Wall stress distribution on three-dimensionally reconstructed models of human abdominal aortic aneurysm

PURPOSE

Abdominal aortic aneurysm (AAA) rupture is believed to occur when the mechanical stress acting on the wall exceeds the strength of the wall tissue. Therefore, knowledge of the stress distribution in an intact AAA wall could be useful in assessing its risk of rupture. We developed a methodology to noninvasively estimate the in vivo wall stress distribution for actual AAAs on a patient-to-patient basis.

METHODS

Six patients with AAAs and one control patient with a nonaneurysmal aorta were the study subjects. Data from spiral computed tomography scans were used as a means of three-dimensionally reconstructing the in situ geometry of the intact AAAs and the control aorta. We used a nonlinear biomechanical model developed specifically for AAA wall tissue. By means of the finite element method, the stress distribution on the aortic wall of all subjects under systolic blood pressure was determined and studied.

RESULTS

In all the AAA cases, the wall stress was complexly distributed, with distinct regions of high and low stress. Peak wall stress among AAA patients varied from 29 N/cm(2) to 45 N/cm(2) and was found on the posterior surface in all cases studied. The wall stress on the nonaneurysmal aorta in the control subject was relatively low and uniformly distributed, with a peak wall stress of 12 N/cm(2). AAA volume, rather than AAA diameter, was shown by means of statistical analysis to be a better indicator of high wall stresses and possibly rupture.

CONCLUSION

The approach taken to estimate AAA wall stress distribution is completely noninvasive and does not require any additional involvement or expense by the AAA patient. We believe that this methodology may allow for the evaluation of an individual AAA's rupture risk on a more biophysically sound basis than the widely used 5-cm AAA diameter criterion.

Etiologic factors in progression of carotid stenosis: a 10-year study in 905 patients

PURPOSE

The purpose of this study was to determine the etiologic factors in the progression of carotid stenosis.

METHODS

We performed prospective serial duplex scan surveillance of 1470 carotid arteries in 905 asymptomatic patients during a 10-year period, with an average follow-up interval of 29 months and an average of 3.0 scans per carotid artery. Vascular laboratory and hospital records were used to collect risk factor information. The data were analyzed with proportional hazards modeling.

RESULTS

We examined several demographic, clinical, and laboratory risk factors that were chosen because of their potential relevance to atherosclerotic disease. These factors were analyzed with univariate proportional hazards modeling, in which time to progression of stenosis was the outcome variable. The six significant predictors (P <.05) were age, sex, systolic pressure, pulse pressure (systolic pressure - diastolic pressure), total cholesterol, and high-density lipoprotein (HDL). All, except HDL, were positive predictors of time to disease progression. With multivariate modeling, only pulse pressure and HDL remained as significant independent predictors of stenosis progression. The risk ratio for a 10-mm Hg rise in pulse pressure was 1.12, and the risk ratio for a 10-mg/dL decrease in HDL was 1.20.

CONCLUSION

In this large cohort of patients who were followed prospectively for carotid stenosis, pulse pressure and HDL were found to be the key risk factors for carotid stenosis progression. The fact that pulse pressure superseded systolic pressure in multivariate modeling may shed light on the biology of carotid plaque progression. Further, our identification of these modifiable risk factors may help in the design of therapeutic trials for the prevention of progression of carotid atherosclerosis.

Thrombin injection versus compression of femoral artery pseudoaneurysms

OBJECTIVE

The compression of femoral artery pseudoaneurysms is a time consuming, painful, and sometimes unsuccessful procedure. Thrombin injection has been advocated as a superior alternative. In this study, we compare our experiences with both techniques.

METHODS

All the records of femoral artery false aneurysms that were treated in the vascular laboratory from January 1996 to April 1999 were retrospectively reviewed. Treatment with ultrasound scan-guided compression was compared with treatment with dilute thrombin injection (100 U/mL).

