Self-check cards

Hint: Think about what the heart does before pressure drops.

Compensated shock: the heart speeds up to preserve cardiac output before the blood pressure falls. Treat tachycardia with borderline-low BP as early shock until proven otherwise.

Because the body compensates. It works hard to keep numbers normal until it can no longer keep up, so a normal reading can coexist with a serious hidden process.

Tachycardia (rising heart rate). The heart accelerates early to preserve cardiac output, making it one of the first and most reliable signals.

Bacterial infection or inflammation. Neutrophilia is the classic response to bacterial infection.

Allergy, parasite, or drug reaction. Eosinophils rise in these settings.

A single number is a photograph; a series is a movie. A platelet count falling from 200 to 60 over two days is an emergency, while a single low value is just a data point.

An unmeasured acid: toxic ingestion, ketoacidosis, or lactic acidosis. It is a launchpad for the differential because something is producing acid the body cannot clear.

Hint: They make the brake pedal work harder.

They bind an allosteric site and enhance the effect of GABA, boosting chloride influx and neuronal inhibition. They do not open the channel directly.

All three depress the CNS. The additive braking can suppress breathing to a dangerous degree (respiratory failure).

Acute seizures and severe alcohol withdrawal, where rapid CNS inhibition protects against excitotoxicity and autonomic instability.

They block beta-1 adrenergic receptors, blunting the effects of adrenaline on heart rate and contractility - slowing it, steadying it, and reducing oxygen demand.

Rebound tachycardia and angina (and even acute coronary events) can occur as the sympathetic system suddenly loses its brake.

They convert plasminogen to plasmin, which degrades the fibrin mesh of a clot - reopening the blocked vessel. Time is brain (stroke), time is muscle (heart attack).

Serious bleeding, including intracranial hemorrhage. It is used only when reopening the vessel outweighs the bleeding risk.

Powerful anti-inflammation (asthma, autoimmune flares, brain swelling) but immunosuppression, raised blood sugar and pressure, bone loss over time, and a need to taper to avoid adrenal crisis.

Hint: Favor a single explanation when one fits everything.

The simplest explanation that accounts for all the findings is usually correct - one unifying diagnosis rather than many separate ones.

The patient can have as many diseases as they please - sometimes several separate conditions coexist, especially in older patients with chronic disease. It is the counter to Occam.

Settling on a diagnosis before all the evidence is in and ignoring findings that do not fit. It is a leading cause of diagnostic error.

Because an obvious, wrong diagnosis is a classic false lead. When treatment based on the obvious answer fails, the team re-opens the differential.

If broad therapy (e.g., antibiotics or steroids) does not improve the patient, the team concludes the cause is not what the therapy targets - narrowing the hunt.

Hint: The fluid around the brain and cord.

Cerebrospinal fluid (CSF) bathing the brain and spinal cord - the definitive test for meningitis and a key tool for hemorrhage, inflammation, and CNS malignancy.

Bacterial meningitis. This classic CSF triad points to bacterial infection of the meninges.

Subarachnoid hemorrhage (bleeding into the space around the brain).

Because it examines the tissue itself rather than chemical footprints - directly confirming cancer, autoimmune inflammation, infection, or deposition disease.

Sampling can miss the affected area, so a negative result does not always rule out the condition.