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Check a Pulse! When to Question SpO 2 , NIBP & EtCO 2 Readings

Check a Pulse! When to Question SpO 2 , NIBP & EtCO 2 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

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Check a Pulse! When to Question SpO 2 , NIBP & EtCO 2 Readings

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  1. 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

  2. Learning Objectives Upon completion of the presentation the participant will: • Recall two common sources of user error in non-invasive vital sign measurement • Discuss the methodology used to obtain a non-invasive blood pressure reading • State one response of a pulse oximeter when unable to detect a pulse Talk Code = 711

  3. Case # 1 - Desaturation • While charting… • SpO2 alarms 74% • Patient in no distress, good color • Repositioning sensor yields same 74% sat • ABG shows 98% sat

  4. Well appearing patient, 74% SpO2 • Why me?

  5. Case # 2 – O2 Sat Out Of Nowhere… • Patient discharged 2 hours ago • Mysteriouswaveformand 100% sat

  6. Model of Light Absorption At Measurement Site Without Motion • ACVariable light absorption due pulsatile volume of arterial blood • DCConstant light absorption due to non-pulsatile arterial blood. • DCConstant light absorption due to venous blood. • DC Constant light absorption due to tissue, bone, ... Absorption • Time

  7. Model of Light Absorption At Measurement Site With Motion • ACVariable light absorption due pulsatile volume of arterial blood • DCConstant light absorption due to non-pulsatile arterial blood. • ACVariable light absorption due to moving venous blood • DCConstant light absorption due to venous blood. • DC Constant light absorption due to tissue, bone ... Absorption • Time

  8. Influence of Perfusion on Accuracy of Conventional Pulse Oximetry During Motion Good Perfusion (Conventional PO) SpaO2=98 SpO2=93 SpvO2=88 Poor Perfusion (Conventional PO) SpaO2=98 SpO2=74 SpvO2=50

  9. Conventional Pulse Oximetry Algorithm MEASUREMENT R/IR CONFIDENCE Post Processor % Saturation % Saturation Digitized, Filtered & Normalized R & IR 3 options during motion or low perfusion: • Freeze last good value • Lengthen averaging cycle • Zero out

  10. Next Generation Pulse Oximetry

  11. Next Generation Pulse Oximetry

  12. Masimo SET: Signal Extraction Technology MEASUREMENT R/IR(Conventional Pulse Oximetry) CONFIDENCE MEASUREMENT DSTTM CONFIDENCE Post Processor Confidence Based Arbitrator % Saturation Digitized, Filtered & Normalized MEASUREMENT R & IR FSTTM CONFIDENCE DST SET – 97% MEASUREMENT SSTTM CONFIDENCE 0 50% 66% 97% 100% SpO2% MEASUREMENT Proprietary Algorithm 4 CONFIDENCE Masimo SET “Parallel Engines” SET “Parallel Engines”

  13. Variable Constant Variable Constant Averaging - inaccurate SpO2 Separating - accurate SpO2 0 50% 66% 86% 97% 100% 0 50% 66% 86% 97% 100% SpO2% SpO2% Measure Through Motion Pulse Oximetry 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) Conventional Pulse Oximetry

  14. Certainty…

  15. 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%

  16. Carbon Monoxide (CO) • Gas: • Colorless • Odorless • Tasteless • Nonirritating • Physical Properties: • Vapor Density = 0.97 • LEL/UEL = 12.5 – 74% • IDLH = 1200 ppm

  17. 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 CO-Oximeter Blood Sample [Blood] Barker SJ, Tremper KK. The Effect of Carbon Monoxide Inhalation on Pulse Oximetry and Transcutaneous PO2. Anesthesiology 1987; 66:677-679

  18. 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

  19. Pulse CO-oximetry

  20. Hgb Signatures: CO, Met, Hgb…

  21. 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.

  22. Pulse Oximetry Problems: • Accuracy • Motion & artifact • Dyshemoglobins

  23. Case # 4 – Which Pressure Is Right? 78 yo trauma patient  BP • A-line = 70/42 (50) • NIBP = 90/50 (52)

  24. Blood Pressure Monitoring Direct Indirect vs Pressure Flow

  25. 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

  26. 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)

  27. 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

  28. 150 90 60

  29. Waveform Capnography Available for spontaneously breathing and for intubated patients

  30. 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 • ???

  31. Circulation The heart and lungs are inextricably linked together

  32. Cardiac Arrest! • Little O2 delivery or consumption • Little CO2 production or venous return

  33. CO2 Clearance Reflects Perfusion In other words: CO2 production is largely dependent on oxygen consumption!

  34. Case # 6 – Misplaced ETT? • Cardiac arrest on med-surg floor • CRNA intubates without difficulty, visualizes tube pass through cords • EtCO2 circuit connected = flatline • ???

  35. Circuit Connector

  36. Case # 7 – EtCO2≠ PaCO2 • Post CABG patient EtCO2 drops to 6 • ABG PaCO2 = 48 mmHg • Why?

  37. Another Cause of Low EtCO2 • Profound metabolic acidosis • pH = 6.93

  38. Questions? Slides available at: www.mikemcevoy.com

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