AIIMS PG (DM/MCh) Entrance Radiology, Anesthesiology and Critical Care Syllabus

Which radioisotope is most commonly used in nuclear medicine and why?

Technetium-99m - ideal 140 keV gamma energy, short 6-hour half-life, pure gamma emission (low radiation dose), and readily available from a Mo-99 generator.

What radiotracer is used in PET imaging and what does its uptake reflect?

F-18 fluorodeoxyglucose (FDG) - a glucose analog whose uptake reflects metabolic/glycolytic activity, high in tumors, infection, and inflammation.

What is the radiotracer of choice for a thyroid scan and how is it used to differentiate hot vs cold nodules?

Technetium-99m pertechnetate or radioactive iodine (I-123). Hot nodules concentrate tracer (usually benign/hyperfunctioning); cold nodules show no uptake (higher malignancy risk).

State the three core principles of radiation protection (ALARA).

Time (minimize exposure duration), Distance (maximize distance - inverse square law), and Shielding (use lead/barriers). ALARA = As Low As Reasonably Achievable.

What is the inverse square law in radiation safety?

Radiation intensity is inversely proportional to the square of the distance from the source; doubling the distance reduces exposure to one-quarter.

What are the SI units for absorbed dose and effective (equivalent) dose?

Absorbed dose: Gray (Gy, J/kg). Effective/equivalent dose: Sievert (Sv), which accounts for radiation type and tissue sensitivity weighting factors.

What does the ASA Physical Status Classification grade, and what is ASA III?

It grades a patient's preoperative physical fitness (I-VI). ASA III = patient with severe systemic disease that limits activity but is not incapacitating/constantly life-threatening.

What is the Mallampati classification used for?

Predicting difficulty of intubation by assessing oropharyngeal visibility (Class I: faucial pillars, soft palate, uvula visible -> Class IV: only hard palate visible). Higher class = harder intubation.

List the components of the LEMON assessment for a difficult airway.

Look externally, Evaluate 3-3-2 rule, Mallampati, Obstruction/Obesity, Neck mobility.

What are standard ASA preoperative fasting guidelines for clear fluids, breast milk, and solid food/full meal?

Clear fluids: 2 hours. Breast milk: 4 hours. Light meal/non-human milk/formula: 6 hours. Fatty/full meal: 8 hours.

What is the mechanism of action of most inhalational (volatile) anesthetic agents?

Primarily potentiation of inhibitory GABA-A receptors (and effects on glycine and NMDA receptors), producing dose-dependent CNS depression.

Define MAC (Minimum Alveolar Concentration).

The alveolar concentration of an inhaled anesthetic at 1 atm that prevents movement in 50% of patients in response to a surgical (skin) incision; a measure of anesthetic potency.

What is the mechanism and key advantage of propofol as an IV induction agent?

GABA-A receptor agonist; advantages: rapid onset, rapid smooth recovery, antiemetic properties. Drawbacks: hypotension, pain on injection, no analgesia.

Which IV induction agent is most cardiostable and what is its main adverse effect?

Etomidate - maintains hemodynamic stability (good in shock/cardiac patients); main adverse effect is adrenocortical suppression (inhibits 11-beta-hydroxylase).

What is unique about ketamine's anesthetic action and hemodynamics?

NMDA receptor antagonist producing 'dissociative anesthesia' with analgesia and bronchodilation; it increases BP, HR, and cardiac output (sympathomimetic), useful in shock/asthma. Side effect: emergence delirium/hallucinations.

What is the mechanism of action of local anesthetics?

Reversible blockade of voltage-gated sodium channels on the inner axonal membrane, preventing depolarization and nerve impulse conduction.

What is the difference between depolarizing and non-depolarizing neuromuscular blockers? Give an example of each.

Depolarizing (succinylcholine): agonist causing persistent depolarization, rapid onset/short duration, fasciculations. Non-depolarizing (rocuronium, vecuronium): competitive ACh-receptor antagonists, reversible by neostigmine/sugammadex.

What are the classic signs/triggers of malignant hyperthermia and its specific treatment?

