Effectiveness and cost of screening for abdominal aortic aneurysm: results of a population screening program

OBJECTIVES: We undertook this study to calculate the cost per life-year gained in the first round of a screening program for abdominal aortic aneurysm (AAA) and to estimate the costs in a subsequent round. METHODS: This was an intervention study, with follow-up for ruptured aneurysms. Men older than 50 years were screened for asymptomatic AAA. Outcome measures included cost per life-year saved and number of men needed to be screened to save one life. RESULTS: The incidence of ruptured AAA was 2.6 per 10,000 person- years in the screening group and 7.1 per 10,000 person-years in the control group. Screening is estimated to have prevented 10.8 ruptured AAA and 8 deaths per year, gaining 51 life-years per year for the study population, and to have reduced the incidence of ruptured AAA by 64% (95% CI, 42%-77%). Each life-year gained during the first screening round cost $1107. To save one life, 1000 men need to be screened and 5 elective operations performed. We predict that a second round of screening can be cost neutral. CONCLUSIONS: The cost-effectiveness of screening for AAA compares favorably with screening programs for other disorders in adults.     

Langzeitergebnisse nach Operation eines Bauchaortenaneurysmas im Alter über 80 Jahre

Abdominal aortic aneurysm repair in patients 80 years of age and older (82.3 ± 2.0 years) was performed in 51 patients over a period of 10 years from 1985 to 1995; 34 of these patients underwent elective aneurysm repair and 17 emergency operations for rupture. Of these 51 patients, 50 cases were reviewed for long-term survival, and 44 case reports were reviewed for preoperative risk factors, postoperative complications, discharge to nursing homes and duration of hospitalisation. After 30 days, the mortality for asymptomatic or symptomatic intact aneurysm repair was 5.9%; in the case of emergency repair for rupture the mortality was 64.7%. After elective operations 9.4% of the patients were discharged to nursing homes. All patients who survived emergency operations went on to live normal lives in their previous housing areas. The survival probability was 81% for 1 year, 56% for 3 years, and 42% for 5 years. After surviving the emergency operation, life expectancy was similar to the group of elective aneurysm repair. The analysis did not show any risk factors with predictive value for long-term survival after elective surgery. The results justify elective abdominal aneurysm repair in octogenarians. Even in the case of aneurysm rupture every patient should be operated on. The mortality in elective surgery did not differ very much from that of other patients younger than 80 years old, and life expectancy after surgery was similar to the general population of 80 years of age and older.     

Results of 101 ruptured abdominal aortic aneurysm repairs from a single surgical practice

Hypotheses The results of ruptured abdominal aortic aneurysm repairs from a solo community hospital-based practice are comparable to those reported from large university referral medical centers. Patients younger than 70 years, arriving in the emergency department with stable hemodynamics, and undergoing prompt operation have better outcome. DESIGN: A retrospective review from an ongoing vascular surgery registry. SETTING: Two midsized (300-bed) community hospitals. One hundred one consecutive patients with ruptured abdominal aortic aneurysms who were undergoing open surgical repair by a single surgeon (S.S.H.) during a 21-year period were reviewed. MAIN OUTCOME MEASURES: Operative mortality; cardiac, pulmonary, renal, and gastrointestinal complications; and coagulation abnormalities were recorded. Iatrogenic complications and length of hospital stay were noted. Preoperative and intraoperative factors affecting mortality were studied. RESULTS: Fifty-three patients survived ruptured abdominal aortic aneurysm repair (operative mortality, 47.5%). A favorable outcome was observed in patients (1). younger than 70 years, (2). with a hematocrit of more than 35% at presentation, and (3). with emergency department to operating room times of less than 120 minutes. Increasing experience of the surgeon did not result in improved survival. CONCLUSION: The results of ruptured abdominal aortic aneurysm repairs from community-based practice are comparable to those reported from university referral medical centers.     

