Introduction
Oxygen was discovered by Joseph Priestly in the late 18th century. Some time later it was used as a treatment for patients in hospital with acute and chronic respiratory failure. The benefits of oxygen therapy include relief of breathlessness (dyspnoea), improvement in activities such as mobility and a reduction in limb swelling (peripheral oedema) (Hall and Wood 1991).
Oxygen, the colourless, odourless gas, is a drug commonly used in a variety of settings to treat or prevent tissue hypoxia – diminished amount of oxygen in the tissues (Jamieson et al, 2007). However, despite its wide and frequent use in health care, oxygen is often accurately prescribed, resulting in inappropriate administration, monitoring and evaluation of the therapy (Kor and Lim 2000, Wong et al2000, Thomson et al2002, kbar and Campbell 2006). It's indicated in patients with acute hypoxemia (PaO2 less than 60 mm Hg or SaO2 less than 90%) and those with symptoms of chronic hypoxemia or increased cardiopulmonary workload. Oxygen is also given to help with the removal of loculated air in the chest, as you would see with pneumothorax or pneumomediastinum.
Indications for Oxygen Theraphy
Respiratory failure is one of the main indications for oxygen therapy. Respiratory failure is the inability to maintain adequate gas exchange and is characterised by abnormal arterial blood concentrations of oxygen and, in certain cases, carbon dioxide (CO2 ) (British Thoracic Society (BTS) Standards of Care Committee 2002).
A raised respiratory rate is another indication for oxygen therapy. The accurate monitoring and recording of respiratory rate for acutely ill patients are key markers for the deteriorating patient (National Institute for Health and Clinical Excellence (NICE) 2007).
Documented or suspected hypoxaemia – adiminished amount of oxygen in arterial blood –is a further indication for oxygen therapy. Hypoxaemia is characterised by either the arterial oxygen level being below 8kPa (BTS Standards of Care Committee 2002, Resuscitation Council (UK) 2005), the oxygen saturations being less than 90%, or either value being below the desirable range for the clinical situation. Importantly, the arterial CO2 level is normal or low. This is also referred to as type I respiratory failure (BTS Standards of Care Committee 2002).
Patients with type II respiratory failure also have an arterial oxygen concentration level below 8kPa, however, the arterial CO2 concentration is greater than 6kPa (BTS Standards of Care Committee 2002). The hypercapnia (raised CO2 level in arterial blood) and hypoxaemia occur as a result of decreased alveolar ventilation.
Hypoxia can also result from cardiac respiratory arrest; acute myocardial infarction resulting in a reduced cardiac output; severe trauma, including severe head injury; anaemia with reduced haemoglobin available to transport the oxygen; infection through increased metabolic demand; surgical intervention; and anaesthesia (Kallstrom and American Association for Respiratory Care (AARC) 2002, Pruitt and Jacobs 2003, Higgins 2006).
Hypoxia can be divided into five types namely hypoxic, histotoxic, anemic, stagnant and hypemic. Histotoxic hypoxia is associated with the cells inability to utilize the oxygen provided by the blood. Anemic hypoxia is the lack of oxygenated blood content. Stagnant hypoxia is when there is some kind of obstruction in the flow of blood which hinders the blood to reach the related parts of the body. Hypemic hypoxia is caused due to the inability of the blood to transport oxygen to different parts of the body which is usually caused due to carbon monoxide poisoning.
Asessing Patients for Oxygent Theraphy
The initial needs assessment for oxygen therapy is made clinically, considering what we see when we evaluate the patient, lab findings, and what we know about the underlying disease process. Pay particular attention to three systems when addressing the potential need for oxygen therapy. Typically, we jump to the respiratory system and look for respiratory signs and symptoms, which may include alteration in rate (tachypnea, bradypnea, or apnea) or depth of respiration (hypopnea), difficulty breathing (dyspnea), and changes in color (pallor or cyanosis). However, neurologic signs and symptoms, as well as cardiac response, can provide important clues that will help direct your search for hypoxemia.