RESULTS

Both groups had similar demographics and aneurysm sizes (P >.2). Of the pseudoaneursyms, 88% were caused by cardiac catheterization and the others were the results of femoral artery access for cardiac surgery (6%), arteriography (5%), and renal dialysis (1%). Compression was successful in 25 of 40 patients (63%). Nine persistent aneurysms necessitated operation, and six were treated successfully with thrombin injection. Primary thrombin injection successfully obliterated 21 pseudoaneurysms in 23 patients. Overall, 27 of 29 pseudoaneurysms were treated successfully with thrombin injection (93%). Thrombosis occurred within seconds of the thrombin injection and required, on average, 300 units of thrombin (100 to 600 units). The patients who underwent successful compression required an average of 37 minutes of compression (range, 5 to 70 minutes) and required analgesia on several occasions. No patients in the thrombin group required analgesia or sedation. Neither group had complications. A cost analysis shows that thrombin treatment results in considerable savings in vascular laboratory resource use but not in overall hospital expenditures.

CONCLUSION

Ultrasound scan-guided thrombin injection is a safe, fast, and painless procedure that completely obliterates femoral artery pseudoaneurysms. The shift from compressive therapy to thrombin injection reduces vascular laboratory use and is less expensive, although it does not significantly impact hospital costs.

Embolotherapy of persistent endoleaks after endovascular repair of abdominal aortic aneurysm with the ancure-endovascular technologies endograft system

PURPOSE

Endoleak is a potential complication after endovascular repair of abdominal aortic aneurysm (AAA). It may result in continued growth of the aneurysm and potentially result in aneurysm rupture. The authors present their experience with embolotherapy in patients with persistent perigraft flow treated with the Ancure-Endovascular Technologies endograft system.

MATERIALS AND METHODS

Between February 1996 and August 1998, 54 patients underwent successful repair of AAA with use of the Ancure system. All underwent operative angiography and discharge computed tomography (CT). Follow-up included CT at 6, 12, and 24 months, and CT was also performed at 3 months if an endoleak was present on the discharge CT. Persistent endoleak was defined as perigraft flow still present on the 6-month CT. Seven of 21 initial endoleaks persisted at 6 months. Six patients returned for embolization of the perigraft space and outflow vessels including lumbar arteries and the inferior mesenteric artery (IMA).

RESULTS

Five of the six patients had leaks from the proximal (n = 1) or distal attachment sites (n = 4) of the Ancure system with outflow into lumbar arteries and/or the IMA; one leak was caused by retrograde IMA flow. The six patients underwent nine embolization procedures with only one minor complication. Follow-up CT showed complete resolution of endoleak and decrease in size of the aneurysm sac in all patients.

CONCLUSIONS

Although endoleak is commonly seen initially with the Ancure system, persistent leak occurred in 13% of the patients in the study. Persistent flow in most patients arises from a graft attachment site combined with patent outflow vessels such as the IMA or lumbar arteries. Persistent endoleaks can be effectively and safely embolized with use of a combination of coil embolization of the perigraft space and embolization of outflow vessels. Such intervention resulted in a decrease in size of the aneurysm sac.

Oxygen-dependent chronic obstructive pulmonary disease does not prohibit aortic aneurysm repair

BACKGROUND

Severe oxygen-dependent chronic obstructive pulmonary disease (COPD) is considered by many to be a contraindication to open abdominal aortic aneurysm (AAA) repair. We reviewed our own experience with this patient population.

METHODS

From July 1995 to March 1999, 14 consecutive patients limited by home oxygen-dependent COPD underwent elective open infrarenal AAA repair. Their medical records were reviewed.

RESULTS

The mean aortic aneurysm size was 6.3 cm. The mean PaO2 = 70 mm Hg, PaCO2 = 45 mm Hg, forced expiratory volume in 1 second (FEV1) = 34% of predicted, and forced vital capacity (FVC) = 67% of predicted. All 14 patients were extubated within 24 hours, mean length of hospital stay was 5.9 days, and there were no perioperative deaths.

