Association of WWI With Difficult Intubation

This prospective observational cohort study was conducted at Kasr Alainy Hospitals, Cairo University, Egypt. The study protocol was approved by the Anesthesia Department Research Committee and the Kasr Alainy Research and Ethics Committee. Written informed consent was obtained from all participants prior to enrollment. All procedures followed the ethical standards of the institutional research committee and the 1964 Helsinki declaration and its later amendments.

I. Study design:

This study was designed as a cohort study, conducted to evaluate the association between the weight-adjusted waist index (WWI) and the incidence of difficult tracheal intubation.

II. Study population:

Adult patients undergoing elective surgical procedures under general anesthesia requiring endotracheal intubation at Kasr Al-Ainy Hospitals.

III. Study Procedures:

1. Preoperative Assessment:

   All eligible patients underwent a standardized pre-anesthetic evaluation performed by an anesthesiologist or a trained anesthesia resident, including:

   • Detailed medical and surgical history
   • Physical examination
   • Routine laboratory investigations Anthropometric Measurements and WWI Calculation Waist circumference (WC) was measured in centimeters while patients were wearing disposable non-woven clothing and no footwear, at the midpoint between the iliac crest and the lowest rib.

   Body weight was measured using a calibrated digital scale.

   WWI Calculation:

   • WWI was calculated using the formula:
   • WWI=Waist Circumference (cm) ÷ √Weight (kg)
   • Higher WWI values indicate greater central adiposity. Airway Assessment

   Preoperative airway evaluation included:

   • Modified Mallampati classification
   • Thyromental distance
   • Mouth opening (inter-incisor distance)
   • Neck movement
   • Prognathism
   • Neck circumference (measured at the level of the thyroid cartilage)
   • El-Ganzouri Risk Index (EGRI) The El-Ganzouri Risk Index was calculated using its standard components: Mouth opening, Thyromental distance, Mallampati score,Neck movement,Prognathism,Body weight
   • History of difficult intubation The score was calculated using MedCalc software.
2. Intraoperative Management:

Patient Positioning and Monitoring Upon arrival to the operating theatre, patients were positioned in the dorsal decubitus position. The head was supported with a pillow to achieve the sniffing position, aligning the external auditory meatus with the sternal notch.

Standard monitoring was applied, including:

• Electrocardiography (ECG)
• Non-invasive blood pressure
• Pulse oximetry
• Capnography
• Temperature monitoring Premedication After intravenous cannulation, all patients received midazolam 2 mg IV as premedication.

Preoxygenation Preoxygenation was performed using a tight-fitting face mask for 3 minutes to ensure adequate oxygen reserves before anesthesia induction.

Induction of General Anesthesia

• General anesthesia was induced using:
• Propofol (1.5-2.5 mg/kg)
• Fentanyl (1 μg/kg)
• Atracurium (0.5 mg/kg) Mask Ventilation Following induction, bag-mask ventilation (BMV) was initiated using a two-handed double C-E technique. The attending anesthesiologist who performed mask ventilation had more than one year of experience. Ventilation was continued for approximately 3 minutes to allow adequate neuromuscular blockade.

Assessment of BMV

• Adequacy of ventilation was confirmed by:
• Visible chest and abdominal rise
• Presence of a well-formed capnography waveform

BMV was graded using a 4-point scale:

1. Ventilated without an oral airway
2. Ventilated with oral airway/adjunct
3. Difficult Ventilation:characterized as unstable,inadequate,or requiring two providers despite oral airway/adjunct.
4. Impossible ventilation:unable to ventilate despite multiple providers or adjuvants.

Laryngoscopy Direct laryngoscopy was performed with a Macintosh blade (sizes 3-5) by an anesthesiologist with at least 1 year of experience. The laryngeal view was classified according to the Cormack-Lehane grading system.

Endotracheal Intubation Following laryngoscopy, endotracheal intubation was attempted using an appropriately sized tube (7.0-8.0 mm).

The following were recorded:

• Number of intubation attempts
• Cormack-Lehane grade
• Success or failure of intubation Management of Failed Intubation

If the first intubation attempt failed, one or more adjuncts were employed as appropriate, including:

• Application of the BURP (backward, upward, rightward pressure) maneuver
• Use of an endotracheal tube stylet/Bougie
• Change of laryngoscope blade (from Miller to Macintosh or vice versa or McCoy)
• Substitution of the laryngoscopist with a more experienced anesthesiologist (a senior anesthesia resident, or a consultant anesthesiologist)
• Use of video laryngoscopy
• Use of supraglottic airway devices If the second intubation attempt by the consultant anesthesiologist failed, a third attempt was performed by the consultant anesthesiologist after selecting an alternative adjunct from the previously mentioned options.

Failed intubation was defined as the inability to achieve successful tracheal intubation after three attempts by an experienced anesthesiologist.

Maintenance of Anesthesia and Ventilation

After successful intubation:

• Anesthesia was maintained using sevoflurane (2%) in 50% oxygen
• Mechanical ventilation was initiated using volume-controlled mode
• Ventilation was adjusted to maintain end-tidal CO₂ between 32-34 mmHg Definition of Difficult Airway

A difficult airway was defined as any of the following:

• BMV grade ≥3
• Cormack-Lehane grade ≥3
• ≥3 intubation attempts Reversal and Emergence

At the end of surgery:

• Anesthesia was discontinued
• Neuromuscular blockade was reversed using:
• Neostigmine (0.05 mg/kg)

• Atropine (0.02 mg/kg) IV. Data Collection and Measurements The following variables were recorded: Demographics and Patient Characteristics Age (years) Sex Weight (Kg) Height BMI ASA score Type of surgery Anthropometric Waist circumference WWI Neck circumference (cm) Airway Variables Mallampati score Sternomental distance (cm) EGRI score BMV grade Cormack-Lehane grade Intubation Data Number of attempts Use of adjuncts V. Study Outcomes

  1. Primary outcome:

• The correlation coefficient between WWI and the incidence of difficult intubation.

  2. Secondary outcome(s)

• Incidence of difficult intubation.Difficult intubation was defined as requiring two or more attempts, as this threshold allows earlier detection of clinically relevant airway difficulty and has been adopted in recent airway research.
• Predictive accuracy of WWI to predict (ROC curve, sensitivity, specificity, AUC).
• The cutoff value of WWI to predict difficult intubation.
• Comparing the predictive ability of WWI to BMI to predict difficult airway
• Correlation between WWI and: Difficult mask ventilation , El-Ganzouri score , Neck circumference, sternomental distance, Mallampati score VI. Sample Size Calculation The sample size was calculated using MedCalc software (version 20), based on an expected correlation coefficient (r = 0.41) derived from a pilot study conducted on 5 patients. With a power of 80% and a significance level of 5%, the required sample size was determined. To account for potential dropout, 6 additional patients were included, resulting in a total sample size of 50 patients.