Cystic Fibrosis for RNs and LPNs Nursing CE Course

to produce a thin, freely flowing substance called mucus. Mucus is a slippery fluid that lubricates and protects the lining of the various organ systems, such as the airways, digestive system, and reproductive system. The CFTR protein is present on the surface of many epithelial cells, including those lining the airways, bile ducts, sweat glands, pancreas, sinuses, and the vas deferens. Pathogenic mutations in the CFTR gene cause CF. When the CFTR gene is mutated, it does not work correctly and inhibits the transport of fluids and ions between cell membranes. Chloride becomes trapped in the cells, and water cannot hydrate the cellular surface, causing mucus build-up. CF mucus is dehydrated and viscous from defective chloride secretion and excess sodium absorption. As a result, the mucus that lines body cavities, especially the airways, becomes thick, copious, and sticky. This leads to mucostasis, as mucus plaques and plugs accumulate in the airway and other body surfaces (McCance & Heuther, 2019; McKelvey et al., 2021; MedlinePlus, 2021; Turcios, 2020). 

The CFTR gene is extensive and complex, with more than 2000 variants known to cause CF. This is important because different mutations may affect which treatment options are available to patients. The variants are categorized into six classes based on how the mutation defect changes the functionality of the gene and correlates with disease severity. Classes I through III are associated with more severe disease manifestations and higher mortality. F508del, which is categorized as a class II defect, is the most common CFTR mutation, accounting for more than 70% of all patients diagnosed with CF. Classes IV through VI are linked to milder pulmonary disease. An overwhelming majority of affected persons with CF have class I or class II mutations. A brief overview of each class is outlined in Table 2 (Brown et al., 2017; CFF, n.d.-b; Lopes-Pacheco, 2016; Stanford Children’s Health, 2021; Veit et al., 2016).

The clinical consequences of the mutations outlined in Table 2 are decreased chloride secretion and increased sodium reabsorption into the cellular space. The increased sodium reabsorption leads to the production of more viscous secretions from exocrine tissues. The mucus accumulates within nearly all organ systems, leading to obstructive pathologies.  Exocrine glands secrete tears, sweat, milk, saliva, and digestive juices into a ductal system to an epithelial surface (e.g., the skin, gastrointestinal [GI] tract, or airways). Nearly all exocrine glands are affected by CF to some degree during their lifespan. The most commonly affected organs include the lungs, sinuses, pancreas, biliary and hepatic systems, intestines, and sweat glands. The glands become obstructed, malfunction, or produce excessive secretions that are extra sticky and thick. The sweat glands produce salty sweat, the lungs are more prone to infection, and the biliary and pancreatic ducts become frequently blocked. Sinus disease occurs when secretion viscosity increases and obstructs the sinus cavities. Over time, impaired sinus secretion clearance results in chronic sinusitis and secondary structural damage (Brown et al., 2017; Lopes-Pacheco, 2016; McCance & Heuther, 2019; Veit et al., 2016).

Signs and Symptoms

The symptoms of CF depend on which organ systems are affected and the severity of the disease. While CF has clinical implications across various organs, its most detrimental impact is on the lungs and digestive tract. The thicker and stickier mucus saturates the lungs, makes breathing and coughing more difficult and exhaustive, and heightens the risk of lung infections. People with milder forms of CF may have little to no symptoms, whereas others experience severe to life-threatening complications. As the condition advances with age, symptoms tend to evolve based on the impact and consequences on underlying organs. Since newborn screenings are required across the US, CF is often diagnosed before symptoms develop. Typically, the earliest signs of CF in newborns and infants include meconium ileus, prolonged neonatal jaundice, or early lung infections. Young children may present with chronic cough, wheezing, anemia, or recurrent sinus and/or pulmonary infections. Others may present with poor weight gain, malabsorption in the GI tract, and failure to thrive. Boys may present with undescended testicles (FTT; Brown et al., 2017; Rosenstein, 2021; Turcios, 2020). According to an analysis of 31,199 newborns, 27.9% were asymptomatic at the time of routine newborn screening.  Among symptomatic infants, 35.5% demonstrated signs of acute or persistent respiratory abnormalities, 27.3% experienced FTT/malnutrition, 21.2% had steatorrhea (i.e., bulky, oily, foul-smelling stools) or otherwise abnormal stools, and 17% endured meconium ileus or other intestinal obstruction. Three percent had electrolyte abnormalities, 3.7% had nasal polyps/sinus disease, and 2.6% suffered rectal prolapse (CFF, 2020). Adults with CF commonly present with recurrent exacerbations of one or more affected organ systems. Table 3 lists some of the most common signs and symptoms of CF (Brown et al., 2017).

CF is a multiorgan disease with many associated complications, with the most common ones listed in Figure 4 (Lamella, 2021).

The most significant effect of CF is on the lungs, as respiratory failure is the leading cause of death. Although the lungs are usually normal at birth, most patients develop pulmonary disease during infancy or early childhood. The thickened mucus creates plugs, clogs airways, impairs airway clearance, and facilitates the accumulation and colonization of bacteria. The clinical trajectory of illness is typically characterized by intermittent exacerbations with repeated infection and lung injury. Collectively, the disease results as a cascade effect following recurrent infections and chronic inflammatory processes. Mucus plugging in the bronchioles leads to obstructive lung disease, including bronchiectasis (i.e., abnormal dilation and damage to the bronchi), respiratory insufficiency, progressive airway destruction, and deteriorating pulmonary function. The abnormally thick mucus provokes the initial pulmonary injury in CF, as it causes diffuse obstruction within the bronchioles (i.e., small airways; see Figure 5; Brown et al., 2017; Rosenstein, 2021).

Bronchiolitis is the most common lung infection in infancy and early childhood, causing inflammation and congestion within the bronchioles. In CF, chronic mucopurulent (i.e., secretions that contain both mucus and pus) plugging of the airways occur secondary to obstruction and infection. The airways release proinflammatory cytokines, and repeated exacerbations lead to chronic inflammation and lung injury. When the lungs become colonized with pathogenic bacteria, it becomes difficult to treat and eradicate the infections effectively, leading to clinical sequelae of multi-drug resistant bacteria colonization. In patients with advanced pulmonary disease, chronic hypoxemia (i.e., low blood oxygenation) can lead to pulmonary artery enlargement, pulmonary hypertension, and right ventricular hypertrophy (MedlinePlus, 2021; Turcios, 2020).

