Glottic Visualization & Ease of Intubation With Different Laryngoscope Blades
Condition: Tracheal Intubation Morbidity
Study type: Interventional

Summary: 
      Orotracheal intubation the commonest method used to secure and maintain airway during
      anaesthesia. A variety of methods are available for orotracheal intubation such as digital or
      tactile method, use of lighted orotracheal intubating stylet, use of intubating LMA (which is
      becoming increasing popular, particularly in cased of anticipated difficult intubation),
      fibreoptic endoscopic orotracheal intubation (also used when a difficulty is predicted), and
      conventional and most common method, direct laryngoscopy. Orotracheal intubation is most
      commonly achieved after visualization of laryngeal inlet with direct laryngoscopy following
      induction of general anaesthesia and muscle relaxation achieved by administration of a muscle
      relaxant.

      Due to the hazards seen with failed intubation, anaesthetists are also on the lookout for
      techniques which will improve visualization of the laryngeal inlet, i.e. glottis. View
      obtained during laryngoscopy can be classified in a variety of ways such as Cormack Lehane
      grading, the percentage of glottic opening (POGO Score)Literature suggests that straight
      blade gives better glottic visualization while tracheal intubation is easier with the curved
      blade. We therefore wanted to compare the Macintosh and Miller laryngoscope blades in terms
      of visualization of Laryngeal inlet and ease of intubation in patients with normal predicted
      intubation. We also compared the McCoy blade, a modified curved blade, and the Trueview
      Laryngoscope, which incorporates a prism in a straight blade, for glottic view and ease of
      intubation.
    

Detailed description: 
      This prospective observational study was conducted after obtaining approval from the
      Institutional Review board of our institute. One hundred and twenty adult patients were
      included who had given written informed consent. These patients were ASA I or II, between
      18-70 yrs of age, were undergoing elective oncosurgery procedure under general anaesthesia
      requiring endotracheal intubation. Patinets were excluded if they refused consent, were
      pregnant, had potential difficult mask ventilation and /or anticipated difficult intubation
      or had pathology in neck, upper respiratory tract and upper alimentary tract. A detailed
      routine pre-anaesthetic check-up was performed and routine laboratory investigations were
      done. The patients were randomly divided in four groups of 30 each per laryngoscope blade.
      Group 1: Macintosh Group Group 2: McCoy's Group Group 3 Miller Group and Group 4: TrueView
      Group. : included 30 patients.

      In the operating room, patients' medical history was again confirmed in brief before
      subjecting the patient to anaesthesia. Demographic data such as age, sex and weight of the
      patient was noted. Pulse oximeter, electrocardiograph, capnography and automated non-invasive
      blood pressure were used for monitoring. Airway assessment was done clinically using Samsung
      and Young's modification of the Mallampati classification for oropharyngeal view. The patient
      was asked to assume sitting position, open the mouth maximally, and protrude the tongue but
      not to phonate. Visibility of the oral and pharyngeal structures was then classified by an
      observer sitting at the same level as the patient.

      Class I: Soft palate,fauces,uvula,pillars visible Class II: Soft palate,fauces,portion of
      uvula visible Class III: Soft palate,base of uvula visible Class IV : Only hard palate
      visible A Doughnut-shaped pillow and hard sponge square pillow, totalling about 7 cm in
      height, was placed under the head of the patient. The patient was preoxygenated with 100%
      oxygen for three minutes. Anaesthesia was then induced with 1-3 mg/kg of Propofol or
      thiopentone sodium 5 mg/kg, fentanyl 2 µg/kg. Feasibility of ventilation with a face mask was
      checked prior to injection of non-depolarising muscle relaxant. After ventilation was
      confirmed a vecuronium was administered and the patient was ventilated with isoflurane 0.5-1%
      in a 50:50 mixture of O2 and N2O for 3 minutes then ventilated for 1 minute with 100% O2.
      Then laryngoscopy and tracheal intubation accomplished with the selected laryngoscope blade.
      The laryngoscopy and intubation were carried out by a single anaesthesiologist who had
      trained with all laryngoscope blades till he had obtained sufficient familiarity all four
      laryngoscope blades. We studied following aspects during tracheal intubation.

      Visualization of laryngeal inlet: This was graded using Cormack Lehane Grades:

      Grade 1: complete glottis visible Grade 2: anterior glottis not seen Grade 3: epiglottis seen
      but not glottis Grade 4: epiglottis not seen

      Ease of intubation: This was graded as follows:

      Grade 1: Intubation easy Grade 2: Intubation requiring an increased anterior lifting force
      and assistance to pull the right corner of the mouth upwards to increase space Grade 3:
      Intubation requiring multiple attempts and a curved stylet Grade 4: Failure to intubate with
      the assigned laryngoscope Number of attempts: We noted the number of attempts needed for
      intubation with that particular blade in each patient.

      Requirement of external laryngeal manipulation: Classified as Grade 1: No requirement of
      external laryngeal manipulations and Grade 2: Requirement of external laryngeal manipulation.

      Statistical analysis: Demographic data, Mallampatti Classification and other variables were
      compared using the Chi Square test. A p value of > 0.05 was taken to assume statistical
      significance.
    

Intervention name(s): Macintosh Laryngoscope blade; MacCoy; Miller; TrueView
Intervention type(s): Device; Device; Device; Device
Intervention description(s): Laryngoscopy performed with Macintosh Laryngoscope; Laryngoscopy performed with MacCoy Laryngoscope; Laryngoscopy performed with Miller Laryngoscope; Laryngoscopy performed with TrueView laryngoscope
Other intervention name(s): Conventional Curved laryngoscope blade; Curved laryngoscope blade with a hinged tip; Conventional Straight laryngoscope blade; Straight blade with prism
Intervention MeSH terms: Pyrithione zinc
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: None (Open Label)
Keywords: Macintosh laryngoscope blade; MacCoy laryngoscope blade; Miller laryngoscope blade; TrueView laryngoscope