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. When a patient with a closed head injury experiences a decrease in oxygen saturation, it is crucial to rule out potential causes such as a pneumothorax or lung contusion, which can compromise ventilation and oxygenation. A chest x-ray will help identify any underlying pulmonary issues. Decreasing tidal volume (B) or PEEP (C) may not address the specific cause of decreased oxygen saturation in this case. Increasing the rate of assisted ventilations (D) without addressing the underlying issue may not be effective and could potentially worsen the patient's condition.

Correct Answer: D

Rationale: Rationale for Correct Answer (D): Widened symphysis pubis is normal in pregnancy due to hormonal changes softening the ligaments, allowing for increased flexibility during childbirth. This physiological adaptation helps in the delivery process. Summary of Incorrect Choices: A: "Increased residual lung volume" is not normal in pregnancy. Respiratory changes include increased tidal volume and minute ventilation, but residual lung volume does not significantly change. B: Decreased plasma volume is not normal in pregnancy. Plasma volume increases to support the growing fetus and maternal circulation. C: Decreased total RBC mass is not normal in pregnancy. Total RBC mass increases to support increased oxygen demands for the mother and fetus.

Correct Answer: A

Rationale: The correct answer is A: "10 min". The brain can be anoxic, or deprived of oxygen, for about 10 minutes before irreversible damage occurs. During oxygen deprivation, brain cells begin to die within minutes, leading to permanent brain damage. Oxygen is essential for brain function and prolonged anoxia can result in cognitive impairment, disability, or even death. Choice B (5 min), C (2 min), and D (20 min) are incorrect because they do not align with the typical timeframe for irreversible brain damage due to oxygen deprivation.

Correct Answer: C

Rationale: The correct answer is C: Traumatic brain injury. In this scenario, the patient's hemodynamic changes are primarily related to fluid resuscitation, as evidenced by the initial response to crystalloid infusion. Traumatic brain injury typically does not cause such acute and direct hemodynamic changes. Ongoing blood loss (choice A) is a common cause of hemodynamic instability and should be considered. Blunt cardiac injury (choice B) can lead to hemodynamic compromise, especially with changes in blood pressure. Inadequate resuscitation (choice D) can also contribute to hemodynamic instability. However, in this case, traumatic brain injury is the least likely cause given the patient's response to fluid infusion and the nature of the presentation.

Correct Answer: B

Rationale: The correct answer is B: Dementia. Dementia is characterized by a significant decline in cognitive function, affecting memory, thinking, and reasoning abilities. Terminal illness (A), heart disease (C), and chronic disorder (D) do not specifically refer to the loss of mental abilities as seen in dementia. Dementia is a specific condition that is distinct from physical illnesses like heart disease and chronic disorders.