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!