Water drinking during aerobic exercise improves the recovery of non-linear heart rate dynamics in coronary artery disease: crossover clinical trial

Introduction

The post-exercise recovery is a period of vulnerability of the cardiovascular system in which autonomic nervous system plays a key role in cardiovascular deceleration. It is already known that individuals with coronary artery disease (CAD) are at greater risk due to delayed vagal reactivation in this period. Water ingestion has been studied as a strategy to improve autonomic recovery and mitigate the risks during recovery. However, the results are preliminary and need further confirmation. Therefore, our aim was to investigate the influence of individualized water drinking on the non-linear dynamics of heart rate during and after aerobic exercise in CAD subjects.

Methods

30 males with CAD were submitted to a control protocol composed of initial rest, warming up, treadmill exercise, and passive recovery (60 min). After 48 hours they performed the hydration protocol, composed of the same activities, however, with individualized water drinking proportional to the body mass lost in the control protocol. The non-linear dynamics of heart rate were assessed by indices of heart rate variability extracted from the recurrence plot, detrended fluctuation analysis, and symbolic analysis.

Results and discussion

During exercise, the responses were physiological and similar in both protocols, indicating high sympathetic activity and reduced complexity. During recovery, the responses were also physiological, indicating the rise of parasympathetic activity and the return to a more complex state. However, during hydration protocol, the return to a more complex physiologic state occurred sooner and non-linear HRV indices returned to resting values between the 5th and 20th minutes of recovery. In contrast, during the control protocol, only a few indices returned to resting values within 60 minutes. Despite that, differences between protocols were not found. We conclude that the water drinking strategy accelerated the recovery of non-linear dynamics of heart rate in CAD subjects but did not influence responses during exercise. This is the first study to characterize the non-linear responses during and after exercise in CAD subjects.

The impact of modified fluid gelatin 4% in a balanced electrolyte solution on plasma osmolality in children-A noninterventional observational study

BACKGROUND

Intravenous fluids for perioperative infusion therapy should be isotonic to maintain the body fluid homeostasis in children. Modified fluid gelatin 4% in a balanced electrolyte solution has a theoretical osmolarity of 284 mosmol L^-1 , and a real osmolality of 264 mosmol kg H₂ O^-1 . Because both values are lower than those of 0.9% saline or plasma, gelatin would be expected to be hypotonic in-vitro and in-vivo.

AIM

We thus hypothesized that the infusion of gelatin would be expected to decrease plasma osmolality. We performed an in-vitro experiment and an in-vivo study to evaluate the impact of gelatin on the osmolality in children.

METHODS

In the in-vitro experiment, full blood samples were diluted with gelatin 4% or albumin (50 g L^-1 ) from 0% (pure blood) to 100% (pure colloid), and the osmolality was measured by freezing-point depression. In the in-vivo study, blood gas analyses from children undergoing major pediatric surgery were collected before and after gelatin infusion, and the osmolality was calculated by a modified version of Zander's formula.

RESULTS

In the in-vitro experiment, 65 gradually diluted blood samples from five volunteers (age 25-55 years) were analyzed. The dilution with gelatin caused no significant changes in osmolality between 0% and 100%. Compared with gelatin, the osmolality in the albumin group was significantly lower between 50% and 100% dilution (p < .05). In the in-vivo study, 221 children (age 21.4 ± 30 months) were included. After gelatin infusion, the osmolality increased significantly (mean change 4.3 ± 4.8 [95% CI 3.7-4.9] mosmol kg H₂ O^-1 ; p < .01) within a normal range.

CONCLUSIONS

Gelatin in a balanced electrolyte solution has isotonic characteristics in-vitro and in-vivo, despite the low theoretical osmolarity, probably caused by the (unmeasured) negative charges in the gelatin molecules contributing to the plasma osmolality. For a better evaluation of the (real) tonicity of gelatin-containing solutions, we suggest to calculate the osmolality (mosmol kg H₂ O^-1 ) using Zander's formula.

TRIAL REGISTRATION

ClinicalTrials.gov (ID: NCT02495285).

