Introduction

Infants born with critical CHD experience multiple feeding disruptions. Regardless of the disease severity or the type of surgical intervention, 43–64% of patients are diagnosed with dysphagia. ^{Reference Narawane, Rappazzo, Hawney, Clason, Roddy and Ongkasuwan1,Reference Jones, Desai and Fogel2} Patient, medical, surgical, and environmental factors during the hospital course for infants with critical CHD significantly contribute to dysphagia risk during a key time period of oral skill development. Dysphagia is associated with respiratory instability, increased metabolic demand that requires increased nutritional volume or calories to gain weight normally, increased risk for aspiration that contributes to feeding disruptive patterns or oral aversion, and reduced state regulation with difficulty waking for feeding and demonstrating low energy and stamina for reliable participation. ^{Reference Jones, Desai and Fogel2} Dysphagia may be a consequence of brain injury or dysmaturity, associated genetic syndromes and reduced gastrointestinal tolerance of feedings. ^{Reference Jones, Desai and Fogel2} Patients with critical CHD have prolonged intubation periods with negative oral stimulation, extended hospitalisation, stressful surroundings such as bright lights and loud sounds, painful procedures, and separation from family/caregivers. In addition, early therapeutic interventions such as catheterizations, surgery, and transesophageal echocardiogram disrupt the infant’s feeding skill acquisition and increase the risk for aspiration related to exposure to sedation medication, deconditioning, intubation, length of stay, and surgical complications. ^{Reference Narawane, Rappazzo, Hawney, Clason, Roddy and Ongkasuwan1–Reference Kohr, Dargan and Hague6} These complications can include vocal cord and diaphragm motion impairment. ^{Reference Narawane, Rappazzo, Hawney, Clason, Roddy and Ongkasuwan1–Reference Kohr, Dargan and Hague6} Many infants with critical CHD and dysphagia require additional support to maintain adequate growth such as increased caloric density of feedings, supplemental nutrition via feeding tubes, and/or the use of other forms of nutrition such as total parenteral nutrition and lipids.

Historically, thickened liquids are used to treat gastrointestinal reflux, weight gain, and oropharyngeal dysphagia or swallowing deficits. Feeding therapists, physicians and advanced practice providers utilise thickened liquids as a modification to address swallowing deficits, specifically aspiration, when swallowing dysfunction is diagnosed with a formal instrumental evaluation such as videofluoroscopic swallow study (X-raying patients while consuming barium) or flexible endoscopic evaluation of swallowing (inserting a thin fiberoptic endoscope through the nose and above the pharynx to visual liquid or food bolus movement while swallowing). ^{Reference Luca, Miron and Mîndru7–Reference Madhoun, Siler-Wurst, Sitaram and Jadcherla14} Current studies suggest that thickened liquids have increased viscosity and thus move slower than thin liquids. This is thought to improve the infant’s ability to control the liquid in their pharynx and provide better coordination of airway closure during the swallow response. Appropriate airway closure decreases the occurrence of deep laryngeal penetration and aspiration, thus decreasing dysphagia, improving swallowing mechanics, and decreasing length of hospitalisation. ^{Reference Goldfield, Smith, Buonomo, Perez and Larson11,Reference Duncan, Amirault, Mitchell, Larson and Rosen15} The use of thickened liquids provides an opportunity for infants experiencing dysphagia to continue oral feeding and develop feeding skills during critical periods of recovery and growth.

When consideration is taken for the type of thickener, the level of thickened liquids prescribed, and ongoing support from a feeding therapist, most infants aged 8–9 months with dysphagia, identified on a swallow study, had symptomatic improvement. ^{Reference Luca, Miron and Mîndru7} Parents reported significant decrease in the frequency of apnoea, reduced coughing/choking, less resistance to feeding, decreased vomiting, and improved volume of oral intake following the use of thickened oral feedings. ^{Reference Krummrich, Kline, Krival and Rubin16,Reference Duncan, Cohen and Du17} Parental attitude towards the use of thickened oral feeding was positive when thickening is used to manage dysphagia compared to gastrointestinal reflux disease. ^{Reference Duncan, Cohen and Du17} Studies suggest additional benefits to thickened oral feeds including improved lung health with fewer respiratory admissions, shorter hospital length of stay, and better swallowing mechanics. ^{Reference McSweeney, Kerr, Amirault, Mitchell, Larson and Rosen13,Reference Duncan, Cohen and Du17} Additionally, in animal and adult models, there was no difference in the amount of hydration received from even the highest level of thickened liquid, indicating a possible decrease in concern for hydration with thickened liquids. ^{Reference McCallum18}

