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Mechanical Ventilator - Comprehensive Guide (EMT/Paramedical Level)

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1. BASIC PHYSIOLOGY YOU MUST KNOW

Minute Volume (VE)

• Normal VE = 7-10 L/min
• VT = Alveolar Volume (VA) + Dead Space Volume (VDS)
• Anatomic dead space ~ 2.2 mL/kg lean body weight (trachea + larger airways)
• Alveolar ventilation determines PaCO2 (carbon dioxide in blood)

Key Pressure Concepts

• Stiffer lungs (low compliance) = higher pressures for same volume
• Bigger volume = higher pressure

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2. VENTILATOR SETTINGS (Key Parameters)

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3. VENTILATOR MODES

A. Spontaneous / Support Modes

• Patient triggers every breath; ventilator adds a set pressure boost
• Patient controls rate and tidal volume
• No set respiratory rate (backup apnea rate present)
• Used for: weaning, alert/breathing patients

• Constant positive pressure throughout breathing cycle
• Patient breathes spontaneously against set pressure
• Used for: sleep apnea, mild respiratory failure, post-extubation support

• IPAP (inspiratory) + EPAP (expiratory) pressures set separately
• IPAP initial: 10-25 cm H2O | EPAP initial: 5-8 cm H2O
• PSV = IPAP - EPAP (the support given to each breath)
• Titrate FiO2 to maintain SpO2 86-92%

B. Mandatory (Machine-Controlled) Modes

• Ventilator delivers a set tidal volume regardless of pressure needed
• Clinician sets: VT, RR, FiO2, PEEP, flow rate
• Advantage: guaranteed volume delivery
• Risk: pressure can spike if lungs become stiffer

• Ventilator delivers gas to a set pressure; volume varies with compliance
• Clinician sets: pressure target, RR, FiO2, PEEP
• Advantage: safer pressures, better for stiff lungs
• Risk: VT drops if compliance worsens

• Every patient breath triggers a full machine-assisted breath
• Machine also delivers breaths if patient doesn't breathe at set rate
• Most common initial mode in emergency/ICU
• Can be used with VCV (AC-VCV) or PCV (AC-PCV)

• Machine delivers set number of mandatory breaths synchronized with patient effort
• Patient can breathe spontaneously between mandatory breaths
• Add PSV on top of SIMV for patient comfort

C. Advanced/Specialty Modes

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4. INITIATING MECHANICAL VENTILATION

Indications

• Respiratory or cardiac arrest
• Coma / altered consciousness
• Refractory hypoxemia (SpO2 < 90% despite O2)
• Severe respiratory acidosis
• Paradoxical breathing / impending fatigue
• Failure of non-invasive ventilation

RSI (Rapid Sequence Intubation) for Asthma/Bronchospasm

• Ketamine 1-2 mg/kg - preferred induction (bronchodilator + sympathomimetic)
• Propofol 1.5-2 mg/kg - alternative (bronchodilator but can cause hypotension)
• Succinylcholine 1.5 mg/kg OR Rocuronium 1 mg/kg for paralysis
• Use large ETT ≥ 8.0 mm to allow suctioning and bronchoscopy

Initial Settings for a Standard Adult Patient

• RR: 10-14 | VT: 7-8 mL/kg IBW | PEEP: 5 | FiO2: 100%
• Flow rate: 60 L/min | Waveform: Decelerating

• RR: 12-16 | Pressure high: ~20 cm H2O | PEEP: 5 | FiO2: 100%
• Monitor VT obtained; adjust pressure to achieve ~7-8 mL/kg IBW

• Low-high approach: IPAP 10 / EPAP 5 / FiO2 100%, titrate IPAP up
• High-low approach: IPAP 20-25 / EPAP 5 / FiO2 100%, titrate down
• Reassess at 30 minutes; check ABG within 1-2 hours

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5. VENTILATOR EMERGENCIES & TROUBLESHOOTING

The DOPES Mnemonic (Sudden Deterioration on Ventilator)

Alarm Troubleshooting Table

Hypotension on Ventilator

1. Auto-PEEP / air trapping - most common in asthma/COPD
   • Action: Disconnect patient from ventilator for 20-30 seconds to allow full expiration; reduce RR; increase flow rate
2. Tension pneumothorax
   • Action: Needle decompression (2nd ICS MCL or 4th-5th ICS AAL)
3. Decreased venous return from high PEEP/hyperinflation
4. Volume depletion (give IV fluids)
5. Sedative-induced vasodilation

Barotrauma

• Prevention: Keep plateau pressure < 30 cm H2O, tidal volume 6-8 mL/kg IBW
• Permissive hypercapnia (accept higher CO2 to keep pressures safe) - especially in asthma/ARDS

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6. LUNG-PROTECTIVE VENTILATION (Critical Concept)

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7. WEANING FROM VENTILATOR

When to Consider Weaning

• Underlying cause of respiratory failure is resolving
• Patient is awake, following commands
• Hemodynamically stable (minimal/no vasopressors)
• FiO2 ≤ 40-50% and PEEP ≤ 5-8 cm H2O
• Adequate oxygenation (SpO2 > 92% on low settings)

Rapid Shallow Breathing Index (RSBI) = f/VT

• Most validated weaning predictor
• Measure during spontaneous breathing (no pressure support)
• RSBI < 100 = likely successful weaning
• RSBI > 100 = rapid, shallow breathing = likely weaning failure

Spontaneous Breathing Trial (SBT)

• Place patient on T-piece, low-level CPAP (5 cm H2O), or minimal PSV (5-8)
• Duration: 30 minutes to 2 hours
• Monitor: RR, SpO2, heart rate, BP, work of breathing, mental status
• If patient tolerates → proceed to extubation
• If patient fails → resume full ventilatory support; identify and treat cause

4 Methods for Weaning Trial

1. T-tube trials - patient breathes through T-piece; oldest method
2. SIMV - gradually reduce mandatory breath rate
3. PSV - gradually reduce pressure support level
4. CPAP - patient breathes spontaneously at low PEEP

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8. QUICK REFERENCE - WAVEFORM SELECTION

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9. NON-INVASIVE VENTILATION (NIV/NPPV) KEY POINTS

• Best evidence: COPD exacerbation, cardiogenic pulmonary edema, immunocompromised patients
• Contraindications: respiratory arrest, inability to protect airway, excessive secretions, facial trauma, vomiting
• Mask fit is critical - check for leaks
• Reassess response within 30 minutes
• If no improvement or deterioration → intubate

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Summary - EMT/Paramedic Priority Actions

1. Any sudden deterioration - disconnect from ventilator, give BVM, use DOPES mnemonic
2. High pressure alarm - suction first, then bronchodilator, then check for pneumothorax
3. Low pressure alarm - check all circuit connections immediately
4. Hypotension - think auto-PEEP (disconnect briefly) or tension pneumothorax
5. Power failure - switch to BVM; never leave patient without ventilation
6. Always use ideal body weight for tidal volume calculations, not actual weight