toxicology grand rounds: carbon monoxide poisoning mark yarema, md frcpc poison and drug information...
TRANSCRIPT
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Toxicology Grand Rounds:Carbon Monoxide
Poisoning
Mark Yarema, MD FRCPCPoison and Drug Information Service
Calgary, Alberta
PADIS/Emergency Medicine/Critical Care RoundsJanuary 27, 2011
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Acknowledgements PADIS: Rosalee Sears-Ford, Nina Walny Critical Care: Paul Boiteau, Sid Viner Emergency Medicine: Ian Rigby, Jay Green, Kevin
Hanrahan Miscericordia Hospital: Malcolm Young HBOT Clinics: Terry Stewart, Karen Keats, Caroline
Bain AHS Telehealth PLP: Marianna Hofmeister, Holly Donaldson, Kyle
Dormer Podcast website: http://www.ucalgary.ca/plppodcasts/
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Disclosure
I have no commercial interest in any of the products or therapies discussed in this presentation.
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Cases Intro to CO Pathophysiology Clinical features Diagnosis Management Special presentations:
Misericordia Hospital HBO Unit HBOT Clinics Inc.
Q and A
Outline
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Case 1
63 y.o. male Last seen July 1 Found by wife July 2 AM in garage with
riding tractor running EMS called, pt. in cardiorespiratory
arrest Intubated, ventilated, CPR Return of spontaneous circulation 15
minutes after resuscitation initiated
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Case 1
In E.D.: ABG: pH < 6.8 PC02 58, p02 31, HC03 15,
Lactate > 20, COHb 61% ST depression on EKG Another cardiac arrest resuscitated Multiple pressors
PADIS consulted: candidate for HBO?
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Case 1
d/w PADIS: meets accepted criteria for HBO. Recommended speaking with Misericordia HBO MD on call
Transferred to Misericordia 1 HBO treatment given July 2 Transferred to ICU July 3 Died 19:29 hours July 3
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Case 1.5 4 days after death of Case 1 21 y.o. male Texted girlfriend at 0400, found
asystolic in car by EMS at 0500 ROSC after 30 minutes CPR by EMS In E.D.:
intubated, unresponsive ABG pH 6.82, COHb 57.3%, Lactate 22
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Case 1.5 d/w PADIS: meets accepted criteria for
HBO. Recommended speaking with Misericordia HBO MD on call
Pt. deemed not appropriate candidate Died 1700 hrs July 7th
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Case 2
62 y.o. female, 16 y.o. male, 35 y.o. male
Hx of ‘faulty furnace’ in home Furnace turned on during last period of
Canucks game, then everyone fell asleep
4.5 hour ‘soaking period’
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Case 2 1:00am: 16 y.o. gets up to go to fridge,
falls 62 y.o. hears the fall and wakes up EMS called
16 y.o. and 35 y.o.: headache, nausea, no other symptoms
62 y.o.: disoriented, combative, vomiting, headache
Does anyone need HBO?
