Airway Management Flashcards
Airway anatomy
- resistance to airflow through nasal passages accounts for approximately 2/3 of total airway resistance
- pharyngeal airway extends from posterior aspect of the nose to cricoid cartilage
- glottic opening (triangular space formed between the true vocal cords) is the narrowest segment of the laryngeal opening in adults
- the glottic opening is the space through which one visualizes proper placement of the ETT
- the trachea begins at the level of the thyroid cartilage, C6, and bifurcates into the right and left main bronchi at T4-T5 (approximately the sternal angle)
Methods of supporting airways
- non-definitive airway (patent airway)
■ jaw thrust/chin lift
■ oropharyngeal and nasopharyngeal airway
■ bag mask ventilation
■ LMA - definitive airway (patent and protected airway)
■ ETT
■ surgical airway (cricothyrotomy or tracheostomy)
Bag and Mask advantages/indications
Basic
Non-invasive
Readily available
Bag and Mask disadvantages/contraindications
Risk of aspiration if decreased LOC
Cannot ensure airway patency
Inability to deliver precise tidal volume
Operator fatigue
Bag and Mask other
Facilitate airway patency with jaw thrust and chin lift
Can use oropharyngeal/ nasopaharyngeal airway
Laryngeal Mask Airway (LMA) advantages/indications
Easy to insert
Less airway trauma/irritation than ETT
Frees up hands (vs. face mask)
Primarily used in spontaneously ventilating patient
Laryngeal Mask Airway (LMA) disadvantages/contraindications
Risk of gastric aspiration
PPV <20 cm H20 needed
Oropharyngeal/retropharyngeal pathology or foreign body
Does not protect against laryngospasm or gastric aspiration
Laryngeal Mask Airway (LMA) sizing
Sizing by body weight (approx)
40-50 kg: 3
50-70 kg: 4
70-100 kg: 5
Endotracheal tube (ETT) advantages/indications
Indications for intubation (5Ps)
Patent airway
Protects against aspiration
Positive pressure ventilation
Pulmonary toilet (suction)
Pharmacologic administration
also hemodynamic instability
Endotracheal tube (ETT) disadvantages/contraindications
Insertion can be difficult
Muscle relaxant usually needed
Most invasive
Endotracheal tube (ETT) other
Auscultate to avoid endobronchial intubation
ETT sizing
intubation Sizing (approx):
Male: 8.0-9.0 mm
Female: 7.0-8.0 mm Pediatric Uncuffed (>age 2) (age/4) + 4 mm
Equipment required for intubation
MDSOLES
Monitors
Drugs
Suction
Oxygen source and self-inflating bag with oropharyngeal and nasopharyngeal airways
Laryngoscope
Endotracheal tubes (appropriate size and one size smaller)
Stylet, Syringe for tube cuff inflation
Medications that can be given through the ETT
NAVEL Naloxone Atropine Ventolin Epinephrine Lidocaine
Preparing for ETT intubation
- failed attempts at intubation can make further attempts more difficult due to tissue trauma
- plan, prepare, and assess for potential difficulties (see Pre-Operative Assessment, A2)
- ensure equipment is available and working (test ETT cuff, check laryngoscope light and suction, machine check)
- pre-oxygenate/denitrogenate: patient breathes 100% O2 for 3-5 min or for 4-8 vital capacity breaths
- may need to suction mouth and pharynx first
Proper positioning for intubation
• align the three axes (mouth, pharynx, and larynx) to allow visualization from oral cavity to glottis
■ “sniffing position”: flexion of lower C-spine (C5 C6), bow head forward, and extension of upper C-spine at atlanto-occipital joint (C1), nose in the air
■ contraindicated in known/suspected C-spine fracture/instability
• laryngoscope tip placed in the epiglottic vallecula in order to visualize cord
Tube insertion
• laryngoscopy and ETT insertion can incite a significant sympathetic response via stimulation of cranial nerves 9 and 10 due to a “foreign body reflex” in the trachea, including tachycardia, dysrhythmias, myocardial ischemia, increased BP, and coughing
• a malpositioned ETT is a potential hazard for the intubated patient
■ if too deep, may result in right endobronchial intubation, which is associated with left-sided atelectasis and right-sided tension pneumothorax
■ if too shallow, may lead to accidental extubation, vocal cord trauma, or laryngeal paralysis as a result of pressure injury by the ETT cuff
• the tip of ETT should be located at the midpoint of the trachea at least 2 cm above the carina and the proximal end of the cuff should be placed at least 2 cm below the vocal cords
■ approximately 20-23 cm mark at the right corner of the mouth for men and 19-21 cm for women
Confirmation of tracheal placement of ett
• direct
■ visualization of ETT passing through cords
■ bronchoscopic visualization of ETT in trachea
• indirect
■ ETCO2 in exhaled gas measured by capnography – a mandatory method for confirming the ETT is in the airway
■ auscultate for equal breath sounds bilaterally and absent breath sounds over epigastrium
■ bilateral chest movement, condensation of water vapour in ETT visible during exhalation and no abdominal distention
■ refilling of reservoir bag during exhalation
■ CXR (rarely done): only confirms position of the tip of ETT and not that ETT is in the trachea
Esophageal intubation suspected when
■ ETCO2 zero or near zero on capnograph
■ abnormal sounds during assisted ventilation
■ impairment of chest excursion
■ hypoxia/cyanosis
■ presence of gastric contents in ETT
■ breath sounds heard when auscultating over epigastrium/LUQ
■ distention of stomach/epigastrium with ventilation
Differential diagnosis of poor bilateral breath sounds after intubation
DOPE
Displaced ETT
Obstruction
Pneumothorax
Esophageal intubation
Complications during laryngoscopy and intubation
- dental damage
- laceration (lips, gums, tongue, pharynx, vallecula, esophagus)
- laryngeal trauma
- esophageal or endobronchial intubation
- accidental extubation
- insufficient cuff inflation or cuff laceration: results in leaking and aspiration
- laryngospasm
- bronchospasm
Predicting difficult intubation in apparantly normal patients
A combination of the Mallampati score and thyromental distance is the most accurate at predicting difficult intubation. The PLR (9.9) is supportive of the test as a good predictor of difficult intubation.