In the GI tract, CF interferes with digestion; the pancreas, intestines, liver, and bile ducts are among the most commonly affected. When gastric contents pass into the duodenum, the pancreatic exocrine glands are triggered to excrete pancreatic enzymes into the small intestines to facilitate digestion; specifically, amylase (to digest carbohydrates), protease (to digest protein), and lipase (to digest fats). The mucus build-up obstructs the pancreatic ducts, preventing the release of digestive enzymes resulting in pancreatic insufficiency (PI) and maldigestion (i.e., the inability to digest food properly). The increased viscosity of secretions and obstruction of the pancreatic ducts inhibits the digestive process. In addition, decreased sodium bicarbonate composition lowers the gastric pH, impairing the breakdown of chyme. Chyme is a thick, semi-fluid mass of partially digested food and digestive secretions formed in the stomach and intestine during digestion. The abnormal acidity degrades the pancreatic enzymes before they reach the intestines, thereby preventing the digestion of food. Since the chyme is not enzymatically processed appropriately, it leads to greasy stools, colicky abdominal pain, and malabsorption. Up to 95% of patients develop PI. In several of the most common CFTR mutations, the destruction of the pancreas may occur in utero; thus, the infant is born lacking the pancreatic enzymes. Patients with PI are incapable of absorbing essential nutrients, specifically fat-soluble vitamins (i.e., vitamins A, D, E, and K), which are notably deficient. Collectively, the destruction of pancreatic tissue, pancreatic duct obstruction, and insufficient enzymatic activity lead to malabsorption, malnutrition, and FTT (CFF, 2019b; McCance & Heuther, 2019; Turcios, 2020).

Impaired glucose tolerance or diabetes mellitus (DM) occurs in about 2% of children (MedlinePlus, 2021). According to the American Diabetes Association (ADA), CF-related diabetes (CFRD) is the most common comorbid condition associated with CF, occurring in approximately 20% of adolescents and up to 50% of adults (ADA, 2018). While the onset of CFRD is usually insidious, typically occurring between 18 and 24 years, autodigestion of the pancreas may occur as the pancreatic enzymes target the pancreatic tissues and result in pancreatitis. In the most severe cases, this can cause endocrine pancreatic failure when the pancreatic enzymes consume the islets of Langerhans. In most cases of CFRD, the underlying pathophysiology is related to the loss of function of the pancreatic islet cells leading to insulin insufficiency. Other mechanisms include insulin resistance, progressive deterioration in glucose tolerance, delayed gastric emptying, altered intestinal motility, and liver disease. These patients require high caloric intake due to increased energy expenditure, malabsorption, and malnutrition (Moran et al., 2018). Compared to other populations with diabetes, CFRD is associated with poorer nutritional status, more severe inflammatory lung disease, and higher mortality (ADA, 2018). 

CF-related liver disease (CFLD) is another common complication, affecting approximately one-third of patients and causing significant morbidity and mortality. The term CFLD broadly refers to a spectrum of conditions affecting the liver in patients with CF. The pathogenesis of CFLD is poorly understood since CFTR is expressed in the bile duct cells and gallbladder but not in the hepatocytes (i.e., the primary functional cells of the liver). Thickened CF mucus can irritate and block the bile ducts, preventing bile drainage out of the liver and gallbladder, leading to hepatic fibrosis (i.e., early stage of liver scarring) or cirrhosis (i.e., advanced or late stage of liver scarring). The liver becomes hard and nodular when it is scarred, causing increased pressure in the portal vein (a blood vessel bringing blood into the liver), enlarged blood vessels (varices), and splenomegaly (enlarged spleen). 

Approximately 30% of patients experience hepatic fibrosis, and 4% develop irreversible cirrhosis and portal hypertension by adolescence. Portal hypertension is the most significant form of CFLD and is typically related to cirrhosis. Additional hepatobiliary complications of CF include cholelithiasis (gallstones), affecting up to 15% of those with CF, and cholecystitis (inflammation of the gallbladder; Hercun et al., 2019; Leung & Narkewicz, 2021; MedlinePlus, 2021).

Intestinal involvement is also relatively common in CF. Roughly 15% of neonates with CF present with meconium ileus at birth, an obstruction of the small intestines at the terminal ileum from abnormally thick and sticky meconium (feces). The cause of meconium ileus is multifactorial, but it is primarily due to increased fluid absorption due to the abnormal CFTR channel. The dehydrated intestinal contents cause constipation. In addition, some neonates can experience meconium plugging, in which the feces become enclosed in a mucus coat, making it more difficult to pass. Intestinal obstruction is expected later in life and can lead to inflammation, scarring, and stricture formation. Other common GI complications include the following:

• intussusception (a form of bowel obstruction in which part of the intestines slides into an adjacent portion of the intestines)
• volvulus (a loop of the intestine that twists around itself and the mesentery that supplies it)
• rectal prolapse 
• gastroesophageal reflux disease (GERD)
• esophagitis (inflammation of the esophagus; Sabharwal & Schwarzenberg, 2020)

The sweat glands exhibit a distinct manifestation from all other tissues containing CFTR channels as the flow of chloride is reversed. Under normal conditions, sweat glands transport chloride from the extracellular space into the intracellular space, and the sodium and water are reabsorbed from the sweat gland tissues into the body. However, failure of the chloride channel to reabsorb chloride leads to sodium loss (excretion) onto the skin surface and a subsequent fluid loss. These mechanisms cause the classical salty skin manifestation of CF. This mechanism is troublesome in warm environments or more severe cases, leading to hyponatremic dehydration (Brown et al., 2017; Rosenstein, 2021).

In males, CF is known to cause infertility. The thickened mucus can block the vas deferens, the long tube that extends from the testes to the urethra. The epididymis is a series of tubes positioned posterior to the testicles where sperm are stored until they are made available at ejaculation. The vas deferens connect the epididymis to the ejaculatory ducts and serve as the canal to transport mature sperm through the penis during ejaculation. Nearly 95% of men with CF are infertile because of an absent vas deferens, known as congenital bilateral absence of the vas deferens (CBAVD). In this condition, the sperm never reach the semen, making it impossible to fertilize an egg through sexual intercourse. Less commonly, males may be diagnosed with obstructive azoospermia (OA), in which the spermatozoa are absent in the ejaculate despite normal spermatogenesis. In addition, females may have reduced fertility due to thickened cervical mucus, preventing conception (CFF, n.d.-e). 

