Preoperative Laboratory Testing — MCQs
In the immediate postoperative period, how is body potassium typically managed?
In an accident case, after the arrival of medical team, all should be done in early management except;
In a Down's syndrome patient posted for surgery, the necessary preoperative investigation to be done is –
In a comatose patient with a blood glucose level of 750 mg/dL, which test is most important to perform in addition to serum potassium?
Among the following, which test is essential in pre-treatment evaluation for lithium therapy:
Preoperative medication of thyrotoxicosis are all except?
In the immediate postoperative period, body potassium is
A patient scheduled for elective inguinal hernia surgery has a history of myocardial infarction (MI) and underwent coronary artery bypass grafting (CABG). What should be included in the preoperative assessment?
A 50 year old male is posted for elective laparoscopic cholecystectomy. No history of comorbidities. His surgery is scheduled at 2 PM on the day of surgery. Which of the following is against the ASA guidelines for preoperative fasting
Preanaesthetic medication glycopyrrolate is primarily used for:
Preoperative Laboratory Testing Indian Medical PG Practice Questions and MCQs
Question 1: In the immediate postoperative period, how is body potassium typically managed?
- A. Increased due to fluid retention
- B. Remains stable
- C. Excreted excessively (Correct Answer)
- D. Conserved by aldosterone action
Explanation: ***Excreted excessively*** - **Stress responses** to surgery, including increased aldosterone and cortisol, can lead to enhanced **potassium excretion** via the kidneys. - Additionally, cell breakdown and fluid shifts can contribute to a net loss of potassium from the **intracellular** to **extracellular** space. *Increased due to fluid retention* - While **fluid retention** can occur post-operatively, it's typically associated with **dilutional hyponatremia**, not hyperkalemia from increased body potassium. - The stress response and associated hormonal changes usually promote potassium excretion, not retention. *Remains stable* - The **stress of surgery** significantly impacts electrolyte balance due to hormonal changes, fluid shifts, and tissue injury, making it unlikely for potassium levels to remain stable. - **Aldosterone effects** and increased cortisol levels actively alter potassium handling. *Conserved by aldosterone action* - **Aldosterone**, a key hormone in the postoperative stress response, primarily promotes **sodium reabsorption** and **potassium excretion** in the kidneys. - Therefore, its action leads to potassium loss rather than conservation.
Question 2: In an accident case, after the arrival of medical team, all should be done in early management except;
- A. Glasgow coma scale
- B. Check BP (Correct Answer)
- C. Stabilization of cervical vertebrae
- D. Check Respiration
Explanation: ***Check BP*** - In the **immediate/early management** of trauma (primary survey), while circulation assessment is crucial, the **initial assessment of circulation** focuses on: - **Pulse rate and quality** (radial, carotid) - **Capillary refill time** - **Skin color and temperature** - **Active hemorrhage control** - **Formal blood pressure measurement** with a cuff, while important, is typically recorded during or after these rapid initial assessments, as it takes more time to obtain an accurate reading. - In the context of this question, among the four options listed, BP measurement is relatively less immediate compared to the other life-saving priorities (airway protection, breathing assessment, C-spine stabilization, and GCS). - **Note:** This is a nuanced distinction - BP is assessed during primary survey, but the other three options have more immediate life-threatening implications if not addressed. *Glasgow coma scale* - **GCS assessment** is part of the **"D" (Disability)** step in the ATLS primary survey. - It is performed early to assess neurological status and level of consciousness. - GCS <8 indicates need for **definitive airway protection** (intubation). - This is a critical early assessment that guides immediate management decisions. *Stabilization of cervical vertebrae* - **C-spine immobilization** is part of the **"A" (Airway)** step - "Airway with cervical spine protection." - It is performed **simultaneously** with airway assessment using a **rigid cervical collar**. - This is the **first priority** in trauma management to prevent secondary spinal cord injury. - All trauma patients should be assumed to have C-spine injury until proven otherwise. *Check Respiration* - **Respiratory assessment** is part of the **"B" (Breathing)** step in the ATLS primary survey. - This involves checking: - **Respiratory rate and pattern** - **Chest wall movement** - **Air entry bilaterally** - **Signs of tension pneumothorax or flail chest** - This is an immediate life-saving priority and must be assessed early.
