A 42-year-old man injured in a motor vehicle crash suffers a closed head injury. His oxygen saturation decreases. The most appropriate next step is to:

Correct Answer: A

Rationale: The correct answer is A: Obtain a chest x-ray. In a closed head injury with decreased oxygen saturation, it is crucial to rule out potential concomitant injuries like a pulmonary contusion or pneumothorax. Obtaining a chest x-ray will help identify these conditions. Decreasing tidal volume (B) or PEEP (C) may worsen oxygenation. Increasing the rate of assisted ventilations (D) without addressing the underlying cause may not improve oxygen saturation.

Correct Answer: D

Rationale: Step-by-step rationale for why option D is correct: 1. During pregnancy, the hormone relaxin causes the symphysis pubis to widen to accommodate childbirth. 2. This widening of the symphysis pubis is a normal physiological change in pregnancy to facilitate the passage of the baby. 3. It is essential for the baby to pass through the birth canal during labor. 4. Therefore, a widened symphysis pubis is a normal finding in pregnancy. Summary of why other choices are incorrect: A. "Increased residual lung volume" is not normal in pregnancy as lung volume decreases due to the elevation of the diaphragm. B. "Decreased plasma volume" is not normal in pregnancy as plasma volume increases to support the growing fetus. C. "Decreased total RBC mass" is not normal in pregnancy as RBC mass increases to meet the increased oxygen demands.

Correct Answer: A

Rationale: The correct answer is A (10 min). Brain cells start to die within 4-6 minutes without oxygen. After 10 minutes, irreversible damage is likely due to lack of oxygen causing cell death. Choice B (5 min) is too short for significant irreversible damage. Choice C (2 min) is even shorter and wouldn't allow for any meaningful recovery. Choice D (20 min) is too long and underestimates the critical window for preserving brain function.

Correct Answer: C

Rationale: The correct answer is C: Traumatic brain injury. In this scenario, the patient's response to fluid resuscitation indicates that her hemodynamic instability is likely due to ongoing blood loss rather than blunt cardiac injury, inadequate resuscitation, or traumatic brain injury. The improvement in BP and HR after fluid infusion suggests that the patient is responding appropriately to volume replacement, making ongoing blood loss the most likely cause of her hemodynamic changes. Blunt cardiac injury could lead to similar symptoms, but the patient's response to fluid makes it less likely. Inadequate resuscitation would lead to persistent hypotension, which is not the case here. Traumatic brain injury typically does not cause acute hemodynamic changes like the ones observed in this case.

Correct Answer: B

Rationale: The correct answer is B: Dementia. Dementia is characterized by a serious decline in cognitive abilities such as memory, thinking, and reasoning. It is not a terminal illness (A), a heart disease (C), or a chronic disorder (D). Dementia specifically refers to the loss of mental abilities, which distinguishes it from the other choices.