A patient's blood pressure drops from 120/76 to 90/60 mm Hg as soon as positive end-expiratory pressure is initiated for the treatment of hypoxemia. What is the most likely cause of this decrease in blood pressure?
Decrease in cardiac output
Hypovolemic shock
Increase in venous return
Neurogenic shock
The Correct Answer is A
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.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
Rationale:
A. CPAP (Continuous Positive Airway Pressure) and BiPAP (Bilevel Positive Airway Pressure) are forms of noninvasive positive pressure ventilation (NIPPV). They are versatile tools in respiratory care and can be used for multiple purposes, including supporting oxygenation, reducing the work of breathing, and preventing intubation when appropriate.
B. Patients with conditions such as acute exacerbations of asthma or COPD often benefit from a combination of NIPPV and pharmacologic therapy. Steroids reduce airway inflammation, bronchodilators open the airways, and CPAP or BiPAP improves alveolar ventilation.
C. NIPPV can provide temporary respiratory support in patients with respiratory distress or failure, potentially avoiding or delaying the need for invasive mechanical ventilation. This is particularly useful in patients with exacerbations of chronic respiratory diseases or pulmonary edema.
D. CPAP or BiPAP can be used as part of a weaning strategy from invasive mechanical ventilation. They provide partial ventilatory support while allowing the patient to resume spontaneous breathing, facilitating a smoother transition and reducing complications associated with prolonged intubation.
Correct Answer is B
Explanation
Rationale:
A. PaCO2 represents the partial pressure of carbon dioxide in arterial blood and reflects the respiratory component of acid-base balance. In metabolic acidosis, the primary problem is low bicarbonate (HCO3-). The body often compensates with hyperventilation (Kussmaul respirations) to blow off CO2, which lowers PaCO2, not increases it. A PaCO2 above 45 mm Hg would indicate hypoventilation and could worsen acidosis.
B. Metabolic acidosis is characterized by a decrease in blood pH (<7.35) due to excess acid accumulation (e.g., lactic acidosis, ketoacidosis, renal failure) or loss of bicarbonate (e.g., diarrhea). The low pH is the hallmark finding in metabolic acidosis and confirms the acidic state of the blood.
C. PaO2 indicates the oxygen level in arterial blood. Metabolic acidosis does not directly affect oxygenation, so a PaO2 below 70 mm Hg is not a defining feature of metabolic acidosis. Low PaO2 may occur in respiratory or hypoxic conditions, but it is not specific to metabolic acidosis.
D. HCO3 (bicarbonate) is low (<22 mEq/L) in metabolic acidosis because the body has either lost bicarbonate or accumulated acids that consume bicarbonate. An HCO3 above 26 mEq/L would indicate metabolic alkalosis or compensation for chronic respiratory acidosis, not metabolic acidosis.
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