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GRAND ROUNDS

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GRAND ROUNDS Dr. Jay Green, Emergency Medicine Resident, PGY-3 February 12, 2009 Emergency Medicine Grand Rounds abstract * First clinical study, no manufacturer ... – PowerPoint PPT presentation

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Title: GRAND ROUNDS


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 Qs
  • 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 200846461-9
7
Case continued
  • O/E
  • 37.0C, HR 93, 160/82, RR 14, SpO2 95RA
  • CNS, HN, 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 200846461-9
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 200846461-9
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

Oxygen source CO half-life
RA 4-5 hours
NRB 60-90min
HBOT 15-30min
12
CO Poisoning Review
  • Diagnosis
  • Clinical suspicion ? COHb level
  • Management
  • Supportive
  • Oxygen
  • HBOT indications (controversial)
  • COHb gt 25
  • Ongoing end-organ ischemia
  • Loss of consciousness
  • Pregnancy COHb gt 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 2002347(14)1057-67
14
2) HOW DO CO PULSE OXIMETERS WORK?
15
How do these things work?
  • Step 1) probe on finger
  • Step 2)
  • Step 3) read SpO2 off screen

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
  • N20 healthy volunteers
  • 10 inhaled CO to COHb15
  • 10 given sodium nitrite 300mg IV (MetHb12)
  • Compared arterial COHb with Rad-57 SpCO values
  • Results
  • SpCO level accurate ? 2.2
  • SpMet level accurate ?0.45

Anesthesiology 2006105(5)892-7
25
Accurate?
  • Mottram et al
  • SpCO vs COHb (ABG)
  • Measured simultaneously (convenience sample)
  • N31
  • Results
  • Most COHb lt 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
  • N12 over 7 months
  • Results
  • COHb mean 13?8.3 vs SpCO mean 15?9

Undersea Hyperb Med 200835(2)107-11
27
Coulange et al.
Undersea Hyperb Med 200835(2)107-11
28
Accurate?
  • Suner et al
  • Prospective observational study, urban ED
  • SpCO screening at triage over 3 months
  • N10,856
  • Results
  • 28 cases of CO toxicity, 11 unsuspected
  • 22 cases of false positives
  • Correlation r0.72

J Emerg Med 2008 34441450
29
Suner et al
  • Results continued
  • Normal values for COHb
  • Smokers (5.2 95 CI 5.075.33)
  • Non-smokers (2.9 95 CI 2.842.96)
  • Calculated upper limit of normal (mean 2SD)
  • Smokers (12)
  • Non-smokers (8)

J Emerg Med 2008 34441450
30
Accurate?
  • OMalley 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 (N14,000)
  • False ves decreased over time (technique issue?)

Annals EM 200648(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
  • N157
  • 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 (7th8th?) vital sign
  • Chee et al, 2006
  • Observational study, tertiary care ED
  • 12 days of SpCO screening at triage
  • N1,756
  • 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 200613(5)S179
36
The 6th (7th8th?) vital sign
  • Chee et al, 2008
  • Observational study, urban ED (95,000pts/y)
  • Inclusion pts gt18y
  • 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 (7th8th?) vital sign
  • Partridge et al
  • Triage screening in large urban ED over 3 months
  • N4,955
  • 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
  • N94
  • 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 12115
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 25235236
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
  • R0.88

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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