Advanced Hemodynamic and Cardiopulmonary Ultrasound for Critically Ill Patients in the Emergency Department
Focused echocardiography, advanced hemodynamic, and cardiopulmonary point-of-care ultrasound studies provide time-sensitive evaluation of critically ill patients, guiding and facilitating earlier implementation of life-preserving treatment and supportive therapies.
From the same apical view, tissue Doppler at the lateral tricuspid annulus will give a tricuspid annular peak velocity, a measure of the isovolumetric contraction velocity. This measurement will provide a measure of the contractile reserve of the RV (Figure 10b). A measure of less than 10 cm/sec indicates that further volume and inotropic challenges to the RV will not be effective, and the focus should be to decrease RV afterload with pulmonary vasodilators.34,39,40
Fluid Resuscitation Assessment
Restoring circulating volume to increase cardiac output and improve oxygen delivery is the primary objective when managing patients in shock. Patient outcomes improve dramatically with early aggressive fluid resuscitation.41-44 However, many critically ill patients do not respond to fluid resuscitation, which is generally defined as the rise of cardiac output of more than 15% in response to volume expansion. Not all patients found to be fluid responsive will require volume expansion.45,46
Excessive fluid resuscitation has been shown to increase intensive care unit length of stay, morbidity, and mortality.47,48 Further, pathophysiological processes such as RV dysfunction and severe diastolic dysfunction can significantly alter the hemodynamic profile such that fluid management can be quite challenging in critically ill patients.
Distinguishing responders from nonresponders prior to fluid administration is the goal of early resuscitation. Unfortunately, this distinction cannot be made based on the patient’s vital signs or the physical examination.49 Static filling pressures and volumetric measures are unreliable markers of fluid responsiveness.50,51 The practice of administering a fluid challenge and observing the clinical effect on cardiac output is undesirable because it requires, by definition, on administering fluids, which ultimately may be harmful to the patient.
Dynamic measures of fluid responsiveness that reliably predict cardiac response to a preload challenge are proven to be of greater utility.52,53 These assessments determine volume responsiveness by evaluating the change in LV output with intrathoracic pressure changes due to the respiratory cycle, (ie, cardiopulmonary interaction). Ultrasound studies to assess cardiopulmonary interactions include IVC variability, arterial flow variability, brachial artery peak velocity variability, and common carotid artery (CCA) flow. In addition to echocardiography, lung ultrasound may be used to determine the endpoint of fluid resuscitation by monitoring for the appearance of extravascular lung water.
Inferior Vena Cava Variability
The IVC is a large extrathoracic vein which is easily insonated and accessible, even to a clinician with basic bedside ultrasound competency. Static IVC measures, such as diameter alone, correlate with central venous pressure but do not predict fluid responsiveness.54-56 Dynamic IVC evaluation provides an upstream assessment of cardiopulmonary interactions.
In the spontaneously breathing patient, the IVC collapses with inspiration as the RA pressure falls below atmospheric pressure, collapsing the intrathoracic veins for a short period until the intravascular pressure at the entry to the thorax exceeds atmospheric pressure, causing a bolus of venous return to the right heart. The overall effect is an increase in venous return59. Conversely, in the mechanically ventilated patient, the IVC will distend with insufflation as increased intrathoracic pressure results in increased RV afterload and a transient increase in pulmonary artery pressure with an overall net decrease in venous return.60
