Airway assessment Bran Retnasingham Andy McKechnie
The average Camberwell patient?
Airway assessment There is one skill above all else that an anaesthetist is expected to exhibit and that is to maintain the airway impeccably M Rosen and IP Latto 1984 The most compelling educational effort for the anaesthesia community should be to reduce the frequency and severity of complications related to managing the airway Benumof 1995
Airway assessment Major complications of airway management are rare but can be amongst the most lifethreatening in medicine CICV < 1 in 5000 routine Gas ESA (Emergency Surgical Access) ~ 1 in 50 000 (but accounts for up to 25% of anaesthesiarelated deaths)
Airway assessment Minor complications (incl difficulty with components of airway Mx eg lung ventilation via FM or LM or DL) are common (each ~ 0.5-1%) Airway complications are more frequent in patients with difficult airways, but the infreq of such cases means many complications occur far more often in patients with an easy airway Eg 80% of laryngeal injuries follow easy intubation, primarily in healthy low-risk pts
Airway assessment Incidence of failed intubation: ~ 1 in 2000 in elective setting ~1 in 300 during RSI in obs setting ~1 in 50-100 in ED, ICU and pre-hosp setting Rate of CICV requiring ESA may incr to 1 in 200 in ED
Airway assessment Most catastrophes are due to unexpected difficulty Airway assessment has traditionally focused on detecting difficult DL/tracheal intubation Prediction of diff mask ventilation, LMA placement and other rescue techniqees just as important
Airway assessment FM ventilation is difficult in ~ 1 in 20 cases Patients with multiple predictors of difficulty or predictors of hypoxaemia (eg pregnancy, obesity, children) need great care
Airway assessment - History Congenital airway difficulties Pierre Robin, Klippel-Feil, Down s syndrome Acquired airway difficulties Still s disease, AS, acromegaly, pregnancy, diabetes Iatrogenic problems TMJ surgery, cervical fusion, oral/pharyngeal radiotherapy, laryngeal/tracheal surgery Reported prev anaesthetic problems Eg dental damage, severe sore throat check anaes notes, med-alerts, databases
Airway assessment - Examination Adverse anatomical features small mouth, receding chin, high arched palate, large tongue, bull neck, morbid obesity, large breasts Acquired problems Head/neck burns, tumours, abscesses, radiotherapy injury, restrictive scars Mechanical limitation Reduced MO and ant TMJ movement, poor cervical spine movement
Airway assessment - Examination Poor dentition (eg anterior gaps, rotten,sharp, loose teeth, protruding or awkwardly placed teeth Nasal patency (if nasal intubation route) Facial hair may hide adverse adanotmical features
Airway assessment - Radiology Recent CT/MRI may help define potentially difficult anatomy and guide management Occipito-atlanto-axial disease is more predictive of difficult laryngoscopy than disease below C2 Plain radiographs are poor predictors of cervical stability flexion/extension views are only indicated for potentially dangerous ligamentous (usuallly atlanto-axial) disruption
Difficult FM ventilation Mask ventilation requires the ability to cover the mouth and nose with a FM and produce a seal and open the airway Predictors of difficulty with FM ventilation: Age> 55 yr BMI > 26 History of snoring Beards/facial hair Absence of teeth (presence of 2 or more of above has >70% sensitivity) Facial abnormalities Receding or markedly prognathic jaw OSA
Difficult cricothyroidotomy Rare that this anatomic point has poor exposure: Morbid obesity Neck immobility Trauma to the area
Difficult cricothyroidotomy
Airway assessment predictive tests Laryngoscopy and tracheal intubation requires creating a clear line of view from the upper teeth to the glottis Requires MO, extension of the upper C sine and ability to create a submandibular space (ie move soft tissues within the arch of the mandible out of the way) Most tests of difficult intubation test one or more of these capacities
Airway assessment predictive tests Low specificity and ppv. Large numbers of false +ves. <10% of pts with features of predicting difficult laryngoscopy prove to be difficult to intubate Sensitivity often <50% - around 50% of cases not predicted by tests
Airway assessment predictive tests Combining multiple tests increases the specificity (ie reduces the false +ves) but decreases sensitivity (ie leads to missing more truly difficult cases) C/L grades of laryngeal view frequently used
Airway assessment predictive tests Interincisor gap Distance b/w incisiors with the mouth open maximally < 3cm makes intubation difficulty more likely < 2.5 cm LMA insertion will be difficult
Airway assessment predictive tests Patient protrusion of mandible (overbite/ulbt) Class A able to protrude the lower incisors anterior to the upper incisors Class B lower incisors can just reach the margin of the upper incisors Class C lower incisors cannot protrude to the upper incisors (classes B and C associated with increased difficulty)
Airway assessment predictive tests Mallampati test Class 1 faucial pillars, soft palate and uvula visible Class 2 faucial pillars and soft palate visible, uvula tip masked Class 3 soft palate visible only Class 4 Soft palate not visible (hard palate) Class 3 and 4 views (ie when no posterior pharyngeal wall view) assoc with incr diff laryngoscopy interobserver variation, used alone predicts 50% of diff laryngoscopies, false +ve rate up to 90%
Airway assessment predictive tests Extension of the upper C-spine When limited (<90%) risk of difficult laryngoscopy is increased
Airway assessment predictive tests Thyromental distance (Patil s test) Distance from the tip of the thyroid cartilage to the tip of the mandible, neck fully extended Normal > 7cm, <6cm predicts approx 75% of difficult laryngoscopies Combined Patil and Mallampati tests (<7cm and class 3-4) incr specificity (97%) but reduces sensitivity (81%)
Airway assessment predictive tests Sternomental distance (Savva test) Distance from the upper border of the manubrium to the tip of mandible, neck fully extended and mouth closed <12.5 cm assoc with difficulty (ppv 82%)
Wilson score 5 factors wt, upper c-spine mobility, jaw movement, receding mandible, buck teeth each scored 0-2 (subjectively normalabnormal)
Airway assessment predictive tests A thick neck (neck circumference >45 cm) is associated with a short neck and poor cervical extension and has been correlated with a significant risk of failed DL (esp in obese)
Avoidance of airway complications Believe the history act on a history of previous airway difficulty Assess every patient for risk of airway difficulty and of aspiration where such risk is identified ensure airway strategy (techniques, devices and back up plans) is consistent with the findings
Avoidance of airway complications Never fail to be prepared for failure Communicate strategies to the team Do what you can but do not do what you cannot for the patient
Avoidance of airway complications Do not intubate when it is not indicated the idea of intubation as the gold standard for all airway Mx is outdated Do intubate when indicated Pre-oxygenate fully before every GA
Avoidance of airway complications Know and practice a wide range of anaesthetic airway techniques (VL, intubation via SAD), how to rescue a failed airway, and when and how to wake a patient if difficulty occurs Learn techniques you think you will never use If it is not working, stop and do something different repeating the same failing technique increases both the likelihood of complications and failure of alternative techniques
Avoidance of airway complications Do not ever forget the possibility of oesophageal intubation and always use capnography to confirm successful intubation and ventilation Treat ICU and ED as places of danger
Now you can intubate anybody?
The End