Intubation and Ventilation

Indications for intubation

• Airway protection
• Prophylactic airway protection e.g. burns, transfers
• GCS <8/obtunded
• Invasive ventilation
• Hyperventilation required e.g. coning, tricyclic antidepressant toxicity
• High inspiratory O2 delivery
• Selective lung ventilation e.g. massive haemoptysis, bronchopleural fistula
• Volatile hydrocarbon ingestion
• Hyperthermia
• Drug delivery

Anaesthetic risk

• ASA Class
  • I – Healthy, no medical problems
  • II – Mild systemic disease e.g. HTN
  • III – Severe systemic disease but not incapacitating
  • IV – Severe systemic disease, constant threat to life
  • V – Moribund, life expectancy <24 hours irrespective of operation
  • E – Operation is an emergency

Rapid sequence induction

• The sequential administration of an induction agent and neuromuscular blocking agent to facilitate endotracheal intubation
• Highest intubation success rate in properly selected cases and superior to sedation alone
• Those deeply comatosed or in cardiorespiratory arrest may be intubated without pharmacological assistance
• If bag-mask-ventilation or rescue device is unlikely to succeed, or if anatomic alterations exist that will not improve with RSI (oedema, mass, bony disruption), do not extinguish intrinsic airway protection and respirations with paralysis

Pre-intubation stomach decompression

• Consider passage of NG if:
  • Children
  • Already applied BVM
  • Suspected gastric aspiration
  • Bowel obstruction
  • Haematemesis

Pre-oxygenation

• Desaturation in 45-60 sec without pre-ox
• With pre-ox
  • 8 minutes if well
  • 5 minutes if moderately unwell
  • 2.7 minutes if obese
• 3 minutes ideal. If time critical can get 8 quick large tidal volume breaths
• Apply PEEP valve to improve pre-intubation SpO2 as increases time to desaturation

Apnoeic oxygenation

• If maintained open airway, continuous intranasal O2 can delay desaturation by 90 seconds following paralysis
• No evidence for improved significant outcomes
• THRIVE study
  • Transnasal Humidified Rapid-Insufflation Ventilatory exchange
  • 25 adult patients with 100% O2 via HFNP with jaw thrust maintained throughout
  • Median apnoea time of 14 minutes with no desaturations
• NO DESAT
  • Nasal cannulae set to 15LPM to prolong apnoea time without desaturation

Shoulder we avoid bagging during apnoeic period?

• Latest difficulty airway society guidelines suggest this may be beneficial if done in safe manner i.e. low pressure and advise the bag mask ventilation should begin as soon as induction occurs
• Benefits practitioner in confirming bag-mask ventilation is possible also
• Pressures <15cmH20 rarely insufflate gas to stomach. Pressures >25cmH20 routinely will.
• No strong evidence for the complete avoidance of bag mask ventilation in preventing aspiration

Pre-treatment agents

• No evidence for benefit in terms of outcomes
• In adults, sympathetic response (issue in head injury, MI, aortic dissection) and centrally-mediated raised ICP (if loss of autoregulation) predominate
• In children, vagally-mediated bradycardia predominates
• Duration and finesse of laryngoscopy is the most important factor in physiologic perterbations seen with intubation
• If used, should give 3-5 minutes prior to RSI
• Fentanyl 3mcg/kg IV over 30-60 seconds may attenuate the reflex sympathetic response
• Atropine 0.02mg/kg IV in response to bradycardia in children (not recommended routine)

Induction

• Etomidate 0.3-0.5mg/kg IV; onset <1 min; 10-20 min duration
  • Non-barbiturate hypnotic with minimal haemodynamic depression and short duration of action
  • Not analgesic and does not blunt sympathetic response to intubation
  • Adrenal suppression does occur but no evidence that this worsens patient outcomes after a single dose in ED

• Propofol 1-2mg/kg; onset 20-40 seconds; 3-5min duration (up to 4mg/kg for children)
  • Sedative with more rapid onset of action than etomidate and shorter duration of action
  • Distribution half-life 2-3 minutes with rapid redistribution and elimination half-life 3-8 hours
  • Hepatically metabolised
  • Anticonvulsant and antiemetic properties
  • May lower ICP without triggering histamine release
  • Can cause hypotension through myocardial depression and vasodilation
    • >20mmHg drop in SBP in 15%
  • Painful on injection (can mix 2mL of 1% lignocaine into 20mL propofol to reduce pain)
  • Avoid in trauma patients and any patient with hypovolaemia or hypotension
  • Trismus and dystonic reactions are rare side effects
  • Apnoea seen in 1.5% (usually >1.5mg/kg dose)
  • 0.02% unplanned intubation rate

