A system configured to monitor the dead space fraction of a subject, the system comprising: a blood gas information interface configured to receive blood gas information related to one or more blood gas parameters that indicate concentrations of one or more molecular species in the blood of a subject; a respiration information interface configured to receive respiration information related to one or more respiration parameters of the breathing of the subject; and a processor configured to execute computer program modules, the computer program modules comprising: a blood gas module configured to obtain values for one or more blood gas parameters from blood gas information received via the blood gas information interface; a respiration parameter module configured to obtain values for one or more respiration parameters from respiration information received via the respiration information interface; and a dead space fraction module configured to determine the dead space fraction of the subject based on values for the one or more blood gas parameters obtained by the blood gas module and based on values for the one or more respiration parameters obtained by the respiration parameter module, characterized in that the dead space fraction module is configured to determine the dead space fraction of the subject at the end of measurement intervals based on values of the one or more blood gas parameters used in a previous determination of the dead space fraction of the subject if blood gas information is not received by the blood gas information interface during that measurement interval, and based on the values of the one or more respiration parameters obtained from the respiration information received during that measurement interval if respiration information is received by the respiration information interface during that measurement interval. a blood gas information interface configured to receive blood gas information related to one or more blood gas parameters that indicate concentrations of one or more molecular species in the blood of a subject; a respiration information interface configured to receive respiration information related to one or more respiration parameters of the breathing of the subject; and a processor configured to execute computer program modules, the computer program modules comprising: a blood gas module configured to obtain values for one or more blood gas parameters from blood gas information received via the blood gas information interface; a respiration parameter module configured to obtain values for one or more respiration parameters from respiration information received via the respiration information interface; and a dead space fraction module configured to determine the dead space fraction of the subject based on values for the one or more blood gas parameters obtained by the blood gas module and based on values for the one or more respiration parameters obtained by the respiration parameter module, characterized in that the dead space fraction module is configured to determine the dead space fraction of the subject at the end of measurement intervals based on values of the one or more blood gas parameters used in a previous determination of the dead space fraction of the subject if blood gas information is not received by the blood gas information interface during that measurement interval, and based on the values of the one or more respiration parameters obtained from the respiration information received during that measurement interval if respiration information is received by the respiration information interface during that measurement interval. a blood gas module configured to obtain values for one or more blood gas parameters from blood gas information received via the blood gas information interface; a respiration parameter module configured to obtain values for one or more respiration parameters from respiration information received via the respiration information interface; and a dead space fraction module configured to determine the dead space fraction of the subject based on values for the one or more blood gas parameters obtained by the blood gas module and based on values for the one or more respiration parameters obtained by the respiration parameter module,