Ventilator Settings Based on Pathophysiology

Ventilator Settings Based on Pathophysiology

Understanding Respiratory Disease Management

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• Introduction to Ventilator Settings
• Restrictive Lung Disease
• Obstructive Airways Disease
• Management of COPD Exacerbations
• BIPAP and Invasive Ventilation
• Special Considerations & Airway Pressures
• Conclusion

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Restrictive Lung Disease

Characteristics, Examples, and Management

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• Characterized by reduced lung volumes
• Increased work of breathing
• Inadequate ventilation and/or oxygenation
• Caused by alteration in lung parenchyma or disease of pleura/chest wall
• Examples: ARDS, aspiration pneumonitis, pneumonia, pulmonary fibrosis, pulmonary edema, alveolar hemorrhage, chest trauma

• Characterized by damage to alveolar epithelium
• Etiology (mnemonic PAST):
• Pneumonia
• Aspiration
• Shock, Sepsis
• Trauma

• After adjusting PEEP, check plateau pressure (PPLAT)
• If PPLAT > 30 cm H2O, decrease tidal volume until PPLAT < 30 (minimum 4 mL/kg PBW)
• Inspiratory time adjusted to keep I:E ratio 1:1.5 or 1:2
• If exhaled tidal volume > 6 mL/kg, lower inspiratory pressure to 4-6 mL/kg range
• After initiating ventilation, check arterial blood gas (15-20 min for gas exchange)
• Adjust respiratory rate to change PaCO2 (higher rate lowers PaCO2)
• Maintain tidal volume in 4-6 mL/kg range, PPLAT ≤ 30 cm H2O
• Lung protection is more important than normal ventilation

Obstructive Airways Disease

Characteristics, Examples, and Management

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• Associated with increased respiratory system compliance
• Obstruction to expiratory airflow (easy to get air in, hard to get it out)
• Difficulty exhaling all air from lungs leading to shortness of breath
• Exhaled air comes out more slowly than normal due to lung damage or airway narrowing
• Abnormally high amount of air may remain in lungs after full exhalation
• Examples: COPD, Emphysema, Asthma, Chronic Bronchitis

• O2 Therapy Indication: PaO2 < 55 or SaO2 < 88%
• Target SpO2: 88-92%
• Administration: Nasal cannula (low concentration)
• Non-invasive Mechanical Ventilation Indications:
• Dyspnea: moderate, severe
• Tachypnea: RR > 25
• Acute respiratory acidosis: pH < 7.35, PaCO2 > 45
• After Extubation, Re-intubation

• Disturbed consciousness
• Craniofacial trauma
• Nasopharyngeal abnormalities
• Hemodynamic instability
• Increased secretions
• Respiratory arrest
• Gastroesophageal surgery

• FiO2: Adjust to maintain SpO2 88-92%
• IPAP: Initially 8 cmH2O, then increase gradually per case
• EPAP: Initially 5 cmH2O, adjust according to saturation
• IPAP-EPAP: Titrate to keep difference at 10 cmH2O or at least IPAP double EPAP (PS)

• Gradually decrease IPAP (e.g., 15-13-11-9)
• Intermittent off non-invasive ventilation, gradually increase interval
• Combination of both techniques

• Failure of non-invasive ventilation
• Disturbed consciousness
• Severe respiratory acidosis (pH < 7.2)
• Hemodynamic instability
• Worsening hypercapnia
• Inability to clear secretions or protect airway

• Start with high FiO2: 100% O2 initially
• Target PaO2 > 55 mmHg and SpO2 88%-92%
• Control range for ETT patients (FiO2 desired = (current FiO2 / current PaO2) target PaO2)
• Example: Patient on mechanical ventilation with FiO2 40% and PaO2 55 mmHg, target PaO2 80 mmHg. Desired FiO2 = (0.40 / 55) 80 = 0.58
• For COPD patients without ETT: FiO2% = 21% + PaO2 target (desired) – room air PaO2% / 3

• Main problem with asthmatics is breathing out; ventilator can push air in that can't get out
• Causes dynamic hyperinflation and rise in thoracic pressure
• Can prevent ventilation (airway pressures rise, TV fall), cause pneumothorax, or impair venous return and cause hypotension
• Air trapping MUST be avoided
• Tidal Volume (TV): 6-8 mL/kg
• PEEP: Start low or no PEEP (ZEEP)
• I:E ratio 1:4-5 (expiratory time goal 4-5s)
• Initial settings vary according to patient condition
• Minimum Flow Rate = minute volume * (summation I + E ratio)
• If minute ventilation stays consistent, flow rate should be set 10 L/min higher than calculated

• Expiratory flow time curve: it does not arrive to baseline
• Plateau pressure: end inspiratory pause (hold) > 30 cmH2O
• Auto PEEP: prolonged expiratory pause (hold) > 8-10 cmH2O

• Increase expiratory time
• Increase inspiratory flow rate (decreases inspiratory time, increases expiratory time)
• Decrease minute ventilation (spontaneous ventilation reduced by sedation)

• Perform an inspiratory pause to measure plateau pressure (PPLAT)
• Plateau pressure represents alveolar pressure
• Peak pressure is a combination of alveolar pressure and airway resistance
• Causes of Raised Peak Airway Pressure:
• Obstruction or kinking or narrowing of the endotracheal tube
• Excessive airway secretions
• Bronchospasm
• Clogged heat-moisture exchangers (HME)
• Causes of Raised Plateau Pressure (Low Static Compliance/Stiff Lung):
• Pneumonic consolidation
• Pulmonary edema
• Pleural effusions
• Abdominal distension
• Atelectasis
• ARDS