**Question:** ORS required during 4 hours in a 20 kg child

**Core Concept:** Oral Rehydration Solution (ORS) is a solution used to rehydrate patients suffering from dehydration due to diarrhea and vomiting. It helps to replace fluids, electrolytes, and sugar lost during diarrhea and vomiting, thereby aiding in rapid rehydration and preventing further fluid and electrolyte imbalances.

**Why the Correct Answer is Right:** In the given scenario, we are calculating the total volume of fluids required for rehydration over a 4-hour period in a 20 kg child. First, we need to determine the total fluid deficit and then calculate the volume of ORS required to replace this deficit.

For a 20 kg child, the total body water (TBW) is approximately 20 kg x 0.07 (0.07 is the proportion of TBW that is extracellular fluid). TBW is approximately 1.4 L.

The fluid loss in a 20 kg child due to diarrhea is approximately 500 mL/day. Over a 4-hour period, this loss is approximately:

1.5 hours x 500 mL/hour = 750 mL

Now, we need to calculate the volume of ORS required to replace the fluid deficit:

1.4 L (TBW) x 750 mL (fluid loss) = 1050 mL

**Why Each Wrong Option is Incorrect:**

A. This option does not take into account the fluid loss due to diarrhea, which is essential to determine the total fluid deficit and proper rehydration.

B. This option provides an incorrect rehydration rate (200 mL/kg body weight/hour), which is not based on the actual fluid loss and may lead to inadequate rehydration.

C. This option is incorrect as it directly calculates ORS volume without considering the actual fluid loss and may result in overhydration or underhydration.

D. This option is incorrect as it does not consider the fluid loss due to diarrhea and may result in inadequate or excessive rehydration.

**Clinical Pearl:**

The correct rehydration rate is approximately 20-25 mL/kg body weight/hour, considering the fluid loss due to diarrhea and vomiting. Based on the given scenario, we calculated the volume of ORS required to be 1050 mL over 4 hours, ensuring appropriate rehydration and preventing complications. It highlights the importance of considering fluid loss due to diarrhea when determining the rehydration rate and volume.

Remember, the main goal of rehydration is to achieve euvolemia (normal body fluid balance) while maintaining electrolyte balance.