Localized control of exsanguinating arterial hemorrhage: an experimental model.

UNLABELLED: To develop an arterial injury model for testing hemostatic devices at well-defined high and low bleeding rates. MATERIAL AND METHOD: A side-hole arterial injury was created in the carotid artery of sheep. Shed blood was collected in a jugular venous reservoir and bleeding rate at the site of arterial injury was controlled by regulating outflow resistance from the venous reservoir. Two models were studied: uncontrolled exsanguinating hemorrhage and bleeding at controlled rates with blood return to maintain hemodynamic stability. Transcutaneous Duplex ultrasound was used to characterize ultrasound signatures at various bleeding rates. RESULTS: A 2.5 mm arterial side-hole resulted in exsanguinating hemorrhage with an initial bleeding rate of 400 ml/min which, without resuscitation, decreased to below 100 ml/min in 5 minutes. After 17 minutes, bleeding from the injury site stopped and the animal had lost 60% of total blood volume. Reinfusion of shed blood maintained normal hemodynamics and both high and low bleeding rates could be maintained without hemorrhagic shock. Bleeding rate at the arterial injury site was held at 395±78 ml/min for 8 minutes, 110±11 ml/min for 15 minutes, and 12±1 ml/min for 12 minutes. Doppler flow signatures at the site of injury were characterized by high peak and end-diastolic flow velocities at the bleeding site which varied with the rate of hemorrhage. CONCLUSION: We have developed a hemodynamically stable model of acute arterial injury which can be used to evaluate diagnostic and treatment methods focused on control of the arterial injury site.

Cytochrome P450 testing for better psychiatric care.

Genotyping for CYP2D6 and CYP2C19 variations is emerging as a potentially useful clinical tool to help mental health professionals prescribe psychiatric medications for their patients. Cytochrome P450 testing uses a blood sample to determine an individual's required dosage of identified drugs that are metabolized by the two enzymes. To provide care for patients and families, nurses should be able to demonstrate identified essential nursing competencies related to genetics and genomics, which include an understanding of cytochrome P450 testing. As patient advocates, nurses are expected to understand how to identify patients most likely to benefit from CYP2D6 and CYP2C19 testing, how to ensure informed consent for such testing, and how to educate patients about testing and test results.

Increased anterior abdominal aortic wall motion: possible role in aneurysm pathogenesis and design of endovascular devices.

PURPOSE: To determine whether variations in aortic wall motion exist in mammalian species other than humans and to consider the potential implications of such variations. METHODS: M-mode ultrasound was used to measure abdominal aortic wall motion in 4 animal species [mice (n=10), rats (n=8), rabbits (n=7), and pigs (n=5)], and humans (n=6). Anterior wall displacement, posterior wall displacement, and diastolic diameter were measured. The ratio of displacement to diameter and cyclic strain were calculated. RESULTS: Body mass varied from 24.1+/-2.4 g (mouse) to 61.8+/-13.4 kg (human); aortic diameter varied from 0.53+/-0.07 mm (mouse) to 1.2+/-1 mm (human). Anterior wall displacement was 2.5 to 4.0 times greater than posterior among the species studied. The ratios of wall displacement to diastolic diameter were similar for the anterior (range 9.40%-11.80%) and posterior (range 2.49%-3.91%) walls among species. The ratio of anterior to posterior displacement (range 2.47-4.03) and aortic wall circumferential cyclic strain (range 12.1%-15.7%) were also similar. An allometric scaling exponent was experimentally derived relating anterior wall (0.377+/-0.032, R2=0.94) and posterior wall (0.378+/-0.037, R2=0.93) displacement to body mass. CONCLUSION: Abdominal aortic wall dynamics are similar in animals and humans regardless of aortic size, wih more anterior than posterior wall motion. Wall displacement increases linearly with diameter, but allometrically with body mass. These data suggest increased dynamic strain of the anterior wall. Increased strain, corresponding to increased elastin fatigue, may help explain why human abdominal aortic aneurysms initially develop anteriorly. Aortic wall motion should be considered when developing endovascular devices, since asymmetric motion may affect device migration, fixation, and sealing.

Duplex scanning after endovascular aneurysm repair: an alternative to computed tomography.

Late complications following endovascular aneurysm repair indicate the need for long-term surveillance. Clinical trials involving endoluminal stent grafts have typically used computed tomography angiography as the main imaging modality for surveillance. However, computed tomography angiography exposes the patient to higher levels of ionizing radiation, nephrotoxic agents, and increased cost compared to duplex ultrasound. Duplex ultrasound scanning has been widely used for surveillance of abdominal aortic aneurysms for many years. It is well established and the procedure of choice for noninvasive imaging of the aorta. It offers the advantages of easy access, decreased cost, no radiation exposure, and no nephrotoxicity. There is little controversy about duplex scanning for preoperative patient evaluation or surveillance of patients with small aneurysms. However, the use and reliability of duplex scanning in the evaluation and surveillance of patients following endovascular repair is controversial. This article will discuss the benefits, techniques, and limitation of duplex ultrasound in the long-term surveillance of endografts following endovascular abdominal aortic aneurysm repair.

Intrasac flow velocities predict sealing of type II endoleaks after endovascular abdominal aortic aneurysm repair.

