Cystic Fibrosis

May 27, 2020 12 min read


Written by Anne Wright, RD. Reviewed by Harriet Smith, RD.

 

Section 1: Background Information

 

Introduction

Cystic fibrosis (CF) is a life limiting, autosomal recessive disorder leading to respiratory congestion, multiple organ failure, and metabolic changes 1. It is characterised by abnormal transport of chloride and sodium across the epithelium, leading to thick, viscous secretions.

 

Key Statistics 2

  • In the United Kingdom (UK) one in 2,500 babies are born with CF
  • Currently >10,500 people are registered in the UK with CF
  • Worldwide prevalence is 100,000
  • A baby born with CF in the UK today has an estimated median survival of 47 years
  • Compared with males, females have a greater deterioration of pulmonary function, with increasing age and younger mean age at death
  • The leading cause of mortality in CF is respiratory failure secondary to bronchiectasis and recurrent lung infection

Disease progression and survival in CF is influenced by screening, genetics, healthcare provisions and adherence to treatment 3. Studies from diverse countries and healthcare settings have shown that demographic factors, including socioeconomic, ethnic and racial minority status, have a profound influence on health and survival 4.

 

Signs and Symptoms

Common signs and symptoms of CF include: 5

  • Frequent respiratory tract infections
  • Shortness of breath, wheezing
  • Poor weight gain and growth
  • Tiredness, lethargy
  • Infertility in males
  • Very salty tasting skin
  • Steatorrhoea
  • Gut meconium ileus in infants

 

Aetiology

CF is an autosomal recessive disease caused by defects in the cystic fibrosis transmembrane conductance regulator (CFTR) gene 6. It is inherited when two carrier parents (who have one normal gene and one defective) each contribute the abnormal CFTR gene to their child. The likelihood that two parents will have an affected child is 1:4 for each pregnancy. 7

The CFTR gene encodes for a protein which regulates the flow of sodium, chloride and water across epithelial cells lining the respiratory, digestive and genital tracts. Gene mutations result in abnormal transport of these ions across the cells leading to increased viscosity and tenacity (stickiness) of secretions within the tracts. 8 In the airways, this results in reduced clearance of inhaled bacteria, leading to persistent infection and chronic inflammation.

In about 85% of cases, the pancreatic exocrine ducts become sufficiently blocked to cause maldigestion and intestinal malabsorption (pancreatic insufficiency). 9

 

Screening and Diagnosis

Infant screening

All babies born in the UK are screened for CF shortly after birth (>5 days) using the “heel prick” test 10. This measures immunoreactive trypsinogen (IRT), which is raised in CF. Diagnosis of CF is confirmed using a sweat test. 11

Infant screening for CF has been in place across the UK since 2007 12. Prior to this, people were diagnosed with CF if they had a family history of CF and presented with symptoms through a clinical assessment, genetic testing and the sweat test.

Sweat Test

During a sweat test, the axillary sweat glands are encouraged to produce sweat via application of a medication (pilocarpine) and mild electrical stimulation. CF is confirmed when the concentration of chloride in collected sweat is 60 mmol/l or more. A borderline measure of 30 - 60 mmol/L can also indicate a positive diagnosis of CF for patients who are symptomatic. 13

Diagnosis

The diagnosis of CF can be based on 14:

  • Positive test results in people with no symptoms (i.e. a positive heel prick test followed by positive sweat and gene tests) or;
  • Clinical manifestations, supported by positive sweat or gene test results or;
  • Clinical manifestations alone, in the rare case of people with symptoms who have normal sweat or gene test results.

 

Treatment Overview

Treatments aim to improve clearance of mucus secretions, eliminate infection and slow the progression of lung damage. 15

Airway clearance techniques (ACTs) such as breath control, coughing exercises or chest percussion are designed to loosen thick, sticky mucus from the airway in CF patients. 16 Additionally, exercise and physiotherapy, including a positive expiratory pressure (PEP) device or a high frequency chest wall oscillation device (a percussion vest), is recommended. 17

Antibiotics are often prescribed for preventing and controlling lung infections. For control of airway inflammation, non-steroid anti-inflammatory drugs (NSAIDs), inhalers and systemic steroids may also be prescribed. Mucolytic agents, such as dornase alfa are recommended to reduce viscoelasticity of airway secretions. 18 Cystic fibrosis transmembrane conductance regulator (CFTR) modulator therapies, a newer form of medications which work by targeting the faulty protein made by the CFTR gene, may also be prescribed.

