WHY DO YOU NEED TO RUSH THIS HYPOTENSIVE PATIENT?
By Dr. Ammar Ismail
Early recognition and appropriate treatment of shock have been shown to ecrease mortality. Incorporation of bedside ultrasound in patients with undifferentiated hock allows for rapid evaluation of reversible causes of shock and improves accurate diagnosis in undifferentiated hypotension.
Rapid Ultrasound in Shock/Hypotension (RUSH) has been suggested for the past few years to rapidly evaluate patients with undifferentiated shock to guide clinicians to provide the appropriate interventions. Emergency and critical care providers may encounter situations where it is not clear how to mange a hypotensive patient and to just “give more fluid” may not fix the problem. One way to approach a hypotensive patient with an ultrasound evaluation is to follow the pneumonic “HI MAP” Heart-IVC-Morison- Aorta-Pulmonary, as the goal is to improve the patient’s Mean Arterial Pressure (MAP).
Goal-directed echocardiogram looking for three specific findings: pericardial effusion, left ventricular contractility, and right ventricular dilation.
Pericardial effusion: Small effusions may be seen as a thin stripe inside the pericardial space, while larger effusions tend to wrap circumferentially around the heart. An exception to this rule may be found in the patient with a loculated effusion, which may exist in both post-operative or post-trauma states and in purulent pericarditis. Fresh fluid or blood tends to have a dark or anechoic appearance, whereas clotted blood or exudates may have a lighter or more echogenic appearance. Ultrasound findings in tamponade represent a spectrum from subtle inward serpentine deflection of the right atrial and/or the right ventricular wall, to complete diastolic compression of a chamber. The inferior vena cava (IVC) can also be evaluated for additional confirmatory signs of tamponade; an enlarged plethoric vessel suggests obstructive shock. If tamponade is identified in the presence of hemodynamic instability, an emergent pericardiocentesis is indicated, unless the effusion is thought to be caused by aortic dissection in which prompt cardiothoracic surgical consult is warranted.
Left Ventricular Contractility: Contractility can be broadly categorized as being normal, decreased (mild or moderate) or hyperdynamic. Bedside ultrasound focuses on evaluating motion of the left ventricular walls by a visual estimation of the volume hange from diastole to systole. A ventricle that has good contractility will have a large volume change between the two cycles. In contrast, a poorly contracting heart will have a small percentage change in the movement of the walls between diastole and systole. The M-mode tracing for a hyperdynamic heart shows the left ventricular walls almost touching during systole and a high fractional shortening. In a poorly contracting heart, the M-mode tracing demonstrates wide systolic separation between the ventricular walls and a low fractional shortening. Minimal distance between the anterior leaflet of the mitral valve and the septum can be used to assess contractility. Measurement of 7mm and below is considered to be normal. The degree of excursion of the mitral valve directly correlates with the contractile state of the left ventricle. As cardiac contractility decreases, the distance between the mitral valve and septum increases. To obtain this, E-point septal separation (EPSS) is measured by placing the M-mode cursor is over the tip of the anterior mitral leaflet in parasternal long view. As the mitral valve moves during diastole, the M-mode tracing reveals a characteristic pattern of two repeating waves. The first is the E-wave, which reflects the initial and maximal opening of the valve to allow passive filling of the left ventricle. Immediately following is the A-wave, which is usually smaller and corresponds to left atrial contraction. The EPSS is the minimal distance between the E-wave and the septum and is normally less than 7mm. Studies have demonstrated that
EPSS greater than 1 cm reliably correlates with a low ejection fraction. Limitation of EPSS that it does not reflect systolic dysfunction in the setting of mitral valve abnormalities (stenosis, regurgitation), aortic regurgitation, or extreme left ventricle hypertrophy.
Right Ventricular Size: In the emergency department setting, any evidence of acute right heart strain should raise the suspicion for large pulmonary embolism especially if there is associated hypotension. Acute dilation of the right side of the heart can be due to any condition that causes sudden increase pressure within the pulmonary vasculature. Dilation of the right ventricle, especially to a size greater than the left ventricle, may be a sign of a large pulmonary embolus in the hypotensive patient. In addition, deflection of the inter-ventricular septum toward the left ventricle signals higher pressures within the right side of the heart and the pulmonary artery.
Inferior Vena Cava
The relative vessel size and its respiratory dynamics can be used to determine how volume status. The IVC provides an indication of intravascular volume and has been used to estimate the central venous pressure (CVP). The IVC diameter should be evaluated just inferior to this point, at a position approximately 2 cm from the junction of the right atrium and the IVC. With inspiration the IVC collapses due to the negative pressure generated in the chest leading to increased blood flow from the abdominal to the thoracic cavity. M-mode sonography of the IVC provides an excellent mean to measure and document the degree of inspiratory IVC collapse. Newly published guidelines by the American Society of Echocardiography support the general use of evaluation of IVC size and collapsibility in assessment of CVP. In spontaneously breathing patients IVC diameter < 2.1 cm that collapses > 50% with inspiration correlates to a normal CVP pressure of 3mmHg (range 0–5mmHg). A larger IVC > 2.1 cm that collapses < 50% with inspiration suggests a high CVP pressure of 15mmHg. Intermediate value of 8mmHg (range 5–10mm) is inconclusive. In mechanically ventilated patients the respiratory dynamics of the IVC will be reversed. However, in most intubated patients, the IVC becomes larger
Morison’s Pouch and the rest of the Focused Assessment with Sonography in Trauma (FAST)
In traumatic conditions, the clinician must quickly determine the presence of hemoperitoneum by examining the right and the leftupper quadrants and the pelvic regions in addition to the heart for presence of effusion. A ruptured ectopic pregnancy should beassumed if free fluid is found in abdominal or pelvic views in a female patient of childbearing age.
The ability to quickly diagnose vascular catastrophes, such as a ruptured abdominal aortic aneurysm (AAA) or an aortic dissection is crucial. Examination of the abdominal aorta along its entire course is essential to rule out an aneurysm, paying special attention to the aorta below the renal arteries where most AAAs are located. AAA is diagnosed when the vessel diameter exceeds 3 cm in the shortaxis plane, measuring the aorta from outer wall to outer wall and should include any thrombus present in the vessel. Rupture is more common with aneurysms measuring larger than 5 cm. Rupture of an AAA typically occurs into the retroperitoneal space, which is an area difficult to visualize with ultrasound. Therefore, it should be assumed in an unstable patient with clinical symptoms and an AAA diagnosed by ultrasound. Evaluation for an aortic dissection by the presence of aortic root dilation and an aortic intimal flap is as important, although more difficult, than AAA.
Ultrasound is noninvasive, repeatable, dynamic, reproducible, easily teachable and one of the excellent methods to provide optimum patient care but it is not the only one as clinical correlation is required. The RUSH / HI MAP protocol is to help with “undifferentiated” shock and should not delay obvious care and interventions.
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