Managing Thirst in the Critically Ill

Thirst is a homeostatic mechanism involved in sodium and water balance. Although thirst is prompted by both osmotic and hypovolemic stimuli, hyperosmolality is the primary trigger, as a 10% reduction in blood volume is needed (independent of osmolality) before the renin-angiotensin system and adrenergic action are activated. Thus, as small increases in blood osmolality occur via cellular dehydration, antidiuretic hormone is released. When this compensatory mechanism is ineffective, the sensation of thirst triggers initiation of water intake.1–6Imagine not being able to relieve this sensation. Critically ill patients have described thirst as a constant overwhelming experience that is as intense as other distressing symptoms like pain, fear/anxiety, isolation, sleep deprivation, and feeling cold.2,5,7,8 In a recent qualitative study, patients receiving mechanical ventilation recalled a "paramount thirst with little relief." Thirst was described as a foreign sensation, continuous dryness and desire for something cold/relieving, if only temporarily. Patients recognized that they had to accept and adapt to the yearning and deprivation, which were made worse by the patients' being unable to express their needs. Overall, patients associated thirst with anxiety, powerlessness, and desperation—states negatively affecting their psychological well-being and overall illness experience.9Many factors increase the risk for oral mucosal dryness and thirst presence, intensity, or distress (see Figure). Thirst experiences may be even more prevalent among patients receiving mechanical ventilation because of changes in sedation practices9,11 toward lighter sedation and daily breaks. Yet, while so distressing, thirst is poorly understood and underrecognized and consequently not routinely treated.4,10,12 In a survey of critical care nurses, more than half of the respondents did not recognize that mechanical ventilation was associated with thirst and few reported a plan of care to alleviate thirst.13 More recently, intense thirst persisting more than 24 hours has been associated with a higher risk of delirium14 and post–intensive care syndrome (anxiety, depression, posttraumatic stress disorder) at 1 year.15 In an effort to manage thirst and reduce critical care morbidity, the PICO (patient/population/problem, intervention, comparison, and outcome) question for this evidence synthesis was this: What interventions can critical care nurses use for palliation of thirst intensity and distress?The strategy included searching CINAHL, PubMed, Up-to-Date, Cochrane Reviews, and TRIP databases. Key words included thirst, critically ill, intensive care, and interventions. The search was limited to original research.Table 1 outlines findings of 6 studies: 1 observational, 1 before/after, 1 quasi-experimental, and 3 randomized controlled trials. Most studies enrolled both patients who were receiving mechanical ventilation and patients who were not. Thirst intensity and distress were commonly assessed on a 5- or 10-point numeric rating scale (NRS). Oral mucosal dryness was evaluated via an NRS of 0 to 10, a modified revised oral assessment guide, or oral moisture-checking devices. Single interventions (oral care, mini-mint ice cubes) were evaluated immediately or 1 hour after administration and found to maintain oral moisture and quickly but temporarily reduce thirst intensity and distress.12,16,19 Bundled interventions involving hourly to 3-times-a-day ice water oral swabs or sprays (sterile ice-cold water, vitamin C), peppermint water mouthwash, and lip moisturizers (menthol, glycerin) evaluated after 7- or 10-hour intervention periods10,17 reduced oral mucosal dryness, thirst intensity, and thirst distress.Many studies involved testing of cold and/or menthol-containing interventions whose effectiveness may be attributed to activation of "cold" thermoreceptors such as transient receptor potential melastatin 8 located throughout the oral cavity. When cold or menthol is applied to mucosal surfaces, calcium channels open, triggering reflexes in the trigeminal and glossopharyngeal free nerve endings. These reflexes project through 3 neurons to the Brodmann areas 3-2-1 in the cingulate cortex. Activation of this region results in preabsorptive satiety involving a pleasant, refreshing, and thirst-relieving cooling sensation.3,4,20,21 Cold interventions20 and vitamin C sprays10 also stimulate salivary flow, hydrating oral mucosa and further reducing thirst perception.Both single and bundled interventions reduced oral mucosal dryness, thirst intensity, and thirst distress, representing level B evidence (Table 2). Intervention effects on thirst intensity and distress were variable owing to differences in thirst protocols and assessment intervals among the studies. Some interventions had immediate effect, reducing thirst intensity 1.0 to 4.5 points and thirst distress 1.8 to 3.0 points. Bundled interventions had longer but weaker effects, reducing thirst intensity 1.27 to 2.83 points and oral mucosal dryness 0.36 to 3.15 points. Importantly, no standard for the minimally clinically significant improvement for thirst has been established.10,19 Using pain as the criterion, Puntillo et al19 advocated a score of 0 to 4 for minimal thirst, 5 to 6 for moderate thirst, and 7 to 10 for severe thirst. According to these parameters, the reported studies (Table 1) reduced thirst to minimal or moderate levels (2.0-5.0), indicating that further symptom management to promote patient comfort is needed. Duration of action also varied across interventions. Oral care lasted 1 hour16 and mini–ice cubes provided fast but temporary relief.12 Although the optimal dosing and frequency for thirst-relieving interventions need more study,10 the significant impact of hourly scheduled thirst bundles on mouth dryness, thirst intensity, and thirst distress represents the best available evidence. Therefore, these simple, safe, and cost-effective thirst interventions can be embedded into routine nursing rounding practices.17 Incorporating family members who are interested in performing simple oral care is another option to help regularly meet these comfort needs.11,17Undeniably, thirst competes with other problems that pose greater threats of undesirable outcomes in the critically ill.17 Yet thirst has been identified as one of the most severe and distressing experiences, and therefore comfort interventions can reduce associated critical care morbidity and enhance quality of life.16 Most critically ill patients will have a positive thirst risk factor profile (see Figure) and have conveyed that thirst would have been easier to endure had feelings associated with this experience been explained.9 As the inability to express needs is a risk factor for posttraumatic stress disorder, recognition of thirst through frequent assessment can let conscious patients know that nurses are aware of and concerned about intervening to reduce this distressing symptom. A simple 0 to 10 NRS can be used8 to assess thirst intensity or thirst distress when feasible. The modified revised oral assessment guide23 can also be used to assess the lips, tongue, and mucous membranes for dryness or cracking,8 with the understanding that oral moisture alone may not be a reliable predictor of thirst intensity.16 Management of thirst can also be incorporated into unit-based comfort management programs focused on alleviating distressing symptoms associated with the intensive care unit such as thirst, noise, excessive light, sleep deprivation, discomfort due to catheters/devices, and isolation to reduce risk of posttraumatic stress disorder.15 The IPREA (Inconforts des Patients de Réanimation) questionnaire24 is a validated tool to assess intensity of 18 discomforts related to intensive care on an NRS from 0 to 10. Higher intensity assessments could be incorporated into daily goals checklists and discussed during unit rounds to raise awareness about the importance of symptom management.8 This simple assessment could also be performed on a sample of patients at discharge from the intensive care unit to determine how well the unit is managing symptoms overall and thus guide continuous improvement to enhance the immediate experience for critical care patients.Scientific data are emerging on thirst management in critically ill patients. As new knowledge unfolds, especially with regard to minimally clinically important differences and frequency of interventions to achieve desired clinical effects, nurses can use preabsorptive strategies to temporarily satisfy thirst. These comfort measures can improve patients' experience in critical care units.