Screening

Since 2010, newborn screening (NBS) for CF has been required in all US states. Some cases of CF are identified in utero during a prenatal ultrasound, which may demonstrate meconium peritonitis, bowel dilation, or absent gallbladder. These findings often lead to prenatal CF screening tests, although most patients are diagnosed via NBS following birth. While the particular screening protocol for CF may vary by state and institution, the screening algorithm is universally performed as a multi-step process. The NBS starts with testing for immunoreactive trypsinogen (IRT), an inactive precursor produced by the pancreas that is vital for breaking down the protein in food. In healthy people, trypsinogen is generated in the pancreas and transported to the small intestine, where it is converted to the enzyme trypsin to aid in digestion. In patients with CF, mucus blocks the pancreatic ducts, preventing trypsinogen from reaching the small intestine. This obstruction causes hypertrysinogenemia or increased levels of trypsinogen in the blood. IRT is performed by collecting a blood sample via a heel stick using approved blood collection forms (i.e., Guthrie cards; See Figure 6). There are strict criteria for heel sticks, including an optimal collection time between 24- and 48- hours after birth, precise collection, care, and air-drying procedures. The dried blood spot is also used to screen for many diseases aside from CF.  Two IRT tests may be performed during the NBS, from the initial blood spot, and then a second one is collected about 2 weeks later. Approximately 20% of states routinely collect a second newborn blood specimen on every newborn in the US. The repeat testing practice is performed to demonstrate persistent hypertrysinogenemia.  Further, monitoring the IRT can correlate with the severity of CF as it can decline below detectable levels, signifying the need to initiate pancreatic enzyme replacement (CFF, n.d.-f; Farrell et al., 2017).

Diagnosis

A positive NBS does not confirm a diagnosis of CF; all positive NBSs must be followed up by a confirmatory sodium chloride (sweat) test. False-positive NBS results can occur for various reasons such as misattributed or hemolyzed blood samples, medical errors in the laboratory analysis of the sample, labeling errors, or contamination with blood from other infants. The sweat test is the universally recognized gold standard diagnostic test required to confirm a diagnosis of CF. Sweat testing is necessary for all patients with positive NBS, even those with two positive NBS samples. In addition, the sweat test verifies the physiologic abnormality found in CF. The sweat test may be performed as early as clinically indicated but should ideally be postponed until after 48 hours of life. Newborns with positive NBS should have a confirmatory sweat test performed bilaterally. According to best practice guidelines, the sweat test is most accurate when the following conditions are met:

• the infant weighs more than 2 kilograms (kg)
• the corrected gestational age is more than 36 weeks
• the infant is at least 10 days old (CFF, n.d.-f; Farrell et al., 2017).

The sweat test measures the amount of chloride in the infant’s sweat. As demonstrated in Figure 7, a small amount of a colorless, odorless chemical (e.g., pilocarpine) and electrical stimulation are applied to an area of the infant’s arm or leg. The sweat is collected and then analyzed in the laboratory to measure the quantity of chloride present in the sample. The sweat test is painless and usually takes about 30 minutes to complete (CFF, n.d.-f; Farrell et al., 2017).

In addition, CF or a CF-related disorder should be suspected and considered in patients who have a normal sweat test but have the following signs and symptoms suspicious for CF:

• a sibling with CF
• a positive NBS
• clinical symptoms consistent with CF in at least one of the following organ systems:
  • chronic sinus and/or pulmonary disease
  • GI or nutritional abnormalities (including malnutrition and FTT)
  • salt loss syndromes
  • CBAVD or obstructive azoospermia in males (Brown et al., 2017; CFF, n.d.-d, n.d.-f; Farrell et al., 2017)

All infants with known or suspected CF should be tested for PI via fecal pancreatic elastase-1, a fecal test quantifying elastase. Elastase is an enzyme produced by the pancreas and excreted in the stool. Elastase is not broken down by other enzymes in the digestive tract and is eventually eliminated in the stool. Therefore, elastase can be detected and measured in the stool when the pancreas is functioning normally. The level in the stool is decreased when the exocrine tissues of the pancreas are not producing sufficient elastase and other digestive enzymes. Infants are diagnosed with PI if they have low fecal elastase (CFF, 2019b; Lab Tests Online, 2020; Lamella, 2021). 

The ADA (2018) recommends annual screening for CFRD starting at age 10 in all patients with CF not previously diagnosed with CFRD. Patients with CFRD should be treated with insulin to attain strict glycemic goals (ADA, 2018).

Management

CF is a systemic illness with broad implications for both quality and quantity of life when poorly controlled. There is currently no standard therapy for CF, and the condition is not curable. Management focuses on infection control and symptom management, intending to optimize function and maintain health for as long as possible. Treatment is geared towards preserving lung function by aggressively controlling respiratory infections, taking steps to thin secretions, clearing airways of mucus, and maintaining airway clearance. Emphasis should also be placed on optimizing nutritional status with pancreatic enzyme supplements and multivitamins. Given the high acuity level of these patients and their complex and multifaceted needs, CF is best managed using a team approach incorporating specialists experienced in managing the condition and its complications. The ultimate goal is to preserve the quality of life and help patients optimize their functioning (Brown et al., 2017; Lamella, 2021; Mogayzel et al., 2013).

Infection Prevention and Control (IPC)

Patients with CF are more susceptible to infections and have a reduced capacity to recover, increasing the risk of fatal outcomes. Therefore, IPC strategies are the cornerstone of CF care. Specific guidelines outline the specialized precautions pertinent to this population. Adherence to IPC guidelines is encouraged to avoid infections, the transmission of CF pathogens, and the potential for pulmonary exacerbations. Last updated in 2013, the IPC clinical care guidelines were created by an interdisciplinary team and are endorsed by the CFF. The guidelines aim to help patients with CF and their healthcare team reduce the risk of transmitting infectious microorganisms. According to the guidelines, the following IPC strategies should be applied to all daily activities (Saiman et al., 2014):

