Clinicians who manage patients with dysphagia face especially difficult challenges when working with patients who exhibit the aspiration of dietary fluids. These patients must be kept safe from aspiration while still meeting requirements for hydration intake. Although it is possible to hydrate the body through non-oral routes such as nasogastric tubes, IV infusion, total parenteral nutrition, etc., these methods can pose serious health consequences. Consequently, a primary goal of dysphagia management is to meet nutrition and hydration needs by mouth while reducing the risks of aspiration.

Three primary methods are used to accomplish this end: thickened liquids, swallowing compensations/maneuvers, and swallowing therapy. Logemann (1998) argued that diet modifications including thickened liquids should be used only when other methods have failed. Although that scenario may represent the ideal, McCullough et al. (2004) reported that the use of thickened liquids has become one of the most common recommendations made by clinicians. The researchers concluded that this method is used because it is easy to implement. In a survey of long-term care facilities, Castellanos et al. (2004) reported that a mean of 8.3% of residents were receiving thickened liquids. In one facility, the figure was a strikingly high mean of 28%. Although the method is commonly used, the evidence base supporting thickened liquids remains limited (Robbins, et al., 2002; Steele, 2005) and their use can present challenges in dysphagia management.

Hydration with Thickened Liquids

Viscosity is a property of solids, liquids, and gases that represents their resistance to flow (Miller, 1972). Nearly all dietary fluids that we drink are "thin" or have low viscosity (Mills, 2000). For patients with dysphagia, these thin liquids pose the greatest risk for direct aspiration into the airway (Siebens & Linden, 1985; Curran & Groher, 1990; Logemann, 1998). There is a well-accepted belief among clinicians that many of these patients will demonstrate a reduced aspiration risk if provided with liquids of increased viscosity, and the use of thickened liquids is based on this belief. Unfortunately, few naturally occurring dietary fluids are sufficiently viscous to offer protection from aspiration; therefore, a variety of artificially produced thickened liquids are marketed for use in dysphagia management.

Two issues are of primary concern in maintaining hydration with thickened liquids. The first concern is whether the water present in the thickened liquid will be available for release into the patient's system as usable hydration. If a significant portion of the water remains bound to the molecules of thickener and passes through the system, then the patient will be required to drink greater amounts of thickened liquid to achieve hydration goals. Sharpe et al. (2007) reported that all of the starch- and gum-based thickeners tested in rats and humans released 95+% of the fluid content to the subject's systems. Thus the use of thickened liquids will not contribute to patient dehydration.

The second issue is the amount of a thickened liquid consumed by the patient, which is heavily dependent on the "likeability" of the thickened fluid (Garcia, Chambers, & Molander, 2005). Likeability is influenced by several important variables. The first variable is the thickener "base" used to produce the thickened liquid. Corn starch and food starch are most commonly used. Food thickeners marketed in a dry granular form are mixed with dietary liquids at specific ratios to produce a desired viscosity. Likeability also depends on the amount of thickener in the mixture. Whelan (2001) reported that patients will consume more of a thinner, nectar-thickened liquid than a more viscous product. When a starch base is used, these more viscous thickened liquids have more starch and less flavor (Huckabee & Pelletier, 1999). As the amount of starch increases, the amount of "flavor masking" increases and likeability decreases. As likeability decreases so may consumption, which may increase the risk for dehydration.

The mixing characteristics of granular starch-based products can be problematic. When mixed with dietary liquids the granules may not hydrate uniformly, resulting in a thickened liquid that contains lumps and clumps. This texture may negatively affect a patient's desire to consume the product.

Mertz Garcia and colleagues (2008) measured the viscosities of thickened preparations created using two granular, starch-based, thickening products and one that was based on Xanthan gum. The viscosities were measured at three post-mixing intervals: the manufacturer's recommended post-mixing serving time as well as at 10 and 30 minutes after mixing. The results showed remarkable instability for preparations created with the starch-based products. Some starch-based nectar preparations increased in viscosity as much as from 260 centipoise (cP) to 830 cP over the intervals tested. Honey liquid preparations based on starch-based products also proved unstable, with one preparation increasing from 200 cP to nearly 3,000 cP over the same period. Because it cannot be determined precisely when the liquid will be consumed, it becomes difficult to know what viscosity the patient will actually receive.

Additionally, Mertz Garcia and colleagues (2008) tested the effect of temperature change on the preparations (4° C versus 70° C). They found significant increases in viscosity of starch-based preparations as temperature increased and concluded it was caused by the characteristic of starch particles to "gelatinize" when heat is applied. Finally it was noted that these preparations lacked "repeatability" because the resulting viscosity varied depending upon whether they were added to milk, coffee, water, or orange juice. The sensitivity of starch to the pectin, ions, acids, and solids that are variably present in the base liquids may account for the wide variations observed.

The authors found that when Xanthan gum was used, however, the thickened liquid remained stable across base liquid types and over time. Only in 2% milk did it show a slight decrease in viscosity over time. Still it was by far the most stable of the three products tested. In unpublished trials with the same Xanthan thickener mixed into a variety of base liquids and dietary supplements, Mills (2008) found the viscosity to be relatively stable across a 48-hour period. This stability is a significant consideration because some institutions mix thickened liquids in bulk in the kitchen perhaps hours before the meal is served.

Cellulous gum-based thickener was also found to provide viscosity stability unmatched by any of the starch-based products tested across temperature and liquid variables (Mertz Garcia et al., 2005).

Thickener Choices

Clinicians and patients have an increasing number of thickener choices. Although data are preliminary, it does appear that the stability of preparations produced with gum-based thickeners are superior across time, temperature, and base liquids to those produced with granular starch-based products. This inference is not to suggest that any thickener currently available represents the "ideal." Though greatly improved in important respects, the gum-based thickeners tested can require specific mixing methods for a resultant smooth mixture and can produce a "slick" feel in the mouth when consumed. Additional study and continued development are needed with these new products. However, we cannot ignore the improvements they provide.

It is this author's belief that clinicians can no longer accept granular starch-based products that have produced the abysmal results in the past. We are obligated to encourage our institutions to consider the use of these second-generation products and to encourage manufacturers to continue product refinements. With these efforts we can provide our patients the best opportunity to meet their hydration needs.