Findings in respiratory depression and alveolar hypoventilation:
(1) decline in oxygen saturation
(2) rise in end-tidal CO2
Findings to look for:
(1) oxygen desaturation: decline in oxygen saturation >= 5% for > 5 seconds
(2) hypoxemia: oxygen saturation <= 90% for > 1 minute (severe if < 85%)
(3) rise in carbon dioxide with hypercarbia: ETCO2 >= 50 mm Hg for > 15 seconds
(4) apnea: decrease in exhaled partial pressure of CO2 (< 8 mm Hg) for > 15 seconds
Problems that can arise while monitoring:
(1) sampling CO2 using nasal cannula at the same time as high-flow oxygen administration
(2) sampling CO2 through a nasal cannula in a person who mouth breaths
(3) increase in oxygen saturation associated with high levels of supplemental oxygen
(4) failures by monitoring personnel
Cutaneous monitoring of CO2 can avoid some of the issues in end-tidal monitoring.
Other things that can be helpful to monitor:
(1) pulse, with bradycardia if heart rate < 50 beats per minute
(2) blood pressure, with hypotension if systolic blood pressure < 90 nmm Hg
(3) body temperature in °C
