What is your response?

A family of 4 comes into your ED after being exposed to carbon monoxide (CO). They were in an idling car, running the engine and heater to stay warm. You want to get a carboxyhemoglobin level on the whole family but cannot get a blood gas from the youngest child.

What is your response?

  • A) Check an oxygen saturation, and if the oxygen saturation is normal, be reassured.
  • B) Check a venous carboxyhemoglobin level.
  • C) Check a venous carboxyhemoglobin and correct for the difference between venous and arterial samples. D) None of the above.

0 voters

Answer: B Discussion
The correct answer is B. A venous carboxyhemoglobin is just as accurate as an arterial carboxyhemoglobin, and it is much less painful to draw. Answer A is incorrect because the pulse oximeter does not reflect hypoxia in carbon monoxide poisoning. Thus, pulse oximetry is useless in determining the carboxyhemoglobin level. Answer C is incorrect because there is no correction needed.

When determining which patients need hyperbaric oxygen on the basis of a carboxyhemoglobin level, the level to rely upon is:

  • A) The carboxyhemoglobin level on arrival to the ED.
  • B) The carboxyhemoglobin level at 4 hours after exposure.
  • C) The carboxyhemoglobin level projected to “time zero” (e.g., at the time of exposure).
  • D) None of the above.

0 voters

Answer: C Discussion The correct answer is C. A major consideration regarding the institution of hyperbaric oxygen therapy is the patient’s clinical situation. More severely ill patients with CO poisoning (e.g., severe acidosis, unconscious, unresponsive, etc.) should be considered candidates for hyperbaric oxygen. Also, treatment should be based on the carboxyhemoglobin level projected to time zero. This is the level that gives the most accurate information about the degree of exposure.

The father has a headache and a time zero carboxyhemoglobin level of 12%. The mother, who is pregnant, is asymptomatic and has a carboxyhemoglobin level of 16%. One of the children, age 6, has a level of 18%, while another has a level of 23% and was asymptomatic at the scene.

The first step in the treatment of these patients is:

  • A) Start an IV and administer saline.
  • B) Start N-acetylcysteine, which is a free radical scavenger.
  • C) Start CPAP to maximize air flow by keeping the airways from collapsing.
  • D) Administer 100% oxygen.
  • E) Intubate the most severe patient, 100% oxygen for the others.

0 voters

Answer: D Discussion The correct answer is D. Because CO competitively binds to hemoglobin in place of oxygen and in fact has greater affinity for hemoglobin than oxygen, highflow 100% oxygen is the cornerstone of treating CO poisoning. Thus, the first step in CO poisoning is to administer 100% oxygen. The rest of the answers are incorrect. If the patient is not ventilating well and requires intubation, this would be appropriate. However, our patients are breathing well and there will be no advantage (and a substantial downside) to intubation.

All of the following can be seen with carbon monoxide poisoning EXCEPT:

  • A) Rhabdomyolysis.
  • B) Cardiac ischemia.
  • C) Long-term neurologic sequelae, including dementia.
  • D) Pulmonary edema.
  • E) All of the above can be seen with carbon monoxide toxicity.

0 voters

Answer: E Discussion The correct answer is E. All of the above can be seen with carbon monoxide poisoning. Additional findings include acidosis, cardiac ischemia, seizures, syncope, and headache. Answer C deserves a bit more discussion. Long-term neurologic sequelae can develop days to months after the exposure and can include cognitive deficits, focal neurologic deficits, movement disorders, and personality changes. Such neurologic sequelae do not appear to be related to the level of carboxyhemoglobin but are more likely to occur when a patient has lost consciousness during
his or her CO exposure. It appears that using hyperbaric oxygen in the appropriate patient will reduce long-term neurologic sequelae.

Your closest diving chamber is about 90 minutes away. You need to make a decision about who to send for hyperbaric oxygen.

Which patient will benefit most from hyperbaric oxygen therapy?

  • A) Asymptomatic pregnant mother, time zero carboxyhemoglobin of 16%.
  • B) Asymptomatic 6-year-old, time zero carboxyhemoglobin of 18%.
  • C) Asymptomatic 8-year-old, time zero carboxyhemoglobin of 23%.
  • D) A and C.
  • E) All of the above need hyperbaric oxygen.

0 voters

Answer: A Discussion The correct answer is A. Criteria for hyperbaric oxygen include mental status changes, carboxyhemoglobin level >25%, acidosis, cardiovascular disease, and age >60. Obviously, these are relative criteria. An otherwise normal 60year-old with a mild exposure need not have HBO. Pregnancy is an indication for HBO therapy because fetal hemoglobin has a high affinity for carbon monoxide and the fetus is highly susceptible to carbon monoxide.

All of the following are well-established consequences of hyperbaric oxygen EXCEPT:

  • A) Seizures.
  • B) Psychosis.
  • C) Myopia.
  • D) Ear and pulmonary barotraumas.
  • E) Direct pulmonary oxygen toxicity.

0 voters

Answer: B Discussion The correct answer is B. All of the rest are found as a result of hyperbaric oxygen. Answer C, myopia, is actually found in up to 20% of patients being treated with hyperbaric oxygen. It is due to direct toxicity of oxygen on the lens and usually resolves within weeks to months.