Glossary

A resting heart rate faster than about 100 beats per minute in adults.

An abnormally fast heart rate. The heart is a pump, and its rate is one of its two key levers (rate × stroke volume = how much blood it moves per minute). Tachycardia is often the first sign that the body is under stress and is accelerating the pump to keep blood pressure and flow up.

A resting heart rate slower than about 60 beats per minute in adults.

An abnormally slow heart rate. A slow rate is normal in athletes and during sleep, but if the pump is too slow to move enough blood, it can cause low pressure, lightheadedness, or fainting.

Abnormally low blood pressure.

Blood pressure that is too low to keep adequate blood flowing to organs. Because organs need pressure to push blood through their vessels, very low pressure starves the brain, kidneys, and heart of oxygen.

Persistently high blood pressure.

A chronic elevation of blood pressure that puts strain on the heart, arteries, brain, kidneys, and eyes. Because it is usually silent, it is called a 'silent killer' and is a major risk factor for heart attack, stroke, and kidney disease.

The average pressure driving blood into the organs throughout the cardiac cycle.

The time-averaged arterial pressure that actually pushes blood into the brain, kidneys, and heart. It sits between systolic and diastolic pressure and is the number clinicians use to judge whether organs are being perfused.

The volume of blood the heart pumps per minute.

The amount of blood the heart ejects each minute, equal to heart rate × stroke volume. It is the 'flow' side of blood pressure and determines how much oxygen-rich blood reaches the tissues.

The amount of blood pumped with each heartbeat.

The volume of blood ejected by the left ventricle with each contraction. It depends on how much blood returns to the heart, how hard the muscle contracts, and how much resistance it must overcome.

The overall resistance the blood meets in the body's small arteries.

The sum of the resistance offered by all the small arteries and arterioles. Together with cardiac output it determines blood pressure (MAP = CO × SVR). Vessels can narrow (raise resistance) or relax (lower it).

The heart's natural pacemaker.

A small cluster of cells in the right atrium that generates each heartbeat's electrical trigger. It sets the resting rhythm and speeds up or slows down in response to the autonomic nervous system.

Sinoatrial node - the heart's pacemaker.

Short for the sinoatrial node, the heart's natural pacemaker in the right atrium.

The If current that drives the heart's pacemaker cells to fire.

A sodium/potassium ion current (called If, or 'funny') that flows in SA node cells between beats. It leaks positive charge in, pushing the cell toward its firing threshold - the engine of spontaneous heartbeat.

The slow voltage rise that makes pacemaker cells fire spontaneously.

The gradual buildup of positive charge inside pacemaker (SA node) cells between beats that eventually triggers the next action potential. It is the electrical basis for automatic, rhythmic heartbeat.

A pressure sensor in the neck and aorta.

Stretch-sensitive nerve endings in the carotid arteries and aortic arch that constantly measure blood pressure. When pressure falls, they send fewer signals, prompting a reflex that raises heart rate and constricts vessels.

A fast heart rate triggered by a drop in blood pressure or flow.

The heart speeding up in response to a sensed fall in blood pressure. It is a compensatory reflex, not the primary disease - it tells you the pump is working harder to defend pressure.

Shock caused by losing too much blood or fluid.

A state of inadequate organ perfusion caused by low circulating volume - from bleeding, severe dehydration, or fluid loss (vomiting, diarrhea, burns). The tank is too empty to fill the pump.

Shock from vessels dilating too much.

A form of shock in which blood pressure falls because the small vessels lose tone and dilate, even when the heart pumps hard. The blood is there, but it pools instead of being pushed to organs.

Shock caused by the heart failing as a pump.

Inadequate organ perfusion because the heart cannot pump enough blood, most often after a major heart attack or in severe heart failure. The pump itself is the problem.

Shock caused by something physically blocking blood flow.

A form of shock where a physical blockage prevents the heart from filling or pumping - a tension pneumothorax compressing the chest, a massive pulmonary embolism, or cardiac tamponade squeezing the heart.

A measure of how acidic or alkaline a fluid is.

The concentration of hydrogen ions in the blood. Normal blood is kept in a very narrow range because enzymes and cells only work within it. Acid-base disorders push pH out of this range.

Abnormally high blood acidity (low pH).

A state in which blood pH falls below normal. It can result from too much acid added, too little acid removed, or too much bicarbonate lost.

Abnormally low blood acidity (high pH).