• All people with CF should be separated by at least 6 feet (6-foot rule) from other people with CF in all settings. This practice reduces the risk of cross-contamination or transmission of CF-prevalent pathogens between patients. Research has shown that patients with CF can transmit dangerous microorganisms and infections to each other, referred to as cross-infection. Depending on the situation, cross-infection can lead to progressive illness, a decline in lung function, and death. It is essential to recognize that the 6-foot rule does not apply to members of the same household.
• Only one person with CF should attend any event, camp, educational retreat, or CF-sponsored indoor event or activity. However, family members without CF and individuals with CF who live together in the same household may attend these activities. 
• All healthcare professionals, family members, friends, and close contacts of patients with CF should regularly perform hand hygiene using an alcohol-based hand sanitizer or antimicrobial soap and water when hands could be potentially contaminated with pathogens.
• Smoking, vaping, second-hand smoke, and any other respiratory irritant exposure should be avoided.
• It is strongly recommended that all infants and children with CF receive all the routine immunizations recommended by the American Academy of Pediatrics (AAP). This recommendation includes the following vaccinations: 
  • measles, mumps, and rubella (MMR) 
  • diphtheria-pertussis-tetanus 
  • varicella
  • Haemophilus influenza (HIB) 
  • Prevnar (protects against common strains of Streptococcus pneumoniae)
  • annual influenza vaccine starting at 6 months of age
    • If infants are younger than 6 months of age, all household contacts should be vaccinated against influenza (Saiman et al., 2014)

According to the CFF (n.d.-g), the following IPC recommendations apply to healthcare settings and healthcare workers:

• Generate protocols, checklists, and audits to standardize safety and infection control practices when caring for patients with CF.
• Disinfect surfaces before and after a person with CF is in contact with them.
• Engage in routine hand hygiene. According to the CDC (2020b), proper hand hygiene is the most effective IPC risk reduction strategy. Table 4 provides detailed guidance on hand hygiene practices for healthcare professionals.
• Ensure that patients with CF wear a surgical or isolation mask in all common areas, including hallways, elevators, and waiting rooms.
• Actively ensure patients with CF always maintain a safe, 6-foot distance in all settings. 
• All healthcare professionals caring for patients with CF should wear personal protective equipment (PPE), including gowns and gloves.
• Dedicate a single room to each patient with CF.
• Evaluate patient activity on a case-by-case basis before advising a patient about participating in activities outside of a hospital room.
• Clean and disinfect nebulizers.
• Engage in respiratory hygiene/cough etiquette. The components of respiratory hygiene/cough etiquette include the following:
  • covering the mouth and nose during coughing and sneezing
  • using disposable facial tissues to contain respiratory secretions, with prompt disposal into a hands-free receptacle
  • wearing a surgical mask when coughing to minimize contamination of the surrounding environment
  • turning the head when coughing and staying at least 6 feet away from others, especially in common waiting areas
  • washing hands with soap and water or alcohol-based hand rub after contact with respiratory secretions
• Get vaccinated. Vaccination of healthcare workers and the public is one of the most prominent and compelling infection prevention and control strategies. The safest and most effective way to develop immunity and fight against a potential illness before it becomes dangerous is accomplished through vaccination. Vaccines work by impersonating the infectious agent, stimulating the immune system to generate antibodies against it without inducing the disease. If the pathogen subsequently attempts to invade the body, the body responds quickly, producing additional antibodies to combat the infection and thwart illness (CDC, 2018, 2020b; CFF, n.d.-g).

Respiratory Assessment

Monitoring lung disease progression is one of the most significant challenges in caring for infants and young children with CF. Airway inflammation, infection, and structural lung disease can begin during infancy and progress during early childhood. In addition, it is essential to have monitoring tools for children who are experiencing a new onset or an increase of symptoms and those who are experiencing a pulmonary exacerbation.

Chest imaging may demonstrate evidence of regional or diffuse lung disease in CF. CXR remains the most frequently selected modality for monitoring lung disease. It is the most practical, is widely available, easy to perform, and utilizes a low level of ionizing radiation. However, CXRs in infants and young children may appear normal and may not necessarily correlate with presenting respiratory symptoms or functional impairment as seen clinically. Therefore, a CXR should be obtained at least every 1 to 2 years to monitor disease progression in young children. More frequent monitoring with CXR should be considered in children with increased symptoms or those who fail to respond to appropriate treatment. Unfortunately, CXR imaging is limited; it is not sensitive enough to detect emerging small airway disease or early bronchiectasis. Chest computed tomography (CT) can more readily detect early changes in airway caliber, bronchial thickening, and air trapping and is the gold standard for diagnosing bronchiectasis. These changes may predate the development of respiratory symptoms, changes in physical exam, or lung function abnormalities. However, there are ongoing concerns about exposure to higher ionizing radiation, although protocols and technological advances have been developed to mitigate this risk. Further, infants and young children often require sedation or anesthesia to obtain acceptable CT images. For young children with CF, the routine use of chest CT to monitor the progression of lung disease is acceptable, but it is recommended that it be performed at less frequent intervals (every 2-3 years) and in place of a CXR. Abnormal findings on CT may correlate with early lung function abnormalities. Chest ultrasound is being increasingly used in acute pediatric settings when available. However, ultrasound images are limited in their assessment of airway caliber or thickness. Additionally, they cannot diagnose bronchiectasis or monitor the progression of structural lung disease in CF (Lahiri et al., 2016; Mogayzel et al., 2013).

PFTs are a vital tool for evaluating and monitoring lung disease and progression in CF and the most common method for longitudinal assessment. Spirometry is the most commonly used PFT and monitoring tool for pulmonary function in children and adults with CF (see Figure 8). With proper instruction and cooperation, spirometry can be performed successfully in children with CF as young as 3 years old (Lahiri et al., 2016).

Spirometry measures the forced vital capacity (FVC), the total volume of air exhaled during a forceful and complete exhalation after a maximal inhalation. The volume exhaled in the first second is known as the forced expiratory volume in 1 second (FEV1). The ratio between these two (i.e., FEV1/FVC) is the most important value reported from spirometry. These values allow for interpretation of the status of the lung ventilation function. They are compared to an expected normal for age, height, and gender. The measured value is calculated as a percentage of normal (e.g., normal equals 100%). A normal or high FEV1 with a low FVC may signify restrictive lung disease (e.g., interstitial lung disease, neuromuscular disease, pulmonary fibrosis). A low FEV1 with a high FVC indicates obstructive lung disease with airway trapping. Patients with CF typically demonstrate air trapping patterns with low FEV1 values proportional to the severity of the disease. PFTs will worsen from baseline during a pulmonary exacerbation or illness. Table 5 lists pertinent PFT-related terms and their functions (Lahiri et al., 2016; Mogayzel et al., 2013).

