Prehospital triage to stroke centres: Is it a solution to the problem?

Commentary

CJEM 2000;2(2):106-108

The problem

Thrombolytic therapy for acute ischemic stroke is receiving wide attention and has been advocated in emergency medicine literature¹ and by the Canadian Stroke Consortium, a national network of neurologists.² Unfortunately, because of late presentation to the emergency department (ED), most acute stroke patients are ineligible for thrombolytic treatment.³ This situation is primarily caused by the public’s lack of awareness of stroke signs and symptoms,^4,5 which leads to delays in presentation to the ED.^3,6,7

Current Canadian guidelines recommend administration of thrombolytic therapy within 3 hours of stroke onset.² Because of this urgency, many facets of prehospital and ED care are being examined to discover ways of reducing time to treatment.⁸ One broad recommendation is to develop specially trained stroke care teams to respond to patients with apparent acute stroke.⁹ This has led to an interest in prehospital stroke scales^10–12 that would enable paramedics to identify patients with acute stroke, and then pre-notify and triage that patient to the designated stroke centre.¹³ Prehospital stroke scales are analogous to widely used trauma triage guidelines.

However, little information has been published describing the impact of stroke triage on stroke centres. Accordingly, we sought to evaluate the potential impact of a recently published stroke scale^10,11 on our urban emergency medical services (EMS) and ED system, which is considering prehospital triage to stroke “centres of excellence.”

The evidence

The recently proposed Cincinnati Prehospital Stroke Scale^10,11 (CPSS) is a 3-item scale that was derived from the 15-item National Institutes of Health stroke scale. The items of the CPSS include the presence or absence of facial droop, arm drift and abnormal speech. An abnormality in at least one of these items was found to have a sensitivity of 100% and a specificity of 88% when tested by an emergency physician on a group of patients in which the prevalence of acute stroke was 25%.¹¹ The CPSS is also said to have excellent reliability when used by prehospital personnel and physicians to evaluate ED and neurology service patients.¹⁰ In this study, where the prevalence of acute stroke or transient ischemic attack (TIA) was 29%, the scale was 63% sensitive and 88% specific. If these 2 studies provide a valid assessment of CPSS diagnostic parameters, then its actual sensitivity and specificity are likely to be approximately 80% and 88% respectively.

The assumptions

The prevalence of acute stroke in prehospital patients is far lower than 25% to 29% and may be as low as 0.7%.¹⁴ Our assumption is that the prevalence of acute stroke in our EMS patients is roughly 1%. Since our EMS system responds to 125,000 emergency calls per year, EMS personnel would be expected to transport approximately 1250 acute stroke patients.

Not every EMS patient should be the subject of a pre-hospital stroke scale. Our EMS system uses the Medical Priority Dispatch System (MPDS),¹⁵ which requires emergency medical dispatchers to assign patients into broad diagnostic and chief complaint categories. It was the consensus of 2 EMS physicians and 3 paramedics that acute stroke patients are likely to fall into the following MPDS categories: convulsions/seizures, diabetic problems, headache, sick person, stroke, unconsciousness/fainting, or unknown problem. These groups account for 43,000 calls per year and would include most of the patients requiring a stroke triage scale assessment. If 1250 of 43,000 transported patients have acute stroke, then stroke prevalence in this group is 3%.

Analysis and discussion

Table 1 illustrates what would happen to a cohort of 2500 patients triaged according to the CPSS (assuming a sensitivity of 80%, a specificity 88%, and a stroke prevalence of 3%). Note that the positive predictive value (PPV) is only 17%,^16,17 which means that for every 60 patients correctly triaged to a stroke centre 291 non-stroke patients would be incorrectly triaged to the centre. This equates to 4.9 “nonstroke” patients for every stroke patient.

The PPV of a diagnostic test is greatly influenced by the prevalence of the condition in the population being tested.¹⁶ If we assume a higher stroke prevalence estimate of 10%, the CPSS would still triage 1.4 “non-stroke” patients to the stroke centre for every stroke patient. These “non-stroke” patients could seriously impact the ED and admitting service of a stroke centre. Most patients triaged as a “falsepositive” stroke have serious medical problems such as urosepsis, aspiration, uremia, drug overdose, seizure and syncope.^11,18 These patients frequently require hospitalization, usually by a general internal medicine service rather than a neurology service. As well, no research has been published to indicate how many “true-positive” stroke patients actually meet current thrombolytic guidelines; however, it is probably a small minority. At our centre, patients not meeting thrombolytic guidelines are usually admitted by general internal medicine.

Finally, prehospital stroke triage may impact negatively on the care of “false-negative” stroke patients who have acute stroke but are not recognized as such by the paramedics. Table 1 suggests that, for every 4 stroke patients triaged correctly to the stroke centre, 1 patient with acute stroke will be triaged to a “non-stroke” centre, and this hospital will still be obligated to offer appropriate emergent stroke care.

Conclusion and recommendations

Current stroke scales are not adequate tools for prehospital triage of apparent stroke patients to designated centres. There is a risk of overwhelming designated EDs and general internal medicine units with seriously ill “non-stroke” patients and stroke patients who do not meet thrombolytic guidelines. A prehospital stroke triage system does not obviate the need of “non-stroke centres” to provide high quality emergent stroke care to patients who are triaged incorrectly or “walk in” off the street.

Our recommendation for a more appropriate urban EMS system is for all hospitals to be “stroke ready.” A tool such as the CPSS could be used for prehospital stroke identification, not triage, and to indicate the need to pre-notify a receiving ED of an incoming possible acute stroke patient. Once treatment has been administered, the EMS system should be prepared to rapidly respond to a request to transfer a patient to a designated stroke centre for ongoing care.

References

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