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Changing neurologic status after EVD placement
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Placement of an EVD frequently results in a significant improvement in neurologic status. Comatose patients may start to localize to painful stimulation and may even open their eyes. Although this is not always seen, when it happens, it may possibly indicate a favorable outlook (eg, a patient, who presents with HH grade V after aneurysmal SAH, wakes up after EVD placement and begins to follow verbal commands: if such patient remains awake and continues to follow commands throughout the course of his/her illness, then the patient is behaving like a low-grade HH [ie, grades I to III], not like a grade V who presents and remains in coma).
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Patients with HH grade V have extremely poor prognosis. Many physicians and surgeons disclose such a poor prognosis to the patient's family and this often leads to withdrawal of life-sustaining care prior to any treatment. While the decision of treating versus not treating should be made based on the prognosis and for the best interest of the patient, the initial prognosis is mostly based on the bedside neurologic assessment, and physicians should be aware that the patient's clinical status may dramatically change after placing an EVD, which has significant implications for the prognosis. 7
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There are several SAH grading systems worth mentioning here. In 1967, Hunt and Hess have reported 275 consecutive patients who were treated at the Ohio State University over a 12-year period. They believed that the intensity of the meningeal inflammatory reaction and the severity of neurologic deficit and the presence or absence of significant systemic disease should be taken into account when classifying SAH patients. From the original manuscript, their grading system (which is now known and widely used as the Hunt and Hess Grade) was a classification of patients with intracranial aneurysms according to surgical risk (Table 1-1). 8
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Higher grades are associated with increased surgical risk for the repair of ruptured intracranial aneurysms. The Hunt and Hess original report included the presence of significant systemic disease (such as "hypertension, diabetes, severe arteriosclerosis, chronic pulmonary disease, and severe vasospasm seen on angiography") as a negative sign, and the presence of such disease resulted in placement of the patient in the next less favorable (higher surgical risk) grading category. 8 This grading system is not flawless as it can be challenging sometimes to differentiate between each category. For example, consider a patient with SAH with mild headache and nuchal rigidity versus another patient with moderate headache and nuchal rigidity (which means grades I and II, respectively, according to the original HH grading system). The only differentiating variable here would be the intensity of the headache, and that can be problematic as the intensity of headache is subjective and patients often cannot differentiate mild from moderate headache (most people would say "very bad" headache and cannot provide further details than that).
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This criticism has been actually predicted, and the original authors have mentioned it in their journal article: "It is recognized that such classifications are arbitrary and that the margins between categories may be ill-defined." 8 For this reason, it has been pointed out that the HH system has poor interobserver reliability and reproducibility. 9 Nevertheless, the HH grading system is widely used and numerous studies have shown that the higher grade (or sometimes called poor grade, which usually refers to HH grades IV and V) is associated with a poor outcome. 10-13
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Another grading system to consider is the one that is the most universally accepted system for patients presenting with altered level of consciousness, the Glasgow Coma Scale (GCS). In 1975, Jennet and Bond, from the University of Glasgow, reported a scale called Assessment of Outcome After Severe Brain Damage, a Practical Scale (Table 1-2). 14
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The GCS is a more general grading system and was not developed specifically for SAH patients. However, studies show that for patients with aneurysmal SAH, the initial GCS score has positively correlated with long-term outcome. 15
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In 1988, the World Federation of Neurosurgical Societies (WFNS) developed a grading system that incorporated both the GCS and bedside neurologic assessment focusing on any focal deficit (Table 1-3). 16
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The HH and WFNS grading systems are by far the two most commonly used systems for grading patients with acute aneurysmal SAH. Despite the frequently raised criticisms regarding the inter-observer variability, the HH grade is used even more commonly than the WFNS scale (71% of reported studies from 1985 to 1992 used the HH grade compared to 19% that used the WFNS scale), 17, 18 and both grading systems have been shown to correlate reasonably well with the long-term outcome. 19
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In 1980, Fisher and colleagues reported the relationship between the amount of SAH and risk of developing severe vasospasm (defined as delayed clinical symptoms and signs, Table 1-4). 20
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The Fisher group's grading system is based on the description of CT findings mainly focusing on the actual volume of blood in the subarachnoid space. There is a linear relationship between the amount of hemorrhage and the rate of developing symptomatic vasospasm. 20 This grading system has been extensively studied and there are numerous clinical studies validating its usefulness. 21-25 In multiple studies, the risk of developing symptomatic cerebral vasospasm appears to increase along with the increasing amount of acute hemorrhage in the subarachnoid space. The original report by Fisher et al does describe the low risk of vasospasm, and yet there is a clearly observed risk of vasospasm even for patients with minimal blood in the subarachnoid space and for those with intraparenchymal or intraventricular hemorrhage. 20
