A patient is exposed to the hepatitis B virus (HBV) and develops immunity against future infections. Which type of immunity is primarily responsible for this protection?

Correct Answer: C

Rationale: Humoral immunity is primarily responsible for protecting against infections by pathogens like viruses. In the case of the hepatitis B virus (HBV), the individual is exposed to the virus and develops immunity, which is typically mediated by antibodies produced by B cells. These antibodies circulate in the blood and can neutralize the virus, preventing future infections. This type of immunity is known as humoral immunity, as it involves the production of antibodies that target specific antigens, such as those present on the surface of the hepatitis B virus. In contrast, passive immunity is when antibodies are transferred from an external source, innate immunity provides immediate, non-specific defenses against pathogens, and cell-mediated immunity involves the activation of T cells to combat intracellular pathogens.

Correct Answer: A

Rationale: Selective IgA deficiency is a primary immunodeficiency disorder characterized by low or absent levels of immunoglobulin A (IgA) in the blood. Since IgA plays a crucial role in mucosal immunity and defense against pathogens at mucosal surfaces, individuals with this deficiency are more susceptible to recurrent bacterial infections, particularly of the respiratory and gastrointestinal tracts. In contrast, severe combined immunodeficiency (SCID) is a more severe immunodeficiency disorder affecting T and B lymphocytes, chronic granulomatous disease (CGD) is a disorder of phagocytes, and autoimmune hemolytic anemia is an autoimmune disease involving red blood cells, none of which are directly associated with selective IgA deficiency.

Correct Answer: B

Rationale: In a patient experiencing an acute asthma exacerbation with severe respiratory distress and hypoxemia, the most appropriate intervention is to initiate non-invasive positive pressure ventilation (NIPPV). NIPPV can help improve ventilation, decrease work of breathing, and correct hypoxemia by providing positive pressure to keep the airways open, reduce air trapping, and increase the elimination of carbon dioxide. This intervention can help improve oxygenation and reduce the need for invasive mechanical ventilation in patients with severe asthma exacerbations. Administering high-flow oxygen via nasal cannula alone may not provide enough support for patients with severe respiratory distress. Nebulized albuterol/ipratropium combination therapy and intravenous corticosteroid therapy are also important treatments for asthma exacerbations but are not the first-line interventions for patients with severe respiratory distress and hypoxemia.

Correct Answer: C

Rationale: In a pregnant patient with suspected pulmonary embolism (PE), the most appropriate imaging modality for evaluation is contrast-enhanced computed tomography (CT) pulmonary angiography. This imaging technique has been shown to be safe for the fetus when necessary, especially if the benefits of making a diagnosis outweigh the minimal risks associated with radiation exposure. It provides quick and accurate detection of PE with high sensitivity and specificity.

Correct Answer: A

Rationale: In this case, the patient is experiencing respiratory acidosis as indicated by the low pH (7.28), elevated PaCO2 (65 mmHg), and elevated HCO3- (30 mEq/L). The primary acid-base disturbance is respiratory acidosis due to the retention of carbon dioxide (PaCO2 >45 mmHg) leading to an increase in HCO3- as a compensatory mechanism to maintain pH within normal limits. The elevated HCO3- levels (metabolic compensation) are trying to counterbalance the increased PaCO2 levels (respiratory acidosis) by increasing bicarbonate to attempt to normalize the pH. Overall, the ABG analysis shows respiratory acidosis with metabolic compensation in this COPD patient with an acute exacerbation and severe dyspnea.