Please prepare detailed, point‑wise notes on mechanical ventilation using the latest guidelines and articles, with subheadings highlighting all important points for maximum exam marks.

Mechanical Ventilation: Comprehensive Exam-Focused Notes

Initial Ventilator Settings

Tidal Volume (VT)

• Set tidal volume at 6 ml/kg predicted body weight (PBW) as the starting point for all mechanically ventilated patients 1, 2
• Calculate PBW using: Males = 50 + 0.91[height (cm) − 152.4] kg; Females = 45.5 + 0.91[height (cm) − 152.4] kg 1
• If the patient does not tolerate 6 ml/kg, adjust within the range of 4–8 ml/kg PBW, but never exceed 8 ml/kg PBW 1, 2
• Traditional tidal volumes of 10–15 ml/kg PBW are obsolete and harmful 1
• The tidal volume gradient (difference between low and traditional volumes) inversely correlates with mortality—larger gradients show greater mortality reduction 1

Plateau Pressure (Pplat)

• Maintain plateau pressure strictly below 30 cmH₂O at all times to prevent ventilator-induced lung injury (VILI) and barotrauma 1, 2, 3
• If plateau pressure exceeds 30 cmH₂O, immediately reduce tidal volume to 4 ml/kg PBW 2
• Plateau pressure is measured during an inspiratory hold maneuver and reflects alveolar pressure 3
• This parameter is critical for preventing overdistention and compression stress on the alveolar-capillary membrane 4

Positive End-Expiratory Pressure (PEEP)

• Set initial PEEP at minimum 5 cmH₂O; zero PEEP is explicitly contraindicated 2, 5
• For moderate-to-severe ARDS, use higher PEEP levels (≥10 cmH₂O) 2
• PEEP prevents atelectasis, maintains functional residual capacity, and recruits underventilated lung regions 2, 5
• In COPD patients, use PEEP of 4–8 cmH₂O to offset intrinsic PEEP and improve triggering 2
• Never set external PEEP higher than measured intrinsic PEEP in COPD patients, as this worsens hyperinflation 2

Respiratory Rate (RR)

• Set respiratory rate at 10–15 breaths/minute for most patients 2, 5
• For COPD patients, prefer the lower end of this range to allow adequate expiratory time and prevent auto-PEEP 2
• Avoid hyperventilation (RR >15 breaths/minute) as it causes respiratory alkalosis, decreases cerebral blood flow, and provides no benefit 5
• Higher respiratory rates prevent adequate expiratory time and cause dangerous auto-PEEP accumulation 2

Fraction of Inspired Oxygen (FiO₂)

• Begin FiO₂ at 0.4 (40%) and titrate downward to maintain target SpO₂ 2, 5
• Target SpO₂ of 88–95% for most patients; 88–92% specifically for COPD patients 2
• Use the lowest FiO₂ possible to achieve target saturation to avoid absorption atelectasis and worsening V/Q mismatch 2, 5
• In COPD, excessive oxygen worsens hypercapnia by correcting hypoxemia but increasing PaCO₂ 2

Inspiratory-to-Expiratory (I:E) Ratio

• Use prolonged expiratory time with I:E ratio of 1:2 to 1:4 in obstructive lung disease 2
• This prevents breath stacking and auto-PEEP accumulation 2
• In acute distress with high minute ventilation, peak inspiratory flows can exceed 60 L/min, requiring careful flow adjustments 6

ARDS-Specific Management

Low Tidal Volume Strategy

• Apply the ARDSNet protocol for all ARDS patients: tidal volume 6 ml/kg PBW, plateau pressure <30 cmH₂O 1, 2
• This strategy showed moderate confidence in reducing mortality when combined with higher PEEP 1
• Meta-regression demonstrated that larger tidal volume gradients (difference between intervention and control) significantly reduced mortality (P = 0.002) 1
• Trials combining low tidal volume with high PEEP showed greater mortality benefit (RR 0.58; 95% CI 0.41–0.82) 1

