NONINVASIVE VENTILATION FOR PULMONARY EDEMA
Lower mortality and intubation rates support its use.
Patients with acute cardiogenic pulmonary edema often are intubated because of respiratory compromise but, through a systematic literature review, researchers have found that by first using externally applied ventilation methods, such as continuous positive airway pressure (CPAP) and bilevel noninvasive pressure support ventilation (NIPSV), better outcomes--lower mortality and intubation rates--can be attained, and a comparison of the two noninvasive methods revealed no significant differences in those outcomes.
The researchers searched the MEDLINE and EMBASE databases and the Cochrane Central Register of Controlled Trials. The review consisted of all randomized clinical trials and review articles found through the use of search words related to externally applied ventilation, and additional data were obtained from the references found in original research and from contact with authors. Only trials in which one method of external ventilation was compared with another, or with standard oxygen therapy, were included.
Ultimately, 15 trials representing 727 patients with acute pulmonary edema were considered in the analysis and were evaluated according to the primary end points of death in the hospital and treatment failure (the need for intubation). The condition was precipitated primarily by acute coronary syndrome (31% of cases), followed by hypertension (27%), and the most common cause of death (when specified) was shock.
The researchers found that when the trials were evaluated collectively, mortality rates were lower, as compared with standard oxygen therapy, when externally applied ventilation methods were employed, especially CPAP (the mortality rate was not statistically significantly lower with NIPSV). Upon investigation of the treatment failure rate, CPAP and NIPSV collectively diminished the necessity of intubation by 57%, in comparison with standard oxygen therapy. An analysis of six of the 15 trials in which CPAP and NIPSV were directly compared didn't reveal either one to be superior to the other in regard to either mortality or treatment failure rates.
The researchers do point out a number of limitations to the review, such as the variability of the criteria used in the trials for diagnosing pulmonary edema. Still, they contend, the results are persuasive enough to elevate the use of noninvasive ventilation to a first-line treatment in this population.
Masip J, et al. JAMA 2005;294(24): 3124-30.
ASSESSING CHEST PAIN ORIGINS
No specific feature is identified.
Determining whether chest pain is attributable to either acute cardiac syndrome (ACS) or acute myocardial infarction (AMI) or to a more benign cause is a challenging clinical scenario often presented to acute care practitioners. To help clinicians perform more accurate triage, researchers conducted a comprehensive literature review and analyzed the findings of numerous studies of chest pain to determine which, if any, reported features is likely attributable to cardiac causes. The review revealed that, while some indicated a greater likelihood of cardiac involvement, no one feature or even group of features could be solely used to evaluate the probability of the occurrence of AMI.
From a search of the MEDLINE and Ovid data bases covering the years 1970 to 2005, the researchers chose to review only reports from controlled trials involving at least 80 participants and that were written in English. Reference lists in the articles and current textbooks were also consulted.
After the data were synthesized, the researchers found several features of chest pain to be associated with a greater probability of the presence or later occurrence of ACS or AMI. Pain that radiates to the arms or shoulders (either right or left side), pain precipitated by physical exertion, pain accompanied by sweating, nausea, or vomiting, pain that is either more severe than previously or comparable to that accompanying a previous AMI, and pain described as pressure were all associated with a higher probability of AMI. Conversely, pain on inhalation, pain either alleviated or exacerbated by a change in position, sharp pain, chest wall tenderness, and pain in the inframammary region all were associated with a lower probability of AMI. Also, the researchers noted findings of recent studies that challenge commonly held conceptions concerning chest pain-that its relief by nitro-glycerin is indicative of the presence of AMI, for example.
The researchers conclude that chest pain history can help clinicians identify patients at risk for ACS or AMI, and that the factor associated with the greatest risk is the presence of radiating pain. They note, however, that because of the degree of subjectivity in the description of chest pain and the conflicting findings or insufficient statistical significance of some of the clinical studies, clinicians shouldn't rely entirely on the patient's history of chest pain in evaluation or for discharge. Instead, the history can serve as an important component of the initial workup, accompanied by the consideration of other risk factors, in the determination of the urgency and intensiveness of the diagnostic and monitoring strategy.
Swap C, et al. JAMA 2005;294(20):2623-9.
PATIENTS WITH CHEST PAIN
Identifying those at low risk.
Patients who arrive at the ED with chest pain are usually either admitted to the hospital or subjected to an extended stay in the ED before a cardiac cause is ruled out. Now a group of Canadian researchers has developed a new clinical prediction rule that may be useful to ED clinicians in identifying patients at low risk for an acute coronary syndrome, thereby facilitating their prompt and safe discharge.
