PGIM MD Medicine key terms

The difference between measured serum sodium and the sum of chloride and bicarbonate, used to classify metabolic acidosis. A raised gap suggests accumulation of unmeasured acids such as ketones, lactate, urate, or toxins.

A metabolic acidosis where unmeasured anions accumulate, commonly from ketoacidosis, lactic acidosis, renal failure, or ingestion of methanol or ethylene glycol. Treatment targets the underlying cause rather than the bicarbonate value alone.

The difference between measured and calculated serum osmolality. A gap above roughly 10 mOsm/kg suggests an unmeasured osmole such as methanol, ethylene glycol, isopropanol, or mannitol, guiding toxicology workup.

The physiological adjustment that limits pH change in a primary acid-base disorder. Respiratory compensation alters carbon dioxide within minutes to hours, while renal compensation changes bicarbonate over days and is often incomplete.

A calculation predicting expected arterial carbon dioxide in metabolic acidosis: 1.5 times bicarbonate plus 8, plus or minus 2. A measured value outside this range indicates an additional respiratory disorder.

Two or more primary acid-base disturbances occurring together, so that compensation is inadequate or excessive for the expected pattern. Recognising it prevents attributing all abnormalities to a single cause and missing a second process.

A cardiac muscle protein released into blood when myocytes are injured. High-sensitivity assays detect small rises; interpretation requires serial sampling and clinical context because elevation is not synonymous with acute coronary occlusion.

Myocardial cell death from prolonged ischaemia, diagnosed when cardiac troponin rises or falls with supporting clinical or electrocardiographic evidence. ST-elevation and non-ST-elevation patterns carry different urgency for reperfusion.

The spectrum of ischaemic presentations including unstable angina, non-ST-elevation myocardial infarction, and ST-elevation myocardial infarction. Management is guided by electrocardiography, troponin, and risk of ongoing ischaemia.

A rise of the ST segment on electrocardiography above the isoelectric line, indicating transmural myocardial injury when new and in a coronary territory. It prompts emergency reperfusion decisions.

Occlusion of pulmonary arteries by thrombus, usually from deep veins of the legs. Presentation ranges from pleuritic pain to obstructive shock; risk stratification determines whether anticoagulation alone suffices.

A fibrin degradation product that rises when clot is formed and broken down. Its high sensitivity and low specificity make it useful mainly to exclude venous thromboembolism in patients with low or intermediate pretest probability.

A clinical prediction tool that estimates pretest probability of deep vein thrombosis or pulmonary embolism from history, examination, and likelihood of alternative diagnoses. It determines whether D-dimer testing can safely exclude disease.

Life-threatening organ dysfunction caused by a dysregulated host response to infection. Organ dysfunction is commonly quantified using the Sequential Organ Failure Assessment score, and early recognition changes outcome.

Sepsis with persisting hypotension requiring vasopressors to maintain mean arterial pressure and a raised lactate despite adequate fluid resuscitation. Mortality is high and source control is central to management.

A bedside screening score for sepsis using respiratory rate, systolic blood pressure, and altered mentation. It predicts poor outcome in suspected infection but is not a rule-out test for sepsis.

The fall in blood lactate over time during resuscitation, reflecting improved tissue perfusion. Failure to clear lactate suggests ongoing hypoperfusion or an uncontrolled source and predicts worse outcome.

A catecholamine vasopressor that raises vascular tone through alpha-adrenergic receptors. It is first-line for septic shock after fluids, aiming for a mean arterial pressure of about 65 mmHg in most adults.

The average arterial pressure across the cardiac cycle, approximated as diastolic pressure plus one third of pulse pressure. It represents the perfusion pressure that vasopressor therapy is titrated to achieve.

Pharmacological dissolution of thrombus using agents such as alteplase or tenecteplase. It is used in acute ischaemic stroke, ST-elevation infarction when primary angioplasty is unavailable, and massive pulmonary embolism with instability.

Sudden focal neurological deficit from arterial occlusion causing brain infarction. Urgent imaging distinguishes it from haemorrhage, and reperfusion therapy is time-dependent within a narrow window.

A brief episode of focal neurological dysfunction without infarction on imaging. It signals high short-term stroke risk and warrants urgent assessment and secondary prevention.

Acute metabolic decompensation of diabetes with hyperglycaemia, ketonaemia, and high anion gap acidosis. Management requires fluids, insulin, and careful potassium replacement because total body potassium is depleted.

Severe hyperglycaemia with marked hyperosmolality and dehydration, usually without significant ketosis, seen mainly in older people with type 2 diabetes. It carries high mortality and demands slow, careful fluid and electrolyte correction.

A life-threatening exaggeration of thyrotoxicosis with fever, tachyarrhythmia, agitation, and multi-organ dysfunction. Treatment combines beta blockade, thionamide, iodine, and glucocorticoid with supportive care.

The clinical state resulting from excess circulating thyroid hormone, from any cause. Symptoms include weight loss, tremor, heat intolerance, and palpitations; the cause is distinguished by antibody and uptake testing.

Acute adrenal insufficiency presenting with hypotension, hyponatraemia, hyperkalaemia, and hypoglycaemia, often precipitated by infection or steroid withdrawal. Immediate parenteral hydrocortisone and fluid resuscitation are life-saving.

Serum sodium below the reference range, reflecting disturbed water balance rather than simply salt loss. Assessment of volume status and urine osmolality identifies whether the cause is hypovolaemic, euvolaemic, or hypervolaemic.

Elevated serum potassium that risks cardiac arrhythmia and arrest. Urgent treatment combines membrane stabilisation with calcium, intracellular shift using insulin and salbutamol, and removal via dialysis or binders.

An abrupt fall in glomerular filtration over hours to days, marked by rising creatinine or falling urine output. Classification by stage guides fluid management, drug dosing, and the need for renal replacement.

The percentage of filtered sodium excreted in urine, calculated from paired serum and urine sodium and creatinine. Low values suggest prerenal states, while high values suggest intrinsic tubular injury, though diuretics confound interpretation.

Advanced liver fibrosis with regenerative nodules, causing portal hypertension and impaired synthetic function. Complications include ascites, variceal bleeding, encephalopathy, and hepatocellular carcinoma, each requiring specific surveillance and treatment.

Infection of ascitic fluid without an evident intra-abdominal source, common in cirrhosis. Diagnosis rests on a raised ascitic neutrophil count, and treatment requires antibiotics with albumin support to reduce renal failure.

Functional renal impairment in advanced liver disease caused by splanchnic vasodilatation and renal vasoconstriction, without structural kidney damage. Treatment uses vasoconstrictors with albumin, and transplantation offers definitive cure.

Persistent airflow limitation from airway and parenchymal disease, usually related to tobacco smoke. Exacerbations are managed with bronchodilators, steroids, antibiotics when indicated, and controlled oxygen with ventilatory support if needed.

Respiratory support delivered through a mask rather than an artificial airway. It reduces intubation and mortality in acute hypercapnic exacerbations of chronic obstructive pulmonary disease and in cardiogenic pulmonary oedema.

Hypoxaemia with hypercapnia from alveolar hypoventilation, seen in airway obstruction, neuromuscular weakness, or obesity. Management addresses the cause and may require ventilatory support rather than oxygen alone.

A severity score for community-acquired pneumonia using confusion, urea, respiratory rate, blood pressure, and age. It helps decide between outpatient, ward, and critical care management alongside clinical judgement.

Lower respiratory infection with fever, cough, and new infiltrate acquired outside hospital. Severity scoring and knowledge of local resistance guide whether treatment is ambulatory or inpatient and which antibiotic is chosen.