Mechanical Ventilation

Aka: Mechanical Ventilation, Ventilator, Assist Control, Intermittent Mandatory Ventilation, Pressure Support Ventilation, Lung Protective Ventilator Strategy, Obstructive Lung Disease Ventilator Strategy

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II. Indications

  1. See Advanced Airway

III. History

  1. First described by Andreas Vesalius in 1555
  2. Negative pressure Ventilators (IronLung) first used
  3. Positive pressure Ventilator first used in 1955
    1. Response to Polio epidemic of 1955
    2. Emerson company tested at Massachusetts General

IV. Types

  1. Volume cycled (VC) Ventilators
    1. Newer devices
    2. Deliver constant volume independent of lung mechanics
    3. Best initial setting for most patients and typically used in ED (unless pressure needs to be limited)
      1. Example ideal patient: Metabolic Acidosis
      2. Easiest to implement for lung protective strategy
        1. Control over Tidal Volume (Vt), Minute Ventilation and minute volume
        2. Decreased risk of Ventilator-associated lung injuries
    4. However, pressure may increase unexpectedly with increased risk of lung injury
      1. Decreased Lung Compliance (stiff lungs, such as in ARDS)
      2. Increased airway resistance
      3. Acute forceful expiration (e.g. increased cough)
  2. Pressure Cycled (PC) Ventilators
    1. Initial Ventilator design
    2. Inflates lungs until preset pressure is reached
    3. Requires preset of ventilation duration (length of time pressure is applied, e.g. 1 second)
      1. Greater volume is administered when a given pressure is applied for a longer duration
    4. Difficult to keep inflation volume constant
    5. Best for patients for whom you wish to set a maximum inspiratory pressure
      1. Example ideal patient: ARDS (stiff lungs)

V. Physiology

  1. Ventilator functions as a mechanical bellows
  2. Mechanical Ventilation Respiratory Cycle
    1. Inspiration Start (Triggering)
      1. Assisted Breath
        1. Patient initiates breath and Ventilator delivers breath at that time
      2. Manditory or Controlled Breath
        1. Breath is administered after a specific elapsed time (if no assisted breath taken)
    2. Expiration Start (Cycling)
      1. Volume-Cycled Breath (Volume Assist-Control Breath)
        1. Preset Tidal Volume delivered over a specified time and flow curve (square, sine, decel)
        2. Increases peak pressures (up to limit) when there is increased airway resistance
      2. Time-Cycled Breath (Pressure Assist-Control Breath)
        1. Breath delivered with constant pressure for a preset time period
        2. Results in variable Tidal Volume delivered based on airway and lung resistance
      3. Flow-Cycled Breath (pressure support breath)
        1. Spontaneous ventilation mode with patient initiating every breath
        2. Ventilator delivers preset inspiratory pressure
        3. As patient ends inspiration, in-flow decreases, and Ventilator stops inspiration
  3. Cardiac Output
    1. Enhanced by modest thoracic positive pressure
      1. Reduces left Ventricular Afterload
    2. Decreased by excessive intrathoracic pressure
      1. Reduces diastolic ventricular filling (Preload)

