This article uses a case study to illustrate why patients with COPD require holistic assessment and arterial blood gas analysis before non-invasive ventilation is used
Steve Hunter, BSc, RGN, is critical care outreach nurse at Princess Royal Hospital, Haywards Heath, West Sussex.
Hunter, S. (2009) Holistic assessment of patients with COPD before the use of non-invasive ventilation. Nursing Times; 105: 20, early online publication.
The use of non-invasive ventilation (NIV) to manage patients with exacerbations of COPD has increased in the past 10 years. However, the intervention can be counterproductive. This article highlights why holistic patient assessment as well as arterial blood gas analysis are important before NIV is used.
Keywords: Arterial blood gases, COPD, Non-invasive ventilation, Respiratory care
- This article has been double-blind peer reviewed
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Lung function tests and respiratory symptoms are used to diagnose COPD. Periodic worsening of these symptoms indicates an exacerbation of COPD (Box 1).
Box1. Exacerbation of COPD
This is a sustained worsening of the patient’s symptoms from her or his stable state that is beyond normal day-to-day variations, and is acute in onset.
Commonly reported symptoms are worsening breathlessness, a cough, an increase in sputum production and a change in sputum colour.
Source: NICE (2004)
Pharmaceutical management of an acute exacerbation of COPD includes:
- Increased frequency of bronchodilators;
- Antibiotics to treat signs of infection;
- Theophyllines and respiratory stimulants.
Many patients improve rapidly if oxygen therapy is used alongside pharmaceutical management (British Thoracic Society Standards of Care Committee, 2002).
However, optimising oxygen therapy requires careful monitoring of both oxygen and carbon dioxide levels in the blood using arterial blood gas analysis.
Interpreting arterial blood gas is complicated but analysis is used with increasing regularity on general wards in the acute hospital (Lynes, 2003), and nurses need to understand when and why blood gases are monitored.
Allen (2005) and Lynes (2003) provide a comprehensive examination of blood gas monitoring and the procedure for collecting samples.
Types of respiratory failure
Type 1 respiratory failure describes an abnormally low concentration of oxygen in the blood where the partial pressure of oxygen dissolved in arterial blood (PaO2) is low (<8kPa), while the carbon dioxide level (PaCO2) is normal or low (4.5–5.8kPa or <4.5kPa).
Type 2 respiratory failure occurs when a patient has low oxygen levels but carbon dioxide levels are raised. Definitions are summarised in Box 2.
Box 2. Definitions of respiratory failure
Type 1: A failure of oxygenation
Normal or low PCO2
Type 2: A failure of ventilation
In type 2 respiratory failure, blood gas analysis helps to clarify the speed at which the failure has occurred.
- If the deterioration is rapid (acute), the rising level of carbon dioxide in the blood will affect the body’s ability to compensate for the increased acidity. The result is that the pH of the blood becomes acidic. (It will move below the normal pH of 7.4.)
- If the deterioration is chronic, the body has time to compensate for the retention of carbon dioxide by retaining bicarbonate ions (which are alkaline). The blood gas will display an elevated PaCO2 and an elevated HCO3 (bicarbonate ion concentration) but the pH will remain normal.
- Acute-on-chronic type 2 respiratory failure will display a mixture of the above. An acute exacerbation of COPD may result in an acidic pH (<7.4), depicting the acute phase of the condition, but the patient will have raised carbon dioxide and bicarbonate levels associated with the chronic disease.
Box 3 outlines the systematic approach that should be used to analyse arterial blood gas. It is possible to adopt an inappropriate management plan if the final step of interpreting the blood gas within the context of the patient’s presenting symptoms is missed.
Box 3. Systematic assessment of arterial gases
- Interpret the pH (normal, acid or alkaline)
- Find the cause (respiratory and/or metabolic)
- Assess for compensation
- Assess oxygenation
- Interpret the results in the light of the patient’s history
Source: Pratt (2006)
Using non-invasive ventilation
Non-invasive ventilation in the form of biphasic positive airway pressure (BIPAP) may be appropriate if the patient has acute or acute-on-chronic type 2 respiratory failure that fails to respond to standard medical therapy.
It can be used:
- As a holding measure while the use of additional therapies is discussed;
- As a trial, with a view to mechanical ventilation if the patient fails to improve;
- As a ceiling of treatment (NICE, 2004).
Contraindications to its use are listed in Box 4.
Box 4. Contraindications to the application of BIPAP
- Recent facial or upper airway surgery
- Facial abnormalities, burns or trauma
- Fixed upper airway obstruction
- Recent upper gastrointestinal surgery
- Copious respiratory secretions
- Life-threatening hypoxaemia
- Severe co-morbidity
- Untreated pneumothorax
Updated BTS guidelines (Royal College of Physicians et al, 2008) recommend that a stratification system is used, whereby patients are classified according to the most appropriate treatment depending on their co-morbidities.
These classifications are:
- Immediate intubation and ventilation;
- Suitable for non-invasive BIPAP and intubation if the non-invasive BIPAP fails;
- For non-invasive BIPAP but not for intubation or intensive care if the non-invasive BIPAP fails.
- Not suitable for non-invasive or invasive ventilation but for active medical treatment.
- For palliative care only.
The indications and contraindications do not highlight the real consequences of using BIPAP inappropriately. The following case study identifies how it is possible to use BIPAP in an acute situation to resolve an immediate clinical problem but how this can also lead to mismanagement of a patient’s condition.
