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Lessons Learned from Pulse Oximetry
Juliann M. Di Fiore Rainbow Babies & Children’s Hospital
Case Western Reserve University Cleveland, OH
Conflicts of Interest
• No conflicts of interest to disclose
Background
• Due to the high incidence of desaturation events in preterm infants, non-invasive continuous measurement of oxygenation is needed to stabilize this fragile infant cohort.
• Pulse oximetry has become the most widely used modality to detect desaturation events in the NICU setting.
Purpose
• Identify the available features of pulse oximetry monitoring
• Discuss the limitations of current pulse oximeters
• Describe how to maximize monitoring strategies in the NICU
Calibration: Healthy Adults
Johnston: Arch Dis Child Fetal Neonatal Ed, 2011
SpO2 vs SaO2: Infants <33wks GA with an umbilical arterial line.
Rosychuk: Neonatol, 2012
Mean Difference Overall, 1.85% SpO2 85-89%, 2.4% SpO2 91-95%, 1.87%
65 70 75 80 85 90 95 100
65
70
100
95
90
85
80
75
SpO
2
SaO2
SpO2 vs SaO2: Newborn Lambs
Dawson: Arch Dis Child Fetal Neonatal Ed, 2014
Mean Difference SaO2 ≥70%, 3% SaO2 <70%, 13-17%
SpO2 in the NICU Setting
SpO2
ECG
ABD
RC
Sum
Martin et al, 2012
10 sec
Factors Influencing Arterial O2 Desaturation during Apnea
alveolus
venous
arterial
METABOLIC O2
CONSUMPTION
PULMONARY
O2 STORES
TOTAL BLOOD O2 CAPACITY
SLOPE OF Hb/O2
DISSOCIATION
CURVE
Adapted from Sands SA: PLOS Computational Biology 2009
O2 UPTAKE BY ALVEOLI
Intermittent Hypoxia During Early Postnatal Life
Di Fiore: J Pediatr, 2010
24-28wks gestation, n=79
-
IH defined as <80% for 10sec-3min
Nuisance Alarms!
Documentation of Alarms
0
50
100
150
200
250
Video documentation Nursing Notes
Num
ber o
f Ala
rms (
per d
ay)
Events Requiring Intervention
Brockmann: Arch Dis Child Fetal Neonatal Ed, 2013
How do We Reduce Alarms?
Avoid Alarm Fatigue • Reduce false alarms • Identify desaturation events
that require intervention
Maintain Stable Oxygenation • Increase time in target • Decrease time in Hyperoxia/Hypoxia
What are we try to achieve?
Pulse Oximeter Parameters
• Motion Artifact Filter • Alarm threshold • Averaging time • Alarm delay
Standards for Oximeter Settings
• There are currently no published universal standards for oximeter settings
• Limited data on making recommendations
• Every unit must set their own standards
Motion Artifact Filter
• The most common cause of false alarms • Early generation pulse oximeters
• Assumed arterial pulse is the only source of blood moving at the monitoring site.
• During motion venous blood also moves – Signal failure, SpO2=0 – Falsely low SpO2
– Red/infrared= 1, false SpO2 = 82%
New Generation Algorithms
• Masimo SET Technology • Adaptive filters that identify the
energy present at each saturation level from 1-100%
• Scan for the energy peak which is reported as the infant’s SpO2
Motion Artifact 26 neonates
Hay: J Perinatol, 2002
Masimo SET* Nellcor N-200
Events Duration (min)
Events Duration (min)
“False” hypoxemia 50 25.8 213 174.6
“False” bradycardia 1 0.1 41 38.9
Data drop-outs 11 5.4 217 214.4
True bradycardia 12/14 (86%) 2/14 (14%)
New Generation vs Conventional Oximeter
* p<0.05
False Alarms: Additional Causes
• Excessive light interference – flooding of the photodetector
• Probe position • Low pulse volume
– Hypovolemic shock, dysrhythmias
• Low pulsatile flow – Vasoconstriction/Hypothermia
True Alarms
How do we reduce alarms due to minor events that do not
require intervention?
