• Clinical science

Airway management and ventilation

Abstract

Airway management is the evaluation, planning, and use of medical procedures and devices for the purpose of maintaining or restoring ventilation in a patient. These procedures are indicated in patients undergoing general anesthesia and in patients with respiratory failure or acute airway obstruction.

In endotracheal intubation, a tube is inserted orally into the trachea to provide oxygen via mechanical ventilation during general anesthesia. The tube should be placed under direct visualization with the help of a laryngoscope. Correct placement is established based on measurement of exhaled CO2 and evidence of bilateral breath sounds on auscultation. Complications of endotracheal intubation include dental damage, esophageal misplacement of the tube, infections, and tracheal stenosis. If long-term intubation is expected, a tracheostomy is usually performed. This procedure involves the creation of a reversible or permanent stoma below the cricoid cartilage. Cricothyrotomy is an airway of last resort and performed in emergency situations, such as acute obstruction of the airway by blood, edema or a foreign body. An incision is made in the membrane between the thyroid and cricoid cartilage to obtain airway access.

Once access to an airway has been established by any of the above mentioned routes, mechanical ventilation is used to assist or replace spontaneous breathing. The breathing rate, amount of oxygen per breath, applied pressure, and other parameters can be adjusted to achieve best possible ventilation and oxygenation. Complications of mechanical ventilation include barotrauma (e.g., pneumothorax, pneumomediastinum) and ventilator-induced lung injury, which clinically resembles ARDS. Once patients show sufficient spontaneous breathing, they are weaned off ventilation support.

Intubation

Endotracheal intubation

  • Definition: orotracheally or nasotracheally placement of a cuffed tube below the vocal cords
  • Indications
    • General anesthesia
    • Failure (or pending failure) of ventilation or oxygenation
    • Glasgow Coma Score ≤ 8
  • Procedure
    1. Preoxygenation: administration of 100% oxygen via face mask prior to intubation to ensure sufficient time to perform intubation.
    2. Sedation (e.g., propofol)
    3. Muscle relaxation (e.g., succinylcholine)
    4. Positioning of patient with mild cervical flexion (sniffing position)
    5. Placement of the endotracheal tube with the help of a laryngoscope: observe the tip of the tube passing into the larynx through the vocal cords (direct visualization).
    6. Signs of proper tube placement
      • Auscultation of bilateral breath sounds over lungs
      • Measurement of CO2 in the exhaled air (end-tidal CO2)
      • Distal tip should be 2–6 cm above carina (check with chest x-ray and reposition if necessary)
    7. Inflate the cuff to secure the tube if proper placement is ensured.

Tube types

  • Magill tubes
  • Spiral tube
    • Description: tube with an integrated, flexible metal spiral for orotracheal intubation with a guide wire
    • Features: tube cannot be bent due to stiffening→ to be applied in, e.g., surgery in a prone position
  • Oxford non-kinking tube
  • Double-lumen endotracheal tubes
    • Description: various tubes (Carlens, White, and Robert Shaw tubes) for bilateral and/or unilateral lung ventilation
    • Features: unilateral ventilation possible (e.g., surgery in the thoracic cavity)

  • Recommended inner diameter for the endotracheal tube
    • Adults
      • : 8–8.5 mm
      • : 7.5–8 mm
    • Children: The patient's little finger can serve as reference for selecting tube diameter.

In the case of insufficient mask ventilation, air can easily enter the stomach. With the aid of a valve gear, a ventilatory pressure of 20 cm H2O should therefore not be exceeded, which approximately corresponds to the closing pressure of the lower esophageal sphincter!

Difficult intubation conditions

Potentially difficult intubation conditions are assessed in a preoperative briefing. Difficult conditions include:

  • Muscular alterations: myotonia, torticollis, conditions following ENT surgery
  • Restricted cervical movement: e.g., in ankylosing spondylitis
  • Craniofacial features
    • Long beard → may impede complete seal of mask
    • Small mouth → difficult access during intubation
    • Large and/or loose incisors; prognathism and receding chin; short neck → difficult adjustment of the larynx with the laryngoscope

Assessment of intubation conditions

  • Prior to intubation: evaluation of the palate and throat according to the modified Mallampati classification
Mallampati I Uvula and soft palate are completely visible.
Mallampati II The tip of the uvula is covered by the tongue; the soft palate is completely visible.
Mallampati III The uvula is completely covered by the tongue; the soft palate is mostly visible.
Mallampati IV Only the hard palate is recognizable.

Cormack-Lehane Grade I The entire glottis is visible and adjustable with the laryngoscope.
Cormack-Lehane Grade II The glottis is visible (at the posterior extremity) but only partially adjustable with the laryngoscope.
Cormack-Lehane Grade III The glottis is not adjustable with the laryngoscope. Only the epiglottis can be recognized.
Cormack-Lehane Grade IV Neither the laryngeal structures nor the epiglottis are adjustable. Only the soft palate is visible.

