Pediatric Anesthesia Calculator

Airway Equipment Sizing

Fluid & Blood Loss Requirements

Normal Physiological Values

Toxicity Meter (Real-time)

Maximum Dose Reference Table

L.A.S.T. Rescue (20% Intralipid)

Caudal & MLAD Calculator

Drug Calculations

Infusion Calculations

Infusion Rate Calculator

Antibiotics

A Deeper Dive into Pediatric Calculations

The axiom "children are not small adults" is the guiding principle of pediatric anesthesia. A child's physiology is in a constant state of change. Factors like a higher metabolic rate, larger body surface area-to-weight ratio, immature organ function, and different body compositions (e.g., higher total body water) drastically alter pharmacokinetics (what the body does to a drug) and pharmacodynamics (what the drug does to the body).

For this reason, precise, weight-based calculations are the foundation of safety. This guide provides context for some of the most common formulas used in daily practice.

Fluid and Blood Management

Maintenance Fluid Rate (The "4-2-1" Rule)

The Holliday-Segar ("4-2-1") rule estimates the hourly fluid required to replace basal losses for a 24-hour period. It is the foundation for calculating both maintenance infusions and fasting deficits.

• First 0-10 kg of body weight: 4 mL/kg/hr
• Next 10-20 kg of body weight: 2 mL/kg/hr
• For weight > 20 kg: 1 mL/kg/hr

NPO Fasting Guidelines (The '2-4-6' Rule)

This safety standard is designed to minimize the risk of pulmonary aspiration of stomach contents while also preventing dehydration. The "2-4-6" rule is a common mnemonic:

• 2 Hours: Clear liquids (water, pulp-free juice)
• 4 Hours: Breast milk
• 6 Hours: Formula, non-human milk, light meal (e.g., toast, cereal)
• 8 Hours: Heavy, fatty, or fried meal

Fasting Fluid Deficit

Patients are NPO (nil per os) before surgery, creating a fluid deficit. This is calculated as:

This deficit is often replaced intraoperatively, typically by giving 50% in the first hour, 25% in the second hour, and 25% in the third hour, in addition to ongoing maintenance fluids.

Estimated Blood Volume (EBV)

A child's blood volume (in mL/kg) is higher than an adult's (65-70 mL/kg) and varies significantly with age. This is critical for estimating MABL.

Maximum Allowable Blood Loss (MABL)

This formula estimates the volume of blood loss (in mL) that can be tolerated before the patient's hemoglobin (Hb) reaches a pre-determined "target" level, often 8-10 g/dL. This calculator uses the initial Hb (Current Hb) for this formula.

Airway Management Formulas

Endotracheal Tube (ETT) Sizing (Age > 1 Year)

ETT size is based on the internal diameter (ID) in millimeters. Formulas provide an estimate; the correct size must be confirmed by assessing for an audible air leak around the tube.

Historically, uncuffed tubes were preferred due to the belief that the cricoid cartilage provided a natural "cuff." However, modern, high-volume, low-pressure cuffed tubes are now widely used as they offer a more reliable seal, reduce anesthetic gas pollution, and may lower aspiration risk.

• Uncuffed ETT Size (Cole's Formula): (Age in years ÷ 4) + 4
• Cuffed ETT Size: (Age in years ÷ 4) + 3.5 (or 0.5 mm smaller than uncuffed)

ETT Insertion Depth (Oral)

These are estimates. Tube placement must always be confirmed clinically (bilateral breath sounds, chest rise) and with end-tidal capnography.

• For Neonates: Weight (kg) + 6 = Depth (cm at lip)
• For Children (>1 year): ETT Internal Diameter (mm) × 3 = Depth (cm at lip)

Supraglottic Airway (LMA/i-gel) Sizing

Unlike ETTs, supraglottic airways are sized based on weight categories, which vary slightly by brand. A common approximation is:

Drug Dosing & Emergency

The Weight-Based Dosing Principle

All dosing is in mg/kg or mcg/kg. A simple "decimal point error" (e.g., 10 mcg/kg vs 1.0 mcg/kg) can be catastrophic, especially with potent drugs. For neonates and small infants, doses are often drawn up in a 1 mL syringe to improve accuracy. Understanding drug concentration (e.g., mg/mL) is as important as the dose itself.

