Crystalloids and colloids

Crystelloids & Colloids

• Septic shock: Balanced fluids (RL, Plasma-Lyte) > NS

• Trauma with hypotension: 1:1:1 blood products, not crystalloids

• Burns: RL preferred

• DKA: NS first, then balanced fluids

• Cirrhosis: Albumin in SBP / post-paracentesis / hepatorenal syndrome

• Crystalloids expand ECF, and colloids expand plasma

• D5W = “IV free water” after glucose is metabolised.

• Hypertonic saline shifts water from ICF → ECF.

• Fluid given ≠ intravascular volume gained (NS: only 1/4 stays intravascular)

• 0.9% NS --> hyperchloremic acidosis + kidney vasoconstriction

• HES colloids -->  renal injury + coagulopathy

Crystalloids fill space (→ diffuse everywhere ECF), & Colloids generate oncotic pull → stay mainly in vessels (unless capillary leak)

NS versus Balanced Crystalloids: 

• NS has a high chloride load, causing hyperchloremic acidosis. In the kidney,  Cl⁻ excretion ↑  → ↓ HCO₃⁻ (exchange at DCT) → acidosis & ↓ renal blood flow via afferent vasoconstriction (TGF mechanism)

  • • • • • TGF: ↑ NaCl (NS load) --> MD mediator is adenosine --> constrict GFR

↓ NaCl (hypovolemia) --> MD mediator is Prostaglandins --> dilate GFR

• Balanced crystalloid (RL, Plasma-Lyte); Cl- is closer to plasma, less acidosis and better kidney outcome. Mortality benefit in septic shock (SMART trial)

RL versus Plasma Lyte:

Plasma-Lyte:

• Very close to plasma composition

• Neutral pH

• No calcium → safe with blood transfusions and ceftriaxone

• Buffer works in shock without relying on the liver

RL:

• Hypotonic → can lower sodium slightly

• Contains Ca → incompatible with citrate blood in the same line

• Lactate metabolism may lag in severe shock/liver failure

• Lactate level on labs may rise (cosmetic lab issue, not true worsening)

Plasma-Lyte is physiologically better than Ringer’s Lactate in biochemical precision, kidney protection, and shock physiology.

Tonicity:

• Tonicity moves water. Osmolarity doesn’t.

• D5W = water, not resuscitation fluid.

• NS causes hyperchloremic acidosis in large doses.

• Balanced crystalloids protect the kidneys.

• Hypertonic saline shrinks the brain.

Points:

• If shock → think perfusion, not sodium.

• If hypernatremia → think water, not ECF volume.

• If DKA → resuscitation first, free water later.

• If ileostomy → replace Mg, not just Na/K.

• If burns → use RL, NS makes acidosis worse.

• If pancreatic/biliary leaks → replace base losses with balanced crystalloid.

• Shock ≠ fluids. Shock = perfusion failure.

• Fluids are a medication — administer only when necessary.

• PLR is the stethoscope of fluid management.

• CVP alone is useless for deciding fluids.

• Non-responsive shock → early norepinephrine saves lives.

• RL does NOT worsen lactic acidosis in sepsis or DKA.

• Never give hypotonic fluids in raised ICP.

• Large-volume NS → hyperchloremic metabolic acidosis.

• Shock + fluid nonresponsive → pressors, not more fluids.

• DKA = NS first, then balanced fluids, then D5W.

• Blood loss → blood products, not crystalloids.

• Albumin is a treatment (not maintenance) in cirrhosis.

Fluid responsiveness and dynamic assessment:

1. Passive Leg Raise (PLR) — best bedside test

   1. • Autotransfusion of ~300 mL from legs → central circulation

      • If pulse pressure ↑ ≥ 10% or CO ↑ ≥ 10% → patient is responsive

2. Stroke Volume Variation (SVV) / Pulse Pressure Variation (PPV)

Works only if:

2. 1. • Mechanically ventilated

      • Sinus rhythm

      • Tidal volume ≥ 8 mL/kg

      • Poor in obesity, high PEEP, RV failure

      • Parameter Interpretation

        1. SVV > 13% Fluid responsive

PPV > 13% Fluid responsive

2. 1. • 2. If SVV/PPV is low → don’t give fluids.

Do not give more fluids if:

• Lungs: ↑ oxygen demand, crackles, CXR edema

• Heart: no MAP gain

• Kidneys: ↓ urine output despite rising MAP

• Labs rising lactate after fluids