Abstract
Impedance cardiography has not achieved popularity in the Intensive Care Unit (ICU) to date probably because of the limitations in technique and interpretation associated with the altered physiology of critically ill patients, and also because of interference from other machinery in the ICU. The current climate of questioning the existing technology for bedside cardiovascular assessment however spurs the need to evaluate impedance cardiography as a noninvasive alternative. Validation in noncritically ill patients is good when compared to other technologies (e.g., thermodilution, Fick, dye dilution (r>0.9)). Reliability is good with a coefficient of variation in an ICU population of 8.9%, (compared to 18.6% for thermodilution). It has also shown promise in detecting the clinically significant changes of central intravascular volume. Impedance cardiography appears to be useful for measurement of stroke volume (SV) and ejection fraction (EF). From these, left ventricular end-diastolic volume (VED) can be calculated, probably a more reliable estimate of left ventricular filling than pulmonary capillary wedge pressure (PW), measured by pulmonary artery (PA) catheter. In addition, VES can be calculated and with the knowledge of left ventricular end-systolic pressure (PES) (from invasive arterial monitoring), an end-systolic pressure-volume (ES-PV) (relationship can be derived. This is thought to be a measure of contractility that is independent of preload and afterload.
The ultimate test in the ICU for impedance cardiography is whether clinical outcome of critically ill patients is altered by the use of this technology. Such outcome testing is essential before the true value of impedance cardiography in the management of critically ill patients can be determined.
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Abbreviations
- a :
-
aortic stiffness
- dZ/dt :
-
first time derivitive of impedance tracing
- dZ/dt min :
-
maximum negative deflection ofdZ/dt
- E :
-
slope of ES-PV relation
- EF:
-
ejection fraction
- ES-PV:
-
relationship between end-systolic pressure and end-systolic volume
- ICU:
-
intensive care unit
- L :
-
interelectrode distance
- LV:
-
left ventricle
- LVF:
-
left ventricular failure
- PA:
-
pulmonary artery
- P AO :
-
aortic pressure
- P D :
-
diastolic blood pressure
- P ED :
-
end diastolic pressure
- P ES :
-
end systolic pressure
- P VED :
-
ventricular end diastolic pressure
- P W :
-
pulmonary capillary wedge pressure
- RVF:
-
right ventricular failure
- SV:
-
stroke volume
- T z :
-
sum of minimum deflection ofdZ/dt during theC wave plus maximum deflection ofdZ/dt during theA wave
- V ED :
-
end diastolic volume
- V ES :
-
end systolic volume
- VET:
-
ventricular ejection time
- ΔZ :
-
chest impedance wave form
- Z O :
-
baseline thoracic impedance
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Fuller, H., Raskob, G., ter Keurs, H. et al. The current status and future directions of impedance cardiography in ICU. Ann Biomed Eng 17, 483–494 (1989). https://doi.org/10.1007/BF02368068
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DOI: https://doi.org/10.1007/BF02368068