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Non-invasive positive pressure ventilation for COPD patients

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Denise Gibbons, MA, Advanced Practice (Nursing), Dip Respiratory Care; Pauline Milner, RN, Dip Nursing Studies.

Denise-Respiratory Nurse Specialist; Pauline- Sister, Acute Respiratory Assessment Service, South Tyneside District Hospital, South Shields, Tyne and Wear

Chronic obstructive pulmonary disease (COPD) is a major world-wide health problem, placing a significant burden on the provision of health-care resources (Barnes, 2000). Acute exacerbations are a common cause of hospital admission and account for up to 25% of all acute medical admissions during the winter. Conventional strategies for treatment are well established, and include: controlled oxygen therapy, nebulised or high-dose inhaled bronchodilator therapy, antibiotic therapy, systemic corticosteroids, intravenous aminophylline and physiotherapy. However, despite initiation of these treatments, a number of patients deteriorate as a result of respiratory muscle fatigue causing hypoventilation, which eventually leads to carbon dioxide (CO2) retention and type 2 respiratory failure (Box 1) (Juniper and Hardinge, 1998).

Transfer to the intensive therapy unit (ITU) and initiation of invasive mechanical ventilation provides temporary relief to the respiratory muscles, enabling the correction of arterial blood gases by the artificial delivery of gases in and out of the patient’s lungs. There is, however, a reluctance to admit these patients to ITU, where difficulties are experienced in weaning them from the ventilator (Simmonds, 1996). Mechanical ventilation also exposes the patient to increased risks of infection, laryngeal and tracheal injury (Mahamid, 2000), tension pneumothorax, pneumonia and sinusitis (Preston, 2001).

Over the past decade, an alternative method of non-invasive positive pressure ventilation (NIPPV) has been established for these patients. Its main aim is to give the patient ventilatory support using a face mask or nasal mask instead of an endotracheal tube (Brigg, 1999). NIPPV assists the patient by:

- Reducing the work involved in breathing

- Resting the respiratory muscles

- Reducing the respiratory rate

- Reducing CO2 levels, increasing oxygen (O2) levels and correcting pH as alveolar ventilation improves

- Increasing the volume of each breath (Brigg, 1999; Preston, 2001; Sawkins, 2001).

Other benefits of this method include: reduction in use of ITU beds, improvement in mortality rates and decreased overall length of hospital stay (Hess, 1997; Brigg, 1999; Doherty and Greenstone, 2000).

This treatment is used in high-dependency units (HDUs) and, more commonly, in general medical wards that specialise in respiratory care (Juniper and Hardinge, 1998). It is therefore essential that health-care professionals caring for these patients understand the importance of selection of appropriate equipment, patient selection criteria, issues related to ventilator management, nursing care of the patient, potential complications, weaning issues and recognition of treatment failure.

Ventilators in NIPPV

The application of NIPPV usually refers to the use of a portable positive-pressure ventilator connected to the patient via tubing and a nasal or full-face mask. Ventilators may be pressure- or volume-cycled and may include a humidification port and attachments for entraining supplemental oxygen (Juniper and Hardinge, 1998).

A pressure-cycled ventilator uses two different pressure settings: high pressure for the inspiratory phase and low pressure for the expiratory phase. Pressure-cycled machines are usually smaller and more compact than volume-cycled models and work by giving a pressure-assisted breath as the patient breathes in. Although they compensate for small leaks around the nose or mouth, these machines are often less powerful than the volume-cycled models in relation to the amount of flow pressure that can be generated (Brigg, 1999).

Volume-cycled ventilators deliver a predetermined tidal volume but the inflation pressure varies. It works best if the patient’s breaths are synchronised with the machine. This mode is not well tolerated by patients due to the high inspiratory pressures needed to increase tidal volume, particularly if there are changes in airway resistance due to bronchospasm. There are also potential problems with leaks from the mask.

Positive-pressure ventilators work by pushing air into the lungs via the interface - the facial or nasal mask plus head harness. The interface itself can play just as important a role in the effectiveness of NIPPV as the ventilator (Turner, 1997).

Patient-ventilator interface

To ventilate the patient as effectively as possible and to ensure maximum comfort, the mask chosen must fit well. Proper placement and positioning of the mask is the key (Reynolds, 1997). If the mask is too tight, the patient will be uncomfortable and over time pressure-induced tissue ischaemia will develop. If the mask is too loose, a leak may develop. Proper sizing and fitting is aided by a variety of masks and gauging tools available. Both systems have advantages and disadvantages (Table 1).

