A 34-year-old man with primary sclerosing cholangitis underwent orthotopic liver transplantation 6 hours ago. His other medical history includes obesity treated with sleeve gastrectomy 6 years ago, esophageal diverticulum, and peptic ulcer disease with remote gastrointestinal bleeding. He remains intubated and sedated in the ICU with current vital signs of:
He is currently receiving infusions of norepinephrine at 30 mcg/min and vasopressin at 0.04 units/min. He remains hypotensive despite rapid blood transfusion. An attempt at transthoracic cardiac ultrasound revealed no adequate windows. In deciding whether to perform a transesophageal echocardiogram (TEE) to work up his refractory shock, which of his medical problems would most likely be considered an absolute contraindication to TEE probe placement?
Correct Answer: D
Bedside cardiac ultrasound is indicated in critically ill patients when unexplained hypotension is present. If TEE views are not adequate, then a TEE examination is indicated. This patient has unexplained hypotension following liver transplantation despite high doses of vasopressors and has not demonstrated volume responsiveness. Cardiac ultrasound is required to rule out pathology such as right or left ventricular dysfunction, acute valvular disorders, and hemodynamically significant pericardial effusion. Because no transthoracic views could be obtained, transesophageal echocardiography would offer insight into cardiac function.
According to the ASE/SCA Guidelines for Performing a Comprehensive Transesophageal Echocardiographic Examination, the absolute contraindications for TEE probe placement include:
The esophageal diverticulum would represent the absolute contraindication in this patient. The remainder of the patient’s pathology falls under relative contraindications. Of note, at many centers transesophageal echocardiography is a standard monitor during liver transplantation, even in patients with nonbleeding esophageal varices. A series of small studies has shown relatively good safety of TEE in patients with varices, though the risk of bleeding is higher than in the general population.
A 55-year-old man underwent bilateral lung transplantation for idiopathic pulmonary fibrosis with intraoperative central venoarterial ECMO support. After implantation of the second lung, the team is unable to wean the patient off the ECMO circuit despite dobutamine and norepinephrine infusions. TEE images of the midesophageal long axis view at end-diastole (A) and mid-systole (B) are shown in the figures below.
Based on the TEE findings, which of the following is the next best step in management?
Correct Answer: C
The diastolic picture shows a mid-esophageal long axis view of the left atrium, left ventricle, mitral valve, and aortic valve. The basal septum appears disproportionately thick, but without more information one cannot distinguish between disproportionate upper septal thickening and hypertrophic cardiomyopathy (HCM). In the systolic frame, one can see several abnormalities. The anterior leaflet of the mitral valve has moved into the left ventricular outflow tract (LVOT). A visible space is seen between the anterior and posterior mitral leaflets, which should have a tight coaptation point in systole. The aortic valve, which should be widely open during systole, appears only partially open. Taken together these findings lead to the diagnosis of systolic anterior motion (SAM) of the mitral valve. In SAM, the mitral valve moves into the LVOT during systole, creating an outflow tract obstruction. The force of the blood moving through the LVOT may pull the anterior mitral leaflet away from the posterior leaflet, leading to mitral regurgitation. The interrupted systolic ejection can lead to early aortic valve closure or partial opening in systole. SAM is most commonly seen in HCM or after mitral valve repair. However, it can also be seen in hyperdynamic or hypovolemic states, when small LV size combined with excessive inotropy can lead to SAM in otherwise normal hearts.
Medical management of SAM hinges around volume loading, reducing inotropy, and increasing peripheral resistance. Therefore, stopping the dobutamine infusion would be the first step of the options provided. Adding epinephrine would likely worsen the SAM through increased inotropy and reduced diastolic filling time. An intra-aortic balloon pump reduces LV afterload and would not be beneficial here. Finally, the aortic valve likely has no pathology and only opens incompletely due to a small stroke volume (SV). Valve replacement is not indicated.
A 42-year-old woman with Crohn’s disease is admitted to the ICU following laparotomy for small bowel obstruction. She is persistently hypotensive despite vasopressor and volume administration. She is breathing spontaneously on high-flow nasal cannula. Ultrasound imaging of her IVC reveals a 1.5 cm vessel diameter and >50% decrease in vessel diameter during inhalation. The critical care fellow concludes that these findings indicate the patient would increase her cardiac output with intravascular volume administration.
Which of the following, if present, would confound that conclusion?
