Anesthesia: Difficult Airway Management Predictors

Difficult Airway Management Predictors

• Difficult airway: a clinical situation where a trained anesthetist experiences difficulty with facemask ventilation, laryngoscopy, intubation, or all of these.
• Difficult facemask ventilation: unable to provide due to inadequate mask seal, excess gas leak (BOOTS).
• Difficult laryngoscopy: unable to visualize any portion of the vocal cords after multiple attempts (LEMON).
• Difficult SGA ventilation: unable to provide adequate ventilation due to difficult SGA placement, SGA requiring multiple attempts, excessive resistance (RODS).
• Difficult extubation.
• Difficult FONA airway - SHORT acronym.
• Preoperative airway assessment: additionally consider aspiration risk and desaturation risks.

Aspiration Risk

• Active GERD symptoms, acute trauma, GI problems, patients on a lot of narcotics, pregnancy 12+ weeks and even up to 10 weeks postpartum, GLP1 receptor antagonists.
• Neuromuscular disease or any other disease that causes gastroparesis (diabetes).
• Oral contrast.

Desaturation Risks

• Pediatrics, obese, COPD, OSA, anyone that hypoventilates or has decreased FRC, pulmonary dysfunction.
• Kids and septic patients desat faster due to lower FRC and increased O2 consumption.

Inadequate Ventilation

• Gas leak out of mask and increasing use of oxygen flush valve, need for airway adjunct, need for 2-handed BVM technique, poor chest rise, absent/inadequate ETCO2, gastric air entry/dilation, decreasing O2 sat, cyanosis, hemodynamic changes associated with hypoxemia, hypercarbia.

Cannot Intubate/Cannot Oxygenate (CICO)

• Failure to maintain adequate alveolar oxygenation by face mask, SGA, or ETT despite optimal attempts.
• Repeat attempts without changing technique are not likely to work.
• Multiple attempts increase risk of trauma.
• Multiple attempts decrease effectiveness of other attempts and other techniques.

Basic Airway Management

• Oxygen delivery, oral and nasal airways, mask ventilation, confirming ventilation.
• Preoxygenation requires a tight seal against face - 100% FiO2 at a high flow (10-12 LPM) for 3-5 mins.

Nasal Cannula

• Oxygen delivery depends on oxygen flow, nasopharyngeal volume, patient's TV, and inspiratory time.
• Inspired oxygen increases roughly 2% per liter with quiet breathing.
• 5LPM delivers 40% FiO2.
• Cannot deliver >6 LPM for extended periods.

Apneic Oxygenation

• Used for short-term apneic episodes (e.g. induction, emergence).
• Requires a patent airway.
• Even without lung expansion/diaphragmatic movement, alveoli will continue to receive oxygen if a higher gradient exists.
• Helps maintain PaO2 but does NOT prevent hypercarbia and acidosis.
• Provide apneic oxygenation via NC at 15 LPM.

Simple Mask

• Not as well tolerated as a NC.
• Do not completely seal against the face - not used for preoxygenation.
• 5-6 LPM = FiO2 30-45%.
• 7-8 LPM = FiO2 40-60%.
• Minimum flow of 5 LPM must be maintained to limit breathing.

Partial Rebreathing and NRB

• Contains one-way valves over exhalation ports and between reservoir bag and mask.
• Masks with gas reservoirs do not seal against the face - NOT for preoxygenation.
• Partial rebreather = % of patient's exhaled TV refills the bag.
• NRB 7-15 LPM = 40-100% FiO2.

High Flow Nasal Cannula

• Can utilize flow rates up to 60 LPM.
• Generates FiO2 near 100%.
• Allows nasopharynx to act as O2 reservoir.
• Better tolerated than face mask and noninvasive PPV.

Adult Face Masks

• Goal is an airtight seal.
• BVM technique - EC technique.
• Put mask on from eyes to chin to prevent mask from getting into pt's eyes.
• Normally use size 5 for adults.

