Clinical review

Accident and emergency medicine

Sarah A Stahmer, associate residency program director. 

Department of Emergency Medicine, Hospital of the University of Pennsylvania, Philadelphia, PA 19104-4283, USA

Correspondence to: stahmer{at}mail.med.upenn.edu

Emergency medicine is rapidly evolving as a medical specialty. It provides immediate and universal care to over 90 million patients a year in the United States alone. In addition to life saving treatment, the emergency department provides a safety net, giving unrestricted care to people with little or no access to other types of health care. Recent developments reflect the varied nature of emergency medicine. These include improvements in emergency management of acute cardiac ischaemia, identification of victims of domestic violence, and the use of diagnostic tools such as ultrasound examination by specialists in emergency medicine.

	Methods

Topics were chosen after reviewing articles published during the past two years in those peer reviewed journals commonly referred to by specialists in emergency medicine. Selection was based on the number of quality studies published on a particular topic and the topic's actual or potential impact on clinical practice in emergency medicine. A Medline search was performed using the terms cardiac markers, domestic violence, ultrasound, and emergency medicine.

	Screening for acute cardiac ischaemia

In the United States alone, over six million patients each year present to the emergency department with chest pain. The goals of the doctor are to identify rapidly those patients who are candidates for thrombolytic treatment; to differentiate between patients with chest pain caused by acute coronary ischaemia and chest pain from other causes in order to avoid unnecessary admission to hospital; and to stratify those patients with possible ischaemic chest pain into risk groups.

In addition to the routine medical history, physical examination, and 12 lead electrocardiography, the specialist in emergency medicine now has access to a growing number of ancillary tests and technologies that can help in the management of patients with chest pain. Those which seem particularly promising include new markers of cardiac ischaemia, stress testing, and acute perfusion imaging with technetium-99m labelled sestamibi.

	Markers of cardiac ischaemia

Markers of myocardial necrosisspecifically, myoglobin, creatinine kinase, and troponin I and Thave undergone prospective testing of their diagnostic performance in acute myocardial infarction. Available data suggest that although a single creatine kinase MB test as a screen for acute myocardial infarction is only 50% sensitive when sampled at the time of the patient's arrival in the emergency department,¹ serial tests over several hours seem to have better diagnostic sensitivity.² Sensitivity reached more than 90% when assayed over three hours and 95% within six hours.² The results of serum creatine kinase MB tests help specialists in emergency medicine to make clinical decisions, particularly with regard to patients with acute myocardial infarction.³

Myoglobin
Myoglobin is a low molecular weight marker for acute myocardial infarction and is detectable in serum before creatine kinase MB. In patients with acute myocardial infarction, serum myoglobin concentrations doubled within two hours of evaluation in the emergency department, and peak values were reached at four hours.⁴ Serial measurements of myoglobin within the first few hours of the onset of symptoms are very sensitive for myocardial infarction, but they are much less specific than creatine kinase MB determinations. Carbonic anhydrase III, a protein identified in type I skeletal muscle, is highly specific for non-cardiac muscle injury, and the ratio of myoglobin to carbonic anhydrase III has been shown improve the specificity yet maintain early sensitivity of myoglobin for acute myocardial infarction. This ratio, when determined within the three hours of presentation, identified twice as many patients with acute myocardial infarction as creatine kinase MB.⁵

Troponin
Single values of troponin T and I, both highly specific markers of myocardial injury, are comparatively insensitive early screening tests for acute myocardial infarction because they are not present in serum until relatively late.⁶ Assays of troponin concentrations may be most useful in stratifying the risk of infarction in patients with unstable angina. Several reports have suggested that higher concentrations of troponin in these patients are associated with an increased risk of cardiac events and death.⁷ Early markers of myocardial injury such as myoglobin, combined with more specific markers such as creatine kinase and troponin, are potentially useful in identifying acute myocardial infarction and in triage of patients with chest pain. However, the impact of routine use of these newer markers (either alone or in combination) in the emergency department is currently unknown.

	Stress testing

The electrocardiographic exercise stress test has been used extensively by cardiologists to screen stable patients for ischaemic heart disease. Recent trials show that it can also be useful in managing patients admitted to the emergency department with acute chest pain.^8-11 The goals are to reduce unnecessary admissions to hospital and expedite outpatient investigations. Stress testing is usually performed in observation units set up in or near the emergency department, and it is overseen and interpreted by cardiologists. To date, only low risk patients (determined by negative electrocardiogram, enzyme markers, and telemetry monitoring for variable lengths of time) have been tested as part of clinical trials. Results have shown that for this low risk group of patients, stress testing can be performed safely, and may reduce the number of patients with chest pain admitted to hospital.

	Technetium-99m sestamibi

Technetium-99m labelled sestamibi is rapidly gaining acceptance as a way of detecting myocardial ischaemia in patients with chest pain. When injected intravenously, ^99mTc labelled sestamibi is taken up by the myocardium in proportion to myocardial blood flow. Unlike thallium-201, it does not wash out over time, and images taken up to several hours after administration will reflect myocardial perfusion at the time of injection (fig 1). The results from several small prospective trials show that it is highly sensitive and specific for predicting acute myocardial infarction and unstable angina in patients with atypical medical histories or electrocardiograms that do not provide a diagnosis.^12-14 Negative predictive values as high as 94% to 100% have been reported for normal ^99mTc labelled sestamibi studies.^12-14 Although large scale clinical trials are lacking, ^99mTc labelled sestamibi is a promising agent for use in selected patients with chest pain.

