Transcript New Technologies in Non Invasive Monitoring

Check a Pulse!
When to Question SpO2,
NIBP & EtCO2 Readings
Mike McEvoy, PhD, RN, CCRN, NRP
Senior Staff RN – Cardiothoracic Surgical ICUs
Albany Medical College – Albany, New York
Chair – Resuscitation Committee – Albany Medical Center
EMS Coordinator – Saratoga County, New York
EMS Editor – Fire Engineering magazine
Learning Objectives
Upon completion of the presentation the participant will:
1. Recall two common sources of user error in noninvasive vital sign measurement
2. Discuss the methodology used to obtain a noninvasive blood pressure reading
3. State one response of a pulse oximeter when unable
to detect a pulse
Talk Code = 711
Case # 1 - Desaturation
• While charting…
• SpO2 alarms 74%
• Patient in no distress,
good color
• Repositioning sensor
yields same 74% sat
• ABG shows 98% sat
Well appearing patient, 74% SpO2
• Why me?
Case # 2 – O2 Sat Out Of Nowhere…
• Patient discharged 2 hours ago
• Mysterious
waveform
and 100% sat
Model of Light Absorption At Measurement
Site Without Motion
Absorption
AC Variable light absorption due
pulsatile volume of arterial blood
DC Constant light absorption due to
non-pulsatile arterial blood.
DC Constant light absorption due to
venous blood.
Time
DC Constant light absorption due to
tissue, bone, ...
Model of Light Absorption At Measurement
Site With Motion
Absorption
AC Variable light absorption due
pulsatile volume of arterial blood
DC Constant light absorption due to
non-pulsatile arterial blood.
AC Variable light absorption due to
moving venous blood
Time
DC Constant light absorption due to
venous blood.
DC Constant light absorption due to
tissue, bone ...
Influence of Perfusion on Accuracy of
Conventional Pulse Oximetry During Motion
Good Perfusion (Conventional PO)
SpaO2=98
SpvO2=88
SpO2=93
Poor Perfusion (Conventional PO)
SpaO2=98
SpvO2=50
SpO2=74
Conventional Pulse Oximetry Algorithm
R & IR
Digitized,
Filtered &
Normalized
MEASUREMENT
R/IR
CONFIDENCE
Post
Processor
% Saturation
3 options during motion or low perfusion:
1. Freeze last good value
2. Lengthen averaging cycle
3. Zero out
Next Generation Pulse Oximetry
Next Generation Pulse Oximetry
Masimo SET: Signal Extraction Technology
R/IR
(Conventional Pulse
Oximetry)
MEASUREMENT
CONFIDENCE
MEASUREMENT
DSTTM
R & IR
Digitized,
Filtered &
Normalized
CONFIDENCE
MEASUREMENT
FSTTM
CONFIDENCE
Confidence
Based
Arbitrator
Post
Processor
% Saturation
DST
SET – 97%
MEASUREMENT
SSTTM
CONFIDENCE
0
MEASUREMENT
Proprietary
Algorithm 4
CONFIDENCE
Masimo SET “Parallel Engines”
SET “Parallel Engines”
50%
66% 97% 100%
SpO2%
A Solution for Patient Motion
Discrete Saturation Transform (DST)
In the presence of motion, SET separates the venous and
arterial saturation values resulting in accurate saturation
readings without false alarms (compared to conventional
oximetry that averages the values to produce a reading)
Variable
Constant
Variable
Averaging inaccurate SpO2
0
50%
66%
86%
Constant
97% 100%
SpO2%
Conventional Pulse
Oximetry
0
50%
Separating accurate SpO2
66%
86%
97%
100%
SpO2%
Measure Through
Motion Pulse Oximetry
Certainty…
Case # 3 – Smoke Inhalation
ED Triage Desk:
• 35 yo male presents
with diff breathing
• States, “My furnace
exploded.”