Rhabdomyolysis Due to Salmonellosis: A Case Report of a Rare Presentation

Salmonella infection has been commonly associated with gastrointestinal symptoms, such as diarrhea, abdominal pain, and nausea. However, in some cases, patients can develop rare and life-threatening complications such as rhabdomyolysis. Here, we report a case of gastroenteritis due to Salmonella enteritidis infection complicated by rhabdomyolysis. The patient was successfully treated with fluids and antibiotics. Despite rare, the association of Salmonella infection and rhabdomyolysis may occur. Prompt diagnosis and treatment with aggressive fluid replacement and antibiotics are paramount to prevent acute kidney injury.

Extreme Ultra-Trail Race Induces Muscular Damage, Risk for Acute Kidney Injury and Hyponatremia: A Case Report

A case study involving a healthy trained male athlete who completed a 786 km multi-stage ultra-trail race. Several markers were analyzed in blood and urine samples: creatinine (SCR) for kidney damage, sodium ([Na⁺]) for hyponatremia, creatine kinase (CK) for exertional rhabdomyolysis, as well as other hematological values. Samples were taken before and after the race and during the recovery period (days 2 and 9 after the race). Results showed: SCR = 1.13 mg/dl, [Na⁺] =139 mmol/l and CK = 1.099 UI/l. Criteria for the determination of acute kidney damage were not met, and [Na+] concentration was above 135 mEq/L, indicating the absence of hyponatremia. Exertional rhabdomyolysis was suffered by the athlete (baseline CK increased fivefold), though this situation was reverted after 9 days of recovery. Ultra-trail races cause biochemical changes in athletes, which should be known about by healthcare professionals.

Hydration Status, Fluid Intake, Sweat Rate, and Sweat Sodium Concentration in Recreational Tropical Native Runners

AIM

The purpose of this study was to evaluate hydration status, fluid intake, sweat rate, and sweat sodium concentration in recreational tropical native runners.

METHODS

A total of 102 males and 64 females participated in this study. Participants ran at their self-selected pace for 30-100 min. Age, environmental conditions, running profiles, sweat rates, and sweat sodium data were recorded. Differences in age, running duration, distance and pace, and physiological changes between sexes were analysed. A p-value cut-off of 0.05 depicted statistical significance.

RESULTS

Males had lower relative fluid intake (6 ± 6 vs. 8 ± 7 mL·kg-1·h-1, p < 0.05) and greater relative fluid balance deficit (-13 ± 8 mL·kg-1·h-1 vs. -8 ± 7 mL·kg-1·h-1, p < 0.05) than females. Males had higher whole-body sweat rates (1.3 ± 0.5 L·h-1 vs. 0.9 ± 0.3 L·h-1, p < 0.05) than females. Mean rates of sweat sodium loss (54 ± 27 vs. 39 ± 22 mmol·h-1) were higher in males than females (p < 0.05).

CONCLUSIONS

The sweat profile and composition in tropical native runners are similar to reported values in the literature. The current fluid replacement guidelines pertaining to volume and electrolyte replacement are applicable to tropical native runners.

Movement Technique and Standing Balance After Graded Exercise-Induced Dehydration

CONTEXT

Hypohydration has been shown to alter neuromuscular function. However, the longevity of these impairments remains unclear.

OBJECTIVE

To examine the effects of graded exercise-induced dehydration on neuromuscular control 24 hours after exercise-induced hypohydration.

DESIGN

Crossover study.

SETTING

Laboratory.

PATIENTS OR OTHER PARTICIPANTS

A total of 23 men (age = 21 ± 2 years, height = 179.8 ± 6.4 cm, mass = 75.24 ± 7.93 kg, maximal oxygen uptake [VO2max] = 51.7 ± 5.5 mL·kg-1·min-1, body fat = 14.2% ± 4.6%).

INTERVENTION(S)

Participants completed 3 randomized exercise trials: euhydrated arrival plus fluid replacement (EUR), euhydrated arrival plus no fluid (EUD), and hypohydrated arrival plus no fluid (HYD) in hot conditions (ambient temperature = 35.2°C ± 0.6°C, relative humidity = 31.3% ± 2.5%). Each trial consisted of 180 minutes of exercise (six 30-minute cycles: 8 minutes at 40% VO2max; 8 minutes, 60% VO2max; 8 minutes, 40% VO2max; 6 minutes, passive rest) followed by 60 minutes of passive recovery.