A state in which blood pH rises above normal, from too much base, too much acid loss, or excessive CO2 blowing off.

A drop in blood pH from something other than breathing.

Acidosis originating in metabolism or kidney/bicarbonate handling rather than the lungs. The pH falls because too much acid is made, acids are not excreted, or bicarbonate is lost. The lungs compensate by blowing off CO2.

A rise in blood pH from something other than breathing.

Alkalosis from acid loss or bicarbonate gain. The body compensates by breathing more slowly to retain CO2 and, slowly, by the kidneys excreting bicarbonate.

Acidosis caused by failing to exhale enough CO2.

When the lungs cannot blow off carbon dioxide (too slow or too shallow breathing, or lung disease), CO2 builds up and dissolves into acid, lowering pH.

Alkalosis caused by exhaling too much CO2.

When breathing is too fast or deep, CO2 is blown off faster than produced, so blood acid falls and pH rises.

The body working to push abnormal vitals or pH back toward normal.

The body's corrective responses that mask or limit an underlying problem. The lungs and kidneys compensate for acid-base shifts on different timescales, and the heart and vessels compensate for pressure changes.

A calculation that flags unmeasured acids in the blood.

A value computed from the major measured ions that catches the presence of 'unmeasured' acids (lactate, ketoacids, toxins). A high anion gap means some acid is present that the standard panel does not directly measure.

The blood's main chemical buffer (HCO3-).

Bicarbonate is the chief buffer in the blood, soaking up hydrogen ions to keep pH stable. The kidneys control its level, so bicarbonate is a key number on the blood gas.

A waste product that reflects kidney filtration.

A byproduct of muscle metabolism that the kidneys filter out. Because it is produced at a fairly steady rate, a rising creatinine means the kidneys are filtering less well.

Blood urea nitrogen - a waste of protein metabolism.

A waste product made as the body breaks down protein. It is filtered by the kidneys and rises when filtration drops or when the body is dehydrated and reabsorbing water.

The main charged particle controlling water balance (Na+).

The dominant electrolyte in the blood, which controls how water is distributed in the body and is essential for nerve and muscle signaling. Its level changes reflect body water, not just salt.

The electrolyte that sets the heart's electrical rhythm (K+).

A charged particle concentrated inside cells that is critical for the electrical activity of nerves, muscles, and especially the heart. Both high and low potassium disturb heart rhythm.

A charged mineral in the blood that runs the body's electricity.

Dissolved salts (sodium, potassium, calcium, magnesium, chloride, bicarbonate) that carry electric charge. They are essential for nerve signaling, muscle contraction, hydration, and many chemical reactions.

The iron protein in red cells that carries oxygen.

The molecule inside red blood cells that binds oxygen in the lungs and releases it in the tissues. Hemoglobin levels reflect how much oxygen the blood can carry.

The fraction of blood made up of red cells.

The percentage of blood volume that is red blood cells. It tracks hemoglobin and rises or falls with red-cell mass and hydration.

A cell fragment that forms blood clots.

Small fragments that plug leaks in blood vessels and build clots. Too few platelets (thrombocytopenia) raises bleeding risk; too many raises clotting risk.

An immune cell that fights infection and inflammation.

A family of blood cells (neutrophils, lymphocytes, monocytes, eosinophils, basophils) that defend the body. The total and the breakdown (differential) help point to infection versus inflammation.

The percentage of hemoglobin carrying oxygen.

A noninvasive measure (by pulse oximeter) of how much of the blood's oxygen-carrying capacity is currently loaded. Low saturation means little oxygen is being delivered to tissues.

The organ that filters blood and balances water, salt, and acid.

One of two organs that filter the blood, remove wastes, regulate water and electrolytes, and control acid-base balance. Each contains about a million filtering units (nephrons).

The kidney's microscopic filtering unit.

The functional unit of the kidney, made of a filter (glomerulus) and a tubule that adjusts what is reabsorbed and excreted. About a million nephrons work in each kidney.

The kidney's blood filter.

A ball of tiny blood vessels where blood is filtered. It holds back blood cells and large proteins while letting water, salt, and small wastes through to become urine.

A life-threatening reaction to infection that injures organs.

A serious condition in which an infection triggers a widespread, dysregulated inflammatory response that can damage organs and drop blood pressure. When blood pressure falls despite fluids, it becomes septic shock.

Sepsis with dangerously low blood pressure despite fluids.