VI. Technique: Ventilation Modes

  1. Assist Control (AC)
    1. Assist
      1. Patient initiates mechanical breath, and a preset Tidal Volume is delivered (volume-cycled breath)
      2. As alternative, the less common Time-Cycled Breath (Pressure Assist-Control Breath) may be used
    2. Control
      1. Provides ventilations that are not patient initiated at a back-up, minimum Respiratory Rate
      2. Total number of breaths = patient-initiated + Ventilator-initiated
      3. When the patient initiates no assisted breaths, known as Continuous Mechanical Ventilation (CMV)
        1. Seen in paralyzed patients or in Deep Sedation
    3. Indications
      1. Obtunded patient without respiratory drive
      2. Pneumonia with Sepsis (decrease work of breathing)
    4. Advantages over SIMV Mode
      1. Decreased work of breathing
      2. Decreased respiratory muscle Fatigue
      3. Better response to patient's Ventilatory needs (patient can increase Ventilatory support)
    5. Disadvantages
      1. Requires that patient and Ventilator breaths are synchronized and matched to demand
        1. Otherwise, results in increased work of breathing
      2. Risk of Breath Stacking (multiple full Tidal Volume breaths) and secondary Respiratory Alkalosis
        1. Increased risk in awake or Agitated Patients
      3. Barotrauma risk
        1. Excessive inspiratory pressure risk
    6. Presets
      1. Tidal Volume
      2. Respiratory Rate
      3. Fraction of Inspired Oxygen (FIO2)
      4. Positive End-Expiratory Pressure (PEEP)
  2. Synchronized Intermittent Mandatory Ventilation (SIMV)
    1. Background
      1. Delivers volume-cycled (or less commonly time-cycled breaths) at preset minimum rate
      2. Breaths are triggered by patient or after elapsed time (based on minumum rate)
      3. Breaths are supported up to a preset minimum (mandatory) rate
      4. Breaths above the minumum rate are not supported (unless SIMV combined with pressure support)
        1. Combined SIMV with pressure support (see below) is typically recommended
    2. Two phases of cycle: SIMV and Spontaneous
      1. SIMV Phase
        1. Any patient initiated breath is supported with delivery of a preset Tidal Volume
        2. If no patient initiated breath in first 90% of SIMV, machine delivers a full breath
      2. Spontaneous Phase (if SIMV not combined with pressure support)
        1. Patient initiated breaths above minimum rate will not trigger additional Ventilator support
        2. Ventilation Tidal Volume is 100% dependent on patient's own unsupported inspiration
    3. Indications
      1. Introduced in 1971 for neonates with RDS
      2. Often used for Ventilator Weaning of adults
      3. May be used if Respiratory Rate is rapid
    4. Advantages over Assist Control Mode
      1. Less Respiratory Alkalosis
      2. Improves Cardiac Output
      3. Prevents respiratory Muscle atrophy theoretically (but unlikely significant benefit)
    5. Disadvantages compared with Assist Control Mode
      1. Increased work of breathing (unless combined with pressure support - see below)
    6. Presets
      1. See Assist Control above
  3. Pressure Support Ventilation (PSV)
    1. Mechanism
      1. Augments spontaneous breathing (as with SIMV) on every breath (as with assist mode)
      2. Inspired gas to desired pressure (typically starts at 12-15 cmH2O)
        1. Pressure titrated to desired MV, Tidal Volume (6-8 cc/kg), Respiratory Rate <30
      3. Flow cycled breaths
    2. Indications
      1. Ventilator Weaning
      2. Intubation for airway protection (e.g. Angioedema)
        1. Use AC or SIMV first until RSI wears off and patient starts to wake up
    3. Advantages over SIMV
      1. Increases Tidal Volume
      2. Decreases work of breathing
    4. Precautions
      1. Apnea alarms and backup Respiratory Rate are critical
      2. Endotracheal Tube cuff leak may result in cycling problems (flow does not drop enough to cycle off)
    5. Methods of Setting Pressure
      1. Method 1: Maximum Inspiratory Pressure
        1. Pressure = Maximum Inspiratory Pressure / 3
      2. Method 2: Proximal Airway Pressure
        1. Pressure = Peak Pressure - Plateau Pressure
      3. Method 3: Approximation
        1. Start with pressure 12-15 cmH2O (normal Lung Compliance, non-rigid chest wall)
        2. Adjust based on observation of first few breaths (increase pressure if TV too low)
    6. Presets (patient controls Respiratory Rate, flow rate and Tidal Volume)
      1. Inspiratory pressure
      2. Fraction of Inspired Oxygen (FIO2)
      3. PEEP Pressure