Question 3: In a Down's syndrome patient posted for surgery, the necessary preoperative investigation to be done is –
- A. CT Brain
- B. X-ray cervical spine (Correct Answer)
- C. Ultrasound Abdomen
- D. Echocardiography
Explanation: X-ray cervical spine - Patients with Down syndrome have an increased risk of **atlantoaxial instability (AAI)** due to ligamentous laxity and bony abnormalities, which can lead to spinal cord compression during neck manipulation for intubation. - A **preoperative X-ray of the cervical spine** (flexion/extension views) is crucial to assess for AAI and guide anesthetic management to prevent neurological damage. *CT Brain* - While some Down syndrome patients may have structural brain differences, a **CT brain** is not a routine preoperative investigation for all surgeries unless specific neurological symptoms are present. - It is not primarily indicated for assessing the immediate surgical risks associated with conditions common in Down syndrome, such as atlantoaxial instability. *Echocardiography* - Many Down syndrome patients have congenital heart defects (e.g., **AV canal defects**), and an echocardiogram is essential to evaluate cardiac function and structure, especially for major surgeries. - However, compared to the immediate risk of spinal cord injury during airway management, assessing **atlantoaxial instability** with a cervical spine X-ray takes precedence as a necessary and specific preoperative investigation for general surgery. *Ultrasound Abdomen* - Down syndrome patients have a higher incidence of certain gastrointestinal anomalies (e.g., **duodenal atresia**, Hirshsprung's disease) and often develop premature aging of organs. - An **abdominal ultrasound** is not a standard preoperative screening test unless there are specific abdominal symptoms or indications for evaluating potential anomalies or complications.
Question 4: In a comatose patient with a blood glucose level of 750 mg/dL, which test is most important to perform in addition to serum potassium?
- A. Serum creatinine
- B. Serum sodium
- C. Serum ketones
- D. Arterial blood gases (Correct Answer)
Explanation: ***Arterial blood gases*** - In a comatose patient with severe hyperglycemia (750 mg/dL), **arterial blood gases (ABGs)** are crucial to assess for **acidosis**, which could indicate **diabetic ketoacidosis (DKA)** or **hyperosmolar hyperglycemic state (HHS)** with lactic acidosis [1], [4]. - The **pH**, **bicarbonate (HCO3-)**, and **pCO2** levels from ABGs help determine the severity and type of metabolic derangement, guiding immediate treatment, especially for potential **cerebral edema** [3], [4]. *Serum creatinine* - While important for assessing **kidney function** in hyperosmolar states, it does not directly evaluate the immediate acid-base status that is critical for neurologic function in a comatose patient. - Renal insufficiency can exacerbate electrolyte imbalances and fluid overload but is secondary to the immediate need for acid-base assessment. *Serum sodium* - **Serum sodium** is important for calculating **effective serum osmolality**, which is elevated in both DKA and HHS, contributing to mental status changes [2]. - However, while important, it does not provide information about the **acid-base balance**, which is a more critical determinant of immediate neurologic stability and treatment in deep coma. *Serum ketones* - **Serum ketones** are essential for distinguishing between **DKA** (high ketones) and **HHS** (low or absent ketones) [4]. - While vital for diagnosis, ketones alone do not give the full picture of **acid-base status** (pH, bicarbonate) which is directly assessed by ABGs and more immediately actionable in managing a severely ill, comatose patient [1].
Question 5: Among the following, which test is essential in pre-treatment evaluation for lithium therapy:
- A. Fasting blood sugar
- B. Serum creatinine (Correct Answer)
- C. Liver function tests
- D. Platelet count
Explanation: ***Serum creatinine*** - **Lithium** is almost entirely excreted by the kidneys, so baseline renal function assessed by **serum creatinine** and estimated glomerular filtration rate (eGFR) is crucial. - This helps determine the appropriate starting dose and monitor for potential **lithium-induced renal impairment** during therapy. *Fasting blood sugar* - While important for general health screening and monitoring metabolic syndrome, **lithium** does not directly impact glucose metabolism to the extent that it requires pre-treatment evaluation for dosing or safety reasons. - This test is not considered essential specifically for lithium pre-treatment. *Liver function tests* - **Lithium** is not metabolized by the liver, and **hepatotoxicity** is not a known side effect. - Therefore, baseline liver function tests are not considered essential for initiating lithium therapy. *Platelet count* - **Lithium** rarely causes significant hematological abnormalities like **thrombocytopenia** or **thrombocytosis**. - A baseline platelet count is generally not required for pre-treatment evaluation unless there are other clinical indications.