Alarm Thresholds
0
20
40
60
80
100
120
80-97% 85-95%
Num
ber o
f Ala
rms (
per d
ay)
Oxygen Saturation Target
Ketco: Pediatrics, 2015
Averaging Time
Time
SaO
2 (%
)
100
70
90
80
short averaging time (3 sec)
long averaging time (21 sec)
Farré: SLEEP, 1998
0
20
40
60
80
100
0 5 10 15 20
SpO
2 (%
)
2 sec average
Effect of Increasing Averaging Time
Averaging time
No. of IH events
2 sec 26
8 sec 11
16 sec 6
0
20
40
60
80
100
0 5 10 15 20
SpO
2 (%
)
Time (min)
8 sec average
0
20
40
60
80
100
0 5 10 15 20 Time (min)
16 sec averaging
70
80
90
100
110
120
Averaging Time
0
500
1000
1500
2000
Averaging Time (sec)
Num
ber o
f IH
eve
nts
<20 sec
≥20 sec
Vagedes: Arch Dis Child Fetal Neonatal Ed, 2012
3 5 8 10 12 14 16
3 5 8 10 12 14 16
Averaging Time
• Long • Reduce motion artifact and false alarms • Distort the true oxygen saturation waveform • Falsely increase long desaturation events • Understate event severity • Delay response time
• Short • Increase response time • Provide more accurate detection of short events and
event severity • Dramatically increase nuisance alarms
70
80
90
100
110
120
Reduce Alarms to Short Events
0
500
1000
1500
2000
Averaging Time (sec)
Num
ber o
f IH
eve
nts
<20 sec
≥20 sec
Vagedes: Arch Dis Child Fetal Neonatal Ed, 2012
3 5 8 10 12 14 16
3 5 8 10 12 14 16
0
20
40
60
80
100
0 5 10 15 20
SpO
2 (%
)
2 sec average
Monitor Alarm Delay
Averaging time
Alarms with No delay
Alarms with 15 sec delay
2 sec 26 12
8 sec 11 10
SpO
2 (%
)
0
20
40
60
80
100
0 5 10 15 20 Time (min)
8 sec average
Monitor Alarm Delay
• Eliminates alarms due to short desaturation events
• Does not alter the true oxygen saturation waveform
Accurate Documentation
0
10
20
30
40
50
60
In Target ≥98% 80-84%
Perc
ent T
ime
Nurse Transcription Oximeter
*
* *
*p <.0001 vs Transcribed, 24 VLBW infants Ruis: J Perinatol, 2014
85-93%
Bedside visual tool to increase time in target
Use of Histograms in Vermont Oxford Network
Pulse oximeters capable of generating histograms All monitors 46.7% Some monitors 20.7% No monitors 32.6%
Center uses histogram for daily care or QI Never 72.8% Sometimes 19.6% Routinely 7.6%
What About the Future of Pulse Oximetry in the NICU?
IH and Retinopathy of Prematurity
Di Fiore: J Pediatr, 2010
2sec average
Pattern of Intermittent Hypoxia Events
Di Fiore: Pediatr Res 2012
80 _
SpO
2 (%
)
Duration:
Time Interval: (Between Events)
Duration of Intermittent Hypoxemia
Di Fiore: Pediatr Res, 2012
Postnatal Age (days)
Mea
n Du
ratio
n (s
)
Di Fiore: Pediatr Res, 2012
SpO
2 (%
)
80 -
Time Interval Between IH
Intermittent Hypoxemia and Morbidity
• 972 ELBW infants • 16 sec averaging time • IH defined as <80% • Percentage of time with hypoxemia
– 100 x total duration of hypoxemic episodes/ total duration of the recording
Canadian Oxygen Trial (COT)
Poets: JAMA, 2015
Time with SpO2 <80% and Outcome at 18 months of Age
IH <1min IH≥1min
Outcomes
OR (95% CI)
RR (95% CI)
P value
OR (95% CI)
RR (95% CI)
P value
Late Death or Disability
1.04 (.61-1.77)
1.01 (.77-1.32)
.88 3.4 (1.95-5.93)
1.66 (1.35-2.05)
<.001
Cognitive/ language delay
.96 (.56-1.64)
.96 (.72-1.29)
.87 2.88 (1.65-5.02)
1.61 (1.29-2.03)
<.001
Motor Impairment
2.27 (.90-5.74)
1.90 (.90-4.04)
.08 5.20 (2.48-10.92)
3.51 (2.16-5.72)
<.001
Severe ROP 1.84 (0.86-3.95)
1.46 (0.86-2.47)
.12 2.95 (1.47-5.90)
1.93 (1.26-2.98)
.002
Poets: JAMA, 2015
Alarm based on high risk patterns of intermittent hypoxemia that are
associated with morbidity
Create a Smarter Pulse Oximeter
Automated Control Systems
0
10
20
30
40
50
60
70
In Target >98% <80%
Tim
e (%
)
Auto
Manual
*
* *
van Kaam: J Pediatr, 2015
0
2
4
6
8
10
12
14
16
#IH <80% (>60sec)
Num
ber o
f Eve
nts
*p<.05 Auto vs Manual
*
Summary
• There are currently no published standards for oximeter settings
• Oximeter settings such as the alarm threshold, alarm delay and averaging time can reduce nuisance alarms
• Histograms can provide overall information on time in target
Future Clinical Applications
• “Smarter” oximeters with alarm settings based on high risk patterns of intermittent hypoxemia
• Automated control systems to increase time in target and reduce staff fatigue
THANK YOU!