Ultrasound assessment of the retro-hepatic IVC can provide insights into a patient’s volume status. The assessment hinges around changes in intrathoracic pressure throughout the respiratory cycle being transmitted to the IVC via the right atrium. As a nonmechanically ventilated patient inhales, pressure in the thorax is reduced. This pressure reduction is transmitted to the thin-walled right atrium and then to the IVC.
Patients who are volume-responsive tend to have low right-sided filling pressures and an IVC that has not reached its maximum distensibility. When the right atrial pressure decreases during inspiration, the IVC luminal pressure decreases relative to the intra-abdominal pressure and the vessel collapses. In patients who are not volume responsive, the rightsided filling pressures are higher relative to the changes in thoracic pressure and the vessel size changes less.
The exact cutoff of IVC diameter change for predicting volume responsiveness is not well defined. Some studies identify >40% to 45% collapse during tidal breathing as a cutoff for volume responsiveness in spontaneously breathing nonventilated patients. However, these studies exclude many patients where the technique is prone to drawing the wrong conclusion. If the intra-abdominal pressure is elevated, as in choice C, then the IVC may collapse even in a patient who would not be volume responsive. This would call the fellow’s conclusion into question and makes choice C the correct answer.
Both a hemodynamically significant pneumothorax and pericardial effusion would increase the right atrial pressure without changing the abdominal pressure, leading to a distended IVC even if a patient would indeed be volume responsive. A unilateral DVT would not alter venous return enough to be the correct answer in this case.
A 54-year-old man is admitted to the ICU following Impella placement for cardiogenic shock. Routine screening ultrasound for Impella position shows the following parasternal long axis image. The distance between the calipers is 2 cm
Which of the following is the best next step in management?
Correct Answer: A
The image in this case demonstrates the utility of cardiac ultrasound in assessing placement of percutaneous left ventricular assist devices. The devices are frequently placed under fluoroscopy in the cardiac catheterization laboratory, but fluoroscopy is rarely available in the ICU. A parasternal long axis view shows the Impella crossing the aortic valve and entering the LV. The device draws blood from the LV inflow port and pumps it into the aortic root via the outflow port. The inflow port should be positioned 3.5 to 4 cm beyond the aortic valve. Thus, in this case, the device should be advanced by 1.5 cm. It is important that the pigtail portion of the device is not included in the measurement.
If the device is pulled back into the aorta too far, both the inflow and outflow ports will be on the same side of the aortic valve and the device will not provide hemodynamic support. Additionally, turbulence from the aortic valve interfering with blood inflow can lead to hemolysis. If the device is advanced too far into the LV, the papillary muscles and aortic valve can interfere with inflow and outflow, respectively, leading to hemolysis. The pigtail can tangle with the mitral apparatus, leading to worsening mitral regurgitation.
Use of pulsed-wave Doppler in which of the following views allows for calculation of cardiac output?
Correct Answer: B
Cardiac ultrasound provides an opportunity to estimate cardiac output in a noninvasive manner. This can be a useful tool in the assessment of undifferentiated shock and correlates very well with thermodilution cardiac output measurements by PA catheter. The technique involves obtaining the velocity time integral (VTI) at the LVOT. When pulsed-wave Doppler is applied to a specific area of blood flow, a tracing is produced that has velocity of blood flow on the y-axis and time on the x-axis, as shown in the image below. This is the blood flow velocity versus time at that specific location, in this case the LVOT. When the integral (area under the curve) of that tracing is obtained for a single systolic period, the result is a specific distance. This is the distance that a disc that has the cross sectional area of the LVOT travels in systole. Thus, we end up with a 2D area of the LVOT and a height, allowing us to calculate the LV SV. The LVOT area is calculated by measuring the diameter in the parasternal long axis (transthoracic echocardiogram) or mid esophageal long axis (TEE). Assuming there is no aortic regurgitation, the SV calculated here multiplied by the heart rate provides us the cardiac output.
LVOT Area = (LVOT diameter/2) 2 × 3.14SV = LVOT VTI × LVOT AreaCO = HR × SV
To accurately measure the LVOT VTI, we must align the probe with the direction of blood flow. In typical hearts, this is best done in the apical 5- chamber view (transthoracic echocardiogram) and the deep transgastric 5- chamber view (TEE), making B the correct answer here. In the other answer choices, the Doppler beam will not align with the direction of blood flow and therefore the VTI will be underestimated.
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