MAIN OUTCOME MEASURE(S)

We used the Landing Error Scoring System and Balance Error Scoring System (BESS) to measure movement technique and postural control at pre-exercise, postexercise and passive rest (POSTEX), and 24 hours postexercise (POST24). Differences were assessed using separate mixed-design (trial × time) repeated-measures analyses of variance.

RESULTS

The magnitude of hypohydration at POSTEX was different among EUR, EUD, and HYD trials (0.2% ± 1%, 3.5% ± 1%, and 5% ± 0.9%, respectively; P < .05). We observed no differences in Landing Error Scoring System scores at pre-exercise (2.9 ± 1.6, 3.0 ± 2.1, 3.0 ± 2.0), POSTEX (3.3 ± 1.5, 3.0 ± 2.0, 3.1 ± 1.9), or POST24 (3.3 ± 1.9, 3.2 ± 1.4, 3.3 ± 1.6) among the EUD, EUR, and HYD trials, respectively (P = .90). Hydration status did not affect BESS scores (P = .11), but BESS scores at POSTEX (10.4 ± 1.1) were greater than at POST24 (7.7 ± 0.9; P = .03).

CONCLUSIONS

Whereas exercise-induced dehydration up to 5% body mass did not impair movement technique or postural control 24 hours after a prolonged bout of exercise in a hot environment, postural control was impaired at 60 minutes after prolonged exercise in the heat. Consideration of the length of recovery time between bouts of exercise in hot environments is warranted.

The accurate prediction of sweat rate from energy expenditure and air temperature: a proof-of-concept study

This proof-of-concept study used a web application to predict runner sweat losses using only energy expenditure and air temperature. A field study (FS) of n = 37 runners was completed with n = 40 sweat loss observations measured over 1 h (sweat rate, SR). Predictions were also compared with 10 open literature (OL) studies in which individual runner SR was reported (n = 82; 109 observations). Three prediction accuracy metrics were used: for FS, the mean absolute error (MAE) and concordance correlation coefficient (CCC) were calculated to include a 95% confidence interval [CI]; for OL, the percentage concordance (PC) was examined against calculation of accumulated under- and over-drinking potential. The MAE for FS runners was 0.141 kg [0.105, 0.177], which was less than estimated scale weighing error on 85% of occasions. The CCC was 0.88 [0.82, 0.93]. The PC for OL was 96% for avoidance of both under- and over-drinking and 93% overall. All accuracy metrics and their CIs were below acceptable error tolerance. Input errors of ±10% and ±1 °C for energy expenditure and air temperature dropped the PC to between 84% and 90%. This study demonstrates the feasibility of accurately predicting SR from energy expenditure and air temperature alone. Novelty Results demonstrate that accurate runner SR prediction is possible with knowledge of only energy expenditure and air temperature. SR prediction error was smaller than scale weighing error in 85% of observations. Accurate runner SR prediction could help mitigate the common risks of over- and under-drinking.

The Utility of Thirst as a Measure of Hydration Status Following Exercise-Induced Dehydration

The purpose of this study was to examine the perception of thirst as a marker of hydration status following prolonged exercise in the heat. Twelve men (mean ± SD; age, 23 ± 4 y; body mass, 81.4 ± 9.9 kg; height, 182 ± 9 cm; body fat, 14.3% ± 4.7%) completed two 180 min bouts of exercise on a motorized treadmill in a hot environment (35.2 ± 0.6 °C; RH, 30.0 ± 5.4%), followed by a 60 min recovery period. Participants completed a euhydrated (EUH) and hypohydrated (HYPO) trial. During recovery, participants were randomly assigned to either fluid replacement (EUH_FL and HYPO_FL; 10 min ad libitum consumption) or no fluid replacement (EUH_NF and HYPO_NF). Thirst was measured using both a nine-point scale and separate visual analog scales. The percent of body mass loss (%BML) was significantly greater immediately post exercise in HYPO (HYPO_FL, 3.0% ± 1.2%; HYPO_NF, 2.6% ± 0.6%) compared to EUH (EUH_FL, 0.2% ± 0.7%; EUH_NF, 0.6% ± 0.5%) trials (p < 0.001). Following recovery, there were no differences in %BML between HYPO_FL and HYPO_NF (p > 0.05) or between EUH_FL and EUH_NF (p > 0.05). Beginning at minute 5 during the recovery period, thirst perception was significantly greater in HYPO_NF than EUH_FL, EUH_NF, and HYPO_FL (p < 0.05). A 10 min, ad libitum consumption of fluid post exercise when hypohydrated (%BML > 2%), negated differences in perception of thirst between euhydrated and hypohydrated trials. These results represent a limitation in the utility of thirst in guiding hydration practices.

