New Technology Offers Modular Convenience
By Julie Crawshaw, CRC Plus Editor
Capnography, the ventilation-monitoring process that uses infrared spectrography to measure the amount of expired CO2, may be coming to an ICU near you very soon. ICU nursing staff and physicians don’t really see it as a monitoring modality yet, but they will, because it’s an earlier warning of respiratory difficulties," says William W. Feaster, MD, MBA, medical director of Anesthesia for Community Medical Centers in Fresno, CA.
"Capnography provides a real-time graphic assessment of respiratory activity," Feaster says, "and advances in manufacturing technology mean ICU staff can use capnography to monitor nonintubated as well as intubated patients. Capnography, Feaster says, offers medical staff the advantage of an earlier warning that something’s going wrong than does pulse oximetry, which measures the oxygen-saturation in blood hemoglobin."
ICU-Friendly Technology Available
Several companies are bringing out modular capnography-monitoring systems that can be plugged into a bedside monitor and measure expired CO2 very effectively, adds Jay Falk, MD, director of medical education in the Orlando (FL) Regional Healthcare System and clinical professor of medicine and emergency medicine at the University of Florida College of Medicine. "The new Microstream technology gives excellent results on non-intubated patients through a nasal cannula," Falk says.
Falk observes that although monitoring expired CO2 has been the standard of care in operating rooms for the past decade, it hasn’t been routinely used in the ICU. He adds that end-tidal CO2 monitoring, long considered only as a monitor of ventilation, offers more innovative uses to today’s intensivist.
As an example, he points to the difficulty in determining the best level of positive expiratory pressure (PEEP). By comparing the arterial CO2 level to the end-tidal CO2 level in the exhaled gas, staff can easily determine when best PEEP is reached because there will be a very small difference between the two measurements. Too much or too little PEEP over-widens the gradient between the blood-level and end-tidal CO2, so increasing or decreasing PEEP followed by rechecking the gradient allows staff to accurately determine the best PEEP level.
At very low flow states, Falk says, his own research shows that the end-tidal CO2 becomes a monitor for cardiac output, important for emergency room physicians who lack the arterial lines and other monitors available in the ICU. "In the emergency room we can monitor expired CO2 during a code and know how we’re doing," he says. "It’s noninvasive and cheaper than other monitors as well."
Falk adds that data now show if the end-tidal PCO2 is below 10 mm Hg after 20 minutes of code it’s very unlikely the patient can be resuscitated. In rural areas this can signal paramedics they can stop doing CPR.
The Benefits of Capnography
Researchers in one recent study1 described interpreting the capnograph as intuitive and requiring approximately 30 minutes to learn. They compared simultaneous respiratory rate measurements obtained by capnography and by auscultation with a pre-tracheal stethoscope and concluded that capnography was an excellent indicator of respiratory rate when compared to auscultation.
Feaster sees the greatest potential application for capnography in non-intubated patients, patients who have recently been extubated or have a severe respiratory problem such as asthma, and patients undergoing heavy sedation. "Technology is now available that allows non-intubated patients to have quite accurate end tidal CO2 measurement," Feaster says. "There are many more potential applications as well for non-intubated patients with conditions that could lead to hypoventilation. The next step is patient studies and peer-review."
Recommendations from the American Society of Anesthesiologists, he adds, suggest that monitoring for apnea using the detection of exhaled CO2 is a useful adjunct to pulse oximetry in assessing ventilation of patients undergoing sedation and analgesia.
(For more information contact William Feaster at (559) 459-2417 or Jay Falk (407) 237-6324.)
1. Vargo J, et al. Automated graphic assessment of respiratory activity is superior to pulse oximetry and visual assessment for the detection of early respiratory depression during therapeutic upper endoscopy. Gastrointest Endosc. 2002;55:826-831.