• Soot in mouth/nares
• O2 sat 98%
Carbon Monoxide (CO)
• Gas:
• Colorless
• Odorless
• Tasteless
• Nonirritating
• Physical Properties:
• Vapor Density = 0.97
• LEL/UEL = 12.5 – 74%
• IDLH = 1200 ppm
Limitations of Pulse Oximetry
Conventional pulse oximetry can not distinguish between COHb, and O2Hb
From Conventional
Pulse Oximeter
SpCO-SpO2 Gap:
The fractional difference between
actual SaO2 and display of SpO2
(2 wavelength oximetry) in
presence of carboxyhemoglobin
From invasive COOximeter Blood
Sample
[Blood]
Barker SJ, Tremper KK. The Effect of Carbon Monoxide Inhalation on Pulse Oximetry and Transcutaneous PO 2. Anesthesiology 1987; 66:677-679
CO: The Leading Cause of Poisoning Deaths
30-50 % of CO-exposed patients presenting to
Emergency Departments are misdiagnosed
Barker MD, et al. J Pediatr. 1988;1:233-43
Barret L, et al. Clin Toxicol. 1985;23:309-13
Grace TW, et al. JAMA. 1981;246:1698-700
Pulse CO-oximetry
Hgb Signatures: CO, Met, Hgb…
14,438 Patient Brown University Study
• Partridge and Jay (Rhode Island Hospital, Brown University
Medical School), assessed carbon monoxide (CO) levels of
10,856 ED patients
• 11 unsuspected cases of CO Toxicity (COT) were discovered.
Overall mean SpCO was 3.60%
• Occult COT was 4 in 10,000 during cold, 1 in 10,000 during
warm months
• They concluded “unsuspected COT may be identified using
noninvasive COHb screening and the prevalence of COT may
be higher than previously recognized”
Non-Invasive Pulse CO-Oximetry Screening in the Emergency Department Identifies
Occult Carbon Monoxide Toxicity. Suner S, Partridge R, Sucov A, Valente J, Chee K,
Hughes A, Jay G. J Emerg Med 2008 Department of Emergency Medicine, Rhode
Island Hospital, Brown Medical School, Providence, RI.
Pulse Oximetry
Problems:
• Accuracy
• Motion & artifact
• Dyshemoglobins
Case # 4 – Which Pressure Is Right?
78 yo trauma patient  BP
• A-line = 70/42 (50)
• NIBP = 90/50 (52)
Blood Pressure Monitoring
Direct
Indirect
vs
Pressure
Flow
Errors in BP Measurement
Cuff Size:
• Too large =  BP
• Too small =  BP
• 2/3 extremity length
Mid Heart Level:
• Higher =  BP
• Lower =  BP
• Best sitting, arm @ side
How does NIBP work?
• Measures flow (pulsatile)
• Determines HR and MAP
• By formula, calculates
SBP and DBP
• Subject to same interferences
as auscultated BP
• Important to confirm HR (if
wrong, SBP and DBP wrong)
Mean Arterial Pressure (MAP)
• A clinical parameter useful in assessing perfusion
• Represents the average pressure within the arterial
system throughout the cardiac cycle
• MAP = 2 (diastolic) + systolic
3
• 2/3 time in diastole only when HR = 70
150
90
60
•28
Waveform Capnography
Available for spontaneously breathing and for intubated patients
Case # 5 – Bad Day in OR
• 37 yo male cholecystectomy
• No significant PMH, smooth induction
• Shortly after incision, EtCO2 gradually declines
• Manual BVM with good compliance & chest rise
• ???
Circulation
The heart
and lungs
are
inextricably
linked
together
Cardiac Arrest!
• Little O2 delivery or consumption
• Little CO2 production or venous return
CO2 Clearance Reflects Perfusion
In other words: CO2
production is largely
dependent on
oxygen
consumption!
Case # 6 – Misplaced ETT?
• Cardiac arrest on med-surg floor
• CRNA intubates without difficulty, visualizes
tube pass through cords
• EtCO2 circuit connected = flatline
• ???
Circuit Connector
Case # 7 – EtCO2 ≠ PaCO2
• Post CABG patient EtCO2 drops to 6
• ABG PaCO2 = 48 mmHg
• Why?
Another Cause of Low EtCO2
• Profound metabolic acidosis
• pH = 6.93
Questions?
Slides available at: www.mikemcevoy.com