TechNote
Smart Capnography™ addresses patient safety
P
reserving caregiver vigilance to alarms is essential for patient safety. 1 Virtually every patient-
connected device uses audible alarms to notify caregivers of a change in patient condition or device status.
However, numerous alarms that do not signal clinical significance are a distraction to busy caregivers. Reducing
distractions from clinically insignificant alarms* helps preserve caregiver alarm vigilance, leading to improved
patient safety. 2,3
Smart Capnography™ is a family of algorithms developed by Oridion that simplifies the use of etCO2 monitoring
on Microstream® enabled products to reduce alarms and provide clinical utility for improved patient safety.4,5 The
Smart Breath Detection Algorithm™ (BDA) rejects shallow, non-breath CO2 excursions from being counted as
breaths. The Smart Alarm for Respiratory Analysis™ (SARA) recognizes and reduces clinically insignificant* respiratory rate alarms.6 Together, these two technologies accurately reflect the patient’s condition and help to preserve
clinically significant alarm vigilance. SARA can be found only in Microstream Capnography equipped patient
monitors, including the Oridion Capnostream® 20.
The Smart Breath Detection Algorithm (BDA)
Unlike traditional breath detection algorithms, the Smart BDA rejects shallow, non-breath CO2 excursions from
being counted as breaths. Instead, the Smart BDA suite of proprietary filter and pattern recognition techniques
screens out the low-amplitude CO2 changes superimposed on the CO2 waveform. Talking, snoring, and cardiogenic artifacts can cause such non-breath excursions.
Figure 1: S mart Capnography Breath Detection Algorithm at work. The Smart BDA rejects shallow CO2 excursions that are counted by the
traditional breath detection algorithm and only captures actual end-of-breath excursions.
* a clinically insignificant alarm is defined as a respiratory rate alarm lasting continuously for less than 30 seconds or less than 45 seconds over a period of 60 seconds when compared to the previous respiratory rate algorithm
1. The Hazards of Alarm Overload: Keeping Excessive Physiologic Monitoring Alarms from Impeding Care. (ECRI Guidance Article,
March 2007.)
2. Weinger MB. Dangers of postoperative opioids: APSF workshop and white paper address prevention of postoperative respiratory
complications. APSF Newsletter Winter 2006-2007; 21:61-67.
3. O
verdyke FJ et al. Continuous oximetry/capnometry monitoring reveals frequent desaturation and bradypnea during patientcontrolled analgesia. Anesthesia & Analgesia. August 2007; Vol. 105, No. 2, 412-418.
4. D
etection of respiratory depression prior to evidence of hypoxemia in procedural sedation. Respiratory Care. November 2007; Vol.
52, No. 11, 1568.
5. M
cCarter TG, et al. Capnography monitoring enhances safety of postoperative patient-controlled analgesia. American Health &
Drug Benefits. June 2008;28-35.
6. H
ockman S, Glembot T, Niebel K. Comparison of capnography derived respiratory rate alarm frequency using the SARA algorithm
versus an established non-adaptive respiratory rate alarm management algorithm in bariatric surgical patients. 2009 Open Forum
Abstracts, Respiratory Care, December.
The SARA respiratory rate-averaging algorithm
The SARA adaptive respiratory rate-averaging algorithm is an embedded Smart alarm management technology
that works with Smart BDA to:
• Increase the respiratory rate-averaging time during periods of high breath-to-breath time
period variability; the type of variability seen during periods of talking, snoring, coughing
and episodes of pain.
• Reduce the averaging time during periods of low breath-to-breath variability.
How the SARA algorithm works
Traditionally, two types of respiratory rate algorithm methods have been used with patient monitors. The first
type determines the rate by counting how many breath cycles are detected within a fixed time period, such as over
30 seconds. The time period typically would be “moving,” updating at a fixed time period. The second method
measures the time period of detected breaths and updates for every detected breath.
Unlike these methods, SARA employs an adaptive approach. SARA evaluates the stability of the detected breathto-breath intervals and adjusts (adapts) the measurement period accordingly. During unstable periods, the averaging time period used for calculating the respiratory rate is increased; during stable periods, the averaging period is
decreased. By extending the averaging time period during unstable periods, noise and transient fluctuations are
averaged out, providing a more realistic respiratory rate. During stable periods free of artifacts, the shorter averaging period increases response time to low respiratory rate events.
To evaluate the variability of the capnogram, SARA uses a Variability Index (VI), defined as the standard deviation
of the last five breath intervals divided by the mean value of the last five breath intervals. The VI and the respiratory rate are calculated in parallel.
At startup, the Capnography Respiratory Rate (RRc) is calculated after every new detected breath by using the average of the last five breath-to-breath intervals.
N is the number of breath-to-breath time intervals.
X = breath-to-breath intervals in seconds.
X = mean of breath-to-breath intervals.
When the VI goes up, it indicates breath-to-breath variability and possible artifacts. If the VI exceeds a set limit,
the number of breaths averaged for the RRc is increased by n intervals, where “n” is the accumulated number of
occurrences where the variability index was consecutively greater than the threshold. Conversely, for every breathto-breath interval where the VI shows stability, n is decremented by 1 to a minimum of 5. .
Figure 2: A four-minute long capnogram with the RRc trends and breath detections, with and without the SARA and BDA algorithms. Note
how SARA accurately tracks the patient’s true respiratory rate.
BPM
0:40:30
How does SARA help?
Benefits patients
• Provides an accurate indication
of patient respiratory status
changes (by providing accurate
respiratory rate values)
• Accurately responds to clinically
significant events
• Reduces the number of alarms
(potentially fewer disruptions to
patient’s sleep)
Clinical validation for SARA
With SARA, respiratory rate (RR) alarms were reduced by 53% overall, and
short duration alarms, lasting less than 10 seconds, were reduced by an
additional 19%. No significant RR alarms were missed with SARA. See
Figure 3 for the comparison of reduction of RR alarms and alarm
duration.7
Figure 3: Comparison of alarm events with and without SARA. 56 two-hour long monitoring
periods with the low respiratory rate alarm set at 8 breaths per minute.
Benefits clinicians
• May reduce distractions and
time spent responding to clinically insignificant alarms
In an Oridion-sponsored study at the Medical University of South Carolina (MUSC), SARA alarmed less frequently than the existing alarm algorithm, but identified all episodes of respiratory depression (requiring rescue).
When SARA was installed at Mercy Hospital in Canton, Ohio, the institution reported a significant reduction in
RR alarms and Respiratory Therapy staff complaints.
SARA received 510K clearance by the FDA in October 2007.
Summary
SARA automatically adjusts the Capnography Respiratory Rate (RRc) averaging time based on the stability of the
measured breath-to-breath intervals, filtering out noise and transient fluctuations. With the SARA adaptive averaging algorithm, the respiratory rate accurately reflects the patient’s condition without missing true alarms.
7. Colman J, Cohen J, Lain D. Smart alarm respiratory analysis (SARA) used in capnography to reduce alarms during spontaneous breathing. STA. Poster presentation 2008.
Microstream and Capnostream are registered trademarks and Smart Capnography, Smart Breath Detection Algorithm, and Smart Alarm Respiratory Analysis are trademarks of Oridion Medical 1987 Ltd.
Oridion products are covered by one or more of the following US patents: 6,422,240; 5,857,461; 6,437,316; 6,926,005; 5,657,750; 7,383,839 and their foreign equivalents. Additional patent applications pending
Oridion Capnography Inc.
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Fax: (781) 453-2722
Oridion Medical 1987 Ltd.
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Tel: +972 2 589 9158
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www.oridion.com
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