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Procedural Skills (SLO6)

Question 78 of 127

You are working in the anaesthetics department on your ACCS rotation being supervised during a routine surgical list. This is your view at direct laryngoscopy. How would you classify the Cormack-Lehane grade?

Answer:

Cormack and Lehane classification of view at direct laryngoscopy:
  • Grade I: vocal cords are fully visible
  • Grade II: vocal cords are only partly visible
  • Grade III: only epiglottis is seen
  • Grade IV: epiglottis can't be seen

Advanced Airway Management: Airway Assessment

During elective anaesthesia, a failed airway occurs in 0.01 - 0.03% of cases. A difficult intubation, occurs in 1.15 - 3.8% of cases. However, the characteristics of patients requiring intubation or assisted ventilation outside the operating room are different to those undergoing elective surgical procedures, and the incidence of difficult intubation is significantly higher in emergency departments. A failed airway may occur at least ten times more frequently in the emergency setting. Given this data, difficulties with the airway must be expected in all emergency patients and appropriate preparation undertaken. Some features may indicate a particularly high likelihood of airway difficulties, and in these cases, modification of practice may reduce complications and improve outcomes.

Definitions

A difficult airway is categorised by:

  • Difficult mask ventilation
    • Occurs when the patient's anatomy or injuries make it impossible to maintain adequate ventilation and oxygenation with a facemask and simple airway adjuncts alone
  • Difficult intubation
    • Defined when an experienced laryngoscopist, using direct laryngoscopy, requires:
      1. more than two attempts with the same blade or;
      2. a change in the blade or an adjunct to a direct laryngoscope e.g. bougie or;
      3. use of an alternative device or technique following failed intubation with direct laryngoscopy
  • Difficult view at laryngoscopy
    • Classified by Cormack and Lehane and defined as being unable to see any portion of the vocal cords with conventional laryngoscopy (Cormack and Lehane grades 3 and 4)
  • Difficult cricothyroidotomy
    • Failure to intubate the trachea combined with an inability to oxygenate the patient using a bag-mask or supraglottic airway device will necessitate a surgical airway. Occasionally, patient-specific features may render the cricothyroid membrane inaccessible. This makes induction of anaesthesia particularly risky because if the airway is lost it may be irretrievable and oxygenating the patient will be impossible.

General assessment

Pre-anaesthetic assessment of emergency patients where time allows:

  • Comprehensive history
    • Details of current condition
    • Current medication and allergies
    • Previous medical and surgical problems (including previous anaesthetics and any history of a difficult airway)
    • Last oral intake
  • Cardiorespiratory status
  • Conscious level
  • Focal/global neurological signs
  • Assessment of face and neck
  • Assessment for pneumothorax
  • Abdominal and pelvic assessment for surgical signs
  • Body morphology

Predicting difficult airways

The LEMON mnemonic can be used to remember how to assess for difficult intubation.

LEMON Assessment
Look
  • Externally
    • Age
    • Obesity
    • Facial hair
    • Sunken cheeks (cachexia, missing teeth)
    • Small mouth
    • Large overbite
    • Receding chin
    • Short, muscular neck
    • Significant maxillofacial or mandibular trauma
  • Internally
    • Poor mouth opening
    • High arched palate
    • Edentulous (no teeth)
    • Prominent upper incisors
    • Macroglossia
    • Insecure/loose teeth or dental prosthesis
Evaluate the 3-3-2 rule
  • Distance between the patient's incisor teeth should be at least 3 finger breadths (3)
  • Distance between hyoid bone and chin should be at least 3 finger breadths (3)
  • Distance between thyroid notch and floor of mouth should be at least 2 finger breadths (2)
Mallampati score
  • Class I - Soft palate, uvula, fauces, pillars visible
  • Class II - soft palate, uvula, fauces visible
  • Class III - soft palate, base of uvula visible
  • Class IV - hard palate only visible
Obstruction of airway
  • Clinical Features
    • Dysphagia
    • Stridor
    • Muffled voice
  • Causes
    • Peritonsillar abscess
    • Epiglottitis
    • Retropharyngeal abscess
    • Trauma
    • Tumour
    • Burns
    • Infection
    • Anaphylaxis
Neck mobility
  • Cervical spine immobilisation
  • Elderly
  • Arthritides
  • Ankylosing spondylitis
  • Previous neck injuries or surgery

Mallampati classification

  • Class I - Soft palate, uvula, fauces, pillars visible
  • Class II - soft palate, uvula, fauces visible
  • Class III - soft palate, base of uvula visible
  • Class IV - hard palate only visible

Mallampati Classification. (Courtesy of Jmarchn (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL , via Wikimedia Commons)

View at direct laryngoscopy

View at Direct Laryngoscopy. (Via Wikimedia Commons)

Cormack and Lehane classification of view at direct laryngoscopy

  • Grade I: vocal cords are fully visible
  • Grade II: vocal cords are only partly visible
  • Grade III: only epiglottis is seen
  • Grade IV: epiglottis can't be seen

Cormack-Lehane Grading Scheme for Laryngoscopy. (Via Wikimedia Commons)

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  • Biochemistry
  • Blood Gases
  • Haematology
Biochemistry Normal Value
Sodium 135 – 145 mmol/l
Potassium 3.0 – 4.5 mmol/l
Urea 2.5 – 7.5 mmol/l
Glucose 3.5 – 5.0 mmol/l
Creatinine 35 – 135 μmol/l
Alanine Aminotransferase (ALT) 5 – 35 U/l
Gamma-glutamyl Transferase (GGT) < 65 U/l
Alkaline Phosphatase (ALP) 30 – 135 U/l
Aspartate Aminotransferase (AST) < 40 U/l
Total Protein 60 – 80 g/l
Albumin 35 – 50 g/l
Globulin 2.4 – 3.5 g/dl
Amylase < 70 U/l
Total Bilirubin 3 – 17 μmol/l
Calcium 2.1 – 2.5 mmol/l
Chloride 95 – 105 mmol/l
Phosphate 0.8 – 1.4 mmol/l
Haematology Normal Value
Haemoglobin 11.5 – 16.6 g/dl
White Blood Cells 4.0 – 11.0 x 109/l
Platelets 150 – 450 x 109/l
MCV 80 – 96 fl
MCHC 32 – 36 g/dl
Neutrophils 2.0 – 7.5 x 109/l
Lymphocytes 1.5 – 4.0 x 109/l
Monocytes 0.3 – 1.0 x 109/l
Eosinophils 0.1 – 0.5 x 109/l
Basophils < 0.2 x 109/l
Reticulocytes < 2%
Haematocrit 0.35 – 0.49
Red Cell Distribution Width 11 – 15%
Blood Gases Normal Value
pH 7.35 – 7.45
pO2 11 – 14 kPa
pCO2 4.5 – 6.0 kPa
Base Excess -2 – +2 mmol/l
Bicarbonate 24 – 30 mmol/l
Lactate < 2 mmol/l

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