EMS World

FEB 2017

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EMSWORLD.com | FEBRUARY 2017 41 Hypovolemia Volume status can be estimated by assessing the func- tion of the left ventricle as well as the inferior vena cava (IVC). A healthy heart typically produces an ejection fraction (EF) of 55%–65%. Put simply, that means the left ventricle (LV) collapses 55%–65% dur- ing the systolic phase. The ejection fraction increases in a hypovolemic state as the heart struggles to circu- late as much fluid as possible. Severely hypovolemic patients may have an EF approaching 100%, and the walls of the LV may appear to "kiss." In addition the LV will appear smaller than usual due to the lower volume of fluid filling it. The shape and behavior of the IVC, having little structure on its own, depends on fluid. Typically the IVC is easily seen and has some diameter variability during respiration due to pressure changes. As circu- lating volume reduces, the IVC diameter shrinks and the respiratory variability increases. While there is some controversy on the utility of IVC measurement to estimate volume status on its own, by combining it with LV assessment, it becomes a valuable tool to the prehospital provider. Cardiac Tamponade Fluid buildup in the pericardium is referred to as a pericardial effusion. When the pressure within the pericardium grows to where hemodynamics are affected and the right ventricle (RV) begins to collapse, it becomes a pericardial tamponade. The textbook finding in pericardial tamponade is Beck's triad: jugular vein distension (sensitivity of 54%), hypotension (sensitivity of 28%) and muffled heart tones (sensitivity of 22%). As with many physical exam findings we're taught to look for during schooling, the true utility of Beck's triad tends to be exaggerated. In the patient suffering from cardiac arrest secondary to pericardial tamponade, survival is questionable at best whether the cause is traumatic or medical, as no amount of CPR or epinephrine will be able to over- come the structural pathology of a nonfunctioning RV. Contrary to popular belief, this is not necessarily a rare condition. One study showed that of 51 patients presenting with PEA, five (9.8%) were suf- fering from tamponade. 4 Fortunately POCUS makes the detec- tion and treatment of pericardial effusion easy. Fluid around the heart will be seen as a distinct black collection, and in the case of tamponade, the RV will be distorted if it's visible at all. In cases of severe tamponade, the heart can be seen swinging around like a pendulum within the pericardium—which is the cause of electrical alternans. Ultrasound can then be used to guide a needle directly to the largest point of fluid collection in the pericardium and drain it. As the needle is guided visually, any car- diac view can be used to perform pericardiocentesis, eliminating the need for the typical landmarks and subxiphoid approach. Pulmonary Embolism Pulmonary embolism is responsible for more than 10% of arrests of non- cardiac origin and is associated with a low survival rate. 5 Just as with cardiac tamponade, CPR and epinephrine will do nothing for a massive clot in the pulmonary vasculature. When you view the heart with ultra- sound, the LV should be grossly larger than the RV. In the case of pulmonary embolism, the RV increases in size until it's as big as or even larger than the LV. As the right heart attempts to pump blood to the lungs, blood is unable to effectively complete its journey due to the embolism. This causes blood to back up into the RV, which dilates like an overfilled balloon. This is best seen in the apical four-chamber view, as this view allows visualization of the entire heart in proper proportion, and clues may be seen in the IVC Pericardial effusion in the parasternal long axis view Subxiphoid (subcostal) view Apical four-chamber view Patrick J. Lynch and C. Carl Jaf fe Enlarged RV suggestive of pulmonary embolism

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