CONCLUSIONS

Severe home oxygen-dependent COPD is not a contraindication to safe elective open AAA repair.

Progression of asymptomatic carotid stenosis: a natural history study in 1004 patients

PURPOSE

The purpose of this study was to delineate the natural history of the progression of asymptomatic carotid stenosis.

METHODS

In a 10-year period, 1701 carotid arteries in 1004 patients who were asymptomatic were studied with serial duplex scans (mean follow-up period, 28 months; mean number of scans, 2.9/patient). At each visit, stenoses of the internal carotid artery (ICA) and the external carotid artery (ECA) were categorized as none (0 to 14%), mild (15% to 49%), moderate (50% to 79%), severe (80% to 99%), preocclusive, or occluded. Progression was defined as an increase in ICA stenosis to >/=50% for carotid arteries with a baseline of <50% or as an increase to a higher category of stenosis if the baseline stenosis was >/=50%. The Cox proportional hazards model was used for data analysis.

RESULTS

The risk of progression of ICA stenosis increased steadily with time (annualized risk of progression, 9.3%). With multivariate modeling, the four most important variables that affected the progression (P <.02) were baseline ipsilateral ICA stenosis >/=50% (relative risk [RR], 3.34), baseline ipsilateral ECA stenosis >/=50% (RR, 1.51), baseline contralateral ICA stenosis >/=50% (RR, 1.41), and systolic pressure more than 160 mm Hg (RR, 1. 37). Ipsilateral neurologic ischemic events (stroke/transient ischemic attack) occurred in association with 14.0% of the carotid arteries that were studied. The progression of ICA stenosis correlated with these events (P <.001), but baseline ICA stenosis was not a significant predictor.

CONCLUSION

In contrast to recently published studies, we found that the risk of progression of carotid stenosis is substantial and increases steadily with time. Baseline ICA stenosis was the most important predictor of the progression, but baseline ECA stenosis also was identified as an important independent predictor. Contralateral ICA stenosis and systolic hypertension were additional significant predictors. We found further that the progression of ICA stenosis correlated with ischemic neurologic events but not baseline stenosis. The data provide justification for the use of serial duplex scans to follow carotid stenosis and suggest that different follow-up intervals may be appropriate for different patient subgroups.

Bilateral subclavian steal syndrome through different paths and from different sites--a case report

Cases of cerebro-subclavian steal syndrome have been reported in the medical literature since 1960. This most often occurs on the left side because of the higher rate of involvement of the left subclavian artery in comparison to the other brachiocephalic branches of the aortic arch. With the use of the internal mammory artery as a conduit for coronary artery bypass, in the past three decades increasing numbers of coronary-subclavian steal in addition to the cerebro-subclavian steal have been observed. The authors report a case of bilateral subclavian steal syndrome through both vertebral arteries, the right common carotid artery, and the left internal mammory artery, without significant signs and symptoms of cerebral ischemia or anginal pain.

Arterial thromboembolic events in patients with the factor V Leiden mutation

BACKGROUND

The factor V Leiden mutation affects 6% of the United States population and is known to be associated with venous thrombosis. We identify, herein, 30 individuals with the Leiden mutation and known arterial thromboembolic events.

METHODS

The factor V mutation was assessed using polymerase chain reaction.

RESULTS

In the 16 patients sustaining a cerebrovascular accident, the mean age was 44.1 and 11 (69%) were younger than 50. Similarly, the 13 patients presenting with an acute myocardial infarction were relatively young with a mean age of 45.5, and 9 (65%) patients presented at less than 50 years of age. Radiographic information was available for 19 patients in this study. No significant arterial atherosclerotic disease was demonstrated in 18 (95%) of these patients.

CONCLUSIONS

This study demonstrates an association between the factor V Leiden mutation and the development of unexplained arterial thromboembolic events, especially in younger patients without existing atherosclerotic disease.

