The oxygen therapy It consists of the administration of oxygen (02) to patients for therapeutic purposes in order to maintain adequate levels of oxygenation at the tissue level. It can be administered in all those cases in which the patient cannot maintain an adequate O2 saturation by himself.
Oxygen therapy can be administered in cases of respiratory distress, during surgical procedures during which the patient is unable to breathe on their own, or in cases of severe trauma or poisoning, to ensure maximum oxygen delivery to the tissues..
Oxygen therapy is a medical procedure, and as such it must be administered by qualified personnel. The oxygen used in this treatment is considered a medicine, so it is subject to strict regulations.
In this sense, there are various techniques, materials and procedures, which the health professionals responsible for the administration of this therapeutic measure should know..
Likewise, it is essential to know in detail the physiological principles that support the therapeutic administration of oxygen, since otherwise it is impossible to perform the necessary calculations to guarantee an adequate supply of this gas..
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The first concept to be handled in the field of oxygen therapy is that of the inspired fraction of oxygen, since this parameter is modified with the administration of O2 by any of the available methods..
The inspired fraction of oxygen (Fi02) is understood to be the amount of O2 that enters the airway with each inspiration..
Under normal standard conditions (breathing ambient air, at sea level and with an average temperature of 27 ºC) the FiO2 is 21%, which represents a partial pressure of oxygen of 160 mmHg or 96 kPa.
In healthy individuals, the pressure and amount of oxygen are sufficient to achieve an O2 saturation between 95 and 100%. This brings us to the second parameter of importance: blood oxygen saturation..
Oxygen circulates in the blood attached to a transport molecule known as hemoglobin (Hb), which represents more than 50% of the content of red blood cells.
This protein has the ability to accommodate oxygen inside it, increasing the O2 transport capacity in the blood well above what it could carry if this gas only dissolved in it..
Generally, arterial blood has an oxygen saturation that ranges between 95 and 100%; that is, practically all Hb molecules carry their full oxygen charge.
Under abnormal environmental conditions or due to particular pathological conditions, the percentage of Hb molecules that transport O2 may decrease, that is, the O2 saturation in the blood decreases..
To prevent this (or correct it if it has already happened), supplemental oxygen administration is sometimes necessary..
As mentioned above, the inspired partial pressure of oxygen is calculated with a standard model at sea level. However what happens when the altitude is changed?
Well, up to 10,000 meters above sea level, the composition of the air almost does not vary. Therefore, each liter of ambient air will contain:
- 21% oxygen.
- 78% nitrogen.
- 1% other gases (of which CO2 is the most abundant).
However, as the atmospheric pressure rises, so does the inspired pressure of oxygen. This can be better visualized with an example.
At sea level, the atmospheric pressure is 760 mmHg and the amount of oxygen is 21%; therefore the inspired oxygen pressure is 760 x 21/100 = 160 mmHg
When you ascend 3,000 meters above sea level, the amount of oxygen in the air remains the same (21%), but now the atmospheric pressure has dropped to about 532 mmHg.
Now, when applying the formula: 532 x 21/100 we obtain a much lower inspired oxygen pressure, around 112 mmHg.
With this oxygen pressure, gas exchange in the lung is less efficient (unless the individual is acclimatized), and therefore the O2 saturation in the blood tends to decrease somewhat..
If this decline is severe enough to compromise the delivery of enough oxygen for the tissues to function well, the person is said to suffer from hypoxia..
Hypoxia is understood as a decrease in blood O2 saturation below 90%. In those cases where the figure falls below 80%, it is referred to as severe hypoxia..
Hypoxia implies a vital risk for the patient, since as the O2 saturation decreases, the supply of oxygen to the tissues is compromised. If this happens, they can stop working, since oxygen is essential for cellular metabolic functions..
Hence the importance of guaranteeing adequate saturation which in turn ensures an optimal tissue oxygen supply..
There are a number of methods to diagnose hypoxia and, unlike what is common, the clinical signs are often the least accurate. This is because they usually present only with severe hypoxia..
However, it is essential to know them, since they give a clear idea of the severity of the situation and, above all, of the effectiveness of oxygen therapy..
Hypoxia is clinically characterized by:
- Tachypnea (increased respiratory rate).
- Use of accessory muscles of respiration (nonspecific symptom, as there may be respiratory distress without evolving to hypoxia).
- Altered state of consciousness.
- Cyanosis (purplish coloration of the nails, mucous membranes and even the skin in very severe cases).
For a more precise determination of hypoxia, there are diagnostic tools such as pulse oximetry and the measurement of arterial gases..
Pulse oximetry allows the determination of the O2 saturation in the blood through a device capable of measuring the absorption of red and infrared light by the blood that passes through the capillaries of the skin..
It is a non-invasive procedure that allows the hemoglobin saturation level to be determined in a few seconds and with considerable precision. This in turn gives healthcare personnel the ability to make oxygen therapy adjustments in real time..
For its part, the measurement of arterial gases is a more invasive procedure, since a sample of arterial blood from the patient must be extracted by puncture. This will be analyzed in a special equipment capable of determining with great precision not only the saturation of O2, but also the partial pressure of oxygen, the concentration of CO2 in blood and several other parameters of clinical utility..
