intraoperative/perioperative care:Vascular surgery.Cardiac surgery.Moderate/high risk patients receiving goal‐directed resuscitation.
Undifferentiated shock.
Direct measurements
Right atrial pressure (0–8 mmHg).
Right ventricular pressure (systolic 20–30, diastolic 0–5 mmHg).
Pulmonary artery pressure (systolic 20–30, diastolic 8–12 mmHg).
Indirect measurements
Pulmonary artery wedge pressure (PAWP): surrogate for left ventricular preload
