Oxygen is prescribed for hypoxaemic patients to increase alveolar oxygen tension and decrease the effort of breathing. Although principally life saving, in certain circumstances it can be lethal if prescribed and/or administered incorrectly. To ensure safe, effective delivery of oxygen, health professionals dealing with the administration, titration and monitoring of oxygen therapy should understand the principles that underpin its use. Carol Kelly and Anne Riches discuss administering oxygen therapy in the acute situation
Authors Carol Kelly, PGDE, BSc, RGN, is senior lecturer, Edge Hill University/Respiratory Education UK. Anne Riches, MA, BSc, RGN, is respiratory specialist nurse, Countess of Chester Hospital, and associate lecturer, Respiratory Education UK.
Abstract Kelly, C,. Riches, A. (2007) Emergency oxygen for respiratory patients. Nursing Times; 103: 45, 40–42.
Room air contains 21% oxygen. If a patient requires a higher concentration than this, usually due to disease process or trauma, supplemental oxygen must be given. Oxygen therapy is used to correct hypoxaemia and prevent hypoxia (Box 1). It is administered as an emergency treatment in the acute phase of illness or as domiciliary oxygen for long-term use.
When is emergency oxygen used?
It is essential to ensure adequate oxygenation to the tissues and vital organs during an acute illness. The major risk for most patients is that they will be given too little oxygen (Murphy et al, 2001a). Insufficient oxygen therapy can lead to cardiac arrhythmias, tissue injury, damage to the vital organs and ultimately death.
Successful oxygen delivery depends on adequate ventilation, gas exchange and circulation. The way oxygen is transported to the tissues must be considered, and any impairment of these mechanisms must be addressed to ensure optimal delivery of oxygen to cells (Richardson, 2002).
Emergency care will often require the delivery of high concentrations of oxygen (40–60%). Most patients who are acutely short of breath will have conditions such as asthma, heart failure, pneumonia or pulmonary embolism (Murphy et al, 2001a).
Assessing need for oxygen therapy
Early recognition of the need for oxygen can be difficult as clinical features are often non-specific, including altered mental state, dyspnoea, cyanosis, tachypnoea, cardiac arrhythmias and coma. To enable assessment of the patient’s oxygen status, specific investigations are required.
Oxygen saturation (SpO2) should be checked by pulse oximetry in all breathless and acutely ill patients. It is described as the ‘fifth vital sign’. Pulse oximetry should be available in all places where emergency oxygen is used (British Thoracic Society (BTS), 2007). All staff using pulse oximeters must be trained and made aware of its limitations.
Pulse oximeters do not measure the pH or carbon dioxide (CO2) levels. Therefore arterial or arterialised capillary blood gases should be measured, with the fraction of inspired oxygen (FiO2) noted. Pulse oximetry can be normal in the presence of a grossly deranged pH and PaCO2. Patients with anaemia may have a normal SpO2 despite low blood oxygen levels and a full blood count is required to identify this problem (Box 2).
Administration of oxygen therapy
Oxygen therapy administration can be described as controlled or uncontrolled. It is also referred to as high and low flow (Box 3). During an acute episode of illness it is important to decide how oxygen should be delivered and this is determined by the patient’s condition and diagnosis.
Oxygen should be prescribed and the prescription should include flow rate, concentration, delivery device, duration and method for monitoring treatment (Dodd et al, 2000). It is considered good practice to document the SpO2 and FiO2 together with vital signs and sign the prescription sheet at drug rounds (BTS, 2007).
Humidification is not normally required for oxygen delivery in the emergency situation but may be necessary for patients with a tracheotomy or an artificial airway.
Choosing controlled or uncontrolled oxygen
A number of variables can determine the amount of oxygen a patient receives, including depth and rate of breathing, which in turn influence the total volume of air breathed in and out. In the majority of patients, a device that provides uncontrolled or variable oxygen can be used with no adverse effects.
The BTS (2007) recommends target saturations for the administration of all emergency oxygen therapy. They recommend that oxygen should be prescribed to achieve a target saturation of 94–98% for patients aged <70 and 92–98% for those 70 or above. The exception is patients with COPD or respiratory failure (see below).
