Blood Gases
We have two important gases in our blood: Oxygen (O2) from the air we inhale and Carbon Dioxide (CO2) which leaves our body when we exhale. As breathing muscles weaken, shallower breathing cannot effectively remove (CO2). Measurement of Carbon Dioxide (CO2) level is important, but the time of day when it is measured is key. In Neuromuscular Disease (NMD), Oxygen saturation may be normal even though Carbon Dioxide is elevated above normal ranges. The concept is complex, but the “Oxygen Dissociation Curve” explains how this phenomenon is possible because of the body’s ability to compensate for a period of time. Measuring CO2 during the day, except for measurements taken just after awakening, often show a normal reading even though the individual is experiencing elevation of CO2 during sleep. Eventually, CO2 that is elevated only during sleep may “spill over” into daytime hours.
Arterial blood gas (ABG) sampling (blood drawn from an artery, not a vein) can be difficult and painful but has become the US “gold standard” for measuring blood gases. NMD patients can have a difficult time with ABG sampling, so ultrasound guidance may be warranted. In this process, a radiology clinician will use an ultrasound wand to identify the artery location, mark it on the skin, and a typically faster and safer artery puncture can be made. Less painful venous or capillary (finger prick) blood gas measurements can be taken, but some clinicians question the accuracy of these over arterial blood gas levels.
Pain-free but less readily available alternatives for measuring Carbon Dioxide level include 1) capnography, a measure of end-tidal Carbon Dioxide (PetCO2) from exhaled breath, and 2) transcutaneous Carbon Dioxide (PtcCO2), measured through the skin by one or more sensors. Both allow for intermittent and real-time monitoring of daytime and nocturnal carbon dioxide levels. Most medical practices and Durable Medical Equipment (DME) providers in the US do not routinely offer these painless, noninvasive alternatives, but some patients/families have gained access by making a request or privately purchasing a device for home use.
See also:
Sleep Study
Swallowing
Pulmonary Function/Spirometry
We have two important gases in our blood: Oxygen (O2) from the air we inhale and Carbon Dioxide (CO2) which leaves our body when we exhale. As breathing muscles weaken, shallower breathing cannot effectively remove (CO2). Measurement of Carbon Dioxide (CO2) level is important, but the time of day when it is measured is key. In Neuromuscular Disease (NMD), Oxygen saturation may be normal even though Carbon Dioxide is elevated above normal ranges. The concept is complex, but the “Oxygen Dissociation Curve” explains how this phenomenon is possible because of the body’s ability to compensate for a period of time. Measuring CO2 during the day, except for measurements taken just after awakening, often show a normal reading even though the individual is experiencing elevation of CO2 during sleep. Eventually, CO2 that is elevated only during sleep may “spill over” into daytime hours.
Arterial blood gas (ABG) sampling (blood drawn from an artery, not a vein) can be difficult and painful but has become the US “gold standard” for measuring blood gases. NMD patients can have a difficult time with ABG sampling, so ultrasound guidance may be warranted. In this process, a radiology clinician will use an ultrasound wand to identify the artery location, mark it on the skin, and a typically faster and safer artery puncture can be made. Less painful venous or capillary (finger prick) blood gas measurements can be taken, but some clinicians question the accuracy of these over arterial blood gas levels.
Pain-free but less readily available alternatives for measuring Carbon Dioxide level include 1) capnography, a measure of end-tidal Carbon Dioxide (PetCO2) from exhaled breath, and 2) transcutaneous Carbon Dioxide (PtcCO2), measured through the skin by one or more sensors. Both allow for intermittent and real-time monitoring of daytime and nocturnal carbon dioxide levels. Most medical practices and Durable Medical Equipment (DME) providers in the US do not routinely offer these painless, noninvasive alternatives, but some patients/families have gained access by making a request or privately purchasing a device for home use.
See also:
Sleep Study
Swallowing
Pulmonary Function/Spirometry