The arterial blood gas results of pH 7.55, PaCO2 40 mmHg, and HCO3 32 mEq/L align with which acid-base imbalance?

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.

Choice A rationale

Kidney stones, or nephrolithiasis, cause acute kidney injury by creating a physical obstruction in the urinary tract, either in the ureters or the urethra. This blockage prevents the outflow of urine, leading to increased retrograde pressure within the renal pelvis and parenchyma, which impairs glomerular filtration. Because the problem occurs after the urine has already been formed and is located within the collecting system, it is classified as a post-renal cause of injury.

Choice B rationale

Fluid volume deficit, such as that caused by severe dehydration or hemorrhage, leads to decreased systemic blood volume. This reduction in volume results in decreased renal perfusion pressure, which prevents the kidneys from receiving enough blood to maintain an adequate glomerular filtration rate. Since the injury is caused by factors that reduce blood flow to the kidneys before it reaches the renal vasculature itself, it is categorized as a pre-renal acute kidney injury.

Choice C rationale

Low blood pressure, or hypotension, directly diminishes the mean arterial pressure required to drive blood through the renal arteries and into the glomeruli. Without sufficient pressure, the kidneys cannot effectively filter waste products from the blood, leading to a rise in blood urea nitrogen and creatinine. Similar to fluid volume deficit, the underlying issue is a lack of adequate perfusion to the kidney, which defines this as a pre-renal cause of acute kidney injury.

Choice D rationale

Benign prostatic hypertrophy involves the enlargement of the prostate gland, which can compress the urethra and obstruct the normal flow of urine out of the bladder. This urinary retention creates back-pressure that can eventually damage the kidneys and impair their function if the obstruction is bilateral or sufficiently severe. Like kidney stones, this is an obstructive issue occurring distal to the kidney itself, making it a classic example of a post-renal acute kidney injury.

Choice E rationale

Glomerulonephritis is an inflammatory condition that directly damages the glomeruli, the filtering units within the kidney. This inflammation can be caused by autoimmune reactions or infections and leads to the destruction of the basement membrane and capillary endothelium. Because the pathological process is occurring within the actual tissue and functional units of the kidney, it is classified as an intra-renal, or intrinsic, cause of acute kidney injury, as the damage is internal.