Airway

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    Airway Assessment

    • LEMON Mnemonic
    • Look - Externally for foreign objects
    • Evaluate - 3:3:2 rule
      • 3 fingers between incisors (patient) [TM Joint Assessment]
      • 3 fingers between mentum to hyoid bone (Ant-Posterior Distance - shorter = more difficult)
      • 2 fingers between hyoid and thyroid (neck length)
    • Mallampati Score
    • Obstruction - anything in the way, soft tissue? etc..
      • Examples: smoke inhalation, burns, broken necks, trauma to the face or neck, foreign bodies in the airway, and excessive soft tissue from obesity
    • Neck Mobility

    Non-Invasive Positive Pressure (NIPPV)

    • Be careful: NIPPV can worsen outcomes by delaying intubation in sick patients.
    • Elective intubation may be appropriate if pts don't respond to 1-2h of NIPPV.
    • Two forms:
      • CPAP
      • BiPAP

    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:

    Invasive Ventilation

    • ET tube sizes: 8 (men), 7 (women)
    • LMA Sizes: 4-5 (men) [5=most men], 3-4 (women) [4=most women]
      • King LMA - has two cuffs... one supraglotic and one over the esophagus.
      • Supreme LMA - is like a regular LMA but has a port at the bottom to put NG tube if patient vomits.  Also has protection at the teeth to prevent patient from biting down and obstructing tube.
    • Intubation - Rapid Sequence Intubation (RSI)
      • asthmaIntubation.jpg

    Ventilators

    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).

     

    • inspHold2.jpg

     

    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. 

    Challenges in Obstructive Lung Disease

    • Allow adequate time of exhalation before next breath, and minimize airway resistance by optimizing PEEP.
    • Lower minute ventilation occurs, which is OK called "permissive hypercapnia".
    • Delivering volume before full expiration is called "breath stacking", leading to auto-PEEP.
      • Check expiratory pressure during an end-expiratory pause (no air flow) allows pressure to equilibrate with alveoli and confirm presence/absence of auto-PEEP.
      • Breath stacking can be dangerous --> barotrauma and hypotension.
    • Set ventilator for rapid inspiratory flow rate, and allow time to exhale.
      • If patient is anxious, triggering lots of breaths, sedation may be required to avoid auto-PEEP.
      • Hypercapnia is a potent stimulus to increase expiratory rate.

     

    Acute Inhalational Injury

    • Common, especially in burn victims.  (50% of burn deaths).
    • Damage to lung parenchyma is a serious issue. 
    • Two types:
      • Soluble Toxin (or brief heat exposure) --> upper airway damage.
      • Less soluble toxin or prolongued heat exposure --> distal airways and lung parenchyma.
    • May not be evident for 12-24hrs post-exposure.
    • Specific
      • Carbon monoxide toxicity
        • Causes carboxyhemoglobin, tissue hypoxia
        • O2 sat is overestimated!!
        • Need blood gas analysis.
      • Cyanide (plastic/acryllic combustion):
        • Can get systemic absorption from inhalation.
        • Sodium thiosulfate (use instead of nitrites) - both accepted.
          • Nitrites can cause methemoglobin, which worsens situation.
    • Management:
      • (Supportive)
      • IV fluids
      • Intubation / mechanical ventilation
      • Chest physio
      • Bronchoscopic suctioning/debridement for retained secretions.
      • Inhaled bronchodilators for bronchospasm
      • Antibiotics

     

    Intubation (Under Construction)

    Source: "Little ICU Book" by Marino 2008

    • ET tube sizes: 8 (men), 7 (women)
    • LMA Sizes: 4-5 (men) [5=most men], 3-4 (women) [4=most women]
      • King LMA - has two cuffs... one supraglotic and one over the esophagus.
      • Supreme LMA - is like a regular LMA but has a port at the bottom to put NG tube if patient vomits.  Also has protection at the teeth to prevent patient from biting down and obstructing tube.
    • Non-invasive ventilation post-extubation for 24hrs reduced need for re-intubation.  Useful to bridge.
      • Incentive spirometry reducres risk of post-op resp complications, but never shown to help with extubation. 
    • Once Patient is intubated:
      • Use ETCO2 (End Tidal CO2)
      • Listening for breath sounds is unreliable.
      • Chest Xray should be obtained (end of ET tube 3-5cm above carina)

     

    ***Discontinuing Mechanical Ventilation***

    • Step 1: Is the patient ready?
      • Once patients demonstrate clinical improvement, they can be trialed off the ventilator:
      • Checklist in the 1st table should be used to identify candidates for spontaneous breathing trial:
        • Checklist for Spontaneous Breathing Trial

          1. Respiratory Criteria:

          • PaO2 ≥ 60 on FiO2 < 40-50% and PEEP ≤ 5-8 cmH2O
          • PaO2 normal or baseline
          • Able to initiate inspiratory effort

          2.  Cardiovascular Criteria

          • No evidence of cardiac ischemia
          • Heart rate ≤ 140 bpm
          • BP normal without vasopressors or minimum
            pressor support (i.e. dopamine < 5 ug/kg/min)

          3.  Adequate Mental Status

          • Rousable or GCS ≥ 13

          4.  Absence of Correctable Comorbid Conditions

          • Patient is afebrile
          • No significant electrolyte abnormalities

           
    • Step 2: Spontaneous Breathing
      • Once above criteria met --> remove ventilator and allow patient to try to breathe on own
      • Two ways to do this:
        • Breathing through ventilator (more resistance, but can measure volumes)
        • Breathing through a T-piece (delivers humidified 100% O2 through T-piece)
      • Once spontaneously breathing use the following table for predict success:
        •  
          • Measurement Reference Range Threshold for Successful SBT
            Tidal Volume 5-7 mL/kg 4-6 mL/kg
            Resp Rate 10-18 bpm 30-38 bpm
            Total Ventilation (Ve) 5-6 L/min 10-15 L/min
            RR/Vt Ratio 20-40/L 100/L
            Maximum Inspiratory Pressure -90 to -120 cmH2O -15 to -30 cm H2O
      • Patients initially breathe rapid and shallow
        • (Rapid Shallow Breathing Index - RSBI) developed to predict success of weaning attempt
        • RR/Vt
          • if > 105/L  = 95% failed weaning
          • if < 105/L  = 80% successful weaning
    • Step 3: Decannulation
      • Is patient protecting airway?
        • Awake, easily roused, follows commands.
        • Minimal respiratory secretions?
        • Able to gag reflex, cough and clear secretions? (piece of paper 1-2cm, allow cough, wetness should appear on paper)
      • Laryngeal Edema?
        • High risk of upper airway obstruction in patients after intubation? (laryngeal injury)
        • Use "Cuff-Leak Test" 
        • "Cuff-Leak Test"

          • Used to identify patients with severe laryngeal edema (reduces risk of obstructed decannulated airways.
          • Volume of exhaled gas is measured with cuff inflated and again after cuff is deflated.
          • Deflated cuff should allow some air to escape around the ET tube
          • If exhaled volume measured through ET tube is the same with cuff on and off, then cuff leak is absent == severe airway edema, do not extubate yet.
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