Ricky's grandmother has been suffering from persistent vomiting for two days now.
She appears to be lethargic and weak and has myalgia.
She is noted to have dry mucus membranes and her capillary refill takes >4 seconds.
She is diagnosed as having gastroenteritis and dehydration.
Measurement of arterial blood gas shows pH 7.5, Pa 85 mm Hg, PaCO2 40 mm Hg, and HCO3 34 mmol/VL. What acid-base disorder is shown?
Metabolic Acidosis, with Partial Compensation.
Respiratory Acidosis, with Partial Compensation.
Respiratory Alkalosis, Uncompensated.
Metabolic Alkalosis, Uncompensated.
The Correct Answer is D
Choice A rationale
Metabolic acidosis is characterized by a primary reduction in serum bicarbonate, typically below 22 mmol/L, which drives the pH below the normal range of 7.35. While compensation mechanisms would involve a decrease in PaCO2, the provided arterial blood gas values demonstrate an elevated pH and elevated bicarbonate, which are inconsistent with metabolic acidosis.
Choice B rationale
Respiratory acidosis is primarily defined by an increase in arterial carbon dioxide (PaCO2), above the normal range of 45 mm Hg, leading to a decrease in blood pH below 7.35. Compensation would involve an increase in bicarbonate. The given values, particularly the elevated pH and normal PaCO2, do not align with the characteristics of respiratory acidosis.
Choice C rationale
Respiratory alkalosis is characterized by a primary decrease in PaCO2, below the normal range of 35 mm Hg, leading to an elevated pH above 7.45. Uncompensated means the bicarbonate level remains within the normal range of 22-26 mmol/L. The provided PaCO2 is within normal limits, and bicarbonate is elevated, which contradicts the criteria for respiratory alkalosis.
Choice D rationale
Metabolic alkalosis is characterized by a primary increase in serum bicarbonate (HCO3), typically above the normal range of 26 mmol/L, which results in an elevated blood pH above 7.45. Uncompensated metabolic alkalosis indicates that the PaCO2 remains within its normal range (35-45 mm Hg) as the respiratory system has not yet initiated or completed compensatory hypoventilation. The provided pH of 7.5, PaCO2 of 40 mm Hg, and HCO3 of 34 mmol/L precisely fit this definition.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is C
Explanation
Choice A rationale
Reverse Trendelenburg positions the patient with the head higher than the feet. While this can reduce venous pressure in the lower extremities, it is not the optimal position for infratentorial tumor resection as it may not adequately facilitate venous drainage from the posterior fossa and could increase pressure on the incision site.
Choice B rationale
Semi-Fowlers position, with the head of the bed elevated to 30-45 degrees, is often used for supratentorial surgeries to promote venous drainage. However, for infratentorial tumor removal, this position can put undue pressure on the operative site due to gravity, potentially leading to complications such as swelling and CSF leakage.
Choice C rationale
Positioning the patient flat on their side is the recommended approach after infratentorial surgery. This position prevents pressure on the incision site and promotes optimal venous and cerebrospinal fluid drainage from the posterior fossa. It also helps to prevent complications such as tentorial herniation and brainstem compression.
Choice D rationale
High Fowlers position, with the head of the bed elevated to 60-90 degrees, is generally contraindicated after infratentorial surgery. This position significantly increases pressure on the posterior fossa incision due to gravity and can compromise cerebral venous outflow, potentially leading to increased intracranial pressure and other neurological deficits.
Correct Answer is D
Explanation
Choice A rationale
The Chvostek test assesses for neuromuscular excitability, specifically facial twitching when the facial nerve is tapped. It is used to evaluate for hypocalcemia, not to determine the patency of collateral circulation before an ABG. Performing this test would not provide any relevant information for the safety of obtaining an arterial blood sample.
Choice B rationale
The Blumberg test, also known as rebound tenderness, is used in abdominal assessment to detect peritoneal inflammation. It involves pressing deeply on an area of abdominal tenderness and then quickly releasing the pressure. This test has no relevance to assessing arterial patency or collateral circulation prior to an ABG.
Choice C rationale
The Cushing's test is not a recognized medical test or diagnostic procedure. There is a "Cushing's reflex" which refers to a physiological response to increased intracranial pressure, but this is a clinical sign, not a test performed prior to an ABG. This choice is medically inaccurate in this context.
Choice D rationale
The Allen test is performed prior to obtaining an ABG, especially when considering the radial artery. It assesses the patency of the ulnar artery and ensures adequate collateral blood flow to the hand if the radial artery is compromised during or after the arterial puncture. This prevents potential ischemia to the hand, making it a crucial safety step.
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