After receiving midazolam and fentanyl prior to a bronchoscopy, an older adult's respiratory rate drops to 8 breaths/minute with periods of apnea. The client's arterial blood gas levels are obtained and evaluated. Which laboratory value indicates respiratory depression that can lead to respiratory arrest if left untreated? Reference Range: pH [7.35 to 7.45] PaCO2 [35 to 45 mm Hg] HCO3 [21 to 28 mEq/L] PaO2 [80 to 100 mm Hg]