Patient selection

It is vital that patients meet the criteria for treatment. It is crucial that the cause of the respiratory failure is established and treated with maximal therapy, which may consist of nebuliser therapy, intra-venous aminophylline, antibiotics, corticosteroids, physiotherapy and, in some instances, diuretics. NIPPV should act as an adjunct to all other therapies, not as a replacement.

NIPPV should be considered in patients whose blood gases indicate type 2 respiratory failure (Box 1) where high levels of CO2 (hypercapnia), low levels of oxygen (O2) (hypoxaemia) and low pH persist despite the above maximal therapy.

The patient should be able to breathe spontaneously and be able to maintain his or her own airway (Carlin and Kaplin, 1996; Sawkins, 2001). Adequate gag and cough reflexes should also be present and the patient should be able to clear his or her secretions adequately (Reynolds, 1997). It is preferable if patients are alert and able to co-operate, although the authors have found that this therapy can be used when patients are agitated.

One contraindication to NIPPV is a patient’s inability to maintain his or her own airway; in this case endotracheal intubation would be recommended. Other relative contraindications include:

- Haemodynamic instability demonstrated by hypotension

- Cardiac instability demonstrated by arrhythmia

- Bullous lung disease or any other disease that would increase the risk of a pneumothorax

- Copious respiratory secretions

- Patients with facial or skull trauma

- Active gastrointestinal bleeding

- Sinusitis, epistaxis, active haemoptysis (AARC, 1993; Mahamid, 2000; Wunderink and Hill, 1997).

Before the initiation of treatment, it is important that the consultant responsible for the care of the patient establishes the resuscitation status in case of a cardiorespiratory arrest or treatment failure.

If a patient meets the above criteria for treatment, patient co-operation and compliance is crucial to the success of establishing NIPPV.

Establishing NIPPV

Patients may often be agitated due to hypoxaemia and/or hypercapnia, will have severe dyspnoea, have difficulty in speaking and show signs of exhaustion due to the work of breathing (Sawkins, 1997). Spending time establishing NIPPV will significantly enhance the effectiveness of the treatment (Place, 1997). Involving relatives and carers fully by demonstration and explanation may enable them to assist in gaining the confidence and co-operation of the patient, especially if the patient is agitated and/or confused. Involvement of the patient throughout the process empowers him or her and allows a degree of control over what is happening (Sawkins, 2001) (Box 2).

It is important to note that, even in the initial stages of establishing NIPPV, it is vital to monitor the patient continuously for signs of worsening respiratory depression.

Patient monitoring

It is recognised that initially the patient will need an increased level of support, nursing care and time. Kannan (1999) recommends that all patients undergoing NIPPV should be given the same priority as those undergoing invasive ventilation. Clinical assessments should initially be made every 15-30 minutes (Sawkins, 2001) (Box 3).

Pulse oximetry is an important method of monitoring oxygenation. During the initial stages of the therapy, oxygen saturation should be monitored continuously; the aim is to keep saturation levels above 85%. Pulse oximetry allows for accurate determination of the required flow of entrained oxygen (Brigg, 1999).

However, pulse oximetry does not measure the partial pressure of carbon dioxide (PaCO2) level, which is important when managing patients undergoing NIPPV. It is vital that arterial or capillary blood gas analysis of pH, PaCO2 and partial pressure of oxygen (PaO2) is performed. Timing will depend on the patient’s condition. Generally, measurements are taken at one and four hours post-commencement. Thereafter frequency of measurements will depend on the patient’s progress. Inspiratory and expiratory pressures and the percentage of oxygen administered are altered according to the blood gas results and on consultation with the medical staff.

Patients require a high level of support and psychological preparation during the initial stages of NIPPV (Preston, 2001). However, once the patient is stable and comfortable, the demand for nursing time is reduced, and is found to be no greater than for conventionally treated patients (Hill, 1997).

Nursing care

Skin protection is an important nursing consideration and the use of a hydrocolloid dressing to prevent damage to the bridge of the nose and forehead is advocated (Sawkins, 2001). Patients have also been known to develop pressure damage around their ears if the headgear is too tight.

Regular observation of the eye area is necessary. The ventilator compensates for small leaks, which are permissible provided they are not near the patient’s eyes as this can lead to dryness and the development of conjunctivitis (Kannan, 1999).

Using a facial mask increases the risk of aspiration if the patient vomits. Therefore medicines that may cause nausea should be avoided and the use of anti-emetics should be considered (Sawkins, 2001). As gastric distension is a possible side-effect, the abdomen should be assessed at regular intervals and a nasogastric tube should be used intermittently to release the air (Preston, 2001).

