Study Design, Population, and Setting
This is a retrospective, population-based observational study based on the ambulance records of Osaka Municipal Fire Department. The study period was from January 1, 1998 to December 31, 2007. This study was approved by the Ethics Committee of Kyoto University Graduate School of Medicine.
All adult patients aged > =18 years who suffered impaired consciousness, and were transported to medical institutions by EMS in Osaka City were enrolled in this study. Diagnoses of stroke and its subtypes such as subarachnoid hemorrhage (SAH), intracranial hemorrhage (ICH), and ischemic stroke (IS) were clinically determined by the physicians caring for the patients in collaboration with the EMS personnel.
Japan Coma Scale
Table 1 shows Japan Coma Scale (JCS) for grading impaired consciousness. The level of consciousness among emergency patients was recorded by EMS personnel according to JCS. The JCS is a simple way for evaluating neurological disturbance focused on patient's awareness. EMS personnel have generally been using it in prehospital settings. The JCS was roughly divided into the three categories (e.g., mild disturbance, moderate disturbance, and severe disturbance).
Emergency Medical Service Systems and Hospitals in Osaka City
Osaka City, which is a largest urban community in western Japan, has an area of 222 km2, and its population was approximately 2.7 million in 2000 (population density, approximately 12,000 persons/km2). The municipal EMS system has been previously described. Briefly, the EMS system is operated by the Osaka Municipal Fire Department and activated by dialing 119 on the telephone. There were 25 fire stations and a dispatch center in 2007 in Osaka City. Life support is provided 24 hours every day. Usually, each ambulance has a crew of three emergency providers including at least one Emergency Life-Saving Technician (ELST), a highly-trained prehospital emergency care provider. Osaka City included 194 hospitals (34,209 beds) in 2007. Of them, 90 hospitals including 5 critical care centers can accept patients transported by ambulance.
Data Collection and Quality Control
Data were uniformly collected using the specific forms that included sex, age, location, vital signs such as first documented systolic and diastolic blood pressure measured manually with sphygmomanometer, heart rate, respiratory rate, and oxygen saturation. The diagnosis was determined by the physician responsible for the care of the patient before admission in the emergency department. The data form was filled out by the EMS personnel in cooperation with the physicians caring for the patient, transferred to the EMS Information Center of Osaka Municipal Fire Department, and then checked by the investigators. If the data sheet was incomplete, the investigators returned it to the relevant EMS personnel for data completion.
The association between the occurrence risk of stroke and SBP (every 20 mmHg) was "a priori" analyzed considering its subtype (SAH, ICH, or IS). Patient characteristics with and without SBP measurements were evaluated with the use of the t-test for numeric variables and the chi-square test for categorical variables. Trends in categorical values and numerical values were tested with logistic regression models and linear tests for trend, respectively. Multiple logistic regression analysis was used to assess the occurrence risk of stroke and its subtype among emergency patients with impaired consciousness by 20 mmHg stratum; Adjusted Odds ratios (AORs) and their 95% confidence intervals (CIs) were calculated. Potential confounding factors were sex, age, and level of consciousness. In addition, the relationship between prehospital SBP and stroke occurrence by impaired consciousness level was evaluated. Statistical analyses were performed with SPSS statistical package version 17.0 J (SPSS, INC., Chicago, IL). P value of <0.05 was considered statistically significant.
BMC Emerg Med. 2013;13(24) © 2013 BioMed Central, Ltd.