VII. Technique: Starting Parameters - MIscellaneous

  1. General
    1. Assist Control - Volume is a default Ventilator setting appropriate for most patients
    2. Measure the patient length on presentation (to estimate Ideal Weight, and hence Tidal Volume)
  2. Most cases will start with either lung protective strategy (ARDS) or Obstructive Lung Disease Ventilator Strategy
    1. See lung protective strategy (ARDS) below
    2. See Obstructive Lung Disease strategy (Asthma, COPD) below
  3. Airway Protection (obtunded patient)
    1. Ventilator Setting: Volume cycled (VC)
    2. Tidal Volume: 6 to 8 ml/kg based on Ideal Body Weight (IBW)
    3. Respiratory Rate: 12-16 breaths per minute
      1. Match the patient's pre-intubation Respiratory Rate in Metabolic Acidosis! (see below)
      2. Too slow of a Respiratory Rate will result in worsening acidosis and decompensation
    4. PEEP: 5 cm H2O
    5. FIO2 titrated to Oxygen Saturation >92%
  4. Asymmetric Lung Disease (e.g. Lung Contusion, localized Pneumonia, gastric aspiration)
    1. Start with standard mechical ventilation settings
    2. If initial management inadequate
      1. Uninjured lung has least resistance to air flow and is therefore best aerated
      2. Place the patient in decubitus position with the less involved lung down (closer to bed)
      3. Allows for dependent pulmonary Blood Flow to best ventilated lung segments
  5. Pulmonary Hypertension
    1. Present unique challenges in Mechanical Ventilation due to high sensitivity to Preload and Afterload changes
    2. Limit vascular Preload changes by decreasing intrathoracic pressure
      1. Maintain low Tidal Volume
      2. Maintain low plateau pressures
      3. Maintain low PEEP
    3. Limit right Ventricular Afterload changes (resulting from pulmonary Vasoconstriction)
      1. Maintain normal pO2
      2. Maintain normal pCO2 (35-45 mmHg)
        1. Pulmonary Hypertension is intolerant to permissive hypercapnia
  6. Children (under age 8 years)
    1. Precaution: Reduce rate and Tidal Volume for Asthma Exacerbation (allow for permissive hypercapnia)
    2. Respiratory Rate: 20-25 breaths per minute
    3. Tidal Volume: 5-7 cc/kg
    4. Set peak inspiratory pressure to 12-20 cm H2O in infants
  7. References
    1. Murphy and Maldonado (2018) Crit Dec Emerg Med 32(12): 14-5
    2. Weingart and Orman in Herbert (2016) EM:Rap 16(6):14-5
    3. http://emcrit.org/wp-content/uploads/vent-handout.pdf
    4. http://emcrit.org/archive-podcasts/vent-part-1/
    5. http://emcrit.org/podcasts/vent-part-2/