Ventilation Basics

• Use right hand to squeeze bag.
• APL = adjustable pressure limiter valve.
• Avoid squeezing too hard/fast to prevent gastric distention.
• Pressure you want to generate 25 degrees bend in tube, high flows, corrugated tubing, ETT tube (smaller tubes are more turbulent).

Pulmonary Blood Flow

• Pulmonary vessels are much shorter than systemic vessels and therefore have decreased resistance - Poiseuille's law.
• Bronchial arteries:
  • Like coronary arteries in heart.
  • Feed the lungs.
  • 2% of CO.
  • Do not participate in gas exchange.
• Pulmonary arteries:
  • Transport - bring unoxygenated blood to the lungs to receive oxygenation.
  • Low pressure system (PVR is low) and is very sensitive to small changes.
  • Changes in circulation are locally mediated by changes in O2 and CO2.

V/Q Basics

• Normal Ventilation/Perfusion is 4L/5L.
• Things that cause dead space (i.e. block perfusion) = PE, cardiogenic shock.
• Things that cause shunt (i.e. block ventilation) = shunt, pneumonia, atelectasis, airway obstruction.

Dead Space

• Ventilated but not perfused.
• Volume of conducting airways = anatomic dead space = 2mL/kg.
• Alveolar dead space + anatomic dead space = physiologic dead space.
• Bohr equation describes the amount of physiologic dead space in a person's lungs by comparing the amount of CO2 in arterial blood to that in exhaled gas.
• Non-perfused areas equilibrate with inspired air.
• High V/Q - high O2 and low CO2.

Shunt

• Perfused but not ventilated.
• Perfused areas equilibrate with arterial CO2 (mixed venous).
• Low V/Q - low O2 and high CO2.

Hypoxic Pulmonary Vasoconstriction

• Hypoxic pulmonary vasoconstriction (HPV) = diversion of blood flow from hypoxic or atelectic alveoli to an area of better ventilation or diffusion.
• Increase blood flow to lungs to improve gas exchange.
• High O2 tension and hypocapnia vasodilate pulmonary vessels so they can pick up more O2.
• Hypercarbia and acidosis cause vasoconstriction - increase PVR.

All Ventilator Modes

• Pplat is a reflection of the pressure inside the alveoli at the end of inspiration where there is no airflow and directly correlates with lung compliance.
• Higher Pplat indicates lower compliance.

Restrictive Lung Disease

• Reduced compliance limits expansion of lungs, increased resistance in lung tissue.
• PIP and Pplat elevated.
• Require higher PIP and higher PEEP due to reduced lung compliance and risk of atelectasis.

Obstructive Lung Disease

• Increased compliance due to air trapping, loss of elasticity due to overexpansion of lungs, increased airway resistance.
• PIP elevated, Pplat normal or elevated depending on degree of air trapping.
• Require higher PIP to overcome airway resistance with potentially normal or elevated Pplat depending on degree of hyperinflation with lower PEEP.

Pplat

• Plateau pressure = pressure that remains in alveoli during plateau phase with no air flow.
• Measure of static lung compliance.
• Target.

High Flow Nasal Cannula

• Can utilize flow rates up to 60 LPM
• Generates FiO2 near 100%
• Allows nasopharynx to act as O2 reservoir
• Better tolerated than face mask and noninvasive PPV

Difficult Airway Management Predictors

• Difficult airway: clinical situation in which a trained anesthetist experiences difficulty with facemask ventilation, laryngoscopy, intubation, or all of these
• Difficult facemask ventilation: not able to provide due to inadequate mask seal, excess gas leak (BOOTS)
• Difficult laryngoscopy: not able to visualize any portion of the vocal cords after multiple attempts (LEMON)
• Difficult SGA ventilation: not able to provide adequate ventilation due to difficult SGA placement, SGA requiring multiple attempts, excessive resistance (RODS)
• Difficult extubation
• Difficult FONA airway – SHORT acronym
• Preoperative airway assessment: additionally consider aspiration risk and desaturation risks
• Aspiration risk: active GERD symptoms, acute trauma, GI problems, pt’s on a lot of narcotics, pregnancy 12+ weeks and even up to 10 weeks postpartum, GLP1 receptor antagonists
• Desaturation risks: pediatrics, obese, COPD, OSA, anyone that hypoventilates or has decreased FRC, pulmonary dysfunction

