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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)
- EPAP = 5-12 (increase if oxygenation 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.
- However if you remove all PEEP, alveoli will collapse again (because those airways don't have surfactant).
- 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)
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.
- Some ventilators (newer ones like Dragger) can have PC-PSV
- 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.
- Support: patient initiating breaths.
- Support vs. Controlled (aka AC)
- 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)
- Pressure you apply to small airways (causes baro trauma).
- 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).
- Pressure applied to large airways.
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.
- Place patient on T-piece with no positive pressure, only supplemental O2.
- 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.
- Carbon monoxide toxicity
- 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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