VIII. Technique: Starting Parameters - Lung Protective Ventilator Strategy (ARDS, hypoxemic Respiratory Failure)

  1. Indications (lung protective strategy)
    1. Hypoxemic Respiratory Failure (most cases)
    2. Acute Respiratory Distress Syndrome (ARDS)
  2. Goals
    1. Adequate increase in mean airway pressure to allow for alveolar recruitment
    2. Avoid excessive alveolar pressure (risk of Ventilator associated lung injury or VALI)
      1. Permissive hypercapnia
      2. Low Tidal Volumes
  3. Tidal Volume
    1. Key parameter in lung injury and its prevention
    2. Setting: 6 to 8 ml/kg Ideal Body Weight, based on patient height (lung protective strategy)
      1. Avoid Tidal Volume >8 ml/kg
    3. Typically start at 8 ml/kg and decrease to 6 ml/kg over the first 4 hours
      1. Decrease by 1 ml/kg every 2 hours as tolerated from 8 down to 6 ml/kg
  4. Inspiratory flow rate (IFR)
    1. Setting: 60 to 80 liters per minute (lpm)
    2. Start at 60 lpm and adjust for patient comfort
      1. Faster breaths tend to be more comfortable
  5. Respiratory Rate
    1. Setting: 16-18 breaths per minute
    2. Increase or decrease based on pCO2 (increase RR to decrease pCO2)
      1. Recheck ABG 30-40 minutes after change in Respiratory Rate
      2. Rates may need to be increased to 30-40 breaths per minute
  6. FIO2
    1. Initial
      1. Start for first 5 minutes at 100% FIO2 with PEEP 0-5
      2. Decrease FIO2 toward 30-40% with PEEP 5, with a goal Oxygen Saturation 90% to 95%
        1. Some recommend immediately decreasing FIO2 toward 30-40% without delay
        2. Persistently high FIO2 >50-60% results in shunting with ineffective blood oxygenation
    2. Titration
      1. Obtain Arterial Blood Gas (after first 15 minutes on Ventilator)
      2. Titrate up on FIO2 and PEEP together at 5-10 min increments based on PEEP Table (see below)
  7. PEEP (Positive End-Expiratory Pressure)
    1. PEEP keeps alveoli and distal airways open (improving oxygenation)
    2. Adjust PEEP in concert with FIO2 based on PEEP Tables (minimum PEEP 5 cm H2O)
    3. Start at 5 cm H2O, with optimal PEEP setting 8-15 cm H2O
    4. See PEEP Adjustments below
  8. Monitoring
    1. Goal PaO2 55-80 mmHg (Oxygen Saturation 88-95%)
    2. pH > 7.15 or 7.20
    3. Decrease Tidal Volume until plateau pressure <30 cm H2O (see below)
      1. Check plateau pressure every 30 to 60 minutes (press inspiratory hold)
      2. Decrease Tidal Volume in 1 ml/kg increments until Vt 4 ml/kg or pH 7.15
  9. Adjunctive Modalities in Refractory Cases (see ARDS)
    1. Prone Positioning
    2. Paralysis (e.g. Vecuronium)
    3. ECMO

IX. Technique: Starting Parameters - Obstructive Lung Disease (Asthma, COPD, Hypercapnic Respiratory Failure)

  1. Indications
    1. Hypercapnic Respiratory Failure
    2. Obstructive Lung Disease
      1. Status Asthmaticus
      2. Emergency Management of COPD Exacerbation
  2. Goals
    1. Minimize hyperinflation
    2. Rest compromised respiratory Muscles
    3. Allow for adequate expiration (avoiding Breath Stacking)
  3. Precautions
    1. Consider Delayed Sequence Intubation
    2. Continue Nebulized Albuterol via Endotracheal Tube
    3. Status Asthmaticus patients will often respond to aggressive Asthma Management AND BiPap
      1. Asthma patients who require intubation have lost all respiratory drive
    4. Expect a high peak pressure in Asthma due to airway resistance
      1. High peak pressure (unlike plateau pressure) is a sign of airway obstruction
        1. Check plateau pressure (press and hold the inspiratory hold button) as below
        2. Set peak pressure alarm to trigger >80 cm H2O
        3. Aggressive Obstructive Lung Disease management with Bronchodilators and steroids
      2. However, do not confuse peak pressure with plateau pressure
        1. Plateau pressure >30 cm H2O is a sign of Breath Stacking and must be corrected
        2. Decrease plateau pressure by decreasing Respiratory Rate (see Auto-PEEP below)
    5. Auto-PEEP (Dynamic Hyperinflation, Breath Stacking)
      1. Presents with increased plateau pressure and Hypotension
      2. Auto-PEEP may also be measured
        1. Check by depressing Ventilator expiratory hold button
        2. Auto-PEEP is present if the end-expiratory pressure exceeds the Ventilator PEEP setting
      3. Increase expiratory time
        1. Decrease Respiratory Rate and inspiratory time
        2. May also decrease Tidal Volume
  4. Tidal Volume
    1. Dose: 8 ml/kg Ideal Body Weight
  5. Inspiratory flow rate (IFR)
    1. Setting: 80 L/min (up to 100 L/min)
    2. Increase to provide faster breath, completes early in cycle (allows greater expiratory time)
    3. High flow rates may be limited by increased peak pressures
  6. Respiratory Rate (RR)
    1. Most important parameter in Obstructive Lung Disease ventilation
      1. Allows for full expiration (typical I:E ratio 1:4 or 1:5) and prevents Breath Stacking
    2. Set rate at 8 to 10 breaths per minute (do not set this too high)
      1. Permissive hypercapnia with lower Ventilatory rates is preferred
  7. FIO2
    1. Start at 30-40% and titrate upward
    2. Use lowest FIO2 that will maintain Oxygen Saturation 88 to 95%
  8. PEEP
    1. Minimal (0-3 mmHg) to NO PEEP ("PEEP Zero Strategy") is recommended in Obstructive Lung Disease
      1. Contrast with ARDS, in which PEEP is increased in step with FIO2
    2. Higher PEEP in Obstructive Lung Disease is associated with worse outcomes and difficult weaning
      1. Fixed airflow obstruction risks increased Lung Volumes, airway pressure and intrathoracic pressure
      2. Resulting increased intrathoracic pressure may lead to cardiovascular collapse
  9. Monitoring
    1. Check plateau pressure (or flow/time graph) for Breath Stacking
      1. Decrease Respiratory Rate until plateau pressure <30 cm H2O
    2. Follow Arterial Blood Gas
      1. Permissive hypercapnia is goal in Obstructive Lung Disease ventilation
      2. Expect pCO2 50-70 mmHg (maintain pH > 7.2, or per some guidelines >7.15)

