NPLEX II cheat sheet

Cardiac output = heart rate × stroke volume; mean arterial pressure ≈ diastolic pressure + 1/3 (systolic − diastolic), so a wide pulse pressure raises MAP disproportionately.

Renal clearance C = (urine concentration × urine flow) / plasma concentration; inulin clearance equals GFR, PAH clearance approximates renal plasma flow, and glucose clearance is zero below transport maximum.

Henderson–Hasselbalch: pH = 6.1 + log([HCO3−]/(0.03 × PaCO2)); respiratory acidosis raises PaCO2, metabolic acidosis lowers HCO3−, and compensation never fully normalizes pH.

Anion gap = Na+ − (Cl− + HCO3−); normal is roughly 8–12 mEq/L, and a gap acidosis suggests ketoacidosis, lactic acidosis, renal failure, or toxin ingestion (methanol, ethylene glycol, salicylate).

Osmolality ≈ 2[Na+] + glucose/18 + BUN/2.8; an osmolar gap >10 mOsm/kg suggests unmeasured osmoles such as methanol or ethylene glycol.

Action potential sequence: resting −90 mV, threshold −70 mV, rapid depolarization via voltage-gated Na+ channels, plateau via Ca2+ influx in cardiac and smooth muscle, repolarization via K+ efflux.

Autonomic rules: alpha-1 causes vasoconstriction and mydriasis, beta-1 increases heart rate and contractility, beta-2 causes bronchodilation and vasodilation, muscarinic effects are bradycardia, secretions, and miosis.

Enzyme kinetics: Km is the substrate concentration at half Vmax and reflects affinity (lower Km = higher affinity); competitive inhibitors raise Km with unchanged Vmax, noncompetitive inhibitors lower Vmax.

Innate versus adaptive immunity: IgM is the first antibody produced and fixes complement, IgG crosses the placenta and dominates secondary responses, IgA protects mucosa, and IgE mediates type I hypersensitivity.

First-line hypertension agents: thiazides for most patients, ACE inhibitors or ARBs for diabetes with proteinuria and heart failure, and calcium channel blockers or thiazides in older adults; ACE inhibitors are contraindicated in pregnancy.

Acute coronary syndrome: ST-elevation MI warrants immediate reperfusion (PCI within 90 minutes of first medical contact); aspirin plus a P2Y12 inhibitor and anticoagulation are standard, and oxygen is reserved for hypoxia.

Diabetes thresholds: fasting glucose ≥126 mg/dL, 2-hour OGTT ≥200 mg/dL, or HbA1c ≥6.5% establish diabetes; metformin is first-line unless contraindicated by renal impairment or lactic acidosis risk.

Thyroid patterns: primary hypothyroidism shows high TSH with low free T4, subclinical hypothyroidism shows high TSH with normal free T4, and primary hyperthyroidism shows low TSH with high free T4 or T3.

Anemia classification by MCV: microcytic (iron deficiency, thalassemia, lead, sideroblastic), normocytic (chronic disease, hemolysis, blood loss), macrocytic (B12, folate, alcohol, hypothyroidism, myelodysplasia).

Asthma versus COPD: asthma shows reversible obstruction with diurnal variation and eosinophilia; COPD shows persistent airflow limitation with smoking history, hyperinflation, and reduced diffusing capacity.

Meningitis decision rule: bacterial meningitis suggested by CSF neutrophil predominance, glucose <40 mg/dL or CSF/serum ratio <0.4, and protein >200 mg/dL; viral shows lymphocytosis with normal glucose.

Anticoagulation reversal: warfarin by vitamin K plus 4-factor PCC, heparin by protamine sulfate, and dabigatran by idarucizumab; andexanet alfa is used for factor Xa inhibitors.

Pediatric milestones: head control around 3–4 months, sitting without support 6–8 months, walking 12–15 months, and two-word phrases by 24 months; loss of milestones warrants developmental evaluation.