• Ketamine 1.5-2mg/kg; onset 30-60 seconds; 5-15min duration
  • IM dosing onset 3-8 minutes and duration 10-30 minutes
  • Additional IV doses 0.5-1mg/kg can be given to prolong sedation
  • Phencyclidine derivative
  • Dissociative anaesthetic with analgesic and amnestic properties
  • Preserves respiratory drive
  • Can cause increase in BP and HR through catecholamine release, useful in hypotensive/hypovolaemic patients
  • Causes direct smooth muscle relaxation and bronchodilation so ideal in status asthmaticus
  • Does not cause consistent increased ICP in sedated and ventilated patients
  • May have cerebroprotective effects
  • Good option for head injuries and hypotension
  • Not ideal for the elderly or patients at risk of cardiac ischaemia due to tachycardia and hypertension induction
  • Ketofol shows no reduction in incidence of respiratory depression

• Thiopentone
  • Hypnosis and amnesia without analgesia
  • Most useful for acute head injury or seizures
    • Decreases cerebral metabolic rate, rise in ICP with intubation and is a potent anti-convulsant
  • Rapid onset, duration of action 20-30 minutes
  • Elimination half-life 9 days
  • Rapid redistribution allows clinical offset time
  • Similar adverse reactions as propofol
  • 5mg/kg IV bolus in healthy fit adults
  • 2mg/kg more appropriate if ALOC or hypovolaemic

• Fentanyl
  • Less hypotensive effect than thiopentone/propofol
  • Ideal for painful conditions
  • Induction dose 3-10mcg/kg (200mcg in 70kg adult male)
• Midazolam
  • Slow onset makes it less useful for induction
  • Causes less hypotension than propofol
  • Onset 2 min IV
  • Hepatically metabolised with elimination half-life 1-3 hours (but active metabolite)
  • 0.15mg/kg IV increments
  • 2 hours required for full recovery from midazolam induced anaesthesia

• Anaphylaxis in anaesthesia
  • NAP 6 findings:
    • 1/10 000 rate of anaphylaxis
    • Antibiotics are the most common trigger (47%), muscle relaxants (33%), chlorhex (9%)
    • Low blood pressure occurred in all cases
    • 90% of apparent penicillin allergic patients are not truly penicillin allergic
    • Teicloplanin highest risk agent
    • Sux rate 1/9000 (almost twice as likely to cause anaphylaxis as other NMBA’s)
    • Rocuronium 1/17000
    • Atracurium 1/24000

Paralysis

• Succinylcholine
  • Depolarising paralytic with high affinity for cholinergic receptors at motor end plate and resistant to acetylcholinesterase
  • Depolarisation results in fasciculations and accelerated desaturation as compared to non-depolarising agents
  • Not antagonised and may be enhanced by anticholinesterase agents
  • 1.5mg/kg (2mg/kg in infants and 3mg/kg in neonates) – Dosed on actual body weight (vs. non-depolarising on ideal body weight)
    • Get less fasciculations and muscle pain with 1.5mg/kg than with 1mg/kg
  • Most commonly used RSI paralytic in ED
  • Rapidly hydrolysed by plasma cholinesterase
  • 45-60 second onset at 1.5mg/kg dose (fastest) and 5-9 min duration of action (shortest)Delayed if poor perfusion
  • Wait until 20 seconds after large muscle groups fasciculate (as large before first) and premature attempt is most common cause of failure in inexperienced operators
  • Maximal paralysis at 2-3 minutes and duration of intubating conditions 5 minutes
  • Effective respirations resume at 8-12 minutes
  • Probably preferable if status epilepticus as rapid resolution allows continued monitoring for seizure activity and if possible difficult airway as quicker than suggamadex reversal of roc
  • Adverse reactions
    • Hyperkalaemia a risk if:
      • Burns (9-66 days and >20%)
      • Neuromuscular disease (10 days to 6 months at least)
      • Crush injuries
      • Renal impairment
      • Upper motor neuron lesions including stroke (up to 6 months at least)
      • Usually transient (15min) and 1mmol/L rise within 4-5 minutes)
      • Can be used in myaesthenia gravis (preferred)
  • Bradycardia (esp. children and with repeated doses)
  • Raised ICP (not clinically significant), intragastric pressure, intraocular pressure
  • Post-operative muscle pain
  • Malignant hyperthermia (masseter spasm is early sign, treat with dantrolene 2mg/kg IV repeated q5min until total dose 10mg/kg)
  • Sux apnoea (prolonged paralysis in families)