X. Precautions

  1. See Rapid Sequence Intubation regarding peri-intubation precautions (e.g. Hypotension)
  2. Avoid Hyperventilation (results in lung hyperexpansion and decreases venous return)
  3. Start with low Respiratory Rate and low Tidal Volume (and gradually advance as needed)
  4. Limit peak pressures
  5. Asthma and COPD are very high risk for Hyperventilation-related complications (including Barotrauma)
  6. Do not attempt to fix acid-base abnormalities initially (Permissive hypercapnea is preferred)
    1. Allow a wider range of pH (7.2 to 7.5) in most patients
  7. Contraindications to Permissive Hypercapnea (maintain normal pCO2 35-45 mmHg in these patients)
    1. Increased Intracranial Pressure
    2. Intracranial Hemorrhage
    3. Pregnancy
    4. Severe Pulmonary Hypertension (see above)
    5. Severe ventricular failure (left or right)
    6. Metabolic Acidosis resulting in intubation (match pre-intubation Respiratory Rate)
      1. Salicylate Overdose
      2. Sodium Channel BlockerOverdose (e.g. Tricyclic Antidepressant Overdose)
  8. Metabolic Acidosis (e.g. Diabetic Ketoacidosis)
    1. Observe Minute Ventilation prior to intubation and approximate this for Mechanical Ventilation settings
    2. Increased Respiratory Rates are citical to acid excretion and correction of Metabolic Acidosis
      1. Metabolic Acidosis will continue to worsen if Respiratory Rate is set too low
    3. Consider bridging with Non-Invasive Positive Pressure Ventilation (NIPPV)
      1. See Delayed Sequence Intubation
      2. Allows for determination of mechanical Ventilator settings, esp. Respiratory Rate
    4. High ventilator Respiratory Rates used in Metabolic Acidosis require other modifications
      1. High inspiratory flow rate (allows adequate time for expiration)
      2. Observe for Breath Stacking at higher Respiratory Rates
      3. Adequate sedation and analgesia (high Ventilator rates are uncomfortable)
    5. References
      1. Weingart and Swaminathan in Herbert (2021) EM:Rap 21(2): 2-3

