01The three fluid families
- Crystalloids — routine OR fluids: lactated Ringer's (LR), normal saline (NS), Plasma-Lyte.
- Colloids — pull fluid into the intravascular space for volume: albumin, hetastarch.
- Blood products — replace lost blood and clotting components.
| Blood product | Holds | Notes |
|---|---|---|
| Packed red cells (PRBC) | Oxygen-carrying cells | Kept cold → warm through a fluid warmer; filtered tubing; pump OK |
| Platelets | Platelets | Room temp; filtered, by gravity (pumps destroy them) |
| Fresh frozen plasma (FFP) | Clotting factors | |
| Cryoprecipitate | Fibrinogen |
Give blood through a line primed with normal saline (or another compatible isotonic) — not LR, whose calcium can promote clotting in the tubing.
02Maintenance & deficit math
Maintenance — the 4-2-1 rule (mL/kg/h): 4 for the first 10 kg, 2 for the next 10 kg, 1 for every kg after. - A 70 kg adult: (4×10) + (2×10) + (1×50) = 110 mL/h. - Shortcut for adults > 20 kg: weight (kg) + 40.
Deficit — what they're "behind" from being NPO = maintenance rate × hours without fluid, capped at ~8 hours (most people concentrate urine and don't accrue more than ~8 h of deficit). - That 70 kg patient overnight ≈ 110 × 8 ≈ 880 mL.
Replace the deficit during surgery: ½ in the first hour, ¼ in the second, ¼ in the third — on top of ongoing maintenance.
03Surgical losses & blood replacement
Add ongoing third-space / evaporative losses by case size:
| Surgery | Extra fluid |
|---|---|
| Superficial | ~2 mL/kg/h |
| More invasive | ~4 mL/kg/h |
| Open bowel | ~6 mL/kg/h |
Replacing measured blood loss (per mL lost): - ~3 mL crystalloid per 1 mL blood, or - ~1 mL colloid per 1 mL blood, or - ~1 mL PRBC per 1 mL blood.
- Warm large-volume and rapid fluids — and all blood — to avoid hypothermia and its coagulation/drug effects.