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| Category | Rationale | Basic Cost per 100 kcal | Modifiers |
| Insensible Water Loss | Each calorie dissipated is associated with the evaporation of 1.7g of water (about 1/3 lungs, 2/3 skin). IWL is different from frank perspiratory losses. | 43 mL | Dry air, wind currents, hyperventilation increase IWL |
| Sweat Water Loss | Water is lost via skin to regulate body temperature | 5-20 mL | Increased in dry, hot environment; proportionally worse in infants due to high surface area to volume ratio |
| Stool Water Loss | Some water is not resorbed by the large bowel | 5-10 mL | About 5 mL in breast fed babies, and 10 mL in normal adult. May be up to 60 mL in diarrhea and 100 mL in secretory diarrhea |
| Renal Water Loss | Endogenous solute load is 10-15 mOsm/100 calories and maintenance fluids contribute another 10 mOsm/100 calories | 50 mL | The amount of fluid required to excrete a given solute load depends on age and renal function. Newborn urine contains 75-700 mOsm/L; by 5 days, the range is 50-1000 mOsm/L. |
| Water of Oxidation | Water is produced during oxidation of fats and carbohydrates | 12-17 mL | This assumes that an energy source is provided |
| Preformed Water | Water from tissue catabolism | 3 mL | In disease states, with tissue breakdown. |
| Total | 86-111 mL | on average, about 100 mL/100 kcal |
| Condition | Problem | Compensation |
| Hyperventilation | Increased respiratory IWL | May double normal requirement |
| Tracheostomy | Decreased dead air fraction of tidal volume, increased pulmonary IWL | Increased requirement |
| Fever | Increase sweat IWL | Increase 10% per Celsius degree above 38. |
| Increased physical activity | Increased basal metabolic rate | Increase up to 30% for extreme activity |
| Anuria | Decreased renal fluid requirement | Decrease by 50% |
| Other fluid losses | E.g., sweating, GI losses, blood losses. | Replace with equal volume of ionically similar solution. |
| Example. A 15 year old male who weighs 60 kilograms is
admitted for typhoid fever. His temperature is 40 degrees celcius.
He is experiencing rigors and chills. He is sweating profusely and
his respiratory rate 30. He does not feel well enough to drink
fluids.
The Holiday-Segar method can be used to approximate his basic caloric requirement of 2.3 L per day. His requirement is adjusted upward 20% for his temperature. He is shivering and moving about due to the rigors, so add another 15%. His tachypnea is also significant, so additional fluid should be added. Although it is somewhat subjective, his maintenance fluids can be increased about 50% to start with and then adjusted according to this clinical picture. Thus, fluids would run at about 145 cc per hour. |
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