PEEP Strategy in ARDS

• For moderate-to-severe ARDS, target higher PEEP levels (≥10 cmH₂O) 2
• The combination of low tidal volume and higher PEEP provides synergistic mortality reduction 1
• PEEP maintains alveolar recruitment and prevents cyclic atelectasis 2

Prone Positioning

• For severe ARDS (PaO₂/FiO₂ <150), implement early prone positioning for ≥12 hours per day—this is a strong recommendation with demonstrated mortality benefit 2
• Prone positioning is mandatory when PaO₂/FiO₂ <100 2
• Verify hemodynamic stability before and after prone positioning 5
• Consider slightly higher PEEP (6–7 cmH₂O) in prone position to counteract increased abdominal pressure on the diaphragm 5

Recruitment Maneuvers

• Consider recruitment maneuvers as part of the ARDS management strategy 2
• These maneuvers help open collapsed alveoli and improve oxygenation 2

Driving Pressure (ΔP)

• Driving pressure = Plateau pressure − PEEP 3, 4
• This parameter reflects dynamic strain (ratio between tidal volume and end-expiratory lung volume) 4
• Monitor driving pressure as it correlates with VILI risk 3, 4

COPD-Specific Modifications

Ventilation Strategy

• Set respiratory rate at 10–15 breaths/min, preferring the lower end to allow adequate expiratory time 2
• Use prolonged expiratory time with I:E ratio of 1:2 to 1:4 to prevent breath stacking 2
• Accept mild hypoventilation (permissive hypercapnia) with pH >7.2 to reduce barotrauma risk 2

PEEP Management

• Use PEEP of 4–8 cmH₂O to offset intrinsic PEEP and improve triggering 2
• Never set external PEEP higher than measured intrinsic PEEP, as this worsens hyperinflation 2
• Intrinsic PEEP (auto-PEEP) results from incomplete exhalation and air trapping 2

Oxygenation Targets

• Titrate FiO₂ to SpO₂ 88–92% to avoid worsening hypercapnia from excessive oxygen 2
• Never use excessive FiO₂, as oxygen administration corrects hypoxemia but worsens V/Q mismatch and contributes to increased PaCO₂ 2

Bronchodilator Therapy

• Administer nebulized bronchodilators via ventilator circuit: salbutamol 2.5–5 mg or ipratropium 0.25–0.5 mg every 4–6 hours 2
• Administer systemic corticosteroids: prednisolone 30 mg/day orally or hydrocortisone 100 mg IV for 7–14 days 2

Monitoring Parameters

Essential Measurements

• Dynamic compliance should be measured regularly to evaluate lung mechanics and guide ventilator adjustments 2, 3
• Monitor peak pressure (Ppeak), plateau pressure (Pplat), and driving pressure (ΔP) 3, 4
• Measure intrinsic PEEP to detect auto-PEEP in obstructive lung disease 3
• Calculate transpulmonary pressure (PL) to assess true alveolar distending pressure 3

Blood Gas Monitoring

• Obtain arterial blood gas before initiating ventilation and recheck 30–60 minutes after any ventilator change 2
• Target pH of 7.35–7.45 with normocapnia (PaCO₂ 35–45 mmHg) for patients with healthy lungs 5
• Maintain PaO₂ >80 mmHg or SpO₂ 92–97% 5
• Monitor end-tidal CO₂ continuously to assess adequacy of ventilation 5

Advanced Parameters

• Mechanical energy and mechanical power reflect the amount of energy imparted to the lungs per breath and per minute 4
• Pressure-time product per minute (PTP/min) should be evaluated during assisted ventilation 3
• Pressure generated 100 ms after onset of inspiratory effort (P0.1) assesses respiratory drive 3

Patient Positioning

Head-of-Bed Elevation

• Position the patient with head of bed elevated to 30° unless contraindicated 2, 5
• This reduces aspiration risk and improves lung mechanics 2, 5

