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💧 Fluids at a glance
What is actually in a bag of Hartmann's, and the potassium rules
Per litre, and worth knowing because the composition explains the complication. 0.9% saline has half again the chloride of plasma, which is where hyperchloraemic acidosis comes from after several litres.
5% dextrose is free water in disguise. The glucose is metabolised within minutes and what is left distributes through total body water — so it is a poor resuscitation fluid and a fast way to drop the sodium.
Composition, mmol/L
| Plasma (for comparison) | Na 135–145 · K 3.5–5.3 · Cl 95–108Osmolality 275–295 mOsm/kg. |
|---|---|
| 0.9% sodium chloride | Na 154 · Cl 154Osmolarity ~308. No potassium, no buffer. Chloride well above plasma. |
| Hartmann's / compound sodium lactate | Na 131 · K 5 · Ca 2 · Cl 111 · lactate 29Osmolarity ~278. The lactate is a bicarbonate precursor, not a marker of hypoperfusion. |
| Plasma-Lyte 148 | Na 140 · K 5 · Mg 1.5 · Cl 98 · acetate 27 · gluconate 23The closest to plasma. Calcium-free, so compatible with blood products. |
| 5% glucose | Glucose 50 g · no electrolytesOsmolarity ~278 in the bag, effectively free water in the patient. |
| 0.18% saline / 4% glucose | Na 31 · glucose 40 gA maintenance fluid. Not for resuscitation, and a well-known cause of hyponatraemia if run hard. |
| 4.5% human albumin | Na ~140 · Cl ~128Specific indications — ascites drainage, SBP, hepatorenal. Not a routine resuscitation fluid. |
Potassium — the rules that stop a cardiac arrest
| Peripheral line, maximum | 40 mmol/LHigher concentrations are for a central line. A peripheral 40 mmol bag stings and often needs slowing. |
|---|---|
| Ordinary ward, maximum rate | 10 mmol/hourWhich is why a 40 mmol litre bag runs over four hours, not two. |
| Faster than 10 mmol/hour | Monitoring + central accessContinuous cardiac monitoring and a higher-care area. Not a decision to make alone on a ward at night. |
| Never | Undiluted potassium, IV pushConcentrated potassium ampoules have caused deaths. Use pre-mixed bags wherever one exists. |
Which one, roughly
| Resuscitation | Balanced crystalloidHartmann's or Plasma-Lyte, 500 ml over less than 15 minutes, then reassess. |
|---|---|
| Maintenance | 25–30 ml/kg/day waterWith ~1 mmol/kg/day each of Na, K and Cl, and 50–100 g/day glucose. The Maintenance fluids calculator does the arithmetic. |
| Hyperkalaemia | Avoid Hartmann's by reflex onlyIt contains 5 mmol/L of potassium, but it is not a meaningful load. Do not withhold resuscitation fluid over it. |
| With blood products | Not calcium-containingHartmann's has calcium, which can clot citrated blood in the line. Saline or Plasma-Lyte. |
Prescribe fluids the way you prescribe drugs: for a reason, at a dose, with an endpoint and a review time. "1L stat" with no reassessment is how a breathless patient gets a second litre.
The commonest inpatient fluid error is not the wrong bag, it is continuing to give one nobody has looked at since admission. Check the chart before adding to it.
Source: NICE CG174 IV fluid therapy in adults; BNF; manufacturer summaries of product characteristics