AP Photo/Steve Helber A police officer stands guard as residents of an apartment building where several students were overcome by carbon monoxide remove belongings in Blacksburg, Va., last August.

The latest technology showing up on the market allows medical providers to monitor levels of carbon monoxide in a patient. But before we discuss the benefits of these advances, we must understand the pathophysiology of carbon monoxide — essentially how it works and affects the body.

As a brief, initial overview, CO poisoning is the most common exposure poisoning in the United States and the rest of the world. It is an odorless, colorless gas that can cause sudden illness and death. As it is found in fumes from combustion, CO is produced from a variety of sources such as vehicles, gasoline engines, camp stoves, lanterns, burning charcoal and wood, gas ranges, heating systems and poorly vented chimneys. Structural fires are another common source of CO exposure for both victims and firefighters.

CO poisoning is commonly seen during cold weather because people spend more time in their homes, a time when they are better insulated, which keeps CO in the home. However, it's important to remember that CO poisoning can be experienced throughout the year.

Pathophysiology of carbon monoxide
CO toxicity causes impaired oxygen delivery and utilization at the cellular level. It aggressively competes with oxygen for the limited oxygen-binding receptor sites on hemoglobin in the red blood cell. Because it has a greater affinity to the blood cell than oxygen, a CO molecule will bind to hemoglobin 200 times stronger than that of oxygen. As a person is exposed to more CO, the level of CO attached to the blood — carboxyhemoglobin — increases. This makes the red blood cell incapable of transporting oxygen throughout the body. Once the ability to transport oxygen is lost, the body can not survive without medical intervention.

CO poisoning has adverse effects on all systems of the body. Simply put, the body needs oxygen — and that critical element is being displaced from the hemoglobin by CO. One of the most important systems impacted is the central nervous system. A person exposed to CO may have symptoms such as headaches, confusion and dizziness. As the level of CO increases, the person may have seizures or even go into a coma.

It is also important to know that CO can impact cardiovascular systems, which would present such symptoms as chest pain, dysrhthmias, myocardial ischemia and possibly ventricular fibrillation. This is significant when considering that firefighters may already be at risk for a cardiac event.

Signs and symptoms
The signs and symptoms of CO poisoning often are similar to other illnesses, which may lead to a misdiagnosis by medical providers. Prehospital providers need to be aware of these symptoms and how they may present with patients experiencing elevated levels of carboxyhemoglobin. These symptoms include any of the following:   

• Flu-like illness
  
• Fatigue
  
• Chest pain
  
• Lethargy
  
• Depression
  
• Nausea
  
• Vomiting
  
• Headaches
  
• Abdominal pain
  
• Drowsiness
  
• Coma
  

These may vary with both the level of CO and the time of exposure. As the level of CO in the blood increases, the severity of the poisoning also rises.

CO is eliminated by the lungs; however, this may take some time. The half-life of CO is three to four hours, which means that it will take that amount of time to reduce the amount by one-half. The use of high concentration (100 percent) oxygen will reduce the half-life to 30-90 minutes.

CO affects several different sites within the body but has its most profound impact on the organs with the highest oxygen requirement such as the brain and heart. Misdiagnosis commonly occurs because of the vagueness and broad spectrum of complaints, with symptoms often being attributed to a viral illness such as the flu in winter months.

It is important to remember that you can not use a pulse oximeter to determine if a patient has been exposed to CO. While it may display what appears to be a normal oxygen saturation of the upper 90 percent region, in reality the patient does not have enough oxygen bound to the hemoglobin.

Remember, CO competes with the body's preferred oxyhemoglobin. Basically, pulse oximeter technology measures the percentage of something — normally oxygen — that is bound to hemoglobin. However, a pulse oximeter can not determine if it is oxygen or carbon monoxide.

To determine the percent of CO in the blood, one needs to use the new technology of Pulse CO-oximetry. This can determine both the percentage measurement of CO saturation found bonded to hemoglobin as well that of oxygen.

Those at risk
As with many illnesses, the population groups at increased risk for CO exposure are the very young and old. Often this is due to changes in their physiology. In addition, they may also have longer durations of exposure because they are less likely to be leaving their homes.

Pregnant women, and more importantly the fetus, are at an increased risk for adverse outcomes from CO exposure, largely due to the fetal circulation. The fetal hemoglobin has an even higher affinity for CO than that of the adult.

Other populations at risk include anyone with respiratory compromise, since they may already have a limited ability to oxygenate their circulatory system. Also, those with various types of anemia such sickle-cell, iron deficiency or thalassemia are at high risk, too.

Firefighters are always at risk and should be evaluated while in rehab during firefighting operations. Using a Pulse CO-oximeter is simple, accurate and very fast. This allows you to monitor firefighters, and use high-concentrations of oxygen to help treat for the effects of CO poisoning.

Treatment for CO poisoning
The Centers for Disease Control and Prevention have determined a standard for those with CO exposure. Through the use of testing like Pulse CO-oximetry, if carboxyhemoglobin levels exceed 5 percent for non-smokers and 10 percent for smokers, they should be considered as having some level of CO poisoning. Generally, treatment is indicated when the carboxyhemoglobin levels exceed 10-12 percent. Treatment involves moving the patient to a safe location, and administering high-concentration oxygen. Depending on your system, you may also transport the patient to an ER, use continuous positive airway pressure (CPAP) and/or possibly transport patients for treatment in a hyperbaric chamber.

In addition to oxygen therapy, the patient should be continuously monitored for SpO2 and SpCO levels through use of a Pulse CO-oximeter. Ensure proper documentation of findings on a regular basis. If 12-lead cardiac monitoring is available, it is appropriate to capture an initial 12-lead as well as maintaining cardiac monitoring while the patient is transported to the hospital.

You should also remember:

1. CO binds to blood cells at a higher affinity than oxygen — do not think that just taking someone into fresh air will quickly clear things up. Remember the half-life of CO in the body is hours, not minutes.

2. CO exposure can be a life-threatening situation. If you are treating patients inside their homes, you are also being exposed to CO.

3. CO exposure to patients does not occur just in the winter. Any time fossil fuels are burned, there is a potential for CO poisoning. This means a faulty hot water heater or stove can be the cause.

4. Be sure you treat the patient and be prepared for complications of CO such as seizures, cardiac ischemia and cardiac dysrhythmias.

5. Assess firefighters in rehab. They may have been exposed to CO during firefighting operations and not realize their fatigue may be related to CO exposure.

6. If Pulse CO-oximetry is available, do not forget to check yourself. If you are with patients in the back of a rig or sitting in a chief's car, you may not realize that you are being exposed to CO.

• If you would like a free copy of a Pulse CO-oximeter policy, or a 26-page "Firefighter Lessons Learned" document, feel free to contact Jim Sideras at sideras@post.harvard.edu