The most severe form of sepsis, in which infection causes such widespread vessel dilation and leakiness that blood pressure cannot be maintained, starving organs of oxygen despite fluid replacement.

Too little oxygen reaching the tissues.

A state where body tissues do not get enough oxygen, which can starve organs. It can arise from low oxygen in the blood, poor circulation, too few red cells, or cells unable to use oxygen.

Reduced blood flow that starves a tissue of oxygen.

Insufficient blood supply to a tissue, depriving it of oxygen and nutrients. If severe or prolonged, it causes cell death (infarction) - as in heart attack or stroke.

Relating to the arteries that supply the heart muscle.

The coronary arteries supply oxygenated blood to the heart muscle. Coronary artery disease is narrowing or blockage of these vessels, a leading cause of heart attack.

Bacteria evolving to survive antibiotics.

The ability of bacteria to survive drugs that once killed them. Overuse and broad-spectrum use drive resistance, making infections harder to treat.

Master anti-inflammatory hormones.

Cortisol and its synthetic relatives (e.g., prednisone, dexamethasone) that broadly dampen inflammation and immune activity by altering gene expression.

Receptors that adrenaline acts on.

Cell-surface receptors that respond to adrenaline and noradrenaline. Beta-blockers attach to them, blocking the stimulatory effects on the heart.

The enzyme that dissolves blood clots.

An enzyme that breaks down the fibrin mesh of a clot. Thrombolytic drugs convert plasminogen into plasmin to dissolve dangerous clots.

A spinal tap to sample brain fluid.

A procedure that samples cerebrospinal fluid (CSF) from the space around the spinal cord. It is the definitive test for meningitis and a key tool for other nervous-system conditions.

A cluster of immune cells formed in inflammation.

A collection of immune cells that forms in response to chronic inflammation, seen in sarcoidosis, tuberculosis, and some infections.

Plural of granuloma - clusters of immune cells.

Clusters of immune cells (macrophages and lymphocytes) that wall off persistent inflammation or infection; characteristic of sarcoidosis, tuberculosis, and fungal infections.

SLE, an autoimmune disease of many organs.

An autoimmune disease where the immune system attacks skin, joints, kidneys, blood cells, and brain. It is a 'great imitator' diagnosed with clinical criteria and specific antibodies.

Symptoms caused by a hidden cancer's immune response.

A set of symptoms caused not by the tumor itself but by the body's immune response to it, or by substances the tumor releases. Symptoms can appear before the cancer is found.

The list of conditions that could explain the findings.

The structured list of possible diagnoses that could account for a patient's symptoms and findings, ranked by likelihood and danger, revised as new data arrives.

Mental shortcuts that distort reasoning.

Systematic errors in thinking that distort how evidence is weighed, such as anchoring, confirmation bias, and premature closure. They are a major cause of diagnostic error.

The simplest explanation is usually right.

The principle that the simplest explanation - one disease explaining all findings - is usually correct. It is a useful starting bias, not proof.

Patients can have more than one disease.

The counter-principle to Occam's razor: patients can have as many diseases as they please, so sometimes findings are several separate problems rather than one unifying disease.

A severe, rapid allergic reaction.

A severe, potentially life-threatening allergic reaction causing swelling, breathing trouble, and low blood pressure. It is an emergency treated with epinephrine.

Treatment started before the cause is confirmed.

Treatment begun based on the most likely diagnosis before test results confirm it, often broad-spectrum, then narrowed once the organism or cause is identified.

A binding site that changes a receptor's behavior.

A site on a receptor separate from the main binding site. Binding there (as benzodiazepines do on GABA-A) changes how the receptor responds to its main signal.

Drugs that bind and remove heavy metals.

A treatment that uses drugs to bind heavy metals in the body so they can be excreted. It is used for lead, mercury, and other heavy-metal poisoning under specialist guidance.

A misfolded protein that spreads in the brain.

An abnormal misfolded protein that can recruit normal proteins to misfold, spreading through the brain and causing rare, fatal neurodegenerative disease.

Treatment that thins the blood to prevent clots.

Medication that reduces the blood's ability to clot, used to treat or prevent dangerous clots such as deep vein thrombosis, pulmonary embolism, and some strokes.

A clot-busting drug.

A medication that dissolves blood clots by activating the body's clot-dissolving system. It is used for the most dangerous clots in stroke, heart attack, and pulmonary embolism.

A machine that breathes for a patient.

