CO poisoning/hyperbarics

[Doug]

I had a severe CO poisoning pt. this weekend. Completely unresponsive other than clenching his jaw. He was RSI'd and intubated by the ED after which the search was on for a hyperbaric chamber that was open.

HERE'S MY QUESTION: If the pt is already on a vent and being given 100% O2 what good is a hyperbaric chamber? He is already recieving "targeted" hyperbaric treatment by haveing the vent breath for him, no? Despite what new age quacks may say our skin does not "breathe" so no gas exchange happens there. The only thing I could think of was that by surrounding the body in a high pressure environment you could increase the pressures that the O2 is being delivered at without as much concern for pneumothorax/sub-q emphy. (blowing a hole in the lungs) Am I on the right track?

[FireMedic65]

The hyperbaric chamber reduced CO in the blood stream. Although it does put more pressure on the body, that is the desired affect. They put divers in them all the time to fight the bends (nitrogen poisoning). Never have I heard of such extreme adverse affects. They slowly take the body to the pressure and the capsule is filled with 100% o2.

[cdcmj]

external pressure essentially dislodges the CO off of hemoglobin, which in turn decreases the pt.'s CO levels.

[FireMedic65]

sure, give a more nerdy type answer

[VentMedic]

Review the basic gas laws and respiratory equations to find out where barometric pressure fits in.

The standard treatment for CO poisoning is oxygen, to reverse hypoxia, compete with CO for haemoglobin binding, and promote carboxyhaemoglobin dissociation. Effects are increased at high pressure, shortening carboxyhaemoglobin half-life from 4–6 h to <30 min.

Henry's Law

Most oxygen carried in the blood is bound to hemoglobin, which is 97% saturated at standard pressure. Some oxygen, however, is carried in solution, and this portion is increased under hyperbaric conditions due to Henry's law. Tissues at rest extract 5-6 mL of oxygen per deciliter of blood, assuming normal perfusion. Administering 100% oxygen at normobaric pressure increases the amount of oxygen dissolved in the blood to 1.5 mL/dL; at 3 atmospheres, the dissolved-oxygen content is approximately 6 mL/dL, which is more than enough to meet resting cellular requirements without any contribution from hemoglobin. Because the oxygen is in solution, it can reach areas where red blood cells may not be able to pass and can also provide tissue oxygenation in the setting of impaired hemoglobin concentration or function.

The hyperbaric chamber reduced CO in the blood stream. Although it does put more pressure on the body, that is the desired affect. They put divers in them all the time to fight the bends (nitrogen poisoning). Never have I heard of such extreme adverse affects. They slowly take the body to the pressure and the capsule is filled with 100% o2.

Review Boyle's Law.

[Doug]

Ok, perhaps I am being misunderstood. This pt is on a vent, he is not breathing the surrounding pressurized oxygen present in the chamber. He is already recieving 100% O2 at pressure sufficient to overcome normal atmospheric pressure to expand his lungs (as opposed to the normal way of breathing in which throaxic pressure is decreased with chest expansion resulting in the filling of the lungs to compensate and equalize internal and external pressure.)

So here is my question reworded. If the pt has a tidal volume of 500mL and is on a vent, if the the external pressure is raised 2-3 atmospheres can the pressure being delivered be admin at the increased pressure as well (what would be 1000-1500mL at "normal" pressure) and thus the benefit.

The hyperbaric chamber reduced CO in the blood stream. Although it does put more pressure on the body, that is the desired affect. They put divers in them all the time to fight the bends (nitrogen poisoning). Never have I heard of such extreme adverse affects. They slowly take the body to the pressure and the capsule is filled with 100% o2.

What adverse effects have you never heard of? I am aware of how they are used for divers as well.

The adverse effect would be related to trying to force 1500mL of volume into a 500mL volume pt. at normal atmosphere.

[FireMedic65]

Ok, perhaps I am being misunderstood. This pt is on a vent, he is not breathing the surrounding pressurized oxygen present in the chamber. He is already recieving 100% O2 at pressure sufficient to overcome normal atmospheric pressure to expand his lungs (as opposed to the normal way of breathing in which throaxic pressure is decreased with chest expansion resulting in the filling of the lungs to compensate and equalize internal and external pressure.)

So here is my question reworded. If the pt has a tidal volume of 500mL and is on a vent, if the the external pressure is raised 2-3 atmospheres can the pressure being delivered be admin at the increased pressure as well (what would be 1000-1500mL at "normal" pressure) and thus the benefit.

What adverse effects have you never heard of? I am aware of how they are used for divers as well.

The adverse effect would be related to trying to force 1500mL of volume into a 500mL volume pt. at normal atmosphere.

That is pretty much what I was referring to.

[fireflymedic]

You run the risk the same as any barotrauma with hyperbaric oxygen therapy. However, the benefits far outweigh the risks. More than just carbon monoxide patients benefit from it burn patients, poor healing wounds with diabetics, divers, etc are only a few more that can benefit. It was definitely to the patient's benefit as the affinity of carbon monoxide to hemoglobin is much higher than oxygen.

[FireMedic65]

That is pretty much what I was trying to say, but hard to say when you are tired

[Doug]

You run the risk the same as any barotrauma with hyperbaric oxygen therapy. However, the benefits far outweigh the risks. More than just carbon monoxide patients benefit from it burn patients, poor healing wounds with diabetics, divers, etc are only a few more that can benefit. It was definitely to the patient's benefit as the affinity of carbon monoxide to hemoglobin is much higher than oxygen.

Yes, I know. That is not my question at all, my question was since the pt was on a vent they would not be breathing the pressureized oxygen from the chamber, they will be breathing the 100% oxygen provided via vent, so what would be the benefit of being in a presureized chamber. That being said would the gas mixture have to be 100% oxygen at all, since he will not be breathing it, and by having standard AIR you could have a tech in with the pt without having to worry about oxygen toxicity. The question is not about risk.

These are questions I had intended to ask the techs but they were not available to me at the time.