Oxygen therapy

Oxygen therapy is a treatment that involves inhalation of oxygen. This therapy may help patients with lung diseases (i.e. cystic fibrosis) and extrapulmonary diseases that prevent a sufficient oxygenation of blood (i.e. carbon monoxide poisoning). In such patients, oxygen therapy may increase the life qualify and may increase their livespan. Oxygen therapy is usually prescribed by physician (if necessary, it can be prescribed by nurse); the protocol contains dosing (i.e. oxygen flow in litres per minute and oxygen concentration) and the mechanism of delivery (type of facial mask or nasal oxygen cannula).

Short-term oxygen therapy
It is usually performed during hospitalization of a patient for temporary hypoxia of a patient caused by respiration diseases. The oxygen is usually delivered using nasal oxygen cannula, rarely using full-face mask.

Long-term oxygen therapy
Long-term oxygen therapy is suited for patients with chronic lung insufficiency whose health condition is stabilized (i.e. patient does not experience a subjective decline in ventilation parameters). Such patients usually inhale oxygen for more than 16 hours per day with pauses that do not exceed 2 hours. Oxygen is usually administered using nasal oxygen cannula, rarely using inhalation mask. The source of oxygen can be (a) oxygen concentratior (a device that purifies aerial oxygen), (b) cannister with liquid oxygen or (c) flask of pressurized oxygen.



The aim of the long-term oxygen therapy is to increase the life quality of patients, to decrease the risk of their hospitalization, to decrease the disease exacerbation or death.

Criteria for indication of oxygen therapy
Criteria are:
 * 1) whenPaO2 in arterial blood at ease below 7,3 kPa,
 * 2) when PaO2 in arterial blood is 7,3–8,0 kPa and simultaneously we observe any of following in patient:
 * 3) signs of pulmonary hypertension or right atrium hypertrophy,
 * 4) secondary polycytemia (as a consequence of chronic, long-term hypoxia)
 * 5) desaturation (i.e. low v PaO2) during sleep (can be diagnosed with non-invasive pulse oximeter with overnight monitoring of SpO2), if oxygen saturation in arterial blood decreases below 90% for at least at least 30% of sleep lengh
 * 6) desaturation during physical exercise (when 50 W of activity for at least 5 minut leads to decrease of PaO2 below 8 kPa),
 * 7) bronchopulmonary dysplasia in prematurely born children (when SpO2 is below 92%), without risk of retinopathy

We always aim to reach following partial pressure and saturation levels:
 * PaO2 in arterial blood ≥ 8,0 kPa.
 * SpO2 in arterial blood ≥ 90 %.

Contraindications of oxygen therapy is a major progressive hypercapnia. Oxygen therapy should be used cautiously in smokers and non-complient patients (especially in smorkers, risk of ignition when exposed to flames).

Risks of oxygen therapy:
 * 1) generation of oxygen radicals (reactive oxygen species, ROS),
 * 2) decrease of centilations: especially in patients with high PCO2, where the major breathing stimulus originates from right PCO2; for example in Chronic obstructive lung disease (COLD) – ("blue bloaters"),
 * 3) lung exsudation, congestion, pulmonary oedema,
 * 4) atelectasis: surfactant; may result in alveoli colapse,
 * 5) spasms: breating of O2 under high pressure may inhibit CNS enzymes.

Humidification
Dry gas may lead to dryness of mucous membranes of the patients, which is somewhat unpleasant. To avoid this, a gas humidifier should be employed.
 * Gas humidifies – humidifies the gas with aqueous fumes.
 * Nebiluzer – saturates the air with aerosol.
 * Micronebulizers – may saturate the passing gas with drugs for simultaneous therapeutic purposes, e.g. with Mucosolvan or Bromhexin.

Standard practise

 * Oxygen enhances burning - oxygen may be explosive under specific conditions (in mixtures with gases) - handling must be performed with highers caution;
 * Open flames and other risks of ignition must be avoided
 * Oxygen flow rate and concentrations must be regulated with flow regulator valves.
 * When handling oxygen, no gease can be applied (hands must be grease free), grease cannot be applied to valves
 * When administring oxygen to patients, oxygen must be moisturized (humified) and heated to body temperature
 * When administring oxygen to patients, we observe the patients breathing frequency, oxygen saturation, heart rate and blood pressure.
 * When administring oxygen to patients, we observe the patient for using supplementary breathing muscles.

