Impact of table height on ease of intubation using the video laryngoscope - a prospective, randomised study

SUMMARY OF THE TRIAL

 Operating table height can influence task performance and physical/mental workload.1 2 There have been few studies of the correlation between the operating table height and the quality of laryngeal view during direct laryngoscopic intubation.3 In an editorial on anaesthetist stature and patient positioning, Heath3 highlighted the benefits of using an adjustable operating table and the ergonomic benefits of different heights—high during cannulation to prevent back discomfort, a bit lower for airway management, and even lower for short trainees.

It has been suggested that the patient’s face should be placed at the height of the anaesthetist’s xiphoid process for comfortable intubation without requiring the anaesthetist to bend his/her back4–6 and that the physician’s eyes should be placed 1 foot (~ 30 cm) above the patient’s face to provide proper angles and distances for laryngoscopy.7 However, these results are based on clinical experience rather than scientific validation.

Recent studies have suggested that regardless of the bed height, the intubation time with video laryngoscopes was significantly shorter than that with direct laryngoscopes.8  In reference to a study conducted by Lee et al. 9, higher operating tables (at the xiphoid process and nipple level of the anaesthetist) can provide better laryngeal views with less discomfort during tracheal intubation. Higher the table level, lesser the posture strain on the anaesthetist. However, this will make the flexion of the shoulder joint of the intubator and the lifting of the epiglottis more difficult. We hypothesize that a lower table level for laryngoscopy via a video laryngoscope is not required, since good vocal cord visualization can be obtained without lifting the epiglottis.

 The aim of this study is to study the effects of different table heights - at Nipple vs. at Umbilicus - on the Total Time for Tracheal Intubation (TTTI) by video laryngoscopy (primary variable) and the Time for Glottic Exposure (TGE), Time for Tracheal Intubation (TTI), grades of visualization of vocal cords, number of laryngoscopy attempts, discomfort level of investigator assessed objectively and subjectively, sore throat post-surgical procedure (secondary variables) associated with two different operating table heights during tracheal intubation.

LACUNAE IN EXISTING LITERATURE– The table height is conventionally kept at the level of the Umbilicus of the intubator while using the standard MacIntosh Laryngoscope, in order to make flexion at the shoulder joint easier. However, there is no recommendation in literature on the ideal table height while using a video laryngoscope.

RESEARCH QUESTION – What is the ideal table height during intubation while using a video laryngoscope for good vocal cord visualization and reducing the strain on the anaesthetist?

AIMS AND OBJECTIVES

 Primary Objective - To study the effects of different table heights - at Nipple vs. Umbilicus - on the Total Time for Tracheal Intubation (TTTI) while using a video laryngoscope.

 Secondary Objective - To evaluate the:

·         Time for Glottic Exposure (TGE)

·         Time for Tracheal Intubation (TTI)

·         Number of laryngoscopy attempts

·         Discomfort level of investigator with respect to table height (Subjective)

·         Change in body positioning with respect to table height (Objective)

·         Grades of visualization of vocal cords at different heights

·         Post Operative Sore Throat

P****re-anaesthetic preparation**:**

All patients will undergo pre-anaesthesia checkup where detailed history will be taken, patients will be physically examined and relevant routine and special investigations would be carried out followed by written informed consent.

P****remedication and anaesthetic procedure**:**

All subjects who meet the inclusion and exclusion criteria will be randomly allocated to 2 equal groups. Premedication would be administered by injection glycopyrrolate 0.2 mg, fentanyl citrate 2µg/kg, ondansetron hydrochloride 4mg and midazolam 1mg intravenously and then, the patients will be shifted to operation theatre table which will be followed by pre-oxygenation for approximately for 3 mins. The patients will then be induced with induction dose of Inj. propofol 2 mg/kg and Inj. atracurium 0.5mg/kg followed by bag and mask ventilation for 3 mins with 100% oxygen. Mask ventilation and table height adjustment will be allowed as per the intubator’s ease.

The positioning of the patients will be done by placing a 7cm high pillow beneath the patients’ head with the head in supine neutral position for intubation. The table height would be adjusted with respect to the nasion of the patient – at the level of Nipple of the Anaesthetist (Group N) or at the level of Umbilicus (Group U). Video Laryngoscope of the variety VL400 (UESCOPE) would then be taken in the Anaesthetist’s hand and the blade inserted into the patients’ mouth via the central approach and the vocal cords visualized. The time taken (in seconds) from taking the laryngoscope in hand to satisfactory vocal cord visualization by the Anaesthetist would be noted.

