Clark Kent is a 54-year-old widower with a history of chronic obstructive pulmonary disease (COPD) who was rushed to the emergency department with increasing shortness of breath, pyrexia, and a productive cough with yellow-green sputum.
He has difficulty communicating because of his inability to complete a sentence.
One of his sons, Jacob, says he has been unwell for three days.
Upon examination, crackles and wheezes can be heard in the lower lobes; he has tachycardia and a bounding pulse.
Measurement of arterial blood gas shows pH 7.3, Paco 68 mm Hg, HCO3 28 mmol/L. How would you interpret this?
Respiratory Acidosis, Uncompensated.
Respiratory Acidosis, with Partial Compensation.
Metabolic Acidosis, Uncompensated.
Metabolic Alkalosis, with Partial Compensation.
The Correct Answer is B
Choice A rationale
Uncompensated respiratory acidosis would exhibit a low pH (normal range 7.35-7.45) and an elevated PaCO2 (normal range 35-45 mmHg), with a bicarbonate level (normal range 22-26 mEq/L) that remains within the normal range. In this scenario, the bicarbonate is elevated, indicating a renal compensatory response has begun.
Choice B rationale
The patient's pH of 7.3 indicates acidosis (normal 7.35-7.45). The PaCO2 of 68 mmHg is elevated (normal 35-45 mmHg), indicating a respiratory origin. The HCO3 of 28 mmol/L is elevated (normal 22-26 mEq/L), signifying that the kidneys are attempting to compensate by retaining bicarbonate. Since the pH is still acidic, but the bicarbonate is responding, it is partially compensated respiratory acidosis.
Choice C rationale
Metabolic acidosis is characterized by a low pH (normal 7.35-7.45) and a low bicarbonate level (normal 22-26 mEq/L). The PaCO2 (normal 35-45 mmHg) would either be normal if uncompensated or low if the respiratory system was compensating. Here, the primary disturbance is respiratory.
Choice D rationale
Metabolic alkalosis presents with an elevated pH (normal 7.35-7.45) and an elevated bicarbonate level (normal 22-26 mEq/L). The PaCO2 (normal 35-45 mmHg) would be normal if uncompensated or elevated if the respiratory system was compensating. This patient's pH is acidic, ruling out alkalosis.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is C
Explanation
Choice A rationale
Respiratory acidosis is characterized by a low pH and an elevated PaCO2. In this scenario, the pH is elevated (7.57), indicating alkalosis, and the PaCO2 (37 mmHg) is within the normal range, not elevated. Therefore, this option is inconsistent with the provided ABG results.
Choice B rationale
Metabolic acidosis is characterized by a low pH and a low bicarbonate level. The patient's pH is elevated (7.57), signifying alkalosis, and the bicarbonate (30 mEq/L) is elevated. These findings contradict the definition of metabolic acidosis.
Choice C rationale
The pH of 7.57 is significantly elevated, indicating alkalosis. The bicarbonate (HCO3) level of 30 mEq/L is elevated above the normal range (22-26 mEq/L), which directly accounts for the alkalosis. The PaCO2 of 37 mmHg is within the normal range (35-45 mmHg), indicating no respiratory compensation has occurred. This complete lack of respiratory compensation points to uncompensated metabolic alkalosis. The loss of gastric acid through the NGT contributes to this condition.
Choice D rationale
Respiratory acidosis is characterized by a low pH and an elevated PaCO2. Here, the pH is high (alkalotic) and the PaCO2 is within normal limits. Thus, this option does not match the observed blood gas values.
Correct Answer is D
Explanation
Choice A rationale
Defecation, while it can occur during severe neurological events due to autonomic dysregulation, is a non-specific sign and not a primary or direct indicator of brain herniation. Brain herniation primarily affects vital centers and cranial nerves, leading to more direct neurological compromise.
Choice B rationale
Pinpoint pupils are typically associated with pontine lesions or opioid overdose due to parasympathetic overactivity. In contrast, brain herniation, especially uncal herniation, often causes ipsilateral pupil dilation due to compression of the oculomotor nerve (cranial nerve III), leading to parasympathetic blockade.
Choice C rationale
Tachycardia, an increased heart rate, can be a non-specific response to stress, pain, or hypovolemia. In the context of brain herniation, as intracranial pressure rises and compresses the brainstem, bradycardia (slowing of the heart rate) is a more characteristic finding due to the Cushing reflex, not tachycardia.
Choice D rationale
Bilateral dilated pupils, especially when fixed and non-reactive to light, are a critical and often late sign of severe brain herniation, indicating significant brainstem compression and widespread damage, particularly to the midbrain's oculomotor nerve nuclei or their pathways. This signifies severe cerebral anoxia or irreversible brain injury.
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