Question 6: Preoperative medication of thyrotoxicosis are all except?
- A. Carbimazole
- B. PTU
- C. Propranolol
- D. Levothyroxine (Correct Answer)
Explanation: Levothyroxine - Levothyroxine is a synthetic thyroid hormone used to treat hypothyroidism, meaning it increases thyroid hormone levels, which would worsen thyrotoxicosis [1]. - Its administration would be contraindicated in a patient with thyrotoxicosis, as the goal is to reduce thyroid hormone levels preoperatively. Carbimazole - Carbimazole is a thionamide drug that inhibits the synthesis of thyroid hormones, making it a critical medication for treating hyperthyroidism and preparing patients for surgery [1]. - It reduces the amount of thyroid hormone produced by the thyroid gland, thus mitigating the risks associated with thyrotoxicosis during surgery. PTU - Propylthiouracil (PTU), like carbimazole, is a thionamide that blocks thyroid hormone synthesis and also inhibits the conversion of T4 to T3 [1]. - It is used in the preoperative management of thyrotoxicosis to achieve a euthyroid state and prevent a thyroid storm. Propranolol - Propranolol is a beta-blocker used to manage the symptoms of thyrotoxicosis, particularly the cardiovascular effects such as tachycardia, palpitations, and tremors [1]. - While it does not affect thyroid hormone levels directly, it helps control symptoms and stabilize the patient preoperatively, making them a safer candidate for surgery [1].
Question 7: In the immediate postoperative period, body potassium is
- A. Retained in body
- B. Exchanged with magnesium
- C. Exchanged with calcium
- D. Excreted excessively (Correct Answer)
Explanation: ***Excreted excessively*** - In the immediate postoperative period, the body often experiences **stress-induced hormonal changes**, such as increased cortisol and aldosterone, and activation of the **renin-angiotensin-aldosterone system**. - These hormonal changes can lead to increased renal potassium excretion and **catabolism** of muscle tissue, releasing intracellular potassium which is then excreted. *Retained in body* - **Potassium retention** is typically seen in conditions like **renal failure** or in states of **hypoaldosteronism**, which are not characteristic of the immediate postoperative period. - The stress response and potential for **acidosis** generally shift potassium out of cells, leading to increased excretion rather than retention. *Exchanged with magnesium* - While potassium and magnesium are both important intracellular cations and their levels can influence each other, a direct "exchange" in the immediate postoperative period is not the primary mechanism of potassium handling. - **Hypomagnesemia** can impair potassium reabsorption leading to **hypokalemia**, but this is a secondary effect, not a direct exchange causing excessive excretion. *Exchanged with calcium* - There is no primary physiological mechanism for direct "exchange" of potassium with calcium in the context of general body fluid and electrolyte regulation in the immediate postoperative period. - **Calcium and potassium** have different regulatory pathways and serve distinct roles, though imbalances in one can indirectly affect the other's transport or cellular function.
Question 8: A patient scheduled for elective inguinal hernia surgery has a history of myocardial infarction (MI) and underwent coronary artery bypass grafting (CABG). What should be included in the preoperative assessment?
