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GRAND ROUNDS

GRAND ROUNDS. Dr. Jay Green, Emergency Medicine Resident, PGY-3 February 12, 2009. Emergency Medicine Grand Rounds. Deanna Troi -Star Trek TNG. Medical tricorder. Tricorder. Handheld device for scanning, interpreting, recording Three primary variants Standard tricorder

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GRAND ROUNDS

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  1. GRAND ROUNDS Dr. Jay Green, Emergency Medicine Resident, PGY-3 February 12, 2009 Emergency Medicine Grand Rounds

  2. Deanna Troi -Star Trek TNG Medical tricorder

  3. Tricorder • Handheld device for scanning, interpreting, recording • Three primary variants • Standard tricorder • General-purpose device • Engineering tricorder • Fine-tuned for starship engineering purposes • Medical tricorder • Help diagnose diseases and collect information about a patient • Vital signs, broken bones, toxins (eg. carbon monoxide)

  4. CARBON MONOXIDE PULSE OXIMETRY: FROM STAR TREK TO YOUR ED Jay Green, Emergency Medicine Resident, PGY-3 February 12, 2009 Emergency Medicine Grand Rounds

  5. Objectives 1) Brief review of CO poisoning. 2) How do CO pulse oximeters work? 3) Are CO pulse oximeters accurate? 4) What is their role in our practice? 5) Some potential future directions.

  6. Case • 41y M, lives alone • Sudden onset H/A this am • Vague dizziness upon standing • H/A specific Q’s: • No fever/rigors, no trauma, no other neuro sympt, no eye symptoms, no constitutional symptoms, no hx migraine • PMH: nil • Meds: none • NKDA Chee et al. Clin Tox 2008;46:461-9

  7. Case continued • O/E • 37.0°C, HR 93, 160/82, RR 14, SpO2 95%RA • CNS, H&N, CVS, Resp, abdo normal • ECG NSR • CBC, lytes, Cr N • CT head N • LP no RBC, no xanthochromia • H/A improving while in ED Chee et al. Clin Tox 2008;46:461-9

  8. Case continued • Disposition • D/C home with instructions • If you had SpCO capabilities • SpCO = 33% and COHb (VBG) = 25% • Fire dept sent to house • Markedly elevated CO level in house • Source addressed • CO detector installed • More serious presentation avoided? Chee et al. Clin Tox 2008;46:461-9

  9. 1) BRIEF REVIEW OF CO POISONING

  10. CO Poisoning Review • Odourless, colourless, tasteless gas • Product of hydrocarbon combustion • Or metabolism of methylene chloride (paint remover) • Binds to Fe in heme 240x greater affinity than O2 • O2 delivery/utilization • Displacing O2 • Allosteric change in hemoglobin molecule (L-shift) • Impairs oxidative phosphorylation • Inactivates cytochrome oxidase

  11. CO Poisoning Review • Presentation • Non-specific (H/A, nausea, dizziness, syncope) • Altered mental status, cherry red lips • Severe: seizure, coma, myocardial ischemia, acidosis

  12. CO Poisoning Review • Diagnosis • Clinical suspicion +  COHb level • Management • Supportive • Oxygen • HBOT indications (controversial) • COHb > 25% • Ongoing end-organ ischemia • Loss of consciousness • Pregnancy + COHb > 20% or fetal distress

  13. CO Poisoning Review • Delayed neuropsychiatric syndrome • Up to 40% of severe exposure • COHb level not predictive • Symptoms usually within 20 days • Cognitive deficits • Personality changes • Movement disorders • Focal neurologic deficits • HBOT may prevent • NNT = 5 to prevent cognitive sequelae at 6 wks Weaver et al, NEJM 2002;347(14):1057-67

  14. 2) HOW DO CO PULSE OXIMETERS WORK?

