![Page 1: Mike McEvoy, PhD, RN, CCRN, NRP Senior Staff RN – Cardiothoracic Surgical ICUs Albany Medical College – Albany, New York Chair – Resuscitation Committee](https://reader035.vdocuments.net/reader035/viewer/2022062516/56649e035503460f94aee195/html5/thumbnails/1.jpg)
Mike McEvoy, PhD, RN, CCRN, NRPSenior Staff RN – Cardiothoracic Surgical ICUs
Albany Medical College – Albany, New YorkChair – Resuscitation Committee – Albany Medical Center
EMS Coordinator – Saratoga County, New YorkEMS Editor – Fire Engineering magazine
Check a Pulse! When to Question SpO2, NIBP & EtCO2 Readings
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Learning Objectives
Upon completion of the presentation the participant will:
1. Recall two common sources of user error in non-invasive vital sign measurement
2. Discuss the methodology used to obtain a non-invasive blood pressure reading
3. State one response of a pulse oximeter when unable to detect a pulse
Talk Code = 711
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Case # 1 - Desaturation• While charting…
• SpO2 alarms 74%
• Patient in no distress, good color
• Repositioning sensor yields same 74% sat
• ABG shows 98% sat
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Well appearing patient, 74% SpO2
•Why me?
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Case # 2 – O2 Sat Out Of Nowhere…
• Patient discharged 2 hours ago
• Mysteriouswaveformand 100% sat
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Model of Light Absorption At Measurement Site Without Motion
ACAC Variable light absorption due pulsatile volume of arterial blood
DCDC Constant light absorption due to non-pulsatile arterial blood.
DCDC Constant light absorption due to venous blood.
DC Constant light absorption due to tissue, bone, ...
Abs
orpt
ion
TimeTime
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Model of Light Absorption At Measurement Site With Motion
ACAC Variable light absorption due pulsatile volume of arterial blood
DCDC Constant light absorption due to non-pulsatile arterial blood.
AC Variable light absorption due to moving venous blood
DCDC Constant light absorption due to venous blood.
DC Constant light absorption due to tissue, bone ...
TimeTime
Abs
orpt
ion
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Influence of Perfusion on Accuracy of Conventional Pulse Oximetry During Motion
Good Perfusion (Conventional PO)
SpaO2=98
SpvO2=88SpO2=93
Poor Perfusion (Conventional PO)
SpO2=74
SpaO2=98
SpvO2=50
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Post Processor
R & IRDigitized, Filtered &
NormalizedR/IR
MEASUREMENT
CONFIDENCE % Saturation% Saturation
Conventional Pulse Oximetry Algorithm
3 options during motion or low perfusion:
1. Freeze last good value
2. Lengthen averaging cycle
3. Zero out
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Next Generation Pulse Oximetry
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Next Generation Pulse Oximetry
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Masimo SET: Signal Extraction Technology
SET “Parallel Engines”
Masimo SET “Parallel Engines”
R/IR(Conventional Pulse
Oximetry)
Confidence Based
Arbitrator
0 50% 66% 97% 100%SpO2% SpO2%
Post ProcessorDigitized,
Filtered & Normalized
% Saturation
SSTTM
Proprietary Algorithm 4
DST DST SET – 97%SET – 97%
DSTTM
FSTTM
MEASUREMENT
CONFIDENCE
MEASUREMENT
CONFIDENCE
MEASUREMENT
CONFIDENCE
MEASUREMENT
CONFIDENCE
MEASUREMENT
CONFIDENCE
R & IR
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A Solution for Patient Motion Discrete Saturation Transform (DST)
0 50% 66% 86% 97% 100%
SpOSpO2% %
Measure Through Motion Pulse Oximetry
Separating - accurate SpO2
Conventional Pulse Oximetry
0 50% 66% 86% 97% 100%
SpOSpO2% %
Averaging - inaccurate SpO2
Variable
Constant
Variable
Constant
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)
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Certainty…
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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%
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Carbon Monoxide (CO)
• Gas:• Colorless• Odorless• Tasteless• Nonirritating
• Physical Properties:• Vapor Density = 0.97• LEL/UEL = 12.5 – 74%• IDLH = 1200 ppm
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Limitations of Pulse Oximetry
Barker SJ, Tremper KK. The Effect of Carbon Monoxide Inhalation on Pulse Oximetry and Transcutaneous PO 2. Anesthesiology 1987; 66:677-679
SpCO-SpO2 Gap:
The fractional difference between actual SaO2 and display of SpO2 (2 wavelength oximetry)
in presence of carboxyhemoglobin
SpCO-SpO2 Gap:
The fractional difference between actual SaO2 and display of SpO2 (2 wavelength oximetry)
in presence of carboxyhemoglobin
From Conventional Pulse Oximeter
From invasive CO-Oximeter Blood
Sample
[Blood]
Conventional pulse oximetry can not distinguish between COHb, and O2Hb
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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
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Pulse CO-oximetry
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Hgb Signatures: CO, Met, Hgb…
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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.
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Pulse Oximetry
Problems:
•Accuracy
•Motion & artifact
•Dyshemoglobins
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Case # 4 – Which Pressure Is Right?
78 yo trauma patient BP • A-line = 70/42 (50)• NIBP = 90/50 (52)
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Blood Pressure Monitoring
Direct
Pressure
vs
Indirect
Flow
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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
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How does NIBP work?
• Measures flow (pulsatile)
• Determines HR and MAP
• By formula, calculatesSBP and DBP
• Subject to same interferences as auscultated BP
• Important to confirm HR (if wrong, SBP and DBP wrong)
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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
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•28
150
90
60
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Waveform CapnographyAvailable for spontaneously breathing and for intubated patients
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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• ???
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Circulation
The heart and lungs
are inextricably
linked together
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Cardiac Arrest!• Little O2 delivery or consumption
• Little CO2 production or venous return
• Little O2 delivery or consumption
• Little CO2 production or venous return
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In other words: CO2 production is largely
dependent on oxygen
consumption!
CO2 Clearance Reflects Perfusion
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Case # 6 – Misplaced ETT?
• Cardiac arrest on med-surg floor• CRNA intubates without difficulty, visualizes
tube pass through cords • EtCO2 circuit connected = flatline• ???
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Circuit Connector
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Case # 7 – EtCO2 ≠ PaCO2
• Post CABG patient EtCO2 drops to 6
• ABG PaCO2 = 48 mmHg
•Why?
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Another Cause of Low EtCO2
• Profound metabolic acidosis• pH = 6.93
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Questions?
Slides available at: www.mikemcevoy.com