4/19/2021

Many of us have heard the terms, simple asphyxiant and chemical asphyxiant. While both conditions can be the result of an exposure to an airborne substance, the difference between the two is based on the mechanism of how a person losses his/her ability to supply oxygen to the body; thus, suffering the effects of asphyxia.   

A chemical asphyxiant interferes with the body’s function to absorb oxygen into the body or to allow oxygen – once absorbed – to be distributed into our blood stream, followed by being introduced to our cells so that the crucial metabolic processes are allowed to function as intended. Examples of chemical asphyxiants include carbon monoxide (where the blood protein, hemoglobin has a greater affinity for this substance as opposed to oxygen, and therefore, oxygen does not get appropriately absorbed into the blood) and hydrogen cyanide (which binds to materials in the cells, causing an irreversible condition that prevents aerobic cellular respiration).

A simple asphyxiant merely displaces air (that contains oxygen) within a persons’ breathing environment, thus preventing the proper amount of oxygen from entering the lungs (via inhalation).  In the current legal matter of George Floyd, it is being discussed that due to a particular method of physical restraint, air (oxygen) was not being permitted to enter the lungs.  This is slightly different from simple asphyxia, where the amount of air (oxygen) within the breathing atmosphere is limited.

In addition to simple and chemical asphyxiants, there are two additional conditions that are important in the physiology for proper amounts of oxygen to sustain life: hypoxia and hypoxemia.  Hypoxemia is when you have low levels of oxygen in your blood. This can be caused by a variety of conditions, including asthma, pneumonia, and chronic obstructive pulmonary disease (COPD), as well as asphyxia. It’s a serious medical situation and requires prompt medical attention.

The other term, hypoxia, is closely related to hypoxemia, but does have some important differences.  While hypoxemia refers to low oxygen levels in your blood, hypoxia refers to low levels of oxygen in the tissues of your body. The two can sometimes, but not always, occur at the same time.

Generally, the presence of hypoxemia suggests hypoxia. This makes sense because if oxygen levels are low in your blood, the tissues of your body are also probably not getting enough oxygen.

There are several different types of hypoxemia, and the type depends on the mechanism through which blood oxygen levels are lowered.

The most common type of hypoxemia is referred to as ventilation/perfusion (V/Q) mismatch. Ventilation refers to the oxygen supply in the lungs, while perfusion refers to the blood supply to the lungs. Ventilation and perfusion are measured in a ratio, called V/Q ratio. Normally, there’s a small degree of mismatch in this ratio, however if the mismatch becomes too great, problems can occur. There are two causes of ventilation perfusion mismatch:

1. The lungs are getting enough oxygen, but there’s not enough blood flow (increased V/Q ratio).
2. There is blood flow to the lungs, but not enough oxygen (decreased V/Q ratio).

 

Normally, deoxygenated blood enters the right side of the heart, travels to the lungs to receive oxygen, and then travels to the left side of the heart to be distributed to the rest of the body.

In this type of hypoxemia, blood enters the left side of the heart without becoming oxygenated in the lungs. This is referred to as a Shunt.

 

When oxygen enters the lungs, it fills small sacs called alveoli, where the smallest of capillaries surround the alveoli. Oxygen diffuses from the alveoli into the blood running through the capillaries. Sometimes the diffusion of oxygen from the alveoli to the capillaries are impaired, thus limiting the transmission of oxygen into the blood stream.  This condition is known as diffusion impairment.

Hypoventilation is when oxygen intake occurs at a slow rate. This can result in higher levels of carbon dioxide in the blood and lower levels of oxygen.

Another condition that decreases oxygen from entering the blood stream is Low Environmental Oxygen and is caused at high altitudes where the air pressure decreases substantially. When this happens, the pressure attributed to oxygen (typically making up approximately 21% of air) also decreases and therefore, the driving force that is needed to transfer oxygen across the alveoli into the blood stream, is also reduced.  The higher the altitude, the less the driving force of oxygen and therefore, the ability to have oxygen transfer from the lungs to the circulatory system, diminishes. The result is a condition often referred to as altitude sickness and can – on many occasions – be remedied by returning to a lower altitude so one can adjust to the higher altitude condition. An extreme case of this phenomenon occurs when inexperienced people attempt to climb such notable peaks as Mount Everest where an oxygen tank may be necessary. Without the aid of this addition supply, many attempting to reach the peak would be forced to retreat without making it to the summit.

 

There are many conditions that can cause hypoxemia. These can include:

• acute respiratory distress syndrome (ARDS)
• anemia
• asthma
• a blood clot in the lung (pulmonary embolism)
• a collapsed lung
• congenital heart defects or disease
• COPD (aka chronic obstructive pulmonary disease)
• fluid in the lung (pulmonary edema)
• high altitudes
• interstitial lung disease
• medications that lower breathing rate, such as some narcotics and anesthetics
• pneumonia
• scarring in the lungs (pulmonary fibrosis)
• sleep apnea

To understand how different conditions can cause hypoxemia in different ways, we can look at COPD vs. Anemia.  COPD is a chronic condition in which the flow of air in the lungs is obstructed. Destruction of the walls of alveoli and surrounding capillaries in COPD can lead to problems with oxygen exchange, which can lead to hypoxemia. Meanwhile, Anemia is a condition in which there aren’t enough red blood cells to effectively carry oxygen. Because of this, a person with anemia may have low levels of oxygen in their blood even though oxygen in the environment is readily available.

Additionally, hypoxemia can be a symptom of another condition such as respiratory failure.

Respiratory failure occurs when not enough oxygen passes into the respiratory system – as what the prosecution in the case, “The People v. Chauvin” – has been asserting. Therefore, low blood oxygen levels can be an indicator of respiratory failure.

Someone with hypoxemia may experience the following symptoms:

• shortness of breath
• coughing or wheezing
• headache
• rapid heartbeat
• feeling confused or disoriented
• a blue coloration to the skin, lips, and fingernails

In order to diagnose hypoxemia, your doctor will perform a physical examination, checking both the heart and lungs. They may also check the color of your skin, fingernails, or lips. There are some additional tests that they can perform to assess your oxygen levels and breathing. These can include:

• Pulse oximetry, which uses a sensor placed on your finger to measure blood oxygen levels.
• Arterial blood gas test, which uses a needle to draw a blood sample from an artery to measure blood oxygen levels.
• Breathing tests, which may evaluate your breathing through a machine or by breathing into a tube.

 

Since hypoxemia involves low blood oxygen levels, the aim of treatment is to try to raise blood oxygen levels back to normal. Oxygen therapy is one method to treat hypoxemia. This may involve using an oxygen mask or a small tube clipped to your nose to receive supplemental oxygen.

Hypoxemia can also be caused by an underlying condition such as asthma or pneumonia. If an underlying condition is causing your hypoxemia, it is advisable to seek medical consultation and receive appropriate treatment.

Out of your vulnerabilities will come your strength

Sigmund Freud