Rapid Review·Cardiovascular
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HY Approach
T1Must knowApproach to Fluid Replacement
Focus on
Pick the fluid by the mechanism of loss — blood for bleeding, balanced crystalloid for everything else, small cautious boluses in a failing or obstructed heart — and know the two formulas the exam loves: Parkland for burns (timed from the burn, not arrival) and 4-2-1 for pediatric maintenance. Then check the line you placed.
Key takeaways
Choose the fluid by the mechanism of loss
| Situation | Initial replacement | Endpoint or caution |
|---|---|---|
| Major active hemorrhage | Balanced blood components 1:1:1, minimal crystalloid | Hemostasis; avoid dilution, hypothermia, hypocalcemia (Hypovolemic & Hemorrhagic Shock) |
| Vomiting, diarrhea, third spacing, diabetic ketoacidosis | Isotonic crystalloid (balanced solution or 0.9 percent saline) in 500 mL to 1 L boluses | Reassess perfusion, lungs and electrolytes after each bolus |
| Sepsis | 30 mL/kg balanced crystalloid within 3 hours, then norepinephrine if the mean arterial pressure is under 65 | Stop when non-responsive or overloaded (Distributive Shock) |
| Anaphylaxis | Rapid crystalloid boluses alongside epinephrine | Large volumes may be needed for capillary leak |
| Major burn | Lactated Ringer by the Parkland estimate | Titrate to urine output 0.5 mL/kg/h (1 mL/kg/h in children) |
| Cardiogenic or obstructive shock | Small 250 mL diagnostic bolus only if the right ventricle is preload-dependent (right-ventricular infarct, tamponade, embolism) | Large blind boluses worsen congestion (Cardiogenic Shock) |
| Hypernatremic dehydration | Isotonic bolus for shock, then slow hypotonic correction | Lower sodium by 10 to 12 mEq/L per day at most |
Balanced solutions (lactated Ringer, Plasma-Lyte)
preferred for large-volume resuscitation; less hyperchloremic acidosis and kidney injury than saline.0.9 percent saline
for hyponatremia, hypochloremic alkalosis (vomiting), traumatic brain injury (avoid hypotonic solutions), and in the same line as blood (Ringer's calcium can clot citrated blood).Children
avoid hypotonic maintenance fluids in hospitalized children (hyponatremia).Albumin
no survival advantage over crystalloid in most shock; used in cirrhosis (paracentesis, spontaneous bacterial peritonitis, hepatorenal syndrome).- Starches are harmful (kidney injury, bleeding).
Burns and children
Parkland formula
4 mL x weight (kg) x percent body surface area of lactated Ringer over 24 hours.- Half in the first 8 hours from the time of the burn, the rest over the next 16 hours.
- For burns of 20 percent or more in adults (10 percent in children); count only partial- and full-thickness burns (rule of nines; palm equals 1 percent), not superficial erythema.
Pediatric maintenance (the 4-2-1 rule)
per hour, 4 mL/kg for the first 10 kg, 2 mL/kg for the next 10 kg, 1 mL/kg for each kg above 20, isotonic with dextrose.- A 25 kg child: 40 + 20 + 5 = 65 mL/h.
Pediatric resuscitation boluses
20 mL/kg isotonic crystalloid (10 mL/kg in cardiogenic shock or diabetic ketoacidosis), repeated to 60 mL/kg with reassessment.Access in the right order
Two large-bore (14 to 16 gauge) peripheral intravenous lines
fastest for volume.Intraosseous
when peripheral access fails within minutes in a crashing patient (proximal tibia, distal femur, humeral head); any drug or blood can go through it.- Not into a fractured bone, infected skin, or a limb with a previous attempt.
A central venous catheter
for vasoactive infusions, irritant drugs, monitoring and long-term access; it is slower for volume (long and narrow) and must never delay resuscitation.Central line placement and checks
Placement
ultrasound guidance; the tip should sit in the lower superior vena cava near the cavoatrial junction, not looped into another vein or deep in the right atrium.- As on the Central venous catheter tip position (radiograph after landmark-guided or difficult insertion).
Complications
pneumothorax (subclavian more than internal jugular), arterial puncture, arrhythmia from a wire in the right atrium, air embolism (insert head-down), perforation with tamponade, thrombosis (femoral).Catheter-related bloodstream infection
remove the line and culture (Catheter-Related Bloodstream Infection).Monitoring the response
Dynamic beats static
passive leg raise, stroke volume or pulse-pressure variation, inferior vena cava collapsibility, urine output, lactate clearance, capillary refill.- Central venous pressure alone predicts fluid responsiveness poorly.
Reassess after every bolus
stop when the patient is no longer fluid-responsive or shows congestion (crackles, B-lines, a rising oxygen requirement).A 70 kg adult has partial- and full-thickness burns over 40 percent of the body. How much lactated Ringer is estimated for 24 hours, how fast in the first 8 hours, and what decides the actual rate?
Parkland: 4 x 70 x 40 = 11,200 mL over 24 hours, half (5,600 mL) in the first 8 hours from the time of the burn. The actual rate is titrated to urine output (0.5 mL/kg/h in adults).
How it's tested
A 70-kg man with 30% TBSA burns two hours ago: Parkland = 4 × 70 × 30 = 8,400 mL; 4,200 mL must be in by hour 8 after the burn — six hours remain, so ~700 mL/h; then titrate to urine output.
Maintenance rate for a 25-kg child: 65 mL/h by 4-2-1, isotonic with dextrose.
Bleeding patient on his third liter of saline, getting colder and more acidotic: stop the crystalloid — balanced blood products and source control.
Crashing patient, three failed peripheral IVs: intraosseous access now.
Sudden dyspnea and hypotension minutes after a subclavian line: pneumothorax (or perforation with tamponade) — examine, ultrasound, decompress.
Septic patient with MAP 55 after 30 mL/kg, crackles appearing: norepinephrine, not more fluid.
Go deeper
Guidelines: ACS Trauma Quality Programs Best Practices Guidelines · 2026 Surviving Sepsis Campaign Adult Guidelines
Related Step 2 pages: Approach to Shock, Hypovolemic & Hemorrhagic Shock, Distributive Shock, Cardiogenic Shock, Catheter-Related Bloodstream Infection
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