Oxygen suply

 * Central oxygen distribution – oxygen is stored in one designated place in the hospital and it is delivered via pipelines into the site of need. It is usually delivered by pipes into every room near every bed do a pannel with oxygen connector.
 * Steel cylinder with pressurized oxygen – gas is stored under pressure up to 15,2 MPa (150 atm), work with cylinder requires extreme caution

Reduction valve decreases the pressure of oxygen (it is attached to the central oxygen distribution pannel or to the steel cylinder; decreases the pressure so that we do not expose the patient to these extreme pressures.



Flow meter can also include:
 * High-pressure manometer (enables the measurement of oxygen pressure in cylinder),
 * Low-pressure mamanometer (enables the measurement of oxygen pressure in tubes leading to the patient),
 * main shutdown valve,
 * humidifier.

Cylinder identifiers: Regardless of colour, the content of the cylinder must be clearly stated on its label (usually near its top)
 * blue stripe (old notification, should not be used since 2007, but can still be seen rarely),
 * blue stripe with white stripe and (usually black) letter N (N stands for "new notification").

Note: empty cylinders must be stored separately from full cylinders, cylinders cannot be exposed to heat, direct sunlight or open flames; cylinders cannot be stored in narrow corridors of hallways. During transportation, cylinders must be fastened to prevent their fall

Estimation of residual content of cylinder If a cylinder has a volume of e.g. 10 litres and the original pressure is150 atm., the amount of gasseous oxygen in the cylinder can be exsimated by multiplying the volume (10 litres) times the pressure (150 atm) 10 x 150 = 1500 L O2 Which would be equivalent of approximately 1500 L of gas at ambient temperature and pressure.

If the oxygen is partially consumed and the pressure in the cylinder decreases to e.g. 50 atm, the amount of oxygen can be estimated: 10 x 50 = 500 L O2. Which would be equivalent of approximately 500 L of gas at ambient temperature and pressure.

Which would be sufficient for oxygen therapy with oxygen flow 2 L/min approximately 4 hours 500 : 2 = 250 min., which is equivalent to 4 hours and 10 minutes.

Administration

 * Nasal catether – it is inserted into nose parallel with meatus nasi inferior to the depth of uvula, the insertion may be easier when patient swollows, the flow rate is 4 to 6 or 7 L per min, oxygen concentration in the air patient inhales is then 50 to 60%. Importantly, the nasal catether should be secured so that is does not slip (either out, or into patients oesophagus). The catether should be replaces every 12 hours (otherwise we risk infections or decubites)
 * Poulsen katether – a modified version of nasal catether, its ending contains polyurethane seal around the tube (ca. 2 to 3 cm long), which prevents from oxygen leakage (and thus increases the concentration of inhaled oxygen; does not dry the mucose membranes.


 * Nasal oxygen cannula – used in long-term oxygen therapy, it consists of a flexible tube with two stiff short endings in the middle that are inserted into nostrils. Oxygen flow rate is approximately 5 to 6 litres per minute (higher flow rates usually dry the mucous membranes, which is uncomfortable). Its major benefit is that it almost does not limit the patient; its down side it that the efficacy is fairly low: the oxygen gets mixed with air and the final concentration of oxygen is approximately 30% (if the flow rate is 5 to 6 litres per minute).
 * Oxygen mask – made from transparent material (plastic) with soft metal frame, it is held in position using a rubber band around the head of the patient. The flow rate is usually 7 to 12 litres per minute. Major benefit is a high efficacy and a good tolerance of high flow rates. However, masks should be avoided in patients who tend to vomit; furthermore, some patients do not tolerate the masks well (anxious patients - masks usually increase their anxiety). Oxygen mask can also include a baloon, which functions as a reservoar - it inflates then patient is not breathing in and deflates when patient inhales. The baloon decreases the loses of gas and, importantly, increases the oxygen concentration in the inhaled gas up to virtually 100% (in reality it is still 60 to 80%).
 * Venturi mask – a O2 mask with a specific connector, that enables the regulation of oxygen concentration; used for patients with time-variable oxygen requirements.


 * Incubator – oxygen therapy for prematurely born babies, oxygen concentration, temperature, light and humidity is closely controlled and monitored.
 * Oxygen tent: used in patients that require high concentrations of oxygen but do not tolerate gas masks (e.g. with facial wounds, anxious patients).
 * for children patients – usually manufactured from plexiglas
 * for adults patients – a room for two to three patients, a tent with metal framework and gas-impervious foils
 * Nebulizer – an auxiliary device that enables the formation of aerosol with droplets of drug - used for inhalation drug therapy.
 * Hyperbaric chamber - a specific device - a high pressure chamber that enables to pressurize the air/air-oxygen mixture around patient and thus can increase the oxygen solubility in blood; used in therapy of carbon monoxide poisoning (see below)



Note: The maximum gas flow is always declared by manufacturer.