A machine that supports or replaces a patient's breathing when they cannot do so themselves, delivering oxygen and removing carbon dioxide through an airway tube.

A collapsed lung from air in the chest.

A condition where air collects in the space around the lung, causing it to collapse. It can occur spontaneously or from trauma or procedures and may require drainage.

Coughing up blood.

Coughing up blood from the respiratory tract. It is a concerning symptom that requires investigation for infection, tumor, or bleeding disorders.

The immune system attacking the body's own tissue.

A condition in which the immune system mistakenly attacks the body's own cells and organs, such as lupus, rheumatoid arthritis, and vasculitis.

Difficulty with language from brain injury.

Impaired ability to understand or produce language, caused by damage to the language areas of the brain, such as from stroke, tumor, or inflammation.

Inflammation of the brain.

Inflammation of the brain, usually from infection or an autoimmune cause, causing fever, confusion, seizures, and neurologic symptoms.

Inflammation of the membranes around the brain.

Inflammation of the meninges, the membranes covering the brain and spinal cord, usually from infection. It is a medical emergency diagnosed by lumbar puncture.

Marked by granuloma formation.

Describing a pattern of inflammation that forms granulomas, seen in sarcoidosis, tuberculosis, and certain fungal infections.

Inflammation of the blood vessel walls.

Inflammation of blood vessel walls that can affect any organ, causing a wide range of symptoms depending on which vessels are involved.

Abnormal protein deposits in organs.

Insoluble clumps of misfolded protein that deposit in organs such as the heart, kidneys, and nerves, disrupting their function in amyloidosis.

Locking onto the first diagnosis.

A cognitive bias in which the clinician fixates on an initial diagnosis and fails to adjust it as new, conflicting evidence arrives.

Seeking evidence that supports your theory.

The tendency to notice and value evidence that supports a favored hypothesis while ignoring evidence against it, a major cause of diagnostic error.

Stopping once you have a plausible answer.

The cognitive error of accepting a diagnosis once a plausible explanation is found, without fully considering alternatives.

The brain's main inhibitory neurotransmitter.

Gamma-aminobutyric acid, the primary inhibitory neurotransmitter in the brain. It dampens neuronal activity and is the target of many sedative and anticonvulsant drugs.

The receptor benzodiazepines act on.

An ion-channel receptor for GABA that, when activated, allows chloride ions in and inhibits the neuron. Benzodiazepines bind an allosteric site on it to enhance GABA's effect.

The receptor benzodiazepines act on.

An ion-channel receptor for GABA that, when activated, allows chloride ions in and inhibits the neuron. Benzodiazepines bind an allosteric site on it to enhance GABA's effect.

Ativan, a benzodiazepine.

A benzodiazepine (brand name Ativan) used for anxiety, seizures, and sedation. It enhances GABA-A receptor function, producing calming and anticonvulsant effects.

White cells that fight bacteria.

The most abundant type of white blood cell, a first-line defender against bacterial infection. High counts suggest bacterial infection or inflammation; low counts raise infection risk.

White cells central to immune memory and viral defense.

White blood cells that include T cells and B cells. They drive viral immunity and antibody production; high counts suggest viral infection or certain blood disorders.

White cells linked to allergy and parasites.

A white blood cell type that rises with allergic reactions, asthma, and parasitic infections. High eosinophils are a useful diagnostic clue.

A rare white cell involved in allergic responses.

The least common white blood cell, involved in allergic and inflammatory responses. Abnormal levels can point to certain blood or allergic conditions.

White cells that become tissue macrophages.

White blood cells that migrate into tissues and become macrophages, engulfing debris and pathogens. They rise in chronic infection and inflammation.

A dangerous buildup of acids from fat metabolism.

A metabolic state in which the body breaks down fat for fuel, producing acidic ketones. It occurs in diabetic ketoacidosis and starvation and causes a high-anion-gap acidosis.

The contrast agent used in MRI.

A contrast agent used in MRI that brightens areas of abnormal blood-brain barrier, inflammation, or tumor. It is generally avoided in severe kidney disease.

Tissue death from lack of blood flow.

Death of tissue caused by interruption of its blood supply. Common examples include heart attack (myocardial infarction) and stroke (cerebral infarction).

A widened gap flagging unmeasured acids.

See 'Anion gap'. A high anion gap metabolic acidosis means extra acid is present that routine panels do not directly measure.

Deep, labored breathing that blows off CO2 to correct acidosis.