• Rocuronium
  • Analogue of vec with faster onset
  • Time to 25% recovery 29 minutes
  • Time to 75% recovery 60 minutes
  • Hypersensitivity is the only adverse reaction
  • 1.2mg/kg is usual RSI dose to achieve intubating relaxation within 45-60 seconds
  • Dosed as per ideal body weight (like all non-depolarising blockers)
  • Reversed by sugammadex 16mg/kg
• Vecuronium
  • Aminosteroid compound used to maintain paralysis 
  • Time to 25% recovery 45 minutes, time to 75% recovery 55 minutes
  • 0.3mg/kg for RSI; 0.1mg/kg for maintenance of paralysis (20mg for 70kg) or 7mg
  • Takes 2-3 minutes to achieve adequate intubation conditions
  • Modified priming regimen: 0.01mg/kg priming then 3 minutes later 0.15mg/kg
  • No histamine release, less haemodynamic effect than pancuronium and no vagolytic effect

• Pancuronium
  • Rarely used
• Atracurium
  • Favourable intubating conditions in 3 minutes with 0.4-0.5mg/kg
  • 20-30 minutes duration of paralysis
  • Half-life 20 minutes
  • Metabolised by ester hydrolysis and non-enzymatic (Hoffman) degradation
    • Hoffman degradation to laudanosine (seizure risk)
    • Hoffman degradation increased by alkalosis and hyperthermia
  • No effect on autonomic ganglia or cardiac muscarinic receptors
  • Slight histamine release (Cisatracurium isomer to a lesser degree)
    • Risks hypotension mimicing anaphylaxis

Orotracheal intubation

• Adult male – 8 to 8.5mm
• Adult female – 7.5 to 8mm
• Curved Macintosh blade
  • May cause less trauma and is less likely to stimulate an airway reflex as does not touch larynx directly
  • Allows more room for adequate visualisation and helpful in the obese patient
  • #3 in usual adult patient; #4 in larger patients
• Straight blade
  • Mechanically easier to insert if doesn’t have large central incisors
  • #2 in average adult; #3 in larger patients
• Video laryngoscopy
  • Preferred in morbid obesity, difficult airway prediction or limited neck mobility
  • Improved glottic visualisation in 20% when used by inexperienced operators
  • 5% increase in first-pass intubation success

• Pre-oxygenation
  • Begin as soon as possible in all patients
  • 100% O2 for at least 3 minutes and up to 10 minutes, using NRBM on 15L/min
  • Nasal cannulas alone DO NOT provide adequate pre-oxygenation
  • Displaces nitrogen in FRC and optimises blood oxygen content
  • BVM will deliver 90-97% O2 but requires either active bagging or enough negative inspiratory pressure from the patient to open the one-way valve
  • If SpO2 remains <95% despite above, a short period of NIV may assist, particularly in obese patients
  • Elevating head 20-30 degrees also improves pre-oxygenation
  • HFNP >15L/min throughout apnoeic phase of RSI also prolongs the period of safe apnoea during paralysis and is wise in all patients

• Patient positioning
  • Sniffing position
  • Padding under shoulders NOT neck
  • Ear aligned with sternal notch
  • Ramping 20-30 degrees for obese patients
• Sellick maneuver/cricoid pressure
  • Can impair BVM, worsen laryngoscopic view and hamper tube insertion
  • May trigger vomiting
  • If it is used, apply cricoid (not thyroid) pressure and release if visualisation is difficult
• Techniques to avoid oesophageal placement
  • Assist pulling right side of mouth laterally
  • BURP
  • Bimanual laryngoscopy

• Causes of failure to pass tube
  • Failure to maintain adequate view
  • Too larger tube
  • Cricoid pressure
  • Undesirable curve on stylet (>35 degrees)
• Can attempt to rotate tube 90 degrees to the right to align bevel with cords (to the left with bougie – BLT)
• Target cuff pressure <25cmH20

