Hypoxia and pulse oximetry
Oxygen in human body
With every breath, you inhale oxygen and exhale carbon dioxide. Oxygen is an indispensable requirement for the proper function of the human body. Ninety percent of our body’s energy comes from oxygen respiration.
Most of the metabolism process in our body consumes oxygen to some extent. Oxygen detoxifies the blood, and enhances the body's absorption of nutrients. The brain is the most sensitive organ in our body to oxygen deprivation. Brain cells will deteriorate rapidly and begin to die within five minutes after the oxygen supply is interrupted.
Symptoms of hypoxia
Deficiency of oxygen in the human body is known as hypoxia. Hypoxia may cause many diseases. Symptoms of oxygen deficiency include: overall body weakness, stomach irritation, bacterial, viral, or parasitic infection, bronchial problems, depression, dizziness, fatigue, irrational behavior, irritability, lowered immunity to colds, flu and infections, memory loss, muscle aches, poor digestion, Cyanosis, headache, euphoria, visual impairment, etc. [1] In severe cases, or hypoxia of very rapid onset, loss of consciousness, seizures, coma and death may occur. [2]
Causes and types of hypoxia
Hypoxia may be caused by many factors, from environmental oxygen deficiency to tissue problems in the human body. Hypoxia can be categorised in following types according to the causes [2]:
(1) Hypoxemic hypoxia
Hypoxemic hypoxia is caused by hypoxemia, an abnormal deficiency in the concentration of oxygen in arterial blood. [3] In this case, partial pressure of oxygen in arterial blood is low.
Hypoxemic hypoxia may be caused by:
- Low partial pressure of oxygen in atmosphere, for example the high altitudes that pilots or mountain climbers usually reach;
- A decrease in oxygen saturation of the blood caused by sleep apnea or hypopnea;
- Abnormal pulmonary function or respiratory obstruction.
(2) Anaemic hypoxia
Literally, anaemic hypoxia is caused by anaemia. While partial pressure of oxygen in the blood is normal, oxygen supply to human body is insufficient due to qualitative or quantitative deficiency of haemoglobin. Anaemia is normally caused by haemorrhage, deficient red blood cell production and excessive blood cell destruction.
(3) Hypemic hypoxia
Hypemic hypoxia is caused by the failure of delivering oxygen by blood. For example, the binding of carbon monoxide with haemoglobin prevents oxidation of haemoglobin and thus prevents haemoglobin carrying oxygen into the body. Another hypemic hypoxia is caused by methaemoglobinemia, an abnormal accumulation of methaemoglobin, a form of haemoglobin without binding oxygen [4].
(4) Histotoxic hypoxia
Histotoxic hypoxia is caused by the inability of the tissues to use oxygen. This condition may be caused by cyanide poisoning, or from the use of narcotics, tobacco and alcohol.
(5) Ischemic, a.k.a. stagnant hypoxia
Ischemic hypoxia is caused by constriction or obstruction of the blood vessels, which occurs when a person remains still for or is exposed to low temperatures for a long period of time.
Pulse oximetry for hypoxia
Modern technology allows non-intrusive measurements of the oxygen level in blood and thus makes the monitoring of hypoxia more convenient. The device from which oxygen saturation is derived is known as a pulse oximeter because it calculates the oxygenation and deoxygenation of haemoglobin from arterial blood in between heart pulses.
There are two types of pulse oximeters for medical purposes, handheld oximeters, such as OctiveTech 300A and fingertip pulse oximeters, such as OctiveTech 300C for adults and OctiveTech 300PN for newborns or infants oximeter. Handheld oximeters are mainly used for continuous monitoring in clinic or intensive home care, while fingertip pulse oximeters are for spot checking, which meets most needs for home care.
It is worth noting that a pulse oximeter cannot detect arterial carbon monoxide, so if one is suffering from carbon monoxide poisoning, your doctor may use other devices such as a cooximeter or monoximeter to assist the diagnosis.
References:
[1] Oxygen deficiency, http://www.aerobicoxygenuk.com/Oxygen_Deficiency/oxygen_deficiency. html.
[2] Hypoxia (medical), http://en.wikipedia.org/wiki/Hypoxia_(medical)
[3] Hypoxemia, http://en.wikipedia.org/wiki/Hypoxemia
[4] Methaemoglobinaemia , http://en.wikipedia.org/wiki/Methaemoglobinaemia
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