Practical Hydration Solutions for Sports

Personalized hydration strategies play a key role in optimizing the performance and safety of athletes during sporting activities. Clinicians should be aware of the many physiological, behavioral, logistical and psychological issues that determine both the athlete’s fluid needs during sport and his/her opportunity to address them; these are often specific to the environment, the event and the individual athlete. In this paper we address the major considerations for assessing hydration status in athletes and practical solutions to overcome obstacles of a given sport. Based on these solutions, practitioners can better advise athletes to develop practices that optimize hydration for their sports.

Fluid management in Acute Respiratory Distress Syndrome: A narrative review

Acute Respiratory Distress Syndrome remains a major source of morbidity and mortality in the modern intensive care unit (ICU). Major advances in the understanding and management of this condition were made in the last two decades. The use of low tidal ventilation is a well-established therapy. Conservative fluid management is now another cornerstone of management. However, much remains to be understood in this arena. Assessing volume status in these patients may be challenging and the tools available to do so are far from perfect. Several dynamic measures including pulse pressures variation are used. Ultrasound of the lungs and the vascular system may also have a role. In addition, the type of fluid to administer when needed is still open to debate. Finally, supportive measures in these patients, early during their ICU stay and later after discharge continue to be crucial for survival and adequate recovery.

Preemptive volume therapy to prevent hemodynamic changes caused by the beach chair position: hydroxyethyl starch 130/0.4 versus Ringer's acetate-a controlled randomized trial

BACKGROUND

Hemodynamic instability frequently occurs in beach chair positioning for surgery, putting patients at risk for cerebral adverse events. This study examined whether preoperative volume loading with crystalloids alone or with a crystalloid-colloid combination can prevent hemodynamic changes that may be causative for unfavorable neurologic outcomes.

METHODS

The study randomly assigned 43 adult patients undergoing shoulder surgery to 3 study groups. Each group received an infusion of 500 mL of Ringer's acetate between induction of anesthesia and being placed in the beach chair position. The crystalloid group received an additional bolus of 1000 mL Ringer's acetate. The hydroxyethyl starch group was administered an additional bolus of 500 mL of 6% hydroxyethyl starch 130/0.4. Hemodynamic monitoring was accomplished via an esophageal Doppler probe. Cerebral oxygen saturation was examined with near-infrared spectroscopy. Changes in stroke volume variation between the prone and beach chair positions were defined as the primary outcome parameter. Secondary outcomes were changes in cardiac output and cerebral oxygen saturation.

RESULTS

The control group was prematurely stopped after enrollment of 4 patients because of adverse events. In the hydroxyethyl starch group, stroke volume variation remained constant during positioning maneuvers (P = .35), whereas a significant increase was observed in the Ringer's acetate group (P < .01; P = .014 for intergroup comparison). This was also valid for changes in cardiac output. Cerebral oxygen saturation significantly decreased in both groups.

CONCLUSIONS

Preprocedural boluses of 500 mL of 6% hydroxyethyl starch 130/0.4 as well as 1000 mL of Ringer's acetate were efficient in preserving hemodynamic conditions during beach chair position.

Plasmapheresis: A Retrospective Audit of Procedures from a Tertiary Care Center in Southern India

Introduction:

The term plasmapheresis/plasma exchange refers to the removal of the plasma component of blood and its replacement with various fluids. Plasma Exchange (PE) has been used to treat a variety of conditions that are associated with an aberrant immune response. We undertook this retrospective study aiming to look at plasmapheresis procedures conducted in the nephrology department over a fixed time period.

