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 (Ω) [ōm]
the SI unit of electrical resistance, named for Georg Simon Ohm; one ohm is produced when a current of 1 ampere flowing through a conductor produces a potential difference of 1 volt. Impedance is also measured in ohms.


 (O) [ok´sĭ-jen]
a chemical element, atomic number 8, atomic weight 15.999. (See Appendix 6.) It is a colorless and odorless gas that makes up about 20 per cent of the atmosphere. In combination with hydrogen, it forms water; by weight, 90 per cent of water is oxygen. It is the third most abundant of all the elements of nature. Large quantities of it are distributed throughout the solid matter of the earth because it combines readily with many other elements. With carbon and hydrogen, oxygen forms the chemical basis of much organic material. Oxygen is essential in sustaining all kinds of life. Among the land animals, it is obtained from the air and drawn into the lungs by the process of respiration. See also blood gas analysis.
Oxygen Balance andOxygen Debt.‡‡‡‡‡‡‡‡‡‡‡” The need of every cell for oxygen requires a balance in supply and demand. But this balance need not be exact at all times. In fact, in strenuous exercise the oxygen needs of muscle cells are greater than the amount the body can absorb even by the most intense breathing. Thus, during athletic competition, the participants make use of the capacity of muscles to function even though their needs for oxygen are not fully met. When the competition is over, however, the athletes will continue to breathe heavily until the muscles have been supplied with sufficient oxygen. This temporary deficiency is called oxygen debt.

Severe curtailment of oxygen, as during ascent to high altitudes or in certain illnesses, may bring on a variety of symptoms of hypoxia, or oxygen lack. A number of poisons, such as cyanide and carbon monoxide,, as well as large overdoses of sedatives, disrupt the oxygen distribution system of the body. Such disruption occurs also in various illnesses, such as anemia and diseases of lungs, heart, kidneys, and liver.
oxygen 15 an artificial radioactive isotope of oxygen having a half-life of 2.04 minutes and decaying by positron emission. It is used as a tracer in the measurement of regional blood volume and flow and oxygen metabolism by positron emission tomography.
oxygen analyzer an instrument that measures the concentration of oxygen in a gas mixture. There are three types of handheld analyzers: physical/paramagnetic, electric, and electrochemical analyzers.
oxygen blender a device used to mix oxygen with other gases to any concentration between 21 per cent and 100 per cent.
oxygen concentrator an electronic device that removes nitrogen from room air, thus increasing the oxygen concentration; commonly used by patients who require long-term oxygen administration at home.
oxygen consumption the amount of oxygen consumed by the tissues of the body, usually measured as the oxygen uptake in the lung. The normal value is 250 ml/min (or 3.5 to 4.0 ml/kg/min), and it increases with increased metabolic rate.
oxygen hood a device that fits over the head of an infant or small child for administration of oxygen or aerosolized medications.
hyperbaric oxygen oxygen under greater than atmospheric pressure.
liquid oxygen oxygen in liquid form, a common storage form of oxygen; one liter of liquid oxygen will produce 860 liters of gas.
oxygen tent a large plastic canopy that encloses the patient in a controlled environment, formerly much used for oxygen therapy, humidity therapy, or aerosol therapy.
oxygen therapy
1. in the nursing interventions classification, a nursing intervention defined as administration of oxygen and monitoring of its effectiveness.
2. a form of respiratory care involving administration of supplemental oxygen for relief of hypoxemia and prevention of damage to the tissue cells as a result of oxygen lack (hypoxia). Oxygen can be toxic and therefore, as with a drug, its dosage and mode of administration are based on an assessment of the needs of the individual patient. Although many types of hypoxia can be treated successfully by the administration of oxygen, not all cases respond to this therapy. There also is the possibility that the injudicious use of oxygen can produce serious and permanent damage to the body tissues. The administration of oxygen should never be considered a “routine” or harmless procedure.
Adverse Effects of Oxygen. Although it is true that all living organisms require oxygen to maintain life, an environment of 100 per cent oxygen inhibits growth of living tissue cultures, and laboratory experiments have shown that hyperoxygenation of body tissues can cause irreversible damage. It is known that high concentrations of inhaled oxygen can result in collapse of alveoli because of displacement of nitrogen by oxygen. retinopathy of prematurity in premature infants was found to be caused in part by excessively high levels of oxygen in the blood.

Another serious complication of high-oxygen concentration therapy is the development of a hyaline membrane because of a deficiency of pulmonary surfactant; surfactant is vitally important to normal expansion and deflation of the alveoli. Prolonged exposure to inspired oxygen concentrations in excess of 50 per cent can impair the production of this surfactant in a patient of any age. The result is a loss of lung compliance and reduction of the transport of oxygen across the alveolar membrane.

