Airway Management

American Society of Anesthesiologists (ASA) Physical Status Classification

  • ASA 1: Normal Healthy Patient
    • Example: varicose veins in otherwise healthy patient
  • ASA 2: Mild Systemic Disease That Does Not Impair Normal Activity
    • Example: controlled HTN, controlled DM, chronic bronchitis, etc
  • ASA 3: Severe Systemic Disease That is Not Incapacitating
    • Example: IDDM, angina, pulmonary insufficiency, etc
  • ASA 4: Severe Systemic Disease That is a Constant Threat to Life
    • Example: CHF, major organ insufficiency, etc
  • ASA 5: Moribund Patient Who is Not Expected to Survive for 24 hrs With or Without Surgery
    • Example: intracranial hemorrhage in coma, etc
  • ASA 6: Declared Brain Dead with Plan for Organ Donation

Pre-Intubation Airway Assessment

LEMON Mnemonic

  • Look
    • Dentition: assess for dentures, prominent maxillary incisors, broken/loose teeth, and crowns
    • Incisor Size
    • Scars
    • Tongue Size
  • Evaluate Using the 3-3-2 Rule
    • At Least 3 Fingers Between the Incisors
    • At Least 3 Fingers for the Thyromental Distance: distance from thyroid prominence to the and point of chin (mentum) with the neck extended
      • Thyromental distance is considered important because during direct laryngoscopy, the tongue is displaced by the laryngoscope into the thyromental distance space: a short thyromental distance indicates less space for the tongue to be displaced into by the laryngoscope blade
    • At Least 2 Fingers for the Hyomental Distance: distance between hyoid bone (just above thyroid cartilage) and point of chin (mentum)
  • Mallampati Airway Class/Score: assessed in upright patient with mouth wide open and tongue out -> allows assessment of oral size and anatomy of tongue and oropharynx
    • Class I: hard palate, soft palate, entire uvula, fauces, and pillars visible
    • Class II: hard palate, soft palate, part of uvula, and fauces visible
    • Class III: hard palate, soft palate, and base of uvula visible -> predicts difficult mask ventilation and difficult intubation
    • Class IV: only hard palate visible -> predicts difficult mask ventilation and difficult intubation

MALLAMPATI

  • Obstruction of Airway
  • Neck Mobility: assess for next extension
    • Neck Extension May Be Limited with History of C-Spine Surgery
    • Neck Extension May Be limited Due to Rheumatoid Arthritis (RA) (see Rheumatoid Arthritis, [[Rheumatoid Arthritis]]): neck extension during intubation in some patients with RA may result in atlanto-axial subluxation, resulting in spinal cord injury

Difficult Mask Ventilation

General Comments

  • Difficult Intubation is More Likely with Difficult Mask Ventilation
    • Difficult Intubation Occurs in 30% of Patients with Difficult Mask Ventilation, as Compared to Only 8% of Patients without Difficult Mask Ventilation (Anesthesiology, 2000) [MEDLINE]
  • Difficult Mask Ventilation is Associated with a “Can’t Intubate, Can’t Ventilate” Scenario

Predictors of Difficult Mask Ventilation (Anesthesiology, 2000) [MEDLINE] and (Anesthesiology, 2006) [MEDLINE]

  • Age >55 y/o: age is associated with increased pharyngeal resistance to airflow (from choanae to epiglottis) in men, but not in women
  • BMI >26 kg/m2: obesity is associated with decreased posterior airway space behind the base of the tongue, impaired airway patency during sleep, and is a risk factor for OSA
  • Lack of Teeth
  • Presence of Beard
  • History of Snoring
  • Limited Mandibular Protrusion

Induction and Paralysis

Sedatives

  • Etomidate (Amidate) (see Etomidate, [[Etomidate]]) (duration 3-5 min): 0.3 mg/kg IVP
  • Midazolam (Versed) (see Midazolam, [[Midazolam]]): 2-10 mg IVP
  • Propofol (Diprivan) (see Propofol, [[Propofol]])

Paralytics

  • Vecuronium (see Vecuronium, [[Vecuronium]])
    • Dose: 10 mg IV push
    • Duration: 45 min
  • Rocuronium (see Rocuronium, [[Rocuronium]])
    • Dose: xxx
    • Duration: xxx
  • Succinylcholine (see Succinylcholine, [[Succinylcholine]])
    • Dose: 1-1.5 mg/kg IV push
    • Duration: 7-10 min
    • Avoid Succinylcholine With:
      • Burns (within 24 h-2 years)
      • CVA/SCI (within 1 wk-6 mo)
      • Neuromuscular Disease: MS/ALS
      • Muscle Crush Injury (within 7-90 days)
      • Penetrating Eye Trauma
      • History of Malignant Hyperthermia

Direct Laryngoscopy

Sellick Maneuver

  • Definition: cricothyroid pressure applied throughout the entire rapid sequence intubation procedure to prevent vomiting -> maintain until ETT cuff is inflated

Direct Laryngoscopy Blades

  • Macintosh Blade
    • Curved blade
    • Tip is inserted into valleculae
    • Size: 3 or 4 for adults
  • Miller Blade
    • Straight blade
    • Tip is inserted on top of epiglottis
    • Size: 3 or 4 for adults
  • Glidescope
    • Tip is inserted into valleculae