The advantage of arterial blood gas is the wide variety of data it provides. However, there is a delay of between 5 and 10 minutes between the moment of taking the sample and the reporting of the results..
That is why the measurement of arterial gases is complemented with pulse oximetry to have a global vision and at the same time in real time of the patient's oxygenation status..
There are multiple causes of hypoxia, and although in each case a specific treatment must be instituted to correct the etiological factor, oxygen should always be administered for the initial support of the patient..
Among the most common causes of hypoxia are the following:
- Travel to areas with an altitude higher than 3,000 m.a.s.l. no prior acclimatization period.
- Shortness of breath.
- Poisoning (carbon monoxide, cyanide poisoning).
- Poisoning (cyanide).
- Respiratory distress (pneumonia, chronic bronchitis, chronic obstructive bronchopulmonary disease, heart disease, etc.).
- Myasthenia gravis (from paralysis of the respiratory muscles).
In each case it will be necessary to administer oxygen. The type of procedure, flow and other details will depend on each particular case, as well as the response to the initial treatment..
The oxygen therapy technique will depend on the clinical condition of the patient, as well as their ability to ventilate spontaneously..
In cases where the person can breathe but is unable to maintain an O2 saturation greater than 90% by himself, the oxygen therapy technique consists of enriching the inspired air with oxygen; that is, increase the percentage of O2 in each inspiration.
On the other hand, in cases where the patient is unable to breathe on his own, it is necessary to connect him to an assisted ventilation system, either manual (ambu) or mechanical (anesthesia machine, mechanical ventilator).
In both cases, the ventilation system is connected to a system that provides oxygen, so that the FiO2 to be administered can be accurately calculated..
The initial procedure consists of evaluating the clinical conditions of the patient, including oxygen saturation. Once this is done, the type of oxygen therapy to implement is decided.
In cases where the patient breathes spontaneously, one of the various types available can be chosen (nasal mustache, mask with or without a reservoir, high-flow systems). The area is then prepared, and the system is placed on the patient..
When ventilatory assistance is required, the procedure always begins with manual ventilation (ambu) through an adjustable mask. Once 100% O2 saturation is reached, orotracheal intubation is performed.
Once the airway is secured, manual ventilation can be continued or the patient connected to a ventilatory support system.
In hospitals, the oxygen administered to patients usually comes from pressurized cylinders or wall outlets connected to a central supply of medicinal gases..
In both cases a humidifier device is required, in order to avoid damage to the airway by dry oxygen.
Once the gas mixes with the water in the humidifier cup, it is delivered to the patient through a nasal cannula (known as a mustache), a face mask, or a reservoir mask. The type of delivery device will depend on the FiO2 to be achieved.
In general, a maximum FiO2 of 30% can be achieved with the nasal cannula. On the other hand, with the simple mask, FiO2 reaches 50%, while using a mask with a reservoir, up to 80% FiO2 can be achieved..
In the case of mechanical ventilation equipment, there are configuration knobs or buttons that allow FiO2 to be set directly on the ventilator..
In the case of pediatric patients, especially in neonatology and with young babies, the use of special devices known as oxygen hoods is necessary..
These are nothing more than small acrylic boxes that cover the head of the lying baby, while the air-oxygen mixture is nebulized. This technique is less invasive and allows monitoring of the baby, something that would be more difficult to do with a mask.
Even though 90% of oxygen therapy cases are normobaric (with the atmospheric pressure of the place where the patient is), sometimes it is necessary to apply hyperbaric oxygen therapy, particularly in the cases of divers who suffered decompression.
In these cases, the patient is admitted to a hyperbaric chamber, which is capable of increasing the pressure to 2, 3 or more times the atmospheric pressure..
While the patient is in that chamber (often accompanied by a nurse), O2 is administered by mask or nasal cannula.
In this way, the inspired pressure of O2 is increased not only by increasing FiO2 but also by pressure..
Oxygen therapy devices are designed to be used by patients outside the hospital. While most patients will be able to breathe normal room air once they recover, a small group will need O2 consistently..
For these cases there are small cylinders with pressurized O2. However, their autonomy is limited, so devices that "concentrate oxygen" are often used at home and then administer it to the patient..
Since the handling of pressurized oxygen cylinders is complex and expensive at home, those patients who require chronic and sustained oxygen therapy benefit from this equipment capable of taking in the ambient air, eliminating part of the nitrogen and other gases to offer an "air" with oxygen concentrations greater than 21%.
In this way, it is possible to increase FiO2 without the need for an external oxygen supply..
Nursing care is crucial for the correct administration of oxygen therapy. In this sense, it is essential that the nursing staff guarantee the following:
- Cannulas, masks, tubes or any other O2 delivery device must be correctly positioned over the patient's airway.
- The liters per minute of O2 in the regulator must be those indicated by the doctor.
- There should be no kinks or kinks in the tubes that carry O2.
- The humidifying glasses must contain the necessary amount of water.
- Elements of the oxygen delivery system must not be contaminated.
- Ventilation parameters of ventilators (when used) must be appropriate according to medical indications.
In addition, the patient's oxygen saturation should be monitored at all times, since it is the main indicator of the effect of oxygen therapy on the patient..
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