The danger of oxygen toxicity can be minimized by careful assessment of each patient's need for oxygen therapy and systematic blood gas analysis to determine patient response and effectiveness of treatment. Symptoms of oxygen toxicity are substernal distress, nausea and vomiting, malaise, fatigue, and numbness and tingling of the extremities.
Indications for Oxygen Therapy. In general, the clinical situations in which the administration of supplemental oxygen is indicated are: (1) Profound but potentially reversible hypoxia that appears amenable to the short-term administration of high concentrations of oxygen. Examples would include the patient who is apneic, is suffering from cardiovascular collapse, or is a victim of carbon monoxide poisoning. (2) Conditions in which there is a need to reduce the work load of the cardiovascular and pulmonary systems and at the same time assure an adequate supply of oxygen to the tissues. Congestive heart failure, myocardial infarction, and such acute pulmonary diseases as pulmonary embolism and pneumonia are examples of the types of clinical situations that are best treated by the administration of moderate levels of oxygen concentration. (3) Evidence of hypoventilation, whether from anesthesia and sedation, chronic obstructive pulmonary disease, or other conditions. The patient who is hypoventilating is in danger of suffering from an adverse effect of oxygen therapy because increased oxygenation can lead to decreased respiratory effort. In other words, the oxygen acts as a respiratory depressant and may produce an increase in partial pressure of carbon dioxide in the arterial blood, thus contributing to rather than overcoming the problem of hypoxia. If there is evidence that the patient is hypoventilating, it may be necessary to administer the oxygen by assisted or controlled ventilation.

The delivery of appropriate and effective oxygen therapy requires frequent monitoring of arterial blood gases. An initial blood gas analysis at the time the therapy is started provides baseline data with which to evaluate changes in the patient's status.

In addition to monitoring blood gases to assess the patient's need for and response to supplemental oxygen, it is helpful to observe the patient closely for signs of hypoxemia. However, these signs are not as reliable as blood gas analysis because the clinical manifestations of hypoxemia vary widely in individual patients. The typical clinical manifestations of hypoxemia are confusion, impaired judgment, restlessness, tachycardia, central cyanosis, and loss of consciousness.
Dosage and Method of Administration. It must be kept in mind that oxygen is considered a drug and should be prescribed and administered as such; thus it is apparent that vague orders about its administration are never acceptable. There must be specific written orders for flow rate and mode of administration. Decisions about the initial dosage, as well as any changes in mode of administration and dosage, including the discontinuance of oxygen therapy, should be based on evaluation of the PO2, the PCO2, and the blood pH. (See also transcutaneous oxygen monitoring and pulse oximeter.)

The clinical signs and symptoms of hypoxemia may vary from patient to patient, and they should not be depended upon as valid indications of oxygen insufficiency. This is especially true of cyanosis, a symptom that depends on local circulation to the area, the red cell count, and hemoglobin level. In addition to the data obtained from blood gas analyses, an oxygen analyzer should be used occasionally to check inspired oxygen concentration.

In general, the dosage and mode of administration fall into the following categories. High concentrations above 50 per cent usually are prescribed when there is a need for the delivery of high levels of oxygen for a short period of time to overcome acute hypoxemia, as in cardiovascular failure and pulmonary edema. The flow rate may be as high as 12 liters per minute, administered through a close-fitting face mask with or without a rebreathing bag, or via an endotracheal tube.

Moderate concentrations of oxygen are indicated when the patient is suffering from impaired circulation of oxygen, as in congestive heart failure and pulmonary embolism, or from increased need for oxygen, as in thyrotoxicosis, in which the increased metabolic rate creates a need for more oxygen. The rate of flow should be 4 to 8 liters per minute, administered through an air entrainment mask that delivers concentrations above 23 per cent, or in a dosage of 3 to 5 liters per minute through a nasal cannula.

Low concentrations of oxygen are indicated when the patient is receiving oxygen therapy over an extended period of time, as in chronic obstructive pulmonary disease, and there is the possibility of hypoventilation and the danger of increased CO2 retention. The rate of flow should be 1 to 2 liters per minute, administered through a nasal cannula, or via an air entrainment mask that delivers 24 to 35 per cent oxygen.

Other methods of oxygen administration include the nasal catheter and the oxygen tent. The nasal catheter can cause some discomfort to the patient, and since it is no more and no less effective than the cannula, most therapists and patients prefer not to use it. The oxygen tent is considered by many to be obsolete, its use being limited to the administration of oxygen to children who cannot or will not tolerate other modes of delivery, and to children in whom the objective is to provide oxygen and humidity or humidity alone.
Patient Care. No matter what mode of administration is used, it is essential that the inspired air be moisturized. This is necessary to prevent drying of the respiratory mucosa and thickening of secretions that can further inhibit the flow of air through the air passages. Humidity may be provided by humidifying the oxygen with water, or by aerosoling the water into fine particles and adding it to the oxygen. Most patients need 60 to 65 per cent relative humidity at room temperature. Patients with endotracheal tubes require as close to 100 per cent humidity as possible.

