Temperature Monitoring — MCQs
Which does not cause malignant hyperthermia –
Hypothermia is used in all except:
A patient aged 24 years is said to have 'severe hypothermia' requiring intensive care management, if his core body temperature is-
Shivering observed in the early part of the postoperative period is due to
Malignant hyperthermia is due to
Adverse effects of hypothermia are all except:
A 72-year-old man undergoes resection of an abdominal aneurysm. He arrives in the ICU with a core temperature of 33°C (91.4°F) and shivering. Which of the following is a physiologic consequence of the shivering?
Artery cannulated most commonly for invasive blood pressure monitoring is:
About diagnosing air embolism with transesophageal echocardiography, which of the following is false?
Which of the following anesthetic agents does not trigger malignant hyperthermia?
Temperature Monitoring Indian Medical PG Practice Questions and MCQs
Question 1: Which does not cause malignant hyperthermia –
- A. Enflurane
- B. N2O (Correct Answer)
- C. Desflurane
- D. Isoflurane
Explanation: ***N2O*** - **Nitrous oxide** is a weak inhaled anesthetic and does not trigger **malignant hyperthermia** (MH). - Its mechanism of action does not involve the **ryanodine receptor** or calcium release, which are central to MH pathophysiology. *Enflurane* - **Enflurane** is a volatile inhaled anesthetic that is a known trigger for **malignant hyperthermia**. - It induces uncontrolled **intracellular calcium release** in skeletal muscle, leading to hypermetabolism. *Desflurane* - **Desflurane** is another potent volatile inhaled anesthetic and a classic trigger agent for **malignant hyperthermia**. - Its use can result in a rapid onset of MH symptoms due to its quick pharmacokinetics. *Isoflurane* - **Isoflurane** is also a volatile inhaled anesthetic and is well-established as a trigger for **malignant hyperthermia**. - Like other volatile agents, it can bind to the **ryanodine receptor** (RyR1), causing excessive calcium efflux.
Question 2: Hypothermia is used in all except:
- A. Hyperthermia
- B. Arrhythmia (Correct Answer)
- C. Neonatal asphyxia
- D. Cardiac surgery
Explanation: ***Arrhythmia*** - While sometimes used in specific cardiac procedures or to protect organs during cardioplegia, **therapeutic hypothermia** is not a primary treatment for general cardiac arrhythmias due to its potential to exacerbate certain rhythm disturbances. - **Hypothermia** can paradoxically induce **arrhythmias** itself, particularly bradycardia and ventricular fibrillation, making it unsuitable for general arrhythmia management [1]. *Hyperthermia* - **Therapeutic hypothermia** is used to reduce high body temperatures in conditions like **malignant hyperthermia** and **heatstroke** to prevent organ damage [2]. - By actively cooling the body, hypothermia counteracts the harmful effects of sustained, extreme elevations in body temperature. *Neonatal asphyxia* - **Therapeutic hypothermia** is a standard treatment for **neonatal hypoxic-ischemic encephalopathy** (HIE) to reduce brain injury. - Cooling the infant's body temperature helps to slow down damaging metabolic processes after oxygen deprivation. *Cardiac surgery* - **Hypothermia** is commonly employed during **cardiac surgery** to protect organs, especially the brain and heart, from ischemia during periods of reduced blood flow. - **Moderate to deep hypothermia** can significantly reduce metabolic demands, extending the safe duration of cardiopulmonary bypass and aortic cross-clamping [3].
Question 3: A patient aged 24 years is said to have 'severe hypothermia' requiring intensive care management, if his core body temperature is-
- A. <25degC
- B. <28degC (Correct Answer)
- C. <32degC
- D. <35degC
Explanation: ***<28degC*** - Core body temperatures falling below **28°C** are classified as severe hypothermia, as per most clinical guidelines [1], [2]. - This level of hypothermia requires **intensive care management** due to the high risk of severe complications like **cardiac arrhythmias**, especially **ventricular fibrillation** [2]. *<25degC* - While a core temperature of less than **25°C** is certainly a critical medical emergency, it falls under the category of **profound hypothermia**, which is even more severe than general severe hypothermia. - At this temperature, the risk of **cardiac arrest** and multi-organ failure is exceptionally high, and it represents an extreme rather than the general threshold for severe. *<32degC* - A core body temperature between **28°C and 32°C** is classified as **moderate hypothermia** [2]. - While requiring medical attention and monitoring, it is generally not deemed "severe" enough to immediately necessitate the same level of intensive critical care intervention as temperatures below 28°C. *<35degC* - A core body temperature between **32°C and 35°C** is classified as **mild hypothermia**. - At this stage, the body's compensatory mechanisms are often still active, and initial management typically involves passive or active external rewarming, without immediate intensive care.