Triggered by volatile anesthetics and succinylcholine; signs: rising end-tidal CO2, masseter spasm, tachycardia, hyperthermia, rigidity, acidosis. Treatment: dantrolene plus supportive cooling.

What are the standard ASA basic intraoperative monitoring requirements?

Continuous evaluation of oxygenation (pulse oximetry, FiO2), ventilation (capnography/end-tidal CO2), circulation (ECG, blood pressure at least every 5 min), and temperature.

What does capnography (end-tidal CO2) confirm and what is a normal EtCO2 value?

Confirms correct endotracheal tube placement, ventilation adequacy, and circulation/cardiac output. Normal EtCO2 = 35-45 mmHg.

What is a sudden drop in EtCO2 to near zero most concerning for intraoperatively?

Esophageal intubation, circuit disconnection/obstruction, or cardiac arrest (loss of pulmonary blood flow).

What does the pulse oximeter measure, and what is its key limitation?

Measures peripheral oxygen saturation (SpO2) by differential absorption of red/infrared light by oxy- vs deoxyhemoglobin. Limitation: unreliable in carbon monoxide poisoning, methemoglobinemia, poor perfusion, and motion.

Describe the WHO analgesic ladder for pain management.

Step 1: non-opioids (NSAIDs/paracetamol) +/- adjuvant. Step 2: weak opioids (codeine/tramadol) +/- non-opioid/adjuvant. Step 3: strong opioids (morphine) +/- non-opioid/adjuvant for moderate-to-severe pain.

What is the mechanism of action of opioids in pain control?

Agonism at mu (and kappa/delta) opioid receptors in CNS, inhibiting ascending pain transmission and altering pain perception; mu effects include analgesia, respiratory depression, and miosis.

What is the antidote for opioid overdose and a key caution with its use?

Naloxone (mu-receptor antagonist). Caution: short half-life may require repeat dosing, and it can precipitate acute withdrawal in dependent patients.

What class of drugs is first-line for neuropathic pain and give examples?

Anticonvulsants (gabapentin, pregabalin) and tricyclic antidepressants (amitriptyline) or SNRIs (duloxetine); standard NSAIDs/opioids are less effective for neuropathic pain.

Classify the four main types of shock by mechanism.

Hypovolemic (volume loss), Cardiogenic (pump failure), Obstructive (mechanical obstruction - PE, tamponade, tension pneumothorax), and Distributive (vasodilation - septic, anaphylactic, neurogenic).

Compare hemodynamic profiles (CO, SVR, preload) of hypovolemic vs septic (distributive) vs cardiogenic shock.

Hypovolemic: low CO, high SVR, low preload (cold). Cardiogenic: low CO, high SVR, high preload (cold). Septic/distributive: high CO, low SVR, low/normal preload (warm).

What is the qSOFA score and its criteria?

A bedside screen for sepsis-related mortality risk: RR >=22/min, altered mentation (GCS <15), systolic BP <=100 mmHg. Score >=2 suggests higher risk.

State the formula for Mean Arterial Pressure (MAP) and the typical resuscitation target in shock/sepsis.

MAP = DBP + 1/3(SBP - DBP), or (CO x SVR). Target MAP in sepsis resuscitation is >= 65 mmHg.

In acute respiratory failure, distinguish Type I from Type II by blood gases.

Type I (hypoxemic): low PaO2 with normal/low PaCO2 (e.g., pneumonia, ARDS, PE). Type II (hypercapnic): low PaO2 with high PaCO2 (ventilatory failure - COPD, drug overdose, neuromuscular).

What are the Berlin criteria diagnostic features of ARDS?

Acute onset within 1 week, bilateral pulmonary infiltrates not fully explained by cardiac failure/overload, and impaired oxygenation graded by PaO2/FiO2 ratio (mild <=300, moderate <=200, severe <=100, on PEEP >=5).

What is the lung-protective ventilation strategy for ARDS?

Low tidal volume (~6 mL/kg predicted body weight), plateau pressure <30 cmH2O, adequate PEEP, and permissive hypercapnia; prone positioning for severe ARDS.