• False-negative capnography
  • Cardiorespiratory arrest
  • Massive PE
  • Massive obesity
  • Tube obstruction
• False-positive capnography
  • Recent ingestion of carbonated beverage (Will not persist >6 breaths)
  • Heated humidifier, nebuliser or endotracheal adrenaline (Transient)
• Complications
  • Unrecognised oesophageal intubation, aspiration, desaturation, hypotension, dysrhythmia and cardiac arrest
  • First-attempt success in ED 80-95% of the time
  • Higher first-pass success seen with more experienced clinicians, trained emergency physicians, use of RSI, use of video laryngoscopy, and absence of predictors of difficult airway
  • Multiple intubation attempts is associated with increased adverse outcomes so very important to optimise first-pass success
  • Soft tissue injury can occur rarely (arytenoid cartilage avulsion or displacement)
  • Pyriform sinus intubation, pharyngeal-oesophageal perforation, stenosis
  • Pneumothorax (esp. untrained bougie use)
  • Right main bronchus intubation

Intubation complications

• Worsening of Cx spine injuries
• Mandibular dislocation
• Aspiration (1/7000)
• Morbidity (1/16000)
• Death (1/100 000)
• ED incidence likely higher than above
• Oesophageal intubation

Laryngospasm

• Causes
  • Incomplete paralysis
  • Touching cords with ETT
  • Irritation
  • Aspiration
  • Foreign body
  • Hypocalcaemia
  • Usually when intubation attempted too early before relaxation, following extubation or in failed intubation attempts
• Rx
  • Increase sedation
  • Sustain PPV to break spasm
  • Half-dose sux
  • Larson’s point pressure

High risk patients

• Aortic stenosis
• AMI in previous 6 months
• Cardiac failure
• Ventricular ectopics on resting ECG
• Respiratory e.g. COAD

Larygnoscopic grade

• 1 – All laryngeal structures visible – <1% likelihood of difficult intubation
• 2a – Cords partly visible – 4%
• 2b – Arytenoids visible, cords not visible – 67%
• 3 – Epiglottis only – 87%
• 4 – Glottis and epiglottis not seen – Very likely

Depth of insertion

• Average
  • 21-23cm in males
  • 20-21cm for females

Should I use a bougie or stylet or neither?

• Driver et al. 2017 in Ann Emerg Med showed bougie use improved first-pass success in the ED in a retrospective study
• The BEAM trial (Driver et al. 2018) was a prospective randomised trial comparing bougie vs. stylet
  • Over 1 year in an urban, tertiary trauma centre all adult patients with a planned Mac blade (direct or video) first attempt
  • Patients were randomised 1:1 to bougie or ETT + stylet
  • Stylets had 25-35 degrees angulation at the cuff
  • Not a blinded study
  • Primary outcome was first-attempt intubation success in patients with at least 1 difficult airway characteristic (body fluids obscuring view, airway obstruction/oedema, obesity, short neck, small mandible, large tongue, facial trauma or C-spine immobilisation)
  • Secondary outcomes were first-pass success in all patients, first-pass success without hypoxaemia, first-attempt duration, oesophageal intubation and hypoxaemia
  • First-pass success in those with at least 1 difficult airway characteristic were 96% in the bougie group vs. 82% in the ET+Stylet group and 98% vs. 87% in all patients

Difficult intubation

• 1-3% of all ED intubations
• Impossible in 0.5%
• Predictable in 90% of elective cases
• Risk factors
  • Increasing age
  • Obesity
  • Spinal immobilisation
  • Anatomical abnormalities
    • Congenital: Pierre-Robin, cystic hygroma, Achondroplasia, Marfan’s
    • Anatomical: Obesity, short muscular neck, full set of teeth, dentures, dental abnormalities, high-arched palate and narrow mouth, receding mandible, limited neck/jaw movement, large swellings, previous neck surgery, orofacial trauma

• Acquired anatomical issues
  • Acute neck swelling of any cause
  • Restricted jaw opening: Trismus, fibrosis of TMJ, mandibular fractures
  • Decreased neck movement: OA, RA, neck scarring, cervical spine fusion, AS
  • Neck instability: Cervical spine injury, Down syndrome, RA

• Prediction
  • 3 distance technique (need to upright, cooperative in sniffing position)
    • 75% sensitive for difficult airway
    • Mouth opening 3 finger breadths, hyomental distance 3 and thyrohyoid 2 finger breadths
  • Mallampati
    • Performed at rest and not during phonation
    • Have to be sitting up and cooperative
  • Cormack-Lehane grading on laryngoscopy
• Paralysis
  • Rocuronium if establishing airway control is vital i.e. cannot wake them back up as will provide better intubating conditions for longer
  • Suxamethonium if establishing airway control is less crucial i.e. can wake them up (rare in ED)

