Intraoperative Aneurysm Rupture and Complication Avoidance

A novel predictor of ischemic complications in the treatment of ruptured middle cerebral artery aneurysms: Neck-branching angle

Objective

The risk factors of procedural cerebral ischemia (CI) in ruptured middle cerebral artery (MCA) aneurysms are unclear. This study proposed the neck-branching angle (NBA), a simple quantitative indicator of the aneurysm neck and branch vessels, and analyzed its usefulness as a predictor of procedural CI in ruptured MCA aneurysms.

Methods

We retrospectively analyzed 128 patients with ruptured saccular MCA aneurysms who underwent surgical or endovascular treatment between January 2014 and June 2021. We defined the NBA as the angle formed by the MCA aneurysm neck and M2 superior or inferior branch vessel line. The superior and inferior NBA were measured on admission via three-dimensional computed tomography angiography on admission. We divided the patients into clipping (106 patients) and coiling (22 patients) groups according to the treatment. Risk factors associated with procedural CI were analyzed in each group.

Results

Both groups showed that an enlarged superior NBA was a significant risk factor for procedural CI (clipping, P < 0.0005; coiling group, P = 0.007). The receiver operating characteristic curve showed the closed thresholds of the superior NBA with procedural CI in both groups (clipping group, 128.5°, sensitivity and specificity of 0.667 and 0.848, respectively; coiling group, 130.9°, sensitivity and specificity of 1 and 0.889, respectively).

Conclusion

The NBA can estimate the procedural risk of ruptured MCA aneurysms. In addition, an enlarged superior NBA is a risk factor for procedural CI in both clipping and coiling techniques.

Management of Intraoperative Rupture of Intracranial Aneurysms: Agony and Ecstasy

Intraoperative rupture (IOR) of an intracranial aneurysm is a serious complication, often with catastrophic consequences that are difficult to manage even by the best hands. Like most surgical complications, this one is better to avoid than to treat, but any vascular neurosurgeon should know how to deal with IOR of an aneurysm, because it is bound to occur. The aims of this study were to evaluate the incidence and factors associated with IOR during clipping of intracranial aneurysms, to analyze strategies for controlling hemorrhage in such cases, and to assess outcomes. Overall, 911 cases of intracranial aneurysms, which were treated surgically by the author during 26 years of his professional career, were reviewed. IOR was never noted during clipping of an unruptured intracranial aneurysm (65 cases) but was encountered in 49 of 846 cases (5.8%) presenting with subarachnoid hemorrhage. This complication occurred most often in cases of internal carotid artery aneurysms (22 cases; 45%), followed by anterior communicating artery aneurysms (12 cases; 24%), distal anterior cerebral artery aneurysms (6 cases; 12%), middle cerebral artery aneurysms (6 cases; 12%), and posterior circulation aneurysms (3 cases; 6%). IOR was mostly encountered during early surgery (within 3 days) after the ictus (26 cases; 53%) and most frequently occurred during dissection of the aneurysm (26 cases; 53%). Overall, 22 patients (45%) had good outcome, 18 (37%) had variable morbidity, and 9 (18%) died. Fatal consequences of IOR were noted only in cases of big or multilobulated internal carotid artery aneurysms. Detailed planning of the surgical procedure, application of meticulous microdissection techniques, and anticipation of possible intraoperative incidents during intervention aimed at clipping of an intracranial aneurysm can reduce the risk of IOR, as well as the associated morbidity and mortality.

The Morphological and Hemodynamic Characteristics of the Intraoperative Ruptured Aneurysm

Background and Objectives

Intraoperative aneurysm rupture (IOR) is a difficult event during the clipping process for intracranial aneurysms, and could result in a bad prognosis. Preoperative discrimination of aneurysms with high risk of IOR is vital for operators. The aim of this study was to explore the hemodynamic-morphological risk factors for the IOR.

Methods

In the present study, patients admitted for unruptured IA from January 2012 to April 2018 were retrospectively reviewed. A propensity score matching was performed to match patients. The morphological features and the hemodynamic features were extracted. Differences in the morphologic and hemodynamic parameters were compared. Risk factors associated with IOR were explored. Subsequently, the hemodynamic characteristics in different rupture stages and different regions in IOR aneurysm were compared.