XI. Technique: Parameters

  1. Tidal Volume (TV)
    1. Ventilator Tidal Volume: 6-8 ml/kg of Ideal Body Weight
      1. Prior levels of 10 to 15 ml/kg were too high
      2. ARDS: Start at 6 ml/kg based on Ideal Body Weight (lung protective strategy)
    2. Indications to Reduce Tidal Volume
      1. Lung Resection history (reduce Tidal Volume by percent loss in lung)
      2. Plateau pressure >30 cmH2O
        1. In Obstructive Lung Disease, decrease RR first (indicates Breath Stacking)
    3. Indications to Increase Tidal Volume
      1. Neuromuscular disease
      2. Stiff Lungs (e.g. Pulmonary Edema)
        1. High Peak Inflation Pressure (>20-40 cm H2O)
        2. Results in large loss of Tidal Volume in tubing
  2. Respiratory Rate (RR, "Ventilation")
    1. Set at 12 to 14 breaths per minute (many patients may require 16-18, esp. lung injury)
    2. Set Respiratory Rate closest to patient rate prior to intubation (especially in Metabolic Acidosis)
    3. Ensures adequate carbon dioxide removal
    4. Keep to a minimum to avoid Respiratory Alkalosis
    5. Increased Respiratory Rate needed in Metabolic Acidosis
      1. Observe patient's own Respiratory Rate prior to intubation and use as a guide
      2. Recheck Arterial Blood Gas (ABG) at 20 minutes after initial settings
    6. Indications to decrease Respiratory Rate
      1. Obstructive Lung Disease with Breath Stacking
  3. Minute Ventilation (Alveolar Minute Ventilation)
    1. Reflects gas exchanged per minute and determines CO2 clearance
    2. Typically 7 to 8 L/min, but up to twice as much may be needed in certain conditions
    3. Minute Ventilation = (Vt - Vd) * RR
      1. Where Vt is Tidal Volume, Vd is dead space and RR is Respiratory Rate
  4. Fraction of Inspired Oxygen (FIO2)
    1. Start: 80% or higher
    2. Titrate: decrease in 10-20% steps
    3. Goal: Keep FIO2 <60% (<50% in the first 24 hours if possible)
      1. Higher FIO2 is associated with Oxygen Toxicity
      2. Target Oxygen Saturations 90-94% (>88% may be used as target in severe ARDS)
      3. Increasing PEEP can reduce FIO2 requirements (see below)
    4. Monitoring: Arterial Blood Gas
      1. Wait 20 minutes after each change in FIO2
      2. Keep PaO2 60 to 80 mm Hg (90-95% O2 Sat)
  5. Inspiratory flow rate (IFR)
    1. Describes how quickly a breath is delivered (anologous to Peak Flow)
    2. Faster breaths tend to be more comfortable, and result in less Air HungerSensation for patient
    3. Adjust for patient comfort
  6. Positive End-Expiratory Pressure (PEEP)
    1. Prevents distal airspace collapse (especially dependent lung fields)
    2. Most important in conditions that shunt blood past collapsed alveoli (e.g. Pneumonia, Atelectasis)
    3. Start PEEP at 5 cm H2O (minimum)
    4. Higher PEEP Indications
      1. Extensive alveolar collapse (8-10 cm H2O)
      2. Obesity or pregnancy
      3. High FIO2 (esp. >60%) required or Hypoxemia refractory to oxygenation (PEEP Table in ARDS)
        1. Goal Oxygen Saturation 88-95% (PaO2 55-80 mmHg)
        2. FIO2 30%: Set PEEP 5 cmH2O (high PEEP to FIO2: 5-8-10-12-14 cmH2O)
        3. FIO2 40%: Set PEEP 5-8 cmH2O (high PEEP to FIO2: 14-16 cmH2O)