Prone Positioning Protocol

• For severe ARDS (PaO₂/FiO₂ <150), implement prone positioning for ≥12 hours per day 2
• Verify hemodynamic stability before and after positioning changes 5
• Monitor for pressure ulcers and ensure proper padding of bony prominences 2

Ventilator Liberation (Weaning)

Ventilator Liberation Protocols

• Manage acutely hospitalized adults mechanically ventilated for >24 hours with a ventilator liberation protocol (conditional recommendation, low certainty) 1
• Ventilator liberation protocols reduce duration of mechanical ventilation by approximately 25 hours 1
• Protocols reduce ICU length of stay by approximately 1 day 1
• The protocol may be either personnel-driven or computer-driven; insufficient evidence exists to recommend one over another 1

Weaning Outcomes

• Mortality is not significantly different between protocolized and non-protocolized weaning (RR 1.02; 95% CI 0.82–1.26) 1
• Failed extubation rates (reintubation within 48 hours) show no significant difference (RR 0.74; 95% CI 0.44–1.23) 1
• Duration of mechanical ventilation is reduced by 25 hours with protocols (MD −25; 95% CI −35.5 to −12.5) 1

Weaning Predictor Tests

• Screen for weanability through use of weaning predictor tests before attempting liberation 7
• Use T-tube trials to assess patient work of breathing in the absence of pressure support 7
• Before extubation, patients must demonstrate ability to breathe successfully without pressure support and PEEP 7

Complications and Prevention

Ventilator-Induced Lung Injury (VILI)

• VILI results from compression stress on the alveolar-capillary membrane and extracellular matrix 4
• Mechanisms include barotrauma (high pressures), volutrauma (high volumes), and atelectrauma (cyclic collapse) 4
• Prevent VILI by maintaining plateau pressure <30 cmH₂O, tidal volume 4–8 ml/kg PBW, and adequate PEEP 1, 2
• Barotrauma rates are not significantly different between low and traditional tidal volume strategies (RR 0.96; 95% CI 0.67–1.37) 1

Patient Self-Inflicted Lung Injury (P-SILI)

• P-SILI occurs when vigorous spontaneous breathing efforts generate excessive transpulmonary pressure 4
• Monitor for patient-ventilator dyssynchrony to detect P-SILI risk 8, 4
• Adjust ventilator settings to minimize work of breathing and align with patient's intrinsic respiratory rhythm 7

Hemodynamic Complications

• Positive-pressure ventilation reduces venous return and cardiac output 4
• Monitor for hypotension, especially in patients on vasodilators (e.g., losartan) or in prone position 5
• Increased intrathoracic pressure impairs cerebral perfusion pressure (CPP) and renal vein drainage 4

Auto-PEEP and Hyperinflation

• Auto-PEEP results from incomplete exhalation and air trapping, particularly in COPD 2
• Avoid high respiratory rates that prevent adequate expiratory time, as this causes dangerous auto-PEEP accumulation 2
• Measure intrinsic PEEP and adjust external PEEP accordingly 2, 3

Intra-Abdominal Hypertension

• Positive-pressure ventilation can increase intra-abdominal pressure, impairing lung and organ function 4
• Limit sedation, fluids, and vasoactive drugs to achieve resuscitative goals at lower normal limits 1
• Consider percutaneous drainage of intraperitoneal fluid before surgical decompression 1

Special Considerations

Non-Invasive Ventilation (NIV) and BiPAP

• BiPAP provides two pressure levels: inspiratory positive airway pressure (IPAP) and expiratory positive airway pressure (EPAP) 6
• Pressure support (PS) = IPAP − EPAP; this difference augments tidal volume and improves ventilation 6
• EPAP maintains airway patency, recruits lung regions, offsets intrinsic PEEP, and flushes exhaled CO₂ from the circuit 6
• A minimum EPAP of 3–5 cmH₂O is required to adequately vent exhaled air and prevent CO₂ rebreathing 6