Lung transplantation is the final therapeutic option for patients with end-stage lung disease. 19

 

Section 2: The Impact of Cystic fibrosis

CF is a multisystem, life-limiting disorder. Fifty years ago most children with CF died before six years of age, but we’ve come a long way in terms of treatment - the current, (UK), estimated median survival age for patients with CF is 47 years.

 

Physical Impact

Respiratory symptoms are common amongst all CF patients. 95% of patients die from complications related to pulmonary infection, with females more at risk of mortality than males. 20

Other ways CF can impact physical health include:

  • Exocrine pancreatic insufficiency (PI) (> 85% of individuals)
  • CF-related diabetes (CFRD) in an estimated 50% of adults over 30 years old
  • Liver damage
  • Increased risk of intestinal obstruction
  • Infertility, (present in 95% of males, due to absence of the vas deferens, and in 20% of females due to problems such as abnormal cervical mucus 21 ).
  • Pain is common throughout the disease course 22 .

 

Psychological Impact

CF patients and their families face significant psychosocial challenges 23 . For example, patients with CF have an increased likelihood of mood disorders such as depression. They are also more likely to have a reduced quality of life due to frequent hospitalisations, high treatment burdens and body image issues. People with CF can sometimes have problems with sexuality, platonic relationships and independence. 24

 

Nutritional Impact

CF has been associated with undernutrition in children, which can lead to stunted growth and development. 25 In adults with CF, nutritional status is directly associated with both pulmonary status and survival. 26 Therefore, ensuring sufficient energy and protein intake (along with other important micronutrients) is important amongst the CF population.

Common causes of undernutrition and/or nutritional deficiencies in CF patients include 27 :

High energy (calorie) requirements

CF patients have an increased Resting Energy Expenditure (REE), which can be caused by the disease itself, inflammation, pancreatic insufficiency (see section on ‘malabsorption’ below) and genetic CFTR mutation issues. Meeting these high energy requirements through food alone can be an extremely challenging part of the dietetic treatment plan.

Reduced energy (calorie) intake

Reduced energy intake is common amongst CF patients. This can occur due to a number of psychosocial issues (i.e mealtime anxiety, body image issues) , physical issues (i.e. poor airway clearance or breathing difficulties), low appetite, fatigue, early satiety, pain, medication side effects and bacterial infections, which can cause gastro intestinal obstruction and discomfort.

Increased energy (calorie) losses

CF patients may experience increased energy losses due to impaired liver function, abnormal bile acid metabolism, and CFRD. CFRD is present in 50% of patients with CF and contributes to energy losses through glycosuria, (loss of sugar in the urine).

Nutrient malabsorption

PI affects at least 85% of CF patients. A build-up of thick, sticky mucus secretions in the pancreas can block the entrance of pancreatic digestive enzymes into the small intestine. This results in malabsorption of fats and the fat-soluble vitamins A, D, E, and K.

Up to 40% of patients with CF have been shown to be deficient in vitamin D and vitamin A 28 . Additionally, essential fatty acid deficiency and sodium depletion can be seen in many CF patients. CF patients may also present with micronutrient deficiencies in calcium, iron, magnesium, selenium and zinc.

 

Section 3: Nutritional Strategies for Managing CF

Nutritional management is a critical and highly individualised part of CF care. It should be continually adjusted to meet nutritional requirements throughout the lifecycle. The aim of nutritional management is to enable normal growth in infants and children and to maintain or optimise weight and Body Mass Index (BMI) in adults.

 

Energy (Calorie) and Macronutrient Requirements

Recommended energy requirements for those with CF are 110–200% of those required by healthy individuals of the same age and gender, 29 although patients without PI may have lower requirements.There are currently no guidelines for the optimal daily protein intake required by people with CF. More research is needed to establish protein recommendations 30

To assist in meeting energy requirements, high-fat diets are recommended for patients with CF. 31 The types of fat ingested should be considered as intakes of monounsaturated and polyunsaturated (vs saturated) are beneficial for overall health.