The factor V Leiden mutation: spectrum of thrombotic events and laboratory evaluation

PURPOSE

This study aims to describe the spectrum of clinical thrombotic events and to compare the methods of laboratory evaluation for the newly described prothrombotic factor V Leiden mutation.

METHODS

Specimens from 1376 patients with thrombotic events or their relatives were tested for the factor V Leiden mutation by polymerase chain reaction plus restriction digest from Jan. 1, 1995, to Mar. 31, 1996. Activated protein C (APC) resistance test data was available for 554 of these patients. Clinical information was available for 166 patients with the mutation.

RESULTS

Of 1376 patients tested for factor V Leiden mutation, 270 (19.6%) were positive, with 12 homozygotes and 258 heterozygotes. Of 554 patients for whom APC resistance data was available, 221 (39.9%) had low APC resistance ratios (< or = 2.4); of these only 97 (43.9%) were factor V Leiden-positive. Among 333 samples with normal or elevated APC resistance ratios, 19 (5.7%) were later identified with the factor V Leiden mutation, despite the normal screening test. One hundred fourteen of 166 patients (68.7%) with the mutation had at least one thrombotic event, most commonly deep venous thrombosis and pulmonary embolus. Arterial cerebrovascular thrombotic events occurred in 11 patients (10%), and myocardial infarctions in eight (7%). The mean age of all patients with arterial thrombotic events was 45.4 years.

CONCLUSIONS

The factor V mutation is a common cause of venous thromboses but may also be associated with the early presentation of arterial thrombotic events. The APC resistance test is a sensitive screening assay but has limitations of its specificity in clinical practice.

Utility of clinical pathway and prospective case management to achieve cost and hospital stay reduction for aortic aneurysm surgery at a tertiary care hospital

PURPOSE

We reviewed our experience with a clinical pathway instituted in December 1993 for all nonurgent abdominal aortic aneurysm (AAA) surgery.

METHODS

We analyzed a reference group of 49 consecutive pre-pathway AAA patients (group I) and the 44 patients enrolled in the first year of the pathway (group II). On the basis of the interim review of data collected during the first year, pathway modifications were made, and 34 patients enrolled after these modifications (group III) were also analyzed.

RESULTS

Comparison of groups I and II showed that institution of the pathway resulted in a marginally significant reduction in mean charges of 14.7% (p = 0.09), and a slight fall in mean length of stay (LOS) (13.8 vs 13.1 days, NS) and mortality rate (4.1% vs 2.3%, NS). For group II, a significant correlate (p < 0.05) of increased charges was fluid overload as diagnosed by chest radiograph. This recognition led to active efforts to reduce perioperative fluid administration. Comparison of groups II and III revealed that the practice modifications led to marked reduction in the incidence of fluid overload (73% vs 24%; p < 0.01), mean charges (30.4% reduction; p < 0.05), mean LOS (13.1 vs 10.2 days; p < 0.05), and median LOS (11 vs 8 days). Multiple regression analysis of all pathway patients showed that preoperative renal insufficiency is a significant predictor of both increased LOS (p < 0.01) and charges (p < 0.01), but that age, sex, and coronary disease were not predictive. Of the postoperative parameters analyzed, important correlates of increased charges were acute renal failure (p < 0.01) and fluid overload (p < 0.01).

CONCLUSIONS

Institution of a clinical pathway for AAA repair resulted in significant charge reduction and a slight reduction in stay. Practice modifications based on interim data analysis yielded further significant reductions in charges and LOS, with overall per-patient charge savings (group I vs III) of 40.6% (p < 0.05) and overall LOS reduction of 3.5 days (p < 0.05). The reduction in actual charges was seen despite an overall increase in the hospital rate structure. Comparing groups I, II, and III, we found no indication of increasing mortality rate. Ongoing analysis has identified correlates of increased charges, potentially permitting identification of high-cost subgroups and more focused cost-control efforts. Rather than restricting management, clinical pathways with periodic data analysis may improve quality of care.