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Case 2
d/w PADIS: 62 y.o. most concerning, meets accepted criteria for HBO. Recommended speaking with HBOT Clinics MD on call
MD speaks with HBOT clinics HBO MD on call
Patient accepted by HBOT, treated with HBO
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Intro to CO
Colorless, odorless, tasteless gas Formed by incomplete combustion of
carbon-containing compounds Normal byproduct of hemoglobin
degradation Many different sources of exposure
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Sources of CO Fires Auto exhaust Cigarette smoke Malfunctioning water heaters, gas stoves,
furnaces Wood-burning fireplaces, blocked chimneys Propane forklifts Ice resurfacing machines Generators Inappropriate heat sources (e.g. barbecues)
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Source: The Arizona Republic,November 29, 2000 (Maureen West and Judd Slivka, reporters)
www.coolestspringbreak.com
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Deadly houseboatsCO
concentration in ppm
Scenario
25 Maximum exposure allowed by Can. OSHA for 8 hours
300 Home CO detector cutoff level (10 minute exposure)
800 CNS symptoms, Death ~ 2 hours
1200 Immediately Dangerous to Life and Health (IDLH)
5000-10,000 Measured in open air near swim platform
12,000 Death within 2-3 minutes
7000-30,000 Measured under houseboat swim platforms
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Physiology Rapidly diffuses across alveolar-
capillary membranes Binds to hemoglobin with 200-250X
greater affinity than oxygen 10-15% of total body CO taken up by
tissue, bound to extravascular proteins Myoglobin Cytochrome oxidase Catalase Peroxidases
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Pathophysiology
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Pathophysiology
Left shift oxyhemoglobin dissociation curve
Binding to cytochrome oxidase Activation of excitatory amino acids Binding to myoglobin Nitric oxide (NO)
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Left shift
CO increases the affinity of oxygen for hemoglobin
Oxygen not displaced by CO is bound more tightly to Hb
Lower oxygen delivery to cells Hypoxia
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www.modernmedicine.com
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Left shift / hypoxia
Does not explain all manifestations of poisoning
Patients may remain comatose even after COHb undetectable
Dissolved CO in plasma and delivery to target organs also important
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Cytochrome oxidase inhibition CO interferes with cellular respiration Decreased ATP production Initiates inflammatory cascade Lipid peroxidation Ischemic brain injury Binding may be increased under
hypotensive or hypoxic conditions
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Yong-Ling P. Ow, Douglas R. Green, Zhenyue Hao & Tak W. MakNature Reviews Molecular Cell Biology 9, 532-542 (July 2008)
Cytochrome oxidase
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Activation of excitatory amino acids Tissue hypoxia increases excitatory
amino acid levels Glutamate stimulates NMDA receptors
and causes intracellular Ca++ release Delayed neuronal cell death
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Myoglobin CO binds with 60X > affinity than O2
Binding enhanced under hypoxic conditions Leads to myocardial depression Carboxymyoglobin may explain
dysrhythmias and ischemia that may occur with mild exposures Especially with pre-existing CAD
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Oh NO!
CO displaces nitric oxide (NO) from platelets
Actions of NO: Vasodilator Forms peroxynitrite radicals inactivate
cytochrome oxidase Formation of platelet-neutrophil
aggregates neutrophil adhesion in brain microvasculature
End result: delayed lipid peroxidation
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Weaver. NEJM 2009
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Simpler version of previous slide Too much CO = Bad
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Clinical features of poisoning
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Clinical features
Early symptoms very nonspecific Often confused with other illnesses:
Influenza Food poisoning Gastroenteritis Colic
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Neurologic
Initial Headache, dizziness, nausea
Later (higher levels/longer exposures) Syncope, focal neuro sx suggesting CVA,
LOC, confusion, seizures, coma Persistent neurologic sequelae Delayed neurologic sequelae (DNS)
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Delayed Neurologic Sequelae Incidence between 2-43%
2 days – 5 weeks after initial poisoning Neurologic and psychiatric symptoms
amnesia ■ headaches psychosis ■ apraxia parkinsonism ■ incontinence paralysis ■ periph. neuropathy chorea ■ dementia
50-75% of cases resolve (may take months 1 year)
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Who is at risk for DNS? post-hoc analysis of Weaver 2002 RCT
plus additional pts treated only with NBO not in trial
Those most at risk of DNS: History of LOC Patients with long exposures (> 24 hours) Age > 36 COHb > 25%*
*Randomized trial data only, not separate NBO patients
Weaver et al. Am J Resp Crit Care Med 2007;176:491-7.