A pattern of very deep, sometimes rapid breathing seen when the body tries to compensate for metabolic acidosis by exhaling carbon dioxide, which is acidic in solution.

The kidneys slowly correcting acid-base by saving base and excreting acid.

Over 24-72 hours, the kidneys adjust acid-base balance by retaining or generating bicarbonate and excreting hydrogen ions. It is slower than lung compensation but can handle a large acid load.

The kidney making ammonia to carry acid out in urine.

The kidney's process of producing ammonia from amino acids, used to shuttle hydrogen ions out in the urine as ammonium. It is a key way the kidneys excrete acid during metabolic acidosis.

The expected CO2 for a given metabolic acidosis.

A formula that predicts the degree of respiratory compensation expected for a metabolic acidosis, so a mismatched result flags a mixed acid-base disorder.

Listening to body sounds with a stethoscope.

Listening to internal body sounds - heart, lungs, and vessels - with a stethoscope. It turns the examiner into a sensor, spotting murmurs, crackles, wheezes, and added heart sounds.

The familiar 'lub-dub' of the heartbeat.

S1 ('lub') is the sound of the atrioventricular valves closing as the ventricles begin to contract; S2 ('dub') is the semilunar valves closing as the ventricles relax. They mark the two phases of the mechanical cycle.

An extra sound from turbulent blood flow.

A blowing or whooshing sound caused by turbulent flow through a valve or vessel. Murmurs are timed (systolic vs diastolic) and graded, and help identify valve disease.

A tracing of the heart's electrical activity.

A recording of the heart's electrical signals from electrodes on the skin. It reveals rate, rhythm, ischemia, and damage by showing the sequence of electrical activation.

The ECG wave of the atria contracting electrically.

The first small wave on the ECG, representing the atria depolarizing (electrically firing) to squeeze blood into the ventricles.

The ECG wave of the ventricles firing.

The tall deflection on the ECG representing the ventricles depolarizing and contracting - the main pumping event. A wide QRS means the impulse is spreading slowly.

The ECG flat segment that reveals ischemia.

The flat portion between the QRS and the T wave, representing the ventricle between depolarization and repolarization. Elevation or depression here flags heart ischemia or injury.

The ECG wave of the heart recharging.

The upright wave after the QRS representing the ventricles repolarizing (recharging) after a beat. Abnormal T waves can signal ischemia or electrolyte imbalance, especially potassium.

A tiny air sac where gas exchange happens.

One of millions of tiny air sacs in the lungs where oxygen enters the blood and carbon dioxide leaves it, across a thin membrane.

Molecules moving from high to low concentration.

The passive movement of molecules from an area of higher concentration to lower concentration, across a membrane. It is how oxygen and CO2 move in the lungs and how many drugs act.

The chemical that keeps air sacs from collapsing.

A soap-like substance lining the alveoli that reduces surface tension, keeping the tiny air sacs open on exhalation. It is key to normal breathing.

The kidney tubule segment that concentrates urine.

The hairpin-shaped middle segment of the nephron that creates a concentration gradient in the kidney, allowing water reabsorption and concentrated urine.

A kidney tubule segment that fine-tunes salt and calcium.

A nephron segment after the loop of Henle that adjusts salt reabsorption and calcium balance, and is a site for certain diuretics (thiazides).

The kidney tubule segment that sets the final water and acid content of urine.

The final nephron segment where antidiuretic hormone (ADH) controls water reabsorption and where acid is finally adjusted, deciding how concentrated and acidic the urine is.

The hormone that makes you retain water (vasopressin).

A hormone released when the body is dehydrated that acts on the kidney's collecting duct to reabsorb water and concentrate urine, preserving body water.

The hormone that makes you retain salt (and water).

A hormone that acts on the kidney to reabsorb sodium and excrete potassium, which pulls water with the sodium and raises blood pressure.

How full the heart's chamber is before it beats.

The degree of stretch of the ventricular muscle at the end of filling, determined by how much blood returns to the heart. More stretch usually means a stronger squeeze (Frank-Starling).

The resistance the heart must pump against.

The pressure the ventricle must overcome to push blood out. High afterload (like hypertension or a narrowed valve) makes the heart work harder to eject.

More blood in = stronger squeeze.

The principle that the heart contracts more forcefully when its chambers are more filled before a beat, up to a physiological limit. It matches cardiac output to venous return.

A trapped pocket of air that collapses a lung and compresses the heart.

