Evaluating and testing hydration status is increasingly requested by rehabilitation, sport, military and performance-related activities. Besides commonly used biochemical hydration assessment markers within blood and urine, which have their advantages and limitations in collection and evaluating hydration status, there are other potential markers present within saliva, sweat or tear. This literature review focuses on body fluids saliva, sweat and tear compared to blood and urine regarding practicality and hydration status influenced by fluid restriction and/or physical activity. The selected articles included healthy subjects, biochemical hydration assessment markers and a well-described (de)hydration procedure. The included studies (n=16) revealed that the setting and the method of collecting respectively accessing body fluids are particularly important aspects to choose the optimal hydration marker. To obtain a sample of saliva is one of the simplest ways to collect body fluids. During exercise and heat exposures, saliva composition might be an effective index but seems to be highly variable. The collection of sweat is a more extensive and time-consuming technique making it more difficult to evaluate dehydration and to make a statement about the hydration status at a particular time. The collection procedure of tear fluid is easy to access and causes very little discomfort to the subject. Tear osmolarity increases with dehydration in parallel to alterations in plasma osmolality and urine-specific gravity. But at the individual level, its sensitivity has to be further determined.

IntroductionThe global volume of surgery is growing and the population ageing, and economic pressure is rising. Major surgery is associated with relevant morbidity and mortality. Postoperative reduction in physiological and functional capacity is especially marked in the elderly, multimorbid patient with low fitness level, sarcopenia and malnutrition. Interventions aiming to optimise the patient prior to surgery (prehabilitation) may reduce postoperative complications and consequently reduce health costs.Methods and analysisThis is a multicentre, multidisciplinary, prospective, 2-arm parallel-group, randomised, controlled trial with blinded outcome assessment. Primary outcome is the Comprehensive Complications Index at 30 days. Within 3 years, we aim to include 2×233 patients with a proven fitness deficit undergoing major surgery to be randomised using a computer-generated random numbers and a minimisation technique. The study intervention consists of a structured, multimodal, multidisciplinary prehabilitation programme over 2–4 weeks addressing deficits in physical fitness and nutrition, diabetes control, correction of anaemia and smoking cessation versus standard of care.Ethics and disseminationThe PREHABIL trial has been approved by the responsible ethics committee (Kantonale Ethikkomission Bern, project ID 2020-01690). All participants provide written informed consent prior to participation. Participant recruitment began in February 2022 (10 and 8 patients analysed at time of submission), with anticipated completion in 2025. Publication of the results in peer-reviewed scientific journals are expected in late 2025.Trial registration numberNCT04461301.

The ventilatory efficiency (VE/VCO2) can be assessed with cardiopulmonary exercise testing (CPET). In many trials preoperative exercise testing was conducted in patients before major elective surgery. After the surgery complications were registered and assessed in regard to the preoperative test results. Some CPET variables (maximum oxygen consumption or the oxygen consumption at the anaerobic treshold) are relatively well established for preoperative risk assessment and have some predictive value in regard to postoperative complications. The VE/VCO2 is a parameter that has gained some interest in preoperative risk-stratification in the last years. We therefore aim to summarize current evidence.

The ventilatory efficiency (VE/VCO2) can be assessed with cardiopulmonary exercise testing (CPET). In many trials preoperative exercise testing was conducted in patients before major elective surgery. After the surgery complications were registered and assessed in regard to the preoperative test results. Some CPET variables (maximum oxygen consumption or the oxygen consumption at the anaerobic treshold) are relatively well established for preoperative risk assessment and have some predictive value in regard to postoperative complications. The VE/VCO2 is a parameter that has gained some interest in preoperative risk-stratification in the last years. We therefore aim to summarize current evidence.