A medical device comprising: a first port configured to receive pulse-oximetry measurements (SpO 2 ) of a patient's peripheral arterial blood oxygen saturation during a first time period; a second port configured to receive breathing samples of the patient during a steady-state breathing of the patient during the first time period; and a control unit configured to: determine oxygen partial pressure measurements (P A O 2 ) using the breathing samples of the patient and an oxygen sensor ; determine carbon dioxide partial pressure measurements (P A CO 2 ) using the breathing samples of the patient and a CO2 sensor ; determine at least one of (a) an arterial oxygen partial pressure (P a O 2 ) and (b) an oxygen deficit (P A O 2 - P a O 2 ) of the patient using the pulse-oximetry measurements (SpO 2 ) , the oxygen partial pressure measurements (P A O 2 ) and the carbon dioxide partial pressure measurements (P A CO 2 ) 356); generate one or more signals based on the determining of the at least one of the arterial oxygen partial pressure (P a O 2 ) and the oxygen deficit (P A O 2 - P a O 2 ) of the patient; and notify the patient or a caregiver of the patient of the one or more signals . a first port configured to receive pulse-oximetry measurements (SpO 2 ) of a patient's peripheral arterial blood oxygen saturation during a first time period; a second port configured to receive breathing samples of the patient during a steady-state breathing of the patient during the first time period; and a control unit configured to: determine oxygen partial pressure measurements (P A O 2 ) using the breathing samples of the patient and an oxygen sensor ; determine carbon dioxide partial pressure measurements (P A CO 2 ) using the breathing samples of the patient and a CO2 sensor ; determine at least one of (a) an arterial oxygen partial pressure (P a O 2 ) and (b) an oxygen deficit (P A O 2 - P a O 2 ) of the patient using the pulse-oximetry measurements (SpO 2 ) , the oxygen partial pressure measurements (P A O 2 ) and the carbon dioxide partial pressure measurements (P A CO 2 ) 356); generate one or more signals based on the determining of the at least one of the arterial oxygen partial pressure (P a O 2 ) and the oxygen deficit (P A O 2 - P a O 2 ) of the patient; and notify the patient or a caregiver of the patient of the one or more signals . determine oxygen partial pressure measurements (P A O 2 ) using the breathing samples of the patient and an oxygen sensor ; determine carbon dioxide partial pressure measurements (P A CO 2 ) using the breathing samples of the patient and a CO2 sensor ; determine at least one of (a) an arterial oxygen partial pressure (P a O 2 ) and (b) an oxygen deficit (P A O 2 - P a O 2 ) of the patient using the pulse-oximetry measurements (SpO 2 ) , the oxygen partial pressure measurements (P A O 2 ) and the carbon dioxide partial pressure measurements (P A CO 2 ) 356); generate one or more signals based on the determining of the at least one of the arterial oxygen partial pressure (P a O 2 ) and the oxygen deficit (P A O 2 - P a O 2 ) of the patient; and notify the patient or a caregiver of the patient of the one or more signals . <EOS>