A 56-year-old male is admitted to the intensive care unit (ICU) with a diagnosis of an acute descending thoracic aortic dissection. Which of the following echocardiographic findings is MOST helpful when distinguishing the true lumen from the false lumen?
Correct Answer: D
It is important to distinguish the true from the false lumen in an acute aortic dissection, especially when the dissection involves the ascending aorta, as there is a potential in compromising the patency of the coronaries and head and neck vessels, or distally, the visceral arteries as these may originate from the false lumen. Additionally, identification of the true lumen is critical to guide aortic wire placement during interventions. There are certain characteristics that help to identify the true lumen on echocardiography. In the descending aorta, the true lumen is usually smaller than the false lumen (A) and expands during systole (B). In the ascending aorta, the true lumen tends to be larger than the false lumen because proximal aortic pressures (closer to the left ventricle) are higher and thus keep the true lumen pressurized. The false lumen has a concave appearance compared to the convex appearance of the true lumen in systole. Echo findings of cobwebs (fibrinous remnants sheared from the intima during separation from media) are 100% specific for the false lumen in acute aortic dissection (C). Color-flow Doppler pattern is always inphase with the cardiac cycle as opposed to the out-of-phase pattern in the false lumen (D).
Echocardiographic features of true and false lumen are important to recognize compression of the true lumen, which may result in organ malperfusion to identify the origin of important aortic branches (if they originate from the true vs false lumen) and provide live guidance for cannula placement in the true lumen.
References:
A patient presents to the hospital for elective abdominal aortic aneurysm (AAA) repair. Which of the patients would MOST likely benefit from surgical intervention?
Correct Answer: B
Based on the 2018 Society for Vascular Surgery practice guidelines, the strongest level recommendation is to pursue elective surgical repair in patients with AAA >5.5 cm, saccular aneurysms, and any aneurysm that is symptomatic (B) (back pain, abdominal pain), as these incur the highest risk of rupture. Likewise, strong evidence exists to serially monitor aortic dilation <4.0 cm, as the risk of rupture is low. However, a gray area exists for patients with aneurysms 5.0 to 5.4 cm. Several studies did not show statistically significant improvement in the clinical outcomes when comparing early intervention to surveillance for both endovascular and open repair. Weak evidence suggests that young patients, especially women, may benefit from earlier intervention (D). Similarly low-level recommendation suggests that repair for patients with smaller aneurysms who will require chemotherapy, radiation therapy, or solid organ transplant may be considered (C).
Ultrasonography is the standard method for screening and serially monitoring AAAs. Ultrasonography has a nearly 100% sensitivity in the diagnosis of AAAs and is preferred because of its relatively low cost, widespread availability, and noninvasive nature. It is accurate to within ∼0.3 cm aneurysm diameter and is highly reproducible with different operators. However, it is limited by potentially suboptimal imaging in obese patients and disruption from bowel gas, and it cannot identify proximal and distal extent of the aneurysm. CT is the imaging modality of choice when ultrasound images are suboptimal. It also provides additional information regarding the extent of the aneurysm and its relationship to surrounding structures.
Strong evidence suggests elective surgical intervention for patients with AAA >5.5 cm, symptomatic aneurysms, and saccular aneurysms, as these carry the highest risk of rupture.
A 78-year-old female with a previous history of a thoracic endovascular aortic repair (TEVAR) complicated by endoleak presents to the ICU after undergoing additional endovascular graft placement for extension of the original repair.
Which of the following IS NOT a risk factor for postoperative spinal cord ischemia (SCI)?
Correct Answer: C
The risk of SCI following thoracic endovascular aortic repair (TEVAR) is ∼10%. Early identification and treatment of this devastating complication is critical in preventing permanent neurologic deficit. Prior aneurysm repair (A), magnitude of the repair, coverage of the left subclavian artery (B), and pre-existing chronic renal insufficiency (D) have all been shown to have higher incidences of SCI post TEVAR. Spinal cord perfusion is dependent on one anterior and two posterior spinal arteries as well as a cervical vascular network proximally and pelvic vascular network distally. Proximal supply to the cervical vascular network is via the subclavian arteries that give rise to the vertebral arteries and then the anterior spinal artery. Thus, left carotid subclavian artery bypass should be considered before TEVAR when the proximal stent graft is expected to cover the origin of the left subclavian artery. The distal spinal cord is supplied by a pelvic vascular network, which arises from the lumbar and sacral arteries and forms a collateral network with branches of the inferior mesenteric and hypogastric arteries. Disruptions of either the proximal or distal collateral networks can place watershed areas of the spinal cord at risk of ischemia.