Materials and Methods:

Retrospective analysis of PE procedures from January 2013 to October 2016 was conducted in the nephrology and Intensive Care Unit of a tertiary care teaching hospital. The goal was to achieve a total removal of 150–200 ml/plasma per kg body weight. As replacement, we used a standard protocol of 100 ml of 20% albumin in 1 L of normal saline and 2–3 units of fresh frozen plasma. All results were expressed as mean ± standard deviation and statistical analysis was done using the Student's t-test for continuous and Fisher's exact test for categorical data.

Results:

A total of 192 procedures performed on 40 patients (22 males and 18 females). Age ranged from 15 to 79 years with a mean age of 37.5 years. Guillain–Barre syndrome accounted for 67.5% (>two-third of causes) for PE. Vascular access was femoral catheter in 27 (67.5%) and internal jugular catheter in 13 (32.5%). Mild hypotension occurred in 15 procedures (7.8%) of patients and allergic reactions such as rashes and chills occurred in 5 cycles (2.6%). A total of 36 patients (90%) showed significant improvement in condition, 2 did not show any change, while one worsened and one died due to respiratory complications.

Conclusion:

Our small series of data of plasmapheresis procedures from nephrology perspective has reaffirmed the safety and efficacy of the therapy in an experienced setup.

Fluid replacement modulates oxidative stress- but not nitric oxide-mediated cutaneous vasodilation and sweating during prolonged exercise in the heat

The roles of nitric oxide synthase (NOS), reactive oxygen species (ROS), and angiotensin II type 1 receptor (AT1R) activation in regulating cutaneous vasodilation and sweating during prolonged (≥60 min) exercise are currently unclear. Moreover, it remains to be determined whether fluid replacement (FR) modulates the above thermoeffector responses. To investigate, 11 young men completed 90 min of continuous moderate intensity (46% V̇o2peak) cycling performed at a fixed rate of metabolic heat production of 600 W (No FR condition). On a separate day, participants completed a second session of the same protocol while receiving FR to offset sweat losses (FR condition). Cutaneous vascular conductance (CVC) and local sweat rate (LSR) were measured at four intradermal microdialysis forearm sites perfused with: 1) lactated Ringer (Control); 2) 10 mM NG-nitro-l-arginine methyl ester (l-NAME, NOS inhibition); 3) 10 mM ascorbate (nonselective antioxidant); or 4) 4.34 nM losartan (AT1R inhibition). Relative to Control (71% CVCmax at both time points), CVC with ascorbate (80% and 83% CVCmax) was elevated at 60 and 90 min of exercise during FR (both P < 0.02) but not at any time during No FR (all P > 0.31). In both conditions, CVC was reduced at end exercise with l-NAME (60% CVCmax; both P < 0.02) but was not different relative to Control at the losartan site (76% CVCmax; both P > 0.19). LSR did not differ between sites in either condition (all P > 0.10). We conclude that NOS regulates cutaneous vasodilation, but not sweating, irrespective of FR, and that ROS influence cutaneous vasodilation during prolonged exercise with FR.

Effects of Fluid Ingestion on Brain-Derived Neurotrophic Factor and Cognition During Exercise in the Heat

We investigated the effects of fluid ingestion during exercise in different environments on the serum brain-derived neurotrophic factor and cognition among athletes. Ten collegiate male athletes (soccer, n = 5; rugby, n = 5) were enrolled, and they completed running tests in the following four conditions (60 min each): 1) thermoneutral temperature at 18°C (group 18); 2) high ambient temperature at 32°C without fluid ingestion (group 32); 3) high ambient temperature at 32°C with water ingestion (group 32+W); and 4) high ambient temperature at 32°C with sports drink ingestion (group 32+S). Serum brain-derived neurotrophic factor levels significantly increased in group 18 immediately after exercise when compared with those at rest and were significantly higher than those in group 32 immediately and 60 min after exercise (p < 0.05). In the Stroop Color and Word Test, significantly increased Word, Color, and Color-Word scores were observed in group 18 immediately after exercise compared to those at rest (p < 0.05). However, the Color-Word score appeared to be significantly lower in group 32 immediately after exercise compared to the other groups (p < 0.05) and at 60 min post-exercise compared to group 18 (p < 0.05). We found that the exercise performed in a thermoneutral environment improved cognitive function, but the exercise performed in a hot environment did not. The differences according to the exercise environment would be largely affected by brain-derived neurotrophic factor, and fluid ingestion regardless of the type of drink (water or sports beverage) was assumed to have contributed to the improvement in cognitive function caused by exercising in a hot environment.

