Abstract
Objectives
To determine whether any vital signs can be used to quickly identify brain lesions in patients with impaired consciousness.
Design
Cross sectional observational study.
Setting
Emergency department of an urban hospital, Japan.
Participants
529 consecutive patients (mean age 65 years) presenting with impaired consciousness (score <15 on the Glasgow coma scale) during 2000.
Main outcome measures
The receiver operating characteristic curve was used to quantify the relation between the vital signs on arrival and the final diagnosis of a brain lesion. Stratum specific likelihood ratios were calculated to define strata with optimal discriminating power.
Results
312 (59%) had a brain lesion which accounted for the impaired consciousness. The area under the receiver operating curve for systolic blood pressure was 0.90 (SE 0.01), indicating significantly higher accuracy (P<0.01) in the identification of a brain lesion than using diastolic pressure 0.82 (0.02) or pulse rate 0.63 (0.03). Likelihood ratios for systolic blood pressure lower than 90 mm Hg were less than 0.04, and those for systolic pressure higher than 170 mm Hg were greater than 6.09.
Conclusions
Systolic blood pressure is useful for diagnosing brain lesions in patients with impaired consciousness.
What is already known on this topic
Brain imaging and neurological examination of patients with impaired consciousness are often a waste of time and resources and can delay correct diagnosis
What this paper adds
Systolic blood pressure distinguishes patients with impaired consciousness who are at high risk from those who are at low risk of an organic brain lesion
General use of systolic blood pressure in the diagnosis of impaired consciousness may have clinical and economic benefits
Introduction
Diagnosing impaired consciousness is always a challenge. In many situations in the emergency room, doctors have to save time by doing other examinations first—for example, for hypoglycaemic coma, drug poisoning, and hepatic encaephalopathy. As doctors are not prepared to risk missing an abnormality,1 the use of computed tomography to screen patients with impaired consciousness for a brain lesion has become routine. Computed tomography of the cranium visualises brain lesions, but it does not identify extrinsic or metabolic brain dysfunctions, which affect more than half of patients with impaired consciousness.2
Previous studies suggest that the vital signs—blood pressure and pulse rate—are useful diagnostic tools in patients with impaired consciousness. Patients with acute stroke and those with increased intracranial pressure often have hypertension.3,4 The Cushing response (bradycardia with hypertension) is a well recognised clinical manifestation of increased intracranial pressure.5 Hypotension and tachycardia, on the other hand, are usual in states of depressed consciousness—for example, intoxication, endocrine diseases, and sepsis—because of metabolic brain dysfunction.6
We examined whether vital signs could be used to distinguish between patients with impaired consciousness who are likely to have an intracranial lesion from those who are not.
Methods
During 2000, we conducted a cross sectional observational study at the emergency department of Asahi General Hospital, Asahi, Chiba, Japan. This urban hospital primarily serves a general population and has about 15 000 admissions each year. On arrival, every patient had their systolic and diastolic blood pressure, pulse rate, and body temperature measured, and a score on the Glasgow coma scale was awarded.7 We defined impaired consciousness as a score of <15 on the scale.
We prospectively evaluated 529 consecutive patients with impaired consciousness who were at least 15 years old. We excluded patients with head injury. To determine the cause of their impaired consciousness, we admitted all eligible patients to the ward and followed them up until discharge. We considered the final diagnosis accounting for the impaired consciousness as the reference diagnosis.
Statistical analysis
We used the receiver operating characteristic curve to quantify how well the vital signs could be used to diagnose a brain lesion.8,9 We estimated the diagnostic accuracy of each vital sign by calculating the area under the curve and its standard error.10
The stratum specific likelihood ratio (SSLR) is the probability of a given test result when the disease is present, divided by the probability of the same test result when the disease is absent.9
Results
Patient population
During 2000, we admitted 15 293 patients of whom 529 (3.5%; 235 women) had impaired consciousness of non-traumatic cause. The mean age was 65 years (range 15 to 97 years; SD 21 years). The two groups did not differ significantly in age, sex, or score on the Glasgow coma scale.
Vital signs in patients
Some of the vital signs clearly distinguish between the patients with brain lesions and those without (table). Compared with those patients without a lesion, those with a lesion had significantly higher systolic blood pressure, higher diastolic blood pressure, and significantly lower pulse rate. Body temperature between the groups did not differ.
The large standard deviation for each vital sign indicates considerable overlap between the two groups: using the vital signs to diagnose brain lesions in clinical practice is difficult (fig A1). A clearer view of the diagnostic significance of the vital signs can be obtained by determining the sensitivity and specificity in different strata: we measured the area under the receiver operating characteristic curves and calculated stratum specific likelihood ratios.
Figure A1.
Distribution of systolic blood pressure (top), diastolic blood pressure (middle), and pulse rate (bottom) among patients with impaired consciousness
Firstly, we analysed the diagnostic value of systolic and diastolic blood pressure and pulse rate with area under curves. We found an area of 0.90 (SE 0.01) for systolic and 0.82 (0.02) for diastolic blood pressure and 0.63 (0.03) for pulse. under the receiver operating characteristic curves (fig A2). Systolic blood pressure provides the greatest sensitivity for all specificities. Accordingly, the curve area was significantly higher for systolic than for diastolic blood pressure (z=4.53, P<0.01). Likelihood ratios for systolic blood pressure lower than 90 mm Hg were less than 0.04, and those for systolic pressure greater than 170 mm Hg were more than 6.09 (see also bmj.com).