Grading of the visualized vocal cords (Cormack-Lehane) would also be documented.

Cuffed endotracheal tubes of Internal Diameters 7mm and 8mm for female and male patients, respectively with a stillete would then be taken into the Anaesthetist’s hand and would be inserted alongside the laryngoscope held in place visualizing the entry point of the tube. The tube would be inserted into the trachea, stillete removed and the tube pushed inside upto the appropriate length and the laryngoscope would then be taken out of patient’s mouth. The cuff of the endotracheal tube would be inflated and the tube would be fixed in place. A photograph of the Anaesthetist would be taken without the operation table in frame as he/she passes the tube into the patient’s trachea to interpret any change in the position of the body of the Anaesthetist during the process. The time taken (in seconds) from taking the endotracheal tube in hand till taking out the laryngoscope from patient’s mouth by the Anaesthetist would be noted. All Intubations will be performed by experienced anaesthetists with more than 25 successful intubations with the video laryngoscope.

Subjective discomfort level of the intubator with respect to different table heights would be assessed and documented on a scale of 0 to 3.

In case of more than 2 failed attempts to intubate the patient or more than 60 seconds time taken for intubation using Video Laryngoscope, the anaesthetist will be allowed to adjust the table height. In the event of continued inability to visualise the vocal cords, the standard MacIntosh Laryngoscope will be used for Intubation.

Post-operative assessment**:**

The patients will be assessed 1 hour after the completion of the surgery for any sore throat.

Table Height - taken as the level of standing Anaesthetist’s umbilicus/nipple in relation to the patient’s nasion.

Time of Glottic Exposure (TGE) - taken as the time taken from taking the laryngoscope in hand to satisfactory vocal cord visualization by the Anaesthetist.

Time for Tracheal Intubation (TTI) - taken as the time taken from taking the endotracheal tube in hand to taking out the laryngoscope from patient’s mouth by the Anaesthetist.

Total Time for Tracheal Intubation (TTTI) – TGE + TTI

STATISTICAL ANALYSIS

 The primary objective of the study is to evaluate and compare the time taken to intubate the trachea using the video laryngoscope at two different table heights. Nikola et al. conducted a study on the impact of bed angle and height on intubation success during simulated endotracheal Intubation. This study found a difference of 9 sec (SD=14.4) on the time to intubation between the groups with the table levels at Nipple and Umbilicus of the intubator. Based on this study, we require a sample size of 102 subjects to detect a difference of 4 sec with a power of 80%.

SAMPLE SIZE CALCULATION**:** The following formula is used for this purpose:

where,

z1-α/2 = 1.96, for 5% level of significance

z1-β = 0.84, for 80% power

δ = 4, the minimum difference to be detected

For all statistical tests, p value less than 0.05 will be taken to indicate a significant difference.

REFERENCES

1.      Berquer R, Smith WD, Davis S. An ergonomic study of the optimum operating table height for laparoscopic surgery. Surg Endosc 2002;16

2.      Hanna GB, Shimi SM, Cuschieri A. Task performance in endoscopic surgery is influenced by location of the image display. Ann Surg 1998; 227

3.      Heath ML. Stature of anaesthetic personnel and positioning of patients. Br J Anaesth 1998; 80

4.      Stoelting RK, Miller RD. Basics of Anesthesia, 5th Edn. Philadelphia, PA: Churchill Livingstone, 2007

5.      Benumof J, Hagberg CA. Benumof’s Airway Management: Principles and Practice, 2nd Edn. Philadelphia, PA: Mosby, 2007

6.      Otto C. Tracheal intubation. In: Nunn JF, Utting JE, Brown BR, eds. General Anaesthesia, 5th Edn. London, Boston: Butterworths, 1989

7.      Motoyama EK, Davis P. Smith’s Anesthesia for Infants and Children, 7th Edn. Philadelphia, PA: Mosby, 2006

8.      Kim, Wonhee et al. Comparison of the Pentax Airwayscope, Glidescope Video Laryngoscope, and Macintosh Laryngoscope During Chest Compression According to Bed Height, Medicine: February 2016 - Volume 95 - Issue 5 - p e2631

9.      Lee H-C, Yun M-J et al. Higher operating tables provide better laryngeal views for tracheal intubation. British Journal of Anaesthesia Elsevier BV; 2014; 112: 749–55, 2014