PURPOSE: The purpose of this study was to determine whether intrasac spectral Doppler flow velocities can predict whether or not a type II endoleak will spontaneously seal and to relate intrasac flow to preoperative branch vessel anatomy. METHODS: Between October 1996 and June 2002, 265 patients with abdominal aortic aneurysms underwent endovascular repair. Patients with less than 24 months of follow-up and type I endoleaks were excluded. Type II endoleaks were confirmed with duplex scan and computed tomographic angiography. Two groups were identified: 14 patients with sealed endoleaks (<6 months) without intervention and 16 patients with persistent endoleaks greater than 6 months and without resolution. Spectral Doppler flow velocities were recorded from endoleaks within the aneurysm sac. RESULTS: The two groups were similar in age, demographics, and aneurysm morphology. The mean follow-up times were 29.9 +/- 7.9 months for sealed endoleaks and 30.2 +/- 8.6 months for persistent endoleaks (P = not significant). Spectral Doppler velocities were significantly lower in patients with sealed endoleaks compared with persistent endoleaks (75.5 +/- 78.8 cm/s versus 138.2 +/- 36.2 cm/s; P <.01). Patients with sealed endoleaks and low (<100 cm/s) intrasac Doppler velocities had significantly fewer patent inferior mesenteric arteries (43% versus 81%; P <.01), a smaller inferior mesenteric artery (5.6 +/- 1.8 mm versus 7.2 +/- 1.3 mm; P <.01), and fewer paired lumbar arteries (1.3 +/- 0.8 versus 2.4 +/- 0.6; P <.0001) compared with those with persistent endoleaks and high (>100 cm/s) intrasac flow velocities. Three patients with sealed endoleaks had Doppler velocities of 200 cm/s or greater. However, the diameter of the inferior mesenteric artery in these patients was 4 mm or less with no visualized lumbar arteries before surgery. Aneurysm diameter(-4.6 +/- 5.6 mm) and volume (-0.9 +/- 45.2 mL) decreased in patients with sealed endoleaks. Aneurysm diameter (1.8 +/- 4.9 mm) and volume (18.5 +/- 33.9 mL) increased slightly in patients with persistent endoleaks (P <.05). No ruptures or conversions occurred in any patient. Secondary interventions to treat type II endoleaks were unsuccessful in six of 16 patients (38%) with persistent endoleaks. CONCLUSION: Intrasac Doppler velocities can be used to predict whether a type II endoleak will spontaneously seal. High-velocity type II endoleaks are related to preoperative large branch vessel diameter and number and are resistant to endovascular treatment.

Duplex ultrasound criteria for defining the severity of carotid stenosis.

Duplex ultrasound scan (DUS) criteria for grading >50% carotid artery stenosis is typically divided into broad categories such as 50-79% stenosis, 80-99% stenosis, and occlusion. The purpose of this study is to validate DUS criteria for stratifying 50 to 100% carotid stenosis into 10% intervals using digital substraction cerebral angiography (DSCA) as the standard of comparison. Between 1996 and 2001, 163 patients were evaluated with duplex ultrasound and angiography. A total of 326 carotid arteries were studied using DUS in an accredited ICAVL vascular laboratory. Threshold velocity criteria for determining the degree of carotid stenosis was defined according to seven categories: <50%, 50-59%, 60-69%, 70-79%, 80-89%, 90-99%, and occlusion. Treatment decisions were based on the angiographic findings. In cases where the degree of stenosis as defined by duplex velocity criteria did not correlate with angiographically defined stenosis, each record was reviewed to determine whether the angiographic findings altered the surgeon's treatment decision. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for DUS-defined degree of stenosis as compared to angiographically defined stenosis were determined. There was a high correlation (R = 0.96) between duplex scan and angiography in 93% (302/326) of the cases. Clinical management was altered in only 3% (10/326) of the cases because of the results of angiography. The DUS velocity criteria to grade the severity of carotid disease in 10% intervals is reliable and accurate. Clinical management of patients with carotid stenosis can be based solely on carotid DUS in 97% of patients considered for treatment of carotid artery disease.

"Pseudoendoleak"--residual intrasaccular contrast after endovascular stent-graft repair.

PURPOSE: To present a unique demonstration of postoperative perigraft contrast masquerading as an endoleak following endovascular abdominal aortic aneurysm (AAA) repair. CASE REPORT: A 66-year-old man underwent endovascular stent-graft repair of a 4.6-cm infrarenal AAA. The procedure was uncomplicated, and intraoperative completion angiography demonstrated good proximal and distal fixation of the stent-graft without an endoleak. A spiral computed tomographic (CT) angiogram obtained on postoperative day 2 revealed a large amount of extrastent contrast along the posterior aspect of the aneurysm sac. This defect had the appearance of an endoleak, but it was also present on the non-contrast images. A color-flow duplex examination performed on the same day showed a widely patent stent-graft with no evidence of extrastent flow. CONCLUSIONS: Contrast trapped in the aneurysm sac during endovascular aneurysm repair may be misinterpreted as an endoleak on postprocedural CT scans. "Pseudoendoleaks" can be distinguished from true endoleaks by examination of prebolus, noncontrast CT images, as well as by duplex ultrasound scanning.