The management of diabetic ketoacidosis in children. Diabetes Ther. 2010;1:103-120. [PMID: 22127748 DOI: 10.1007/s13300-010-008-2]

The object of this review is to provide the definitions, frequency, risk factors, pathophysiology, diagnostic considerations, and management recommendations for diabetic ketoacidosis (DKA) in children and adolescents, and to convey current knowledge of the causes of permanent disability or mortality from complications of DKA or its management, particularly the most common complication, cerebral edema (CE). DKA frequency at the time of diagnosis of pediatric diabetes is 10%-70%, varying with the availability of healthcare and the incidence of type 1 diabetes (T1D) in the community. Recurrent DKA rates are also dependent on medical services and socioeconomic circumstances. Management should be in centers with experience and where vital signs, neurologic status, and biochemistry can be monitored with sufficient frequency to prevent complications or, in the case of CE, to intervene rapidly with mannitol or hypertonic saline infusion. Fluid infusion should precede insulin administration (0.1 U/kg/h) by 1-2 hours; an initial bolus of 10-20 mL/kg 0.9% saline is followed by 0.45% saline calculated to supply maintenance and replace 5%-10% dehydration. Potassium (K) must be replaced early and sufficiently. Bicarbonate administration is contraindicated. The prevention of DKA at onset of diabetes requires an informed community and high index of suspicion; prevention of recurrent DKA, which is almost always due to insulin omission, necessitates a committed team effort.

The management of diabetic ketoacidosis in children

The object of this review is to provide the definitions, frequency, risk factors, pathophysiology, diagnostic considerations, and management recommendations for diabetic ketoacidosis (DKA) in children and adolescents, and to convey current knowledge of the causes of permanent disability or mortality from complications of DKA or its management, particularly the most common complication, cerebral edema (CE). DKA frequency at the time of diagnosis of pediatric diabetes is 10%-70%, varying with the availability of healthcare and the incidence of type 1 diabetes (T1D) in the community. Recurrent DKA rates are also dependent on medical services and socioeconomic circumstances. Management should be in centers with experience and where vital signs, neurologic status, and biochemistry can be monitored with sufficient frequency to prevent complications or, in the case of CE, to intervene rapidly with mannitol or hypertonic saline infusion. Fluid infusion should precede insulin administration (0.1 U/kg/h) by 1-2 hours; an initial bolus of 10-20 mL/kg 0.9% saline is followed by 0.45% saline calculated to supply maintenance and replace 5%-10% dehydration. Potassium (K) must be replaced early and sufficiently. Bicarbonate administration is contraindicated. The prevention of DKA at onset of diabetes requires an informed community and high index of suspicion; prevention of recurrent DKA, which is almost always due to insulin omission, necessitates a committed team effort.

Perioperative fluid management

Many colorectal surgeons rely on traditional theories and approaches in addressing perioperative fluid management issues. Often, their training and instincts favor over-resuscitation, especially after bowel or emergent colorectal procedures. However, data are now emerging to support the use of more restrictive approaches to perioperative fluid administration-though uncertainties still exist as to which fluids are optimal, and how and when they should be administered. This article provides a focused, evidence-based review on this topic-highlighting critical considerations that clinicians may wish to address to improve patient outcomes following colorectal surgery.

Sodium replacement and plasma sodium drop during exercise in the heat when fluid intake matches fluid loss

CONTEXT

Sodium replacement during prolonged exercise in the heat may be critically important to maintaining fluid and electrolyte balance and muscle contractility.