  15. How do these things work? • Step 3) read SpO2 off screen • Step 1) probe on finger • Step 2)

  16. How do these things work? • Based on red and infrared light absorption ABSORPTION

  17. How do these things work? • Pulse oximetry • Red and infrared lights • Detector • Translucent site • R/IR ratio calculated  converted to SpO2

  18. In the beginning… • 2 wavelength model invented in 1975 • Assumption that there are only 2 light absorbers • O2Hb and Hb Barker et al 2008

  19. From 2 to 8 wavelengths… • 3 wavelength oximeter invented 2002 •  accuracy of SpO2 • Comment that SpCO can likely be measured • 4 wavelength oximeter invented 2005 • 8-12 wavelength oximeters also in 2005 • Masimo Rad-57

  20. Masimo Rad-57 metHb ABSORPTION O2Hb Hb COHb

  21. Masimo Rad-57 • Limitations: • Still estimate SpO2 the old way • ‘Crosstalk’ between SpMet and SpCO channels • In SpMet you get falsely SpCO • Recognized by machine

  22. Masimo Rad-57 • Cost (USD) • $5,000 for SpCO or SpMet • $9,000 for both • $720 for peds finger probe

  23. 3) ARE CO PULSE OXIMETERS ACCURATE?

  24. Accurate? • Masimo website • Accurate 3% from COHb of 0-40% • Barker et al, 2006 • N=20 healthy volunteers • 10 inhaled CO to COHb=15% • 10 given sodium nitrite 300mg IV (MetHb=12%) • Compared arterial COHb with Rad-57 SpCO values • Results • SpCO level accurate  2.2% • SpMet level accurate 0.45% Anesthesiology 2006;105(5):892-7

  25. Accurate? • Mottram et al • SpCO vs COHb (ABG) • Measured simultaneously (convenience sample) • N=31 • Results • Most COHb < 5% • “SpCO accurate” • SpCO slightly overestimated COHb Respiratory Care 2005; 50(11):1471

  26. Accurate? • Coulange et al • French study at HBOT center • Prospective descriptive study • Excluded smokers • VBG COHb compared to SpCO • N=12 over 7 months • Results • COHb mean 138.3% vs SpCO mean 159% Undersea Hyperb Med 2008;35(2):107-11

  27. Coulange et al. Undersea Hyperb Med 2008;35(2):107-11

  28. Accurate? • Suner et al • Prospective observational study, urban ED • SpCO screening at triage over 3 months • N=10,856 • Results • 28 cases of CO toxicity, 11 unsuspected • 22 cases of false positives • Correlation r=0.72 J Emerg Med 2008; 34:441–450

  29. Suner et al • Results continued • Normal values for COHb • Smokers (5.2%; 95% CI 5.07–5.33%) • Non-smokers (2.9%; 95% CI 2.84–2.96%) • Calculated upper limit of normal (mean +2SD) • Smokers (12%) • Non-smokers (8%) J Emerg Med 2008; 34:441–450

  30. Accurate? • O’Malley et al • Letter to editor • Started to study screening at triage for SpCO • After 2 days had 5/328 false +ve • Study stopped • Suner - response • Initial false +ves (N=14,000) • False +ves decreased over time (technique issue?) Annals EM 2006;48(4):478

  31. False positives • Hampson • Case report • Hemolytic anemia • As Hb   COHb  • Conclusion • Endogenous CO production increased in rapid heme turnover • One source of “false +ve” COHb

  32. Accurate? • Layne et al • SpCO vs COHb (ABG) • ED and outpatient pulmonary lab • N=157 • Results • ED: accurate ± 4.34% • COHb range 0-31% • Pulmonary lab: accurate ± 1.8% • COHb range 0-14% • Conclusion • SpCO pulse oximeter performs well, “quite reliable”

  33. 3) Are CO pulse oximeters accurate? • Summary • Limited data • Needs further study over wide range of COHb • Seems accurate based on what we have • Some false +ves • More during early use?

