Airway

BiPAP

• Can they tolerate BiPAP?
  • Awake, alert, spontenously breathing.
  • Alert enough to say they are vomiting to take off mask.
  • Vomiting is a contraindication to BiPAP!
• Contraindicatons:
  • Severe hemoptysis, cardiac arrest / MI, decreased LOC , vomiting risk, recent oropharyngeal or gastric surgery.
  • Non-cooperative, agitated, face trauma/surgery, facial deformity, upper airway obstruction.
• Always for spontaneous ventilation.
• IPAP and EPAP (inspiratory and expiratory).
  • (EPAP = PEEP) and (IPAP = total inspiratory pressure).
  • IPAP - EPAP = pressure support setting on intubation ventilator.
• Starting pressures:
  • EPAP = 5-12 (increase if oxygenation issues)
    • Also depends on condition (i.e. 5 for CHF, 7 for COPD, 10 for ILD)
  • IPAP = 8-20  (increase if ventilation/pCO2 issues)
• Limited by 20-25 mmH2O maximum airway pressures, as higher pressures open the cardiac esophageal sphincter causing stomach air entry, vomiting, aspiration.
  • If higher pressures needed --> intubate.
• Often order "to keep pH > 7.3".
• If cannot improve pH >7.25 in 2 hours --> INTUBATE
• If O2 not improvement, and IPAP is up to 18-20 --> INTUBATE

• Respond to blood gasses:
  • If CO2 is high = increase deltaP (difference between IPAP and EPAP)
  • if O2 is high = increase the EPAP (aka PEEP).
  • Titrate to NORMAL PH (not CO2) or rather titrate to their baseline CO2 (that is normally compensated)

CPAP vs. BiPAP

• CPAP - For O2 problem (for oxygenation problem) (proven)
  • CHF
  • OSA
  • COPD exacerbation (if CO2 is not up)
  • Pneumonia
    • (Discouraged as can make them worse, pts less likely to cough.  Avoid unless think they will fail.)
  • Initial disease
• BiPAP (for CO2 +/- O2 problem)
  • neuromuscular weakness (myasthenia gravis, GBS, ALS)
  • COPD exacerbation
• Often  atelectasis in the lungs, the idea with PEEP or EPAP is keeping high pressures to keep alveoli open.
  • However if you remove all PEEP, alveoli will collapse again (because those airways don't have surfactant).
    • Need 24-48hrs to build up surfactant to keep airways open. (studies show if drop peep right away, there is no benefit, airways re-collapse)
  • However, with high PEEP there is a risk of barotrauma (popping alveoli) and compressing blood flow and converting shunt to dead sapce.
• Rat Lungs recruitment with peep:
  • https://www.youtube.com/watch?v=oKH7CtsEgHw

Basic Modes

• Step 1:
  • Support vs. Controlled (aka AC)
    • Support: patient initiating breaths.
      • Patient must be able to blow open a valve...you set what defines a triggered "breath".  Often you set "trigger flow", if inspiration flow opens the value, this triggers a breath with a defined support (volume or pressure).
      • May not be initiating breaths fast enough, and underventilating.
      • Typically if apnea occurs, ventilator switches to control mode for 2 minutes.
        • Some ventilators (newer ones like Dragger) can have PC-PSV
          • PC-PSV (Pressure Control - Pressure Support Vent): can set a minimum rate.  If rate falls below minimum, so it triggers a pressure control breath, and allows pressure support to continue if patient can breathe.
    • Control:
      • Defined rate, patient cannot override.
      • Advantages:
        • Maximum control, maximum diaphragm rest
      • Disadvantages:
        • Usually uncomfortable.
        • Preferred for paralyzed patients.
        • Overventilation.
        • Air trapping if insufficient expiratory time before next breath.
• Step 2:
  • Pressure Guarantee vs. Volume Guarantee
  • Pressure Guarantee
    • Provides airway pressure to a set amount.
    • This is a "go-to" mode for most RT's... set pressure, and titrate airway pressures to reach an a certain tidal volume (usually 6-10cc/kg) ~400-500ccs
    • Usually good for COPD/Asthma because you can titrate deltaP. (see below)
    • I:E ratio --> Inspiration:Expiration.  (I is set)
      • I:E ratio is important for airway obstruction.  If COPD/Asthma patient has a short I:E ratio, they need long exhalation time.  If exhalation is not complete they will keep air in their lungs at the end of each breath, causing "PEEP" to build up (called auto-PEEP)
  • Volume Guarantee:
    • Less common, often used by anesthesia because people more healthy.
    • Set volume, and machine will determine airway pressures to achieve that volume.
    • Typically scary, make sure you keep a max pressure.  If patient obstructs, machine can generate high pressures and no volume.  Can cause pneumo etc.. 
  • PAV - Proportional Assist Ventilation
    • Gives proportional pressure assist.
    • Used to wean off of ventilator.
    • The idea is to work the diaphgram... some research into improving weaning off vents.
  • SIMV - Synchronized Intermittent Mandatory Ventilation
    • Mixture of pressure support and pressure control ventilation
    • Machine breaths delivered at scheduled rate with preset tidal volumes
    • Patient triggered breath are pressure supported (instead of volume supported)
    • Advantages:
      • Used for weaning, allowing number of machine breathes to be reduced.
    • Clinical trials: Inferior or less-effective in weaning (still used popularly).
  • IMV
    • Intermittent mandatory ventilation.
    • Patient discomfort - eg. inhales when vent exhales.
  • APRV (Aka Bi-Level)
    • Similar to BiPAP
    • ECHOR?  Extra-corporally
• Lingo:
  • Spontaneous + Pressure Guarantee = Pressure Support
  • Controlled + Pressure Guarantee = Pressure Controlled (PCV)
  • etc..
• Goals:
  • Clear CO2 at minimzied lung volumes
  • Barotrauma, hard to wean if keep on high lung volumes.