OBJECTIVE

To examine the effectiveness of sodium-containing sports drinks in preventing hyponatremia and muscle cramping during prolonged exercise in the heat.

DESIGN

Randomized crossover study.

PATIENTS OR OTHER PARTICIPANTS

Thirteen active men.

INTERVENTION(S)

Participants completed 4 trials of an exercise protocol in the heat (30 degrees C) consisting of 3 hours of exercise (alternating 30 minutes of walking and cycling at a heart rate of 130 and 140 beats per minute, respectively); a set of standing calf raises (8 sets of 30 repetitions); and 45 minutes of steep, brisk walking (5.5 km x h(-1) on a 12% grade). During exercise, participants consumed fluids to match body mass loss. A different drink was consumed for each trial: carbohydrate-electrolyte drink containing 36.2 mmol/L sodium (HNa), carbohydrate-electrolyte drink containing 19.9 mmol/L sodium (LNa), mineral water (W), and colored and flavored distilled water (PL).

MAIN OUTCOME MEASURE(S)

Serum sodium, plasma osmolality, plasma volume changes, and muscle cramping frequency.

RESULTS

During both HNa and LNa trials, serum sodium remained relatively constant (serum sodium concentration at the end of the protocol was 137.3 mmol/L and 136.7 mmol/L, respectively). However, a clear decrease was observed in W (134.5 +/- 0.8 mmol/L) and PL (134.4 +/- 0.8 mmol/L) trials compared with HNa and LNa trials (P < .05). The same trends were observed for plasma osmolality (P < .05). Albeit not significant, plasma volume was preserved during the HNa and LNa trials, but a reduction of 2.5% was observed in the W and PL trials. None of the volunteers experienced cramping.

CONCLUSIONS

The data suggest that sodium intake during prolonged exercise in the heat plays a significant role in preventing sodium losses that may lead to hyponatremia when fluid intake matches sweat losses.

Sweat rates and fluid turnover in professional football players: a comparison of National Football League linemen and backs

CONTEXT

Many National Football League (NFL) teams practice 2 times per day over consecutive days in a hot and humid environment. Large body surface area (BSA) and use of protective equipment result in high sweat rates and total sweat loss in these football players.

OBJECTIVE

To compare sweat rate, sweat loss, fluid consumption, and weight loss between NFL linemen and backs during preseason practices.

DESIGN

Between-groups design.

SETTING

Preseason training camp with wet bulb globe temperature between 19 degrees C and 25 degrees C.

PATIENTS OR OTHER PARTICIPANTS

Eight linemen and 4 backs and receivers participated.

MAIN OUTCOME MEASURE(S)

Data were collected during both practice sessions on 2 separate days during the first week of August. Sweat rate was calculated as change in mass adjusted for all fluids consumed between prepractice and postpractice body mass measurements and the urine produced during practice divided by the length of the practice session. Gross daily sweat losses also were calculated.

RESULTS

Height, mass, and BSA were higher in linemen than in backs. Sweat rate was also higher in linemen (2385 +/- 520 mL/h) than in backs (1410 +/- 660 mL/h, P < .001), as was the total volume of sweat lost during both practices in 1 day (6870 +/- 1034 mL/d versus 4110 +/- 2287 mL/d, P = .014). Compared with backs, linemen consumed more fluids during practice (2030 +/- 849 mL versus 1179 +/- 753 mL, P = .025) but produced less urine (53 +/- 73 mL versus 163 +/- 141 mL, P = .018). There was no difference in postpractice weight loss (linemen = -1.15 +/- 0.83%, backs = -1.06 +/- 0.76%).

CONCLUSIONS

Linemen sweated at higher rates, lost larger volumes of sweat, consumed more fluids, and produced less urine during practice compared with the physically smaller backs, but they did not lose a greater percentage of body weight. Sodium losses could be considerable in NFL players during the preseason because of high daily sweat losses in backs and in linemen.

Fluid replacement in burns. A burns calculator

The successful treatment of major burns depends upon accurate and early fluid replacement in the first 36 h. A burns calculator has been designed, based upon the Muir and Barclay formula, which should facilitate the estimation of fluid requirements in burned patients and therefore improve their immediate management in accident and emergency departments.