Preoperative Laboratory Testing — MCQs

10 questions

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?

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:

Which of the following is the most sensitive and specific initial laboratory test to diagnose iron deficiency?

Q10

Modified Mallampati grading is used in assessment of -

Preoperative Laboratory Testing Indian Medical PG Practice Questions and MCQs

Question 1: 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 2: 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 3: 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 4: 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 5: 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 6: 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 7: 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 8: 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.

Question 9: Which of the following is the most sensitive and specific initial laboratory test to diagnose iron deficiency?

A. Serum iron levels
B. Serum ferritin levels (Correct Answer)
C. Serum transferrin receptor population
D. Transferrin saturation

Explanation: ***Serum ferritin levels*** - **Serum ferritin** directly reflects the body's iron stores and is the **most sensitive and specific indicator of iron deficiency**, even before anemia develops [1]. - A low serum ferritin level (< 15-30 ng/mL) confirms **iron depletion** and distinguishes iron deficiency from other causes of microcytic anemia [1]. *Serum iron levels* - **Serum iron** fluctuates throughout the day and is affected by recent iron intake, making it less reliable for diagnosing iron deficiency compared to ferritin. - While typically low in iron deficiency, it can also be low in **anemia of chronic disease**, leading to false positives [2]. *Serum transferrin receptor population* - **Serum transferrin receptor (sTfR)** levels rise with iron deficiency as cells upregulate receptors to capture more iron. - While useful, especially in differentiating iron deficiency from **anemia of chronic disease**, it is generally less sensitive and specific than ferritin as an initial stand-alone test. *Transferrin saturation* - **Transferrin saturation** (calculated as serum iron / total iron-binding capacity) indicates the amount of iron bound to transferrin. - A low percentage suggests **iron deficiency**, but it can also be low in other conditions and is not as sensitive or specific as ferritin for initial diagnosis.

Question 10: Modified Mallampati grading is used in assessment of -

A. Difficulty of intubation (Correct Answer)
B. Obstruction of the airway
C. Aspiration-related death
D. Endotracheal intubation procedure

Explanation: ***Difficulty of intubation*** - The **Modified Mallampati score** assesses the visibility of pharyngeal structures, which directly correlates with the ease or difficulty of performing **direct laryngoscopy** and **endotracheal intubation**. - A higher Mallampati class (e.g., III or IV) indicates less visibility of the soft palate, uvula, and pillars, suggesting a more difficult airway and increased likelihood of a challenging intubation. *Obstruction of the airway* - While a high Mallampati score might indirectly indicate potential for **airway obstruction** during anesthesia due to anatomical features, its primary purpose is not to diagnose or quantify existing airway obstruction. - Airway obstruction is more directly assessed by monitoring breathing sounds, respiratory effort, and oxygen saturation. *Aspiration-related death* - The **Mallampati score** helps predict the difficulty of securing the airway but does not directly assess the risk of **aspiration**. - Aspiration risk is evaluated based on factors like gastric contents, gag reflex, and patient positioning. *Endotracheal intubation procedure* - The **Modified Mallampati score** helps in **planning the intubation procedure** by identifying potential difficulties but is not a measure of the intubation procedure itself. - It is a **pre-procedure assessment tool** to gauge airway anatomy, not a description or evaluation of the steps involved in endotracheal intubation.

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