Cormack-Lehane (C-L) View of Glottis

  • Grade I: full view of glottis
  • Grade II: partial glottic view
  • Grade III: minimal glottic view
  • Grade IV: no view of glottis

C-L

Techniques to Improve Laryngeal View During Direct Laryngoscopy

  • Backward-Upward-Rightward (BURP) Maneuver: backward-upward-rightward movement of larynx by manipulating the thyroid cartilage
  • Mandibular Advancement: improves view

Extension of Apnea Time During Endotracheal Intubation

  • Clinical Efficacy
    • Pre-Oxygenation with Supplemental Oxygen Bag-Mask Ventilation: removes nitrogen from the lungs and creates an alveolar oxygen reservoir (this reservoir remains fixed at the end of pre-oxygenation and does not get replenished once depleted)
      • Mechanisms to Increase the Reservoir Size
        • Head-Up Patient Positioning: reduces dependent atelectasis
        • Increasing Mean Airway Pressure
    • Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE) Increases Apnea Time During Endotracheal Intubation (Anaesthesia, 2015) [MEDLINE]: high-flow nasal supplemental oxygen (during pre-oxygenation and continuing as post-oxygenation during intravenous induction of anaesthesia and neuromuscular blockade until airway was secured) increases the apnea time during endotracheal intubation
      • Proposed Mechanism: combines the benefits of classical apneic oxygenation with continuous positive airway pressure and gaseous exchange through flow-dependent deadspace flushing
    • Trial of High-Flow Nasal Cannula During Endotracheal Intubation (Crit Care Med, 2015) [MEDLINE]: high-flow nasal cannula oxygen significantly improved preoxygenation and reduced the prevalence of severe hypoxemia compared with non-rebreathing bag reservoir facemask
    • Trial of Apneic Oxygenation During RSI in the ED (Acad Emerg Med, 2016) [MEDLINE]
      • Apneic Oxygenation During RSI Increased the First Pass Success (without Hypoxemia) Rate: defined as successful intubation with SaO2 remaining ≥90%

Video Laryngoscopy

Technique

  • Glidescope

Clinical Efficacy

  • Systematic Review/Meta-Analysis of Video Laryngoscopic vs Direct Laryngoscopic Endotracheal Intubation (Intensive Care Med, 2014) [MEDLINE]: 9 trials (n = 2133) comparing direct laryngoscopic vs video laryngoscopic intubaton in the ICU
    • Compared to Direct Laryngoscopy, Video Laryngoscopy Reduced the Risk of Difficult Orotracheal Intubation [OR 0.29 (95% confidence interval (CI) 0.20-0.44, p < 0.001)], Cormack 3/4 Grade Airways [OR 0.26 (95% CI 0.17-0.41, p < 0.001)], and Esophageal Intubation [0.14 (95% CI 0.02-0.81, p = 0.03)]
    • Compared to Direct Laryngoscopy, Video Laryngoscopy Increased the First-Attempt Success Rate [OR 2.07 (95% CI 1.35-3.16, p < 0.001)]
    • No Statistically Significant Difference was Found for Severe Hypoxemia, Severe Cardiovascular Collapse, or Airway Injury

Fiberoptic Intubation

Technique

Clinical Efficacy

  • Awake Fiberoptic Intubation is Successful in 88-100% of Difficult Airway Patients (Category B3-B Evidence) (American Society of Anesthesiologists Task Force on Management of the Difficult Airway; Anesthesiology, 2013) [MEDLINE]

Extension of Apnea Time During Endotracheal Intubation

  • Clinical Efficacy
    • *High-Flow Nasal Cannula May Be Used to Facilitate Oxygenation During Fiberoptic Intubation (Chest, 2015) [MEDLINE]

Nasotracheal Intubation

  • Disadvantages
    • Higher Incidence of Maxillary Sinusitis

Cricothyroidotomy (Cricothyrotomy)

  • Indications
    • Inability to Intubate Patient

LARYNX

CRIC KIT


Confirmation of Endotracheal Tube (ETT) Placement

Colorimetric CO2 Indicator

  • Principle: colorimetric CO2 indicators (Easy Cap II, etc) use litmus paper that tidally (breath by breath) changes from purple to yellow in the presence of exhaled CO2
    • ETCO2 <0.5%: purple
    • ETCO2 0.5-2%: tan
    • ETCO2 >2%: yellow
  • False-Positive Results
    • Difficult Intubation with Prolonged Bag Ventilation: air previously pushed into the stomach during bag ventilation may cause yellow color change for the first few breaths -> if remains yellow after 4-5 breaths, this indicates that trachea has been successfully intubated
    • Epinephrine (see Epinephrine, [[Epinephrine]]): acidic medication which can cause (non-tidal) yellow color change
    • Lidocaine (see Lidocaine, [[Lidocaine]]): acidic medication which can cause (non-tidal) yellow color change
    • Regurgitation of Gastric Contents During Intubation: gastric acid can cause (non-tidal) yellow color change
  • False-Negative Results
    • Acute Pulmonary Embolism (PE) (see Acute Pulmonary Embolism, [[Acute Pulmonary Embolism]]): false-negative results may occur because pulmonary blood flow and delivery of CO2 to the lungs are reduced
    • Airway Obstruction: indicator may not turn yellow [Emerg Med J 2003: 20: 265-266]
    • Cardiac Arrest (see Cardiac Arrest, [[Cardiac Arrest]]): indicator may or may not turn yellow, even with tracheal intubation (due to lack of blood delivery to the lungs)
      • If chest compressions are adequate (with blood flow to lungs), indicator will likely turn yellow
      • Only has 69% sensitivity for tracheal intubation when used during CPR [Ann Emerg Med, May 1992; 21: 518-523]