For patients with PI, pancreatic enzyme replacement therapy (PERT) is prescribed to be taken with meals and drinks containing fat 32 . Individual dosing for PERT varies and should be determined based on a number of factors, including clinical symptoms such as steatorrhea, pain, bloating, and failure to gain weight. 33

 

Micronutrient Supplementation

Patients with CF should have their plasma fat-soluble vitamin levels (A, D, E and K) checked annually. Supplementation of fat-soluble vitamins is recommended in CF patients with evidence of low plasma levels. For those who have PI, fat-soluble vitamins should be taken with food and PERT. For evidence-based guidelines on supplementation in CF, please refer to Nutritional Management of CF consensus document.

Patients with CF are at-risk of sodium depletion due to increased losses in sweat 34 . Adding salt to meals is recommended for children and adults, especially in times of hot weather or during sporting activities. Sodium supplemented sports drinks may also be useful. This should be assessed on a case-by-case basis.

 

Nutrition Interventions

Breastfeeding should be encouraged for infants with CF. Exclusive breastfeeding has been associated with improved respiratory outcomes in the first two to three years of life 35 . Weaning is recommended from four-months-old, and throughout childhood, encouraging positive eating behaviours (see Table 4) whilst meeting the high energy requirements seen in patients with CF is paramount. 36

Table 4: Positive Eating Behavioural Management Strategies for Children with CF 37

  • Normalise food and eating, making mealtimes enjoyable experiences
  • Encourage a structured approach to meal and snack times
  • Set rules and clear expectations for desired behaviours (e.g. limit mealtimes to 15 mins for toddlers, 20 mins for young children)
  • Set energy (calorie) goals for meals and snacks
  • Encourage new foods, praise the child for eating and complement appropriate eating behaviours
  • Ignore complaints or disruptive behaviours which are incompatible with eating (e.g. turn away from the child or leave the room)
  • Remove distractions at mealtimes (e.g. television, computers, electronic tablets, toys)
  • Provide extra fluids, and ONS (if prescribed), only after a meal is eaten
  • Provide regular reward incentives for meeting caloric goals (e.g. star charts, trophies)

 

Children and adults with CF are encouraged to meet nutritional requirements using a “food first approach”. This includes eating high-fat, energy-dense foods and snacks as well as implementing food fortification techniques. Emphasis should be placed on meeting nutritional requirements, where possible, for ‘at-risk’ nutrients such as calcium and iron.

Studies indicate that some children and young adults with CF struggle to meet energy requirements, despite food-first nutritional interventions. Oral nutritional supplementation (ONS) may be introduced in the short-term as a method of increasing caloric intake 38. Figure 1 illustrates the amount of food and calories required during one day for a 60kg , 25-year-old, active female with CF.

Example One-Day Meal Plan (3,300 kcal) for a Female 25-year-old Patient with CF 37

Breakfast
  • 220g porridge made with full fat milk and sugar
  • 15 almonds
  • Banana (505 Kcal, 20g Protein)
Snack
  • Handful nuts (30g)
  • Flavoured corner yoghurt (200g) (320 Kcal, 12g Protein)
Lunch
  • Large, (buttered) ham, cheese, and salad baguette with ½ avocado and tbsp. mayonnaise
  • Mixed greens salad with oil dressing
  • Orange (large)
  • 250ml full fat milk (765 Kcal, 27g Protein)
Snack
  • Packet of crisps (40g)
  • Chocolate bar (50g) (420 Kcal, 5g Protein)
Dinner
  • Salmon risotto with peas, squash, broccolini (400g)
  • 2 large scoops ice cream and chocolate syrup topping (785 Kcal, 28g Protein)
Supper
  • 2 crumpets with butter and honey (2tbsp)
  • 250ml milk (505 Kcal, 6g Protein)
Total:

Energy (kcal): 3,300

Protein (g) : 100

 

The use of polymeric enteral tube feeding should be considered when oral interventions have failed to achieve acceptable rates of growth and/or nutritional status. 39

 

 

Section 4: Useful Resources for HCPs on CF

 

NICE guidelines for the diagnosis and management of CF

The cystic fibrosis trust

BDA Cystic Fibrosis specialist group

 

To complete CPD questions on this resource

 

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