Figure A2.
Sensitivity and false positive rate (1−specificity) for area under receiver operating characteristic curve for different strata of the vital signs, as given on bmj.com
Discussion
Systolic blood pressure is the best vital sign for distinguishing whether impaired consciousness is because of a brain lesion. Previous clinical batteries to determine the nature and site of a lesion impairing consciousness define individual criteria which are comprehensive but too complex for general use.2,11,12
The accuracy of the area under receiver operating curves is classified as low if the area is between 0.5 and 0.7; as moderate, if between 0.7 and 0.9; and as high, if greater than 0.9. Judged by their areas, the accuracy of diastolic blood pressure (0.82) is moderate and that of systolic blood pressure (0.9), which is significantly higher than that of diastolic blood pressure, is marginally high.
Our findings are limited, because of the characteristics of the patients we studied. Firstly, the older mean age, 65 years, than in previous studies, 54 years and 58 years, may be because of an older population in our local community.3,11 Secondly, the incidence of stroke in our study (49%) was higher than in studies of Plum and Posner (26%; 130/500) and Yamashiro et al (28%; 49/175) but lower than among British patients with coma (57%).2,3,11 Thirdly, the high incidence of diffuse hypoxia or ischaemia (18%) probably reflects the vulnerability of the older patients in our study to severe systemic infections—for example, pneumonia, pyelonephritis, and cholecystitis. Bates et al observed a similar high incidence of diffuse hypoxia or ischaemia among patients with coma.11
Our study confirms the validity of systolic blood pressure for discriminating between patients with impaired consciousness who have a brain lesion and those who do not. Using systolic blood pressure in the diagnosis of impaired consciousness should give both clinical and economic benefits.
Acknowledgments
We thank Toshiaki Furukawa for technical advice on the receiver operating characteristic curves and stratum specific likelihood ratios.
Footnotes
Funding: No additional funding.
Competing interests: None declared.
This is an abridged version; the full version is on bmj.com
References
- 1.Graham ID, Stiell IG, Laupacis A, O'Connor AM, Wells GA. Emergency physicians' attitudes toward and use of clinical decision rules for radiography. Acad Emerg Med. 1998;5:134–140. doi: 10.1111/j.1553-2712.1998.tb02598.x. [DOI] [PubMed] [Google Scholar]
- 2.Plum F, Posner JB. The diagnosis of stupor and coma. 3rd ed. Philadelphia: FA Davis; 1980. [Google Scholar]
- 3.Yamashiro S, Oda Y, Kanegae S, Shirahama M, Yoshihara K, Fukui T, et al. Informative usefulness of age, sex and vital signs in the differential diagnosis of disturbed consciousness among 175 emergency outpatients. Fukuoka Igaku Zasshi. 1994;85:353–360. [PubMed] [Google Scholar]
- 4.Wallace JD, Levy LL. Blood pressure after stroke. JAMA. 1981;246:2177–2180. [PubMed] [Google Scholar]
- 5.Guyton AC, Hall JE. Textbook of medical physiology. 9th ed. Philadelphia: WB Sauders; 1996. pp. 209–220. [Google Scholar]
- 6.Victor M, Ropper AH. Adams and Victor's principles of neurology. 7th ed. New York: McGraw-Hill; 2001. Coma and related disorders of consciouness; pp. 366–389. [Google Scholar]
- 7.Teasdale G, Jennett B. Assessment of coma and impaired consciousness: a practical scale. Lancet. 1974;ii:81–84. doi: 10.1016/s0140-6736(74)91639-0. [DOI] [PubMed] [Google Scholar]
- 8.Peirce JC, Cornell RG. Integrating stratum-specific likelihood ratios with the analysis of ROC curves. Med Decis Making. 1993;13:141–151. doi: 10.1177/0272989X9301300208. [DOI] [PubMed] [Google Scholar]
- 9.Furukawa TA, Goldberg DP, Rabe Hesketh S, Ustun TB. Stratum-specific likelihood ratios of two versions of the general health questionnaire. Psychol Med. 2001;31:519–529. doi: 10.1017/s0033291701003713. [DOI] [PubMed] [Google Scholar]
- 10.Hanley JA, McNeil BJ. A method of comparing the areas under receiver operating characteristic curves derived from the same cases. Radiology. 1983;148:839–843. doi: 10.1148/radiology.148.3.6878708. [DOI] [PubMed] [Google Scholar]
- 11.Bates D, Caronna JJ, Cartlidge N, Knill JR, Levy DE, Shaw DA, et al. A prospective study of nontraumatic coma: methods and results in 310 patients. Ann Neurol. 1977;2:211–220. doi: 10.1002/ana.410020306. [DOI] [PubMed] [Google Scholar]
- 12.Mills ML, Russo LS, Vines FS, Ross BA. High-yield criteria for urgent cranial computed tomography scans. Ann Emerg Med. 1986;15:1167–1172. doi: 10.1016/s0196-0644(86)80859-9. [DOI] [PubMed] [Google Scholar]