        4. FIO2 50%: Set PEEP 8-10 cmH2O (high PEEP to FIO2: 16-18-20 cmH2O)
        5. FIO2 60-80%: Set PEEP 10-14 cmH2O (high PEEP to FIO2: 20 cmH2O)
        6. FIO2 90%: Set PEEP 14-18 cmH2O (high PEEP to FIO2: 22 cmH2O)
        7. FIO2 100%: Set PEEP 18-24 cmH2O (high PEEP to FIO2: 22-24 cmH2O)
        8. http://www.ardsnet.org/files/ventilator_protocol_2008-07.pdf
    5. Precautions: Excessive PEEP
      1. PEEP Levels >15 cm H2O are rarely required and are associated with complications
      2. Use minimal to no PEEP is recommended in Obstructive Lung Disease (see above)
      3. Lung injury risk (alveolar over-distention)
      4. Hypotension risk (increased intrathoracic pressure decreases venous return)
        1. Decrease PEEP if hypotensive response to increasing PEEP
  7. Inspiratory Plateau pressure (pPlat)
    1. Plateau pressure is best estimate of peak alveolar pressure (and in turn, alveolar distention)
      1. Check plateau pressure every 30-60 minutes or at the time of high pressure Ventilator Alarms
      2. Recheck plateau pressure after any Ventilator setting changes
    2. Invoke Plateau Pressure by holding down "inspiratory hold button" for 1-5 seconds
      1. Reflects only the static pressures to overcome lung and chest wall resistance
    3. NOT the same as peak inspiratory pressure or pPeak (which is typically very high in Obstructive Lung Disease)
      1. pPeak is the pressure to overcome airway resistance, lung, chest wall
      2. Includes dynamic factors that do not reflect alveolar pressures or Barotrauma risks
        1. As ET Tube diameter decreases, pPeak increases, but pPlat remains constant
      3. For a given Tidal Volume, Lung Compliance, airway resistance, pPeak -pPlat difference is constant
    4. Strategy if plateau pressure too high (>30 cm H2O)
      1. Increased plateau presure reflects increased airway resistance
      2. General measures that decrease Plateau pressure
        1. Decrease PEEP
          1. Risk of decreased oxygenation and alveolar collapse
        2. Decrease Tidal Volume
          1. May decrease Tidal Volume as low as 4 ml/kg
          2. Risk of hypercapnia due to decreased Minute Ventilation
          3. However, permissive hypercapnia is preferred
        3. Increase Expiratory Time (e.g. shorter breaths or slower rate, decreases Auto-PEEP risk)
          1. Risk of hypercapnia
        4. Address reversible factors impeding Lung Compliance
          1. Increase Post-Intubation Sedation and Analgesia
          2. Consider chemical paralysis (e.g. Rocuronium, cistracuronium)
        5. Consider changing Ventilator mode
          1. Change Ventilator to Pressure Cycled (PC) Ventilation
      3. Lung Injury
        1. Decrease Tidal Volume until plateau pressure <30 cm H2O
      4. Obstructive Lung (Breath Stacking)
        1. Decrease Respiratory Rate until plateau pressure <30 cm H2O
    5. Strategy if Peak Inspiratory Pressure (PIP) is high without increased Plateau Pressure
      1. Increased PIP with normal pPLAT reflects increased airway resistance
      2. Evaluate for Endotracheal Tube obstruction
      3. Evaluate for dessynchrony with Ventilator
      4. Evaluate for mucous plugging or bronchospasm

