Learning Objectives: After reading this article, the physician should be able to:
1. Describe how noninvasive ventilation (NIV) reduces the need for intubation and decreases the mortality of patients presenting with acute pulmonary edema.
2. Identify an anaphylactic reaction to hymenoptera invenomation, and explain how epinephrine is the definitive therapy in these cases.
3. Summarize the technique of knee arthrocentesis and recognize the indications, contraindications, and operating characteristics of the procedure.
Release Date: February 2009
From the 2009 LLSA Reading List
Noninvasive Ventilation in Acute Cardiogenic Pulmonary Edema: Systematic Review and Meta-Analysis
Masip J, et al
Noninvasive ventilation (NIV) has been shown to decrease the need for intubation in patients with severe COPD exacerbations. More significantly in these patients, NIV reduces mortality most likely by avoiding ventilator-associated pneumonia, barotrauma, and other ICU-related morbidities. This meta-analysis examines the role of NIV in another cause of respiratory failure: acute pulmonary edema.
Data were pooled from 11 randomized trials (727 total patients) looking at continuous positive airway pressure (CPAP) and bilevel positive airway pressure (Bi-PAP) compared with standard oxygen therapy for acute pulmonary edema. Six studies compared CPAP with Bi-PAP, and the primary endpoints for the meta-analysis were treatment failure and in-hospital mortality. The most frequently used CPAP pressure was 10 cm H 20, and the most commonly used Bi-PAP pressure was 15/5 cm H 20.
Overall NIV used for acute pulmonary edema was associated with a decreased need to intubate (RR=0.43, p<0.001) when compared with standard oxygen therapy. This decrease was also significant for each type of NIV when analyzed separately: CPAP (RR=0.40, p<0.001), Bi-PAP (RR=0.48, p=0.002).
NIV for acute pulmonary edema also was associated with reduced mortality compared with conventional oxygen therapy (RR = 0.55, p<0.01). When CPAP was analyzed alone, there was still a significant reduction in mortality (RR 0.53, p=0.03). Although there was a trend toward reduced mortality when Bi-PAP was analyzed alone, this reduction was not statistically significant (RR=0.60, p=0.07). In the six studies comparing CPAP with Bi-PAP, there was no significant difference in either endpoint.
Notable difficulties with this meta-analysis include the lack of a standardized definition for acute pulmonary edema and the varied use of NIV pressure settings.
From the 2008 LLSA Reading List
Hypersensitivity to Hymenoptera Stings
N Engl J Med
Ants, bees, and wasps are all part of the Hymenoptera order of insects, and cause approximately 40 deaths in the United States each year. In hypersensitive individuals, anaphylaxis is IgE-mediated, caused by antibodies formed from prior venom exposure. The lethal dose to a non-sensitive person is estimated to be approximately 1500 stings, but only one is required to cause fatal anaphylaxis in a sensitive individual.
Mild stings in nonsusceptible individuals usually result in local redness, swelling, tenderness, and pain, with symptoms resolving within hours. Larger local reactions occasionally occur, may involve larger areas, and usually peak by 48 hours, but are not life-threatening unless they involve the airway. Local reactions, if treatment is necessary, usually improve with NSAIDs, antihistamines, and cold compresses, with steroids reserved for larger reactions. Secondary infection of a hymenoptera site usually can be distinguished from a large local reaction by continued progression after two days, fever, and lymphadenitis.
Anaphylactic reactions either can be limited to cutaneous findings such as pruritus, urticaria, and angioedema or exhibit full systemic features including muscle cramps, vomiting, diarrhea, bronchospasm, hypotension, and arrhythmias. Nervous system symptoms of anaphylaxis include anxiety, dizziness, and lightheadedness, and can be mistaken for hysteria by the inexperienced clinician. A prior history and severity of an anaphylactic reaction are the best predictors of the likelihood and severity of another reaction after a repeat sting.
For systemic anaphylactic reactions, the most urgent and definitive therapy is 0.01 mg/kg epinephrine (children 0.3 mg, adults 0.5 mg; max per dose), either intramuscularly or intravenously if access is readily available. Although epinephrine can cause tachycardia, vasospasm, or arrhythmia, it is the most critical component of anaphylaxis treatment. Failing to administer epinephrine or delaying it in an anaphylactic patient increases the chance of a fatal outcome.
Long-term prevention includes avoiding bright clothes and flowery scents, covering exposed skin, removing Hymenoptera nests, and limiting outdoor activity during peak seasons or in high-risk areas. Allergist referral is warranted in anaphylaxis-prone patients at high risk for repeated exposure. Evaluation may involve IgE antibody testing, skin testing, and/or in vitro testing. Immunotherapy consists of multiple escalating dose injections of venom or whole body extract followed by a maintenance regimen.
Anyone presenting to the ED with anaphylaxis after a Hymenoptera invenomation should be discharged with an epinephrine auto-injector and clear instructions to self-administer it and seek immediate medical care after a sting if anything more than a cutaneous reaction develops.