Respiratory Management 

Respiratory medications serve multiple purposes in CF as they are potent agents frequently used to thin mucus, loosen secretions, kill bacteria, mobilize mucus to facilitate airway clearance, and lessen the work of breathing. The CFF (2019a) recommends that chronic respiratory medications only be administered to patients 6 years and older, as there is insufficient evidence to support the use of chronic respiratory agents in children younger than 6 years (CFF, 2019a). There are many options for respiratory support, including bronchodilators, antibiotics, anti-inflammatories, and mucolytics. Many respiratory medications are available as inhalers, nebulizers, or aerosol treatments. Bronchodilators such as albuterol (Pro-Air, Ventolin) and levalbuterol (Xopenex) are short-acting ß-agonists (SABAs) commonly used during pulmonary exacerbations. These agents are recommended to treat acute hyper-responsiveness as they selectively stimulate ß-2 adrenergic receptors, relaxing the airway smooth muscles (Brown et al., 2017; Mogayzel et al., 2013). Their half-life is 2.7 to 6 hours, and they are available as metered-dose inhalers (MDI) or can be used in nebulizers. Bronchodilators dilate (open) the airways and allow for better penetration of other respiratory treatments. Ipratropium bromide (Atrovent) is another commonly prescribed respiratory medication. It is a short-acting muscarinic antagonist (SAMA) that causes bronchodilation by antagonizing acetylcholine receptors. It has a half-life of 2 hours and is available as a nebulizer solution that can be mixed with albuterol (Pro-Air, Ventolin) or levalbuterol (Xopenex) or used independently as an MDI (Global Initiative for Asthma, [GINA], 2018; Mogayzel et al., 2013).

Mucolytics work by thinning the mucus and helping remove mucus from the lungs. Best practice guidelines consistently recommend the use of mucolytics before performing pulmonary exercises to clear the airways. Two of the most commonly used mucolytics include inhaled hypertonic saline and dornase alpha (Pulmozyme). Hypertonic saline is a sterile solution of saltwater nebulized to facilitate mucus clearance by increasing the amount of salt in the airways, which attracts water (moisture) to the mucus, thinning it and making it easier to cough. Research demonstrates reduced lung infections in patients with CF who use hypertonic saline twice a day. Dornase alpha (Pulmozyme) is a highly purified solution of recombinant human deoxyribonuclease (rhDNase), an enzyme that selectively cleaves DNA. In other words, it disassociates extracellular DNA strands to make the mucus thinner and looser. Splitting the DNA into shorter components helps break up thick mucus. Dornase alpha (Pulmozyme) is delivered to the lungs via a nebulizer and is indicated for use alongside standard therapies in patients aged 6 and older. According to clinical trials, daily use of dornase alpha (Pulmozyme) in patients with an FVC ≥ 40% of predicted was shown to reduce the risk of respiratory infections requiring IV antibiotics. Therefore, the CFF (2020) recommends that patients aged 6 and older use dornase alpha (Pulmozyme) to improve lung function and reduce pulmonary exacerbations. Although it is generally well-tolerated, possible side effects include red, watery eyes, rash, rhinitis, loss of voice, throat discomfort, and fever (Brown et al., 2017; Cystic-Fibrosis.com, 2019a, 2021; US Food & Drug Administration [FDA], 2021; Mogayzel et al., 2013). 

Airway Clearance Therapy (ACT) is the backbone of preventative therapy in CF to preserve lung health for routine maintenance and during acute exacerbations. ACT should be used in conjunction with medication therapy and all other pulmonary interventions offered.  Airway clearance is critical for patients with CF to remove mucus from their lungs and permit clean respiratory hygiene. Adequate airway clearance reduces the risk of lung infections and bacterial colonization. ACT techniques are vital as they help loosen and reduce mucus from the lung (Lamella, 2021). There are several different devices and methods used for ACT. Huff coughing is considered the underpinning of ACT. It includes inhaling, followed by a slow and strong exhale that is less forceful than full-blown coughing. It is credited with higher success since it is considered to be less tiring. Coughing should always be encouraged and never suppressed since it helps get rid of mucus. A typical cycle of 4 to 5 huff coughs is usually combined with other ACT techniques.  Postural drainage and percussion (otherwise called chest physiotherapy) is commonly used in infants and young children. With this therapy, a therapist claps the patient’s chest and lower back simultaneously as they sit, stand, or lie in a position that helps loosen mucus, usually involving alternating between lying in the left and right lateral, prone, and Trendelenburg positions. Research demonstrates that airway inflammation and obstruction exist even in infants, and thus it is recommended that airway clearance be started in the first few months of life. The “clapping method” is most commonly used for young infants to loosen secretions from the smaller airways. As children grow, there is the opportunity to use high-frequency chest wall oscillation devices, which are often referred to as the vest or oscillator. This technique uses an inflatable vest that wraps around the chest and attaches to a machine that vibrates at a high frequency. The vibrations help to loosen and thin the mucus and help facilitate airway clearance. Positive expiratory pressure therapy (PEP) is another commonly used technique through which a mask or mouthpiece attaches to a device called a resistor. The patient breathes in normally and breathes out against the resistance, which helps move air deeper into the lungs. There has not been a consensus statement to delineate which ACT method is the most useful; this decision should be based on patient preference, tolerance, and response. In addition to respiratory medications and ACT, multiple studies demonstrate therapeutic benefits of regular exercise is in patients with CF to maintain and support lung function (Cystic-Fibrosis.com, 2019a; Lahiri et al., 2016; Lamella, 2021).

CFTR modulators 

CFTR modulators are a novel group of medications that target the defective CF gene. These therapies are designed to correct the genetic dysfunction by refining the CFTR protein’s production, intracellular processing, or functioning. Each medication is targeted at a specific dysfunction caused by a particular gene mutation. CFTR modulators help correct the abnormal flow of salts and fluids between the lungs, which helps to avoid thick mucus build-up. A few FDA-approved CFTR modulators are available in the US and will be discussed in this next section (Lahiri et al., 2016; Ren et al., 2017).