Results

96 cases of patients with aneurysms, were found by the matching process in each group. The statistically significant difference was found in the maximum length (L) (p = 0.041), maximum diameter of body (D) (p = 0.032), aspect ratio (AR) (p < 0.001), non-sphericity index (NSI) (p < 0.001), normalized wall shear stress maximum (NWSSm) (p < 0.001) and oscillatory shear index (OSI) (p < 0.001). A regression analysis demonstrated AR (OR = 7.03, p < 0.001), NWSSm (OR = 15.55, p = 0.014) and OSI (OR = 28.30, p < 0.001) as the independent risk factors for IOR. AR was much larger, and NWSSm and NWSSa were much lower for IAs that ruptured in early or pre-dissection stage than those for IAs that ruptured in dissection stage or clip application stage. NWSSa and NWSSm in rupture area were both lower than those in adjacent area.

Conclusion

AR, NWSSm, and OSI are considered three independent risk factors for intraoperative aneurysm rupture, which could serve as predictors. A selection of intervention methods for aneurysms with high AR, low NWSSm, and high OSI should carefully be considered.

Intraoperative Aneurysm Rupture During Microsurgical Clipping: Risk Re-evaluation in the Post-International Subarachnoid Aneurysm Trial Era

OBJECTIVES

Intraoperative aneurysm rupture (IOAR) is a common complication during intracranial aneurysm (IA) surgery. In light of the paradigm shift regarding IA selected for clipping in the post-International Subarachnoid Aneurysm Trial (ISAT) era, we aimed to evaluate the risk factors and effects of IOAR in an institutional series of clipped ruptured IA (RIA) and unruptured IA (UIA).

MATERIAL AND METHODS

All IAs treated with microsurgical clipping at our institution between 2003 and 2016 were eligible for this study. Demographic, clinical, and radiographic factors were correlated with occurrence of IOAR in univariate and multivariate analyses. The effect on outcome was analyzed for RIA and UIA separately.

RESULTS

Nine hundred and three clipped IAs were included in the final analysis (538 UIA and 365 RIA). IOAR occurred in 163 cases (18.1%), mostly during clipping of RIA (37.5% vs. 4.8%) In multivariate analysis, ruptured status (adjusted odds ratio [aOR], 10.46; P < 0.001), sack size (aOR, 1.05 per mm increase; P = 0.038) and IA location in the anterior communicating artery (aOR, 2.31; P < 0.001) independently predicted IOAR. For RIA cases, IOAR was also independently predicted by rebleeding before therapy (aOR, 3.11; P = 0.033) and clinical severity of subarachnoid hemorrhage (aOR, 1.18 per WFNS grade increase; P = 0.049). IOAR independently predicted poor outcome (aOR, 1.83; P = 0.042) after RIA surgery. In turn, IOAR affected only the risk for cerebral infarct (OR, 3.75; P = 0.003) and incomplete IA occlusion (OR, 3.45; P = 0.003) for UIA cases, but not the outcome (P = 0.263).

CONCLUSIONS

IOAR was independently predicted by the ruptured status, location, and size of IA and by initial severity of aneurysmal bleeding and pretreatment rebleeding. The influence of IOAR differed between RIA and UIA cases.

Intraoperative rupture in the surgical treatment of patients with intracranial aneurysms

Intraoperative rerupture (IOR) during clipping of cerebral aneurysms is a difficult complication of microneurosurgery. The aim of this study was to evaluate the incidence of IOR and analyze the strategies for controlling profound hemorrhage. A total of 165 patients with unruptured intracranial aneurysms and 46 patients with subarachnoid hemorrhage (SAH) treated surgically between April 2010 and March 2011, were reviewed. The data were collected with regard to age, sex, presence of symptoms, confounding factors and strategy for controlling intraoperative hemorrhage was analyzed in terms of location of aneurysms, timing of rupture and severity of IOR. 211 patients with 228 aneurysms were treated in this series. There were a total of six IORs which represented an IOR rate of 2.84% per patient and 2.63% per aneurysm. The highest ruptures rates occurred in patients with internal carotid artery aneurysms (25%). Surgeries in the group with ruptured aneurysms had a much higher rate of IOR compared with surgeries in the group with unruptured aneurysms. Of the six IOR aneurysms, one occurred during predissection, four during microdissection and one during clipping. One was major IOR, three were moderate and two were minor. Intraoperative rupture of an intracranial aneurysm can be potentially devastating in vascular neurosurgery. Aneurysm location, presence of SAH and surgical experience of the operating surgeon seem to be important factors affecting the incidence of IOR.