  34. 4) WHAT IS THEIR ROLE IN OUR PRACTICE?

  35. The 6th (7th…8th?) vital sign • Chee et al, 2006 • Observational study, tertiary care ED • 12 days of SpCO screening at triage • N=1,756 • Found 3 cases of unsuspected CO toxicity • All confirmed with COHb measurement HR bp T RR SpO2 C/S Pain? Abuse – Y/N? SpCO Acad Emerg Med 2006;13(5):S179

  36. The 6th (7th…8th?) vital sign • Chee et al, 2008 • Observational study, urban ED (95,000pts/y) • Inclusion: pts >=18y • Exclusion: obvious concern for CO poisoning • Triage SpCO measurement with vitals • N= ~75,000 over 13 months • Results • 7 cases of occult CO poisoning • 4 transferred for HBOT • Incidence of occult CO poisoning 0.03% HR bp T RR SpO2 C/S Pain? Abuse – Y/N? SpCO

  37. The 6th (7th…8th?) vital sign • Partridge et al • Triage screening in large urban ED over 3 months • N=4,955 • Results • 9 cases of occult CO toxicity • All with non-specific symptoms • All had source identified in home • Also tested all patients with presumed CO toxicity • No false –ve HR bp T RR SpO2 C/S Pain? Abuse – Y/N? SpCO Respir Care. 2006; 51(11):1332

  38. Pre-hospital use • Hostler et al • FD carried Rad-57 on truck • Used for CO alarms • N=94 • Results • 9 pts transferred to hospital for  ambient CO level • SpCO = 22.1% (range 17-27.2%) • 85 pts not transferred to hospital • SpCO = 3.2% (range 2.6-3.8%) Prehosp Emerg Care 2008; 12:115

  39. Remote environments? • Crawford & Hampson • British Royal Navy submarine performing exercises under polar ice cap • Explosion/fire put out • Used Rad-57 to document one patient with SpCO of 28% after 15min of 100% O2 • Pt evacuated to HBOT center • Conclusion • Potentially useful in hospitals that lack lab access to COHb or remote environments Emerg Med J 2008; 25:235–236

  40. Where do we use them? • Pre-hospital • EMS has a few units • Supervisors carry them • Triage • FMC, PLC, RGH have units • Used only for patients with potential CO exposure • Not used for screening all patients

  41. 4) What is their role in our practice? • Summary • Probably reasonable to screen patients at triage • Minimal extra time (done at same time as SpO2) • 0.03% x 200,000 = 60 potentially missed cases/yr • Pre-hospital • Probably useful in some situations • Replace COHb measurement in ED? • Not enough evidence • 2nd best option if lack capabilities?

  42. 5) SOME POTENTIAL FUTURE DIRECTIONS.

  43. Future directions • Rad-57 • Primary diagnostic tool in hospitals without ABG • Radical-7 • Non-invasive measurement of Hb (SpHb) • Macknet et al • N = 48 OR patients • 1U blood removed, 30cc/kg IV NS given • Compared arterial Hb and SpHb • Results • R=0.88

  44. Interesting case • Dr. Viljoen walking by as a research team was setting up Radical-7 • “That will never work” • Took his SpHb and found to be low • O/E  FOB+  colonoscopy neg  EGD erosion • Biopsy +ve for neoplastic changes  PET scan showed met to humeral head • Surgical removal of both • SpHb monitor credited with earlier diagnosis of malignancy 14th Annual World Congress of Anesthesiology; March 2008; Capetown, South Africa

  45. Future directions • Other hemoglobins • Fetal, sickle cell, thalassemia • Other blood components • WBC, platelets, glucose, lytes, INR • Medical tricorder?

  46. Objectives 1) Brief review of CO poisoning. 2) How do CO pulse oximeters work? 3) Are CO pulse oximeters accurate? 4) What is their role in our practice? 5) Some potential future directions. Questions?

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