Bias Flow in NIV

• Bias flow delivers continuous fresh gas at 2–3 times the patient's minute ventilation 6
• This flow maintains circuit pressure during spontaneous breathing and actively flushes exhaled CO₂ 6
• Inadequate bias flow or EPAP causes CO₂ rebreathing and hypercapnia 6
• Obstruction of the exhaust port (e.g., by secretions) impairs CO₂ clearance 6

Extracorporeal Membrane Oxygenation (ECMO)

• Additional evidence is necessary to make a definitive recommendation for or against ECMO in severe ARDS 1
• The only recent RCT had limitations including composite primary endpoint, incomplete intervention application, and lack of standardized low tidal volume in controls 1
• In the interim, continue evidence-based lung-protective ventilation 1

Anesthesia-Specific Settings

• For short procedures under general anesthesia, use tidal volume 6–7 ml/kg PBW, respiratory rate 10–12 breaths/minute, FiO₂ 0.4–0.5, and PEEP 5 cmH₂O 5
• Monitor end-tidal CO₂ continuously, especially in patients on medications that reduce anesthetic requirements (e.g., pregabalin) 5
• Plan for immediate extubation at procedure completion once the patient is responsive with adequate spontaneous ventilation 5

Critical Pitfalls to Avoid

Volume and Pressure Errors

• Never use excessive tidal volumes (>8 ml/kg PBW) even if airway pressures seem acceptable 5
• Never allow plateau pressure to exceed 30 cmH₂O 1, 2
• Avoid traditional tidal volumes of 10–15 ml/kg PBW, which are associated with higher mortality 1

Oxygenation Errors

• Never use excessive FiO₂ (>0.6) unnecessarily, as it provides no advantage and causes absorption atelectasis 2, 5
• In COPD, excessive oxygen worsens hypercapnia despite correcting hypoxemia 2

Ventilation Rate Errors

• Avoid hyperventilation (RR >15 breaths/minute), which causes respiratory alkalosis and decreases cerebral blood flow 5
• In COPD, high respiratory rates prevent adequate expiratory time and cause auto-PEEP 2

PEEP Errors

• Never use zero PEEP; minimum 5 cmH₂O is required 2
• In COPD, never set external PEEP higher than intrinsic PEEP 2
• Inadequate EPAP (<3 cmH₂O) in BiPAP allows CO₂ rebreathing 6

Protocol Misuse

• Use of rigid protocols for ventilator settings can lead to complications (including alveolar overdistention) and risk of death 7
• Careful, iterative adjustments of ventilator settings are required to minimize work of breathing 7

Weaning Errors

• Do not attempt to estimate patient work of breathing during pressure support; use T-tube trials instead 7
• Ensure patients demonstrate ability to breathe without pressure support and PEEP before extubation 7
• Mechanical ventilation should be discontinued at the earliest possible time to minimize complications 7

Physiological Principles

Work of Breathing

• The primary purpose of mechanical ventilation is to decrease work of breathing 7
• Achieving this requires careful alignment of ventilator cycling with the patient's intrinsic respiratory rhythm 7
• Problems arise at ventilator triggering, post-trigger inflation, and inspiration-expiration switchover 7

Gas Exchange

• Mechanical ventilation maintains gas exchange by moving gas toward and from the lungs through an external device 9
• Positive-pressure ventilation differs considerably from normal physiologic breathing 4
• Alveolar ventilation depends on tidal volume, dead space, and respiratory rate 9

Respiratory Mechanics

• Compliance reflects the distensibility of the lungs and chest wall 3
• Resistance reflects the opposition to airflow in the airways 3
• Transpulmonary pressure (PL) represents the true distending pressure across the alveolar wall 3, 4

Ventilator Modes

• Pressure-cycled, flow-cycled, or mixed modes are classified by cycling mechanism 9
• Continuous-flow, intermittent flow, or constant basic flow modes are classified by flow type 9
• High-frequency ventilators include intermittent positive pressure, oscillatory, and jet ventilators 9