Friday, November 4, 2011

The New Magic

Perhaps inspired by Z Dogg MD's A Muggle's Guide to Med School I'm drawn to the parallel that modern medicine although seemingly steeped in scientific rigor and experimentally verified practice is still the same witch doctor shamanism that attempted to prognosticate disease since time began. Incidentally time was invented simultaneously with medicine for billing purposes. Rather than tea leaves we have tests, instead of augeries we use electrocardiograms to try and divine not only what is currently wrong with our patients but what is going to happen to them in the future. Each specialty owns its own oracles, which they use to bitterly confuse the initiates of medicine, the residents, and baffle the hedge wizards such as myself, the general internist. Here are some of the specialists go to tricks:
Cardiology: Electrocardiogram (EKG)
Both American and European cardiological societies (Circulation 2007, 116:2634-2653) are quite clear on this: myocardial infarction is defined by an elevation in cardiac markers, particularly troponin, with suggestive symptoms (i.e. chest pain) or electrocardiographic changes (actually that's just one definition there are others). Specific EKG changes such as new ST-elevations or new LBBB need acute cardiac catheterization as does non-ST elevation MI with continued pain. The argument that because the EKG is normal or "nonischemic" that this presentation is not related to cardiac ischemia cannot be validated until subsequent cardiac markers are negative, four to eight hours later. Although if you do suspect cardiac disease, check them sooner as you may be able to detect a positive trend. Remember too that an EKG is a snippet of time, if the patient is asymptomatic at the time, the associated electrocardiographic event may never be recorded on the EKG, particularly in cases of paroxysmal arrhythmia. It just goes to show that an EKG with diagnostic findings need to be corroborated with further diagnostic testing and that a pristinely, normal EKG has about as much association with mortality as tea leaves do. It also shows that telemetry, if it can be correlated with episodes of symptoms,` may increase or decrease the likelihood ratio of a cardiogenic etiology.

Critical Care: Arterial blood gas (ABG)
The ICU is essentially a place for one or both of two things: ventilators and vasopressors. Thus if the patient is in some form of shock to the ICU they go. You don't need an ABG to diagnose shock, although a PaCO2 < 32 mmHg is one of the systemic inflammatory response criteria, and would be useful but not necessary to diagnose sepsis. Elevated lactate > 2 mmol/L and not the pH is criterion for severe sepsis. The decision to intubate can and should be made independent of the blood gas (Manual of Emergency Airway Management), how the patient appears clinically in terms of work of breathing, airway protection, and level of consciousness is a better indicator of requiring invasive positive pressure ventilation. The ABG allows you to assess response to mechanical ventilation and to make adjustments that the patient's body is, hopefully transiently, physiologically unable to do. Thus the arterial blood gas is a powerful tool for assessing how a patient is currently doing and how they have responded to interventions, it does not clinch the diagnosis of shock nor is it the tool to decided whether or not a patient should be intubated.

Endocrinology: Cortisol
No laboratory result is more nebulous than the cortisol level. Although a random cortisol level < 3 ug/dL is highly suspicious for adrenal insufficiency and > 10 ug/dL is unlikely to be adrenally insufficient, further testing using ACTH stimulation is often required to delineate if they actually have adrenal insufficiency. To the endocrinologists chagrin corticosteroids have usually already been given, dexamethasone being the one that shouldn't confuse further diagnostic testing. The amount of ACTH to administer and the time to wait superimposed on the reality that the timing of drug administration to lab draw is seldom accurate makes the subsequent determination of the result a question fraught with perils, particularly when the results make adrenal insufficiency less likely but the administration of stress dose corticosteroids resulted in a marked clinical improvement. This may be why the administration of corticosteroids without checking serum cortisol level is part of the Surviving Sepsis Campaign.

Gastroenterology: Rectal exam and fecal occult blood testing
The rectal exam is the most avoided exam there is, the reason for which is presumably related to provider discomfort and the time it takes. It is only clinically important when it is not done. The rectal exam is touted in the work-up of gastrointestinal bleeding, but is only useful if frankly positive, i.e. active bleeding is observed, indicating that bleeding is most likely rapid and/or in the distal colon. A negative fecal occult blood test does not eliminate gastrointestinal bleeding. A positive test indicates that there is blood in the gastrointestinal tract the source is unclear and swallowed blood from another source is not excluded. In fact Intern Med J. 2010 Feb;40(2):107-11 claims that "there is no place for FOBT in an acute hospital setting."