Waveform Capnography (see Capnography, [[Capnography]])

  • Principle: these devices use infrared absorption to detect CO2
  • End-Tidal CO2 Monitor (which attach to ETT): either display waveform capnography or digital readout
  • Studies of waveform capnography to verify endotracheal tube position in victims of cardiac arrest have shown 100% sensitivity and 100% specificity of this method in identifying correct ETT placement
    • Continuous waveform capnography is now recommended, in addition to clinical assessment, as the most reliable method of confirming and monitoring correct placement of an ETT

Auscultation

  • Auscultation over bilateral lung fields to confirm breath sounds is not adequate alone to confirm placement, must also auscultate over epigastric area to confirm lack of breath sounds

Endotracheal Tube (ETT) Movement with Head Positioning

  • ETT Tip Movement Follows Direction of Chin Movement
    • Neck Flexion (Chin Downward): ETT tip moves downward
    • Neck Extension (Chin Upward): ETT tip moves upward

References

  • Safe intrahospital transport of critically ill ventilator-dependent patients. Chest 1989; 96:631-635 [MEDLINE]
  • Unplanned extubations in the adult intensive care unit. Am J Respir Crit Care Med 1998; 157:1131-1137 [MEDLINE]
  • Death and other complications of emergency airway management in critically ill adults. Anesthesiology 1995; 82:367-376 [MEDLINE]
  • Bedside procedures: solutions to the pitfalls of intrahospital transport. Crit Care Clin 2000; 16:1-6 [MEDLINE]
  • Prediction of difficult mask ventilation.  Anesthesiology 2000;92:1229–1236 [MEDLINE]
  • Difficult airway management in the emergency department. J Emerg Med. 2002 Jan;22(1):31-48 [MEDLINE]
  • Towards evidence based emergency medicine: best BETs from the Manchester Royal Infirmary. Colourimetric CO(2) detector compared with capnography for confirming ET tube placement. Emerg Med J 2003: 20: 265-266 [MEDLINE]
  • The assessment of three methods to verify tracheal tube placement in the emergency setting. Resuscitation 2003; 56:153-157 [MEDLINE]
  • The effectiveness of out-of-hospital use of continuous end-tidal carbon dioxide monitoring on the rate of unrecognized misplaced intubation within a regional emergency medical services system. Ann Emerg Med 2005; 45:497-503 [MEDLINE]
  • Clinical review: management of difficult airways.  Crit Care 2006;10:243.  doi: 10.1186/cc5112 [MEDLINE]
  • Incidence and predictors of difficult or impossible mask ventilation.  Anesthesiology 2006;105:885–891 [MEDLINE]
  • Caution when using colorimetry to confirm endotracheal intubation. Anesth Analg 2007;104:738 [MEDLINE]
  • 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Part 8: adult advanced cardiovascular life support. Circulation 2010; 122(18 Suppl 3):S729-S767 [MEDLINE]
  • Airway management in critically ill patients.  Lung  2011; 189:181-192 [MEDLINE]
  • Emergency airway management: the difficult airway.  Emerg Med Clin North Am  2012; 30:401-420 [MEDLINE]
  • Practice guidelines for management of the difficult airway: an updated report by the American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Anesthesiology. 2013;118:251–270 [MEDLINE]
  • Video laryngoscopy versus direct laryngoscopy for orotracheal intubation in the intensive care unit: a systematic review and meta-analysis. Intensive Care Med. 2014 May;40(5):629-39. doi: 10.1007/s00134-014-3236-5. Epub 2014 Feb 21 [MEDLINE]
  • Transnasal humidified rapid-insufflation ventilatory exchange (THRIVE): a physiological method of increasing apnoea time in patients with difficult airways. Anaesthesia 2015;70:323-9 [MEDLINE]
  • Use of high-flow nasal cannula oxygen therapy to prevent desaturation during tracheal intubation of intensive care patients with mild-to-moderate hypoxemia. Crit Care Med. 2015;43:574–583 [MEDLINE]
  • Heated humidified high-flow nasal oxygen in adults: mechanisms of action and clinical implications. Chest. 2015;148(1):253–261 [MEDLINE]
  • First Pass Success Without Hypoxemia Is Increased With the Use of Apneic Oxygenation During Rapid Sequence Intubation in the Emergency Department. Acad Emerg Med. 2016 Jun;23(6):703-10. Epub 2016 May 13 [MEDLINE]