Aortic aneurysm in heart transplant recipients

PURPOSE

The purpose of this study was to define the clinical features of aortic aneurysms occurring in heart transplant recipients.

METHODS

Among the 734 patients who have undergone heart transplantation at our institution over the last 14 years, we have identified 12 patients (1.6% incidence) with aortic aneurysms (9 infrarenal, 3 thoracoabdominal), making this the largest reported series of aortic aneurysms (AA) in heart transplant recipients.

RESULTS

For nine of the 12 patients with AA (75%), the indication for transplantation was ischemic cardiomyopathy. This indication accounted for only 42% of the overall transplantation group; our data therefore show that the risk of infrarenal AA disease was higher for patients who underwent transplantation for ischemic cardiomyopathy than for other indications (p = 0.02). In two of the patients with thoracoabdominal AA, chronic dissection was identified as the specific AA cause, whereas all of the other patients in the study had nonspecific "atherosclerotic" AAs. All 12 patients were symptom free at the time of initial discovery of the AAs. Two of the patients with infrarenal AA were diagnosed with AAs before transplantation; for the seven remaining patients with infrarenal AAs, the mean time between transplantation and AA discovery was 5.0 years (range 1.2 to 11.8 years). Serial radiologic studies allowed us to determine the AA expansion rate in seven of the 12 patients. This rate varied from 0 to 2.53 cm/yr (mean 1.20 cm/yr; 1.0 cm/yr for infrarenal AA alone). Five patients with infrarenal AA underwent AA repair as the initial treatment. Three others underwent repair after their AAs significantly expanded under observation. Mean AA diameter at the time of repair was 6.9 cm. All three patients with thoracoabdominal AAs died of acute AA rupture before resection could be done, despite their initial asymptomatic state. AA diameters at time of rupture were 3.5, 6.0, and 11 cm. All of the eight patients with AA treated with surgery are alive and well (median follow-up 18 months). The only complication was acute heart transplant rejection, which occurred 11 days after AA repair in one patient.

CONCLUSIONS

Our data suggest that AA occurrence is more likely in patients who undergo heart transplantation for ischemic heart disease than for other indications. Careful serial radiologic surveillance is warranted in any heart transplant patient with an AA, because of the apparent potential for more rapid AA expansion in this patient population than in patients who do not undergo transplantation. We conclude that early repair of infrarenal AA is indicated because excellent operative results and low morbidity rates can be achieved. An aggressive approach to thoracoabdominal AAs in this group may also be appropriate because of the apparent propensity to lethal rupture, sometimes at relatively small AA size.

Compromised cerebral blood flow reactivity is a predictor of stroke in patients with symptomatic carotid artery occlusive disease

PURPOSE

The purpose of this study was to determine whether the hemodynamic consequences of extracranial carotid disease correlate with the risk of subsequent cerebral infarction.

METHODS

In 95 patients with symptoms who had greater than or equal to 70% stenosis (31 patients) or who had occlusion (64 patients) of the ipsilateral carotid artery, cerebral blood flow was measured by the stable xenon/computed tomography technique both at baseline and after vasodilatory challenge with intravenous acetazolamide. Patients were stratified into group 1, 43 patients with no more than a 5% decrease in flow in any vascular territory, and group 2, 52 patients with greater than a 5% decrease in one or more vascular territories after an acetazolamide challenge.

RESULTS

In group 2, 15 (28.9%) of 52 patients had a new stroke, but only one (2.3%) of 43 patients in group 1 did (p = 0.0005). Of patients with total carotid occlusion 10 (26%) of 38 in group 2 and none (0%) of 26 in group 1 had a new stroke (p = 0.003). Of patients with greater than or equal to 70% stenosis, five (36%) of 14 in group 2 and only one (6%) of 17 in group 1 had a stroke (p = 0.067).

CONCLUSION

The loss of cerebral reactivity in patients with symptoms who had greater than or equal to 70% carotid stenosis or occlusion is an important predictor of impending cerebral infarction.