• Change something before next attempt
• Do not perform laryngoscopy for >1 minute before re-bagging
• If difficult due to immobile anterior tissues – Miller straight blade (more force)
• If difficult due to poor neck mobility – McCoy blade (can lift epiglottis)
• If anterior larynx – D-blade video preferred or McCoy or bimanual laryngoscopy

Selective lung ventilation

• Bougie rotation to left or right 90 degrees with advancement until resistance felt
• Highly accurate (Dunn)

Stylet

• Never have inserted past end of tube
• Remove once end of tube through cords and before further insertion into trachea
• Mould into hockey stick form – straight to the cuff then angled 35 degrees

Extubation

• Need to determine
  • Adequacy of airway protection
    • GCS >8, adequate swallowing and gag reflex
  • Adequate strength
    • Lift head off bed, arms held above head
  • Airway patency
    • Airway swellings resolved
    • Cuff leak – Leak >110mL or 15-20% of delivered tidal volume
    • Cough test – Audible cough and detectable leak past deflated cuff
  • Adequate clearance of secretions
    • Good cough, peak flow >60L/min, secretion volume <2.5mL/hr and suctioning required <2 hourly
  • Adequate ventilation
    • At least 30 minutes of spontaneous ventilation, with PS <10, PEEP 5, RR <35, SpO2 >90%, FiO2 <0.4, HR <140, no anxiety/sweating
    • P:F <>200 with PEEP 5 max
  • Minimal vasopressor support
  • Ensure reversal of paralysis (TOF or time/head lift/sustained hand squeeze or eye opening

• Factors associated with high re-intubation rates
  • Poor mental state
  • Large ET >8.0
  • Age >80
  • Agitated
  • Airway pathology

Difficult ventilation after extubation

• Obstruction
  • Insert OPA or NPA
  • Aspiration – Re-intubate
  • Laryngospasm – Gentle PEEP, paralysis and re-intubate
• Non-obstructed
  • Further reversal of paralysis may be required
  • Naloxone for opioids
  • Consider flumazenil for benzo effect
  • Consider spinal cord injury on induction in at risk patients
• Stridor
  • Dex 8mg IV, nebulised adrenaline

Airway management in trauma

• Indications for intubation
  • GCS <9: Should be intubated within 15 minutes of arrival
  • Restless/combative
  • Elective hypocapnoea planned (if coning)
  • Hypoxaemia
• Goals
  • Avoid hypoxia, hypercarbia and gag reflex (raised ICP)
  • Prevent aspiration
  • Safe passage through CT
• MIAS
  • Manual in-line axial stabilisation by assistant kneeling at head of bed

• If ongoing haemorrhage
  • Should try to time intubation as close as possible to definitive haemorrhage control
  • Loss of resting muscle tone can contribute to haemodynamic collapse

Airway management in obesity

• Physiology of obesity
  • High resting incidence of hypoxaemia and hypercarbia in absence of lung disease
  • Reduced TLC and VC due to decreased chest wall compliance and increased abdominal pressure
  • Increased airway resistance
  • Decreased expiratory reserve volume due to basal atelectasis
  • FRC decreases exponentially with BMI
    • 50% shorter time to deoxygenation
  • Increased O2 consumption and CO2 production
  • Pharmacokinetics
    • Higher Vd
      • Lipophilic drugs should be dosed on actual body weight and hydrophilic drugs to ideal body weight
    • Increased elimination half-life of benzodiazepines

• Predict difficult airway
  • Increased neck circumference best predictor
• Pre-ox with 10cm PEEP as increases non-hypoxic apnoea period by 1 minute
• Ramping is crucial
• Tidal volume based on IBW
• Add 10cm PEEP whenever possible

Airway management in critical hypoxia

• Optimise cardiorespiratory parameters
• Pre-oxygenation is key: Will require PEEP10-15cmH20, FiO2 1.0 and likely NIV as pre-oxygenation
• Best shot first
• May require modified/delayed-sequence induction
• Rocuronium then ketamine
• Administer induction agents sitting up then lie to position when ready to intubate

Airway management in poisoning

• 15% of those who aspirate after poisoning have GCS >8
• Gag reflex depressed in 60% of poisoned patients with GCS >8 vs. 10% following trauma
• Indications for airway protection
  • GSC <8
  • GCS >7 and absent gag reflex
  • Established aspiration pneumonitis therapy
  • Haemodynamic instability
  • Respiratory depression/apnoea
  • Airway protection from aspiration
  • Deteriorating patient with Na channel blocker toxicity (intubate early to prevent respiratory acidosis)
• If sodium channel blockade, avoid suxamethonium
  • Promotes transition of voltage-gated Na channels to desensitised state (desensitiation block)
• Actively ventilate during induction

