- Types of insensitive losses
- Skin losses
- Lung losses
- Causes of increasing insensitive losses
- How are insensitive losses calculated?
- References
The insensitive losses refer to the loss of body fluids that are not easily evident; that is, they cannot be measured and are part of the control in the balance of fluids administered and eliminated by the patient. Liquids removed are mainly categorized into sensitive losses and insensitive losses.
Sensitive losses are those that can be measured without difficulty; for example, losses in diuresis or gastrointestinal losses. In contrast, insensitive losses are those that we cannot measure and are virtually devoid of sodium, such as fluid lost through sweating or breathing.
Insensitive skin loss
Because they cannot be measured directly, they are estimated according to the balance of the previous day, taking into account factors that may influence their modification, such as the use of phototherapy, humidified fans, among others.
They account for between 700 and 1000 ml per day, approximately 35% of the total loss of water eliminated per day, and normally increase in the presence of some pathologies such as burns, fevers, sudden climatic changes, hyperventilation or in situations such as exhaustive exercise.
The water balance, with its sensitive and insensitive losses, can be calculated using pre-established formulas according to the weight, sex or pathology of the patient, but it must be borne in mind that the values are not exact but approximate, according to international consensus.
Types of insensitive losses
Skin losses
These are produced by the thermoregulatory mechanism of convection, losing heat through the skin by diffusion. They must be differentiated from common sweat, since it contains solutes, while insensitive skin losses are imperceptible and can reach 400 ml in an adult.
Insensitive skin losses increase in the presence of elevated body temperature (fever) or elevated ambient temperature.
Lung losses
They are produced by the mechanism of evaporation; By heating the air in the alveoli, it becomes saturated with water and is expelled through expiration.
The temperature of the inspired air has an influence: the colder, the greater the loss on expiration.
Insensitive lung losses increase in a hot, dry environment and during hyperventilation, as well as in patients with hyperthyroidism.
Causes of increasing insensitive losses
Baseline insensitive losses are calculated using the formula 0.5 ml / kg / hour, and the exceptional situation must be added according to the pathology presented by the patient.
- Fever increases skin loss by evaporation by 10 to 15% for every 1 ° C increase in temperature above 38 ° C.
- Very low-weight premature infants can produce insensitive losses of 100 to 200 ml / kg / 24 hrs. The lower the weight, the greater the volume of insensitive losses.
- In ICU patients with intubation, 500 ml should be added every 24 hours of insensitive respiratory losses.
- In the case of hyperventilation or tachypnea, 4 ml / hr is added for every 5 breaths above a normal respiratory rate (RR> 20).
- In the case of light sweating, the evaporation losses are calculated through evaporation at 10ml / hr, moderate sweating at 20cc / hr and, in the case of diaphoresis or profuse sweating, at 40cc / hr.
- In burned patients, the loss of the skin barrier generates an increase in insensitive skin losses. These losses are calculated by multiplying the total body surface area by 0.35 (constant), and the result is multiplied by the burned body surface by 100. The result obtained is in ml.
- Other causes of increased insensitive losses can also be postoperative situations, suppurative wounds and cavity drains, among other events.
How are insensitive losses calculated?
The approximate daily insensitive losses - under normal conditions, without stress or pathologies - are calculated by multiplying the patient's weight in kg by 0.7, and the result is multiplied by 24 hours a day.
The result obtained is in ml and represents an approximation of the insensitive losses expected in one day.
The calculation of insensitive losses is of vital importance in hospitalized patients, especially in the intensive care unit or the burn care unit.
According to the data obtained, the necessary parenteral hydration of the patient should be adjusted, so that the sensitive losses plus the insensitive losses do not exceed the ingested fluids and cause dehydration.
Similarly, in cases where the sum of fluids eliminated (sensitive losses + insensitive losses) is considerably lower than the sum of fluids ingested -especially in cases of heart disease, nephrotic syndrome, cirrhosis, among others- the indication is the restriction of fluid intake in order to avoid edema.
References
- William N. Kelley. Diagnosis and treatment of kidney disease and electrolyte disorders. Internal Medicine Volume 1. Second Edition. Editorial Médica Panamericana. Buenos Aires. 1992; 929-930.
- Nelson Treaty of Pediatrics. Volume I. 18 Edition. Chapter 52. Electrolyte and acid-base disorders. 273.
- Roberto Alcazar Arroyo. Algorithms in nephrology. Hydroelectrolyte disorders and acid-base balance. Module 01. Spanish Society of Nephrology. 2011. Recovered from: elsevier.es
- American Academy of Pediatrics. Insensible water loss in low birth weigth infants. Pediatric. August 1972 Volume 50 / Issue 2. Recovered from: pediatrics.aappublications.org
- Spanish Society of Community Nutrition. Consensus Document. Hydration guidelines in comprehensive healthcare. Recovered from: correofarmaceutico.com