Key PALS Emergency Medications

• Epinephrine (Cardiac Arrest): 0.01 mg/kg (or 10 mcg/kg). This is 0.1 mL/kg of the 1:10,000 (0.1 mg/mL) concentration.
• Atropine (Symptomatic Bradycardia): 0.02 mg/kg (or 20 mcg/kg).
  • Minimum dose: 0.1 mg (to prevent paradoxical bradycardia).
  • Maximum single dose: 0.5 mg in children, 1 mg in adolescents.

Maximum Local Anesthetic Doses

Adhering to these limits is essential to prevent LAST (Local Anesthetic Systemic Toxicity), a life-threatening emergency. All areas using local anesthetics should have a LAST rescue kit, including 20% Intralipid emulsion.

Emergency Defibrillation Energy

In a pediatric cardiac arrest (VF/pVT), the energy dose is weight-based.

• Initial Shock: 2 Joules/kg
• Subsequent Shocks: Escalate to 4 Joules/kg

Malignant Hyperthermia (MH) Crisis

MH is a hypermetabolic crisis triggered by volatile anesthetics (e.g., Sevoflurane) or Succinylcholine. Immediate recognition is key.

• Triggers: Hypercarbia (early sign), Tachycardia, Muscle Rigidity, Hyperthermia (late sign).
• Action: Stop volatile agents, hyperventilate with 100% O2, administer Dantrolene, cool patient.

Laryngospasm Management

A common pediatric airway emergency, often occurring during light planes of anesthesia (induction/emergence).

• Step 1: 100% Oxygen, CPAP, Jaw Thrust (Larson's maneuver).
• Step 2 (If Hypoxia): Propofol (0.5-1 mg/kg) IV.
• Step 3 (Refractory): Succinylcholine (0.5-1 mg/kg IV or 4 mg/kg IM) + Atropine.

Frequently Asked Questions (FAQs)

Sources for Further Reading

• Holliday-Segar Method: ncbi.nlm.nih.gov/books/NBK532305/
• Pediatric Airway Formulas: pmc.ncbi.nlm.nih.gov/articles/PMC9663958/
• MABL and Fluid Management: mdcalc.com/calc/3905/maximum-allowable-blood-loss
• PALS Guidelines (AHA): AHA Circulation Guidelines (2020)
• Local Anesthetic Systemic Toxicity (LAST): lipidrescue.org

Clinical Reference Guide & Pharmacology Notes

Pediatric Pharmacokinetics

Dosing in neonates and infants requires adjustment not just for weight, but for physiological maturity. This calculator accounts for standard weight-based dosing (mg/kg). Clinicians must be aware that:

• Total Body Water: Neonates have 70-80% water content compared to 60% in adults, requiring higher loading doses for water-soluble drugs (e.g., Succinylcholine).
• Protein Binding: Lower albumin levels in infants lead to higher fractions of free (active) drug for highly protein-bound agents (e.g., Bupivacaine, Propofol).
• Clearance: Hepatic and renal function are immature at birth. Maintenance intervals for drugs like antibiotics or muscle relaxants may need extension in neonates.

Safety in Emergency Algorithms (PALS)

During critical events like Cardiac Arrest, SVT, or Anaphylaxis, cognitive load is high. This tool digitizes the 2020-2025 AHA PALS algorithms.

Key Considerations:
1. Epinephrine: The calculator distinguishes between Cardiac Arrest (10 mcg/kg) and Anaphylaxis/Hypotension doses to prevent 10-fold dosing errors.
2. Defibrillation: Energy selection (2 J/kg initial, 4 J/kg subsequent) is critical for shockable rhythms (VF/pVT).
3. Adenosine: Rapid administration via a proximal vein is required due to its half-life of <10 seconds.

Airway Equipment Selection

Proper sizing of the Endotracheal Tube (ETT) and Supraglottic Airway (LMA/i-gel) reduces the risk of subglottic stenosis and aspiration.

• Cuffed vs. Uncuffed: Modern pediatric practice favors cuffed tubes (Microcuff) even in infants, provided cuff pressure is monitored (< 20 cmH2O).
• Blade Selection: A straight (Miller) blade is often preferred in infants < 2 years to lift the floppy, U-shaped epiglottis.