Examples for changes in neurologic status associated with hypoxemia can range from irritability and changes in level of alertness in acute settings to complaints of chronic headaches in patients with long-standing hypoxemia. The heart may respond to hypoxia by increasing or decreasing its rate, depending on the severity of the hypoxic insult. BP may be elevated early on and then become markedly decreased if the hypoxic insult is severe.
The pulse oximeter is a noninvasive device that can be used to measure oxygen saturation. This technique utilizes the oxyhemoglobin dissociation curve, which will shift with changes in temperature, pH, or different types of hemoglobin. Arterial blood gases are obtained by arterial puncture and provide information about acid-base balance, specifically pH, PaCO2, PaO2, and bicarbonate levels.
Methods of Oxygen Delivery
Use the three P approach (Purpose, Patient, and Performance). For example, critically ill patients often need a stable, high FiO2. Oxygen delivery devices fall into two main categories – low flow delivery systems or high flow delivery systems (Bennett 2003).
Low flow delivery systems are also referred to as variable performance systems. These systems deliver oxygen at a low flow rate and provide a variable oxygen concentration to the patient. This occurs because the patient’s inspiratory flow rate is greater than the flow rate of oxygen; the patient will draw air in from the atmosphere, which will dilute the oxygen concentration delivered. Low flow oxygen systems include nasal cannula and low flow masks.
The nasal cannula is a comfortable delivery system for patients. It doesn't interfere with talking or eating and comes in sizes appropriate for all age groups. It can deliver FiO2 levels of 0.24 to 0.40 with flow rates up to 8 L/minute in adults. Remember that the amount of oxygen delivery may vary according to inspiratory time and rate and depth of respiration. A good rule of thumb is that for each liter of oxygen provided, the FiO2 should increase by approximately 4%. The formula is FI,O2 = 20% + (4 × oxygen litre flow). The FI,O2 is influenced by breath rate, tidal volume and pathophysiology. The slower the inspiratory flow the higher the FI,O2In infants, flow rates shouldn't exceed 2 L/minute. You'll see nasal cannulas utilized for both short and long-term oxygen delivery.
Low flow oxygen masks, the simple face mask is more cumbersome. Some patients complain of feeling claustrophobic with masks, and they must be removed before meals. For these reasons, you'll see them used for short-term oxygen delivery. Simple face masks can provide FiO2 levels between 0.35 and 0.50. Be careful with patients with chronic obstructive pulmonary disease (COPD) and carbon dioxide (CO2) retention. Low flow rates can cause rebreathing and increased levels of CO2.
Cooper and Cramp (2003) stated that the flow rate for a simple mask should not be below 5L perminute, because the patient could easily breathe in exhaled air that would not be flushed from the mask at the lower flow rates. However, it is essential to refer to the manufacturer’s guidelines because many manufacturers of variable performance masks indicate that both 24% and 28% oxygen are delivered at flow rates below 5L per minute. If the patient is breathing hard and fast, the concentration of oxygen delivered will be lower because the oxygen will be diluted by large volumes of atmospheric air entrained into the mask. If, however, the patient is breathing slowly and deeply, less ambient air is drawn in and the concentration of oxygen delivered through the mask will be greater.
A non-rebreather mask is similar to a simple face mask, however, it has multiple one-way valves in the side ports and a reservoir bag attached. The one-way valve prevents air from being drawn into the mask, but enables the exhaled CO2 to leave the mask, therefore preventing the risk of rebreathing. The reservoir bag fills with oxygen thus providing an oxygen reservoir available for the patient to inspire. The one-way valve between the mask and the reservoir bag prevents exhaled air entering the reservoir bag. Being a variable delivery device, oxygen can be delivered at between 10L and 15L per minute and can provide 80-90% oxygen (Pruitt and Jacobs 2003).