Thickening practices including the type of thickening agent used and the level of thickened liquid prescribed often vary across centres and from clinician to clinician. There are various options for thickening liquids including food-based agents such as rice cereal, oatmeal cereal, pureed fruits/vegetables, and yogurt. ^{Reference Duncan, Larson, Davidson, May, Rahbar and Rosen8,Reference Brinker, Winn and Woodbury9} Commercial thickening agents utilise modified cornstarch or gum-based products (xantham gum used in SimplyThick and tapioca maltodextrin and carob bean gum used in Gelmix). Choosing the appropriate type of thickening agent for an infant is often influenced by the patient’s medical comorbidities including prematurity, history of necrotising enterocolitis, evidence of milk protein intolerance, and the type of milk consumed (human milk versus formula) as not all thickening agents thicken human milk adequately. ^{Reference Duncan, Larson, Davidson, May, Rahbar and Rosen8} The level of thickness required often varies from patient to patient and should be determined via formal evaluation as mentioned above. The International Dysphagia Diet Standardisation Initiative outlined a universal approach to labelling the thickness level of liquids in 2019. ^{Reference Cichero, Lam and Steele19} Liquids are defined in number levels, starting with Level 0 (Thin Liquids), Level 1 (Slightly Thick), Level 2 (Mildly Thick), Level 3 (Moderately Thick), and Level 4 (Extremely Thick/Pureed) (Supplement 1). ^{Reference Cichero, Lam and Steele19} This is an important distinction as it allows for consistent communication of thickening levels with a standard process to be used by clinicians around the world. For example, prior to 2019, often a set recipe was used to achieve a specific consistency level. However, this did not allow for variations in thickness that were affected by temperature changes or length of time a liquid was allowed to thicken prior to consumption. Subjective judgement may be applied to the thickened liquid that appears too thick or too thin. The International Dysphagia Diet Standardisation is a bedside tool that includes measuring 10 mL of the thickened liquid in a 10-mL slip tip syringe, allowing it to drain for 10 s then quantify the remaining volume left in the syringe. This simple drip test ensures consistent thickening levels and may alleviate the feeders’ concerns regarding accurate thickness.

Despite some indication of benefit from thickened liquids, utilisation for dysphagia management in infancy remains a controversial practice given concerns regarding gastrointestinal complications such as constipation, diarrhoea, reduced gut motility, nutrition displacement, exposure to arsenic in cereals, potential allergens, and necrotising enterocolitis. Infants with critical CHD inherently present with potentially increased risk factors for gastrointestinal complications secondary to altered systemic blood flow with the possibility for decreased gut profusion. ^{Reference Kelleher, McMahon and James10} Furthermore, infants with critical CHD may experience differences in their gut microbiome both at baseline and after surgical intervention requiring cardiopulmonary bypass, placing the infant at risk for developing intestinal ischaemia and necrotising enterocolitis. ^{Reference Koc, Magner and Murphy20} The nutritional displacement of human milk and formula with the carbohydrates found in thickeners can also lead to excessive weight gain and changes to the osmolality of the nutrition causing constipation or diarrhoea. Additional concerns include exposure to toxins including high levels of arsenic found in rice cereal. ^{Reference Madhoun, Siler-Wurst, Sitaram and Jadcherla14,Reference McCallum18,Reference Abdulezer21–Reference Carignan, Punshon, Karagas and Cottingham23}

From a psychosocial perspective, parents of infants with dysphagia who require thickened oral feedings can experience distress around thickening the feedings. Barriers exist for families when thickened liquids are prescribed such as access to purchasing commercial thickening agents and the financial burden associated with purchasing thickeners, which have variable insurance coverage state by state. In addition, the process of preparing and offering thickened feeding can be complex and challenging to accurately learn recipes to achieve the appropriate level of thickness recommended for their child. ^{Reference LaManna, Hatfield and McCann25}

Minimal information is available in the literature describing the use of thickened liquids to support feeding outcomes for young infants with critical CHD. The goal of this project was to describe the current state of practice in the use of thickened liquids for dysphagia management in infants with critical CHD across paediatric cardiac surgical centres in the United States of America and internationally.