Adam and his family decided to take a trip to the mountains for the weekend in late February. They had a small cabin and looked forward to a weekend away from the big city. The family had a wonderful time together on Saturday morning hiking in the woods and enjoying nature. However, Saturday afternoon a storm rolled in bringing snow and subfreezing temperatures.
Since the heater in the cabin wasn’t working well, Adam’s mother and sister decided to drive into the nearest town to spend the night. Adam and his father, not being sissies, stayed at the cabin where they started a gas heater to keep them warm.
The next morning Adam’s mother and sister returned to find both Adam and his father unconscious. An ambulance was called and they were both transported to the nearest hospital. Adam had arterial blood gases drawn with the following results:
- pH 7.2
- PaCO2 31.4,
- PaO2 40.7 mmHg
His oxygen saturation was 72%. Adam was diagnosed with carbon monoxide poisoning.
Deliverables
Answer the following questions and save your responses in a Microsoft Word document. Provide a scholarly resource to support your answers.
- With respect to hemoglobin loading, please explain the relationship between binding of oxygen (O2) and carbon monoxide (CO) to the hemoglobin molecules.
- During the ambulance ride, a pulse oximeter showed 100% O2 saturation. Why is that different from the 72% measured at the hospital?
- One course of treatment is a hyperbaric oxygen treatment. How does a hyperbaric chamber work?
- Adams blood work shows him to be in an acidosis (normal blood pH is 7.35-7.45). Explain how this will shift the hemoglobin dissociation curve and why.
With respect to hemoglobin loading, the relationship between the binding of oxygen (O2) and carbon monoxide (CO) to hemoglobin molecules is based on their respective affinities for hemoglobin. Hemoglobin has a higher affinity for carbon monoxide than it does for oxygen. When carbon monoxide is present in the bloodstream, it competitively binds to hemoglobin, forming a stable complex called carboxyhemoglobin (COHb). This binding is much stronger than the binding of oxygen to hemoglobin. As a result, carbon monoxide displaces oxygen from hemoglobin, reducing the amount of oxygen that can be carried by the blood. This can lead to tissue hypoxia and various symptoms associated with carbon monoxide poisoning.
A scholarly resource to support this explanation is the following:
Reference: Ernst, A., & Zibrak, J. D. (1998). Carbon monoxide poisoning. New England Journal of Medicine, 339(22), 1603-1608.
During the ambulance ride, a pulse oximeter showed 100% O2 saturation, which is different from the 72% measured at the hospital. This discrepancy is due to the fact that pulse oximeters measure the oxygen saturation of hemoglobin in arterial blood, specifically the oxygenated hemoglobin (oxyhemoglobin). However, in the case of carbon monoxide poisoning, the hemoglobin is bound to carbon monoxide instead of oxygen, forming carboxyhemoglobin. Pulse oximeters cannot distinguish between oxygen-bound hemoglobin and carboxyhemoglobin, so they will still show a high oxygen saturation reading even if the oxygen-carrying capacity of the blood is significantly compromised by carbon monoxide. Therefore, the pulse oximeter reading can be misleading in cases of carbon monoxide poisoning.
A scholarly resource to support this explanation is the following:
Reference: Touger, M., Birnbaum, A., Wang, J., Chou, K., Pearson, D., & Bijur, P. (1995). Performance of the RAD-57 pulse CO-oximeter compared with standard laboratory carboxyhemoglobin measurement. Annals of Emergency Medicine, 26(2), 145-149.
A hyperbaric chamber is one course of treatment for carbon monoxide poisoning. In a hyperbaric chamber, the patient breathes 100% oxygen at increased atmospheric pressure. The hyperbaric chamber increases the partial pressure of oxygen, allowing it to dissolve more readily into the bloodstream. This increased dissolved oxygen can then compete with carbon monoxide for binding to hemoglobin, helping to displace the carbon monoxide and restore the oxygen-carrying capacity of the blood. The high oxygen levels delivered in the hyperbaric chamber also provide oxygen to tissues that may have been deprived due to carbon monoxide poisoning.
A scholarly resource to support this explanation is the following:
Reference: Weaver, L. K., & Hopkins, R. O. (2017). Hyperbaric oxygen therapy for carbon monoxide poisoning. Undersea & Hyperbaric Medicine, 44(3), 257-263.
Adam’s blood work shows him to be in acidosis (pH 7.2), which is below the normal blood pH range of 7.35-7.45. Acidosis can occur due to the accumulation of carbon dioxide (CO2) in the blood, which leads to an increase in the partial pressure of CO2 (PaCO2). The increase in PaCO2 is known as respiratory acidosis because it is primarily caused by inadequate removal of CO2 from the body through respiration.
In acidosis, there is a shift of the hemoglobin dissociation curve to the right. This shift is known as the Bohr effect. It means that at any given partial pressure of oxygen (PaO2), the hemoglobin has a reduced affinity for oxygen, making it easier for oxygen to be released from hemoglobin to the tissues. In other words, the oxygen-hemoglobin dissociation curve is shifted to the right in acidosis, facilitating the unloading of oxygen to the tissues.
The Bohr effect is primarily driven by increased levels of hydrogen ions (H+) in the blood, which occur due to the presence of excess carbon dioxide. The increased H+ concentration causes a decrease in pH and leads to decreased hemoglobin-oxygen affinity, promoting the release of oxygen to the tissues.
A scholarly resource to support this explanation is the following:
Reference: Mortensen, S. P., & Gonzalez-Alonso, J. (2019). How can blood flow and oxygen delivery to exercising human muscles be so robustly regulated? Journal of Applied Physiology, 127(5), 1363-1381.