Ivacaftor (Kayldeco)

Ivacaftor (Kayldeco) was FDA-approved in 2012 and was the first CFTR modulator brought to market. It can currently be used in patients 6 months of age and older with a single mutation in the CFTR gene responsive to ivacaftor (Kayldec) based on clinical and/or in vitro assay data. Ivacaftor (Kayldeco) is used to treat class III dysfunctions, where a mutation at G551D is the primary abnormality. Ivacaftor (Kayldeco) was added as a recommendation to the CF pulmonary guidelines for use in patients with class III CF mutations. It binds to the defective CFTR protein at the cell surface, restoring the proper function of the protein and opening the chloride channel. Ivacaftor (Kayldeco) was the first medication to directly impact the protein channel rather than treating the effects of CF. It is strongly recommended to reduce exacerbations, increase FEV, improve lung function, and preserve overall lung health (FDA, 2020; Mogayzel et al., 2013). 

Dosing for patients under 6 years is weight-based. Dosing for all patients older than 6 years is 150 mg by mouth every 12 hours. Doses should be taken with fatty foods to increase absorption, although the optimal amount has not been established. When educating patients on this medication, nurses should advise patients to avoid grapefruit and Seville oranges; these foods inhibit CYP3A4, the same enzyme responsible for ivacaftor (Kayldeco) metabolism. In addition, nurses must perform a complete medication reconciliation before a patient starts ivacaftor (Kayldeco) and counsel patients on the risk for harmful dietary supplementation and herbal interactions. Some of the most common medications and herbs that have significant drug interactions with ivacaftor (Kayldeco) include the following:

• strong CYP3A inhibitors (e.g., itraconazole, posaconazole, voriconazole, ketoconazole, clarithromycin)
• moderate CYP3A inhibitors (e.g., fluconazole, erythromycin)
• strong CYP3A inducers (rifampin, rifabutin, phenobarbital, carbamazepine, phenytoin, and St. John’s wort)
• CYP3A substrates (e.g., midazolam)
• P-gp substrate (e.g., digoxin, cyclosporine, tacrolimus; FDA, 2020; Lahiri et al., 2016; Ren et al., 2017)

Ivacaftor (Kayldeco) may increase liver enzymes and increase the risk of cataracts. Other reported adverse effects (AEs) include headache, nasal congestion, oropharyngeal pain, upper respiratory tract infection, abdominal pain, diarrhea, nausea, rash, and dizziness (FDA, 2020; Lahiri et al., 2016; Ren et al., 2017).

Lumacaftor/ivacaftor (Orkambi)

Lumacaftor/ivacaftor (Orkambi) was FDA-approved in 2015 for use in children age 2 years and older who are homozygous for the F508del mutation in the CFTR gene. Lumacaftor/ivacaftor (Orkambi) is a ‘chaperone molecule’ designed to transport the defective CFTR protein from the intracellular organelles, where it is processed, to the cell surface. Clinically, this combination agent has no benefit when either of its components is administered alone. However, when combined as lumacaftor/ivacaftor (Orkambi), it has been shown to have modest benefits for patients in improving PFTs and body mass index (BMI; e.g., weight gain). The BMI increase is beneficial in children with CF who are often underweight due to malnutrition and malabsorption of nutrients. Given the importance of weight in young children, lumacaftor/ivacaftor (Orkambi) may be an important addition to the treatment regimen in patients with poor weight gain (FDA, 2019; Lahiri et al., 2016; Ren et al., 2017).

Lumacaftor/ivacaftor (Orkambi) dosing for patients aged 2 to 5 years is based on weight. Before administration, each dose packet should be mixed with 5 mL of soft food or liquid at room temperature or below. After the powder is mixed, it is stable as a mixture for 1 hour. However, the medication has a flour consistency and a bitter taste, making adherence challenging, particularly in children. Nurses should educate the caregiver on tips to mask the flavor of the drug. As with ivacaftor (Kayldeco), each dose should be taken with fatty foods to enhance absorption (FDA, 2019; Lahiri et al., 2016; Ren et al., 2017).

Lumacaftor/ivacaftor (Orkambi) carries a risk of adverse respiratory events, including chest tightness and shortness of breath, which most commonly occur following the first few weeks of taking the medication. Since these symptoms may be difficult to detect in younger patients, nurses should counsel caregivers on monitoring any acute respiratory changes during early medication therapy. However, this is typically less common in younger than in older patients, which is potentially attributed to the less severe lung disease in children. Hypertension has also been reported, and therefore it is recommended that blood pressure is monitored at routine clinic visits. Other reported AEs include upper respiratory tract infection, abdominal pain, diarrhea, rash, nausea, rhinorrhea, and cataracts. Unlike ivacaftor (Kayldeco), there are no foods to avoid with lumacaftor/ivacaftor (Orkambi). Since lumacaftor is a potent inducer of CYP3A, it inhibits and induces other CYP enzymes. Lumacaftor/ivacaftor (Orkambi) interacts with all types of hormonal birth control (oral contraceptives), significantly reducing their efficacy. Therefore, female patients must be counseled on this risk once they reach puberty or at medication initiation. There are many other drug interactions with lumacaftor/ivacaftor (Orkambi), including the following: 

• strong CYP3A inducers (e.g., rifampin, rifabutin, phenobarbital, phenytoin, St. John’s Wort)
• sensitive CYP3A substrates with a narrow therapeutic index (e.g., midazolam, triazolam)
• immunosuppressants (e.g., cyclosporine, everolimus, sirolimus, tacrolimus) 
• all CYP3A substrates (e.g., clindamycin, erythromycin)
• all CYP2B6 & CYP2C substrates
• acid suppressants (e.g., proton pump inhibitors [PPI] and histamine-2 blockers [H2])
• antidepressants (e.g., citalopram, escitalopram, sertraline)
• corticosteroids (e.g., prednisone, methylprednisolone; FDA, 2019; Lahiri et al., 2016; Ren et al., 2017)

Lung Transplantation

Despite significant advancements in medical therapies for CF, the disease process continues to advance, and the lungs will ultimately fail from the disease process. Patients with CF are estimated to live into their 40s before requiring lung transplantation for continued survival. Lung transplantation is the only definitive treatment for severe bronchiectasis, end-stage lung disease, and an FEV of less than 30%. The median survival following a lung transplant for children is 4.7 years; for adults, it is 7.8 years (Brown et al., 2017; Mogayzel et al., 2013). The timing of the transplant is multifactorial, complex, and individualized. The International Society of Heart and Lung Transplantation (ISHLT) published consensus guidelines to guide the timely referral, assessment, optimization, and listing of potential lung transplant candidates. The intent is to help guide clinical decision-making when considering patients for lung transplant based on multiple influences, recognizing that comorbidities and risk factors can negatively affect the post-transplant survival benefit. Since lung transplantation aims to improve survival and quality of life, the consensus acknowledges that when making recommendations about allocating a scarce resource, survival benefit is prioritized based on the ethical framework described in this document. A few priority criteria include the following: the 5-year predicted survival, baseline FEV1 value, the potential for development of pulmonary hypertension in the absence of a hypoxemic exacerbation, increasing frequency of exacerbations, and clinical decline (Leard et al., 2020). Nearly all lung transplant recipients with CF will need a bilateral transplant since a native, diseased lung could be a source of infection that threatens the transplanted lung and possibly induces respiratory failure. It is important to note that transplantation is not a cure for CF, but it confers a prolongation of life and offers significant symptomatic relief (Yeung et al., 2020). 

