Monitoring technology has tremendous potential to improve patient outcomes—when it’s designed and used properly. Routine use of pulse oximetry and waveform capnography virtually eliminated esophageal intubations and inadequate oxygenation claims against anesthesia providers, transforming their profession from frequent and costly malpractice targets in the 1970s to 1980s into one of the safer fields of practice today.(1) The value of technology lies in collecting meaningful data that a provider can’t easily obtain with their own assessment skills. Lives are saved in hospitals every day through the use of monitoring technology: The more sophisticated the level of care, the more advanced the monitoring technology tends to be.(2)
Technology enhances prehospital patient care as well, enhancing provider assessment abilities and detecting changes in patient condition. This article will review current prehospital technology and discuss current and future evolutions.
The first technology adapted for EMS use was cardiac monitoring. Portable cardiac monitors have evolved since their introduction in the 1970s to include defibrillators, pulse oximeters, non-invasive blood pressure (NIBP) modules, waveform capnography, temperature and, most recently, CPR feedback technologies. Perhaps the most important recent prehospital development has been monitor alarms, intended to alert providers of potential problems.(3) Early prehospital monitors didn’t include alarms, probably under the mistaken notion that an EMS provider caring for a patient would immediately notice significant changes. It’s no secret that EMS providers have many things to do besides continuously watch a monitor screen.
The addition of alarms is a welcome improvement in prehospital monitors. A typical intensive care unit (ICU) patient generates some 700 monitoring alarms per day of which only 15% are clinically significant.(4) This year, the hospital issue known as “alarm fatigue” has been considered the top hospital technology hazard.(3) EMS currently has a unique opportunity to customize monitoring alarms, with the option not to allow silencing such critical alerts as apnea, asystole and lethal rhythms, to avoid desensitization and falling into the trap of “alarm fatigue.”
Now a standard of care included in the EMT curriculum, pulse oximetry was one of the earliest devices to appear in ambulances. Originally introduced in 1974 for use on anesthetized patients during surgery, oximetry has matured tremendously in recent years.(4) Arguably one of the most important patient safety devices ever invented, pulse oximetry has reduced anesthesia deaths by 90%, now promising to protect patients from the damaging effects of hyperoxia seen with routine use of oxygen in patient care.(5) In addition to guiding selection of appropriate oxygen delivery devices, pulse oximetry technology utilizing additional wavelengths of light can now screen for carbon monoxide poisoning, methemoglobin, and even assess fluid volume status from analysis of the pleth waveform.(6) In the future, manufacturers will introduce respiratory rate and blood pressure measurements obtained from pulse oximetry pleth waveforms.
Non-invasive or electronic blood pressure measurement followed pulse oximetry into the prehospital market. Current devices are oscillometric, meaning that they sense arterial oscillations, typically measuring a heart rate and mean arterial pressure then working backwards to calculate a systolic and diastolic pressure. Algorithms vary by manufacturer, making it virtually impossible to validate accuracy, but for the majority of NIBP devices used in EMS the mean arterial pressure is the most accurate value displayed.(7) Like auscultatory measurements, proper cuff size and meticulous attention to keeping the extremity being measured at mid-heart level are key to obtaining good measurements.(8)
Capnography has made major inroads into EMS and, in many systems, is more frequently utilized in prehospital patients than hospitalized patients. The driving force for capnography is patient safety during intubation and, like pulse oximetry, the anesthesia standard of care dictates monitoring every intubated patient with waveform capnography. Many EMS systems mandate continuous waveform capnography for all intubated patients, a common sense standard that virtually eliminates the possibility of not detecting a misplaced endotracheal tube or supraglottic airway.(1,9) Today, there is no excuse for not using continuous waveform capnography on every intubated patient, in my opinion.
Like their anesthesia and critical care counterparts, EMS providers have become quite skilled with analysis of capnography waveforms. In both spontaneously breathing and intubated patients, waveforms demonstrate changes in airway resistance revealing conditions like bronchospasm, airway cuff leaks, ventilator asynchrony and more. In the future, manufacturers will introduce software to quantify capnography waveforms to allow clinicians to measure severity and effects of treatment on conditions detected through waveform analysis.
Miniturization of capnography technology has improved portability and battery life. It also promises in the very near future to further revolutionize the industry with enhancements to a capnometer known as EMMA. The manufacturer of this second generation end-tidal device was recently acquired by Masimo and will very likely transform into a much more robust and usable miniaturized device, perfect for space-limited environments, such as air medical, combat and intrafacility transports. Keep an eye on EMMA.
