Oxygen therapy

Oxygen therapy is the administration of oxygen as a therapeutic modality. Oxygen therapy benefits the patient by increasing the supply of oxygen to the lungs and thereby increasing the availability of oxygen to the body tissues.

Appropriate levels of oxygen are vital to support cell respiration. High blood and tissue levels of oxygen can be helpful or damaging, depending on circumstances. Hyperbaric oxygen therapy is the use of high levels of oxygen for treatment of specific diseases. High levels of oxygen given to infants causes blindness by promoting overgrowth of new blood vessels in the eye obstructing sight. This is Retinopathy of prematurity (ROP). Administration of high levels of oxygen in patients with severe emphysema and high blood carbon dioxide reduces respiratory drive, which can precipitate respiratory failure and death.

Oxygen first aid specifically refers to the use of oxygen in a first aid setting. Oxygen will assist patients with myocardial infarction and hypoxia (low blood oxygen levels). Care needs to be exercised in patients with chronic obstructive pulmonary disease, especially in those known to retain carbon dioxide (type II respiratory failure) who lose their respiratory drive and accumulate carbon dioxide if administered oxygen in moderate concentration. However the risk of the loss of respiratory drive are far outweighed by the risks of withholding emergency oxygen, and therefore emergency administration of oxygen is never contraindicated.

Home or domiciliary oxygen therapy

This refers to the administration of oxygen as ongoing therapy, either continuously or intermittently. Most commonly patients on home oxygen therapy have severe chronic obstructive pulmonary disease caused by smoking. High concentration (approaching 100%) oxygen is used as home therapy to abort cluster headache attacks, due to its vaso-constrictive effects.^[1] It is indicated in COPD patients with PaO₂ ≤ 55mmHg or SaO₂ ≤ 88% and has been shown in a Medical Research Council study to increase survival.

Oxygen sources and delivery

Gas canisters containing oxygen to be used at home. When in use a pipe is attached to the top of the can and then to a mask that fits over the patient's nose and mouth.

There are three typical sources of oxygen used therapeutically:

1. Liquid oxygen is contained in thermally insulating tanks. The liquid has to boil changing into a gas for breathing. Large tanks are used by hospitals. Small tanks can be used domestically. Liquid oxygen tanks are refilled by liquid oxygen suppliers.
2. Cylinders contain compressed gaseous oxygen. Small cylinders are used for first aid and for home oxygen patients when mobility is required. Cylinders are refilled by a gas supplier.
3. Oxygen concentrators are electrically powered devices which remove nitrogen from air. They are most commonly used in a domestic situation, because they do not need refilling. However, a number of manufacturers have introduced portable oxygen concentrators. These have replaced^[2] the need to use liquid or gas cylinders for mobility for many patients. Portable Oxygen Concentrators allow patients to freely travel without the need of gas or liquid. The FAA has approved portable oxygen concentrators for the use on many commercial airlines. Most major airlines allow the three major portable oxygen concentrators; it is necessary to check in advance if a particular brand or model is permitted on a particular airline. These can typically use AC, DC, or battery power. Some portable concentrators have only pulse or demand flow capabilities, while continuous flow portables are available. Pulse or demand flow is similar to the way an oxygen conserving device delivers oxygen from liquid oxygen or a gas cylinder only during inhalation, but on a concentrator, the oxygen made in between pulses is stored for the next pulse. Where a conserving device can make a liquid or gas container last longer, pulse or demand settings on oxygen concentrators can make a certain flow appear as a higher effective flow, or reduce power consumption and/or extend battery life.

First aid kits have been produced that create oxygen gas as the result of a chemical reaction between lightweight or widely available substances such as sodium percarbonate and water, although the rate and duration of oxygen supply is not high.^[3]

Oxygen is most often delivered as continuous gaseous flow, measured in litres per minute (lpm).

Administration

Various devices are used for administration of oxygen.

Low-Flow Devices

Low-flow systems deliver oxygen at flows that are less than the patient's inspiratory flowrate (ie, the delivered oxygen is diluted with room air) and, thus, the oxygen concentration inhaled may be low or high, depending on the specific device and the patient's inspiratory flowrate. ^[4]

1. The nasal cannula (NC) is a thin tube with two small nozzles that protrude into the patients nostrils. It can only comfortably provide oxygen at low flow rates, 0.25-6 litres per minute (LPM), delivering a concentration of 24-40%. Flow rates greater than 4 liters per minute can cause discomfort and dry out the nasal passages and should also be used with a humidifcation system.
2. 

   

   A patient wearing a simple face mask.
   The simple face mask (SFM) is a basic mask used for non-life-threatening conditions but which may progress in time, such as chest pain (possible heart attacks), dizziness, and minor hemorrhages. It is often set to deliver oxygen between 5-15 LPM. The final oxygen concentration delivered by this device is dependent upon the amount of room air that mixes with the oxygen the patient breathes. The general oxygen concentration is between 35% and 50%

1. The Partial rebreathing mask is a simple mask with a reservoir bag. Oxygen flow should always be supplied to maintain the reservior bag at least one third to one half full on inspiration, usually 5-15 LPM. At a flow of 6-10 L/min the system can provide 40-70% oxygen.

