Setting: ED
CC: Patient brought in unresponsive from a fire
VS: BP: 118/82 mm Hg; P:114 beats/minute T: 98°F; R: 32 breaths/minute
HPI: A 78-year-old man is brought to the ED after having been found on the floor of his home during a fire. The patient is barely conscious and not able to offer a clear history. He arrives in the ED within half an hour of being found. Another part of the house was on fire. The neighbors called the police and fire department and they broke down the door. The patient did not sustain burns himself, but several others from the next room sustained significant burn injury.
What is the most common cause of death in fires?
a. Volume depletion and hypovolemic shock
b. Sepsis
c. Carbon monoxide (CO) poisoning
d. Renal failure
e. Hyperkalemia and arrhythmia
f. Respiratory burn
Answer c. Carbon monoxide (CO) poisoning
Sixty percent of deaths on the first day in a fire are from smoke inhalation and CO poisoning. All of the answer choices can cause death in fires. CO poisoning is just the most common one. Sepsis or infection from a skin source is the most common cause of late death several days or weeks after a fire. When respiratory burn occurs, it is extremely lethal, but it is just not as common a cause of death as the others.
Smoke kills at a distance: Burn needs contact.
Smoke spreads easier than fire.
PMHx: (from medical alert bracelet)
Hypertension
Aortic stenosis
Medications: unknown
Fires = Smoke Inhalation = CO Poisoning
Fires and smoke inhalation are reasons to write orders before doing the physical examination. There is a cookbook of standard orders to do before anything. No matter what you see on the physical, in a fire you need to administer oxygen and to measure oxygenation; 100% oxygen is what is needed, but there is no way on CCS to order dosing, including the dosing of oxygen.
Orders:
Oxygen
ABG
Carboxyhemoglobin (COHb) level
CHEM-7
PE:
General: lethargic man lying on stretcher
Chest: clear bilaterally
Cardiovascular: 3/6 murmur radiating to carotid arteries
Neurological: disoriented, lethargic, unable to assess focal findings because of disorientation
How do you die from CO poisoning?
a. Stroke
b. Myocardial infarction
c. Lung infarction
d. Renal failure
e. High output failure
Answer b. Myocardial infarction
Although disorientation and possible coma are apparent from severe smoke inhalation and CO poisoning, the organ that receives fatal damage is the heart. The heart cannot physiologically distinguish between hypoxia, coronary artery stenosis, anemia, and CO poisoning.
For Myocardium: CO = Anemia = Stenosis = Hypoxia
On CCS, if you forget to write an order, such as the ECG in a person with CO poisoning, just add it on as soon as you remember. If you have not moved the clock forward, there will be no points lost.
Orders:
ECG
Repeating the ABG would reflect oxygen use in this patient because doing the physical examination moved the clock forward.
Half-Life of COHb Breathing:
• Room air: 4 to 6 hours
• One hundred percent oxygen: 60 to 90 minutes
• Hyperbaric oxygen: 20 to 30 minutes
Standard pulse oximetry cannot detect CO.
Reports:
ABG: pH 7.32; PCO2 28 mm Hg; PO2 90 mm Hg; 98% saturation
COHb level: 42%
CHEM-7: normal
ECG: ST depression in V2 to V4
What is the mechanism of metabolic acidosis?
a. Decreased perfusion of tissues
b. Lactate from tissue hypoxia
c. Rhabdomyolysis
d. Sepsis
Answer b. Lactate from tissue hypoxia
COHb does not release oxygen to tissues. The tissues become hypoxic. Hypoxic tissues produce lactate. See the previous discussion about lactate buildup from anaerobic glycolysis. The tissues are perfused, but oxygen is not delivered. Without oxygen delivery, the metabolic acidosis that develops would look identical to decreased tissue perfusion or sepsis.
Normal respiratory rate is 8 to 14 breaths/minute.
This patient, at 32 breaths/minute, should have pH >7.4.
Hyperventilation should produce alkalosis.
COHb Elevation + pH <7.4 = Massive Tissue Acidosis
What is the mechanism of cardiac ischemia?
a. Decreased coronary perfusion
b. Increased CO release to tissues
c. Decreased oxygen release from hemoglobin at tissues
d. Decreased oxygen pickup by hemoglobin at lungs
Answer c. Decreased oxygen release from hemoglobin at tissues
CO does not interfere with hemoglobin picking up oxygen at the lungs. CO interferes with the release of oxygen at tissues. That is why the blood is red. Methemoglobinemia interferes with oxygen pickup at lungs.
Move the clock forward 5 to 10 minutes and reevaluate the patient. You will not lose points if you repeat the ABG on oxygen or repeat the ECG. After starting 100% oxygen, your main issues in management are:
1. Does the patient need hyperbaric oxygen?
2. Has respiratory burn occurred and is intubation needed?
Which of the following is the strongest indication to use hyperbaric oxygen in this patient?
a. pH 7.32
b. ST depression on the ECG
c. Confusion
d. COHb level 42%
Answer b. ST depression on the ECG
All of these indicate serious CO poisoning, but the worst one is the myocardial ischemia.
Severe metabolic acidosis with pH <7.2 is an indication, as well as coma. The high COHb level (>25%) is certainly dangerous, but the most dangerous is the ischemia.
Oxygen on hemoglobin (Hb) with COHb will not release to tissues.
COHb = Effects of Anemia
COHb 42% = Effects of Loss of 42% of blood
Transfer the patient to the ICU and order hyperbaric oxygen. Continue 100% oxygen in the meantime.
Orders:
Hyperbaric oxygen
Troponin level
What is the most common presentation of aortic stenosis, which this patient has?
a. Angina
b. Syncope
c. Congestive heart failure (CHF)
Answer a. Angina
Fifty to seventy percent of patients with aortic stenosis have coronary disease. That is what makes this patient’s COHb level so dangerous. If this patient bled and lost a third of his blood volume, he would have myocardial ischemia as well. COHb is the same in its effect on tissues.
Your patient is lucky enough to be in a hospital with a hyperbaric chamber. Move the clock forward 1 hour and recheck the laboratory test results.
Orders:
ECG
COHb
ABG
Remember that a COHb level and hyperbaric oxygen ordered at the same time will not show the effects of the hyperbaric oxygen.
Move the clock forward a half hour and do an Interval History. Hyperbaric oxygen will reduce half of COHb within a half hour.
Interval History: “The patient is more alert and awake. He denies chest pain.”
One hundred percent inspired oxygen should give PO2 >700 mm Hg.
Reports:
ECG: ST segment has normalized.
COHb level is 18%.
The pH is 7.37 and PO2 680 mm Hg on 100% oxygen in the hyperbaric chamber.
The troponin level is elevated.
The patient’s symptoms improve, but the myocardial ischemia should be treated as it would be in a person who had a myocardial infarction (MI) from coronary disease unmasked by the CO poisoning. He should undergo investigation to determine the need for revascularization when stable. The point of the case is understanding that CO poisoning leads to tissue hypoxia from a failure to release oxygen to tissues. This leads to ischemia of every tissue. It is just that the heart and brain are the most vulnerable.
Methemoglobin
• Oxidized blood
• Brown
• Does not pick up oxygen in the lungs
COHb
• Hb picks up 200 times more than oxygen
• Red
• Picks up oxygen in the lungs
• Does not release in tissues