Strategies that increase spinal cord perfusion pressure (mean arterial pressure minus cerebrospinal fluid [CSF] pressure) as well as decrease metabolism and oxygen demand can reduce SCI post repair. Mild hypothermia (C) decreases metabolism and oxygen demand and would therefore be protective rather than a risk factor for developing postoperative ischemia.
CSF drainage is one intervention that can increase spinal cord perfusion pressure and potentially decrease the incidence of SCI after TEVAR. A recent Cochrane review in 2012 based on three randomized controlled trials of 287 patients examined the role perioperative drainage of cerebrospinal fluid in patients undergoing thoracoabdominal and thoracic aortic aneurysm repair. It is the mainstay of neuroprotection along with additional strategies that increase spinal cord perfusion pressure and oxygen delivery, such as augmentation of the mean arterial pressure and correction of severe anemia.
Postoperative SCI is a potentially devastating complication following TEVAR. Maintaining or augmenting spinal perfusion pressure and reducing metabolic demands are the mainstays of therapy for both prevention and treatment.
A 56-year-old male is diagnosed with a contained rupture of a thoracic aortic aneurysm and was emergently taken to the operating room for thoracic endovascular aortic repair. On postoperative day 1, he begins to complain of loss of motor function in his lower extremities. When reviewing the patient’s medication history, which of the following would place him at highest risk of developing a spinal hematoma after spinal drain placement?
Consideration should be given with regard to preoperative placement of prophylactic lumbar spinal drain in patients at high risk for postoperative SCI; however, in patients who present for emergency repair of aortic aneurysm or dissection, a drain may not be placed because of time constraints. Postoperative rescue management of SCI includes therapies aimed at optimizing spinal cord perfusion pressure (the difference between the mean arterial pressure and either CSF pressure or central venous pressure, whichever is higher). This includes drainage of CSF via a subarachnoid drain, augmenting arterial pressure, and reducing central venous pressure or a combination of the three. The American Society of Regional Anesthesia and Pain Medicine (ASRA) published updated guidelines in 2018 for anticoagulation interruption before performing neuraxial techniques, which includes newer oral anticoagulation agents.
The table below includes recommendations from the most updated ASRA guidelines as of 2018.
In situations where the potential benefits outweigh the risks of neuraxial interventions such as lumbar spinal drain placement, clinical judgment as well as knowledge of the guidelines should be used.
Reference:
A 59-year-old female with a past medical history of hypertension, chronic kidney disease, and heart failure with preserved ejection fraction underwent repair of AAA.
Which of the following interventions and goals is MOST likely to reduce her risk of postoperative acute kidney injury?
Postoperative acute kidney injury is a common complication following aortic surgery, which increases hospital length of stay and is associated with significant increases in morbidity and mortality. The incidence varies widely, 18% to 47%, with endovascular repair being associated with a lower incidence as compared to that of an open repair.
The risk factors associated with acute kidney injury after aortic aneurysm repair include pre-existing renal dysfunction, increased age, involvement of the renal arteries in the aneurysm, preoperative exposure to radiocontrast, high complexity, prolonged procedure time, emergency surgery, and perioperative hypotension. These risk factors are related to larger doses of intraoperative contrast, renal microemboli, and inflammatory response. Strategies to prevent kidney injury include adequate perioperative hydration and planning for surgery at least several days from prior contrast administration if feasible. Intravascular ultrasound use intraoperatively can also reduce the dose of contrast needed.
Various strategies of perioperative renal protection have been proposed including: diuretics; furosemide and mannitol (A, D); calcium channel blockers; N acetylcysteine; bicarbonate; angiotensin-converting enzyme inhibitors; and renal vasodilators, fenoldopam, and dopamine. A 2013 Cochrane review did not support any of these pharmacologic interventions. However, a meta-analysis of studies conducted investigating volume expansion alone or in combination with an inotrope to maintain a cardiac index in the normal range (>2.0 L/min/m2 ) (C) did show a reduction in postoperative acute kidney injury
Both the Cochrane review and meta-analysis caution that many of the included studies are subject to small sample size and possible biases that make interpretation of the results challenging. More evidence is needed to support pharmacologic interventions for perioperative renal protection. Currently available literature support individualized hemodynamic optimization utilizing fluids and inotropes as needed to maintain a cardiac index within the normal range.
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