Ruptured abdominal aortic aneurysm: factors influencing operative mortality

Of fifty-eight consecutive patients surgically treated for aneurysm of the abdominal aorta, twenty were emergency cases following the rupture. Associated diseases were found in 85 per cent of patients; hypertension being the most common. Fifty per cent of patients were in shock on admission. The duration between rupture and operation was three hrs to two weeks with the average of 115.5 hrs. In six patients, the diagnosis of abdominal aortic aneurysm was known for over six months. The operative mortality rate in case of ruptured abdominal aortic aneurysm was 45 per cent. The most important determinants of survival were the incidence of shock on admission, the incidence of associated disease, the known duration of the aneurysm, and the time interval from rupture to admission. The intraoperative factors most influencing survival were the type of rupture, intraoperative hypotension, and total blood loss. Comparison of the mortality rate in elective surgery of abdominal aortic aneurysms (5.3 per cent) with that in ruptured aneurysms (45.0 per cent) suggests the necessity for early elective operations whenever abdominal aortic aneurysms are diagnosed.     

Aneurysm of the infrarenal abdominal aorta

Preoperative and postoperative treatment as well as standardisation of surgical techniques over the past 20 years have helped to bring about considerable reduction of operative mortality in cases of asymptomatic aortic aneurysm. Yet, with all improvement, rupture of aneurysm has continued to be associated with high rates of mortality. At the Department of Surgery of Cologne University, between 1963 and 1985, operations were performed on 681 patients for abdominal aortic aneurysm. Asymptomatic aneurysm were surgically removed from 41.7 per cent of them, while 27.5 per cent underwent surgery in symptomatic stages. Aneurysm had ruptured in 210 patients. Operative mortality accounted for 5.3 per cent of all asymptomatic patients. High mortality rates among patients with ruptured aortic aneurysms were attributable to preoperative shock. Only 16.3 per cent of patients survived in this group. The mortality rate among patients without shock amounted to 39.5 per cent.     

Ruptured abdominal aortic aneurysm: Factors influencing operative mortality

Of fifty-eight consecutive patients surgically treated for aneurysm of the abdominal aorta, twenty were emergency cases following the rupture. Associated diseases were found in 85 per cent of patients; hypertension being the most common. Fifty per cent of patients were in shock on admission. The duration between rupture and operation was three hrs to two weeks with the average of 115.5 hrs. In six patients, the diagnosis of abdominal aortic aneurysm was known for over six months. The operative mortality rate in case of ruptured abdominal aortic aneurysm was 45 per cent. The most important determinants of survival were the incidence of shock on admission, the incidence of associated disease, the known duration of the aneurysm, and the time interval from rupture to admission. The intraoperative factors most influencing survival were the type of rupture, intraoperative hypotension, and total blood loss. Comparison of the mortality rate in elective surgery of abdominal aortic aneurysms (5.3 per cent) with that in ruptured aneurysms (45.0 per cent) suggests the necessity for early elective operations whenever abdominal aortic aneurysms are diagnosed. Presented at the Fifteenth Annual Meeting of the Japanese Association for Cardiovascular Surgery, Kanazawa, Japan, May 17–18, 1985.     

Improved results of operation for ruptured abdominal aortic aneurysms.

Of 1,393 consecutive patients operated on for aneurysm of the abdominal aorta between 1964 and 1978, 61 consecutive patients had undergone emergency operation for ruptured abdominal aortic aneurysm, for an incidence of 4.4% (61 of 1,393). There were 57 men and four women; their mean age was 77.5 years, with a range of 49 to 93 years. In 21 patients the diagnosis of aneurysm had been known from 1 day to 5 years prior to rupture. Hypotension (less than 100 mm Hg systolic) was present in 27.9% of patients (17 of 61) on admission to hospital and prior to operation in a total of 44.3% patients (27 of 61). Operation was begun in eight patients with an initially unrecordable blood pressure. The perioperative mortality rate (30 day) was 14.8% (nine of 61). The two factors most influencing survival were age [no patient younger than 60 years died vs. 40% of patients (four of 10) older than 80 years] and the magnitude of blood loss (survivors lost a total of 4,513 ml vs. 8,500 ml in those who died). Thus the most common cause of death was myocardial infarction (six of eight) in elderly patients, secondary to poorly tolerated severe hypovolemia. The results of this study suggest the need for avoidance of technical problems during operations, earlier referral of patients with known abdominal aortic aneurysms, especially the elderly, and early diagnosis with immediate operation for ruptured aneurysms.     