The following blood gas reading was taken when Mr Smith was breathing 28% oxygen from a venturi mask, after admission from a GP to the respiratory ward of a general hospital (the patient’s name has been changed). He has been diagnosed with an exacerbation of COPD.
HCO3 26mEq/L (the nationally accepted units for HCO3 levels on arterial blood gases). See Box 5 for normal levels.
Box 5. Normal arterial blood gases
(May vary with patient age and history)
These arterial blood gas results depict an acute respiratory acidosis (an acidic pH of <7.4, a low PaO2 and a raised PaCO2 or carbon dioxide retention), and conform to the classic definition of type 2 respiratory failure (Box 2).
However, the appropriate management plan for this patient will vary considerably, depending on his presenting signs and symptoms, as well as the acute or chronic nature of his disease.
Management options include:
BIPAP, a form of non-invasive ventilation, could be administered with the key aims of increasing the patient’s depth of breathing (tidal volume) and so reducing his respiratory rate and work of breathing (Tully, 2002).
By optimising the patient’s BIPAP settings in accordance with RCP et al (2008) guidelines, you would expect an improvement/reduction in the acidosis on the next blood gas (pH moving towards 7.4 as a result of the reduction in retained levels of CO2).
Non-invasive BIPAP can be performed on a general hospital ward (Elliott et al, 2002) and, despite its slightly claustrophobic nature, it is generally well tolerated and can offer a lifeline to some patients.
Once the decision to use BIPAP has been made, it is necessary to address the question of whether this form of intervention represents the ceiling of the patient’s therapy or whether mechanical ventilation would be considered if Mr Smith continued to deteriorate.
Making the decision at this point means that further interventions can be started in a controlled manner rather than in haste during an emergency.
If the patient’s consciousness level is deteriorating rapidly, this key symptom will influence the decision to adopt option 2. With no other information available, the appropriate management would be immediate intubation and mechanical ventilation.
Non-invasive ventilation relies on an awake and compliant patient (NICE, 2004) and will assist respiratory effort when spontaneous breathing is present and the patient can maintain an open airway.
Delaying intubation with a trial of BIPAP on a patient whose consciousness level is deteriorating increases the risk of a respiratory arrest.
This is used if auscultation of the patient’s lungs identifies that there are copious upper airway secretions, but the patient is exhausted and is unable to clear them.
An increase in both volume and viscosity of secretions is a common symptom of exacerbations of COPD. The application of BIPAP at this stage may inhibit the removal of these secretions, especially if BIPAP is administered without humidification.
Removal of secretions by oral or deep suctioning (potentially involving the insertion of a nasopharyngeal airway) will keep a patent airway open and may also relieve the acute respiratory symptoms and negate the need for non-invasive ventilation.
This describes the care of Mr Smith during a subsequent hospital admission. Patients with COPD will go on to develop raised bicarbonate levels. This blood gas result is included to highlight the evolving chronic ill health of the patient.
In option 4, the blood gas result is:
PaCO2 1 1.6kPa
The raised bicarbonate level suggests that Mr Smith’s respiratory acidosis has a chronic and an acute element.
The patient has had numerous exacerbations of COPD with the result that his quality of life is severely limited and it may be appropriate to start a discussion about the need for palliative care rather than active treatment of his chronic disease.
While the application of non-invasive BIPAP can give Mr Smith and healthcare team time to review this decision, it may be viewed as a means of extending the life and cause distress to a patient at the terminal stage of a disease process (Prigmore, 2006).
Once the decision to provide palliative care has been made, taking subsequent arterial blood gas samples would be inappropriate as the procedure can cause pain and distress.
Observation of Mr Smith’s respiratory rate, level of consciousness and work of breathing can be used by nurses to inform them of changes in his condition.
Non-invasive BIPAP can be life-saving for some patients admitted with exacerbations of COPD in type 2 respiratory failure.However, without thorough nursing assessment, alongside accurate arterial blood gas interpretation, suboptimal care may be administered.
Nurses need to be vigilant with their observations and be prepared to broach key questions with their medical colleagues about ongoing management of these patients.
Allen, K. (2005) Four-step method of interpreting arterial blood gas analysis. Nursing Times; 101: 1, 42–45.
British Thoracic Society Standards of Care Committee (2002) Non-invasive ventilation in acute respiratory failure. Thorax; 57: 3, 192–211.
Elliott, M. et al (2002) Where to perform noninvasive ventilation? European Respiratory Journal; 19: 6, 1159–1166.
Lynes, D. (2003) An introduction to blood gas analysis. Nursing Times; 99: 11, 54–55.
NICE (2004) Management of Chronic Obstructive Pulmonary Disease in Adults in Primary and Secondary Care. Thorax; 59: 3, (suppl 1), 1–232.
Pratt, P. (2006) Fundamental Aspects of Caring for the Acutely Ill Adult. London: Cromwell Press.
Prigmore, S. (2006) End-of-life decisions and respiratory disease. Nursing Times; 102: 7, 56–61.
Royal College of Physicians et al (2008) Concise Guidance to Good Practice. Non-invasive Ventilation inChronic Obstructive Pulmonary Disease: Management of Acute Type 2 Respiratory Failure. London: RCP.
Tully, V. (2002) Non-invasive ventilation: a guide for nursing staff. Nursing in Critical Care; 7: 6, 296–299.