An Association Between Systolic Blood Pressure and Stroke Among Patients With Impaired Consciousness in Out-of-Hospital Emergency Settings

Taro Irisawa; Taku Iwami; Tetsuhisa Kitamura; Chika Nishiyama; Tomohiko Sakai; Kayo Tanigawa-Sugihara; Sumito Hayashida; Tatsuya Nishiuchi; Tadahiko Shiozaki; Osamu Tasaki; Takashi Kawamura; Atsushi Hiraide; Takeshi Shimazu

Disclosures

BMC Emerg Med. 2013;13(24) 

In This Article

Discussion

From this large registry of ambulance records, we demonstrated a significant positive relationship between prehospital SBP and the risk of stroke occurrence among emergency patients with impaired consciousness. Although little attention has been paid to SBP measured by EMS in prehospital settings in terms of diagnostic information for stroke, this large population-based registry enabled us to evaluate the relationship between prehospital SBP and stroke occurrence among these patients, and would add new insights on the importance of prehospital SBP measurement. Our results also suggest that prehospital SBP measurements in the patient with impaired conscious level might be a helpful guide as to where to transport a patient especially in communities that have both comprehensive stroke centers and primary ischemic stroke centers.

This study showed that the risk of stroke occurrence among emergency patients with impaired consciousness increased with increasing prehospital SBP. A previous study showed that initial SBP at emergency department arrival was of help for diagnosing intracranial lesion of patients with impaired consciousness.[9] However, diagnosis after hospital arrival is too late to transport the stroke patient to appropriate institution and start treatments against stroke in the effective time window.[10] Guidelines for the Early Management of Adults With Ischemic Stroke by American Heart Association recommend quicker transportation of suspected stroke patients to stroke care units to improve better neurological outcome.[11] Importantly, paralysis of stroke patients is frequently difficult to evaluate when their consciousness is disturbed. Therefore, this study showing the association between prehospital SBP measurements and stroke occurrence among patients with impaired consciousness would contribute to earlier detection of stroke and subsequent rapid transport to appropriate hospitals that can conduct specific treatments for them.

In analyses by stroke subtype, increased SBP was more strongly associated with occurrence of stroke among patients with hemorrhagic brain lesions such as SAH and ICH. The mechanism of hypertensive response among stroke patients is unclear[12] although patients with acute stroke and those with increased intracranial pressure often have hypertension. It was reported that 84% of patients with stroke had increased blood pressure in the acute phase.[13] The arterial pressure elevation in response to cerebral ischemia is known as the central nervous system ischemic response.[14] In ischemic stroke, hypertension maybe adaptive response to improve perfusion to the ischemic penumbra protecting the brain from further ischemia. On the other hand, hypertension in hemorrhagic brain lesion like SAH or ICH may cause further damage by worsening cerebral edema, increasing intracranial pressure, or causing hematoma expansion.[15,16] Our result showing difference by the subtype of stroke might be partially explained by such pathophysiological differences between hemorrhagic and ischemic lesions.

From our results, emergency patients with impaired consciousness and high SBP should be considered to be transported to the comprehensive stroke centers with capabilities of either neurosurgery or tissue plasminogen activator (t-PA) administration because these patients might have stroke but prehospital EMS personnel could not distinguish brain hemorrhagic lesions from ischemic ones. In addition, this study showed the strong relationship between high prehospital SBP and the occurrence of SAH and ICH, and those patients should be treated as quick as possible in order to prevent re-rupture of aneurysms and recurrent bleeding.[17,18] Especially, the strength of association between SBP and stroke subtype by impaired conscious level was very powerful with ICH and to some extent with SAH (mild and moderate disturbances), which would suggest that prehospital SBP can be an important triage guide for selecting patients. Further studies identifying an accurate cutoff point in this regard for SBP in conjunction with level of consciousness would make the EMS triage decision more precise and reduces the risk of overwhelming comprehensive stroke centers with patients that do not need the advanced capabilities. On the other hand, the relationship between SBP in prehospital settings and the occurrence of IS was relatively small. Therefore, to improve positive predictive value for IS patients who are most treatable, development of additional clinical indicators should be found out to make it possible to transport patients with IS to the primary ischemic stroke centers where only t-PA administration could be performed.

There were some limitations to this study. First, in Japan, EMS personnel evaluated level of consciousness among prehospital emergency patients by using JCS rather than the commonly-used Glasgow Coma Scale (GCS). JCS is not preferable to GCS as a consciousness evaluation system in the acute phase of SAH.[19] However, traditionally in Japanese prehospital setting, EMS has been evaluating stroke patients with impaired consciousness by JCS. Although our study cannot compare with GCS directly, these results should, nevertheless, provide useful information on the relationship between SBP and stroke occurrence among patients with impaired consciousness. Second, this study did not obtain data on advanced treatments and neurological outcomes among stroke patients after hospital arrival. Third, data on patient's past history and medications that might affect the occurrence of stroke was lacking. Fourth, we did not obtain information on other diagnosis that could mimic stroke such as hypoglycemia, complicated migraine, prolonged seizures, and subdural hematomas. Finally, there might be unmeasured confounding factors and selection bias that might have influenced the relationship between prehospital SBP and stroke occurrence among emergency patients with impaired consciousness.

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