A. Respiratory alkalosis: Respiratory alkalosis occurs when there is excessive loss of carbon dioxide (CO₂), usually from hyperventilation. The PaCO₂ would be low (typically below 35 mm Hg) and the pH would be elevated above 7.45. However, this client has a high PaCO₂ (68 mm Hg) and a low pH (7.22), which points acidosis, not alkalosis. B. Metabolic alkalosis: Metabolic alkalosis results from increased bicarbonate (HCO₃⁻) or excessive loss of hydrogen ions (as in vomiting or diuretic use). While this client’s bicarbonate is slightly elevated (28 mEq/L), it reflects renal compensation for CO₂ retention, not a primary metabolic process. C. Respiratory acidosis: This ABG pattern—low pH, elevated PaCO₂, and slightly raised bicarbonate—fits respiratory acidosis with partial renal compensation. The low respiratory rate (7/min) indicates hypoventilation, leading to CO₂ retention, increased carbonic acid, and a subsequent drop in pH. This is common postoperatively, especially with sedatives or opioid-induced respiratory depression. D. Metabolic acidosis: Metabolic acidosis is characterized by a low pH and low bicarbonate (HCO₃⁻), often with compensatory hyperventilation to lower PaCO₂. In this case, bicarbonate is not decreased, and the respiratory rate is depressed rather than increased.