GRAND ROUNDS

Dr. Jay Green, Emergency Medicine Resident, PGY-3February 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 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)

CARBON MONOXIDE PULSE OXIMETRY: FROM STAR TREK TO YOUR ED

Jay Green, Emergency Medicine Resident, PGY-3February 12, 2009

Emergency Medicine Grand Rounds

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.

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

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

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

1) BRIEF REVIEW OF CO POISONING

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

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

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

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

2) HOW DO CO PULSE OXIMETERS WORK?

How do these things work?

Step 1) probe on finger Step 2)

Step 3) read SpO2 off screen

How do these things work?

Based on red and infrared light absorption

AB

SO

RPTIO

N

How do these things work?

Pulse oximetry Red and infrared lights Detector Translucent site R/IR ratio calculated converted to SpO2

In the beginning…

2 wavelength model invented in 1975 Assumption that there are only 2 light

absorbers O2Hb and Hb

Barker et al 2008

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

Masimo Rad-57

metHb

O2Hb

Hb

COHb

AB

SO

RPTIO

N

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

Masimo Rad-57

Cost (USD) $5,000 for SpCO or SpMet $9,000 for both $720 for peds finger probe

3) ARE CO PULSE OXIMETERS ACCURATE?

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

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

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 138.3% vs SpCO mean 159%

Undersea Hyperb Med 2008;35(2):107-11

Coulange et al.

Undersea Hyperb Med 2008;35(2):107-11

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

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

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

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

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”

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?

4) WHAT IS THEIR ROLE IN OUR PRACTICE?

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

Acad Emerg Med 2006;13(5):S179

HRbpT

RRSpO2

Pain?C/S

Abuse – Y/N?SpCO

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%

HRbpT

RRSpO2

Pain?C/S

Abuse – Y/N?SpCO

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

HRbpT

RRSpO2

Pain?C/S

Abuse – Y/N?SpCO

Respir Care. 2006; 51(11):1332

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

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

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

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?

5) SOME POTENTIAL FUTURE DIRECTIONS.

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

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

Future directions

Other hemoglobins Fetal, sickle cell, thalassemia

Other blood components WBC, platelets, glucose, lytes, INR

Medical tricorder?

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?