Nutrition Therapy

All patients with CF are encouraged to consume a high-fat, high-calorie diet with supplemental fat-soluble vitamins to compensate for malabsorption and help maintain a healthy weight. Oral feedings are preferred; however, if a patient’s intake does not meet metabolic demand, enteral feedings (e.g., gastric tube or jejunal tube) may be considered. Salt supplementation is also needed for infants with CF as the CFTR mutation in the sweat gland causes patients to excrete more salt compounds in their sweat than those without CF. Salt is also vital for normal growth and development. Those living in warm climates or participating in activities that cause excessive sweating are encouraged to consume additional sodium in their diet. Many will also require supplementation with water-soluble formulations of fat-soluble vitamins or CF-specific vitamins. Vitamin D supplementation is recommended in all exclusively breastfed infants and infants consuming less than 30 ounces of formula daily. Clinical practice guidelines also recommend measuring vitamin levels 2 months after starting the supplementation and then annually (Lahiri et al., 2016). Refer to the Nutritional Support in Critical Illness: Enteral and Parenteral Nutrition for RNs NursingCE course for more information on nutritional therapy.

Most patients with CF develop PI, as confirmed via the fecal pancreatic elastase-1. Ongoing, supportive therapy for patients with PI includes pancreatic enzyme replacement therapy (PERT) with pancrelipase. PERT is one of the fundamental aspects of CF care as it replaces the digestive enzymes that are lacking. PERT should be prioritized and initiated as soon as PI is diagnosed, as dietary management is critical for healthy growth and development. PERT dosing often requires the skill of a qualified dietician or nutritionist (Lahiri et al., 2016). The clinical guidelines regarding PERT dosing indicate that enzymes may be dosed based on grams of fat being consumed or based on weight. Adjusting the dosage of enzymes based on intake is more consistent with the body’s natural pancreatic enzyme production, while weight-based dosing is simpler and more convenient. Enteric-coated microencapsulated enzymes are most effective, and patients should consistently use the same brand as they are not interchangeable. There are currently four oral pancreatic enzyme products approved for use in patients with CF by the FDA: Creon®, Pancreaze®, Pertzye®, and Zenpep®. Enzymes should be taken at the beginning of every meal or snack that contains fat, such as dairy, meat, bread, and desserts (CFF, 2019b).

Patients with CF should be encouraged to consume three meals and two to three snacks per day, with the PERT dosing cut in half for a snack. Over-the-counter enzymes and those without an enteric coating are not recommended. Capsules may be opened and sprinkled into non-alkaline food but should not be crushed or allowed to sit for an extended period. Patients with inadequate enzyme activity typically report gastrointestinal symptoms (bloating, flatus, pain, and loose/frequent stools or steatorrhea) or poor growth/weight gain. Therefore, providers should assess patients for these symptoms consistently during regular follow-up visits, as well as evaluate dietary and adherence/compliance habits (CFF, 2019b). Compliance with PERT has been as low as 27-50% in studies (Barker & Quittner, 2016). 

Pancreatic enzymes are generally well-tolerated, although some initially report initial abdominal pain, headache, diarrhea, flatulence, nausea/vomiting, or constipation. Fibrosing colonopathy is a known severe adverse effect that should be discussed with patients and monitored closely. This complication is characterized by colonic strictures and is associated with high doses of PERT. Patients with fibrosing colonopathy typically present with evidence of obstruction, bloody diarrhea, ongoing diarrhea with abdominal pain and weight loss, or chylous ascites (i.e., the extravasation of chyle, milky and rich in triglycerides, into the peritoneal cavity). Risk factors include patients under the age of 12, those taking over 6,000 lipase units/kg/meal for over 6 months, and history of meconium ileus, distal intestinal obstruction syndrome, or previous intestinal surgery (CFF, 2019b).

Psychosocial Support and Mental Health

Anxiety and depression are prevalent in patients with CF and their families or caregivers. In the International Depression Epidemiological Study (TIDES), Quittner and colleagues (2014) evaluated depression and anxiety in patients with CF and their caregivers in the US and Europe. The study includes 3,000 mothers and 1,000 fathers of children with CF, aged from birth to 18 years. The rates of depression in CF caregivers were triple those found in community comparisons, with 34% of mothers and 25% of fathers screening positive for depression. Anxiety was twice the rate of the community sample, with 48% of mothers and 36% of fathers screening positive for anxiety. If a mother was anxious, she was 15 times more likely to be depressed, whereas fathers were 9.2 times more likely to be depressed. Adolescent teens with CF have twice the risk of depression or anxiety if either caregiver has depression or anxiety (Quittner et al., 2104). Research has demonstrated a link between the caregiver’s mental health, adherence, and health outcomes in children with CF. Additional studies have shown that psychological symptoms in patients with CF and their caregivers have been associated with decreased lung function, lower BMI, poorer health-related quality of life, more frequent hospitalizations, and increased healthcare costs. In addition, patients with symptoms of anxiety or depression have reduced participation in ACT, decreased pharmacological adherence, and poorer prognosis. To address the psychological burden of CF, the International Committee on Mental Health developed a consensus statement highlighting the critical importance of mental health screening and treatment in both patients and their caregivers. Coordinated efforts, screening, education, and supportive interventions to help encourage effective coping mechanisms and disease management skills can positively impact patient outcomes and improve mental and physical wellbeing (Barker & Quittner, 2016; Havermans & Willem, 2019; Quittner et al., 2014, 2016).

