In a child with acute diarrhea, dehydration — the loss of body water, and with it plasma volume — is what turns an ordinary illness into a dangerous one. Bedside assessment has two jobs. The first is to grade how much fluid has been lost, so that the rehydration plan matches the deficit. The second is to identify the sodium pattern — whether the serum sodium is likely to be high, normal or low — because that decides how quickly the deficit may be corrected without causing harm.
Grading the deficit
The best single measure of dehydration is the percentage of body weight lost, which requires a reliable pre-illness weight. Classification into no or minimal, mild-to-moderate and severe dehydration is the essential basis for choosing treatment, and the guideline grades that statement as a strong recommendation.
In practice the pre-illness weight is often unknown, and no laboratory test estimates the percentage accurately. Clinical tests of dehydration are imprecise and show only fair-to-moderate agreement between examiners, so the grade is a considered judgement built from several signs rather than a reading off one of them.
What each degree looks like
The features below are the conventional clinical picture. They describe a continuum; a validated scoring tool, the Clinical Dehydration Scale, is what should be relied on for grading. Two of the signs need a word of explanation. Capillary refill is the time it takes for colour to return to a patch of skin after it has been pressed pale. Skin turgor is how quickly a pinched fold of skin flattens again.
| Finding | No or minimal dehydration | Mild-to-moderate dehydration | Severe dehydration |
|---|---|---|---|
| General appearance | Normal | Thirsty, restless or tired, irritable | Drowsy, limp, apathetic or unconscious |
| Tears | Present | Reduced | Absent |
| Oral mucosa | Moist | Dry | Very dry |
| Capillary refill | Normal | Prolonged | Prolonged, markedly delayed |
| Eyes | Normal | Sunken | Very sunken |
| Skin turgor | Returns immediately | Returns slowly | Returns very slowly |
| Peripheral perfusion | Warm | Cool | Cool, mottled, cyanotic |
| Urine output | Normal | Reduced | Minimal |
The signs that carry the most weight
Because the grade is built from several signs, it helps to know which of them carry the most information. A useful operational threshold comes from a prospective study of 186 children aged 1 month to 5 years. Dehydration was defined as a deficit of at least 5% of body weight, and a subset of four findings — capillary refill longer than 2 seconds, absent tears, dry mucous membranes and an ill general appearance — predicted that deficit as well as the full set of ten signs did. The presence of two or more of those four findings indicated a deficit of at least 5%.
Individual findings in that study had generally low sensitivity and high specificity: many dehydrated children lacked any given sign, but a sign that was present seldom occurred in a child who was not dehydrated. That is the underlying reason any single sign is unreliable on its own. Among individual examination signs, the three that assess dehydration best are prolonged capillary refill time, abnormal skin turgor and abnormal respiratory pattern.
The Clinical Dehydration Scale
Where a numerical grade is wanted, the Clinical Dehydration Scale is the tool the guideline points to. It has four items, each scored 0 to 2, giving a total from 0 to 8:
| Item | 0 | 1 | 2 |
|---|---|---|---|
| General appearance | Normal | Thirsty, restless, or lethargic but irritable when touched | Drowsy, limp, cold or sweaty, with or without coma |
| Eyes | Normal | Slightly sunken | Extremely sunken |
| Mucous membranes (tongue) | Moist | Sticky | Dry |
| Tears | Present | Decreased | Absent |
A score of 0 means no dehydration, 1–4 means some dehydration, and 5–8 means moderate to severe dehydration. The scale predicts the need for intravenous rehydration, weight gain, blood testing, admission and length of stay, with moderate-to-good agreement between observers. It is a weak recommendation on low-quality evidence, and it should be used alongside the rest of the assessment rather than instead of it. No single scoring system has been shown to be superior in every setting, and different tools suit outpatient and inpatient use.
Recognising an abnormal sodium
Once the grade is set, the next question is the serum sodium, because a sodium that is too high or too low changes the safe rate of correction before it changes anything else.
Hypernatremic dehydration — a serum sodium above 145 mmol/L — is uncommon in acute gastroenteritis, ranging from under 1% to 4% of cases depending on the setting. It is dangerous partly because it is under-recognised: the usual clinical signs are less prominent, so the degree of dehydration is easily underestimated. Infants, mainly those under 6 months, may instead show doughy skin, tachypnea, and neurological signs — increased muscle tone, hyperreflexia, convulsions, drowsiness or coma. A child who looks relatively preserved while being severely dehydrated should raise the possibility rather than lower it.
Hyponatremia, a low serum sodium, matters in the opposite direction. Hypotonic intravenous solutions — fluids more dilute than plasma — increase the risk of acute hyponatremia, and in one retrospective series 19% of children who were normonatremic (with a normal sodium) on admission developed mild hyponatremia during treatment. This is why isotonic fluid, matched in concentration to plasma, is recommended for initial rehydration in most cases.
The severity grade and the sodium pattern together shape Rehydration Management in Acute Diarrhea, and the escalation decision is acted on in Admission and Shock Management in Acute Diarrhea. The bedside can raise the suspicion of an abnormal sodium, but only a blood measurement gives its value — which leads to the question of when a blood or stool test is worth sending at all, taken up in Investigations in Acute Diarrhea and Dehydration.