A life-threatening condition where air enters the chest and gets trapped, building pressure that collapses the lung and pushes the heart and major vessels, cutting off blood return.

The spectrum of heart attacks and unstable angina from a blocked coronary artery.

A group of conditions caused by sudden reduced blood flow to the heart muscle - unstable angina, and myocardial infarction (heart attack) with or without ST elevation.

A dangerous diabetic emergency of high sugar and high acid.

A serious complication of diabetes (most often type 1) in which, without enough insulin, the body breaks down fat for fuel, producing acidic ketones and causing a high-anion-gap metabolic acidosis.

How well a test catches the disease when it is present.

The proportion of truly diseased patients the test correctly identifies as positive (true positives / all with disease). A very sensitive test rarely misses disease, so a negative result helps rule it OUT.

How well a test avoids false alarms.

The proportion of truly healthy people the test correctly identifies as negative (true negatives / all without disease). A very specific test rarely mislabels healthy people as diseased, so a positive result helps rule disease IN.

How likely the disease is before you test.

The estimated likelihood of the disease in a patient before a test result is known, based on the population, risk factors, and presentation. It determines how much the test actually changes your decision.

PPV - the chance a positive test means real disease.

The proportion of positive test results that are true positives (how likely a positive result is correct). It rises with specificity and with pretest probability.

NPV - the chance a negative test means no disease.

The proportion of negative test results that are true negatives (how likely a negative result is correct). It rises with sensitivity and with how unlikely the disease already is.

How much a test result changes the odds of disease.

The factor by which a test result shifts pretest to posttest probability. A positive likelihood ratio (LR+) raises the odds of disease; a negative one (LR-) lowers it. Values far from 1 are more informative.

Computed tomography - detailed cross-section X-ray imaging.

An imaging method using rotating X-rays to build cross-sectional slices of the body. Fast and detailed, it is excellent for trauma, chest, abdomen, bleeding, and guiding procedures.

Magnetic resonance imaging - detailed soft-tissue imaging without ionizing radiation.

An imaging method using strong magnetic fields and radio waves to image soft tissue in fine detail, ideal for the brain, spinal cord, joints, and soft tissue.

Positron emission tomography - maps metabolic activity.

An imaging method that detects where cells are metabolically active, lighting up cancers, infections, and inflammation rather than just anatomy.

Cerebrospinal fluid - the fluid around the brain and spinal cord.

Cerebrospinal fluid bathes the brain and spinal cord, cushioning and nourishing them. It is sampled by lumbar puncture to diagnose meningitis, hemorrhage, inflammation, and CNS malignancy.

Antinuclear antibody - a screening test for autoimmune disease.

An antibody that attacks the cell nucleus, found in most patients with systemic lupus (SLE) and some other autoimmune diseases. It is sensitive but not very specific.

Antineutrophil cytoplasmic antibody - a marker of certain vasculitides.

An antibody against white blood cells associated with ANCA-associated vasculitides, which inflame small blood vessels and often cause pulmonary-renal syndrome.

Disseminated intravascular coagulation - a clotting catastrophe.

A dangerous condition in which widespread clotting consumes the clotting factors and platelets, then triggers bleeding. It complicates sepsis, trauma, obstetric emergencies, and malignancy.

A severe pregnancy complication - Hemolysis, Elevated Liver enzymes, Low Platelets.

A serious hypertensive disorder of pregnancy characterized by hemolysis (red-cell breakdown), elevated liver enzymes, and a low platelet count, often related to preeclampsia.

A genetic disorder of copper accumulation.

An autosomal-recessive disorder (caused by mutations in ATP7B) in which copper is not properly transported and accumulates in the liver and brain, causing hepatic and neuropsychiatric disease.

HAE - a genetic cause of episodic, non-allergic swelling.

A genetic disorder, often from C1-inhibitor deficiency, causing recurrent episodes of non-hive swelling (skin, abdomen, airway) that does not respond to allergy treatment.

CO - a colorless, odorless gas that blocks oxygen delivery.

A toxic gas, from combustion (fires, heaters, exhaust), that binds hemoglobin far more tightly than oxygen, reducing oxygen delivery to tissues and causing hypoxia without a low SpO2 necessarily obvious.

Inadequate organ perfusion - a medical emergency.

A state in which organs do not receive enough oxygen because of low blood flow, low volume, vessel dilation, pump failure, or obstruction. The four broad types are hypovolemic, distributive, cardiogenic, and obstructive.