Check a Pulse! When to Question SpO 2, NIBP & EtCO 2 Readings Mike McEvoy, PhD, RN, CCRN, NRP Professor Emeritus - Critical Care Medicine Albany Medical College Albany, New York Chair Resuscitation Committee Albany Med Ctr 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 Class Code: 666 While charting SpO 2 alarms 74% Case # 1 - Desaturation Patient in no distress, good color Repositioning sensor yields same 74% sat ABG shows 98% sat
Well appearing patient, 74% SpO 2 Why me? Case # 2 O 2 Sat Out Of Nowhere Patient discharged 2 hours ago Mysterious waveform and 100% sat Model of Light Absorption At Measurement Site Without Motion Absorption Time 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. DC Constant light absorption due to tissue, bone,...
Model of Light Absorption At Measurement Site With Motion Absorption Time 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 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) SpaO 2 =98 SpvO 2 =88 SpO 2 =93 Poor Perfusion (Conventional PO) SpaO 2 =98 SpvO 2 =50 SpO 2 =74 Conventional Pulse Oximetry Algorithm R & IR Digitized, Filtered & Normalized R/IR MEASUREMENT 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 DST TM CONFIDENCE R & IR Digitized, Filtered & Normalized FST TM MEASUREMENT CONFIDENCE Confidence Based Arbitrator Post Processor % Saturation DST SET 97% MEASUREMENT SST TM CONFIDENCE 0 50% 66% 97% 100% SpO2% Proprietary Algorithm 4 MEASUREMENT CONFIDENCE Masimo SET Parallel Engines SET Parallel Engines
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 Averaging - inaccurate SpO 2 Constant Variable Constant Separating - accurate SpO 2 0 50% 66% 86% 97% 100% SpO 2% Conventional Pulse Oximetry 0 50% 66% 86% 97% 100% SpO 2% 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 O 2 sat 98%
Gas: Colorless Odorless Tasteless Nonirritating Carbon Monoxide (CO) 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 O 2 Hb From Conventional Pulse Oximeter SpCO-SpO 2 Gap: The fractional difference between actual SaO 2 and display of SpO 2 (2 wavelength oximetry) in presence of carboxyhemoglobin From invasive CO- Oximeter 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.
Problems: Accuracy Motion & artifact Dyshemoglobins Pulse Oximetry Case # 4 Which Pressure Is Right? 78 yo trauma patient BP A-line = 70/42 (50) NIBP = 90/50 (52) Blood Pressure Monitoring Direct Pressure vs Indirect 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, EtCO 2 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 CO 2 Clearance Reflects Perfusion In other words: CO 2 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 EtCO 2 circuit connected = flatline??? Circuit Connector Case # 7 EtCO 2 PaCO 2 Post CABG patient EtCO 2 drops to 6 ABG PaCO 2 = 48 mmhg Why?
Another Cause of Low EtCO 2 Profound metabolic acidosis ph = 6.93 Questions? Slides available at: www.mikemcevoy.com Class Code = 666