Inadequate Ventilation

• Inadequate ventilation: gas leak out of mask and increasing use of oxygen flush valve, need for airway adjunct, need for 2-handed BVM technique, poor chest rise, absent/inadequate ETCO2, gastric air entry/dilation, decreasing O2 sat, cyanosis, hemodynamic changes associated with hypoxemia, hypercarbia

Cannot Intubate/Cannot Oxygenate (CICO)

• Failure to maintain adequate alveolar oxygenation by face mask, SGA, or ETT despite optimal attempts
• Repeat attempts without changing technique are not likely to work
• Multiple attempts increase risk of trauma
• Multiple attempts decrease effectiveness of other attempts and other techniques

Basic Airway Management

• Oxygen delivery: oxygen delivery depends on oxygen flow, nasopharyngeal volume, patient’s TV, and inspiratory time
• Inspired oxygen increases roughly 2% per liter with quiet breathing
• 5LPM delivers 40% FiO2
• Cannot deliver >6 LPM for extended periods
• Preoxygenation: requires a tight seal against face – 100% FiO2 at a high flow (10-12 LPM) for 3-5 mins
• Nasal cannula: allows nasopharynx to act as O2 reservoir
• Apneic oxygenation: used for short-term apneic episodes, e.g., induction, emergence; requires a patent airway
• Simple mask: not as well tolerated as a NC; do not completely seal against the face – not used for preoxygenation
• Partial rebreathing and NRB: contains one-way valves over exhalation ports and between reservoir bag and mask; masks with gas reservoirs do not seal against the face – NOT for preoxygenation

Adult Face Masks

• Goal is an airtight seal
• BVM technique: EC technique
• Put mask on from eyes to chin to prevent mask from getting into pt’s eyes
• Normally use size 5 for adults

Ventilation Basics

• Use right hand to squeeze bag
• APL: adjustable pressure limiter valve
• Avoid squeezing too hard/fast to prevent gastric distention
• Pressure you want to generate 25 degrees bend in tube, high flows, corrugated tubing, ETT tube (smaller tubes are more turbulent)

Pulmonary Blood Flow

• Pulmonary vessels are much shorter than systemic vessels and therefore have decreased resistance – Poiseuille’s law
• Bronchial arteries: like coronary arteries in heart; feed the lungs; 2% of CO; do not participate in gas exchange
• Pulmonary arteries: transport – bring unoxygenated blood to the lungs to receive oxygenation; low pressure system (PVR is low) and is very sensitive to small changes
• Changes in circulation are locally mediated by changes in O2 and CO2

V/Q Basics

• Normal Ventilation/Perfusion is 4L/5L
• Things that cause dead space (i.e., block perfusion) = PE, cardiogenic shock
• Things that cause shunt (i.e., block ventilation) = shunt, pneumonia, atelectasis, airway obstruction
• Dead Space: ventilated but not perfused
• V/Q: normal Ventilation/Perfusion is 4L/5L
• Bohr equation: describes the amount of physiologic dead space in a person’s lungs by comparing the amount of CO2 in arterial blood to that in exhaled gas

Shunt

• Perfused but not ventilated
• Perfused areas equilibrate with arterial CO2 (mixed venous)
• Low V/Q – low O2 and high CO2

Hypoxic Pulmonary Vasoconstriction

• Diversion of blood flow from hypoxic or atelectic alveoli to an area of better ventilation or diffusion
• Increase blood flow to lungs to improve gas exchange
• High O2 tension and hypocapnia vasodilate pulmonary vessels so they can pick up more O2
• Hypercarbia and acidosis cause vasoconstriction → increase PVR

High Flow Nasal Cannula

• Can utilize flow rates up to 60 LPM
• Generates FiO2 near 100%
• Allows nasopharynx to act as O2 reservoir
• Better tolerated than face mask and noninvasive PPV adult face mask
• Proper mask placement: top should sit on the bridge of the nose, upper border aligned with the pupils, and bottom should sit between the lower lip and chin

