- Clinical science
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.
- Definition: orotracheally or nasotracheally placement of a cuffed tube below the vocal cords
- Preoxygenation: administration of 100% oxygen via face mask prior to intubation to ensure sufficient time to perform intubation.
- Sedation (e.g., propofol)
- Muscle relaxation (e.g., succinylcholine)
- Positioning of patient with mild cervical flexion (sniffing position)
- 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).
- Signs of proper tube placement
- Inflate the cuff to secure the tube if proper placement is ensured.
- Magill tubes
- 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
- Description: rigid, L-form tube for orotracheal intubation with a guide wire
- Features: rarely used today
- Double-lumen endotracheal tubes
Recommended inner diameter for the endotracheal tube
- ♂: 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!
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
Assessment of intubation conditions
|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
- Early complications
- Late complications after intubation: : vocal cord injuries, vocal cord granuloma
- Complications of long-term intubation
- Suction airways prior to extubation to minimize risk of aspiration (e.g., of fluids, foreign material)
- Extubation criteria
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
- Jaw-thrust maneuver: manual procedure to open the upper airway without extending the neck
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
- The patient is in a supine position.
- The physician uses the little, ring, and middle finger of one hand to lift the jaw towards the mask
- The thumb and index finger squeeze the mask onto the face and form a capital C
- 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
- Definition: : Permanent or temporary opening (stoma) in the cervical trachea created through surgical incision below the cricoid cartilage for the placement of a tracheal tube
- Long-term mechanical ventilation (> 3 weeks)
- Acute upper airway obstructions that cause respiratory distress (stridor) and respiratory acidosis, e.g.:
- Tracheal toilet (e.g., comatose patients)
- Severe CPAP therapy in patients intolerant of
- Difficulty weaning off a ventilator
- Definition: emergency procedure in which an incision is made through the skin and cricothyroid membrane to obtain airway access
- Complications: See section on complications of tracheostomy above.
- Definition: use of a respirator to assist or completely replace spontaneous breathing
- Technique: : positive-pressure ventilation
- Tidal volume: amount of air passed through an endotracheal or tracheostomy tube per breath
- 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
- Weaning: Process of easing a patient off mechanical ventilatory support.
Assist control (AC) ventilation: guarantees delivery of a preset tidal volume
- In this mode, breathing can be triggered by the patient or the ventilator.
- Pressure-support ventilation: patients initiate breathing themselves and the ventilator delivers support with a preset pressure value ; used primarily for weaning purposes
- Continuous positive airway pressure: (CPAP): positive pressure ventilation with a mask for patients with
Positive end-expiratory pressure (PEEP): ventilator setting that can be chosen to increase functional residual capacity (FRC) by reducing alveolar collapse during mechanical ventilation
- Definition: Positive pressure (∼ 5 cm H2O); in the lung is maintained over the entire inhalation and expiration phases.
- Indications: if oxygenation is insufficient despite FiO2 of 100%, and no cause can be identified (e.g., pneumothorax, displaced intubation tube) → use PEEP to treat intrapulmonary shunt pathology
Mechanism of action
- PEEP ↑ alveolar pressure and alveolar volume → collapsed or unstable alveoli reopen → improves ventilation/perfusion relation
- Provides an adequate arterial PaO2 at a low and safe concentration of oxygen (< 60%) → reduces the risk of oxygen toxicity
- Side effects
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.
- 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 saturation → ↑ FiO2
- 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 (), a condition clinically resembling ARDS
- ↑ Intracranial pressure: : raise head of bed and initiate hyperventilation < 30 minutes after onset
- Definition: bronchoconstriction during anesthesia; causes severe hypoxia and hypotension, if left untreated
- Epidemiology: incidence ∼ 0.2%
- Reactive airway disease (e.g., , )
- 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