RSI agent dose adjustments

Mechanical ventilation

• ARDS
  • 6-8mL/kg IBW, Pplat <30, PEEP table or to achieve maximal lung compliance
• Asthma
  • Lowest rate, I:E as long as possible, aim PEEP total <10 and Pplat <20
  • May have permissive hypercapnoea
• COPD
  • Like asthma but often not as difficult
• Single lung pathology
  • Pressure control will allow lowest pressures possible to achieve adequate volume vs. volume control with rising pressures due to single lung
  • Can put non-affected lung dependent

Volume modes

• Assist-control ventilation (ACV) aka Continuous mandatory ventilation (CMV)
  • Each breath is either an assist or control breath but all of same volume
  • If patient becomes tachypnoeic – results in respiratory alkalosis/hyperinflation
• SIMV
  • Patient breaths are partially their own so less respiratory alkalosis/hyperinflation
  • Mandatory breaths are synchronised with spontaneous respirations
  • Can result in reduced CO

Pressure modes

• Pressure control ventilation
  • Does not allow for patient initiated breaths
  • Inspiratory flow pattern decreases over time to reduce peak pressures and improve gas exchange by even spread of pressure across alveoli
  • No guaranteed volume so traditionally preferred for neuromuscular disease but no lung pathology
• Pressure support ventilation
  • Augments spontaneous breathing and overcome resistance of ventilator circuit
• Pressure controlled inverse ratio ventilation (PCIRV)
  • Improves oxygenation but risk of dynamic hyperinflation/autoPEEP
• Airway pressure release ventilation (APRV)
  • Like PCIRV but patients can spontaneously ventilate on high or low pressure setting
  • Requires higher sedation

Volume vs. pressure control

• No discernable difference in outcomes
• Volume control delivers equal flow across inspiratory time and thus has initial low pressure and higher peak pressures towards end of breath delivery
• Pressure control delivers same pressure through inspiration and therefore Ppeak and Pplat are equal
  • Means flow gradually reduces throughout breath delivery
• Pressure-regulated volume control
  • Form of volume control where minimum pressure is achieved throughout by decelerating flow pattern
  • Avoids high peak pressures
  • No proven benefit

I:E ratio

• Inverse I:E ratio <1:1 theoretically improves recruitment of long time-constant alveoli but risks gas trapping and generation of PEEPi
• Long I:E ratio >1:3 prevents gas trapping and PEEPi generation but may limit alveolar recruitment and time for inspiration thus causing issues with elevated flow rates/Ppeak/Pplat

PEEP

• Maintains recruitment of collapsed lung, increases FRC and minimizes intrapulmonary shunt
• Increases Pmean and thus improves oxygenation
• May also redistribute lung water from alveolus to interstitium through reduction in venous return and afterload
• Inadequate PEEP may contribute to VILI by promoting tidal opening/closing of alveoli with shear injury
• Excessive PEEP risks haemodynamic collapse, overinflation of non-dependent alveoli
• PEEPi vs. PEEPe
  • Distribution of intrinsic PEEP is less uniform than PEEPe and have differing physiological effects
• RELAx collaborative
  • Tested whether lower PEEP was non-inferior to higher PEEP strategy in patients without ARDS
  • Prospective unblinded RCT in 8 ICUs in the Netherlands
  • Low PEEP was 5cmH20 down-titrated to zero in steps of 1cmH20 if FiO2 <0.6 and target SpO2 92-96% achieved
  • High PEEP was 8cmH20
  • 980 patients enrolled
  • Primary outcome of ventilator-free days at day 28 was non-inferior for low PEEP vs. high PEEP with no significant difference in secondary outcomes (duration of mechanical ventilation, ICU or hospital LOS, mortality, pulmonary complications or rescue therapy for hypoxia)

SIMV

• Inspiratory time is divided into patient-initiated and true spontaneous breaths to avoid breath-stacking
  • If patient makes effort around time of mandatory breath (SIMV assist window), ventilator delivers assist-control breath with volume control but at least it is synchronised
  • If patients makes effort outside of this, patient gets pressure supported breath
• Many clinicians add pressure support ventilation with gradual reduction in respiratory rate with SIMV to overcome added respiratory work of ET and circuit
• Typically need 5-10cmH20 of pressure support to overcome circuit resistance