The effect of arm exercise on regional cerebral blood flow in the subclavian steal syndrome

Reversed vertebral blood flow distal to a subclavian obstruction is not uncommon and rarely leads to stroke. A small subgroup of these patients have obstruction in other portions of the extracranial or intracranial circulation, however, and cerebrovascular symptoms are induced by arm exercise, which may decrease regional cerebral blood flow--at times to critical levels--indicating a true "steal" syndrome. We evaluated six patients with symptomatic subclavian steal syndrome using stable xenon with computed tomography cerebral blood flow mapping. A decrease in flow from 13% to 90% in one or more regional vascular territories was found after arm exercise. Patients with a true "steal" syndrome may be at higher risk for stroke. Measuring regional cerebral blood flow may be a means of detecting patients who have a critical loss of flow reserves and who will be symptomatically improved by cerebral revascularization.

Analysis of lower extremity blood flow in the patient with peripheral vascular insufficiency: a guide for plastic surgeons

Accurate assessment of lower extremity blood flow is critical in selecting appropriate therapy for patients with peripheral vascular disease and nonhealing wounds. Although physical examination provides an idea about the extent and significance of the disease, further evaluation, including both noninvasive and invasive studies, is routinely obtained. Appropriate studies will provide valuable information about the location and severity of disease, the need for revascularization before definitive wound coverage, and the likelihood of wound healing. A brief overview of vascular laboratory tests, highlighting the values and limitations of each, is presented here.

Probability of rupture of an abdominal aortic aneurysm after an unrelated operative procedure: a prospective study

It has been assumed by some authors that patients with abdominal aortic aneurysms may be at increased risk of rupture after unrelated operations. From July 1986 to December 1989, 33 patients (29 men, 4 women) with a known abdominal aortic aneurysm underwent 45 operations. Twenty-eight patients had an infrarenal abdominal aortic aneurysm, and five patients had a thoracoabdominal aneurysm. The abdominal aortic aneurysm ranged in transverse diameter from 3.0 to 8.5 cm (average 5.6 cm). Twenty-seven patients underwent a single operation, and six patients had two or more (range of 1 to 6). Operations performed were abdominal (13); cardiothoracic (9); head/neck (2); other vascular (11); urologic (7); amputation (2); breast (1). General anesthesia was used in 29 procedures, spinal/epidural in 6, and regional/local in 10. One postoperative death occurred from cardiopulmonary failure. One patient died of a ruptured abdominal aortic aneurysm at 20 days after coronary artery bypass (1/33 patients [3%]; 1/45 operations [2%]). Fourteen patients had repair of their abdominal aortic aneurysm at a later date, an average of 18 weeks after operation. Four patients had abdominal aortic aneurysm considered too small to warrant resection (average 3.6 cm). Four patients were considered at excessive risk for elective repair. The five thoracoabdominal aneurysm were not repaired. Four patients are awaiting repair. During this same 40-month period, two other patients, not known to have an abdominal aortic aneurysm, died of a ruptured abdominal aortic aneurysm after another operative procedure, at 21 days and 77 days. All three ruptured abdominal aortic aneurysms were 5.0 cm or greater in transverse diameter.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac risk in vascular surgery. The oral dipyridamole-thallium stress test

The value of the oral dipyridamole-thallium stress test in identifying patients at high risk of myocardial infarction after vascular procedures has not been documented. We studied prospectively 46 patients who underwent an oral dipyridamole-thallium stress test before undergoing vascular operations. Twenty patients (43%) had a positive test result, defined by a thallium defect with reperfusion, while 26 patients had a negative test result. Myocardial infarctions were documented postoperatively in 5 (25%) of 20 of the group with positive results and 1 (4%) of 26 of the group with negative results. Three of the six myocardial infarctions were clinical; all three were in the group with positive results. No correlation was identified between dipyridamole-thallium stress test results and clinical cardiac history. A positive dipyridamole-thallium stress test result is a more sensitive predictor of postoperative myocardial infarction than ejection fraction or history of coronary artery disease. The oral dipyridamole-thallium stress test is as useful as the intravenous test in this setting.