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It is important to understand that the Fisher scale actually did report some incidence of vaso-spasm in groups 1, 2, and 4. The group 3 had the highest incidence of vasospasm, but other groups also had vasospasms, just much lower in frequency. 20 Like all other grading systems, the Fisher scale is not without limitations. There have been concerns in the literature reporting a low correlation between the Fisher grade and the incidence of symptomatic vasospasm (one of the recent studies showed about 50% correlation between the Fisher grade and vasospasm). 26 Another criticism about the Fisher scale is its inevitable interpresonal variability in assessing the estimated blood volume. Also, according to the scale, all cases of CT head showing SAH with greater than 1 mm of vertical thickness is categorized as grade III, but this includes vast majority of patients with SAH who may not in fact have the same risk of developing vasospasm. 26, 27
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In light of these concerns, Claassen et al's group, from Columbia University, proposed another grading system (Table 1-5), the modified Fisher scale (mFS). 28, 29
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Note that the mFS incorporates the presence or absence of IVH, and if a patient has IVH, even if there is no blood in the subarachnoid space, the scale is 2 (as opposed to 1 [no blood seen] or 4 [minimal SAH and the presence of intraparenchymal hemorrhage or IVH] in the original Fisher scale). This scale emphasizes that the presence of IVH increases the risk of developing symptomatic vasospasm. This emphasis is stronger but not completely different from that of the Fisher scale as the original Fisher scale does report some incidence (although low) of vasospasm in those with IVH and absent or minimal SAH. Furthermore, the mFS uses a subjective description and coding of the hemorrhage by the use of "thick" or "thin" clots in the subarachnoid space, and the description of IVH did not take the exact amount of IVH into account (this scale takes the "presence" versus the "absence" of IVH into account, not how much IVH there is). The mFS emphasizes the importance of IVH as well as it highlights how the amount of hemorrhage once again plays an important role. Its grading system is easy and intuitive (unlike the classic Fisher scale in which group 4 actually has a lower incidence of vasospasm than lower grades), as the scale goes from 0 to 4, and the higher grade is the higher risk of developing delayed cerebral ischemia (DCI).
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In order to minimize the interobserver variability in assessing the estimated volume of blood in the subarachnoid space, a volumetric quantification of Fisher grade 3 has been proposed and studied by Friedman and colleagues from the Mayo Clinic. 30 However, while quantification of SAH may provide a more accurate assessment of the volume of blood in the subarachnoid space, it requires manual outlining of the hemorrhage volume, which can be time consuming and less reliable.
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In 2011, Ko and colleagues, from Columbia University, reported a study of volumetric analysis of SAH using a MIPAV (Medical Image Processing, Analysis, and Visualization; version 4.3; National Institutes of Heath, NIH) software package that automatically outlines the hemorrhage on CT at the click of a button. 31 This quantification analysis showed that patients with a higher volume of cisternal plus IVH clot burden developed a greater risk of developing DCI and poor outcome at 3 months (Figure 1-3). It also validated the modified Fisher scale as a reasonable grading system in predicting DCI that can be done easily at the bedside. However, it is important to note that although both the Fisher scale and the mFS have demonstrated the association between blood burden and DCI, a question still remained: Does the location and exact thresholds of blood volume matter? Ko and colleagues have reported:
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Our data show that the quantitative blood volume in contact with the cisternal space, whether directly in the cisternal subarachnoid space or intraventricular space, acts as cumulative blood burden and is associated with an increased risk of DCI. The quantitative volume scale and the mFS were equivalent in predicting DCI, validating the accuracy of the mFS. However, volumetric analysis had no overlaps in the odds ratio for DCI in different blood burden groups, which may suggest more robust association between the total blood burden and DCI.
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Klimo and Schmidt have eloquently summarized a historical review of the literature on the relationship between the CT findings and the rate of developing cerebral vasospasm after aneurysmal SAH using different scales 32 :
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The elucidation of predictive factors of cerebral vasospasm following aneurysmal subarachnoid hemorrhage is a major area of both clinical and basic science research. It is becoming clear that many factors contribute to this phenomenon. The most consistent predictor of vasospasm has been the amount of SAH seen on the postictal computed tomography scan. Over the last 30 years, it has become clear that the greater the amount of blood within the basal cisterns, the greater the risk of vasospasm. To evaluate this risk, various grading schemes have been proposed, from simple to elaborate, the most widely known being the Fisher scale. Most recently, volumetric quantification and clearance models have provided the most detailed analysis. Intraventricular hemorrhage, although not supported as strongly as cisternal SAH, has also been shown to be a risk factor for vasospasm.