Proportional assist ventilation

• Inspiratory pressure support is applied in proportion to patient effort
• Either volume or flow assist utilized
• Need to measure volumes and pressures achieved as these are not targeted
• No clear benefit

Bilevel/APRV

• Allows spontaneous breathing at both low and high PEEP
• Airway pressure release ventilation (APRV)
  • Minute ventilation and CO2 excretion are augmented by brief 1-1.5s periodic cycling to lower level of CPAP
  • Increasingly popular to improve oxygenation in patients with severe airway disease
  • High airway pressure for 3-4 seconds then brief pressure release for 0.5-1 seconds for exhalation
  • Similar to inverse ratio pressure control ventilation
  • Improves alveolar recruitment and mean airway pressure to improve oxygenation
  • Helps maintain spontaneous breathing
  • Higher risk of barotrauma

Weaning

• 20% fail despite meeting clinical criteria
• Rapid shallow-breathing index (f/Vt ratio) >105
  • >57 is a threshold for significant increase in risk for reintubation
• Positive fluid balance prior to extubation also increases risk of reintubation substantially
• Inadequate vital capacity <8-12mL/kg
• Large minute ventilation >15L/min
• FiO2 >0.4
• PEEP >5-8
• PSV >5-7
• Reintubation associated with 7-11 fold increase in hospital death

Patient-ventilator interaction

• Triggering of inspiration
  • Often limited by high PEEPi so MUST match with CPAP at least 80-90% of this value
• Inspiration
  • Steeper P ramp leads to early attainment of target P, greater early rates and reduction of inspiratory drive and work
• Cessation of inspiration
  • During pressure support ventilation, increased airway resistance results in a delayed fall in flow. This normally triggers cycling to expiratory phase and as such, patient may feel continued inspiratory flow despite desire to exhale with subsequent attempt at expiration, rise in end-inspiratory pressure and clinical respiratory muscle contraction towards end of inspiratory cycle

Malignant hyperthermia

• 50% of cases have had previously normal GA
• 1/15 000 children
• 1/40 000 in adults
• Fulminant 1/260 000 overall; 1/60 000 if sux used
• 50% AD inheritance
• Associated conditions
  • Muscular dystrophy
  • Osteogenesis imperfecta
  • Congenital skeletal issues/abdominal hernias
  • SIDS
  • Phaeochromocytoma

• Pathophysiology
  • Defect in excitation coupling in skeletal and cardiac muscle
  • Reduced Ca2+ reuptake by sarcoplasmic reticulum
    • Increased intracellular calcium
      • Leads to increased glycogenolysis, ATP production and heat production
• Precipitants
  • Caffeine
  • Volatile anaesthetic agents
  • Muscle relaxants (esp. suxamethonium)
  • Extensive muscular trauma
  • Amide-type local anaesthetics (lignocaine, prilocaine, bupivacaine, ropivacaine (all have ’I’ before ‘caine’)
  • Cardiac glycosides

• Onset
  • 25% onset within 5 min of precipitant
  • 50% within 1-2 hours
  • 25% >2 hours
  • 11 hours is longest recorded interval
• Presentation
  • etCO2 increases 2-3 times (early sign)
  • Tachy, hypertension, sweating, ventricular arrhythmias
  • Masseter spasm
  • Fever is late sign
• Complications
  • AKI
  • Acute pulmonary oedema
  • Coagulopathy
  • Cerebral oedema (direct thermal injury)
  • Skeletal compartment syndrome

• Management
  • Change IV tubing if agent responsible
  • 100% O2 to compensate for increased O2 consumption
  • Dantrolene 2.5mg/kg IV bolus (up to 6mg/kg may improve survival)
    • 1-2mg/kg boluses q5min up to 10mg/kg
    • 1mg/kg/hr infusion
  • Active cooling
  • Replace insensible fluid losses

PEEP titration

• ARDSnet table
  • FiO2 0.4 = PEEP 5
  • 0.4 = 8
  • 0.5 = 8
  • 0.5 = 10
  • 0.6 = 10
  • 0.7 = 10
  • 0.7 = 12
  • 0.7 = 14
  • 0.8 = 14
  • 0.9 = 14

MACOCHA score

• De Jong et al. (2013)
• ICU-based scoring system to identify high-risk patients for difficult intubation
  • Mallampati III or IV (5 points)
  • Apnoeic (OSA) (2 points) 
  • Cervical spine limitation (1)
  • Opening mouth <3cm (1)
  • Coma (1)
  • Hypoxaemia (1)
  • Non-anaesthetist (1)
• Difficult intubation occurred in 36% of those with score >= 3 and in 2% of those with score <3