XII. Technique: Adjunctive measures

  1. Post-intubation Pain and Sedation (critical)
    1. See Post-Intubation Sedation and Analgesia
  2. Suction
  3. Heat and humidification of inspired air
    1. Heated Humidifiers
    2. Passive Humidifiers
      1. Contraindicated with copious or bloody secretions, Minute Ventilation >12 L/min, large air leak

XIII. Adverse Effects

  1. Barotrauma (Tension Pneumothorax, Auto-PEEP)
  2. Ventilator-Associated Pneumonia
  3. Myocardial Infarction
    1. Consider serial Electrocardiogram and Troponin
  4. Severe Respiratory Alkalosis
    1. Occurs with high Respiratory Rates
    2. Consider IMV ventilation mode or patient sedation
  5. Venous Thromboembolism
    1. See Venous Thromboembolism Prevention
    2. Anticoagulation or if contraindicated, pneumatic compression device
  6. Gastric Stress Ulcer
    1. Empiric intravenous Proton Pump Inhibitor (e.g. Pantoprazole) or H2 Blocker (e.g. Famotidine)
  7. Nosocomial Pneumonia
    1. Head of bed to 30 degrees
    2. Oral Hygiene

XIV. Evaluation: Monitoring parameters

  1. Background
    1. Ventilation
      1. Adjusted with Minute Ventilation = RR x TV
      2. Monitor with pCO2, etCO2
    2. Oxygenation
      1. Adjusted with FIO2, PEEP
      2. Monitor with Pulse Oximetry (preferred as a direct measure), pO2
  2. Adjustments: Formula
    1. RR_a * VT_a * PCO2_a = RR_b * VT_b * PCO2_b
      1. where _a indicates current value and _b indicates future value
      2. where RR_a and RR_b are Respiratory Rates (now and future)
      3. where VT_a and VT_b are Tidal Volumes (now and future)
      4. where PCO2_a and PCO2_b are ABG pCO2 levels (now and future)
    2. Solve for the TV or RR you wish to change to get a desired pCO2_b
      1. RR_b = RR_a * VT_a/VT_b * PCO2_a/PCO2_b
      2. VT_b = VT_a * RR_a/RR_b * PCO2_a/PCO2_b
  3. Arterial Blood Gas (ABG)
    1. Venous Blood Gas (VBG) may be used instead of Arterial Blood Gas
      1. Titrate down FIO2 to keep Oxygen Saturation 90-96% (see below)
    2. Obtain 20-30 minutes after intubation, acute Resuscitation, status change, Ventilator change
    3. PaO2 is most affected by FIO2, mean airway pressure, PEEP
    4. PaCO2 is most affected by Respiratory Rate, Tidal Volume (Vt) and dead space (Vd)
      1. Increasing Respiratory Rate is the first correction for correcting hypercapnia (with pH <7.2)
  4. Oxygen Saturation (O2 Sat)
    1. Target 90-96% Oxygen Saturation (88-92% in COPD and Obesity Hypoventilation Syndrome)
  5. End-Tidal CO2 (EtCO2)
    1. Note the EtCO2 at the time of each ABG
      1. Determine the difference between the PaCO2 and the EtCO2 (PaCO2 to EtCO2 gap)
    2. EtCO2 can be followed as an ABG surrogate during Ventilator setting adjustments
      1. No significant change in patient status
      2. Consistent PaCO2 to EtCO2 gap

XV. Resources

  1. Internet Book of Critical Care (EMCRIT.org)
    1. https://emcrit.org/ibcc/guide/
  2. Dominate the Vent Part 1 (Weingart, EMCrit)
    1. https://www.youtube.com/watch?v=G9TiP3kkK9Q
  3. Dominate the Vent Part 2 (Weingart, EMCrit)
    1. https://www.youtube.com/watch?v=rsArr9tu1yM
  4. Spinning Dials: Dominate the Ventilator (PDF Handout, Weingart, EMCrit)
    1. https://emcrit.org/wp-content/uploads/vent-handout.pdf

XVI. References

  1. Hamm (2018) Fundamental Critical Care Support Course Lecture, St Paul, MN, attended 4/26/2018
  2. Marino (2014) ICU Book, Walters-Kluwer, Philadelphia
  3. Nugent (2011) Bedside Guide to Mechanical Ventilation, 1st ed
  4. Owens (2012) Ventilator Book, First Draught Press
  5. Roginski, Hogan and Buscher (2020) Crit Dec Emerg Med 34(6): 17-27
  6. Schaub, Peluso and Stull (2020) Crit Dec Emerg Med 34(9): 3-12

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