Complications of intubation

Extubation

References:[1][2][2][2][3][4][5]

Mask ventilation

  • Airway establishment and facilitating breathing
    • No spinal injury suspected: open airway using the head-tilt/chin-lift maneuver: The head is tilted back and the chin lifted up.
    • Spinal injury suspected:
      • Jaw-thrust maneuver: manual procedure to open the upper airway without extending the neck
        • Mechanism of action: elevation of the base of the tongue and enlargement of the hypopharyngeal space
        • Procedure:
          1. The patient is in a supine position. The physician is standing at the head of the bed.
          2. The physician places his/her fingers behind the angles of the lower jaw and moves the jaw upwards
          3. At the same time, he/she uses her thumbs to open the mouth slightly.
    • EC-clamp technique procedure to ensure for effective bag-mask ventilation
      • Mechanism of action: create a tight seal between a mask and a patient's face to avoid air leaks
      • Procedure:
        1. The patient is in a supine position.
        2. The physician uses the little, ring, and middle finger of one hand to lift the jaw towards the mask
        3. The thumb and index finger squeeze the mask onto the face and form a capital C

References:[6][7]

Laryngeal mask airway (laryngeal mask, LAMA)

  • Short description: an inflatable mask is attached to the end of a tube, which adapts to the structures in the laryngeal region, enabling secure tracheal ventilation without requiring endotracheal intubation
  • Indications: particularly in short or minor elective procedures
  • Relative contraindications
    • Upper abdominal and thoracic surgery
    • Intoxication
    • High respiratory pressure (> 20 cm H2O)
    • Alternative positions (e.g., prone position or sitting position)

References:[8]

Surgical airway management

Tracheostomy

Cricothyrotomy

References:[3][9][10][11]

Mechanical ventilation

Basics

  • Definition: use of a respirator to assist or completely replace spontaneous breathing
  • Indications
    • General anesthesia
    • Breathing support
      • Respiratory distress or arrest
      • Hypoxemia (PaO2 < 70 mm Hg) or hypercapnia (PaCO2 > 50 mm Hg)
      • Metabolic acidosis
      • Respiratory muscle fatigue
      • Impaired consciousness and inability to protect airways
  • Technique: : positive-pressure ventilation
  • Ventilation parameters
    • Tidal volume: amount of air passed through an endotracheal or tracheostomy tube per breath
      • Healthy lung: 8–12 mL/kg body weight
      • Lung-protective: 6–8 mL/kg body weight
    • Respiratory rate: approx. 10–15/min
    • Inspiratory oxygen concentration (FiO2)
      • Anesthetic induction: 100% (short-term)
      • During surgery: 30%–100%
    • Oxygenation improves with PEEP, FiO2 (additional oxygen supply)
    • Ventilation improves with respiratory rate, tidal volume
  • Capnometry: /capnography: assessment of CO2 concentration in expired air to determine whether oxygenation is adequate
    • Unremarkable capnography cycle: rapid increase of the CO2 concentration → plateau → rapid decrease of the CO2 concentration during inspiration
    • Capnography in airway obstruction: slow increase of the CO2 concentration → no plateau → rapid decrease of the CO2 concentration during inspiration
  • Weaning: Process of easing a patient off mechanical ventilatory support.

Ventilator settings

Mechanical ventilation with a very high PEEP may result in pneumothorax!

Intermittent positive pressure ventilation (IPPV)

  • Intermittent positive pressure (mechanically or manually triggered by a breathing bag): 10–20 cm H2O in adults, whereby there is never negative end-expiratory pressure

Intermittent mandatory ventilation

  • IMV : simultaneous spontaneous and controlled ventilation to guarantee a sufficient respiratory volume → triggering of breaths of air via a machine: The patient can breath unsynchronized on their own between the mechanical breaths of air.
  • SIMV : In this mode, spontaneous breathing activity of the patient, if present, is supported by the ventilator. If the machine detects a certain level of breathing activity, it provides additional pressure as support for the respective breath of air, which is thereby synchronized with the spontaneous breathing of the patient. If there is no spontaneous breathing, the machine emits autonomously in accordance with a predetermined rhythm.

Special scenarios

  • Suspected tube displacement: examination via auscultation of the thorax (lung fields in a side comparison) and abdomen (epigastrium)
  • Insufficient oxygenation: decrease in the peripherally measurable oxygen saturationFiO2
  • Alkalosis in BGA (hypocapnia): tidal volume, respiratory rate
  • Acidosis in BGA (hypercapnia)tidal volume, respiratory rate
  • Patients with COPD or ARDS: : reduce tidal volume to prevent ventilator-induced lung injury (lung-protective ventilation), a condition clinically resembling ARDS
  • ↑ Intracranial pressure: : raise head of bed and initiate hyperventilation < 30 minutes after onset

Bronchospasm

  • Definition: bronchoconstriction during anesthesia; causes severe hypoxia and hypotension, if left untreated
  • Epidemiology: incidence ∼ 0.2%
  • Risk factors
    • Smoking
    • Reactive airway disease (e.g., asthma, COPD)
    • Viral upper respiratory tract infection
  • Clinical features
  • Differential diagnosis: mechanical obstruction (e.g., blocked or misplaced tracheal tube), laryngospasm, anaphylaxis (e.g., caused by medication, blood products), pneumothorax, pulmonary embolism, or aspiration
  • Treatment
    • Basic measures
      • Discontinuation manipulating measures/surgery
      • Manual ventilation with a FiO2 of 100%
      • Deepen anesthesia
      • Exclude differential diagnosis
    • Pharmacotherapy in severe bronchospasm

References:[2][2][2][3][5][12][13][14]