Fraction of inspired oxyge (FiO2)
Fraction of inspired oxygen is a relative volume of oxygen in the inhaled gas. During oxygen therapy, the aim is to increase the FiO2 to 30% or more (aerial FiO2 is 21%). The higher FiO2 is, the more efficient the oxygen therapy is; the efficacy varies with different methods of delivery and oxygen flows.

Hyperbaric chamber
Hyperbaric chamber is a type of oxygen therapy that exposes the patient to almost 100% oxygen at increased gas pressure. The patient is closed into a steel chamber that is slowly pressurized (usually approximately 20 minutes or more); the patient is maintaned at this increased pressure (up to 200 kPa for 90 to 120 minutes), after which the pressure is slowly decreased to reach the atmospheric pressure.

Purpose
 * treatment of tissue hypoxia → improved wound healing,
 * increased perfusion → decrease of oedemas, increased blood return,
 * alteration of metabolic processes in peripheral tissues and skin,
 * neovascularisation (formation of new blood vessels and capillaries),
 * increased functions of blood vessel walls,
 * increased granulation and regeneration.

Types of hyperbaric chambers: By number of seats
 * Single-seat (single patient), usually pressurized directly with the oxygen the patient is breathing
 * Multi-seat chambers are pressurized by air, the patient breathes oxygen using a special device, either a valve (similar to diving automation) or an oxygen helmet (through which oxygen flows continuously). Multi-seat chambers are most often cylindrical in shape for 2 to 16 seated patients. The state-of-the-art facilities are cube-shaped (like a room) and have identical facilities to the intensive care unit's bedside treatment for critically ill patients.

By inhaled gas
 * Filled with air.
 * Filled with oxygen - patients breathe oxygen directly from the chamber environment, but there is a high risk of fire.

In the treatment, a pressure 2.5 to 3 times higher than atmospheric is commonly used, which is a pressure corresponding to immersion to a depth of 15 to 20 meters below the water surface. One session lasts 90 minutes. The treatment is repeated once a day, 5 times a week, for 3 weeks.

It uses the blood's ability to deliver more oxygen to organs at higher atmospheric pressures than under normal conditions. Under high pressure, oxygen dissolves in the plasma, high pressure reduces the volume of air bubbles.

  'Indication:'   urgency assessment. Grade I - HBO - affects the prognosis of survival, it is a vital indication. II. Grade - HBO is an important part of the treatment, prevention of serious complications. III. Grade - HBO is part of a comprehensive treatment, significantly improving clinical outcomes.

Contraindications:
 * absolute – untreated pneumotorax, treatment with cardioxotic cytostatics, disulfiran therapy, cisplatin therapy, doxorubicinem therapy, prematurely born chidren (risk or retinopathy);
 * relative – acute viral infections HCD with elevated body temperature, malignant carcinoma, claustrophobia, pregnancy, acute asthma bronchiale ...

Complications:
 * barotrauma,
 * oxygen toxicity,
 * nitrogen narcosis,
 * myopia,
 * bradycardia.
 * claustrophobia

Process:
 * 1) Compression– slow (!) increase of pressure around the patient; the proces may be uncomfortable for some patients, the chamber heats up (due to gas contraction)
 * 2) Isocompression– the patient is maintaned at 200 to 300 kPa (2 atmospheres) for 90 to 120 minutes; this phase is well-tolerated
 * 3) Decompression– slow decrease of pressure; the temperature of the chamber decreases (due to gas expansion - fog may appear), this process is usually well-tolerated (better than compression phase)

Types of diseases requiring oxygen therapy

 * Hypoxemia, hypoxia, anoxia, anoxemia,
 * lung disease,
 * COPD - usually in stadiums III and IV,
 * pneumoconiosis - very advanced stages,
 * beginning with pulmonary edema,
 * bronchospasm,
 * pulmonary fibrosis, severe asthma,
 * pulmonary vascular disease,
 * pulmonary arterial hypertension,
 * neurological diseases,
 * myopathy,
 * diseases of the chest wall,
 * severe kyphoscoliosis of the thoracic spine,
 * respiratory insufficiency in severe obesity,
 * postoperative period,
 * shock,
 * severe anemia, circulatory disorders, AIM,
 * carbon monoxide poisoning,
 * perinatal period.

 'Oxygen delivered:' 
 * adult - 4-10 l / min,
 * children - 1–4 l / min.

Related articles

 * Oxygen toxicity • Hyperbarická oxygenoterapie • Oxygen • Reactive oxygen species • Oxygen parameters
 * Hypoxia • Hypoxemia • Saturation