A 42-year-old female presents to the ED in shock after suffering a massive pulmonary embolus (PE). Bedside echocardiography shows unequivocal signs of right ventricular (RV) overload. Regarding this case, which ONE of the following statements is TRUE?
Answer: B: Fluid resuscitation should not be withheld in patients with PE presenting with persistent hypotension or shock; however, fluid loading should generally not exceed 1 L unless coexistent dehydration or hypovolaemia is suspected. The reason is that in massive PE the right ventricle is already pressure overloaded and failing and excessive fluids might overstretch an already failing ventricle (Starling’s law). Persistent hypotension will require inotropic support. In the International Cooperative Pulmonary Embolism Registry, the death rate from PE is nearly 58% among haemodynamically unstable patients and about 15% among haemodynamically stable patients. Mortality can be as high as 60% in untreated patients and can be reduced to <30% with prompt treatment. It is acceptable to proceed to immediate thrombolysis without a CT pulmonary angiogram (CTPA) in haemodynamically unstable patients with clinically suspected PE in which a bedside echocardiography has shown unequivocal signs of RV overload. The optimum thrombolytic agent and regime are yet to be studied in patients with acute pulmonary emboli. tPA is the only approved drug so far for this indication and short infusion times (≤2 hours) are recommended over prolonged infusion times. Infusions of 100 mg over 2 hours have been used successfully. Tenecteplase should be just as effective and easier to use, although it has not been properly studied in PE and does not have Therapeutic Goods Administration (TGA) approval for this indication.
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Regarding the use of focused echocardiography in the ED to examine pericardial effusions in a critically ill patient, which ONE of the following is TRUE?
Answer: D: Most emergency clinicians have been taught the subxiphoid approach for pericardiocentesis. However, one large review looked at 1127 pericardiocentesis procedures, and found that the optimal placement of the needle was where the distance to the effusion was the least and the effusion size was maximal3.
The apical position at the point of maximal impulse on the left lateral chest wall was chosen in 80% of these procedures, based on these variables. The subxiphoid approach was only chosen in 20% of these procedures, as the investigators recognized the large distance the needle had to travel through the liver to enter the pericardial sac.
A phased array probe with a median frequency of 3.5 MHz (2.5–5 MHz) has good penetration and is the most appropriate to examine cardiac structures. High-frequency probes have poor penetration but very detailed superficial images and are mainly used for superficial structures like nerves. Effusions can be categorized by maximal width of the echogenic pericardial stripe. One classification system divides effusions into small (<10 mm), moderate (10–15 mm) and large (>15 mm). However, cardiac tamponade is not dependent on the amount of fluid in the pericardial sac but rather on the rate of fluid collection. Because the pericardium is a relatively thick and fibrous structure, acute pericardial effusions may result in cardiac tamponade despite only small amounts of fluid. When cardiac effusion develops acutely, tamponade can occur with as little as 150 mL of fluid. In contrast, chronic effusions can grow to a large volume without haemodynamic instability. Ultrasonographic signs of tamponade include the presence of a pericardial effusion with:
Compression of the right side of the heart occurs first as it is under relatively less pressure compared with the left side due to the lower pressure within the pulmonary vascular circuit. Therefore, most echocardiographers define tamponade as compression of the right side of the heart. High pressure within the pericardial sac keeps the chamber from fully expanding during the relaxation phase of the cardiac cycle and therefore it is best recognized during diastole. As the effusion may affect either chamber, both the right atrium and right ventricle should be closely inspected for diastolic collapse.
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