Temperature regulation US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Temperature regulation. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Temperature regulation US Medical PG Question 1: A 37-year-old man with a history of schizophrenia, obesity, anxiety, recurrent pneumonia, and depression is brought to the emergency department. He was recently discharged from inpatient psychiatric care where he was treated for an acute psychotic episode with fluphenazine and started on a new antidepressant. One week after discharge, during a period of cold weather, he is found outdoors confused and poorly dressed. His rectal temperature is 93.2°F (34°C). Which of the following medications is most likely contributing to his hypothermia?
- A. Fluphenazine (Correct Answer)
- B. Valproic acid
- C. Diphenhydramine
- D. Fluoxetine
- E. Lithium
Temperature regulation Explanation: **Fluphenazine**
- **First-generation antipsychotics** like fluphenazine can impair the body's ability to **thermoregulate** by interfering with dopaminergic pathways in the hypothalamus, increasing susceptibility to hypothermia in cold environments.
- Given the patient's recent discharge from inpatient care and exposure to cold weather while poorly dressed, the addition of an antipsychotic affecting thermoregulation strongly contributes to his hypothermia.
*Valproic acid*
- Valproic acid is an **anticonvulsant** and **mood stabilizer** primarily used for bipolar disorder and epilepsy.
- While it can have various side effects, **hypothermia** is not a commonly reported or significant side effect of valproic acid.
*Diphenhydramine*
- Diphenhydramine is an **antihistamine** with significant **sedative** and **anticholinergic** properties.
- While it can cause sedation and anticholinergic effects that might impact a patient's awareness or ability to seek shelter, it is not directly implicated in causing hypothermia through thermoregulatory dysfunction.
*Fluoxetine*
- Fluoxetine is a **selective serotonin reuptake inhibitor (SSRI)** commonly used for depression and anxiety.
- While SSRIs can have various side effects, **hypothermia** is not a characteristic or significant side effect of fluoxetine.
*Lithium*
- Lithium is a **mood stabilizer** used primarily for bipolar disorder.
- **Hypothyroidism** is a known side effect of long-term lithium use, which could theoretically contribute to an inability to maintain body temperature, but it is less likely to cause acute hypothermia compared to antipsychotics directly affecting thermoregulation.
Temperature regulation US Medical PG Question 2: A 15-year-old boy is brought to the emergency department by his father 10 minutes after falling into a frozen lake during ice fishing. He was in the water for less than 1 minute before his father managed to pull him out. On arrival, his clothes are still wet and he appears scared. His body temperature is 36.2°C (97.1°F), pulse is 102/min, blood pressure is 133/88 mm Hg. Which of the following mechanisms contributes most to maintaining this patient's core body temperature?
- A. Inhibition of the thyroid axis
- B. Involuntary muscular contractions (Correct Answer)
- C. Activation of thermogenin
- D. Increase in hypothalamic set point
- E. Contraction of arrector pili muscles
Temperature regulation Explanation: ***Involuntary muscular contractions***
- **Shivering** is the body's primary mechanism for increasing heat production in response to cold stress, involving rapid, involuntary muscle contractions to generate heat.
- This process significantly increases the **metabolic rate** and heat output, crucial for maintaining core body temperature when exposed to cold environments.
*Inhibition of the thyroid axis*
- The **thyroid axis** is generally activated in response to chronic cold exposure to increase basal metabolic rate, not inhibited.
- Inhibition of thyroid hormones would lead to a decrease in metabolism and heat production, worsening hypothermia.
*Activation of thermogenin*
- **Thermogenin** (uncoupling protein 1) is found primarily in **brown adipose tissue** and its activation leads to non-shivering thermogenesis.
- While present in infants and some adults, shivering is a much more significant and rapid response to acute cold in a 15-year-old.
*Increase in hypothalamic set point*
- An increase in the **hypothalamic set point** is characteristic of **fever**, where the body aims to achieve a higher temperature.
- In this scenario, the body is trying to maintain its normal set point despite cold exposure, not raise it.
*Contraction of arrector pili muscles*
- **Contraction of arrector pili muscles** causes **piloerection** (goosebumps), which traps a layer of air close to the skin.
- While contributing to insulation, this mechanism is relatively minor in humans compared to the heat generated by shivering.
Temperature regulation US Medical PG Question 3: A 49-year-old woman presents to her primary care physician with fatigue. She reports that she has recently been sleeping more than usual and says her “arms and legs feel like lead” for most of the day. She has gained 10 pounds over the past 3 months which she attributes to eating out at restaurants frequently, particularly French cuisine. Her past medical history is notable for social anxiety disorder. She took paroxetine and escitalopram in the past but had severe nausea and headache while taking both. She has a 10 pack-year smoking history and has several glasses of wine per day. Her temperature is 98.6°F (37°C), blood pressure is 130/65 mmHg, pulse is 78/min, and respirations are 16/min. Physical examination reveals an obese woman with a dysphoric affect. She states that her mood is sad but she does experience moments of happiness when she is with her children. The physician starts the patient on a medication to help with her symptoms. Three weeks after the initiation of the medication, the patient presents to the emergency room with a severe headache and agitation. Her temperature is 102.1°F (38.9°C), blood pressure is 180/115 mmHg, pulse is 115/min, and respirations are 24/min. Which of the following is the mechanism of action of the medication that is most likely responsible for this patient’s symptoms?