High-Flow Devices

High-flow systems deliver a prescribed gas mixture -- either high or low FDO2 at flowrates that exceed patient demand.

1. The non-rebreather mask (NRB) is similar to the partial rebreathing mask except it has a series of one-way valves. One valve is placed between the bag and the mask to prevent exhaled air from returning to the bag. There should be a minimum flow of 10 L/min. The delivered FIO2 of this system is 60-80%, depending on the oxygen flow and breathing pattern.^[5],^[6]

1. Air-entrainment masks, also known as Venturi masks, can accurately deliver predetermined oxygen concentration to the trachea up to 40%. Jet-mixing masks rated at 35% or higher usually however do not deliver flowrates adequate to meet the inspiratory flowrates of adults in respiratory distress. Aerosol masks, tracheostomy collars, T-tube adapters, and face tents can be used with high-flow supplemental oxygen systems. A continuous aerosol generator or large-volume reservoir humidifier can humidify the gas flow. Some aerosol generators however, cannot provide adequate flows at high oxygen concentrations.

Filtered Oxygen Masks

Filtered oxygen masks have the ability to prevent exhaled, potentially infectious particles from being released into the surrounding environment. These masks are normally of a closed design such that leaks are minimized and breathing of room air is controlled through a series of one-way valves. Filtration of exhaled breaths is accomplished either by placing a filter on the exhalation port, or through an integral filter that is part of the mask itself. These masks first became popular in the Toronto (Canada) healthcare community during the 2003 SARS Crisis. SARS was identified as being respiratory based and it was determined that conventional oxygen therapy devices were not designed for the containment of exhaled particles.^[7], ^[8], ^[9] Common practices of having suspected patients wear a surgical mask was confounded by the use of standard oxygen therapy equipment. In 2003, the HiOx⁸⁰ oxygen mask was released for sale. The HiOx⁸⁰ mask is a closed design mask that allows a filter to be placed on the exhalation port. Several new designs have emerged in the global healthcare community for the containment and filtration of potentially infectious particles. Other designs include the ISO-O₂ oxygen mask,the Flo₂Max oxygen mask, and the O-Mask. The use of oxygen masks that are capable of filtering exhaled particles is gradually becoming a recommended practice for pandemic preparation in many jurisdictions.

Because filtered oxygen masks use a closed design that minimizes or eliminates inadvertent exposure to room air, delivered oxygen concentrations to the patient have been found to be higher than conventional non-rebreather masks, approaching 99% using adequate oxygen flows. Because all exhaled particles are contained within the mask, nebulized medications are also prevented from being released into the surrounding atmosphere, decreasing the occupational exposure to healthcare staff and other patients.

Resuscitation/Specialized Devices

1. The bag-valve-mask (BVM) is used for patients in critical condition who are either breathing extremely inefficiently, or not breathing at all (respiratory arrest). An oxygen reservoir bag is attached to a central cylindrical bag, attached to a valved mask that administers almost 100% concentration oxygen at 8-15 lpm. The central bag is squeezed manually to deliver a "breath" to the patient, or assist them in inspiration by overcoming airway resistance or thoracic constriction. This is the standard administration method for acute respiratory distress or respiratory arrest.
   

   

   A tightly sealed aviators oxygen mask
2. The pocket mask is a small device that can be carried on one's person. It is used for the same patients who the BVM is indicated for, but instead of delivering breaths by squeezing a reservoir, the care provider must exhale into the mask. Exhaled air from the provider can provide up to 16% oxygen to the patient, or higher if used with supplemental oxygen.
3. The anaesthetic machine is a device used during anesthesia that allows a variable amount of oxygen to be delivered, along with other gases including air, nitrous oxide and inhalational anaesthetics.
4. Aviator type and other specialized tight fitting oxygen masks are used in hyperbaric oxygen chambers and to provide oxygen to carbon monoxide victims.

Related devices

1. A pressure regulator is used to control the high pressure of oxygen delivered from a cylinder to a low pressure controllable by the flowmeter.
2. A flowmeter is used to control and indicate the flow of oxygen. Typiclal flow range is 0-15 lpm.
3. A nebulizer can be used deliver nebulizable drugs such as albuterol or epinephrine into the airways by creating a vapor-mist from the liquid form of the drug. Nebulizers are also commonly used with room air in the home with an electric air pump.

Negative effects

Although most EMS jurisdictions hold that oxygen should not be withheld from any patient, there are certain situations in which oxygen therapy can have a negative impact on a patient’s condition.

Oxygen has vasoconstrictive effects on the circulatory system, reducing peripheral circulation and was once thought to potentially increase the effects of stroke. However, when additional oxygen is given to the patient, additional oxygen is dissolved in the plasma according to Henry's Law. This allows a compensating change to occur and the dissolved oxygen in plasma supports embarrassed (oxygen-starved) neurons, reduces inflammation and post-stroke cerebral edema. Since 1990, hyperbaric oxygen therapy has been used in the treatments of stroke on a worldwide basis. In rare instances, hyperbaric oxygen therapy patients have had seizures. However, because of the afformentioned Henry's Law effect of extra available dissolved oxygen to neurons, there is usually no negative sequel to the event. Such seizures are thought to be caused by hypoglycemia and the risk can be eradicated or reduced by carefully monitoring the patient's nutritional intake prior to oxygen treatment.