- A. History + c/e + routine labs + V/Q scan
- B. History + c/e + routine labs
- C. History + c/e + routine labs + stress test (Correct Answer)
- D. History + c/e + routine labs + angiography to assess graft patency
Explanation: ***History + c/e + routine labs + stress test*** - A **stress test** is crucial in patients with a history of MI and CABG to assess **myocardial ischemia** and functional capacity, guiding perioperative management. - This evaluation helps determine the patient's **cardiac risk** for non-cardiac surgery and the need for further cardiac optimization. *History + c/e + routine labs + angiography to assess graft patency* - **Coronary angiography** is an invasive procedure and is generally not indicated as a routine preoperative assessment unless there are new, significant cardiac symptoms or signs of **graft dysfunction**. - Assessing graft patency through angiography carries risks and would only be justified if there were strong clinical indications suggesting acute or severe **cardiac ischemia**. *History + c/e + routine labs* - While critical for any preoperative assessment, **routine history, physical examination, and basic laboratory tests** are insufficient for a patient with a significant cardiac history like MI and CABG. - This approach would **underestimate the cardiac risk** and might miss undetected ischemia, leading to adverse perioperative cardiac events. *History + c/e + routine labs + V/Q scan* - A **ventilation-perfusion (V/Q) scan** is primarily used to diagnose **pulmonary embolism** or assess regional lung function. - It does not provide information about myocardial ischemia or cardiac functional capacity, making it **irrelevant** for assessing cardiac risk in this clinical scenario.
Question 9: A 50 year old male is posted for elective laparoscopic cholecystectomy. No history of comorbidities. His surgery is scheduled at 2 PM on the day of surgery. Which of the following is against the ASA guidelines for preoperative fasting
- A. Water at 12:00 PM
- B. Black coffee at 5:30 AM
- C. Pancakes at 10:00 AM (Correct Answer)
- D. A non-clear liquid (e.g., orange juice) at 7:30 AM
Explanation: **Pancakes at 10:00 AM** - According to ASA guidelines, the fasting period for solid food is typically **6-8 hours** before surgery. Eating pancakes, which are solid food, at 10:00 AM for a 2:00 PM surgery (4-hour interval) violates this guideline. - This short fasting period for solids increases the risk of **pulmonary aspiration** during induction of anesthesia. *Water at 12:00 PM* - Water is considered a clear liquid, and ASA guidelines typically allow clear liquids until **2 hours** before surgery. Drinking water at 12:00 PM for a 2:00 PM surgery is within these guidelines. - Rapid gastric emptying of clear liquids minimizes the risk of aspiration. *Black coffee at 5:30 AM* - Black coffee is considered a clear liquid, and it is consumed well within the **2-hour** fasting window for clear liquids before a 2:00 PM surgery. - The absence of milk or cream ensures it is treated as a clear liquid, which empties quickly from the stomach. *A non-clear liquid (e.g., orange juice) at 7:30 AM* - Non-clear liquids, such as orange juice, are treated similarly to light meals and generally require a fasting period of **6 hours** before surgery. Drinking orange juice at 7:30 AM for a 2:00 PM surgery (6.5-hour interval) is compliant with these guidelines. - The protein and pulp in non-clear liquids delay gastric emptying compared to clear liquids.
Question 10: Preanaesthetic medication glycopyrrolate is primarily used for:
- A. Decrease secretion (Correct Answer)
- B. Antisialagogue effect
- C. Prevent aspiration
- D. Reduce bronchial secretions
Explanation: ***Decrease secretion*** - Glycopyrrolate is an **anticholinergic drug** that primarily works by blocking muscarinic acetylcholine receptors, thereby reducing glandular secretions throughout the body. - This effect includes reducing **salivary**, **bronchial**, and **gastric secretions**, which is beneficial during anesthesia. *Reduce bronchial secretions* - While glycopyrrolate does **reduce bronchial secretions**, this is a specific aspect of its broader effect of decreasing secretions, making "decrease secretion" a more comprehensive answer. - Reducing bronchial secretions helps in maintaining a **clear airway** and preventing atelectasis. *Prevent aspiration* - By decreasing gastric and salivary secretions, glycopyrrolate can indirectly help to **reduce the risk of aspiration** of gastric contents or saliva into the lungs. - However, preventing aspiration is a beneficial **consequence** of reduced secretions, not the direct pharmacological action described as "decrease secretion." *Antisialagogue effect* - The **antisialagogue effect**, which means reducing saliva production, is a prominent action of glycopyrrolate and is part of its overall secretion-decreasing property. - Reducing salivary secretions creates a **dry operative field** during procedures involving the oral cavity or airway.
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