Hydration, kidney injury and clinical outcome

Studies in health care professional (HCPs) have demonstrated a high prevalence of dehydration, which has been linked with morphological brain changes as well as cognitive impairment in other groups. Moreover, many age-related pathophysiological changes result in increased susceptibility to fluid and electrolyte imbalance, rendering older adults vulnerable to dehydration which may be associated with poor outcome. This thesis investigates the prevalence of dehydration and impact on cognitive function amongst HCPs. It also investigates the prevalence of dehydration in hospitalised older adults and the association between dehydration, acute kidney injury (AKI) and clinical outcome. Hydration status and cognition were objectively assessed in nurses and doctors working on emergency medical and surgical wards. This study demonstrated that a significant proportion of HCPs were dehydrated at the start and end of their shifts and many were oliguric. The prevalence of dehydration varied with level of experience and speciality and was associated with short-term memory impairment. Using serum osmolality, the key regulated variable in fluid homeostasis as a measure of hydration status in hospitalised older adults, prospective assessment of 200 patients demonstrated that over a third had hyperosmolar dehydration (HD) at admission, two-thirds of which were dehydrated 48 hours later. Dehydration at admission was independently associated with a six-fold increase in 30-day mortality. Subsequent retrospective assessment of 32,980 hospitalised older adults demonstrated that dehydration was diagnosed clinically in 8.9% of patients and was independently associated with a two fold increase in mortality. Nearly half of those dehydrated had a concomitant diagnosis of AKI and the median length of hospital stay (LOS) was nearly three times greater than those without the condition. Despite the widespread use of serum osmolality in human physiology studies, it is rarely used clinically to assess hydration. Analysis of published equations estimating osmolality, demonstrated that an equation by Khajuria and Krahn was 90% sensitivity and 97% specificity at diagnosing hyperosmolar dehydration. Using this equation, we demonstrated that 27.2% of 6632 older adults had HD at admission to hospital and the risk of developing AKI 12-24 hours after admission in these patients was five times those euhydrated at admission. Moreover, the 30-day mortality was nearly twice that of euhydrated patients, independent of key confounders. The median LOS in dehydrated patients was almost double. This work has highlighted the need to educate both patients and HCPs on the importance of hydration. Further work is required to prospectively assess the use of serum osmolality as a predictor of dehydration, AKI and outcomes. Given that hydration and nutrition are the hallmarks of compassionate care, there is clear room for improvement with findings from this thesis suggesting the need for further investigation and intervention in both community and hospital settings