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.1–6 

Imagine 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...

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