Patterns in neurosurgical adverse events: open cerebrovascular neurosurgery

OBJECT

As part of a project to devise evidence-based safety interventions for specialty surgery, we sought to review current evidence concerning the frequency of adverse events in open cerebrovascular neurosurgery and the state of knowledge regarding methods for their reduction. This review represents part of a series of papers written to consolidate information about these events and preventive measures as part of an ongoing effort to ascertain the utility of devising system-wide policies and safety tools to improve neurosurgical practice.

METHODS

The authors performed a PubMed search using search terms "cerebral aneurysm", "cerebral arteriovenous malformation", "intracerebral hemorrhage", "intracranial hemorrhage", "subarachnoid hemorrhage", and "complications" or "adverse events." Only papers that specifically discussed the relevant complication rates were included. Papers were chosen to be included to maximize the range of rates of occurrence for the reported adverse events.

RESULTS

The review revealed hemorrhage-related hyperglycemia (incidence rates ranging from 27% to 71%) and cerebral salt-wasting syndromes (34%-57%) to be the most common perioperative adverse events related to subarachnoid hemorrhage (SAH). Next in terms of frequency was new cerebral infarction associated with SAH, with a rate estimated at 40%. Many techniques are advocated for use during surgery to minimize risk of this development, including intraoperative neurophysiological monitoring, but are not universally used due to surgeon preference and variable availability of appropriate staffing and equipment. The comparative effectiveness of using or omitting monitoring technologies has not been evaluated. The incidence of perioperative seizure related to vascular neurosurgery is unknown, but reported seizure rates from observational studies range from 4% to 42%. There are no standard guidelines for the use of seizure prophylaxis in these patients, and there remains a need for prospective studies to support such guidelines. Intraoperative rupture occurs at a rate of 7% to 35% and depends on aneurysm location and morphology, history of rupture, surgical technique, and surgeon experience. Preventive strategies include temporary vascular clipping. Technical adverse events directly involving application of the aneurysm clip include incomplete aneurysm obliteration and parent vessel occlusion. The rates of these events range from 5% to 18% for incomplete obliteration and 3% to 12% for major vessel occlusion. Intraoperative angiography is widely used to confirm clip placement; adjuncts include indocyanine green video angiography and microvascular Doppler ultrasonography. Use of these technologies varies by institution.

DISCUSSION

A significant proportion of these complications may be avoidable through development and testing of standardized protocols to incorporate monitoring technologies and specific technical practices, teamwork and communication, and concentrated volume and specialization. Collaborative monitoring and evaluation of such protocols are likely necessary for the advancement of open cerebrovascular neurosurgical quality.

Does the impact of elective temporary clipping on intraoperative rupture really influence neurological outcome after surgery for ruptured anterior circulation aneurysms?--A prospective multivariate study

BACKGROUND

Elective temporary clipping (ETC) is increasingly used in surgery for aneurysms. This study was to assess whether the impact of ETC on intraoperative aneurysmal rupture (IAR) translates into neurological outcome.

METHODS

Patients who underwent surgery for ruptured anterior circulation aneurysms were prospectively studied for various factors related to ETC, IAR and neurological outcome at 3 months. Univariate and multivariate analyses were performed using SPSS20.

RESULTS

Of the total 273 ruptured aneurysm surgeries studied, IAR was observed in only six out of 132 aneurysms (4.5 %) who had ETC, compared with 78 out of 141 (55.3 %) without ETC (p < 0.001). Aneurysms complicated by IAR had significantly longer clipping time (8.3 min) compared with those without IAR (1.9 min) (p < 0.001). IAR had significant association with unfavorable outcome (38 % vs. 24 %) (p = 0.02). Patients with ETC had significantly shorter clipping time (2.9 min) compared with those without ETC (4.8 min) (p = 0.02). Unfavorable outcome was noted in 30 out of 132 with ETC (23 %), compared with 48 out of 141 without ETC (34 %) (p = 0.04). This beneficial effect was nonsignificantly greater in younger and good clinical grade patients. While episodes of ETC within clipping time of 20 min did not show significant difference in outcome, repeated rescue clipping (45 % unfavorable outcome, p = 0.048) and total clipping time of at least 20 min (75 % unfavorable outcome, p = 0.008) had significant impact on outcome. In multivariate analysis, the use of ETC (p = 0.027) and total temporary clipping less than 20 min (p = 0.049) were noted to result in significantly better outcome, independent of other factors.