Some jurisdictions require that oxygen should not be given to children or people suffering from certain long-term lung conditions by first-responders without medical consultation.

Oxygen first aid has been used as an emergency treatment for diving injuries for years.^[10] The success of recompression therapy as well as a decrease in the number of recompression treatments required has been shown if first aid oxygen is given within four hours after surfacing.^[11] There are suggestions that oxygen administration may not be the most effective measure for the treatment of DCI/DCS and that Heliox may be a better alternative.^[12] Recompression in a hyperbaric chamber with the patient breathing 100% oxygen is the standard hospital and military medical response to decompression illness and decompression sickness.^[10][13][14]

Oxygen should never be given to a patient who is suffering from paraquat poisoning unless they are suffering from severe respiratory distress or respiratory arrest, as this can increase the toxicity. (Paraquat poisoning is rare - for example 200 deaths globally from 1958-1978)^[15]

Oxygen therapy while on aircraft

In the United States, most airlines restrict the devices allowed on board aircraft. As a result passengers are restricted in what devices they can use. Some airlines will provide cylinders for passengers with an associated fee. Other airlines allow passengers to carry on approved portable concentrators. However the lists of approved devices varies by airline so passengers need to check with any airline they are planning to fly on. Passengers are generally not allowed to carry on their own cylinders. In all cases, passengers need to notify the airline in advance of their equipment.

References

1. ^ Sands, George. "Oxygen Therapy for Headaches" (html). http://www.headaches.org/consumer/topicsheets/oxygen.html. Retrieved on 2007-11-26.
2. ^ McCoy, Robert. "Portable Oxygen Concentrators (POC) Performance Variables that Affect Therapy" (pdf). http://www.inspiredrc.com/POC%20AARC%20Dec%202006.pdf. Retrieved on 2007-07-03.
3. ^ Evaluation of the System O2 Inc Portable Nonpressurized Oxygen Delivery System
4. ^ American Association for Respiratory Care. "Oxygen Therapy for Adults in the Acute Care Facility — 2002 Revision & Update" (html). http://www.rcjournal.com/cpgs/otachcpg-update.html. Retrieved on 2008-08-31.
5. ^ Garcia et al. The Oxygen Concentrations Delivered by Different Oxygen Therapy Systems. Chest. 128 (4):389S. 2005.
6. ^ Earl, John. Delivery of High FiO₂. Cardinal Health Respiratory Abstracts.
7. ^ Hui et al. Exhaled air dispersion during oxygen delivery via a simple oxygen mask. Chest.132(2):540. 2007.
8. ^ Mardimae et al. Modified N95 mask delivers high inspired oxygen concentrations while effectively filtering aerosolized microparticles. Annals of Emergency Medicine. 48(4), 391-399. 2006.
9. ^ Somogyi et al. Dispersal if Respiratory Droplets With Open vs Closed Oxygen Delivery Masks: Implications for the Transmission of Severe Acute Respiratory Syndrome. Chest.
   
10. 125(3):1157-7. 2004.
11. ^ ^{a b} Brubakk, A. O.; T. S. Neuman (2003). Bennett and Elliott's physiology and medicine of diving, 5th Rev ed.. United States: Saunders Ltd.. pp. 800. ISBN 0702025712.
12. ^ Longphre, J. M.; P. J. DeNoble; R. E. Moon; R. D. Vann; J. J. Freiberger (2007). "First aid normobaric oxygen for the treatment of recreational diving injuries". Undersea Hyperb Med. 34 (1): 43–49. ISSN 1066-2936. OCLC 26915585. PMID 17393938. http://archive.rubicon-foundation.org/5514. Retrieved on 2008-05-30.
13. ^ Kol S, Adir Y, Gordon CR, Melamed Y (June 1993). "Oxy-helium treatment of severe spinal decompression sickness after air diving". Undersea Hyperb Med 20 (2): 147–54. PMID 8329941. http://archive.rubicon-foundation.org/2133. Retrieved on 2008-05-30.
14. ^ Undersea and Hyperbaric Medical Society. "Decompression Sickness or Illness and Arterial Gas Embolism". http://www.uhms.org/ResourceLibrary/Indications/DecompressionSickness/tabid/275/Default.aspx. Retrieved on 2008-05-30.
15. ^ Acott, C. (1999). "A brief history of diving and decompression illness". South Pacific Underwater Medicine Society journal 29 (2). ISSN 0813-1988. OCLC 16986801. http://archive.rubicon-foundation.org/6004. Retrieved on 2008-05-30.
16. ^ Experience with paraquat poisoning in a respiratory intensive care unit in North India

Source : http://en.wikipedia.org/wiki/oxygen_therapy