Dr Getter,
Pharmacology, Spring 2000
Oxygen Therapy
History
Discoverer is Priestly in 1777. Lavoisier and associates demonstrated the absorption of Oxygen in the lungs, its metabolism in the body, and the expiration of oxygen and water after metabolism, (1780-1790).
Physical Characteristics
Oxygen is a colorless, odorless and tasteless gas. It is not flammable but it supports combustion.
It makes up 20.9% of air. The partial pressure of oxygen at sea level is 159mm of Hg. (20.9% of 760mm hg, air)
The partial pressure of oxygen at the alveolar level is 100mm hg. One hundred ml. of arterial blood carries 20.9ml of oxygen combined with hemoglobin. Only .3ml is dissolved in plasma.
Oxygen Dissociation Curve
The percentage of oxygen saturation of hemoglobin is a function of the oxygen tension in the blood. It is affected by the acidity of the blood and the temperature. The curve will shift to the right or left depending on the acidity or the temperature of the blood.
An increase in oxygen tension of the blood results in a rise in the oxygen carried by the hemoglobin. It is not a linear relationship as is the oxygen increase carried dissolved in plasma.
Oxygen Uses in Dentistry
Oxygen is an essential emergency drug in dentistry. It is used in all medical emergencies except hyperventilation.
Oxygen deprivation is called hypoxia. A reduction in Pa02 is a reduction in arterial blood oxygen tension.
The causes of hypoxia are usually:
A. Inadequate Oxygenation of normal lung tissue
1. air way obstruction
foreign body,edema, bronchial constriction etc.
2. insufficient pulmonary ventilation disease, depression of respiration by drugs, (narcotics, barbiturates etc.)
3. Deficiency of 02 in inspired air altitude
B. Abnormal pulmonary function
1. Edema
2. fibrosis
3. Emphysema
4. AV shunts (congenital heart disease)
Oxygen works best when the hypoxia is a result of poor ventilation. It is also of benefit as an adjunct therapy in impaired circulation (congenital heart disease).
In LTOT (long term low flow therapy) oxygen at less then 50% concentration. used in patients with COPD (chronic obstructive pulmonary disease). This appears to improve the quality and longevity of life in these patients. It is used in a 1-3 lpm flow for up to 15 hours a day as indicated.
Oxygen use in LTOT or in other medical conditions such as AV shunts, fibrosis, acute edema and others is not for dental office therapy.
Oxygen is used in conjunction with nitrous oxide in an inhalation sedation technique. Oxygen concentrations in these techniques should never be below 30% of the gas flow. It is recommended here that no less than 50% oxygen be used during the nitrous oxide sedation technique. Failure to deliver a minimum of 20% oxygen can result in hypoxia and anoxia.
The CNS is very vulnerable to oxygen deprivation. Unconscious will result from a decrease in oxygen saturation of the blood. At 50-65% saturation cyanosis, visual disturbances, aberrations of thinking and unconsciousness can occur. Anoxia for 4-6 minutes can result in irreversible brain changes and brain death.
Toxic Reactions
These are likely to be seen in Hospitals not dental offices. Oxygen toxicity develops as a function of concentration and duration of administration.
1. respiratory tract irritation.breathing 80-100% )2 for 12-24 hours causes coughing, irritation and other tract changes. Breathing 50% O2 does not result in irritation.
2. Hypoxic driven respiration (mediated by the carotid body and aortic arch receptors)
Emphysema, COPD, Barbiturate overdosage severe.
Oxygen could eliminate the hypoxic drive. If needed use artificial ventilation and oxygen therapy. The concentration of the oxygen may have to be altered.
3. Premature Infants
Excess concentrations of Oxygen can cause blindness.
Direct Dental Uses of Oxygen Therapy
Agents such as peroxides and perborates release molecular oxygen. Antibacterial claims are made for the free oxygen. However the free oxygen breaks down in the presence of organic material and the bacterial catalase. The effects are transient.
Hydrogen Peroxide 3% is used as rinse.
Hydrogen Peroxide combined with Sodium Bicarbonate is made into a paste and used as a tooth paste in the Keyes technique of periodontal disease control.
Some of the perborates are also used as a mouth wash.
These agents are never to be swallowed.
Other Indirect Uses in Dentistry
Some patients with refractory osteomyelitis of the facial bones may be treated in a hyperbaric chamber. Here 100% oxygen is breathed at over 2 atmospheres of pressure. It is also used in refractory osteoradionecrosis. The patient is placed in the chamber and breathes the oxygen for several hours each day. It may promote healing. It is best used with surgical and antibiotic therapy. There a some contraindications to its use.