|
| |
Pharmacology
- affinity for Hb 200-250 times that of oxygen
- combines with Hb to form carboxy-Hb and the affinity of the remaining haem for
oxygen is increased
- toxicity caused by tissue anoxia and possibly also inhibition of cellular
respiration as a result of binding to other haem proteins
- elimination t1/2 of CO reduced from 250 mins when breathing air to
59 mins breathing 100% O2 and 22 min when breathing 100% O2 at 2.2 atm
Poisoning
Presentation
- acute exposure: depends on level of carboxy-Hb. Generally no symptoms if
level < 10% while levels > 60% associated with coma and cardiorespiratory
arrest
- late sequelae include neuropsychiatric complications which may develop weeks
after exposure. Include memory loss, impaired intellect, signs of cerebellar and
mid-brain damage
- signs of poisoning include: cherry red skin, coma, hyper-reflexia, convulsion,
arrhythmias
Management
- remove from site of exposure
- 100% O2 by facemask
- if there is respiratory depression or airway compromise intubate and ventilate
- in severe poisoning assume cerebral oedema and treat accordingly
- indications for hyperbaric oxygen:
- conscious patient with carboxy-Hb > 20%
- depressed level of consciousness but able to maintain airway
- recovery of consciousness after initial carboxy-Hb > 40%
- contraindications (single person chamber)
- artificial ventilation
- inability to maintain airway
- hypovolaemia or dependence on inotropes
- arrhythmias potentially requiring urgent treatment
- asthma
Pregnancy
- fetal haemoglobin binds CO with greater affinity than maternal Hb
- T1/2 fetal carboxyhaemoglobin 3.5 longer than maternal
- fetal carboxyhaemoglobin concentration 15% higher than maternal
|
