Cardiac arrest in the emergency setting the palpation

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Cardiac arrest In the emergency setting, the palpation and/or auscultation of peripheral pulses can be difficult to assess in cardiac arrest or hypotensive patients [ 22 ]. Although asystole, ventricular fibrillation, and ventricular tachycardia are usually evident on the cardiac monitor, the diagnosis of pulseless electrical activity (PEA) depends on the determination of a pulse. Cardiac ultrasound is helpful not only because it can detect cardiac motion, but also because it can detect a pericardial effusion or evidence of a dilated right ventricle consistent with pulmonary embolism – two possible causes of PEA [ 23 ]. Sonographic asystole will show an absence of ventricular contraction. Absence of cardiac contractions despite resuscitative efforts can help the clinician formulate a prognosis and determine when resuscitative efforts should be stopped. However, rare contractions of the atria and/or mitral valve may continue despite a terminal event, so it is important to base prognosis on ventricular contractions. One other important point is to ensure that artificial respirations and compressions are held during the ultrasound, because respiratory effort can occasionally appear as ventricular movement. Blaivas and Fox, in their study of ultrasound in cardiac arrest, suggest that patients who arrive in emergency departments with cardiac standstill con- firmed on ultrasound have little to no chance of survival [ 24 ]. Given that the prognosis for asystole compared to PEA during cardiac arrest is so disparate, differentiating between the two with bedside ultrasonography can be quite useful. M-mode can assist in documenting the absence of cardiac activity. The M-mode line should be placed across the ventricular wall of the left ventricle in the parasternal long-axis or subxiphoid position. When the graph of motion over time shows a flat line, this can be a still-image representation of asystole ( Figure 3.28 ). Diagnostic ultrasound 83 Cardiac ultrasound
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Pulmonary embolism Bedside cardiac ultrasound is not sufficiently accurate for the diagnosis of pulmonary embolism (PE) by itself, but there are sonographic findings that may help expedite intervention. Remember that in the normal heart pressures in the right ventricle are lower than in the left. This is why the right ventricular Left atrium Right atrium (A) (B) Figure 3.27 ( A ) This subxiphoid four-chamber view shows enlarged right and left atria suggestive of high intravascular volume states. ( B ) This parasternal long-axis view in a patient with hypertrophic obstructive cardiomyopathy (HOCM) demonstrates a dilated left atrium (LA). 84 Diagnostic ultrasound Cardiac ultrasound
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wall is thinner and more responsive to sudden increases in pressure. The normal right ventricle, therefore, looks triangular ( Figure 3.17 ) and is smaller than the left ventricle because of this lower pressure. When the pressure in the right ventricle rises, the right ventricular wall will bow outward, and the right ventricle will appear to be the same size as or larger than the left ventricle ( Figure 3.29 ) [ 2,25 ]. In the parasternal long-axis view, the normal circularappear-
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