Enteral hydration prior to surgery: the benefits are clear.

• Volume 118 • Number 6 www.anesthesia-analgesia.org 1163 Copyright © 2014 International Anesthesia Research Society DOI: 10.1213/ANE.0000000000000240 A recent piece reported on National Public Radio had this to say about the experience of having an operation: “Surgery can be a necessary misery, endured in hope of health. But what if you took away the misery, and kept the benefits? When hospitals quit subjecting patients to prolonged fasting [. ] a study1 finds, patients feel less pain and recover faster. ”2 As more research focuses on perioperative outcomes, patients will become increasingly informed about perioperative care, partly due to exposure from the popular news media. This piece, reported on national radio, focused on an enhanced recovery after surgery protocol, which was pioneered over a decade ago in Europe. It is a comprehensive approach to perioperative care that includes enteral hydration and carbohydrate loading up until 2 hours before surgery, as well as goal-directed fluid management, early mobilization, early oral intake after surgery, and a multimodal pain regimen. Carbohydrate loading preoperatively, in the form of glucose-containing solutions, has been shown to reduce postoperative loss of muscle mass, decrease anxiety and hunger, and improve nitrogen balance.3 A Cochrane review noted limited data and issues with protocol compliance but found a reduced length of stay and an overall reduction in complications.4 While the full benefit of enhanced recovery after surgery protocols remains unclear, 1 piece of the protocol deserves attention: reduced fasting. Liberalized fluid intake before surgery has multiple clinical benefits and improves patient satisfaction.5 As Ogino et al.6 describe in an article in this issue of Anesthesia & Analgesia, it is possible that this aspect might actually contribute to decreased pain scores as well. In a small crossover study investigating the role of hydration status and pain, Ogino et al.6 describe the correlation between dehydration and increased pain perception. Five volunteers were asked to fast for 12 hours and then perform a dehydrating exercise protocol. The study somewhat simulated an operating room experience, with a prolonged fast followed by either oral rehydration up until the dehydration exercise (i.e., surgery) or a prolonged fast and no oral hydration prior to the dehydration exercise. Using cold-pressor tests and functional magnetic resonance imaging, they found that cortical pathways associated with pain as well as the reported pain threshold were altered in the dehydrated group. The group that was allowed oral rehydration had a significantly increased pain threshold compared with that of dehydrated group. The authors hypothesize that the increased sensation of thirst in the dehydrated group led to an amplification of the perception of pain. This might be one explanation for decreased pain scores in patients who are hydrated up until their surgery, and in those who resume oral intake earlier postoperatively. However, it might be possible that a better-hydrated state itself leads to less pain, with or without the perception of thirst. Dehydration has been shown by others to affect executive functioning, but as far as we know, this is one of the first studies to demonstrate the correlation between pain and dehydration.7 Theoretically, these results would support a protocol that instructs patients to drink clear fluids liberally up until 2 hours before their surgery. The decreased pain levels associated with this approach might in turn reduce opiate use, which could reduce side effects, decrease tolerance, and improve patient satisfaction. This would have the added benefit of reducing the use of excessive intraoperative IV fluids, which has previously been associated with increased ileus and prolonged hospital stay.8,9 However, if we recommend clear fluids preoperatively, are they all the same in benefit and safety? The nil per os (NPO) guidelines laid out by the American Society of Anesthesiologists suggest that patients can drink “clear liquids” up until 2 hours before their surgery and have no increased risk of aspiration.10 Abstaining from clear liquids starting 4 hours before surgery has actually been shown to increase gastric volumes compared with drinking up until 2 hours beforehand. The American Society of Anesthesiologists defines clear liquid as including, but not limited to, carbonated beverages, clear tea, water, black coffee, and fruit juice without pulp. The “but not limited to” phrase causes most institutions to include chicken broth, JELL-O, and clear sports drinks in their definition of clears. It is well known that fried and fatty foods decrease gastric emptying, and thus, they require an increased fasting period but does the composition of the clear liquid, including protein content, osmolality, glucose concentration, or electrolytes affect gastric volume? Enteral Hydration Prior to Surgery: The Benefits Are Clear