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Cardiac
PVC’s and other dysrhythmias Myocardial ischemia Myocardial stunning With CAD, exacerbation of angina and
arrhythmias can occur with COHb < 10%
Acute mortality from CO usually from ventricular arrhythmias
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230 pts with moderate/severe poisoning all treated with HBO
Indications for HBO: LOC Seizure Focal neuro deficit Ischemic chest pain Dysrhythmias COHb > 40% COHb> 25% with Hx CV disease, age > 60, Hgb
< 100, exposure > 2 hours
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85 (37%) had elevated TnI or CK-MB or diagnostic EKG changes of ischemia
32 (38%) eventually died compared with 22 (15%) of patients who had no myocardial injury Effect persisted over many years
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Diagnosis History and physical
Mini mental status exam Laboratory tests
CO pulse oximetry COHb / VBG Select patients: EKG, cardiac markers
Imaging CT MRI
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COHb pulse oximeters
Accurate 3% from COHb of 0-40% Some false +ves
More during early use? Pre-hospital
Incident response paramedics Calgary Zone availability
FMC, PLC, RGH triage UCC’s
www.masimo.com
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[COHb] Measured with co-oximeter Venous blood as accurate as arterial Normal levels 0-5%, up to 10% in smokers Wide variation in clinical manifestations with
identical levels Inaccurate predictor of peak levels
Variations in half lives Effect of 02 given prior to sampling
Not predictive of symptoms or final outcome
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Blood gas Some HBO trials have used lactate >
2.5 or base excess < -2 as indications for HBO
Metabolic acidosis (hydrogen ion concentration) on presentation a better predictor of need for multiple HBO treatments than COHb*
*Turner et al. J Accid Emerg Med 1999
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Neuroimaging
Abnormalities may be seen within 12 hours of CO exposure causing LOC
Basal ganglia most commonly affected Caudate Putamen Globus pallidus
Also subcortical white matter and hippocampus
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cerebellum
caudate
globus pallidus
www.learningradiology.com
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Management ABC’s O2 via nonrebreather
Alters t ½ of COHb 5-6 hours at room air 40-90 minutes on 02 via NRB
Hyperbaric oxygen
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HBO 100% O2 while exposed to increased
atmospheric pressure Reduces the half-life of COHb to 23 minutes Mechanisms:
Increases dissolved plasma [02] tenfold May help regenerate cytochrome oxidase Inhibits leukocyte adherence to the
microvascular endothelium Does HBO prevent development of delayed
neurologic sequelae?
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Non-blinded, randomized study of 629 adults, Rx within 12 h exposure pregnant women, pts < 15 y.o. excluded
Patients separated into LOC vs. no LOC prior to randomization into one of four groups No LOC: 6h NBO vs 4h NBO +1 HBO Rx (2.0
ATA X 1 hour) LOC: 4h NBO + 1 HBO vs 4h NBO + 2 HBO
Rx (all + 4h NBO) Self-assessment questionnaire at 1 month
following Rx re: neurologic sequelae
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% complete recovery at 1 month: No LOC: 66% NBO vs 68% HBO LOC: 54% 1 HBO vs 52 % 2 HBO
Conclusion: HBO not useful in pts with no LOC, and 2 sessions not useful in those who did have LOC
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Randomized, non-blinded, 65 patients with mild poisoning , <6 hours of removal from exposure LOC, cardiac compromise excluded
1 HBO Rx (120 mins, 2.8 ATA) vs NBO until Sx resolved
Mean time from randomization to HBO 2 hours Neuropsych tests done after Rx (baseline) then 3-
4 weeks after poisoning
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Incidence of DNS: 23% NBO group, 0% HBO group
Conclusion: HBO decreased incidence of DNS after CO poisoning
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Scheinkestel et al, Med J Aust March 1999 Randomized, double-blind trial with 191
patients, all severities included pregnancy, peds excluded
Time to treatment 6.6-7.5h HBO: 3 days of 60 min Rx at 2.8 ATA +
continuous NBO potentially 3 more HBO Rx if clinically abN
after the first 3 NBO: continuous hi flow 02 for 3 days +
sham dives
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Scheinkestel et al, Med J Aust March 1999 46% lost to follow up Incidence of DNS: HBO 5/104; NBO 0/87 Conclusion: No benefit from HBO and
may have worsened outcome, cannot be recommended
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Randomized trial of 152 patients Extensive inclusion criteria HBO group: 3 treatments (1 X 2.8 ATA, 2 X
2.0 ATA) NBO group: 100% 02 via NRB during 3 sham
dives Neuropsych testing after chamber sessions 1
and 3, then 2 wks, 6 wks, 6 mos, 12 mos Primary outcome: cognitive sequelae at 6
wks.
