The body can lose fluids through a variety of ways.  The most common include vomiting, diarrhea, and acute bleeding.  When there is inadequate fluid in the body, cells lose their ability to function, and blood doesn’t circulate well.

The main symptom of dehydration is dizziness upon getting up to stand.  Since there isn’t enough fluid for blood circulation to react well, blood pressure drops, and the brain doesn’t get its blood soon enough.  Other dehydration symptoms include thirst, fatigue, not urinating for 6-8 hours, nausea, and irritability or lethargy  in children.

The main physical finding that suggests Dehydration is a rapid pulse (esp. if >110 in an adult).ย  Worse cases also have low blood pressure.ย  But if these vital signs are normal, we can identify Dehydration by checking for an increase in heart rate (pulse) and a fall in blood pressure from lying to standing (when blood pressure drops, the heart rate reflexively speeds up).ย  This is called Checking Postural (or Orthostatic) Vital Signs:

  1. First we have the patient lie down for 5 minutes to normalize blood pressure and pulse.
  2. We count their heart rate (take the pulse) and take their blood pressure.  Heart Rate is most accurately by listening with stethoscope (instead of feeling for a pulse at the wrist).
  3. We have them abruptly stand up, without sitting first.  We keep them standing 2-3 minutes (staying right beside them, in case they might fall).
  4. We count the heart rate and take the blood pressure again

We consider their heart rate abnormal if it increases by 20% (1/5) or more.  The blood pressure is abnormal if  the difference between systolic & diastolic (top & bottom numbers) narrows, like 120/80 becomes 110/90, or more so if both systolic & diastolic numbers fall significantly.

Medicines like beta-blockers (propranolol [Inderalยฎ], metoprolol, atenolol, etc.) will interfere with assessment of heart rate (they keep the pulse slow).ย  Another key finding for Dehydration is a very high specific gravity (means a very concentrated urine) if we do a simple Urinalysis.

Treatment of Dehydration obviously involves determining and treating its cause.  But at the same time (or in the meantime), replacing fluids is key (rehydration).  We often do this with IV’s.  If that’s not available, or especially for children with diarrhea, we can give constant sips of special rehydration fluid every 15-20 minutes (giving too much at once may provoke vomiting, which defeats the purpose) (giving only lots of plain water can cause low sodium, and seizures).

Depending on the cause, we need to keep close follow-up whenever we give somebody IV fluids for dehydration.ย  They may feel a lot better when they leave, but everything can happen again the next day.ย  This is especially true for dehydration from vomiting, since the patient won’t be able to keep liquids down.ย  However, I’ve seen a number of patients with dehydration from diarrhea, then the dehydration itself made them vomit.ย  In that case, the IV fluids stop the vomiting, & the person can keep drinking liquids.

See a Precautionary Tale for a case of Dehydration. Clinicians learn best from adverse outcomes; we just hope that they’re someone else’s.

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