Pulse oximeters can also measure respiratory activity, vasomotor tone, autonomic status, fluid responsiveness, stroke volume, preload, cardiac output, and capillary refill time. (Image source: Thinkstock)

Pulse oximeters can also measure respiratory activity, vasomotor tone, autonomic status, fluid responsiveness, stroke volume, preload, cardiac output, and capillary refill time. (Image source: Thinkstock)

You may think you are walking around with the equivalent of a Cray computer in your pocket, but you aren’t. Your cell phone would flail solving large systems of differential equations. Cray computers can’t make phone calls. However, using crude measurements like megaflops (e.g. LinPack), your cell phone approximately matches the computational horsepower of a 1970s Cray computer.

According to the International Telecom Union, there are 6.8 billion mobile phone subscribers among the 7.1 billion world inhabitants. In the developing world, 89% of the population has cell phone access. Given the computational prowess of modern cell phones, this represents a huge resource of available computing power in areas lacking access to basic medical instrumentation.

In the current issue of Anesthesia & Analgesia, J. Mark Ansermino from the British Columbia Childrens Hospital, in the article “Special Article: Universal Access to Essential Vital Signs Monitoring” suggests that this computing horsepower could help address the lack of adequate monitoring of vital signs in the third world. Ansermino focuses on pulse oximetry, both because of the medical utility of pulse oximetry, and because approximately 77,000 operating rooms lack oximetry, not to mention recovery rooms, intensive care units, and emergency care departments.

With smartphones providing the computational engine, display, user interface, alarms, and pulse tones, it should be possible to design a new generation of inexpensive pulse oximeters that need only include the basic measurement technology and a means of connecting to the phone. Obviously, these devices would measure oxygen saturation and heart rate. However, in a limited resource environment, they could become far more essential monitoring tools.

The waveform produced by the pulse oximeter is known as the photoplethysmograph. That waveform can also be used to measure respiratory activity (amplitude, frequency and intensity), vasomotor tone, autonomic status, fluid responsiveness, stroke volume, preload, cardiac output, and capillary refill time. For additional information, refer to the recently published article, “Photoplethysmography: Beyond the Calculation of Arterial Oxygen Saturation and Heart Rate” in Anesthesia & Analgesia that discusses the utility of the photoplethysmograph wave.

The same waveform could be used to diagnose pneumonia in children. Mortality due to pneumonia is attributable to delays in diagnosis, triage, transportation and treatment. Most of these deaths are seen in low-income areas within Africa and Asia. Pneumonia diagnosis can be problematic even in developed countries because of uncertainty in measuring tachypnea, signs of respiratory obstruction, stridor, and inability to drink. Oxygen saturation is a more objective measure and has been shown to increase diagnostic yield by 20-30%. Other measures that can be derived from the photoplethysmograph waveform, such as heart rate and heart rate variability, respiratory rate, pulse pressure, and capillary refill time, as described above, can also help to diagnose and follow response to therapy.

The same waveform could be used to predict complications from preeclampsia. Preeclampsia is one of the leading causes of maternal mortality globally and most of these deaths occur in South Asia and sub-Saharan Africa. Oxygen saturation has been shown to predict adverse maternal outcome and given that preeclampsia is a state of exaggerated inflammation, it would be expected that low oxygen values would be observed when there is exaggerated inflammation. In a recently validated score to predict complications due to preeclampsia, pulse oximetry was included as one of the values in the model (other factors include gestational age, chest pain/dyspnea, serum creatinine, platelet count, and aspartate transaminase).

Availability of oximetry is dictated by cost. The Quality and Safety of Practice Committee of the World Federation of Societies of Anesthesiologists has identified this issue as a priority and Lifebox is a charity that provides oximeters as well as training, education and peer support. Perhaps an additional initiative could be the development of inexpensive “sensor only” oximetry that sends the light absorption data to a smartphone, where the the computational heavy lifting occurs, provided you aren’t chatting with friends or browsing the Internet.