Functional outcome after open repair of ruptured abdominal aortic aneurysm

BACKGROUND: Outcome after operative repair of ruptured abdominal aortic aneurysm (AAA) has traditionally been assessed in terms of survival. This study examines the functional outcome of patients who survive operation. METHODS: Consecutive patients who survived open repair over an 18-month period were entered into a prospective case-control study. Age- and sex-matched controls were identified from patients undergoing elective AAA repair. The Short Form-36 health survey was administered to both groups of patients at 6 months after operation. Results were compared with the expected scores for an age- and sex-matched normal UK population. RESULTS: Fifty-seven patients underwent open repair of a ruptured AAA, and 30 survived; no patient was lost to follow-up. There were no significant differences in quality of life between patients who had an emergency repair and those who had an elective repair. Both of these groups had poorer health-related quality of life outcomes than the matched normal population. Surprisingly, compared with the normal population, patients after elective repair had poorer outcomes in more health domains than patients who survived emergency operation. CONCLUSIONS: Survivors of ruptured AAA repair have a good functional outcome within 6 months of operation.     

Long-term survival following emergency abdominal aortic aneurysm repair

Survival following emergency surgery for ruptured abdominal aortic aneurysm remains poor and is in stark contrast to that for elective repair. We have carried out a 5-year retrospective observational study to determine the long-term (5-year) survival of patients following emergency surgery for ruptured abdominal aortic aneurysm at a district general hospital in East Anglia. A total of 99 patients presented to the operating theatre for emergency repair of ruptured abdominal aortic aneurysm in this 5-year study period. In-hospital mortality was 70% and was unchanged over the 5 years. Overall long-term survival in those patients discharged from hospital was good. The ICU cost per long-term survivor was calculated to be pound sterling 36750.     

Outcomes after ruptured abdominal aortic aneurysms: the "halo effect" of trauma center designation

BACKGROUND: Trauma centers have an array of services available around the clock that help reduce mortality in injured patients. Having such services available can benefit patients other than those who are injured. We set out to determine whether patients hospitalized with ruptured abdominal aortic aneurysms experience lower morbidity and mortality at regional trauma centers than at other acute care hospitals. STUDY DESIGN: We conducted a retrospective cohort study with the exposure being care at a trauma center and outcomes either mortality or organ failure. We evaluated all patients 40 to 84 years of age with a diagnosis of a ruptured abdominal aortic aneurysm who underwent operation during 2001 in 20 US states with organized systems of trauma care. We determined the relative risk of either death or organ failure at regional trauma centers compared with nondesignated centers. RESULTS: Of 2,450 patients hospitalized for ruptured abdominal aortic aneurysm, 867 (35%) hospitalizations occurred at regional trauma centers. At trauma centers, 41.4% of patients died before hospital discharge, compared with 45.2% of patients at nondesignated hospitals (odds ratio [OR], 0.85; 95% CI, 0.71-1.02). After adjusting for payor, hospital beds, annual hospital admissions, annual inpatient operations, affiliation with a vascular surgery fellowship, and comorbid illnesses, the likelihood of death or organ failure was lower at trauma centers (OR, 0.72; 95% CI, 0.55-0.93). CONCLUSIONS: Care at regional trauma centers after operative repair of ruptured abdominal aortic aneurysm is associated with improved outcomes. We postulate that these benefits reflect the ability of both vascular and general surgeons to immediately mobilize resources for care of the patient requiring urgent operative intervention. The beneficial effects of trauma center designation might extend beyond caring for the critically injured.     