- A. Inhibition of serotonin and norepinephrine reuptake
- B. Inhibition of the adrenergic alpha-2 receptor and serotonin-2 and -3 receptors
- C. Inhibition of serotonin reuptake
- D. Partial agonism of serotonin-1A receptor
- E. Inhibition of amine degradation (Correct Answer)
Temperature regulation Explanation: **Inhibition of amine degradation**
- This mechanism of action describes **monoamine oxidase inhibitors (MAOIs)**. Given the patient's symptoms of **hypertensive crisis** (headache, agitation, hypertension, tachycardia, fever) after starting a new medication and her history of **eating French cuisine** (which could include tyramine-rich foods like aged cheeses and wines), an MAOI is the most likely culprit.
- MAOIs prevent the breakdown of **monoamine neurotransmitters** (serotonin, norepinephrine, dopamine, tyramine), leading to their accumulation. In the presence of **tyramine-rich foods**, this can precipitate a **hypertensive crisis** due to excessive norepinephrine release.
*Inhibition of serotonin and norepinephrine reuptake*
- This describes **SNRIs (serotonin-norepinephrine reuptake inhibitors)** or **TCAs (tricyclic antidepressants)**. While these can cause side effects, a sudden and severe **hypertensive crisis** as described, especially without a clear dietary trigger interaction, is less characteristic than with MAOIs.
- The patient's prior negative experiences with paroxetine and escitalopram (SSRIs) might make a physician choose a different class, but the dramatic symptoms point away from typical SNRI/TCA side effects for this presentation.
*Inhibition of the adrenergic alpha-2 receptor and serotonin-2 and -3 receptors*
- This mechanism is characteristic of **mirtazapine**. While mirtazapine can cause sedation and weight gain (presenting symptoms), it does not typically lead to a **hypertensive crisis** of this severity three weeks after initiation, nor does it have severe food interactions like MAOIs.
- Mirtazapine's primary side effects often include sedation, increased appetite, and weight gain, but not the acute constellation observed here.
*Inhibition of serotonin reuptake*
- This describes **SSRIs (selective serotonin reuptake inhibitors)**. The patient had severe nausea and headache with paroxetine and escitalopram, which are SSRIs. While SSRIs can contribute to **serotonin syndrome** (which shares some features like agitation and hyperthermia), the profound **hypertension** and context of food interaction strongly favor an MAOI-induced hypertensive crisis.
- SSRIs are less likely to cause such a severe **hypertensive crisis** acutely, and the patient's history suggests a physician would likely avoid this class due to past adverse reactions.
*Partial agonism of serotonin-1A receptor*
- This is the mechanism of action for **buspirone**, an anxiolytic. Buspirone is generally well-tolerated and does not cause the severe side effects seen in this patient, particularly **hypertensive crisis** or food interactions.
- Buspirone is often used for generalized anxiety disorder, and while the patient has social anxiety, the described adverse event does not align with buspirone's known side effect profile.
Temperature regulation US Medical PG Question 4: A 33-year-old man presents to the emergency department acutely confused. The patient was found down at a local construction site by his coworkers. The patient has a past medical history of a seizure disorder and schizophrenia and is currently taking haloperidol. He had recent surgery 2 months ago to remove an inflamed appendix. His temperature is 105°F (40.6°C), blood pressure is 120/84 mmHg, pulse is 150/min, respirations are 19/min, and oxygen saturation is 99% on room air. Physical exam is notable for a confused man who cannot answer questions. His clothes are drenched in sweat. He is not making purposeful movements with his extremities although no focal neurological deficits are clearly apparent. Which of the following is the most likely diagnosis?
- A. Heat exhaustion
- B. Nonexertional heat stroke
- C. Neuroleptic malignant syndrome
- D. Malignant hyperthermia
- E. Exertional heat stroke (Correct Answer)
Temperature regulation Explanation: ***Exertional heat stroke***
- This diagnosis is supported by the patient's presentation of **hyperthermia** (105°F), **tachycardia**, **confusion**, and a history of working at a **construction site** (suggesting physical exertion in a hot environment).
- The patient's **drenched clothes from sweat** indicate the body's initial attempt to cool down, but the extremely high core temperature and confusion signify a failure of thermoregulation.
*Heat exhaustion*
- While heat exhaustion also involves **sweating** and can present with elevated body temperature, the core temperature is typically **below 104°F (40°C)**, and **marked altered mental status** (like severe confusion) is less common or less severe.
