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Dehydration

Dehydration is the pathological loss of fluids (and usually accompanying electrolytes).  It may be the primary issue, or merely a manifestation of some other process.

History:

In addition to the usual history, pay particular attention to "ins and outs".  Determine what fluids the patient has had, see if there is a history of poor po intake, or if the patient has been drinking excessive amounts of fluids.  Ask which fluids and foods the patient has been consuming.  Make note of any unusual feeding mechanisms such as parenteral nutrition.  On the output side, get a quantitative sense of what fluids have been lost.  Has the patient been vomiting, had diarrhea, lost blood, had an NG tube present to remove gastric secretions, sweated excessively?  How frequently and how much did the patient urinate?   Place all of this information in a time frame.

Physical:

The most direct way of demonstrating dehydration is to have a patient's weight before and after the onset of an acute disease.  Occassionally, this information can be obtained from parents who have brought their child for a well visit earlier in the week, or from the ER if the patient was seen previously.  The short-term loss of weight reflects lost fluid and can be used to classify the degree of dehydration.  Return to normal body weight can also be a useful indicator during fluid replenishment.  The following table lists the signs and symptoms of dehydration for infants and children:
 

Clinical Assessment of Severity of Dehydration
Percent Dehydration Infant Child Clinical Signs and Symptoms
Mild 5% 3-4% Increased thirst, tears present, mucous membranes moist, ext. jugular visible when supine, capillary refill > 2 seconds centrally, urine specific gravity > 1.020
Moderate 10% 6-8% Tacky to dry mucous membranes, decreased tears, pulse rate may be elevated somewhat, fontanelle may be sunken,oliguria, capillary refill time between 2 and 4 seconds, decreased skin turgor
Severe 15% 10% Tears absent, mucous membranes dry, eyes sunken, tachycardia, slow capillary refill, poor skin turgor, cool extremities, orthostatic to shocky, apathy, somnolence
Shock >15% >10% Physiologic decompensation: insufficient perfusion to meet end-organ demand, poor oxygen delivery, decreased blood pressure.
 
Labs:

The most helpful lab test is serum chemistry (an SMA-7 or CHEM-7).  From this, it is possible to determine if the dehydration is considered to be isotonic, hypernatremic or hyponatremic (see following pages), all of which require specific modes of therapy.

General Treatment Design:

In addition to addressing the cause of the dehydration, therapy involves three steps:

Immediate vascular expansion
Correction of fluid and electrolyte deficit
Maintenance fluids and electrolytes

Immediate vascular expansion:

As detailed on the previous page, IV fluid boluses can be given to rapidly expand circulating volume.  This should be a high priority if the patient appears moderate to severely dehydrated.  Often, the patient will look and feel much better after this simple maneuver; it also halts the patient's progression towards shock.  More than one fluid bolus may be required; however, if large amounts of fluid are given rapidly, signs of fluid overload, pulmonary edema and congestive heart failure should be monitored.

Correction of fluid and electrolyte deficit:

After the initial bolus is given and labs are obtained, a plan is devised to restore normal fluid and electrolyte status through administration of IV fluids.  Usually, this repletion takes place over 24 hours, but can occur over a longer period in special cases where too rapid a correction would be harmful (e.g., hypernatremic dehydration).

The amount of fluid to infuse over this period is the amount of fluid required for correction of the fluid deficit plus the amount of fluid required for simple maintenance over this period minus any amount of fluid that the patient has received as a bolus.  The examples on the following pages should make this more clear.

Maintenance fluid and electrolytes:

IV therapy is continued until the patient can acquire fluids and electrolytes by some other means.  During this period, blood chemistry is monitored intermittently and IV solutions are adjusted appropriately.
 
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Last modification: April 30, 1998