Hematology: Peripheral smear
The peripheral smear are the tea leaves of the hematological world. For the work-up of too much or too few platelets, red, or white blood cells it is the go to test of choice for board examinations, usually with an attached image for our interpretation. While diagnostic in some conditions and helpful in directing clinical decision making in others it is no longer a convenient test. A long time ago in a hospital far, far away residents and fellows performed peripheral smears on the floor. They drew their own blood, prepared their own slides, and viewed them under the microscope. They had clinical information within minutes. In today's hospital peripheral smears are prepared in the lab, reviewed by the pathologists every second Thursday of the month, and finally obtained by the hematologist for a second look. That makes this test more mysterious to the generalist because we don't do it and less diagnostically useful due to the time lag.

Infectious Disease: Gram stain and culture
The potions and poisons of infection are a world with constantly evolving diagnostic results, starting with the Gram stain, followed by the quantitating and qualifying the bacterial type, and finally determining the susceptibility to antibiotics. Testing after antibiotic administration nullifies the accuracy of results, and some infections leak so few bacteria, i.e. endocarditis, that not two sets but three sets of blood cultures are drawn. Unfortunately empiric therapy must be initiated prior to the test results, and even if those results are negative, patient's often improve while antibiotics are on board whether due to them or not is unclear. Antibiotics have a recommended duration, three days for uncomplicated urinary tract infection, and weeks for osteomyelitis, endocarditis and line infection. Once committed to a diagnosis we are committed to a course and the attendant complications of multi drug resistance and C. difficile diarrhea. Oft touted clinical markers of infection such as fever or leukocytosis are not exclusive to infection. As we grow older our febrile response weakens, meaning that an elderly person without a fever can still be septic and bacteremic but treating the marked leukocytosis of CLL with antibiotics is well amusing to our specialist colleagues.

Nephrology: Urine analysis
The urine analysis, the tea leaves or at least the result of them, is the bedeviling test of renal disease. Unfortunately the urine analysis is nonspecific for severity of disease. Furthermore the results are affected not only by what portion of the stream the urine is obtained but the time between acquisition and analysis. The versatility of the urine analysis decreases the worse the renal function becomes. Woe to he or she who obtains the UA in ESRD while in the anuric patient the urine analysis impatiently awaited by the nephrologist isn't going to change anything, there's no pee for them to see.

Neurology: Magnetic resonance imaging of the head
Unless of course the patient has the wrong type and collection of metal in the the wrong location in which case the test of choice is the CTA. Prior to tomographic imaging, neurology used carefully elicited signs to diagnose the diseases neurological. Thus neurologists nearing retirement these days amuse themselves by diagnosing the disease and pinpointing the lesion (Lateralize! Levelize! Localize!) before the imaging can get done. They then sit back and chuckle at our wonder at their acumen. With the advent of three dimensional brain and spine imaging, the need for superior exam skills decreased and reliance on the imager for diagnosis has increased.

Oncology: Biopsy
Despite the cases where endoscopists and radiologists have put their reputation on the line by saying, prior to any pathological data and with minimal clinical data, "looks like cancer", heavens be merciful to anyone who pages the oncologist with the right story and subjective evidence but no pathology. Unless the pathology is back, after being confirmed at a tertiary center, it is not cancer to the cancer doc! In their defense, no cancer will kill before the pathology is back, if it does the disease was so advanced chemotherapy would not have made a difference anyway. Also treatment regimens are titrated to the diagnosis, so pathology is important for directing therapy and prognosis.

Pulmonology: Pulmonary function test (PFT)
In the diagnosis of obstructive versus restrictive lung disease and for the establishment of chronic obstructive pulmonary disease (Global Initiative for Chronic Obstructive Lung Disease) the pulmonary function test is key. However they are performed on patients at their baseline to obtain measures of severity of chronic disease and aren't usually available in-patient. Also PFTs never get better, given the limited therapeutic options we have for pulmonary disease, we don't manage the disease so much as try to decelerate its decline. So with the knowledge they have a chronic problem, we have little evidence to know who will need merely some nebulizer treatments, who will need intubation, and who will die. But still the pulmonologists will ask for or refer back to the PFTs obtained at a time of relative pulmonary stability.

Rheumatology: Inflammatory markers and nearly anything prefaced with anti-
When the signs and symptoms make no sense, the cause is either rheumatologic or psychogenic. Autoimmune and connective tissue disease are diagnosed with inflammatory markers and multisyllabic serum tests starting with anti- (i.e. anti-double stranded DNA antibody or anti-phospholipid antibody). After a battery of these tests, which are oft repeated because of their poor sensitivity and specificity the rheumatologist will arrive at some equally multisyllabic diagnosis (i.e. systemic lupus erythematosus or granulomatosis with polyangiitis (Wegener's)). And then they prescribe corticosteroids.
What is a poor wizard to do?