UMEM Educational Pearls

Asthma, Peak Pressures, and the Ventilator

• In previous pearls, we have highlighted ventilator settings for the asthmatic, along with the differences between peak and plateau pressure measurements.
• When ventilating the asthmatic, pay attention to the ventilator settings placed by your respiratory therapist.
• In general, the respiratory therapist will set the ventilator to stop delivering tidal volumes when the peak pressure exceeds 40-60 cm H₂O.
• For asthmatics, this practice can result in very low tidal volumes.
• Thus, peak pressure limits must be set higher.
• As you know, high peak pressures have not been shown to be injurious, provided that the plateau pressure remains < 30 cm H₂O

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Risk Stratification in Pulmonary Embolism

The following are the principal markers useful for risk stratification:

• Clinical markers (shock, hypotension)
• Markers of RV dysfunction (RV dilatation, hypokinesis or pressure overload on echo, RV dilatation on CT, BNP elevation)
• Markers of myocardial injury (elevated troponin)

Patients with one or more of these markers have a higher mortality rate.

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The majority of "classic" symptoms and signs in elderly patients with pneumonia (fever, cough, sputum production, leukocytosis,chest pain) are unreliably present. However, tachypnea is one of the most reliable early findings in elderly patients with pneumonia, and in fact the same can be said about other serious bacterial illnesses in the elderly. The takeaway point here is simple: always count the respiratory rate in elderly patients (and don't trust those triage respiratory rates)!

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Diverticular Bleeding

• Diverticular bleeding is the  most common source of lower GI bleeds and accounts for 17 to 40 percent of cases
• The most common presentation (80%) is massive painless rectal bleeding. 
• Patients may have some cramping prior to a bloody bowel movement but otherwise will typically have no abdominal pain.
• The majority of the cases will resolve spontaneously, but those requiring more than 4 units of Packed Red Blood Cells should be considered for an angiogram or  surgery.
• Angiography can be used to localize the site of bleeding and embolize the bleeding source. 
• If embolization fails the patient may require a partial colectomy to treat the bleeding source.

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• About 15% of strokes are preceded by TIA.
• Within 90 days after a TIA, 10.5% will suffer a stroke.
• Of these, 21% will be fatal, 64% will be disabling, and half will occur within 1 to 2 days of the patient's emergency department visit.

Pre-existing acidosis and mechanical ventilation

• Not surprisingly, many critically ill ED patients often develop a metabolic acidosis.
• To compensate, patients hyperventilate, thereby producing a respiratory alkalosis.
• When these patients require intubation and mechanical ventilation, be sure to provide the same level of respiratory compensation when setting the ventilator. 
• Failing to provide a rate sufficient to compensate for the pre-intubation acidosis leads to a rapid drop in pH, bradycardia and eventually asystole.
• In general, rates can be increased to about 30-35 breaths per minute, after which auto-PEEP becomes problematic.

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Silent Pulmonary Embolism?

As many as 50% of patients with isolated DVT will be found to have silent pulmonary embolism (i.e. no chest pain or shortness of breath) on VQ scanning. Studies performed in the last year or so with CT scanning show that this percentage is much higher.

The clinical take-home point is NOT to get a pulmonary CTA on suspected DVT patients but to remember that many patients can and do have PE in the absence of cardiopulmonary symptoms. Pretty frightening....

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The WBC count is not an accurate predictor of bacteremia in the elderly. 20-45% of elderly patients with proven bacteremia have a normal WBC on presentation.

[from Caterino JM, et al. Bacteremic elder emergency department patients: procalcitonin and white count. Acad Emerg Med 2004;11:393-396.]

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Odontoid Fractures:

There are three types of C2 odontoid fractures:

1. Type I is an oblique fracture through the upper part of the odontoid process. This fracture is normailly stable and can be treated with a hard cervical collar.
2. Type II is a fracture occurring at the base of the odontoid as it attaches to the body of C2.  These fractures can be treated surgically, or conservatively with hard collar or a halo brace
3. Type III fractures occurs when the fracture line extends through the body of the axis. These fractures are normally treated surgically with or without a halo brace.

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• autossomal dominant disorder most commonly in Scandinavian and British descent due to deficiency of HMB-synthetase
• most heterozygotes are asymptomatic unless some factor increases the production of pyrogens, usually medications
• common drugs include steroids, alcohol, low calorie diets, and drugs (barbituates, sulfonamide antibiiotics, grisefulvin, and synthetic estrogens (birth-control)
• attacks of abdominal pain lasting several hours is the most common symptom and may be secondary to ileus or distension, but tenderness on exam and fever are absent
• peripheral neuropathy and muscle weakness improves over days, but may take years to return to normal
• diagnose: gold standard test measures RBC HMB-synthetase, screening test of normal PBG (porphobilinogen) level in urine rules out the condition
• treatment: narcotics, IV glucose (300g/day), and IV heme (4g/day)
   

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In the state of Maryland, the most common venomous snake is the copperhead. Though not as dangerous as the rattlesnake, it can still cause loss of function of limb and mortality in the pediatric patient.

Treatment has involved the use of CroFab (Protherics, Atlanta). This ovine derived monovalent immunoglobolin is actually made against the following snakes:

• Eastern diamondback rattlesnake
• Western diamondback rattlesnake
• Mojave rattlsnake
• Cottonmouth (Water moccasin)

Though efficacy has been shown with these snakes, we are hoping for cross-reactivity when we treat copperheads. There are case series and case reports (1) that have shown anectdotal improvement. We are still awaiting a real randomized controlled trial - may never happen.