Settings

• Many parameters:
  • Respiratory Rate
  • Tital Volume
  • PEEP
  • FiO2
  • I:E (Inspiratory:Exp ratio)
  • Inspiratory flow rates
  • Alarms to signal issues

• PEEP - Positive End Expiratory Pressure
  • Regulates PaO2
  • Usual Settings: 6-12 mmH2O
    • Natural PEEP is up to 5 mmH2O
    • Use 6 for low PEEP (COPD for high deltaP)
    • Use 12 for high PEEP (CHF - push fluid into vasculature).
    • Or no PEEP if healthy.
• Pressure Control
  • Starting: 6-12.
  • Titrate to tidal volumes of 6-8 cc/kg. (i.e. 80kg = 480cc's).  (8-10 possible, but considered high volumes).
• Total Airway Pressure
  • For BiPAP maximum airway pressure is 20 --> if over 25, open cardiac esophageal sphincter. --> requires definitive airway.
  • Same for LMAs.
• Plateau pressure
  • Pressure you apply to small airways (causes baro trauma).
    • Depends on compliance (in addition to tidal volume)
  • Measured during an "Inspiratory Hold", allowing the air to equalize to alveoli.
  • In ARDS try to keep < 30 cmH2O (improves outcomes)
• Peak Pressure
  • Pressure applied to large airways.
    • Depends on Airway Resistance and Lung Compliance (in addition to tidal volume)
    • i.e. Increase in Ppeak indicates either increase in airway resistance or decrease in compliance.
    • Airway Resistance = Ppeak - Pplateau
  • In asthma: Plat (small airways) is low, and Peak pressure is high (airway obstruction).

How to deal with increase in airway pressures:

• If Ppeak increased, but Pplateau unchanged = problem with airway resistance.
  • ET tube obstruction, secretions, bronchospasm (suction, bronchodilators, etc..)
• If Ppeak and Pplateau are both increased
  • Decrease in thoracic compliance
  • pneumothorax, lobar atelectasis, acute pulmonary edema, worsening pneumonia, progression of ARDS.
    • Auscultate lungs (diminished breath sounds = pneumo?), get STAT chest xray.
• If Ppeak is decreased
  • cuff leak? (air escaping)
  • Hyperventilating patient? (generates negative intrathoracic pressure)
• Bronchodilator titration
  • Favourable response is decrease in Ppeak and no change in Pplateau (Ppeak - Pplateau decreased)

Adjusting Settings Based on ABG

• If PaO2 is low: 
  • Either increase PEEP or increase FiO2
  • Typically increasing FiO2 >50% is less desirable due to toxic lung injury, so many anesthetists/RTs like to go up on the PEEP and keep FiO2 low.
• If PaCO2 is high
  • Increase detaP  (= difference between PEEP and Peak Pressure) or increase respiratory rate.
  • i.e. in COPD who is accummulating CO2, make PEEP low and pressure support high.

Interesting Trials

• Proning: RCT: better oxygenation, but no mortality difference, increase in complication (ET obstruction, accidental extubation, pressure ulcers).
  • Recommended only in experienced centers in severe ARDS, if oxygenation is unsuccessful.

Long-Term Intubation

• Tracheostomy should be performed within 14-21 days of intubation
  • (Many trials checked the length of time, but above is the bottom line.)

Weaning

• Occurs when hemodynamically stable and recovered from respiratory failure.
• Should have a cough strong enough to clear secretions, low secretion burden.
• Rapid Shallow Breathing Index (RSBI) - testing readiness of patient for weaning.
  • Ratio of respiratory rate (F) to tidal volume (VT).
  • If F:VT > 105 --> 95% chance of unsuccessful spontaneous breathing trial.
  • If F:VT < 105 --> 80% chance of success (key number).
• Spontaneous breathing trial:
  • Place patient on T-piece with no positive pressure, only supplemental O2.
    OR
  • Adjusting ventilator to apply only enough pressure to overcome ET tube resistance.
• Daily interruption of sedation and spontanenous breathing trials are a standard of care for Critical Care.
  • Shortened need of mechanical ventilation by avg 1.5 days, and reduce mortality, reduce ICU stay!!!
• Direct extubation to NIPPV is effective in patients with obstructive lung disease from mechanical ventilation (not effective for patients with hypoxemic respiratory failure).

Extubation

• Generally ventilator settings are down-titrated slowly, and when they are at minimal settings.. patient is extubated.
• Several trials support the use of NIPPV post-extubation (reduced risk of re-intubation and shortened ICU stay, improved survival).
  • Not replicated in further studies, only done in specific populations.
  • Many trials, controversial.
• Bottom line: Immediate NIPPV post-extubation should be done for patients with chronic lung disease and hypercapnia.

Ventilator Associated Pneumonia

• Serious!
• Defined as pneumonia with onset at least 48hrs after intubation.
• Affects 10-25% of ventilated patients, 25-50% mortality rate.
• Hard to detect: CXR often already shows infiltrates.
• All patients suspected of having VAP should undergo lower-tract sampling + microscopy + QUANTITATIVE culture of specimen.
• 3 ways to get culture:
  • 1. Bronchoscopic - BAL.
  • 2. Non-Bronchoscopic (suction ET tube and mini-broncho-alveolar lavage / Mini-BAL)
  • (Bronch vs. non-Bronch -> no mortality difference, narrower abx choices for bronch).
• Culture thresholds:
  • Simple Aspiration: 1,000,000 CFU
  • BAL: 10,000 CFU
  • Protected Specimen Brush: 1,000 CFU (more reliable).
• 8 days of abx are sufficient, if quantitative cultures are negative, discontinue abx.