CONCLUSIONS

The use of ETC decreased the occurrence of IAR and the total clipping time, thereby leading to significantly better outcome, independent of other factors. While repeated elective clipping within total clipping time of 20 min did not influence outcome, repeated rescue clipping and total clipping time of at least 20 min had significant impact on outcome.

Adenosine-induced cardiac arrest during intraoperative cerebral aneurysm rupture

BACKGROUND

Rupture of an intracranial aneurysm during surgical clipping may have devastating consequences. Should this happen all methods ought to be considered to stop the bleeding. A short-term cardiac arrest induced by adenosine could be a feasible method to help the surgeon. We present our experiences in the administration of adenosine during an intraoperative aneurysm rupture.

METHODS

Medical records of patients who underwent surgical clipping of a cerebral arterial aneurysm were reviewed from 2 university hospitals' operative database in the years 2003 to 2008. Patients were included in this study if adenosine had been administered during intraoperative rupture of an aneurysm.

RESULTS

Altogether, 16 of 1014 patients were identified with the use of adenosine during an intraoperative rupture of an aneurysm. All of the patients had sinus rhythm and normotension before the rupture of the aneurysm. Twelve patients were administered a single dose of adenosine and 4 multiple boluses for induction of cardiac arrest; the median (range) total dose was 12 (6-18) mg and 27 (18-87) mg, respectively. The clipping of the aneurysm and the recovery of circulation were uneventful in all cases. In a subgroup analysis according to patient outcome as alive/dead, the pre- and postoperative neurologic condition correlated with the outcome, whereas adenosine did not have any effect on the patient outcome.

CONCLUSION

In a case of a sudden aneurysm rupture, adenosine-induced circulatory arrest could be a safe option to facilitate clipping of an aneurysm. However, if adenosine is used, a very close collaboration between the surgeon and the anesthesiologist is required.

Impact of cardio-pulmonary and intraoperative factors on occurrence of cerebral infarction after early surgical repair of the ruptured cerebral aneurysms

OBJECTIVE

Delayed ischemic deficit or cerebral infarction is the leading cause of morbidity and mortality after aneurysmal subarachnoid hemorrhage (SAH). The purpose of this study is to reassess the prognostic impact of intraoperative elements, including factors related to surgery and anesthesia, on the development of cerebral infarction in patients with ruptured cerebral aneurysms.

METHODS

Variables related to surgery and anesthesia as well as predetermined factors were all evaluated via a retrospective study on 398 consecutive patients who underwent early microsurgery for ruptured cerebral aneurysms in the last 7 years. Patients were dichotomized as following; good clinical grade (Hunt-Hess grade I to III) and poor clinical grade (IV and V). The end-point events were cerebral infarctions and the clinical outcomes were measured at postoperative 6 months.

RESULTS

The occurrence of cerebral infarction was eminent when there was an intraoperative rupture, prolonged temporary clipping and retraction time, intraoperative hypotension, or decreased O(2) saturation, but there was no statistical significance between the two different clinical groups. Besides the Fisher Grade, multiple logistic regression analyses showed that temporary clipping time, hypotension, and low O(2) saturation had odds ratios of 1.574, 3.016, and 1.528, respectively. Cerebral infarction and outcome had a meaningful correlation (gamma=0.147, p=0.038).

CONCLUSION

This study results indicate that early surgery for poor grade SAH patients carries a significant risk of ongoing ischemic complication due to the brain's vulnerability or accompanying cardio-pulmonary dysfunction. Thus, these patients should be approached very cautiously to overcome any anticipated intraoperative threat by concerted efforts with neuro-anesthesiologist in point to point manner.

Complications of endovascular treatment of cerebral aneurysms

BACKGROUND

The International Subarachnoid Aneurysm Trial has indicated that endovascular management of acutely ruptured aneurysms may be superior to surgery. Clearly poor results ensue from both forms of treatment, and some of these are because of technical complications (not just poor patient status). This observational study was performed to determine the complications associated with the endovascular treatment of ruptured and unruptured cerebral aneurysms.