The partial rebreathing mask can provide oxygen supplementation between 40% and 70%, with variable stability. This bag requires a minimum flow of 10 L/minute to prevent bag collapse on inspiration. Failure to ensure that the bag is inflated poses a suffocation hazard.
High flow delivery systems High flow devices are also known as fixed performance masks. These deliver oxygen rates above the normal inspiratory flow rate. These systems are often referred to as Venturi masks because they work using the Venturi principle. A Venturi mask mixes oxygen with room air, creating high-flow enriched oxygen of a settable concentration. It provides an accurate and constant FI,O2. Typical FI,O2 delivery settings are 24, 28, 31, 35 and 40% oxygen. Oxygen is passed through a narrow inlet entraining air from the atmosphere. The concentration of oxygen delivered depends on the flow of oxygen via the inlet and the size of the holes through which the air is entrained. The bigger the hole on the port, the greater the volume of air entrained into the mask and the lower the concentration of oxygen delivered. These masks can deliver between 24% and 60% oxygen, depending on which adapter is used (Bennett 2003). These masks are used for patients who require a high or accurate concentration of oxygen.
Methods of Measuring Oxygen Saturation and Respiratory Status
Pulse oximetry. This is a way of being able to measure the oxygen saturation level in a person’s blood. There are many such machines available which are generally small and portable. They are extremely useful, particularly for 'one off' measurements, continuous monitoring or overnight to establish significant oxygen desaturation during sleep. They do not, however,measure PaCO2 (level of CO2 in the blood).
Arterial oxygen content (equation) =
(Hgb x 1.36 x SaO2) + (0.0031 x PaO2)
SaO2 = % of hemoglobin saturated with oxygen
(Normal range: 93-100%)
Hgb = hemoglobin
Normal range(Adults): Male: 13-18 g/dl Female: 12-16 g/dl
PaO2= Arterial oxygen partial pressure
(Normal range: 80-100)
CaO2: Directly reflects the total number of oxygen molecules in arterial blood (both bound and unbound to hemoglobin).
Blood gas analysis. More detailed information relating to respiratory status can be obtained by arterial blood gas analysis. Carbon dioxide levels + pH (acidity) are measured in addition to oxygen and other products of metabolism.
Acid base balance. Chemical reactions in the body are dependent on a balance of acids and bases to maintain a pH of 7.35-7.42. The acid base balance is the normal ratio between the acid ions and the alkaline ions required to maintain this pH. Observations Other bservations that could be carried out when assessing respiratory status include:
- Rate and depth of respiration.
- Patient’s colour.
- Temperature.
- Blood pressure.
Complications/hazards
Oxygen is combustible, so direct contact with oil, grease and alcohol should be avoided. Smoking must also not be allowed within the vicinity of the oxygen delivery system.
A small number of patients with chronic lung disease processes do not respond to changes in the blood level of carbon dioxide as a stimulus to breathing, and may respond to a low blood oxygen level. If this is suspected, care should be taken that the administration of oxygen does not inhibit this drive, so causing carbon dioxide retention/narcosis. Advice should be sought from experienced clinicians.
However, oxygen will almost always be required for acutely ill patients whose condition is deteriorating.
Professional Responsibilities
All nurses who administer oxygen must have received approved training and undertaken supervised practice in drug and oxygen administration. The onus is also on the individual to ensure her or his knowledge and skills are maintained from both a theoretical and practical perspective. Nurses should also undertake this role in accordance with their organisation's protocols, policies and guidelines.
References
Arya, Niharika. 2010. Lack of Oxygen. www.buzzle.com
Bhatti, Shalu. 2001. Oxygen Saturation Levels. www.buzzle.com
Cataletto, Mary. 2011. Fundamentals of Oxygen Therapy. Journals, Nursing Made Incredible Easy
Dunn, Liz and Chrisholm, Hazel. 1998. Oxygen Therapy. Nursing Standard, Royal College of Nursing
McGloin, S. 2008. Administration of Oxygen Therapy. Nursing Standard, Royal College of Nursing
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