Hematuria is an indication of rupture of an abdominal aortic aneurysm into the vena cava

During a period of 13 years 11 patients were operated on because of a spontaneous aortocaval fistula caused by a ruptured abdominal aortic aneurysm. The classic diagnostic signs of an aortocaval fistula (pulsatile abdominal mass with bruit and high output heart failure) were present in approximately half of the patients, whereas hematuria was a constant finding in all patients. Six patients had macrohematuria, and five had microhematuria. Seven patients (64% survived, and four had postoperative complications: 1 ileus, 2 postoperative pneumonias, 2 deep venous thrombosis, 1 postoperative hemorrhage. The mean operative blood loss was 7 L. After operation the average follow-up time was 4 years. In four patients who died the perioperative (within 30 days) causes of death were renal failure, a bleeding duodenal carcinoma, myocardial infarction, and operative bleeding. It is concluded that hematuria is a more frequent finding than earlier assumed among patients whose abdominal aortic aneurysm has ruptured into the vena cava. The presence of hematuria in a patient suffering from an abdominal aortic aneurysm is an indication for aortography to rule out an aortocaval fistula.     

Aneurysm rupture is independently associated with increased late mortality in those surviving abdominal aortic aneurysm repair

PURPOSE: The aim of this study was to define whether veterans who survived repair of ruptured abdominal aortic aneurysms (AAA) experienced late survival rates similar to those surviving repair of intact AAA. METHODS: All veterans undergoing AAA repair in DRGs 110 and 111 during fiscal years 1991-1995 were identified using the Veterans Affairs (VA) Patient Treatment File (PTF). Late mortality was defined using VA administrative databases including the Beneficiary Identification and Record Locator System and PTF. Illness severity and patient complexity were defined using PTF discharge data that were further analyzed by Patient Management Category software. Veterans were followed up to 6 years after AAA repair. RESULTS: During the study, 5833 veterans underwent repair of intact AAA while 427 had repair of ruptured AAA in all VA medical centers. Operative mortality was defined as that which occurred within 30 days of surgery or during the same hospitalization as aneurysm repair. For those undergoing repair of intact AAA, operative mortality thus defined was 4.5% (265/5833). Operative mortality was 46% (195/427) after repair of ruptured AAA. Overall mortality (including operative mortality) during 2.62+/-1.61 years follow-up was 22% (1282/5833) with intact AAA versus 61% (260/427) for those with ruptured AAA (P<0.001). Further analysis of survival outcomes was performed in patients who survived AAA repair (i.e., those who were discharged alive and lived 30 days or more after surgery). Of those who initially survived repair of ruptured AAA, 28% (65/232) died during follow-up versus 18% (1017/5568) who initially survived repair of intact AAA (odds ratio 1.74; 95% confidence limits 1.30-2.34; P<0.001). In those initially surviving AAA repair, stepwise logistic regression analysis revealed that increasing age, illness severity, patient complexity, as well as AAA rupture and aortic graft complications were increasingly and independently associated with late mortality. Mean survival time was 1681 days for those who survived >30 days and who were discharged alive after repair of ruptured AAA versus 1821 days for those who initially survived repair of intact AAA (P< 0.001). CONCLUSIONS: In addition to higher postoperative mortality rates with ruptured AAA, mortality during follow-up for survivors of AAA repair was also greater for those who survived repair of ruptured AAA. The toll taken by ruptured abdominal aortic aneurysms did not end in the immediate postoperative period.     

Late results of peripheral vascular surgery in patients 80 years of age and older

During a seven-year period, 114 patients 80 years of age and older underwent 119 peripheral arterial procedures. There were 26 elective aortic reconstructions, nine ruptured abdominal aortic aneurysm (AAA) repairs, 33 femoropopliteal bypasses, 13 femorotibial bypasses, 21 femoral embolectomies, and 17 miscellaneous procedures. Early mortality, morbidity, and Goldman cardiac risk factors were determined by chart review. All 48 survivors returned for current noninvasive vascular examination and life-style assessment. Perioperative mortality after elective AAA resection was 4.3%, vs 78% after ruptured AAA. Perioperative mortality after infrainguinal bypass was nil. Five-year survivals after elective aortic and infrainguinal reconstructions were 54% and 30%, respectively. Of 18 patients studied 19 to 68 months after infrainguinal bypass, limb salvage was achieved in 83% and graft patency in 76%. Thirty-one long-term survivors (65%) were living at home. Only seven patients (15%) were confined to a wheelchair or were bedridden, and 28 (58%) were fully ambulatory. Peripheral arterial reconstruction in patients 80 years of age and older can be performed safely with excellent long-term survival and quality of life.     