Oxygen is not an explosive gas, but it does support combustion and presents a serious fire hazard. All electrical equipment should be checked for defects that could produce sparks. All appliances that transmit house current must be kept outside an oxygen tent, and all equipment with exposed switches and meters must be considered potential sources of fire. Static electricity is a minimal risk which can be further reduced by maintaining a relatively high humidity in the oxygen tent. Smoking in the immediate area of oxygen administration is prohibited and there should be signs informing visitors and others of this restriction.

When the patient is wearing a mask for an extended period of time, discomfort can be minimized by removing the mask and washing and drying the face at least every eight hours. To be effective the mask must fit snugly and follow the contour of the face. This means that reddened areas will appear where the mask has pressed against the skin. These areas should be gently massaged and the skin lightly powdered to reduce friction.

A program of infection control is especially important in the prevention of cross-infection from the equipment that is used to administer oxygen. Humidifiers and nebulizers may serve as sources of infection because they provide a medium for the growth of bacteria and molds. There is less danger of this happening when disposable equipment is used, but this does not preclude the need for a systematic development of policies and procedures to prevent and control the spread of infection. Every person involved in the care of the patient must be aware of this program and cooperate in its implementation.
transcutaneous oxygen monitoring a method for obtaining data about oxygen levels through electrodes attached to the skin. This method is preferred for ill neonates who cannot tolerate frequent drawing of blood samples for blood gas analysis. The PO2 levels obtained by cutaneous monitoring correlate with those obtained from samples of arterial blood and spare the neonate blood loss and interruption of rest.

The transcutaneous electrodes are heated to encourage an adequate supply of blood to the area of skin to which they are attached and remain in place to permit continuous monitoring of arterial oxygen levels. To avoid burns, the electrode site can be changed every two hours. An ongoing record provides information about the neonate's oxygen level at any given moment. It allows caregivers to observe the neonate's response to handling and other procedures that may require modification to avoid severe anoxia. Placing the electrodes at specific sites can also aid the diagnosis of patent ductus arteriosus.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.


1. Symbol for oxygen; orotidine.
2. Abbreviation for opening (in formulas for electrical reactions).
3. Symbol for a blood group in the ABO system. See ABO blood group, in Blood Groups Appendix.
4. An abbreviation derived from the German phrase ohne Hauch (without film), used as a designation for: antigens that occur in the bacterial cell, in contrast to those in the flagella; specific antibodies for such somatic antigens; the agglutinative reaction between somatic antigen and its antibody.
Farlex Partner Medical Dictionary © Farlex 2012




n. pl. o's or O's also os or Os
1. The 15th letter of the modern English alphabet.
2. Any of the speech sounds represented by the letter o.
3. The 15th in a series.
4. Something shaped like the letter O.
5. O One of the four major blood groups in the ABO system. Individuals with this blood group have neither A nor B antigens on the surface of their red blood cells, and have both anti-A and anti-B antibodies in their blood serum.
6. A zero.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.


Symbol for
1. Objective.
2. Occiput.
3. Oncovin.
4. Ophthalmology.
5. Oral.
6. Orbit.
7. Organ.
8. Orotidine.
9. Orthopedic.
10. Os.
11. Ovary.
12. Ovulation.
13. Oxygen.


Symbol for
1. Organ.
2. Ortho.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.


Abbreviation for orotidine; oxygen.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012

Patient discussion about O

Q. My 11 y/o son eyes appear to have a slight yellow in the whites toward the corners. I am assuming he will need blood work, but does anyone have any idea what may be the cause?

A. If it's not a spot, but rather a diffuse color, it may be jaundice - high levels in the blood of a substance called bilirubin (http://en.wikipedia.org/wiki/Jaundice).

If your child is generally healthy, and this change appeared without any overt problem (e.g. liver disease or blood problem), or your child had fever or fasted recently, this jaundice may represents Gilbert syndrome. It's a syndrome of slightly elevated levels of bilirubin, and considered not dangerous.

You may read more here:http://www.nlm.nih.gov/medlineplus/ency/article/000301.htm

Q. How can you tell that your depressed? and when you find out you are, can you get treatment w/o parents consent I believe i am depressed.. i want to get help but i don't want to go to my parents. They are not the greatest and i want some sort of medicine. I was just wondering if i could get a over the counter medicine for cheap...

A. find something you like to do; my children when they were down, used to go to the net an make a music CD from free music web sites on line.there are a lot,I will give you some----LIMEWIRECOM---ROCKETCOM---IMEST-keep your mind doing somthing-make a play list on your computor,play with your cat/dog-I have 5 cats they keep me going.find out if you like ART/drawing--read a good book--watch a good muvie(not a sad one)----------get better-----mrfoot56

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