What are important preventative measures for difficult airway
pre-op assessment
pre-oxygenation
If difficulty airway expected consider what types of intubation
awake intubation
intubating with bronchocope, trachlight (lighted stylet), fibre optic laryngoscope, glidescope, etc
If intubation is unsuccessful after induction
- CALL FOR HELP
- Ventilate with 100% o2 via bag and mask
- Consider returning to spontaneous ventilation and/or waking patient
If bag and mask ventilation inadquate
- CALL FOR HELP
- Attempt ventilation with oral airway
- consider/attempt LMA
- emergency invasive airway access (e.g. rigid bronchoscope, cricothyrotomy, or tracheostomy)
Cyanosis can be detected at
SaO2 <85%,
frank cyanosis at SaO2 = 67%
What are low flow oxygen systems
- provide O2 at flows between 0-10 L/min
- acceptable if tidal volume 300-700 mL, respiratory rate (RR) <25, consistent ventilation pattern
- dilution of oxygen with room air results in a decrease in FiO2
- an increase in minute ventilation (tidal volume x RR) results in a decrease in FiO2
• e.g. nasal cannula (prongs)
■ well tolerated if flow rates <5-6 L/min; drying of nasal mucosa at higher flows
■ nasopharynx acts as an anatomic reservoir that collects O2
■ delivered oxygen concentration (FiO2) can be estimated by adding 4% for every additional litre of O2 delivered
■ provides FiO2 of 24-44% at O2 flow rates of 1-6 L/min
What things shift the PaO2/SaO2 curve down
Increased pH
Decreased 2,3-BPG
Decreased temp
What things shift the PaO2/SaO2 curve up
Decreased pH
Increased 2,3-BPG
Increased temp
What are reservoir oxygen systems
• use a volume reservoir to accumulate oxygen during exhalation thus increasing the amount of oxygen available for the next breath
• simple face mask
■ covers patient’s nose and mouth and provides an additional reservoir beyond nasopharynx
■ fed by small bore O2 tubing at a rate of at least 6 L/min to ensure that exhaled CO2 is flushed through the exhalation ports and not rebreathed
■ provides FiO2 of 55% at O2 flow rates of 10 L/min
• non-rebreather mask
■ a reservoir bag and a series of one-way valves prevent expired gases from re-entering the bag
■ during the exhalation phase, the bag accumulates with oxygen
■ provides FiO2 of 80% at O2 flow rates of 10-15 L/min
Composition of air
- 1% nitrogen
- 9% oxygen
- 9% argon
- 04% carbon dioxide
What are high flow oxygen systems
- generate flows of up to 50-60 L/min meet/exceed patient’s inspiratory flow requirement
- deliver consistent and predictable concentration of O2
• Venturi mask
■ delivers specific FiO2 by varying the size of air entrapment
■ oxygen concentration determined by mask’s port and NOT the wall flow rate
■ enables control of gas humidity
■ FiO2 ranges from 24-50%
Ventilation and muscle relaxants
- ventilation is maintained with PPV in patients given muscle relaxants
- assisted or controlled ventilation can also be used to assist spontaneous respirations in patients not given muscle relaxants as an artificial means of supporting ventilation and oxygenation
Indications for mechanical ventilation
■ apnea
■ hypoventilation/acute respiratory acidosis
■ intraoperative positioning limiting respiratory excursion (e.g. prone, Trendelenburg)
■ required hyperventilation (to lower ICP)
■ deliver positive end expiratory pressure (PEEP)
■ increased intrathoracic pressure (e.g. laparoscopic procedure)
Complications of mechanical ventilation
■ airway complications
◆ tracheal stenosis, laryngeal edema
◆ alveolar complications
◆ ventilator-induced lung injury (barotrauma, volutrauma atelectatrauma), ventilator-associated pneumonia (nosocomial pneumonia), inflammation, auto PEEP, patient-ventilator asynchrony
◆ cardiovascular complications
◆ reduced venous return (secondary to increased intrathoracic pressure), reduced cardiac output, hypotension
■ neuromuscular complications
◆ muscle atrophy
◆ increased intracranial pressure
■ metabolic decreased CO2 due to hyperventilation
◆ alkalemia with over correction of chronic hypercarbia
Changes in peak pressures in ACV and tidal volumes in PCV may reflect what?