METHODS

Prospective data were gathered on 118 patients undergoing 126 endovascular treatment sessions for 126 nontraumatic cerebral aneurysms (30% unruptured) over a 3-year period. The average age was 51 years (range, 12-85 years). Females comprised 75% of the population treated.

RESULTS

Good outcomes were achieved with 71% of the procedures (59% for subarachnoid hemorrhage [SAH]; 97% for unruptured). No bleeding or rebleeding occurred from treated aneurysms. Vessel or aneurysm perforation occurred in 11 cases and led to adverse outcome in 3 (3%). Thromboembolic complications were felt to cause cerebral infarction in 8 cases (6%). The risk of vessel/aneurysm rupture or thromboembolic stroke was greater in patients with SAH. Eight attempts to coil (6%) were initially unsuccessful. Two of these were later successfully coiled and others had surgery. None of the failed attempts led to clinical deterioration. Balloon-assisted coiling (BAC) was not associated with an increased complication rate.

CONCLUSIONS

Vessel perforation and thromboembolic stroke are significant risks of endovascular treatment, especially after SAH. In our hands, however, BAC does not add to this risk.

Analysis of intraoperative rupture in the surgical treatment of 1694 saccular aneurysms

OBJECTIVE

Intraoperative rupture (IOR) of an aneurysm is a known risk in the surgical management of intracranial aneurysms. The purpose of this study was to determine the incidence of IOR in a modern surgical series and to assess which factors bear upon it.

METHODS

This study retrospectively examined 1269 patients with saccular aneurysms treated surgically between 1986 and 1998. Three vascular neurosurgeons performed 1435 operations on 1694 aneurysms. Multiple factors, including the magnitude and time of occurrence of IOR, aneurysm location, subarachnoid hemorrhage, timing of surgery, and use of temporary occlusion, were analyzed.

RESULTS

There were 113 instances of IOR (7.9% per surgery; 6.7% per aneurysm; 8.9% per patient). If the 59 "minor leaks" are excluded (as in previously published reports), the incidence becomes 3.8% per surgery, 3.2% per aneurysm, and 4.3% per patient. Posteroinferior cerebellar artery and anterior and posterior communicating artery aneurysms were more liable to rupture intraoperatively. The IOR rate was greater in ruptured than unruptured aneurysms (10.7 versus 1.2%, P < 0.0001). There was a lower rate of IOR in operations using temporary arterial occlusion (3.1 versus 8.6%, P < 0.0001). The occurrence of IOR for early surgery was not significantly higher than for surgery performed more than 3 days after subarachnoid hemorrhage (11.1 versus 10.0%, P = 0.6234).

CONCLUSION

The rate of significant IOR can be kept low. Aneurysm location, subarachnoid hemorrhage, and temporary arterial occlusion seem to be important factors affecting the incidence of IOR.

Early surgery-related complications after aneurysm clip placement: an analysis of causes and patient outcomes

Object. Most reports of series on ruptured intracranial aneurysms contain information on select intraoperative complications. An understanding of all surgical complications, however, may guide us toward improved surgical procedures and enrich discussions concerning alternative management strategies, such as endovascular treatment, which are not exempt from complications and aneurysm recurrence.

Methods. The study consists of a retrospective review of the charts, images, and notes from follow-up visits of 143 consecutive patients with subarachnoid hemorrhage (SAH) who were surgically treated during a 3-year period by one neurosurgeon. A surgical complication was determined based on findings of a clinical and/or radiological study in the absence of confounding factors such as the initial SAH ictus, vasospasm, hydrocephalus, and septic status. Functional outcome was assessed between 2 and 3 months post-SAH by using the Glasgow Outcome Scale (GOS). A procedure-related surgical complication was diagnosed in 29 (20.3%) of 143 patients studied. A brain tissue injury, including cerebral edema and hemorrhagic contusions, was diagnosed in 6.3% of patients, an unpredicted residual aneurysm neck in 5.3% of patients, and a cranial nerve deficit in 2.8% of patients. Functional outcome was good in 22 (75.9%) of the 29 patients with surgical complications. Death due to a surgical complication occurred in one (0.7%) of 143 patients.

Conclusions. Surgical complications are more prevalent than previously thought. They may have been overlooked previously because of the high percentage of good functional outcomes and low mortality rates in this group. The identification of surgical complications may encourage the search for solutions to improve surgical treatment of aneurysmal SAH.