Question 4: Shivering observed in the early part of the postoperative period is due to
- A. Hypothermia (Correct Answer)
- B. Pain
- C. Emergence delirium
- D. Drug withdrawal
Explanation: **Hypothermia** - Shivering is a primary physiological response to **hypothermia**, an attempt by the body to generate **heat** by increasing muscle activity. - Patients often experience a drop in core body temperature during surgery due to factors like cold operating rooms, exposed body cavities, and anesthetic effects. *Pain* - While pain can cause discomfort and muscle tension, it typically does not manifest as generalized **shivering** in the early postoperative period. - Pain is usually managed with analgesics, and shivering is more indicative of a **thermoregulatory disturbance**. *Emergence delirium* - Emergence delirium is characterized by disorientation, agitation, and non-purposeful movements, but not primarily by **shivering**. - This condition is often related to the residual effects of anesthetic agents or anxiety upon waking. *Drug withdrawal* - Drug withdrawal can cause tremors and agitation, but it is less likely to present as **shivering** in the immediate postoperative period in a patient without a known history of substance dependence. - Withdrawal symptoms typically manifest hours to days after the cessation of the drug, depending on its half-life.
Question 5: Malignant hyperthermia is due to
- A. Isoflurane
- B. Halothane
- C. Scoline
- D. All of the options (Correct Answer)
Explanation: ***All of the options*** - Malignant hyperthermia is a rare, **life-threatening condition** triggered by exposure to certain anesthetic agents, including **volatile inhalational anesthetics** (like isoflurane and halothane) and the **depolarizing muscle relaxant succinylcholine (scoline)**. - The condition is characterized by a rapid, uncontrollable increase in body temperature, muscle rigidity, and metabolic acidosis due to an uncontrolled release of **calcium** from the sarcoplasmic reticulum in muscle cells. *Isoflurane* - **Isoflurane** is a **volatile inhalational anesthetic** known to be a potent trigger for malignant hyperthermia in susceptible individuals. - It works by affecting ion channels in nerve cells, but in MH-susceptible individuals, it can induce massive calcium release in skeletal muscle. *Halothane* - **Halothane**, another **volatile inhalational anesthetic**, was historically one of the most common triggers for malignant hyperthermia. - While it is less commonly used today due to its potential for liver toxicity and cardiac arrhythmias, it remains a significant trigger for MH. *Scoline* - **Scoline** (also known as **succinylcholine**) is a **depolarizing muscle relaxant** and is a well-known trigger for malignant hyperthermia. - It acts on acetylcholine receptors, causing initial muscle fasciculations followed by prolonged relaxation, but in MH-susceptible patients, it can initiate an uncontrolled calcium release in muscle cells.
Question 6: Adverse effects of hypothermia are all except:
- A. Decreased peripheral resistance (Correct Answer)
- B. Cardiac arrhythmias
- C. Renal failure
- D. Reversible coagulopathy
Explanation: ***Decreased peripheral resistance*** - Hypothermia causes **vasoconstriction** in the periphery, which leads to **increased peripheral resistance**, not decreased. - This effect helps redirect blood flow to vital organs during cold exposure. *Cardiac arrhythmias* - Hypothermia significantly increases the risk of **cardiac arrhythmias**, especially **ventricular fibrillation**, as myocardial excitability changes [1]. - The most common ECG changes include a **prolonged PR interval**, **widened QRS complex**, and the presence of **J (Osborn) waves** [2]. *Renal failure* - Severe hypothermia can lead to **acute kidney injury** or **renal failure** due to reduced renal blood flow, direct cellular damage, and rhabdomyolysis [1], [3]. - Decreased kidney function can also impair the excretion of drugs and metabolic waste products. *Reversible coagulopathy* - Hypothermia causes a **reversible coagulopathy** due to impaired platelet function, decreased activity of coagulation factors, and increased fibrinolysis. - This can manifest as increased bleeding tendencies, particularly in trauma patients.
Question 7: A 72-year-old man undergoes resection of an abdominal aneurysm. He arrives in the ICU with a core temperature of 33°C (91.4°F) and shivering. Which of the following is a physiologic consequence of the shivering?
- A. Rising mixed venous O2 saturation
- B. Rising base excess
- C. Increased production of CO2 (Correct Answer)
- D. Decreased consumption of O2
Explanation: ***Increased production of CO2*** - Shivering is a physiological response to **hypothermia** that involves rapid, involuntary muscle contractions. - This muscle activity significantly increases **metabolic rate**, leading to higher oxygen consumption and consequently, increased **carbon dioxide production**. *Rising mixed venous O2 saturation* - Shivering increases tissue oxygen demand, therefore, the peripheral tissues extract more oxygen from the blood. - This increased extraction would lead to a *decrease* in mixed venous O2 saturation, as less oxygen returns to the heart. *Rising base excess* - Increased metabolic activity from shivering can lead to the production of **lactic acid** if oxygen demand outstrips supply (anaerobic metabolism). - This would result in **metabolic acidosis**, which is characterized by a *negative* base excess (or decreasing base excess), not a rising one. *Decreased consumption of O2* - Shivering is an active process that requires energy, and this energy is primarily generated through **aerobic metabolism** in the muscles. - Therefore, shivering leads to a significant *increase* in oxygen consumption, not a decrease.