changes in lung compliance and/or airway resistance – patient may be getting better or worse
What is positive end expiratory pressure (PEEP)
- Positive pressure applied at the end of ventilation that helps to keep alveoli open, decreasing V/Q mismatch
- Used with all invasive modes of ventilation
Tracheostomy indication
- Tracheostomy should be considered in patients who require ventilator support for extended periods of time
- Shown to improve patient comfort and give patients a better ability to participate in rehabilitation activities
Monitoring ventilatory therapy
- Pulse oximetry, end-tidal CO2 concentration
- Regular arterial blood gases
- Assess tolerance regularly
Management for patients the develop a pneumothorax while on mechanical ventilation
chest tube
Ventilator strategies
- mode and settings are determined based on patient factors (e.g. ideal body weight, compliance, resistance) and underlying reason for mechanical ventilation
- hypoxemic respiratory failure: ventilator provides supplemental oxygen, recruits atelectatic lung segments, helps improve V/Q mismatch, and decreases intrapulmonary shunt
- hypercapnic respiratory failure: ventilator augments alveolar ventilation; may decrease the work of breathing, allowing respiratory muscles to rest
Modes of ventilation
• assist-control ventilation (ACV) or volume control (VC)
■ every breath is delivered with a pre-set tidal volume and rate or minute ventilation
■ extra controlled breaths may be triggered by patient effort; if no effort is detected within a specified amount of time the ventilator will initiate the breath
• pressure control ventilation (PCV)
■ a minimum frequency is set and patient may trigger additional breaths above the ventilator
■ all breaths delivered at a preset constant inspiratory pressure
• synchronous intermittent mandatory ventilation (SIMV)
■ ventilator provides controlled breaths (either at a set volume or pressure depending on whether in VC or PCV, respectively)
■ patient can breathe spontaneously (these breaths may be pressure supported) between controlled breaths
• pressure support ventilation (PSV)
■ patient initiates all breaths and the ventilator supports each breath with a pre-set inspiratory pressure
■ useful for weaning off ventilator
• high-frequency oscillatory ventilation (HFOV)
■ high breathing rate (up to 900 breaths/min in an adult), very low tidal volumes
■ used commonly in neonatal and pediatric respiratory failure
■ occasionally used in adults when conventional mechanical ventilation is failing
• non-invasive positive pressure ventilation (NPPV)
■ achieved without intubation by using a nasal or face mask
■ BiPAP: increased pressure (like PSV) on inspiration and lower constant pressure on expiration (i.e PEEP)
■ CPAP: delivers constant pressure on both inspiration and expiration
Causes of intraoperative hypoxemia
Inadequate oxygen supply - e.g. breathing system disconnection, obsructed or malpositioned ETT, leaks in the anesthetic machine, loss of oxygen supply
Hypoventilation
Ventilation-perfusion inequalities - e.g. atelectasis, pneumonia, pulmonary edema, pneumothorax
Reduction in oxygen carrying capacity - e.g. anemia, carbon monoxide poisoning, methemoglobinemia, hemoglobinopathy
Leftward shift of the hemoglobin-oxygen saturation curve - e.g. hypothermia, decreased 2,3-BPG, alkalosis, hypocarbia, carbon monoxide poisoning
Right-to-left cardiac shunt
Method of weaning patients from mechanical ventilation that leads to extubation more quickly
Once-daily or multiple trials of spontaneous breathing led to extubation more quickly than intermittent mandatory or pressure support ventilation.
Causes of hypocapnea end tidal
Hyperventilation
hypothermia (decreased metabolic rate)
decreased pulmonary blood flow (decreased cardiac output)
technical issues, incorrect placement of sampling catheter, inadequate sampling volume
V/Q mismatch, pulmonary thromboembolism, incipient pulmonary edema, air embolism
Causes of end tidal hypercapnea
Hypoventilation
hyperthermia and other hypermetabolic states
improved pulmonary blood flow after resuscitation or hypotension
technical issues (water in capnography device, anesthetic breathing circuit error, inadequate fresh gas flow, rebreathing, exhausted soda lime, faulty circuit absorber valves)
low bicarbonate