Pulmonary Exacerbations

Since pulmonary disease is the most common cause of mortality in CF, it is vital to have a low threshold for diagnosis and intervention in pulmonary exacerbations. A pulmonary exacerbation denotes an acute worsening of lung function, most commonly caused by an underlying infection. However, there is no universal definition of a pulmonary exacerbation in any age group among patients with CF. Still, they are often characterized by shortness of breath, fatigue, productive cough, chest congestion, and fever. Any acute respiratory illness should prompt admission to a hospital familiar with CF management. Pulmonary exacerbations should be managed with the following two priority objectives: 

• treat the underlying infection 
• improve and maintain oxygenation (Lahiri et al., 2016; Mogayzel et al., 2013)

Pulmonary exacerbations are determined by the presence of cough in the majority of instances, but the differential diagnosis can be very broad (see Table 8). Pulmonary exacerbations can have variable presentations and can range from mild to severe. Some of the most common signs and symptoms include increased cough, change in sputum (e.g., color, volume, or consistency), new findings on respiratory examination (e.g., wheezing, crackles), increased respiratory rate, and increased work of breathing. In addition, patients may also experience fever, anorexia, and weight loss. Regardless of the underlying etiology, antibiotics to treat respiratory symptoms in all patients with CF have consistently been associated with improved outcomes. Viral infections have been shown to increase the frequency of pulmonary exacerbations in children with CF, may be associated with poor outcomes, and increase the risk of acquiring drug-resistant CF pathogens such as Pseudomonas aeruginosa (P. aeruginosa). The CFF (2019c) recommends continuing all of the patient’s regular maintenance respiratory medications and ACT interventions during pulmonary exacerbations. Anti-inflammatory medications such as glucocorticoids or corticosteroids (e.g., prednisone [Deltasone], dexamethasone [Decadron]) are used to relieve airway obstruction by reducing inflammation. These are used for a short duration and should not be prescribed prophylactically to prevent an exacerbation. Nasal cannula oxygen therapy should be prescribed to reduce the work of breathing. Bilevel positive airway pressure (BiPAP) ventilation may be required to overcome airway trapping in more severe cases. While intubation using mechanical ventilation is always an option, best practice guidelines recommend reserving this for cases where respiratory failure is imminent. Ventilation and oxygenation should be supported with respiratory medications (GINA, 2018; Lahiri et al., 2016; Mogayzel et al., 2013).

Studies demonstrate an evolution of pathogens in patients with CF as they age. The most common pathogen in CF-associated lung infection in infancy and childhood is Staphylococcus aureus (S. aureus), followed by Haemophilus influenzae (H. influenza). As the disease advances, adolescent and adult patients become colonized with increasing amounts of drug-resistant pathogens such as P. aeruginosa, Escherichia coli (E. coli), and Klebsiella pneumoniae (K. pneumoniae). Multi-drug resistant strains are more complex, generate more severe illness, and reduce treatment efficacy. For example, in the US, the prevalence of methicillin-resistant S. aureus (MRSA) in the respiratory tract is about 25%. Patients chronically infected with MRSA have a more rapid decline in pulmonary function and lower survival rates than those who are not (MedlinePlus, 2021; Rosenstein, 2021; Turcios, 2020).

P. aeruginosa is the most common infectious etiology among adults with CF. For this reason, best practice antibiotic guidelines include the use of broad-spectrum coverage against this pathogen. However, there are no consensus recommendations on what doses of certain oral antibiotics are most appropriate in patients with CF. Guidelines strongly recommend that a sputum culture and a sensitivity profile be obtained to identify all the pathogens present. Treatment recommendations are based on the most recent culture results, although in clinical practice, most clinicians will base antibiotic selection on the presence of organisms from multiple prior cultures. Guidelines also recommend at least one antibiotic to cover each pathogenic bacteria cultured from respiratory secretions and two antibiotics for P. aeruginosa infections. Early detection and treatment of P. aeruginosa are vital to avoid the progression of CF lung disease and the increased risk of pulmonary exacerbations. Studies have demonstrated that failure to eradicate P. aeruginosa is associated with an increased risk of future pulmonary exacerbations (Lahiri et al., 2016; Mogayzel et al., 2013; Turcios, 2020).

Antibiotics are a mainstay in CF care. Many patients with CF take oral or inhaled antibiotics as part of their daily routines. Research demonstrates that oral antibiotics are the most prevalent treatment for pulmonary exacerbations; however, patients often require intravenous (IV) antibiotics (Stanford et al., 2021). Antibiotic selection and utilization evolve throughout life as the patient develops more resistant and difficult to treat lung infections. According to Mayer-Hamblett and colleagues (2018), a substantial reduction in pulmonary exacerbations was seen among children ages 6 months to 18 years treated with oral azithromycin (Z-Pak) plus inhaled tobramycin (TOBI) for early infection with P. aeruginosa (CFF, n.d.-a; Lahiri et al., 2016; Mayer-Hamblet et al., 2018; Mogayzel et al., 2013). Inhaled antibiotics are commonly used to fight or control bacteria that cause lung infections in CF. Inhaled antibiotics are delivered directly into the small airways in the lungs and are most frequently used to improve respiratory symptoms in people with CF who have P. aeruginosa. According to the CFF guideline (n.d.-a), the most commonly used inhaled antibiotic selections include the following:  

• aztreonam inhalation solution (Cayston)
• tobramycin (TOBI, Bethkis) inhalation solution
• tobramycin (TOBI; Podhaler) inhalation powder (CFF, n.d.-a)

Tables 6 and 7 outline some of the most commonly prescribed oral antibiotics to treat CF-related bacterial infections in pediatric and adult populations, respectively (Mogayzel et al., 2013; Muirhead et al., 2016). The CFF (2019c) states there remains insufficient evidence to recommend an optimal duration of antibiotic therapy for acute pulmonary exacerbations. According to Stanford and colleagues (2021), antibiotic treatment typically lasts for 14 days but can range from 10 to 21 days or longer in severe infections.

Antibiotic-resistant infections are a priority concern for patients with CF, as these can lead to fewer effective treatment options over time. Therefore, nurses must counsel patients on the importance of taking the entire course of the prescribed antibiotic, including the proper sequence for taking the drug with other treatments and what to do if they miss a dose or cannot complete the entire course. The CFF recommends that inhaled antibiotics be used last, after the bronchodilator, mucolytics, and airway clearance techniques. This medication sequencing is important as it helps the antibiotics reach deeper into the lungs and provide more therapeutic benefits. The majority of studies in patients aged 6 years and older have noted a reduction in pulmonary exacerbations requiring IV antibiotics in patients taking chronic inhaled CF medications (CFF, n.d.-a).

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