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• Multiple Sclerosis (MS) is a relapsing condition caused by the destruction of myelin sheaths.
• Ninety percent of MS-related lesions can be detected on T2 MRI images.
• These lesions are typically para-ventricular, sometimes ovoid in shape (referred to as "Dawson's Fingers"), and often located on medullary veins.

Acute renal failure occurs in 1-25% of critically ill patients, with an associated mortality of 28 - 90%. 

The RIFLE Criteria represent the first consensus definition of acute renal failure used to classify critically ill patients as to their kidney function.  Notably, we use the worst possible classification according to the criteria, which measures either serum creatinine, urine output or both. 

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Attachments

1006221408_RIFLE.jpg.doc (103 Kb)

The nitrite test on urine dipstick is commonly used for diagnosis of UTI. However, the test is only reliable in those bacteria that convert nitrates to nitrites, which primarily includes enterobaceriaceae. However, elderly patients often develop UTIs with Staph saprophyticus, pseudomonas, and enterococcus, none of which produce positive nitrites on dipstick testing. The takeaway point here is very simply....don't assume you've excluded UTI (esp. in elderly populations) just because the nitrite test is negative.

reference: Anderson RS, Liang SY. Infections in the elderly. Critical Decisions in Emergency Medicine, April 2010.

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Toxicodendron dermatitis:

This is the contact dermatitis caused by the plant genus Toxicodendronm, better known as Poison Ivy.  Here are some types to prevent the dermatitis and how to treat it:

1. Barrier products like Ivy Block® are on the market that go on like suntan lotion and provides a protective barrier on your skin that prevents the plants urushoil, the toxin responsible for the dermatitis, from making contact with your skin. This can help prevent the dermatitis if you are able to wash the oils off.
2. Most soaps can not remove urushiol and may actually increase its spread. Several products are on the market, one being Zanfel® , that are a little more effective than water in removing the urushiol which can help to minimize the dermatitis and its spread.
3. The mainstay of treatment is systemic steroids.  This condition does not do well with a short (5 day) burst therapy and patients will typically get a rebound dermatitis when the burst is complete.  Patients should be placed on a 14 day steroid taper.

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• Calcium channel blockers, such as nicardipine, play an important role in treating arterial hypertension and cerebral vasospasm, both of which are associated with intracranial hematoma and increased intracranial hypertension.

• Many consider nicardipine to be an excellent choice for treating an acute hypertensive emergency in the setting of intracranial hemorrhage.

• Dosing should start at an infusion of 5 mg/hr.  Titrate by 2.5 mg/hr every 5 to 15 minutes to desired effect, up to a maximum dose of 15 mg/hr. 

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Hypotension after intubation and initiation of mechanical ventilation

• Approximately 25-30% of patients develop hypotension after intubation and initiation of mechanical ventilation (MV).
• Although the literature is not robust, risk factors for hypotension after initiation of MV include:
  • hypotension prior to intubation
  • tachycardia prior to intubation
  • obesity
  • high intrathoracic pressure (COPD)
  • excess catecholamine states (ETOH withdrawal, cocaine intoxication) with rapid relaxation during RSI
• In addition to administering isotonic intravenous fluids (IVFs) while preparing for intubation, consider having a vasopressor medication, such as phenylephrine, available if IVFs alone prove insufficient at maintaining blood pressure.

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Submitted on behalf of Dr. Michael Abraham

Thyrotropin (TSH) 

• Different types of test available:
  • The first tests available were radioimmunoassay. 
  • The next type of test available is the immunometric test.

• As each test is developed there has been a trend to use the term ‘generation’ for a 10 fold increase in sensitivity. ¹

• Indications for ordering in the ED:   Hypothyroidism, Graves Disease, Hashimoto’s Thyroiditis, Thyroid storm.

• Diagnostic Accuracy
  • The original TSH benchmark was the ability to measure euthyroid (0.4 – 4mIU/L) from very low (<0.01 mIU/L) which is suggestive of Graves disease. 
  • Most new tests have a functional sensitivity of <0.02mIU/L. 
  • The clinical sensitivity and specificity have to be determined by each laboratory’s staff. This requires testing of samples over a 6-8 week period as should include a sample of the population that is being tested.²
• Average turnaround time to complete test: 
  • The tests are mainly run on large lab analyzers. There are many commercially available tests the turnaround time is dependent on the manufacturer of the machine.

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Pericardial tamponade is a physiological diagnosis, not an ECG diagnosis. At best, the ECG can suggest the presence of large pericardial effusions--look for the combination of low voltage, tachycardia, and electrical alternans.

Be aware, however, that electrical alternans is only present in < 1/3 of patients with large pericardial effusions. Although it is "classic" and always seems to show up on board exams, in the textbooks, and in lectures, electrical alternans in not a consistent finding in patients with large effusions or tamponade. 

Calcaneus Fractures:

Calcaneus fractures can easily be missed on plain films and the true extent of the injury might not be appreciated until a CT is done.  However, you can increase your change of picking up a calcaneal fracture by evaluating Bohler's Angle. 

Lateral radiographs of the foot are needed to evaluate the Bohler angle.  This is the angle made by drawing a line from anterior process of the calcaneus to the peak of the posterior articular surface and a second one drawn  from the peak of the posterior articular surface to the peak of the posterior tuberosity. (See Picture) The average angle is 25-40°. Angles less than 25' are strongly suggestive of a fracture and the patient should probably get a CT of their foot if there is clinical suspicion.

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