Arthrocentesis of the Knee
Thomsen TW, et al
N Engl J Med
Arthrocentesis of the knee is an important skill that EPs should be comfortable doing. Diagnostically it is important to drain fluid to establish or confirm a diagnosis such as inflammatory arthritis or crystal arthropathy and to rule out septic arthritis, a time-sensitive diagnosis with the potential for severe morbidity and even mortality if the diagnosis is delayed. Arthrocentesis also can be used therapeutically with large effusions or traumatic hemarthrosis to alleviate pain and improve range of motion or to inject anesthetics or corticosteroids.
The only absolute contraindication to arthrocentesis of the knee is overlying cellulitis or abscess above the area of needle entry. Coagulopathy is a relative contraindication and the potential benefits of the procedure should be balanced with the risks associated with the use of reversal agents or blood products.
Being the largest joint in the body, the knee is usually an easy target for arthrocentesis, especially when the effusion is significant. A medial or lateral approach can be chosen depending on what side the effusion is most prominent. The patient should be supine with knee flexed at 15 to 20 degrees.
After obtaining consent and confirming with the patient the appropriate procedure, body part, and side, the site of entry should be clearly marked with a skin-marking pen at the level of the superior third of the patella, approximately 1cm off the medial (or lateral) edge. The skin should be prepped and draped in the usual sterile fashion, and a skin wheal should be made by administering local anesthetic using a 25-gauge needle. Anesthetize deeper tissue in the anticipated trajectory of the arthrocentesis needle, intermittently aspirating to exclude intravascular injection of the anesthetic. Once the track is adequately anesthetized, remove the needle.
Using an 18-gauge needle and a large syringe, advance the needle slowly at the site of entry toward the intracondylar notch while maintaining aspiration pressure on the syringe. The needle should be advanced until the effusion is reached. If the needle is met with significant resistance, it should be carefully withdrawn and redirected.
A dry tap may result from misdiagnosis of an effusion, poor placement of the needle, or needle obstruction from particulate matter. If still suspicious of an effusion, consider redirecting the needle or approaching from the opposite side. If the effusion is aspirated but minimal fluid is obtained, yield can be increased by gently milking the effusion with the opposite hand. Large effusions may require replacing the initial syringe once full with a second syringe while the needle is maintained in position. Once finished, remove the needle, confirm that hemostasis has been achieved, clean the skin, and apply a bandage.
Because every laboratory has specific submission procedures, confirm any special handling with them prior to submitting specimens to prevent delays in processing. Gram stain and culture are definitive in ruling out nongonococcal septic arthritis with sensitivities of 50% to 75% for gram stain and 75% to 90% for culture. On the other hand, yield is extremely low for gonococcal arthritis (gram stain 10%, culture 10%-50%), so if gonococcus is suspected, consider simultaneous testing of blood, pharyngeal, cervical, rectal, or urethral sites as well as empiric therapy.
Cell count and differential are used to differentiate between noninflammatory effusions (e.g., osteoarthritis, trauma) and inflammatory effusions (e.g., crystal-induced arthritis, septic arthritis). Generally, noninflammatory conditions have less than 2000 WBC/ml with less than 75 percent polymorphonuclear cells. Concern for infectious etiologies increases with the WBC count in the fluid, but unfortunately there is a tremendous amount of overlap within the inflammatory spectrum. Crystal analysis helps confirm the presence of gout (monosodium urate crystals) vs. pseudogout (calcium pyrophosphate dihydrate crystals), but does not completely rule out an infectious etiology.
About the LLSA
As part of its continuous certification program, the American Board of Emergency Medicine has developed the Lifelong Learning and Self-Assessment (LLSA) program to promote continuous education of diplomates. Each year, beginning in 2004, 16 to 20 articles are chosen based on the Emergency Medicine Model. A list of these articles can be found on the ABEM web site, www.abem.org.
ABEM is not authorized to confer CME credit for the successful completion of the LLSA test, but it has no objection to physicians participating in such activities. EMN's CME activity, Living with the LLSA, is not affiliated with ABEM's LLSA program, and reading this article and completing the quiz does not count toward ABEM certification. Rather, participants may earn 1 CME credit from the Lippincott Continuing Medical Education Institute, Inc., for each completed EMN quiz.
CME Participation Instructions
To earn CME credit, you must read the article in Emergency Medicine News, and complete the quiz, answering at least 80 percent of the questions correctly. Mail the completed quiz with your check for $10 payable to the Lippincott Continuing Medical Education Institute, Inc., 770 Township Line Road, Suite 300, Yardley, PA 19067. Only the first entry will be considered for credit, and must be received by Lippincott Continuing Medical Education Institute, Inc., by February 28, 2010. Acknowledgement will be sent to you within six to eight weeks of participation.
Lippincott Continuing Medical Education Institute, Inc., is accredited by the Accreditation Council for Continuing Medical Education to provide medical education to physicians. Lippincott Continuing Medical Education Institute, Inc., designates this educational activity for a maximum of 1 AMA PRA Category 1 Credit.™ Physicians should only claim credit commensurate with the extent of their participation in the activities.