View larger version (49K): [in this window] [in a new window]   Fig 1.   Technetium-99m labelled sestamibi scans. Top: normal scan; vertical long axis (left); horizontal long axis (right). Bottom: apical defect; vertical long axis (left); horizontal long axis (right)

	Domestic violence

Considerable attention has been focused recently on the emergency department's role in identifying and intervening in cases of domestic violence. Recent reports in the United States have shown that between a third and a half of women in surveys undertaken in emergency departments claim to have been abused or assaulted at some time. ^{15 16} Prospective studies using a variety of screening tools show that 2% to 25% of visits to an emergency department by women of all ages are a direct result of domestic violence.^15-18 Because the emergency department is often the first place in which current or potential victims can be identified, there is a growing interest in exploring ways to identify these people and linking them effectively with social services.

"At risk" profile
One approach is to identify high risk individuals and patterns of injury or complaints, or both, that could serve as indicators to emergency department staff. Recent studies have shown that domestic violence is reported in all age groups but is more common in younger women. Pregnancy, mental or physical handicap, and a history of substance misuse seem to place women at particular risk. ^{15 16 18} Although domestic violence has been reported in all socioeconomic groups, it may be more prevalent in patients who have no medical insurance or medical assistance. One study looked at the relation between positive screening for domestic violence and insurance status. Those hospitals looking after the greatest number of uninsured patients identified domestic violence in 25.7%, while hospitals in which most patients seen were insured had a rate of 3.3%.¹⁸ Time of presentation to the emergency department is also different for victims of domestic violence. They generally present at those times when social services are not usually available. ^{16 17 19}

Screening for violence
In emergency departments, implementation of screening for domestic violence has had mixed success. One study has shown that incorporating a structured screening item in the medical record can improve case detection rates.¹⁷ Another institution implemented a comprehensive protocol consisting of a screening questionnaire at triage and 24 hour police and social work notification for high risk people. This ambitious programme failed because staff compliance with the protocol was poor.²⁰ A telephone follow up programme for high risk patients was equally unsuccessful in identifying victims of domestic violence; the few patients detected did not justify the programme's costs.²¹

	Ultrasonography

Although the idea of specialists in emergency medicine performing ultrasound examinations is not new, reports of the clinical impact of this are. The clinical applications of ultrasonography in the emergency department are well established. Ultrasound scanning is the best method of screening for ectopic pregnancy (fig 2) and has largely replaced diagnostic peritoneal lavage in detecting free intraperitoneal fluid. It is also reliable in detecting suspected gall stones, hydronephrosis, and abdominal aortic aneurysm. Performing ultrasonography in the emergency department can increase the efficiency and safety of patient management by reducing the time taken to detect potentially life threatening diseases, by expediting the evaluation of patients whose diagnosis is uncertain, and by providing visual guidance during the performance of many procedures. Research to date has focused on the clinical expertise of specialists in emergency medicine in performing limited or focused examinations, the clinical applications of ultrasonography in the emergency department, and new uses of ultrasonography in emergency practice.

View larger version (133K): [in this window] [in a new window]   Fig 2.   Transverse view of uterus (ut) showing interstitial ectopic pregnancy (iep)

Skill is important
Recent studies have shown that specialists in emergency medicine can perform focused studies with excellent sensitivity when compared with radiologists' examinations or other imaging techniques such as computed tomography undertaken by radiologists. Specialists in emergency medicine have shown skill in screening for ectopic pregnancy,^24-26 free intraperitoneal fluid in patients with blunt trauma,^27-30 and haemothorax.³¹ Ultrasonography, performed as part of an overall protocol to evaluate patients in the emergency department with complications during early pregnancy, improved early diagnosis of ectopic pregnancy and reduced the length of stay in emergency departments that did not have a 24 hour ultrasonography service. ^{25 26} Ultrasonography depends on the skill of the operator, however, and experience and training of many emergency department doctors varies widely. Because of this, the findings of many of reports are generalisable only to doctors with similar experience. Training and experience clearly influence the sensitivity and accuracy of results.²⁹

Clinical applications
The full extent of clinical applications of ultrasonography in the emergency department remains to be defined. Preliminary reports have described further uses, including detection of deep venous thrombosis,³² screening for complications of nephrolithiasis (specifically hydronephrosis),³³ and ultrasound guidance during invasive procedures.³⁴ New and potentially useful applications include identification of complications in survivors of non-traumatic cardiac arrest and identification of treatable causes of pulseless electrical activity.³⁵

View larger version (111K): [in this window] [in a new window]   Emergency medicine provides urgent treatment and a safety net

Further study
Nearly all published reports to date are limited by small numbers, wide variability in the training and expertise of the doctors performing the studies, and lack of any data showing clearly the clinical impact of ultrasound examination in the emergency department. Issues begging for clarification include the following: the amount of training necessary to perform limited studies with reasonable accuracy, identification of those clinical applications of ultrasound scanning that have the greatest impact on clinical care in the emergency department, and standardised guidelines for research into ultrasonography in emergency medicine.

	Acknowledgments

I thank Joseph A Maffei for his help in obtaining the technitium-99m labelled sestamibi images and Dr Verena T Valley for the ultrasound images.

Funding: No additional funding.

Conflict of interest: None.

	References

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(Accepted 10 September 1997)