FCPS Part-I flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Anion gap formula

Anion gap equals sodium minus the sum of chloride and bicarbonate, normally 8 to 12 mmol/L. It rises with lactate, ketones, urate, toxins, or renal failure and falls with hypoalbuminaemia.

Winter's formula

Expected PaCO2 equals 1.5 times bicarbonate plus 8, with a range of plus or minus 2. A measured value outside this range indicates a second respiratory acid-base disorder.

Effective osmolality

Tonicity counts only particles that cannot cross membranes, so sodium and glucose but not urea. It predicts water shift across cell membranes and guides hypertonic saline use.

Starling forces

Fluid movement across capillaries depends on hydrostatic pressure outward, interstitial pressure inward, and oncotic pressure pulling water back. Imbalance produces oedema.

Autosomal recessive recurrence

Two carrier parents have a one-in-four risk of an affected child per pregnancy, with two-in-four carriers and one-in-four unaffected. Consanguinity increases the chance both parents carry the same variant.

p53 tumour suppressor

p53 halts the cell cycle at the G1/S checkpoint for DNA repair or triggers apoptosis. Biallelic loss permits propagation of mutations and is common in many carcinomas.

Oxygen dissociation curve shift

Raised carbon dioxide, hydrogen ions, temperature, and 2,3-BPG shift the curve right, releasing oxygen to tissues. Fetal haemoglobin and carboxyhaemoglobin shift it left.

Half-life and steady state

Half-life equals 0.693 times volume of distribution divided by clearance. Roughly four to five half-lives are needed to reach steady-state plasma concentration during constant dosing.

Zero-order kinetics

Saturated elimination enzymes remove a fixed amount of drug per unit time, so clearance falls as concentration rises. Phenytoin, ethanol, and high-dose salicylate behave this way.

Loading dose formula

Loading dose equals volume of distribution times target concentration divided by bioavailability. It fills the apparent distribution volume quickly when immediate therapeutic levels are needed.

Competitive antagonist effect

A competitive antagonist binds reversibly at the agonist site, shifting the dose-response curve right without lowering maximal response. Higher agonist concentration can overcome the block.

Michaelis-Menten Km

Km is the substrate concentration giving half of maximal velocity and reflects enzyme affinity. Competitive inhibitors raise apparent Km, while non-competitive inhibitors reduce Vmax.

First-pass metabolism

Orally absorbed drug passes portal circulation and liver before reaching systemic blood, reducing bioavailability. Sublingual, intravenous, transdermal, and inhaled routes largely avoid this loss.

Ion trapping

Only uncharged drug crosses lipid membranes, so acidic drugs accumulate in alkaline urine and weak bases in acidic compartments. Urine pH manipulation can accelerate elimination.

Plasmid conjugation

Bacteria transfer resistance plasmids through direct cell-to-cell contact via a sex pilus. This horizontal gene transfer spreads multidrug resistance rapidly among Gram-negative organisms.

Volume of distribution

Volume of distribution equals dose divided by plasma concentration. Values above roughly one litre per kilogram indicate extensive tissue uptake, as with tricyclics and chloroquine.

Sepsis-3 definition

Sepsis is life-threatening organ dysfunction from dysregulated host response to infection, marked by a SOFA score rise of at least two points from baseline.

Cushing triad

Hypertension with bradycardia and irregular respiration signals raised intracranial pressure, often from expanding intracranial haematoma. It is a late, pre-herniation sign requiring urgent decompression.

SIADH diagnosis

Euvolemic hyponatraemia with urine osmolality above 100 mOsm/kg and urine sodium above 30 mmol/L suggests inappropriate antidiuretic hormone. Exclude hypothyroidism and adrenal insufficiency first.

Delta ratio interpretation

Delta ratio compares anion gap rise with bicarbonate fall. Values above two suggest coexisting metabolic alkalosis; values below one suggest a concurrent normal-gap metabolic acidosis.

ST elevation management

ST elevation or new left bundle branch block in acute chest pain mandates immediate reperfusion, by primary percutaneous coronary intervention or fibrinolysis when transfer is delayed.

Unconjugated hyperbilirubinaemia

Raised unconjugated bilirubin with otherwise normal liver tests suggests haemolysis or Gilbert syndrome. Conjugated elevation points to hepatocellular or cholestatic disease requiring imaging.

Distributive shock features

Distributive shock shows low systemic vascular resistance with warm peripheries, as in sepsis or anaphylaxis. Treatment is fluid resuscitation plus vasopressors and the specific antidote.

Paediatric dehydration grading

Mild to moderate dehydration shows dry mucosa, reduced skin turgor, and delayed capillary refill; oral rehydration is first line. Shock with lethargy needs intravenous isotonic fluid boluses.

Sensitivity and specificity

Sensitivity is true positives divided by all diseased; specificity is true negatives divided by all healthy. Both are intrinsic test properties independent of disease prevalence.

Positive predictive value

Positive predictive value is true positives divided by all positive results and rises with disease prevalence. Screening low-prevalence populations therefore generates many false positives.

Likelihood ratio positive

Likelihood ratio positive equals sensitivity divided by one minus specificity. Values above ten strongly rule in disease, while values below 0.1 strongly rule it out.

Number needed to treat

Number needed to treat is the reciprocal of absolute risk reduction, the difference between control and treatment event rates. Smaller values indicate greater clinical benefit.

Narrow therapeutic index drugs

Drugs such as digoxin, lithium, warfarin, phenytoin, and aminoglycosides have toxic doses close to therapeutic doses. They require plasma level monitoring and careful dose adjustment.

CYP3A4 inducers

Rifampicin, carbamazepine, phenytoin, and St John's wort induce CYP3A4, lowering concentrations of substrate drugs. Inhibitors include macrolides, azole antifungals, and grapefruit juice.

Heparin-induced thrombocytopenia

Platelets fall five to ten days after heparin exposure with paradoxical arterial or venous thrombosis. Management is stopping heparin and starting a non-heparin anticoagulant such as argatroban.

WHO surgical safety checklist

Three phases, sign in before induction, time out before incision, and sign out before leaving theatre, reduce wrong-site surgery and communication errors. Medication reconciliation complements this at care transitions.