Surgical treatment of abdominal aortic aneurysm in patients over seventy years old

Aneurysmectomy is generally the first choice as treatment in most patients with abdominal aortic aneurysm. However, justification of surgical procedures in the aged has been questioned, because of the risk which increases with chronologic age. In the present study, our experience with patients over 70 who underwent abdominal aortic aneurysmectomy is discussed. Forty patients with abdominal aortic aneurysm underwent surgery in our institution up to January, 1983. Ten of these patients were 70 years or older. Operation was performed electively in 6 and as an emergency in 4. The one operative death (10 per cent) was the case of a 74-year old woman with a ruptured aneurysm. The operative mortality was 17.5 per cent in patients under 70 years of age. It would appear that advanced age,per se, is not a contraindication for abdominal aneurysmectomy.     

Risk factors and operative results of patients aged less than 66 years operated on for asymptomatic abdominal aortic aneurysm.

OBJECTIVE: To report risk factors, early operative results and survival after repair of asymptomatic abdominal aortic aneurysm (AAA) in patients aged less than 66 years. DESIGN: a retrospective study based on a prospectively updated database in a University hospital. PATIENTS AND METHODS: Between 1985 and 1999, 118 patients of less than 66 years were operated for AAA. Pre-operative risk factors, early complications, operative mortality (<30 days), and survival are compared with that of 333 older patients operated during the same period. RESULTS: Risk factors were similar to older patients. Serious early (<30 days) complications were recorded in 20% of both groups. The operative mortality was 1.7% for the younger patients and 6% for the older (n.s.). The eight-year survival of the younger patients was 69%, which was significantly below that of a demographically matched population. The older patients had a significantly poorer eight-year survival of 47% (p<0.01), but their relative survival was significantly better (p<0.05). CONCLUSIONS: Younger patients with an AAA were not healthier than older patients. Complications were equally common among both groups. Although the operative mortality was lower, the long-term relative survival was poorer than that of the older patient. Present data do not support a more aggressive surgical attitude towards the younger patients with an asymptomatic abdominal aortic aneurysm, as compared to the older.     

Clinical management of the symptomatic but unruptured abdominal aortic aneurysm

Pain or tenderness of an abdominal aortic aneurysm is widely believed to signify acute expansion and imminent rupture. To assess the potential benefit of emergency operation for the group of patients with an acutely expanding aneurysm, the clinical course of 19 patients with a symptomatic but unruptured expanding abdominal aortic aneurysm was compared with 117 patients undergoing elective abdominal aortic aneurysm resection, and 69 patients having operation for a ruptured abdominal aortic aneurysm. Postoperative morbidity was high in the patients with an expanding abdominal aortic aneurysm, and included a 21% incidence of myocardial infarction, a 10% incidence of stroke, a 37% risk of ventilatory failure, and a 31% incidence of acute renal failure, which was not statistically different from the results in patients having ruptured abdominal aortic aneurysm resection. Patients undergoing elective abdominal aortic aneurysm resection had only an 8% risk of myocardial infarction, and only a 2% risk of stroke, ventilatory failure, or renal failure. The mortality rate for expanding abdominal aortic aneurysm resection was 26% compared to 35% for ruptured abdominal aortic aneurysm (p = 0.31). Both emergency operations had a mortality rate more than five times greater than the 5.1% after elective procedures (p = 0.008). Our findings emphasize the need for early and aggressive treatment of abdominal aortic aneurysm in the elective setting, even in the patient at high risk, and suggest that the preoperative assessment and modification of risk factors is important to prevent the cardiac, cerebrovascular, pulmonary, and renal complications seen accompanying an emergency operation of this magnitude.     