Does intraoperative aneurysm rupture influence outcome? Analysis of 169 patients

OBJECTIVES

The aim of this study was to evaluate the prognostic value of intraoperative aneurysm rupture (IAR) in patients with subarachnoid hemorrhage (SAH) undergoing surgery for cerebral aneurysms.

PATIENTS AND METHODS

Between July 1997 and April 2000, 292 consecutive patients were admitted to our institution with SAH due to ruptured intracranial aneurysms. Of these, 169 patients were treated surgically according to standard microsurgical procedures and were included in this study. Mean age was 47 years. Initial clinical state was graded according to the classification of Hunt and Hess (HH). Outcome was classified according to the Glasgow Outcome Scale as favorable (grades IV and V) and unfavorable (grades I-III). Outcome of patients with intraoperative ruptured and non-ruptured aneurysms was analyzed in correlation to the preoperative clinical state and with respect to the time of surgery and to aneurysm localization.

RESULTS

Different rupture rates were observed with respect to the localization of the aneurysm: anterior circulation (n=69) 39.1%, middle cerebral artery (n=46) 34.8%, internal carotid artery (n=48) 31.2%, and posterior circulation (n=6) 16.7%. Patients with HH-grades I-III showed a favorable outcome in 72.2% (61 of 84 patients) without intraoperative rupture and in 71.7% (33 of 46 patients) with intraoperative aneurysm rupture. The corresponding values for patients with HH-grades IV/V were: favorable outcome in 34.6% (9 of 26 patients) and 23.1% (3 of 13 patients), respectively. Poor initial clinical condition (HH IV and V) as well as the initial Fisher grades III and IV were strongly associated with poor clinical outcome.

CONCLUSIONS

Intraoperative aneurysm rupture has no impact on the outcome, neither in patients with good initial condition nor for poor grades patients.

Transient cardiac standstill induced by adenosine in the management of intraoperative aneurysmal rupture: technical case report

OBJECTIVE AND IMPORTANCE

Intraoperative aneurysmal rupture represents a potentially catastrophic event. We describe the use of an intravenous adenosine bolus to induce transient cardiac asystole to control a severe intraoperative aneurysmal rupture. This treatment resulted in a brief period of severe hypotension, which enabled successful clipping of the aneurysm.

CLINICAL PRESENTATION

A 55-year-old man was referred to our institution 7 days after experiencing a mild subarachnoid hemorrhage from a fusiform, multilobulated aneurysm of the anterior communicating artery. The patient was found to have multiple additional fusiform aneurysms as well as a large parietal arteriovenous malformation.

INTERVENTION

A craniotomy was performed to clip the aneurysm, but surgical dissection was complicated by premature rebleeding that could not be controlled satisfactorily with tamponade or temporary arterial occlusion. Infusion of adenosine resulted in the rapid onset of profound hypotension, allowing for safe completion of the dissection and clipping of the aneurysm with a good outcome. There were no complications identified in relation to the use of adenosine.

CONCLUSION

In the setting of severe intraoperative aneurysmal rupture, intravenous adenosine represents a potential means of achieving a near-immediate profound decrease in the blood pressure that may allow for safe completion of the dissection and aneurysm clipping.

Adverse effects of limited hypotensive anesthesia on the outcome of patients with subarachnoid hemorrhage

OBJECT

This study was aimed at clarifying the effect of intraoperative hypotensive anesthesia on the outcome of early surgery in patients with subarachnoid hemorrhage (SAH) caused by saccular cerebral aneurysms. Other factors were also screened for possible effects on the outcome.

METHODS

Hospital charts in 84 consecutive patients with SAH who underwent aneurysm clipping by Day 4 were examined. Possible factors affecting the outcome were analyzed using multiple logistic regression with the dichotomous Glasgow Outcome Scale score as the outcome variable. The relationship between the intraoperative hypotension and the occurrence and severity of vasospasm was studied using both single- and multivariate analyses.

CONCLUSIONS

Intraoperative hypotension had a significantly adverse effect on the outcome of SAH. Hypotension was also related to more frequent and severe manifestations of vasospasm. A long-lasting effect of brain retraction is possibly the cause of this phenomenon. The data contained in this study preclude the use of intraoperative hypotension even in a limited form.