- The patient's temperature of 105°F (40.6°C) and profound confusion are more indicative of heat stroke.
*Nonexertional heat stroke*
- Nonexertional (or classic) heat stroke usually affects populations with **compromised thermoregulation** (e.g., elderly, very young, chronically ill) who are exposed to high environmental temperatures **without significant physical exertion**.
- The patient's age (33) and history of working at a construction site make exertional heat stroke more likely than nonexertional.
*Neuroleptic malignant syndrome*
- NMS is characterized by **fever, muscle rigidity** (often "lead pipe" rigidity), **altered mental status**, and **autonomic instability** (including tachycardia and diaphoresis), and is associated with **antipsychotic medications** like haloperidol.
- However, NMS typically develops **gradually over days to weeks**, not acutely. The key differentiator here is the **clear environmental and exertional context** (construction site work), **acute onset** after being found down, and the **absence of characteristic muscle rigidity** that would be prominent in NMS.
- Heat stroke is more probable given the immediate occupational exposure and clinical timeline.
*Malignant hyperthermia*
- Malignant hyperthermia is a rare, life-threatening condition associated with exposure to certain **anesthetic agents** (e.g., succinylcholine, volatile anesthetics) or, less commonly, severe exertion in susceptible individuals.
- The patient's recent surgery was two months prior, and there is no mention of current exposure to triggers, making it unlikely to be the immediate cause of his acute presentation.
Temperature regulation US Medical PG Question 5: A previously healthy 44-year-old man is brought by his coworkers to the emergency department 45 minutes after he became light-headed and collapsed while working in the boiler room of a factory. He did not lose consciousness. His coworkers report that 30 minutes prior to collapsing, he told them he was nauseous and had a headache. The patient appears sweaty and lethargic. He is not oriented to time, place, or person. The patient’s vital signs are as follows: temperature 41°C (105.8°F); heart rate 133/min; respiratory rate 22/min; and blood pressure 90/52 mm Hg. Examination shows equal and reactive pupils. Deep tendon reflexes are 2+ bilaterally. His neck is supple. A 0.9% saline infusion is administered. A urinary catheter is inserted and dark brown urine is collected. The patient’s laboratory test results are as follows:
Laboratory test
Blood
Hemoglobin 15 g/dL
Leukocyte count 18,000/mm3
Platelet count 51,000/mm3
Serum
Na+ 149 mEq/L
K+ 5.0 mEq/L
Cl- 98 mEq/L
Urea nitrogen 42 mg/dL
Glucose 88 mg/dL
Creatinine 1.8 mg/dL
Aspartate aminotransferase (AST, GOT) 210
Alanine aminotransferase (ALT, GPT) 250
Creatine kinase 86,000 U/mL
Which of the following is the most appropriate next step in patient management?
- A. Dantrolene
- B. Acetaminophen therapy
- C. Hemodialysis
- D. Ice water immersion (Correct Answer)
- E. Evaporative cooling
Temperature regulation Explanation: ***Ice water immersion***
- This patient presents with signs and symptoms consistent with **heat stroke**, including high body temperature (41°C), altered mental status, and a history of working in a hot environment (boiler room). **Rapid aggressive cooling** is the most critical immediate intervention to prevent organ damage.
- **Ice water immersion** is the fastest and most effective cooling method for heat stroke, aiming to reduce core body temperature to less than 39°C (102.2°F) within 30 minutes.
*Dantrolene*
- **Dantrolene** is primarily used to treat **malignant hyperthermia** and **neuroleptic malignant syndrome**, conditions caused by abnormal calcium release in muscle cells, not environmental heat exposure.
- While both conditions involve hyperthermia, the underlying pathophysiology and triggers are different from heat stroke.
*Acetaminophen therapy*
- **Acetaminophen** is an antipyretic that works by inhibiting prostaglandin synthesis in the central nervous system, affecting the hypothalamic thermoregulatory center.
- It is **ineffective** for the hyperthermia seen in heat stroke, which is due to a failure of thermoregulation rather than an altered hypothalamic set point, and could potentially worsen liver injury.
*Hemodialysis*
- **Hemodialysis** is indicated for severe **renal failure**, drug overdose, or certain electrolyte imbalances. Although this patient has acute kidney injury (elevated BUN and creatinine, dark urine suggestive of rhabdomyolysis), aggressive cooling is the immediate life-saving intervention for heat stroke.
- While renal support might be necessary later if kidney injury progresses, it is not the most appropriate *initial* next step for hyperthermia and altered mental status.
*Evaporative cooling*
- **Evaporative cooling** (e.g., spraying with lukewarm water and using fans) is a cooling method that can be effective, particularly in environments with low humidity.
- However, for severe heat stroke with a temperature as high as 41°C, **ice water immersion** provides a more rapid and aggressive temperature reduction, which is crucial for improving outcomes.
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