Predictors of Difficult Airway Management

• Difficult airway: clinical situation in which a trained anesthetist experiences difficulty with facemask ventilation, laryngoscopy, intubation, or all of these
• Difficult facemask ventilation: not able to provide due to inadequate mask seal, excess gas leak
• Difficult laryngoscopy: not able to visualize any portion of the vocal cords after multiple attempts
• Difficult SGA ventilation: not able to provide adequate ventilation due to difficult SGA placement, SGA requiring multiple attempts, excessive resistance
• Difficult extubation and FONA airway management

Preoperative Airway Assessment

• Consider aspiration risk and desaturation risks
• Aspiration risk factors: • Active GERD symptoms, acute trauma, GI problems, patients on narcotics, pregnancy > 12 weeks and up to 10 weeks postpartum, GLP1 receptor antagonists • Neuromuscular disease or any other disease that causes gastroparesis (diabetes) • Oral contrast
• Desaturation risk factors: • Pediatrics, obese, COPD, OSA, anyone that hypoventilates or has decreased FRC, pulmonary dysfunction • Kids and septic patients desaturate faster due to lower FRC and increased O2 consumption

Inadequate Ventilation and CICO

• Inadequate ventilation: gas leak out of mask and increasing use of oxygen flush valve, need for airway adjunct, need for 2-handed BVM technique, poor chest rise, absent/inadequate ETCO2, gastric air entry/dilation, decreasing O2 sat, cyanosis, hemodynamic changes associated with hypoxemia, hypercarbia
• CICO (Cannot Intubate/Cannot Oxygenate): Failure to maintain adequate alveolar oxygenation by face mask, SGA, or ETT despite optimal attempts

Basic Airway Management

• Oxygen delivery, oral and nasal airways, mask ventilation, confirming ventilation
• Preoxygenation requires a tight seal against the face – 100% FiO2 at a high flow (10-12 LPM) for 3-5 minutes

Nasal Cannula and Apneic Oxygenation

• Nasal cannula: oxygen delivery depends on oxygen flow, nasopharyngeal volume, patient’s TV, and inspiratory time
• Inspired oxygen increases roughly 2% per liter with quiet breathing
• 5LPM delivers 40% FiO2, cannot deliver >6 LPM for extended periods
• Apneic oxygenation: • Used for short-term apneic episodes (e.g. induction, emergence) • Requires a patent airway • Even without lung expansion/diaphragmatic movement, alveoli will continue to receive oxygen if a higher gradient exists • Helps maintain PaO2 but does NOT prevent hypercarbia and acidosis • Provide apneic oxygenation via NC at 15 LPM

Simple Mask and Partial Rebreathing

• Simple mask: not as well tolerated as a NC, does not completely seal against the face – not used for preoxygenation
• 5-6 LPM = FiO2 30-45%, 7-8 LPM = FiO2 40-60%
• Minimum flow of 5 LPM must be maintained to limit breathing
• Partial rebreathing and NRB: contains one-way valves over exhalation ports and between reservoir bag and mask
• Masks with gas reservoirs do not seal against the face – NOT for preoxygenation
• Partial rebreather = % of patient’s exhaled TV refills the bag
• NRB 7-15 LPM = 40-100% FiO2

Pulmonary Blood Flow and V/Q Basics

• Pulmonary vessels are much shorter than systemic vessels and therefore have decreased resistance – Poiseuille’s law
• Bronchial arteries: • Like coronary arteries in heart • Feed the lungs • 2% of CO • Do not participate in gas exchange
• Pulmonary arteries: • Transport – bring unoxygenated blood to the lungs to receive oxygenation • Low pressure system (PVR is low) and is very sensitive to small changes • Changes in circulation are locally mediated by changes in O2 and CO2
• V/Q basics: • Normal Ventilation/Perfusion is 4L/5L • Things that cause dead space (i.e. block perfusion) = PE, cardiogenic shock • Things that cause shunt (i.e. block ventilation) = shunt, pneumonia, atelectasis, airway obstruction
• Dead Space = ventilated but not perfused • Volume of conducting airways = anatomic dead space = 2mL/kg • Alveolar dead space + anatomic dead space = physiologic dead space • Bohr equation describes the amount of physiologic dead space in a person’s lungs by comparing the amount of CO2 in arterial blood to that in exhaled gas
• Shunt = perfused but not ventilated • Perfused areas equilibrate with arterial CO2 (mixed venous) • Low V/Q – low O2 and high CO2

