Difficult airway characteristics associated with video laryngoscopy failure

Raj Joshi , Cameron D. Hypes,  Jarrod M. Mosieret el published a single center prospective observational study looking at the risk factors for failure of first attempt at intubation using video laryngoscopy in intensive care unit.

 

Background

Macintosh (1943) and Miller (1941) developed direct laryngoscopes and paved the way for modern direct laryngoscopy.  Mainstay of direct laryngoscopy is to align the anatomic axes to obtain a view of the glottic opening to place a tracheal tube.

Intensive care units have been considered and proven more difficult that operating rooms for successful tracheal intubation.  Study by JF Heuer, TA Crozier et el in German ICU looked at the incidence of difficult intubation mainly using direct laryngoscopy and found a rate of 23%.  Compare this with the rate of about 5% in all comer intubations. 

Video Laryngoscopy has overcome the need to align the anatomic axes, and more and more centers are using video laryngoscopy as the first choice for intubation. Despite this, many first attempts are unsuccessful in intensive care unit.

What did they find

They looked at 906 consecutive patients who were intubated in a single ICU using a video laryngoscopy.  Blood in the airway (odds ratio [OR], 2.63; 95% CI, 1.64-4.20), airway edema (OR, 2.85; 95% CI, 1.48-5.45), and obesity (OR, 1.59; 95% CI, 1.08-2.32) were significantly associated with first-attempt failure. Cervical immobility was also a factor(It was not recorded in initial 133 patients).

There were no significant differences in sex, age, reason for intubation, or device used between first-attempt failures and first-attempt successes.

Difficult airway with direct laryngoscopy

American Society of Anesthesiologist define a difficult airway as the clinical situation in which a conventionally trained anesthesiologist experiences difficulty with face mask ventilation of the upper airway, difficulty with tracheal intubation or both.

Difficulty of mask ventilation have been categorised by using a four-point scale 1) ventilated by mask; 2) ventilated by mask with oral airway adjuvant with or without muscle relaxant; 3) difficult ventilation (inadequate, unstable, or requiring two providers) with or without muscle relaxant; 4) unable to mask ventilate with or without muscle relaxant.

Several risk factors have been used to predict difficult intubation with direct laryngoscopy, not all are applicable to video laryngoscopy, though one should keep in mind that he/she may have to resort to direct laryngoscopy if video laryngoscopy fails.

In a review by Prerana N Shah and Vimal Sundaramrisk factors identified for difficult mask ventilation (DMV) were snoring, obstructive sleep apnea, retrognathia, micrognathia, macroglossia, edentulous teeth, short thick neck, Mallampatti grade [III/IV], abnormal SLUX grade, abnormal, experience level of anesthetist, Cormack Lehanne grade [III/IV], and BMI > 26 kg/m2.

Risk factors for difficult intubation were snoring, retrognathia, micrognathia, macroglossia, short thick neck, Mallampatti grade [III/IV], abnormal SLUX grade, Cormack Lehanne grade [II, III/IV], abnormal atlantooccipital extension grading, flexion/extension deformity of neck, protuberant teeth, cervical spine abnormality, mouth opening in cms and BMI > 26 kg/m2.

View of direct laryngoscopy have been graded by Cormack and Lehanne : Grade 1) full view of the glottis; Grade 2) partial view of the glottis or arytenoids; Grade 3) only epiglottis visible; Grade 4) neither glottis nor epiglottis visible.

The modified Mallampati-score was described by Samsoon and Young . 

However, a large metalysis of trials showed it has very poor predictive value for difficult intubation.

SLUX grade is  Protrusion of mandible:  graded as follows:
Grade I : If lower incisors could be protruded anterior to upper incisors.
Grade II : If upper and lower incisors touch each other.
Grade III : If lower incisors could not be brought forward to touch the upper incisors.

 

There is a mnemonic to remember LEMON for predicting difficult airway.

Current status of Video Laryngoscopy

Video laryngoscopy made its introduction to airway management many years ago with the introduction of the GlideScope video laryngoscope (Verathon, Seattle, WA, USA) in 90s. Since then, several other products have been launched and used clinically.

There are several trials which compare head to head the video with direct laryngoscopy. In a recent chochrane review of trials comparing video vs direct, authors found that video laryngoscopes may reduce the number of failed intubations, particularly among patients presenting with a difficult airway. They improve the glottic view and may reduce laryngeal/airway trauma. They also found that there is no evidence that  use of a video laryngoscope  reduces the number of intubation attempts or the incidence of hypoxia or respiratory complications, and no evidence indicates that use of a video laryngoscope affects time required for intubation.

In an earlier meta analysis of trials, David W Healy, Oana Maties, David Hovord and Sachin Kheterpal looked at 77 studies totaling more than 56000 patients. They made following recommendations.

Use in unselected patients – Video laryngoscopes do not offer any advantage over direct laryngoscopes.

Use in patients assessed to be at high risk of difficult direct laryngoscopy – recommended use by experienced operator.

Use in difficult direct laryngoscopy – Recommended

Use as a rescue device after failed direct laryngoscopy – Recommended

 

To complicate the matters further, Jean Baptiste Lascarrou,  Julie Boisrame-Helms,  Arthur Bailly et el  published a multicenter randomized clinical trial comparing video vs direct laryngoscopy for tracheal intubation in ICU patients. Total of 371 patients were enrolled in the study.  There was no significant difference between the video and direct laryngoscopy groups in the proportion of successful first-pass intubations (67.7% vs 70.3%; P = .60). The median time for intubation did not differ (3 minutes in each group; P = .95).

However, in this trial incidence of severe life-threatening complications, such as severe hypoxemia and cardiac arrest, was higher in patients undergoing video laryngoscopy (9.5% vs 2.8%; P = .01).

Furthermore, higher rate rates of pharyngeal soft tissue injury and longer intubation times in patients undergoing video laryngoscopy as compared with direct laryngoscopy is also reported in this review.

 

With current evidence, One should master both techniques as they complement each other, rather than compete.