Acute Caremiddle twist
A 63-year-old man with renal colic is receiving morphine 2.5 mg intravenously every 5 minutes on your instruction. He has now had 12.5 mg and says the pain has eased considerably. He is receiving oxygen at 2 L/min by nasal prongs. Respiratory rate is 14/min, oxygen saturation 97%, pulse 74/min and blood pressure 132/78 mmHg. He will be observed in the cubicle for a further 30 minutes before a decision about admission. Which one of the following most reliably detects opioid-induced respiratory depression in this man?