Hypoxic Pulmonary Vasoconstriction

• Hypoxic pulmonary vasoconstriction (HPV) = diversion of blood flow from hypoxic or atelectic alveoli to an area of better ventilation or diffusion • Increase blood flow to lungs to improve gas exchange • High O2 tension and hypocapnia vasodilate pulmonary vessels so they can pick up more O2 • Hypercarbia and acidosis cause vasoconstriction → increase PVR

Ventilator Modes

• Pplat is a reflection of the pressure inside the alveoli at the end of inspiration where there is no airflow and directly correlates with lung compliance • Higher Pplat indicates lower compliance
• Restrictive lung disease – reduced compliance limits expansion of lungs, increased resistance in lung tissue • PIP and Pplat elevated • Require higher PIP and higher PEEP due to reduced lung compliance and risk of atelectasis
• Obstructive lung disease – increased compliance due to air trapping, loss of elasticity due to overexpansion of lungs, increased airway resistance • PIP elevated, Pplat normal or elevated depending on degree of air trapping • Require higher PIP to overcome airway resistance with potentially normal or elevated Pplat depending on degree of hyperinflation with lower PEEP

Proper Mask Technique

• The position of the mask on the face is crucial for effective use.
• To hold the facemask in place, the left thumb and index finger should form a "C" shape around the collar.
• The middle and ring fingers should be placed on the bony part of the mandible to compress the mask onto the face and lift the chin.
• The 5th finger can be placed at the angle of the mandible to provide additional support and perform an anterior jaw thrust.

Chin Lift

• The chin lift technique pulls the hyoid bone anteriorly, which in turn pulls the epiglottis and posterior tongue superiorly and anteriorly.
• This movement results in the epiglottis and posterior tongue moving away from the posterior pharyngeal wall.
• The chin lift technique is more effective in increasing movement at the C1/C2 level compared to the jaw thrust maneuver.

Jaw Thrust

• The jaw thrust technique involves placing the tips of the fingers behind the angle of the mandible bilaterally and lifting toward the ceiling.
• This action pulls the jaw anteriorly, which in turn lifts the base of the tongue away from the posterior pharynx.
• Larson's maneuver is a variation of the jaw thrust, but it is essentially an exaggerated version of the technique.

Oral Airways

• Only used in unconscious patients
• OPA (Oropharyngeal Airway) pulls the tongue and epiglottis away from the posterior pharyngeal wall, creating a channel for air passage
• Does not enter the larynx
• Different types of OPAs: Berman, Guedel, Williams, and Ovassapian (used for bronchoscopy)
• Use a tongue blade to assist in placing the OPA
• Determine the size of the OPA by measuring from the corner of the mouth to the angle of the jaw from the earlobe

Nasal Airways

• Less noxious than oral airways
• Can be used in awake patients
• Measure the size of the NPA (Nasopharyngeal Airway) by measuring the distance from the patient's nare to the meatus of the ear
• The NPA should rest just above the epiglottis
• Insert the NPA with the bevel facing the nasal septum
• Use Afrin prior to insertion to decrease bleeding risk
• Contraindicated in basilar skull fracture, facial trauma
• Use with extreme caution in: anticoagulated patients, coagulopathy, pregnancy, and uncontrolled hypertension

Cuff Types and Complications

• High pressure/low volume cuffs are associated with a higher risk of ischemic damage
• Low pressure/high volume cuffs are the most commonly used type, but they increase the risk of: • Sore throat • Aspiration • Unintended extubation • Difficult insertion