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Higher cerebellar dysfunction in NBO group (15% vs 4%)
At 6 wks, lower incidence DNS in HBO group (25% vs 46%) persisted when adjusting for cerebellar
dysfunction and also at 12 months (ITT analysis)
Conclusion: 3 HBO Rx within 24h period reduced risk of cognitive sequelae at 6 weeks and 12 months
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Non blinded, randomized trial of 385 pts. aged 15 years and up
Domestic CO poisoning only, October 1989- January 2000
Patients separated into LOC vs. coma prior to randomization into one of four groups LOC: NBO vs NBO +1 HBO Rx (2.0 ATA X 1
hour) coma: NBO +1 HBO Rx (2.0 ATA X 1 hour) vs 2
HBO Rx Self-assessment questionnaire at 1 month re:
neurologic sequelae
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% complete recovery at one month following treatment LOC: 58% NBO vs. 61% HBO Coma: 68% HBO X 1 vs. 47% HBO X 2
(significant) Conclusion: no evidence superiority of HBO
> NBO in patients with LOC. 2 HBO treatments associated with worse outcomes.
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HBO Clinical Trials Study design flaws:
Randomization procedures Blinding Intent to treat analyses Follow up (most 15-20% lost to f/u except one at
46%) Outcomes (questionnaires vs neuropsych battery,
“complete recovery” vs. “cognitive sequelae”) NBO and HBO therapies used (duration, number
of treatments) Excluded patients (pregnant, peds)
Buckley et al. Toxicol Rev 2005;24(2):75-92
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HBO-suggested indications* Syncope Altered LOC Coma Seizure Abnormal cerebellar function Age > 36 years Prolonged CO exposure (> 24 hours) COHb > 25%
Missing: myocardial ischemia
Goldfrank’s Toxicologic Emergencies, 2011
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Pregnant patients Fetal COHb concentrations tend to be
higher than maternal levels (animal studies) Human studies suggest fetal Hgb affinity is
similar to maternal Hgb affinity in low 02 states More important issue is fetal hypoxia
Maternal COHb does not predict fetal outcome
Normal mental status with no LOC in mother = good outcomes, normal deliveries
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Pregnant patients
NBO treatment of pregnant patients similar to nonpregnant patients treat until mother is asymptomatic benefit of prolonged Rx to mother unclear
Indications for HBO in pregnant patients same as for nonpregnant patients except:
lower COHb in mother at which HBO recommended (arbitrarily set at 15-20%)
any features of fetal distress
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Outcomes
Cardiac arrest patients
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18 patients given HBO after cardiac arrest with ROSC
Resuscitation time range 19-45 min. Mean time to HBO 4.3 hours post exposure COHb range 14-55% All patients died during hospitalization (range 9
hours-7 days post discovery) HBO director survey of fictitious CO-induced arrest
case: 100% recommended HBO Chance of survival 74% Chance of recovery w/o neurologic sequelae 28%
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CO poisoning and cardiac arrest Quick summary of other studies:
5 peds smoke inhalations: 0 survivors 10 peds CO patients: 8 died, 2 had DNS 10 adult smoke inhalations: 0 survivors 11 adult CO patients: 0 survivors 23 adult CO patients: 17 died, 6 unknown
outcome ? Role of CN poisoning in smoke
inhalation victims
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Objectives
By the end of the presentation, the participant should be able to: List the mechanisms by which carbon
monoxide (CO) causes toxicity Describe the clinical features seen with acute
and delayed toxicity from CO Discuss the controversies in the management
of CO poisoning, including the role of hyperbaric oxygen (HBO)
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How to reach us
Poison and Drug Information Service: 403- 944-1414 (Calgary) 1-800-332-1414 (Alberta)