Question 8: Artery cannulated most commonly for invasive blood pressure monitoring is:
- A. Radial artery (Correct Answer)
- B. Femoral artery
- C. Ulnar artery
- D. Carotid artery
Explanation: ***Radial artery*** - The **radial artery** is the most common site due to its **superficial location**, ease of access, and presence of collateral circulation via the **ulnar artery** (Allen's test). - This allows for safe cannulation with a low risk of **ischemia** to the hand, even if the radial artery becomes thrombosed. *Femoral artery* - The **femoral artery** is used, especially in emergencies or when radial access is not possible, but it carries a higher risk of **infection** and hematoma. - Its deep location can make cannulation more challenging, and complications like **retroperitoneal hemorrhage** are possible. *Ulnar artery* - The **ulnar artery** is generally avoided for primary arterial cannulation because the radial artery is the more dominant blood supply to the hand. - Cannulating the ulnar artery carries a higher risk of **ischemia** to the hand if an anatomical anomaly exists or if the radial artery's collateral flow is compromised. *Carotid artery* - The **carotid artery** is rarely, if ever, cannulated for routine invasive blood pressure monitoring due to the significant risk of **neurological complications** such as stroke or cerebral embolism. - This artery supplies blood directly to the brain, and any damage or clot formation during cannulation could have devastating consequences.
Question 9: About diagnosing air embolism with transesophageal echocardiography, which of the following is false?
- A. It can quantify the volume of air embolized.
- B. It is a very sensitive investigation.
- C. Interferes with Doppler when used together. (Correct Answer)
- D. Continuous monitoring is needed to detect venous embolism.
Explanation: ***Interferes with Doppler when used together.*** - Transesophageal echocardiography (TEE) is often used in conjunction with **Doppler ultrasonography** to assess blood flow and cardiac function simultaneously, without significant interference. - **Doppler** can help detect turbulent flow caused by air emboli, while TEE provides direct visualization of the heart chambers and great vessels. *It can quantify the volume of air embolized.* - TEE can visualize air emboli within the cardiac chambers but **cannot accurately quantify the precise volume** of air embolized. - TEE provides qualitative assessment and can estimate the **severity of air emboli** (e.g., small, moderate, large shower), but not a specific volume in milliliters. *It is a very sensitive investigation.* - TEE is indeed a **highly sensitive method** for detecting air emboli, even small amounts, within the heart and major vessels. - Its proximity to the heart allows for **excellent resolution** and clear visualization, making it superior to precordial Doppler for detecting intracardiac air. *Continuous monitoring is needed to detect venous embolism.* - **Venous air emboli** can be intermittent or transient, making continuous TEE monitoring crucial for their detection during high-risk procedures. - Without continuous monitoring, a brief embolic event could be **missed**, as air can quickly pass through the right heart or dissipate.
Question 10: Which of the following anesthetic agents does not trigger malignant hyperthermia?
- A. Isoflurane
- B. Suxamethonium
- C. Halothane
- D. Thiopentone (Correct Answer)
Explanation: ***Thiopentone*** - **Thiopentone** is an **intravenous anesthetic agent** that does not trigger **malignant hyperthermia** because it does not interact with the **ryanodine receptor (RyR1)** or lead to uncontrolled calcium release from the sarcoplasmic reticulum. - It is a **barbiturate** and its mechanism of action involves enhancing the effect of **GABA** at the GABA-A receptor, unrelated to the calcium dysregulation seen in malignant hyperthermia. *Isoflurane* - **Isoflurane** is a **volatile anesthetic agent** (inhaled) known to be a potent trigger of **malignant hyperthermia** in susceptible individuals. - It directly activates the **ryanodine receptor type 1 (RyR1)**, leading to a massive and uncontrolled release of calcium from the **sarcoplasmic reticulum** in skeletal muscle cells. *Suxamethonium* - **Suxamethonium** (succinylcholine) is a **depolarizing neuromuscular blocker** that can trigger or exacerbate **malignant hyperthermia**, especially when given with volatile anesthetics. - It causes muscle fasciculations and can lead to a sustained muscle contraction and metabolic derangements characteristic of the condition. *Halothane* - **Halothane** is a prototype **volatile anesthetic agent** and is one of the most well-known and potent triggers of **malignant hyperthermia**. - Its use has significantly decreased due to its association with malignant hyperthermia and hepatotoxicity, but it serves as a classic example of an agent that causes massive calcium release from the **sarcoplasmic reticulum**.
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