Setting the Drip Rate When the Ward Has Two Kinds of IV Set
A 24-year-old man weighing 60 kg is admitted to the male medical ward of a district hospital in Jharkhand with a two-day history of profuse watery diarrhoea and repeated vomiting. A health card he carries records his usual weight as 63 kg. On admission he is drowsy, has dry mucous membranes, and has passed no urine for eleven hours. The duty doctor writes: Ringer lactate 1000 mL intravenously over 8 hours, then 500 mL over the next 4 hours, then review. The ward trolley holds two kinds of administration set: an older batch printed '15 drops = 1 mL' and a new consignment printed '20 drops = 1 mL'. The outgoing shift used the 15-drop set for a similar infusion an hour ago, and both types are now mixed in the same drawer. The family is asking how long the first bottle will take.
1. Calculate the drip rate in drops per minute for both prescribed phases using the 20 drops/mL set, and state whether one setting can serve both phases.
Read the worked answer
Phase 1: 1000 mL in 8 h = 125 mL/h = 125/60 = 2.083 mL/min. Drops/min = 2.083 × 20 = 41.7 → 42 drops/min (round to the nearest whole drop; a fraction of a drop cannot be counted).
Phase 2: 500 mL in 4 h = 125 mL/h - identical to phase 1, so the rate is again 42 drops/min.
Judgement point: both phases happen to have the same mL/h, so no rate change is required at the changeover; only the volume and the review time differ. That is worth checking before assuming a new rate must be set. The reasoning sequence should always be volume ÷ time → mL/h → mL/min → multiply by the drop factor printed on the set actually hanging. Also note the rate must be counted with a watch over a full minute, not estimated by eye, because a 10% error over 8 hours is 100 mL.
2. Estimate the patient's fluid deficit and compare it with the 1500 mL prescribed over 12 hours. What should the nurse monitor and report?
Read the worked answer
Weight loss = 63 − 60 = 3 kg, and 1 kg of acute loss is roughly 1 litre, so the deficit is about 3000 mL. Maintenance for a 60 kg adult is about 30–35 mL/kg/day = 1800–2100 mL/day, i.e. roughly 900–1050 mL over 12 hours.
So the 12-hour requirement is around 3000 mL (deficit, replaced at a safe rate) plus about 1000 mL maintenance, plus ongoing diarrhoeal and vomit losses - far more than the 1500 mL ordered. The prescription is a cautious starting order, not a completed resuscitation.
What to monitor: hourly pulse, blood pressure, respiratory rate, mucous membranes, and above all hourly urine output, with a target of at least 0.5 mL/kg/h (about 30 mL/h). Report a falling urine output, rising pulse, or any sign of overload - basal crackles, breathlessness, raised jugular venous pressure - especially once urine flow starts, because the same infusion that is too little now can become too much in an hour.
3. The nurse finds a set marked 15 drops/mL in the drawer and considers using it, since it is what the previous shift used. Analyse the consequence of keeping the same 42 drops/min setting.
Read the worked answer
With a 15 drops/mL set, 42 drops/min delivers 42/15 = 2.8 mL/min = 168 mL/h, not 125 mL/h.
1000 mL would then finish in about 1000/168 = 5.95 hours instead of 8 - roughly 25% faster, an extra 340 mL in the eight-hour period. In a drowsy, dehydrated adult that is not automatically dangerous, but in an infant, an elderly patient, or anyone with cardiac or renal impairment the same error can precipitate circulatory overload and pulmonary oedema.
The correct judgement is procedural, not arithmetic: the drop factor must be read from the packaging of the set physically connected to the patient, and the rate recalculated every time a set is changed. If a 15-drop set is used, 125 mL/h corresponds to 15 × 2.083 = 31.2, i.e. 31 drops/min. Two sets with different drop factors must never be stored loose in the same drawer, since the wrong set is then picked by habit.