Medical Calculators for Paramedics and EMS

GCS is assessed rapidly at scene: Eye opening (spontaneous=4, to voice=3, to pain=2, none=1), Verbal response (oriented=5, confused=4, words=3, sounds=2, none=1), Motor response (obeys=6, localizes=5, withdraws=4, flexion=3, extension=2, none=1). GCS ≤8 = severe brain injury, indicates airway protection need. Key field consideration: intubation or sedation artificially lowers verbal and motor scores — document pre-intervention GCS. A drop of ≥2 points en route signals deterioration requiring immediate re-assessment and early notification to receiving facility.

Pre-hospital stroke screening tools (FAST — Face drooping, Arm weakness, Speech difficulty, Time to call 911; or Cincinnati Prehospital Stroke Scale) identify likely stroke. Any positive FAST finding warrants immediate stroke center notification. Time targets: door-to-CT ≤25 minutes, door-to-needle ≤60 minutes for tPA. The NIHSS is typically completed by ED staff, but knowing last-known-well time, blood glucose (rule out hypoglycemia), and anticoagulant use is critical pre-hospital information. Bypass non-stroke-capable hospitals when a comprehensive stroke center is within reasonable transport distance.

Shock Index = Heart Rate ÷ Systolic BP. Normal: 0.5–0.7. SI >1.0 indicates significant hemodynamic compromise and predicts need for massive transfusion in trauma. SI >1.4 is associated with high mortality and mandates aggressive resuscitation. In pregnancy, a shock index >0.9 after delivery suggests significant hemorrhage. The shock index detects instability earlier than SBP alone — a patient with HR 110 and SBP 110 (SI=1.0) is at higher risk than the normal BP implies.

The Broselow tape is the most accurate bedside weight estimator for children and should be used when available. When not available, use the APLS formula: for infants 0–12 months, weight (kg) ≈ (age in months + 9) ÷ 2; for children 1–5 years, weight (kg) = 2 × (age + 4); for children 6–12 years, weight (kg) = 3 × age + 7. Drug doses, fluid volumes, and defibrillation energy (4 J/kg) all depend on accurate weight. Always use lean body weight estimates — obesity in children may cause overdose if actual weight is used for resuscitation drugs.

The Rule of Nines divides the adult body into 9% regions: head and neck = 9%, each arm = 9%, chest = 9%, abdomen = 9%, upper back = 9%, lower back = 9%, each thigh = 9%, each lower leg = 9%, perineum = 1%. For irregular burns, the patient's palm (including fingers) ≈ 1% BSA and can be used to estimate scattered burns. Pre-hospital fluid resuscitation (Parkland formula: 4 mL × kg × %TBSA) should begin for burns >20% TBSA in adults. Avoid over-resuscitation — initiate IV access and transport without delay.

In the pre-hospital setting, target MAP ≥65 mmHg as a minimum perfusion threshold for most patients. For traumatic brain injury, target systolic BP ≥110 mmHg (equivalent to MAP ~75–80 mmHg) to maintain cerebral perfusion pressure. For hemorrhagic shock without TBI, permissive hypotension (SBP 80–90 mmHg) is acceptable until surgical hemorrhage control — aggressive fluid resuscitation can worsen coagulopathy. For septic shock, MAP ≥65 mmHg guides vasopressor initiation if available in advanced paramedic scope of practice.