One of the more recent monitoring technologies to make its way into ALS monitors is CPR feedback. The three major monitoring manufactures have feedback devices to provide both real-time and retrospective analysis of CPR. Philips offers Q-CPR, a real-time accelerometer-based technology that incorporates a downloadable resuscitation review. ZOLL offers CPR Dashboard, a real-time accelerometer-based technology with data transmission capability for post-event review. Physio-Control offers CODE-STAT data review software for post CPR review and will very shortly introduce its TrueCPR coaching device in the U.S., a standalone triaxial field induction (TFI) based unit. TFI, once it becomes available, promises to eliminate overestimations of compression depth reported by accelerometer-based devices when CPR is administered on a mattress (regardless of whether a board is in place).(10)
CPR feedback helps rescuers deliver near-perfect compressions and ventilations to victims of sudden cardiac arrest. For anyone who has ever performed CPR using a feedback device, they seem to deliver quite nicely in that regard. Use of post-resuscitation analysis software has led to consistent and sustained improvements in the quality of CPR. Yet a recent study by Hostler and coauthors (and the largest study of real-time feedback yet conducted) suggests that these changes in performance don’t seem to improve outcomes.(11) This is troubling, and it strongly suggests problems not with the feedback devices or rescuers, but with the guidelines themselves. Indeed, anecdotal reports from CPR feedback users show significantly improved markers of better perfusion, such as end-tidal CO2, throughout the peri-arrest period, yet few have seen improved results. If anything, CPR feedback devices are showing us that our “one size fits all” approach to CPR using the same compression depth and rate isn’t appropriate for every patient. Hopefully, the guidelines will change.
Point of Care Testing
Point of care (POC) testing has slowly invaded the prehospital world. Use of glucometers is widespread and is now included in the EMT scope of practice. One promising technology with a broad range of potential uses is saliva osmolality to assess dehydration. Several recent studies have found close correlation between measurement of saliva osmolality, or concentration, and hydration status.(12-13) Firefighters, athletes, and nursing home patients frequently suffer from dehydration, and EMS providers lack good tools to easily determine hydration status. A Menlo Park (Calif.) company, Cantimer Corporation is refining a device similar to a glucometer that will allow field testing of saliva to detect dehydration.
Another technology currently making prehospital inroads is ultrasound. In the emergency department (ED) and ICU, ultrasound has for years been used to quickly detect presence of blood or fluid in the abdomen of trauma patients, place lines, confirm endotracheal tube (ET) placement, assess for pnuemothorax, check cardiac function and volume status in the heart and vascular system, find fractures and examine unborn children. Numerous studies have demonstrated that prehospital providers can accurately use ultrasound, but outcome studies are lacking.(14,15)
There is little doubt in the hospital setting that ultrasound has and will continue to replace more invasive testing. A nurse using ultrasound can avoid placing a foley catheter, saving much discomfort and risk of infection for the patient. A clinician performing a comprehensive ultrasound exam in an unstable patient can very rapidly assess heart function, fluid volume status and visualize the lungs. These exams, however, take considerable practice and require continued use to maintain proficiency. Like ETI, the opportunity to perform ultrasound may not occur often enough to allow prehospital providers in many systems to develop and maintain sufficient proficiency.
Increasing concerns are arising that clinicians may become overwhelmed with the vast amount of data to determine an appropriate plan of care. To that end, monitoring manufacturers are beginning to develop algorithms or fuzzy logic systems that analyze multiple parameters to provide the clinician with an overall wellness score on their patient. One of the first entrants in this market was Integrated Pulmonary Index (IPI) by Oridion.(16) IPI uses waveform capnography combined with pulse oximetry to monitor respiratory rate, EtCO2, heart rate and SpO2, combining these values into an algorithm that produces a score from 1 to 10.
This overall pulmonary score doesn’t replace the need for a clinician to look at each one of the parameters, but it does provide early warning about deterioration so the provider can determine which of the measured parameters is in need of treatment. Although IPI isn’t yet available on prehospital monitors, expect to see it soon along with algorithms from other manufacturers that will help you more effectively analyze and manage large quantities of monitored data.