NAP4

• National Audit Project in UK of major complications of airway management
• In perioperative environments
  • Face mask ventilation failure 1/1500
  • Tracheal intubation failure 1/2000
  • LMA failure 1/50
  • CICV unexpectedly impossible 1/5000 to 1/10 000 cases
  • CICV accounts for 25% of anaesthesia-related deaths
• In emergencies these failure rates multiply several-fold
  • Failed tracheal intubation in emergency 1/300 to 1/800
  • CICV up to 1/200
  • Rates of difficult airway up to 9% and emergency surgical airway up to 0.5% in ED in the UK
• Intubation requiring >2 attempts at laryngoscopy associated with:
  • 14 fold increase in severe hypoxia (28% of cases)
  • 6 fold increase in oesophageal intubation (52%)
  • 7 fold increase in regurgitation (22%)
  • 4-fold increase in aspiration (13%)
  • 7-fold increase in cardiac arrest (11%)

• If difficult to bag mask ventilate
  • 4-fold more likely to be difficult to intubate
  • 12-fold more likely to be impossible to intubate
• Perc tracheostomy failed majority of the time
• Surgical tracheostomy should be procedure of choice
• All suspected difficult intubations should be performed as awake laryngoscopy if possible
• In the CICV situation, ensure patient is completely paralysed (sux may wear off within 5 minutes)

Airway bundles

Montpellier intubation protocol (Jaber et al. 2010)

• Pre- and post-intervention analysis in ICU’s in France of the below Montpellier bundle:
  • Pre-intubation
    • 2 operators
    • 500mL crystalloid fluid load in absence of APO
    • Preparation of sedation
    • Preox for 3 min with NIPPV if in acute respiratory failure (FiO2 100%, PS 5-15cmH20 to obtain Vt 6-8mL/kg and PEEP of 5)
  • During intubation
    • RSI with etomidate or ketamine 1.5-3mg/kg with sux 1-1.5mg/kg (unless CI)
    • Sellick maneuver
  • Post-intubation
    • Capnography confirmation
    • Noradrenaline if DBP <35mmHg
    • Initiate long-term sedation
    • Lung protective mechanical ventilation
• 121 in control group vs. 123 in intervention group
• Life-threatening complications in 21% of intervention group vs. 34% in control phase
• Mild to moderate complications in 9% of intervention and 21% of control phase
• Difficult intubation was unchanged between groups

VAPOX

Grant et al. published VAPOX (Ventilator-assisted pre-oxygenation) protocol based on their experience at GCUH and a case series of 8 patients.

Goals were to reduce the incidence of critical hypoxia through improved pre-oxygenation and avoiding apnoea while limiting risks of gastric insufflation and subsequent aspiration.

Specifically recommended:

• NIV-ST mode
• RR 6-8/min
• PS 10cmH20 water
• PEEP 5
• FiO2 1.0
• NPO2 at 15L/min throughout

While the ventilator settings are not complicated, the pitfalls lie in the practicalities and ergonomics of providing NIV via a mask before and after induction, while managing any ventilator issues and intubating the patient successfully.

I would recommend to utilise either a soft Laerdal mask or the Hamilton NIV mask sized to the patient, with a two-handed technique and avoiding the use of head straps. My practice has been to involve a second operator to manage the mask from an anterior position with the patient sitting upright with ear-to-sternal notch during pre-oxygenation for at least 3 minutes and through induction. Once muscle relaxation has ensued, I have then laid the patient back and attempted intubation.

It is imperative that tidal volumes on the Hamilton T1 are monitored throughout the ‘apnoeic’ period as pressure support may need to be increased once the patients own intrinsic negative pressure ventilation ceases. An individual should be assigned to monitoring this and adjusting as required (not the intubator).

Potential benefits of this process are:

• Avoidance or delay to critical hypoxia
• Controlled maximal pressure support to avoid gastric insufflation and subsequent aspiration (as opposed to manual BVM)
• Hamilton ventilator can compensate for massive negative pressure flow generation by dyspnoeic patients and/or mask leak with a maximal flow rate of 100% O2 at ~250L/min as opposed to wall oxygen limited to ~15-20L/min
• Definitive PEEP delivery during pre-oxygenation and/or induction as compared to PEEP valve on BVM

Last Updated on August 29, 2024 by Andrew Crofton