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)     

25例腹主动脉瘤的外科治疗

为了提高腹主动脉瘤外科手术的成功率及减少术后并发症的发生率，总结报道了２５例腹主动脉瘤的治疗经验。所有病人术前ＤＳＡ、ＭＲＩ等检查明确诊断，根据瘤体的情况行瘤体切除、人工血管或同种异体血管移植手术。结果本组病人手术死亡率１６％，无一例出现因腹主动脉阻断而发生主要脏器缺血性损伤的并发症。作者认为，腹主动脉瘤均应尽早行外科手术治疗。已破裂者或即将破裂的腹主动脉瘤是急诊手术的指征。     

Ruptured inflammatory abdominal aortic aneurysm: insights in clinical management and outcome

BACKGROUND: Ruptured inflammatory abdominal aortic aneurysm (AAA) is relatively rare, and little has been written on the outcome of operative treatment. METHODS: Patients undergoing attempted repair of ruptured inflammatory AAA between 1995 and 2001 were included in a retrospective case-cohort study. Demographic, clinical, and operative factors were analyzed, together with in-hospital morbidity, in-hospital mortality, and duration of postoperative hospital stay. RESULTS: Of 297 patients who underwent attempted operative repair of ruptured AAA, 24 (8%) had an inflammatory aneurysm. Twenty-two patients were men, and two were women; median age was 69 years (range, 51-85 years). Operative findings revealed a contained hematoma in 16 patients (70%), free rupture in 3 patients (13%), aortocaval fistula in 4 patients (17%), and aortoenteric fistula in 1 patient (4%). Of 273 noninflammatory ruptured AAAs, only 2 AAA (1%) were associated with primary aortic fistula. Ten patients (42%) with inflammatory AAA died in hospital, compared with 117 of 273 patients (43%) without inflammation. Median postoperative stay was 10 days (range, 0-35 days). Of the 14 patients with inflammatory lesions who survived, 11 had postoperative complications; 4 patients had acute renal failure, three of whom required temporary renal replacement therapy. CONCLUSIONS: Ruptured inflammatory AAA is associated with a higher incidence of aortic fistula than is ruptured noninflammatory AAA. Repair of ruptured inflammatory AAA is not associated with increased operative mortality compared with repair of ruptured noninflammatory AAA.     

Operative treatment of abdominal aortic aneurysms in octogenarians. When is it too much too late?

OBJECTIVE: This study evaluated the value of operation for treatment of all octogenarians with ruptured abdominal aortic aneurysms (AAA). SUMMARY BACKGROUND DATA: Elective AAA resection in octogenarians is safe, with published operative mortality rates of approximately 5%. Published operative mortality rates of ruptured AAA in this age group, however, vary from 27 to 92%. METHODS: To evaluate this question, we extracted the clinical course of the 34 octogenarians submitted to AAA resection by the authors from our total experience of 548 resections performed during the past 7 1/2 years. In this subgroup of octogenarians, 18 underwent elective AAA replacement, 5 were submitted to urgent resection of active but intact AAAs, and 11 had operations for ruptured AAAs. There were 23 males and 11 females in the group. The ages ranged from 80 to 91 years. RESULTS: Operative mortality in the patients managed electively was 5.6%. Two of the five patients (40%) submitted to operation for active yet unruptured aneurysms died in the preoperative period. Finally, 10 of the 11 patients (91%) with ruptured AAAs were operative mortalities. All of these operative mortalities in the ruptured AAA subgroup had severe hypotension preoperatively (mean systolic blood pressure: 23 mm Hg). The charges associated with the management of the ruptured AAA group averaged $84,486 (range $12,537-$199,233). CONCLUSIONS: Although elective replacement of AAA in properly selected octogenarians appears valuable to prolong worthwhile life expectancy, this experience leads us to consider observation only in the treatment of octogenarians with ruptured AAA who present with severe hemodynamic instability.