It is unusual for children with cystic fibrosis (CF) to require long term oxygen therapy (LTOT). However, CF lung disease eventually results in chronic hypoxaemia (low blood oxygen levels). Progressive damage to lung tissue and spasm of blood vessels due to hypoxia may lead to pulmonary hypertension. Patients with CF and hypoxaemia may suffer from reduced exercise ability, reduced skeletal muscle strength, poor sleep quality and a worse quality of life. There is also evidence from laboratory experiments with rodents that low oxygen levels can contribute to the decline in lung function (Leeper-Woodford & Detmer, 1999) and encourage growth of P. aeruginosa (Borriello et al, 2004).
Reduced oxygen levels are most likely to occur either during sleep or during exercise before they become apparent at rest during the day. In adult practice, measurement of arterial PaO2 is essential in the assessment of patients for hypoxaemia. In paediatric practice SaO2measured by pulse oximetry is the main assessment tool. There is no clear definition of significant hypoxaemia in CF (Urquhart et al, 2005). Recent guidelines suggest that oxygen saturation should be maintained at or above 92%, or arterial PaO2 above 8kPa (Balfour-Lynn et al, 2005).
Night time oxygen
One to two per cent of children with CF in the UK receive supplementary oxygen at night. Although children with CF have significantly lower mean overnight SpO2 when compared to controls (Darracott et al, 2004), there are no accepted guidelines on when to recommend overnight oxygen. One definition of sleep hypoxia, from a recent e-mail survey of CF Units, was defined by a SpO2 of <93% for >25% of the study period (personal communication).
We recommend providing overnight oxygen if:
– the mean overnight SpO2 is 93% or less
We perform overnight oximetry:
– routinely on the first and last night of hospital admissions
– if daytime SpO2 is 95% or less
– there are symptoms of overnight hypoxaemia
Initiation and follow up
It is exceptionally rare for oxygen therapy to cause hypoventilation and hypercapnia in children. We would, however, perform an early morning capillary PaCO2 before organising oxygen at home. Once oxygen is initiated, review with home overnight oximetry should be at four to six weeks, three months and then six monthly.
Day time oxygen
Very few children with CF receive oxygen during the day. Most children start with oxygen at night prior to receiving oxygen during the day. Exercise induced arterial hypoxaemia (EIAH) in children with CF has been defined as a fall in SpO2 during exercise of 4% or more from baseline (Narang et al, 2003). Cystic Fibrosis Trust guidelines suggest annual exercise testing of patients with CF (Cystic Fibrosis Trust, 2001). Nocturnal hypoxaemia is thought to occur more frequently than EIAH (Coffey et al, 1991; Bradley et al, 1999). Even with lightweight cylinders and liquid oxygen the mechanism of delivering day time oxygen has a significant impact on quality of life. We feel it is important that clinical benefit is demonstrated before this therapy is implemented.
If there is a significant discrepancy between respiratory function tests and the level of arterial/capillary hypoxia, the presence of a hepatopulmonary syndrome should be considered.
Oxygen with infective exacerbations
Some children require oxygen during acute exacerbations. We would start oxygen, via nasal cannulae in hospital when the mean overnight SpO2 is 93% or below, or daytime SpO2 95% or less. There is surprisingly little evidence for the benefit of supplementary oxygen in patients with CF. Although supplementation has been shown to lead to improved school or work attendance, it has not been shown to have an effect on disease progression, frequency of hospitalisation or mortality (Zinman et al, 1989). Like so many areas in CF care there is limited long term quality research to direct clinical interventions (Mallory et al, 2005).
The mechanism of provision of home oxygen has changed in the UK (www.airproducts.co.uk).
Oxygen for adults with cystic fibrosis
Hypoxia is defined as an arterial PaO2 <8kPa or SpO2 <90% (Mallory et al, 2005). Nocturnal hypoxia is well demonstrated in CF (Frangolias & Wilcox, 2001; Milross et al, 2001). Hypoxia may also occur during the day and/or with activity.
Hypoxia may be linked with decreased daytime function in patients with CF (Dancey et al, 2002; Dobbin et al, 2005) and may lead to complications such as pulmonary hypertension (Mallory et al, 2005).
Oxygen therapy may be used during an in-patient stay for an acute illness or may also be required at home. The Cochrane Review states that hypoxemia can be eliminated during sleep with supplemental oxygen (Mallory et al, 2005). Oxygen therapy also increases daytime function as measured by days at work or school (Zinman et al, 1989). Other benefits in physical function and mortality rates have been documented in patients with chronic obstructive pulmonary disease and may be applicable to patients with CF.
Oxygen therapy is expensive (Mallory et al, 2005). Recent Department of Health changes to the provision of home oxygen have emphasized the importance of cost and the need for evidence of efficacy through proper assessment. The decision to start and to continue home oxygen therapy should be carefully assessed and reassessed at regular intervals (BTS guidelines, 2006).
Criteria for assessment
At the Leeds Adult CF Unit patients are identified as requiring assessment for supplemental oxygen at either on admission, during home iv antibiotic therapy or /at clinic.
Daytime SpO2 <90%
CBG/ABG, PaO2 <8kPa
Mean overnight oximetry, SpO2 <90%
A fall in SpO2 to <90% with a fall >4% from the resting value during the 6 minute walking distance test (6MWD)
Patients satisfying the above criteria for assessment would generally be admitted. Assessment for domiciliary oxygen should take place at least three days preceding discharge to allow for placement of temporary oxygen at home. Assessment for nocturnal oxygen involves overnight oximetry and early morning blood gases to ensure safe PaCO2 levels. Arterial blood gas or CBG measurements and the 6MWD are used to assess daytime oxygen requirements. Oxygen delivery is titrated and measures repeated pre-discharge with temporary oxygen supplies. The patient’s requirements are reassessed after four to six weeks of oxygen therapy, after three months, and then six monthly. At reassessment oxygen therapy may be continued, adjusted or discontinued.
• Reduced oxygen levels are most likely to occur either during sleep or during exercise before they become apparent at rest during the day
• One to two per cent of children with CF in the UK receive supplementary oxygen at night
• Hypoxia may be linked with decreased daytime function in patients with CF and may lead to complications such as pulmonary hypertension (Mallory et al, 2005).
• The decision to start and to continue home oxygen therapy should be carefully assessed and reassessed at regular intervals
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