The researchers devised the rule in light of the results of a study of 769 patients at least 25 years old recruited at a single hospital who presented with anterior or lateral chest pain. Research assistants collected clinical data such as vital signs, electrocardiographic results, cardiac enzyme levels, risk factors, chest pain characteristics, and medical history pertaining to each patient during the initial two hours in the ED. Thirty days later, they obtained the results of any diagnostic testing conducted during that period of time; according to those data, patients were classified as either having or not having an acute coronary syndrome, defined as acute myocardial infarction (AMI), confirmed unstable angina, or possible unstable angina, the primary outcome being definite acute coronary syndrome (AMI or confirmed unstable angina). Clinical data and diagnostic variables found to be predictive of acute coronary syndrome were then incorporated into the prediction model.
Acute coronary syndrome was diagnosed in 21.4% of the study population (10% with AMI and 11.4% with confirmed unstable angina); approximately 70% were found not to have it or to have had adverse events (such as death, serious arrhythmia, thromboembolism, and aortic aneurysm or dissection, among others). According to the researchers' model, the Vancouver Chest Pain Rule, patients less than 40 years of age who present with a normal electrocardiogram and without a previous history of ischemic chest pain are eligible for expedited discharge from the ED. Those with a normal electrocardiogram and without previous ischemic chest pain who are older than 40 need further evaluation, according to cardiac enzyme level: if the serum creatine kinase MB (CK-MB) level is lower than 3 micrograms per liter, the patient can be considered eligible for expedited discharge; if it's 3 micrograms or higher, a confirmation of the absence of change in either electrocardiographic results or the CK-MB level after two hours is necessary before he can be considered eligible for expedited discharge.
Although the rule manifested a predictive rate of 98.8% in acute coronary syndrome, it has not been validated in additional clinical trials, and multicenter trials are necessary before it can be adopted into standard clinical practice.
Christenson J, et al. Ann Emerg Med 2006;47(1):1-10.
BEDSIDE SCREENING FOR PULMONARY EMBOLISM
Two negative test results might make V/Q scanning unnecessary.
Comparing a new approach that incorporates three bedside tests with the traditional approach of ventilation-perfusion (V/Q) scanning to identify patients with pulmonary embolisms, researchers found that the bedside tests ruled out pulmonary embolism in 34% of cases when two of the three test results were negative, making the diagnostic imaging unnecessary.
The randomized, controlled equivalency trial involved 398 patients 18 years of age or older with suspected pulmonary embolism who were referred for V/Q scanning; criteria for inclusion into the study were the ability to breathe independently and the absence of a history of both pulmonary embolism and the use of full-dose anticoagulants or filter devices.
Three bedside tests were performed on all patients: the seven-variable clinical model (in which point values are assigned to signs and symptoms of pulmonary embolism), the D-dimer assay (a serum blood test), and the alveolar dead-space fraction test (calculations made during at least two minutes of sustained regular breathing and from an arterial blood gas measurement), after which they were randomly assigned to either the bedside testing arm or the V/Q scanning arm. If a patient in the bedside testing arm had at least two negative test results, he underwent a fake V/Q scan (for the purposes of blinding) and received a subsequent radiology report indicating the absence of pulmonary embolism; if one had at least two positive bedside test results, he proceeded to undergo genuine V/Q scanning. In the V/Q scanning arm the patients underwent the three bedside tests first, and the results were not taken into account. Once the results of the V/Q scans were reported, a physician blinded to the arm assignments determined whether additional diagnostic testing was necessary.
At three months the patients were assessed for venous thromboembolism (pulmonary embolism or deep vein thrombosis) or bleeding subsequent to the initial presentation, and found that 2.4% of patients in the bedside testing arm who were not taking anticoagulants had developed venous clots, compared with 3% of patients in the V/Q scanning arm who weren't taking anticoagulants, and that there was no appreciable difference in the rate of bleeding events between the two groups.
Of the 199 patients randomized to the bedside testing arm, 34% had met the criteria for exclusion from V/Q scanning by having at least two negative test results. When the alveolar dead-space fraction test was not included in the analysis, that rate of exclusion decreased to 18%, suggesting that that test is predictive of pulmonary embolism. Furthermore, six of eight patients who had developed a venous thromboembolism upon follow-up had had elevated alveolar dead-space fractions at their initial assessments.
The researchers conclude that the use of the three bedside tests can serve as a viable strategy for ruling out pulmonary embolism.
Rodger MA, et al. Arch Intern Med 2006;166(2):181-87.