Once a patient’s clinical condition begins to stabilise the mask may be removed for short periods to allow for eating and drinking. It is important to maintain adequate hydration, which will also improve sputum expectoration.

Complications

NIPPV is safe and has few major complications when used with appropriately selected patients. The most common complications, their causes and suggested interventions are listed in Table 2.

Weaning

Weaning NIPPV is based on clinical observations, pulse oximetry and arterial blood-gas results. There is no one set of parameters that can predict weaning success, but it is recommended that the following clinical parameters be taken into account:

- Arterial blood gases return to within normal parameters for the patient

- Oxygen saturation >85% on air or 24-28% oxygen delivered by a venturi mask

- Respiratory rate <25 per minute

- No use of accessory muscles

- Able to complete sentences when speaking (Carlin and Kaplin, 1996; Kannan, 1999; Reynolds, 1997).

There are several ways in which to wean the patient from NIPPV, depending upon the patient’s clinical condition. In some instances, NIPPV can simply be discontinued. In other circumstances, it may be possible to discontinue NIPPV for only two to three hours at a time while monitoring the clinical condition of the patient. In some instances it may be necessary to use NIPPV over night while keeping the patient off ventilatory support during the day (Carlin and Kaplin, 1996).

If the patient being weaned begins to show signs of respiratory distress or if the level of oxygen saturation is <85% on low concentrations of supplemental oxygen, local protocol states that the patient should be placed back on NIPPV.

Treatment failure

The initial response to NIPPV and the severity of respiratory failure at presentation are important predictors of success. Rapid improvement of pH, PaCO2, PaO2 and respiratory rate in the first hour of treatment have been shown to be important indicators of success (Elliot, 1995; Hess, 1997). Assessment of treatment failure should include:

- No improvement in respiratory rate

- No improvement in pH, PaO2 and PaCO2 baseline parameters at four to six hours

- Hypotension

- Tachycardia

- No improvement in or reduction in consciousness levels (Elliot, 1995).

Treatment failure will occur in 20-40% of patients (Simmonds, 1996). It is therefore important that a management plan of what to do in case of failure is made before the initiation of treatment by the respiratory physician in charge of the patient’s care.

Cleaning/disinfection

The equipment used in delivering NIPPV may be exposed to potentially infectious material as it comes into contact with patients’ skin, mucous membranes, respiratory secretions and blood.

Appropriate cleaning of equipment and maintenance of machines should be clearly outlined, and all personnel should be aware of such procedures. Because of the increased risk of infection when using this equipment, hospital cleaning procedures are usually stringent (Knebel et al, 1997). Single-use equipment to reduce cross-contamination may be cost-prohibitive. Items stamped ‘single-use only’ should not be used on another patient. Non-disposable masks and equipment must be cleaned according to manufacturers’ recommendations and local hospital policy. Maintenance of ventilators and filter changes should take place according to manufacturer’s recommendations. All machines should have an annual service and electrical check.

Training and education

Treatment is often prescribed by medical staff and initiated by nursing staff and physiotherapists. This highlights the importance of the role of nurses and physiotherapists in caring for these patients.

Since the evolution of the clinical governance concept (DoH, 1999), with emphasis on accountability, it is inappropriate for nurses not to receive training and education in this treatment method. Local evidence-based clinical guidelines for NIPPV are also fundamental in providing high-quality standardised care for this patient group. The use of guidelines reduces the risk in clinical decision-making.

Training should include an understanding of the anatomy and physiology of the respiratory system, the treatment options available, inclusion and exclusion criteria, operation of the equipment, maintenance and cleaning, selection of interfaces and assessment of effectiveness. Staff need to understand how to interpret relevant data and assess patients’ clinical response to treatment (Hess, 1997).

Conclusion

NIPPV has several potential advantages as it prevents complications associated with endotracheal intubation and is effective in improving symptoms of respiratory distress. NIPPV therefore provides another treatment option for those appropriately selected patients with acute respiratory failure secondary to COPD. However, suitably trained staff and established protocols are required to enable this method of treatment to be used successfully in respiratory and general wards, thus preventing the need for admission to an ITU. Studies indicate that NIPPV is no more difficult to implement than conventional treatment and that there is no increase in nursing time (Hill, 1997). However, nurses caring for these patients need to be clinically competent, since these patients require close observation and evaluation of treatment outcomes.

 

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Readers' comments (1)

  • This and other articles that I have used for CPD become difficult to use when the figures, texts, pictures and boxes alluded to are not shown.
    Please try to improve this.
    Thanks
    Janet James

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