The arterial blood gas result of pH 7.30, PaCO2 50 mmHg, and HCO3 24 mEq/L represents which acid-base imbalance?
Metabolic alkalosis.
Respiratory acidosis.
Respiratory alkalosis.
Metabolic acidosis.
The Correct Answer is B
Choice A rationale
Metabolic alkalosis occurs when the pH is above 7.45 and the bicarbonate level is above 26 mEq/L. This condition is typically caused by a loss of hydrogen ions or an excess of bicarbonate. In this clinical scenario, the pH is 7.30 and the bicarbonate is 24 mEq/L, which is within the normal range of 22 to 28 mEq/L. Therefore, the imbalance cannot be classified as metabolic alkalosis based on these laboratory values.
Choice B rationale
Respiratory acidosis is characterized by a pH below 7.35 and a PaCO2 above 45 mmHg. The normal range for pH is 7.35 to 7.45, and for PaCO2 is 35 to 45 mmHg. In this case, the pH of 7.30 indicates acidemia, and the elevated PaCO2 of 50 mmHg identifies the respiratory system as the cause. The normal bicarbonate level suggests that renal compensation has not yet occurred, confirming an acute respiratory acid-base imbalance.
Choice C rationale
Respiratory alkalosis involves a pH greater than 7.45 and a PaCO2 less than 35 mmHg. This state is generally caused by hyperventilation, which leads to the excessive elimination of carbon dioxide from the lungs. Since the patient in this scenario has a low pH of 7.30 and a high carbon dioxide level of 50 mmHg, the laboratory data is the direct opposite of what is required for a diagnosis of respiratory alkalosis.
Choice D rationale
Metabolic acidosis is defined by a pH below 7.35 and a bicarbonate level below 22 mEq/L. While the pH of 7.30 in this scenario indicates acidosis, the bicarbonate level of 24 mEq/L is perfectly within the standard reference range of 22 to 28 mEq/L. Because the primary abnormality is found in the PaCO2 level rather than the bicarbonate level, the source of the acid-base disturbance is respiratory and not metabolic in origin.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is D
Explanation
Choice D rationale
Dysrhythmias are the most common and immediate complication after a myocardial infarction. When heart muscle cells are damaged or die due to lack of oxygen, the electrical conduction system of the heart is disrupted. The ischemic tissue can become irritable, leading to abnormal electrical impulses. These can range from relatively harmless premature contractions to life-threatening rhythms like ventricular tachycardia or ventricular fibrillation, which are the leading causes of death in the early post-infarction period.
Choice A rationale
Endocarditis is an infection of the inner lining of the heart chambers and valves, usually caused by bacteria entering the bloodstream. While a myocardial infarction causes structural damage, it does not inherently introduce pathogens into the heart to cause an infection. Endocarditis is more commonly associated with intravenous drug use, dental procedures, or prosthetic heart valves. Myocardial infarction affects the muscular layer (myocardium) rather than the endocardial lining through an infectious process.
Choice B rationale
Hyperthyroidism is an endocrine disorder characterized by the overproduction of thyroid hormone by the thyroid gland. It is not a complication of a myocardial infarction. While hyperthyroidism can cause cardiac issues like tachycardia or atrial fibrillation which might strain the heart, the reverse is not true. A heart attack is a localized vascular and muscular event in the heart and has no pathophysiological mechanism that would cause the thyroid gland to increase its hormone production.
Choice C rationale
Rheumatic fever is an inflammatory disease that can develop as a complication of an untreated or inadequately treated strep throat infection caused by group A Streptococcus bacteria. It can lead to permanent damage to the heart valves, known as rheumatic heart disease. This process is entirely distinct from a myocardial infarction, which is caused by coronary artery occlusion and ischemia. There is no link between the necrosis of heart muscle and the autoimmune response triggered by a streptococcal infection.
Correct Answer is D
Explanation
Choice A rationale
Heart rate and force of contraction irregularities typically refer to arrhythmias or dysrhythmias. While these can occur as a consequence of myocardial ischemia or damage, they do not define the underlying process of the infarction itself. Arrhythmias result from disrupted electrical conduction pathways within the heart muscle. In a myocardial infarction, the primary issue is the loss of blood supply, not merely a change in the rhythm or the mechanical strength of the heartbeat.
Choice B rationale
A temporary vasospasm that occurs in a coronary artery is known as Prinzmetal or variant angina. This condition involves a sudden constriction of the vessel wall which reduces blood flow but is usually transient and does not lead to permanent tissue death if relieved quickly. Myocardial infarction is characterized by a permanent or prolonged interruption of flow. Vasospasm may contribute to ischemia, but it is distinct from the necrotic process seen in a classic heart attack.
Choice C rationale
Cardiac output being insufficient to meet the metabolic needs of the body is the clinical definition of heart failure. While a myocardial infarction can lead to heart failure by damaging the pump mechanism, they are separate clinical entities. Heart failure is a chronic or acute syndrome of reduced pumping efficiency, whereas an infarction is an acute ischemic event. One describes the systemic result of poor pumping, while the other describes the cellular death of the heart.
Choice D rationale
Myocardial infarction is defined by the total obstruction of a coronary artery, often due to a ruptured atherosclerotic plaque and subsequent thrombus formation. This blockage leads to prolonged ischemia, which eventually results in myocardial necrosis, or irreversible cell death. The lack of oxygenated blood prevents the production of ATP, leading to cell membrane rupture and the release of cardiac biomarkers like troponin into the bloodstream. This tissue death is the hallmark of an infarction.
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