Utility of Impedance Cardiography to Improve Physician
Utility of Impedance Cardiography to Improve Physician
Emergency physicians must often make assessments of complex hemodynamic parameters. To assess the utility of impedance cardiography (ICG) in the emergency department, the authors examined treating physicians’ abilities to assess stroke volume (SV), cardiac output (CO), and systemic vascular resistance (SVR) by comparing the clinicians’ estimates of these values to ICG measurements. Treating physicians were asked to estimate the SV, CO, and SVR of acutely ill patients as being low, normal, or high. ICG measurements of SV, CO, and SVR were also categorized as low, normal, or high. Physician estimates were compared with ICG measures for concordance. Changes of therapy initiated as a result of discordance between physician’s estimates and ICG measurements were recorded. The treating physician assessments and ICG hemodynamic measurements were concordant in 62 of 101 (62%) cases for SV (kappa = 0.068), in 53 of 101 (53%) cases for CO (p = 0.125), and in 50 of 101 (50%) measurements for SVR (=0.148). The low concordance suggests that treating physicians did not consistently estimate SV, CO, and SVR accurately. ICG provides noninvasive hemodynamic measurements of SV, CO, and SVR that offer clinical utility and potential value in the emergency department.
To manage a critically ill patient effectively, an emergency physician must make an accurate assessment of the patient's hemodynamic status. These parameters can be accurately measured through the use of a pulmonary artery (PA) catheter, however, this device has significant limitations in the emergency department (ED) as a result of the time and complexity of placement, high cost, invasive nature, and short-and long-term risks. In most cases, the emergency physician makes an estimate of cardiac output (CO), stroke volume (SV), and systemic vascular resistance (SVR) using clinical judgment in conjunction with measurements of blood pressure, pulse, and respiration. Unfortunately, most physicians cannot accurately assess more complex hemodynamics measurements from the history and physical examination alone.
Impedance cardiography (ICG) is an established and accurate technique for noninvasive determination of hemodynamic parameters. The technique uses changes in electrical impedance to generate a waveform that is dependent upon the volume and velocity of blood injected into the aorta as well as the rate and force of left ventricular contraction. From this curve, along with measured heart rate and blood pressure, values for SV, CO, SVR, and other hemodynamic parameters are derived. To generate the waveform, four sets of dual sensors are placed on the patient which sense thoracic electrical impedance. This allows measurement of the changes in thoracic bioimpedance during the cardiac cycle and calculation of SV from changes in aortic volume. ICG has shown good correlation compared with PA catheters in a variety of settings involving moderately to critically ill patients and in diverse populations including postsurgery, heart failure, pregnancy, and pulmonary hypertension. The objective of this investigation was to determine how well the emergency physician's estimates of the hemodynamic parameters of SV, CO, and SVR correlated with ICG measurements. Secondary goals were to assess physician impressions of the value of ICG and to determine if ICG results affected physician treatment decisions.
Emergency physicians must often make assessments of complex hemodynamic parameters. To assess the utility of impedance cardiography (ICG) in the emergency department, the authors examined treating physicians’ abilities to assess stroke volume (SV), cardiac output (CO), and systemic vascular resistance (SVR) by comparing the clinicians’ estimates of these values to ICG measurements. Treating physicians were asked to estimate the SV, CO, and SVR of acutely ill patients as being low, normal, or high. ICG measurements of SV, CO, and SVR were also categorized as low, normal, or high. Physician estimates were compared with ICG measures for concordance. Changes of therapy initiated as a result of discordance between physician’s estimates and ICG measurements were recorded. The treating physician assessments and ICG hemodynamic measurements were concordant in 62 of 101 (62%) cases for SV (kappa = 0.068), in 53 of 101 (53%) cases for CO (p = 0.125), and in 50 of 101 (50%) measurements for SVR (=0.148). The low concordance suggests that treating physicians did not consistently estimate SV, CO, and SVR accurately. ICG provides noninvasive hemodynamic measurements of SV, CO, and SVR that offer clinical utility and potential value in the emergency department.
To manage a critically ill patient effectively, an emergency physician must make an accurate assessment of the patient's hemodynamic status. These parameters can be accurately measured through the use of a pulmonary artery (PA) catheter, however, this device has significant limitations in the emergency department (ED) as a result of the time and complexity of placement, high cost, invasive nature, and short-and long-term risks. In most cases, the emergency physician makes an estimate of cardiac output (CO), stroke volume (SV), and systemic vascular resistance (SVR) using clinical judgment in conjunction with measurements of blood pressure, pulse, and respiration. Unfortunately, most physicians cannot accurately assess more complex hemodynamics measurements from the history and physical examination alone.
Impedance cardiography (ICG) is an established and accurate technique for noninvasive determination of hemodynamic parameters. The technique uses changes in electrical impedance to generate a waveform that is dependent upon the volume and velocity of blood injected into the aorta as well as the rate and force of left ventricular contraction. From this curve, along with measured heart rate and blood pressure, values for SV, CO, SVR, and other hemodynamic parameters are derived. To generate the waveform, four sets of dual sensors are placed on the patient which sense thoracic electrical impedance. This allows measurement of the changes in thoracic bioimpedance during the cardiac cycle and calculation of SV from changes in aortic volume. ICG has shown good correlation compared with PA catheters in a variety of settings involving moderately to critically ill patients and in diverse populations including postsurgery, heart failure, pregnancy, and pulmonary hypertension. The objective of this investigation was to determine how well the emergency physician's estimates of the hemodynamic parameters of SV, CO, and SVR correlated with ICG measurements. Secondary goals were to assess physician impressions of the value of ICG and to determine if ICG results affected physician treatment decisions.
Source...