The management of aortoenteric and paraprosthetic fistulae

Aortoenteric and aortic paraprosthetic fistulae are devastating complications. Most authors recommend total excision of the graft and revascularization of the lower extremities by extra-anatomic bypass. We reviewed the University of Pittsburgh experience with these fistulae in 15 patients between 1977 and 1987. There were 9 aortoenteric fistulae (AEF) and 6 paraprosthetic fistulae (PPF). Seven of the 9 AEF had no abscess surrounding the graft, but communication of the intestine with the aortic anastomosis. One patient died during operation. Six patients underwent a local repair or in situ replacement of the graft. All 6 of those patients survived operation without limb loss. Two of the 9 patients with AEF had evidence of graft infection and underwent total excision of the graft and extra-anatomic reconstruction. Both patients died, one of sepsis and one of aortic stump rupture. All 6 patients with PPF had clinical and operative evidence of overt graft infection and underwent total graft excision and extra-anatomic bypass. Two of these patients died secondary to sepsis. We conclude that AEF, without evidence of graft infection, were safely treated by local repair. Patients with PPF had infected grafts requiring graft removal with significant morbidity and mortality.

Transcutaneous oxygen measurements in lower extremity ischemia: effects of position, oxygen inhalation, and arterial reconstruction

Transcutaneous oxygen tension (TcPO2) measurement has been successfully applied to the diagnosis and monitoring of patients with peripheral arterial insufficiency. This study was performed to assess the effects of changes in limb position, oxygen inhalation, and arterial reconstruction on TcPO2 values in patients with peripheral vascular disease. In addition, a TcPO2 index (foot TcPO2/chest TcPO2) was compared with the Doppler-derived ankle-to-brachial index (ABI) to determine which was the more effective monitor of the response to revascularization. Foot TcPO2 values of 22 patients with claudication or rest pain were measured before and after vascular reconstruction. TcPO2 increased after revascularization in both groups regardless of limb position or oxygen (O2) administration. The dependent position and O2 inhalation had an additive effect on TcPO2. Preoperative TcPO2 values in patients with rest pain showed the greatest response to the dependent position, increasing from 14 mm Hg to 33 mm Hg at room air and from 21 mm Hg to 53 mm Hg with O2 inhalation. TcPO2 in both patient groups was remarkably enhanced by O2 administration after revascularization. Postoperative supine TcPO2 values measured at room air increased from 50 mm Hg to 124 mm Hg (148%) in patients with claudication and from 40 mm Hg to 109 mm Hg (173%) in patients with rest pain after O2 inhalation. Comparison of the TcPO2 index with the ABI showed that absolute and normalized TcPO2 values are equally effective in monitoring peripheral arterial insufficiency. This study suggests that placing the limb in the dependent position and administering O2 may augment TcPO2 to levels where symptoms may resolve. The response of TcPO2 to O2 inhalation may be an indicator that reflects the response to revascularization.

Oxygen diffusion in chronic venous ulceration

A diffusion barrier to oxygen caused by fibrin deposition around dilated, proliferating capillaries in patients with venous hypertension may contribute to the development of venous ulceration. This diffusion barrier was studied in 18 patients with venous ulcers using the transcutaneous oxygen (TcPO2) monitor (TCM204 Radiometer, America). TcPO2 sensors were placed adjacent to venous ulcers on lower limbs and on the chest and foot of each patient. Readings were taken after a sensor temperature of 44 degrees C was reached (10-15 minutes). TcPO2 values were markedly decreased in skin adjacent to the ulcers (10 +/- 2 mmHg) compared with those of the chest (64 +/- 2 mmHg) and foot (43 +/- 2 mmHg). Inhalation of 100% oxygen for 10 minutes increased chest TcPO2 in all patients (145 +/- 8 mmHg) and increased TcPO2 in skin around the ulcers in 17 of 18 patients (61 +/- 13 mmHg). This study supports the existence of a local pathologic barrier to oxygen diffusion in patients with venous ulcers.