The use of some uncontrolled delivery devices (Box 3) can produce unexpectedly high concentrations of inspired oxygen (hyperoxia) but is generally assumed to be safe. However, there is evidence that in some patients, for example those with acute exacerbations of COPD, hyperoxia may be harmful (Plant et al, 2000).
These patients require controlled oxygen therapy during an acute phase to ensure accurate doses, irrespective of their breathing pattern. This is best achieved with high-flow Venturi masks, available to provide oxygen concentrations of between 24% and 60%. The various devices available have been described elsewhere (Porter-Jones, 2002).
The reasons for this are:
- Some patients with COPD (and some other conditions causing chronic respiratory failure) develop, in the severe stages, hypoxaemia with some CO2 retention. The main ventilatory drive for these patients is hypoxaemia (in contrast to increased levels of CO2 in healthy individuals); this is termed hypoxic drive. In these patients, administration of too much oxygen can result in ‘blunting’ of the hypoxic drive, alveolar hypoventilation with increasing CO2 levels and eventually acute type II respiratory failure (Lynes and Riches, 2003).
- The effect of excess O2 on the CO2 dissociation curve can result in inappropriate ‘dumping’ of CO2, thus further increasing carbonic acid levels in the blood (CO2 combines with water to form carbonic acid: CO2 + H2O = HCO3). This leads to acidosis and the process is known as the Haldane effect (Murphy et al, 2001a).
- Worsening of ventilation perfusion mismatch, caused by hypoxic vasoconstriction (a normal lung response), results in increased dead-space ventilation (Box 4) and CO2 levels rise as a result.
- The injudicious use of oxygen leading to respiratory acidosis may result in the patient requiring mechanical ventilation.
Oxygen therapy during an acute exacerbation of COPD
The need for controlled oxygen therapy for those at risk of developing acute type II respiratory failure is now well recognised and has resulted in both regional (Murphy et al, 2001a; Murphy et al, 2001b) and national guidelines for emergency oxygen use in adult patients (BTS, 2007). These guidelines recommend target oxygen saturations of 88–92% for patients with COPD treated in ambulances or emergency departments prior to the availability of blood gas results. This will prevent most cases of hyperoxia and acidosis and reflects the NICE (2004) guidance for the management of COPD.
Despite this, patients are often inappropriately managed with oxygen therapy. There may be several reasons for this, including: ineffective or a lack of prescribing; junior doctors’ inexperience in managing respiratory patients; or a lack of autonomy for experienced respiratory health professionals to closely monitor and titrate oxygen.
Some clinicians have initiated schemes to identify patients with COPD who are at risk of CO2 retention, such as the use of credit-card sized alert cards (Gooptu et al, 2006). These schemes have been problematic as patients may fail to present their cards on admission to hospital and staff and patients require continuing education (New, 2006). Despite this, the schemes have been recommended by the BTS (2007) and the UK Ambulance Service Clinical Practice Guidelines (Fisher et al, 2006).
Patients who require emergency oxygen therapy are acutely ill and many are in a life-threatening situation. Patients are often frightened, anxious and distressed. It is vital that the health professional is calm and reassuring in her or his approach, especially if the patient feels claustrophobic when a face mask is applied. Effective interpersonal and communication skills are an important component in patient compliance with oxygen therapy.
Stopping oxygen therapy
Like many treatments, oxygen is often commenced without formal evaluation and continued without appraisal of the continuing need. Oxygen therapy should be titrated downwards and stopped when the patient is clinically stable and arterial oxygenation is adequate with the patient breathing room air (BTS, 2007).
Oxygen is a drug and should be prescribed. Health professionals involved in administering and adjusting oxygen therapy should understand the physiology and possible complications of such treatment. Nurses can play an important part in actively managing patients receiving emergency oxygen therapy.
Treatment should be based on achieving target arterial oxygen tensions and saturations rather than on giving predetermined concentrations
or flow rates of inspired oxygen. Pulse oximeters should be available in all clinical areas where acutely ill patients are managed and oxygen
is given. Patients requiring prolonged administration of oxygen should have their blood gases monitored frequently. Appropriate documentation, prescription, titration and monitoring are essential.
British Thoracic Society (2007) Guidelines for Emergency Oxygen use in Adult Patients: Summary of Draft Guideline. www.brit-thoracic.org.uk/c2/uploads/oxygen_ pull_
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