Which set of arterial blood gases will the nurse expect to find in a client who developed a pulmonary embolism 15 minutes ago?
pH, 7.30; HCO3, 22 mEq/L; PCO2, 60 mm Hg; PO2, 66 mm Hg
pH, 7.38; HCO3, 22 mEq/L; PCO2, 45 mm Hg; PO2, 96 mm Hg
pH, 7.47; HCO3, 23 mEq/L; PCO2, 25 mm Hg; PO2, 82 mm Hg
pH, 7.30; HCO3, 28 mEq/L; PCO2, 65 mm Hg; PO2, 75 mm Hg
The Correct Answer is C
Rationale:
A. pH 7.30; HCO3 22; PCO2 60; PO2 66 is incorrect because this reflects respiratory acidosis (low pH, elevated CO2). In the early stages of a pulmonary embolism, the client typically hyperventilates due to hypoxemia and anxiety, which lowers CO2 rather than increasing it. Elevated CO2 is more consistent with hypoventilation, not acute embolism.
B. pH 7.38; HCO3 22; PCO2 45; PO2 96 is incorrect because these values are essentially normal. A pulmonary embolism causes impaired perfusion and ventilation-perfusion (V/Q) mismatch, leading to hypoxemia. Normal oxygen levels would not be expected 15 minutes after an acute embolic event.
C. pH 7.47; HCO3 23; PCO2 25; PO2 82 is correct. Fifteen minutes after the onset of a Pulmonary embolism, the client typically develops acute respiratory alkalosis. The embolus blocks pulmonary blood flow, causing hypoxemia. In response, the client hyperventilates to compensate for low oxygen levels. Hyperventilation decreases PaCO2 (25 mm Hg), which increases pH (7.47), producing respiratory alkalosis. The HCO3 remains normal because renal compensation has not yet occurred (it takes hours to days). The PO2 is decreased (82 mm Hg), reflecting impaired oxygen exchange.
D. pH 7.30; HCO3 28; PCO2 65; PO2 75 is incorrect because this reflects respiratory acidosis with metabolic compensation (elevated CO2 and elevated bicarbonate). This pattern would be more consistent with chronic respiratory failure, not the early phase of an acute pulmonary embolism.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is B
Explanation
Rationale:
A. Prednisone is a corticosteroid used to suppress inflammation and immune responses in conditions such as asthma, autoimmune diseases, and allergic reactions. Prednisone does not have vasodilatory effects and does not interact with sildenafil in a way that could cause life-threatening complications. Therefore, taking sildenafil while on prednisone is not contraindicated.
B. Nitroglycerine is a nitrate commonly prescribed for angina or ischemic heart disease. Nitrates work by releasing nitric oxide, which causes vasodilation and decreased blood pressure. Sildenafil, a phosphodiesterase-5 (PDE5) inhibitor, also enhances nitric oxide-mediated vasodilation, particularly in the systemic and pulmonary circulation. When these two drugs are taken together, the effects add synergistically, which can lead to severe, life-threatening hypotension, syncope, myocardial ischemia, or even cardiac arrest. Because of this risk, the combination of sildenafil and nitrates is considered an absolute contraindication. Patients must be screened carefully for any nitrate use, including short-acting nitroglycerin for chest pain, before starting sildenafil.
C. Phenytoin is an anticonvulsant used to control seizures. It is metabolized by the liver’s cytochrome P450 system and can increase the metabolism of sildenafil, reducing its effectiveness. While this may require dose adjustment or timing considerations, it does not pose a life-threatening risk and is therefore not an absolute contraindication.
D. Metronidazole is an antibiotic used to treat anaerobic bacterial infections. It has no direct cardiovascular interactions with sildenafil and does not cause dangerous hypotension. There may be minor pharmacokinetic interactions in some cases, but these are not contraindications.
Correct Answer is A
Explanation
Rationale:
A. Decrease in cardiac output is correct. Positive end-expiratory pressure (PEEP) increases intrathoracic pressure, which can reduce venous return to the heart, thereby decreasing preload. Reduced preload lowers stroke volume and cardiac output, resulting in hypotension. This is a well-recognized hemodynamic effect of PEEP, especially in patients who are hypovolemic or have borderline cardiac function.
B. Hypovolemic shock is incorrect. While hypovolemia can cause hypotension, the sudden drop in blood pressure immediately after PEEP initiation points to a mechanical effect on cardiac output rather than ongoing fluid loss.
C. Increase in venous return is incorrect. PEEP actually reduces venous return due to increased intrathoracic pressure, so an increase in venous return would tend to raise blood pressure, not decrease it.
D. Neurogenic shock is incorrect. Neurogenic shock results from loss of sympathetic tone after spinal cord injury, causing hypotension and bradycardia. This patient’s hypotension occurred immediately after PEEP initiation, which is a mechanical effect, not a neurogenic event.
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