Wearable DEVICES & sensors
Lastly, pay close attention to the field of wearable devices and sensors. As our population ages, patients are discharged from hospitals earlier, and healthcare providers look for ways to more closely monitor their patients at home, the need for wearable sensors will explode. Remote monitoring systems, such as the ViSi mobile monitor by Sotera Wireless, are rapidly benefiting from miniaturization, faster and more robust internet access, more sophisticated Bluetooth technology and developments in microelectronics and sensor technology.
Fully functional ECG monitors the size of a wristwatch, fabric integrated sensors and electrodes, ambient sensors mounted in the home to monitor patient vitals and activity, and very sophisticated implantable sensors are all in various stages of development.(17)
The same technology that allows closer monitoring of patients outside healthcare settings promises to improve your ability to communicate and consult with medical experts. Researchers using real-time high speed audiovisual connections between prehospital providers and experienced physicians are finding potential to improve outcomes.(18) If you can use your cell phone to video chat with family or friends across the country, then it makes perfect sense that EMS could utilize the same technology.
Medicine is a constantly evolving art and science. It’s highly unlikely that a patient will thank you for using a state-of-the art monitor or the latest in CPR feedback. They will, however, thank you for competently and respectfully integrating the equipment you carry into a care plan that makes them feel better for having met you.
1. Metzner J, Posner KL, Lam MS, et al. Closed claims analysis. Best Pract Res Clin Anesthesiol. 2011;25(2):263–276.
2. Hu X, Sapo M, Nenov V, et al. Predictive combinations of monitor alarms preceding in-hospital code blue events. J Biomed Inform. 2012;45(5):913–921.
3. Cvach M. Monitor alarm fatigue: An integrative review. Biomed Instrum Technol. 2012;46(4):268–277.
4. Severinghaus JW. Takuo Aoyagi: Discovery of pulse oximetry. Anesth Analg. 2007;105(6 Suppl):S1–4.
5. Severinghaus JW. Monitoring oxygenation. J Clin Monit Comput. 2011;25(3):155–161.
6. Roth D, Hubmann N, Havel C, et al. Victim of carbon monoxide poisoning identified by carbon monoxide oximetry. J Emerg Med. 2011;40(6):640–642.
7. Smulyan H, Safar ME. Blood pressure measurement: Retrospective and prospective views. Amer J Hypertens. 2011;24(6):628–634.
8. Brett SE, Guilcher A, Clapp B, et al. Estimating central systolic blood pressure during oscillometric determination of blood pressure: Proof of concept and validation by comparison with intra-aortic pressure recording and arterial tonometry. Blood Press Monit. 2012;17(3):132–136.
9. Westhorpe RN, Ball C. The history of capnography. Anesth Intensive Care. 2010;38(4):611.
10. Perkins GD, Kocierz L, Smith SC, et al. Compression feedback devices over estimate chest compression depth when performed on a bed. Resuscitation. 2009;80(1):79–82.
11. Hostler D, Rea TD, Stiell IG, et al, and the Resuscitation Outcomes Consortium Investigators. Effect of real-time feedback during cardiopulmonary resuscitation outside hospital: Prospective, cluster-randomised trial. BMJ. 2011 Feb 4;342 [Epub].
12. Smith DL, Shalmiyeva I, DeBlois J, et al. Use of salivary osmolality to assess dehydration. Prehosp Emerg Care. 2012;16(1):128–135.
13. Taylor N, van den Heuvel A, Kerry P, et al. Observations on saliva osmolality during progressive dehydration and partial rehydration. Eur J Appl Physiol. 2012;112(9):3,227–3,237.
14. Chin EJ, Chan CH, Mortazavi R, et al. A pilot study examining the viability of a prehospital assessment with ultrasound for emergencies (PAUSE) protocol. J Emerg Med. 2012 May 15 [Epub ahead of print].
15. Hasler RM, Kehl C, Exadaktylos AK, et al. Accuracy of prehospital diagnosis and triage of a Swiss helicopter emergency medical service. J Trauma Acute Care Surg. 2012;73(3):709–715.
16. Waugh JB. Integrated Pulmonary Index stability in healthy adults under changing conditions. Resp Care. 2010;55(11):1,522.
17. Patel S, Park H, Bonato P, et al. A review of wearable sensors and systems with application in rehabilitation. J Neuroeng Rehabil. 2012;4(20)9:21.
18. Skorning M, Bergrath S, Rortgen D, et al. Teleconsultation in prehospital emergency medical services: Real-time telemedical support in a prospective controlled simulation study. Resuscitation. 2012;83(5):626–632.