Bedside Sonography Use In The Emergency Department
Bedside Sonography Use In The Emergency Department
The concept of the "golden hour" is built on strong evidence that the rapid identification of life-threatening conditions and early initiation of time-sensitive and specific treatments are critical to the patient's clinical outcome.3-5,13,14,23,51,86-98 This section explores the emerging role of ultrasound in diagnosing and managing patients with hypotension.
Ultrasound In Hypotension Protocol
Ultrasound has been used by physicians to detect low intravascular volume states, to evaluate cardiac function, to evaluate the aorta, and to detect peritoneal and pleural free fluid accumulations. In one study, an average of six minutes (+/- two minutes) was needed to perform a bundle of goal-directed ultrasound applications to determine unexplained hypotension.99 Indeed, the utilization of ultrasound is becoming more widespread and is being extended to code response teams in the hospital or to prehospital teams performing ACLS care.100
Differentiating whether hypotension with or without pulmonary edema findings is caused by a cardiac (pump) or non-cardiac (non pump) problem is one of the first major steps toward a careful tailoring of the medical treatment during a resuscitation. The invasive method of pulmonary artery catheter (PAC) placement and monitoring was compared to information obtained by performing noninvasive cardiac sonography in a 1994 study by Kaul et al.101 Fortynine consecutive patients presenting with hypotension and/or pulmonary edema were evaluated. Early transthoracic cardiac sonography data was compared with that of pulmonary catheter readings obtained within two hours of each other. Two to three blinded observers were used for each study. Complete agreement between PAC and cardiac sonography information was found in 36 (86%) of the 42 patients. There was complete agreement in patients with hypotension alone and 90% of the 20 patients with pulmonary edema alone. The time taken for pulmonary artery catheter placement was 63 +/- 45 minutes compared to 19 +/- 7 minutes for comprehensive two-dimensional echocardiography.
Studies in hypotensive patients support the diagnostic role of ultrasonographic evaluation of the inferior vena cava (IVC) as an indicator of volume status. A prospective study of 50 patients by Adler et al identified hypovolemia, unrecognized right heart failure, and high volume states based on the longitudinal views of the IVC using ultrasound.102 By looking at the anteroposterior diameter of the IVC and the respiratory variation in size, one could reliably estimate central venous pressure. Another study evaluated the correlation between sonographicallymeasured proximal IVC diameters, the respirophasic variations of the IVC size (caval index), and the central venous pressures (CVP) that were measured invasively. This study showed a definite correlation between caval index and central venous pressure.103 An IVC respiratory collapse of more than 50% represents a caval index above 0.5. Eighty-nine percent of patients with a caval index above 0.5 had RA pressure readings above 10 mmHg. Eighty-six percent of patients with a caval index below 50% had RA pressure readings less than 10 mmHg (Figure 2).
Using a convenience sample, Randazzo et al found that despite good agreement amongst physicians on the left ventricular ejection fraction (LVEF), there was poor agreement on patients with low CVP categories and strong agreement on the high CVP group.104 In this study, CVP was recorded and then the finding was compared to formal echocardiograms performed within a few hours. Bendjelid et al studied 20 mechanically ventilated patients having IVC sonographic measurements obtained while right atrial pressures (RAP) were measured at the same time; IVC diameter at end expiration had a linear correlation with the RAP readings.105,106
Moreno et al studied IVC diameter and respiratory variations in 175 subjects; there were 80 controls, 65 patients with documented right heart cardiac disease, and 30 patients with cardiac disease but no right heart abnormality.107 The patients with right heart abnormalities/disease had greater average IVC diameters and much less respiratory collapsibility than the normal subjects or the ones with cardiac disease without right heart involvement. Even though 30 patients were in atrial fibrillation, the authors found no correlation between IVC size and dynamics and the sex, body surface area, age, and cardiac rhythm of the patients. The size of the IVC was helpful in the further stratification of CVP measurements. The combination of small size and greater collapse confirmed a low CVP. The combination of an IVC diameter above 2.5 cm and a very low caval index (barely any respiratory variation) is termed IVC plethora. In this study, plethora of the IVC was associated with CVP readings over 15 mmHg (Figure 3, 4, and 5).
Elevated right atrial pressures, determined by invasive methods, are associated with a poor prognosis in patients with pulmonary hypertension, congestive heart failure, congenital heart disease, and heart transplantation. Sonographic findings of IVC plethora were also associated with poor survival in a study of 4385 stable male patients in an outpatient setting. It was determined to be an important prognostic finding in the one-year survival rate of patients but less so for the 90-day survival rate. This was independent of the ventricular function, a history of heart failure, other illnesses, and pulmonary artery pressure readings.108 The prognostic impact of IVC plethora in the unstable patient with hypotension remains to be determined. IVC plethora should spur a rapid search for a cause of the elevated RAP in the hypotensive patient.
In addition to using sonographic IVC diameter as a determinant of volemic status, it has also been shown to assist in gauging response to therapy. Barbier et al conducted a prospective study of 23 mechanically ventilated patients with sepsis-related circulatory failure in an ICU setting.109 The presence of respiratory variations in IVC diameter at baseline and after fluid boluses demonstrated that IVC distensibility could dichotomize fluid responders and fluid non-responders with a 90% sensitivity and a 90% specificity.
The visual estimation of LVEF can be reported qualitatively and quantitatively as increased, normal, or decreased (mildly, moderately, or severely) (Table 6). Estimation of LVEF in the ED has been shown to be useful in a number of studies.4,99,104
Pericardial effusion detection is best performed by echocardiography as it provides dynamic real-time information on myocardial motion and physiology. Most pericardial effusions are not loculated. The rate of fluid accumulation, the size of the fluid buildup, and the compliance of the pericardial sac will all determine when intra-pericardial pressure (IPP) exceeds the right atrial wall pressure. Rapid pericardial fluid accumulations will lead to tamponade at a lower fluid volume (e.g., stab wounds) than slow accumulations over months (e.g., uremic effusions). When the IPP exceeds the RAP, it will provoke RA wall invagination or, even worse, right ventricular wall collapse during diastole (tamponade physiology (Figure 6 and 7).
In summary, some of the Class I recommendations for echocardiography by the American College of Cardiology/American Heart Association Task Force on Practice Guidelines for the Clinical Application Echocardiography apply to the patient being cared for in the ED, see Table 7. These indications include, but are not limited to:
Anthony J. Weekes; Ryan J. Zapata; Antonio Napolitano
November 1, 2007