Prospective study of computed tomography in initial management of blunt abdominal trauma

Physical examination is often unreliable in the evaluation of blunt abdominal trauma. The utility of computed tomography (CT) in the early management of abdominal trauma in the absence of definite signs is controversial. CT was prospectively evaluated as an adjunct to physical examination in the initial assessment of blunt abdominal trauma. Indications for emergency abdominal CT were a stable patient with an equivocal abdominal examination, closed head injury, spinal cord injury, hematuria, or pelvic fracture. One hundred twenty patients were studied. CT was accurate in 98.3% of these patients. With associated head injury, combining head and abdominal CT proved to be expeditious. Splenic, hepatic, and renal injuries were reliably detected with CT. Minor injuries which did not require laparotomy were reliably diagnosed. Patients with acute pancreatic injuries may have normal CT findings. Eighty-six per cent of laparotomies were therapeutic. In conjunction with close clinical monitoring, CT was reliable in evaluation of blunt abdominal trauma in a selected group of patients.

TcPO2 values in limb ischemia: effects of blood flow and arterial oxygen tension

Transcutaneous oxygen tension (TcPO2) is determined by blood flow and arterial oxygen tension (PaO2) and has been advocated as a measurement of tissue perfusion in peripheral vascular disease. The purpose of this study was to define the relationship between regional blood flow, PaO2, and TcPO2. TcPO2 sensors were placed on the skin of the anterior tibial regions of the hind limbs of 15 dogs. After occluding collateral blood flow, an external flow probe was placed around the femoral artery and an adjustable clamp was used to produce graded ischemia. Progressive reductions in blood flow were correlated with TcPO2 values at inspired oxygen concentrations (FiO2) of 0.21, 0.50, and 1.00. TcPO2 measured at room air decreased nonlinearly in relation to flow with a marked drop occurring below 20% of baseline flow. TcPO2 measured at increased FiO2 was dependent primarily on PaO2 at flow rates greater than 50% of baseline. With reduction in flow below 25% of baseline, TcPO2 was dependent solely on flow and was not augmented by increases in PaO2. The data suggest that TcPO2 can accurately reflect changes in blood flow to an extremity when flow is severely restricted.

General surgery in adult hemophiliacs

From 1976 to 1984, 23 operations were performed on 22 patients with hemophilia (18 patients with factor VIII and four with factor IX deficiency). Elective procedures included resection of abdominal aortic aneurysm, liver transplantation, vagotomy/pyloroplasty, insertion of Mousseau-Barbin tube, colectomy, cholecystectomy, inguinal herniorrhaphy (four patients), colonoscopy/polypectomy, mediastinoscopy, arteriovenous fistula for dialysis, anal fistulectomy, and miscellaneous skin and soft-tissue procedures (five patients). Emergency operations were appendectomy (two patients), repair of bleeding liver biopsy site, and repair of an incarcerated inguinal hernia. There were two deaths (9%) within 30 days of operation, neither directly caused by the coagulopathy. Four patients had bleeding after surgery, which was treated with additional cryoprecipitate or factor concentrate. There were no nonhemorrhagic complications. Before operation, appropriate replacement therapy with factor VIII concentrate, cryoprecipitate, or fresh-frozen plasma was provided. Coagulation factor levels were measured before operation and monitored daily after operation. Generally, factor levels were raised to at least 1.0 U/ml and maintained at greater than 0.5 U/ml for 7 to 14 days after operation. However, when patients were treated with fresh-frozen plasma, plasma exchange was performed and factor levels of approximately 0.35 U/ml were achieved before surgery. We conclude that operations in patients with hemophilia can be accomplished safely with careful monitoring of coagulation factor levels and appropriate replacement therapy.