Feasibility of Jaw Thrust as an Indicator for Assessing Adequate Anesthesia Depth During Supraglottic Airway Device Insertion in Morbidly Obese Patients
Introduction
The rising global prevalence of obesity has led to increased demand for surgical interventions in this population. Morbid obesity, defined by a body mass index (BMI) ≥40 kg/m², presents significant challenges for airway management during anesthesia due to anatomical and physiological changes. These include reduced functional residual capacity, increased risk of difficult mask ventilation, and higher susceptibility to hypoxemia. Supraglottic airway devices (SADs) are increasingly recommended for obese patients as they facilitate oxygenation and can serve as conduits for tracheal intubation. However, determining the optimal depth of anesthesia for SAD insertion remains critical to suppress airway reflexes while avoiding hemodynamic instability.
Jaw thrust, a maneuver used to relieve upper airway obstruction, has been validated as a reliable indicator of anesthesia depth for SAD insertion in non-obese adults and children. However, its efficacy in morbidly obese patients undergoing sevoflurane inhalational induction with spontaneous breathing had not been studied. This prospective observational study aimed to evaluate the feasibility and validity of jaw thrust as a clinical indicator for assessing adequate anesthesia depth during SAD insertion in morbidly obese patients.
Methods
Study Design and Participants
The study enrolled 30 morbidly obese patients (BMI 40–73 kg/m²) scheduled for elective bariatric surgery at Beijing Friendship Hospital. Exclusion criteria included respiratory tract infections, asthma, severe obstructive sleep apnea, and gastroesophageal reflux. All patients provided informed consent, and ethical approval was obtained from the Institutional Ethics Committee.
Anesthesia Protocol
Patients were positioned in a ramped position to optimize airway alignment. Pre-oxygenation was performed with 100% oxygen until end-tidal oxygen fraction reached ≥0.9. Anesthesia induction commenced with 5% sevoflurane via a closed facemask, followed by incremental increases of 1% every 2 minutes until loss of motor response to jaw thrust or a maximum concentration of 8% sevoflurane. The jaw thrust test was performed every 10 seconds by an experienced anesthesiologist, who applied upward pressure on the mandibular angles for 5 seconds. A negative response (no motor reaction) signaled adequate anesthesia depth.
A size-4 BlockBuster™ SAD, lubricated with lidocaine gel, was inserted immediately after confirming the absence of jaw thrust response. Insertion conditions were graded using the Bouvet scoring system, which evaluates six variables: resistance to mouth opening, resistance to SAD insertion, swallowing, coughing/gagging, head/body movement, and laryngospasm. Scores were categorized as “excellent,” “good,” or “poor.”
Fiberoptic Bronchoscopic Assessment
Following successful SAD placement, a fiberoptic bronchoscope (FOB) assessed the device’s anatomic position using the Brimacombe-Berry scoring system:
- Grade 1: Glottis not visible.
- Grade 2: Glottis and anterior epiglottis visible.
- Grade 3: Glottis and posterior epiglottis visible.
- Grade 4: Glottis fully visible.
Grades 2–4 were considered adequate positioning.
Data Collection
Hemodynamic (heart rate, mean arterial pressure) and respiratory parameters (tidal volume, respiratory rate, end-tidal CO₂) were recorded at baseline, pre-insertion, and post-insertion. Adverse events, including hypoxemia (SpO₂ <92%), apnea, and airway injury, were monitored.
Results
Patient Characteristics
The cohort comprised 22 females (73.3%) and 8 males, with a mean BMI of 46.9 ± 8.5 kg/m². Comorbidities included hypertension (26.7%), diabetes (33.3%), and hyperlipidemia (43.3%).
SAD Insertion Outcomes
All patients achieved successful SAD insertion on the first attempt. Insertion conditions were graded as excellent in 30% (9/30) and good in 70% (21/30). Intermediate resistance to mouth opening and SAD insertion occurred in 66.7% and 60% of cases, respectively. Only one patient exhibited mild swallowing and gagging. No coughing, movement, or laryngospasm was observed.
Fiberoptic Positioning
FOB assessment revealed adequate positioning (Grades 2–4) in 93.3% (28/30) of patients. Two patients (6.7%) had Grade 1 positioning but achieved adequate ventilation after adjusting the SAD using the up-down maneuver.
Anesthesia Depth and Physiological Parameters
The mean end-tidal sevoflurane concentration (ETsev) at loss of eyelash reflex was 2.2% ± 0.2%, increasing to 4.7% ± 0.5% at loss of jaw thrust response. Time to eyelash reflex loss was 96.0 ± 16.2 seconds, while jaw thrust response disappearance occurred at 346.1 ± 47.7 seconds.
Significant hemodynamic and respiratory changes were noted:
- Heart rate increased from 81.5 ± 10.4 to 98.1 ± 8.3 beats/min pre-insertion (P <0.001).
- Mean arterial pressure decreased from 103.5 ± 8.8 mmHg to 92.5 ± 10.5 mmHg pre-insertion (P <0.001).
- Tidal volume decreased from 676.7 ± 139.0 mL to 449.3 ± 102.7 mL pre-insertion (P <0.001).
Post-insertion, respiratory rate and end-tidal CO₂ normalized, confirming effective ventilation.
Adverse Events
Five patients (16.7%) experienced transient apnea during induction, resolved with oropharyngeal airway placement. No hypoxemia, bradycardia, or airway trauma occurred.
Discussion
Validity of Jaw Thrust Test
This study demonstrates that jaw thrust is a reliable indicator of adequate anesthesia depth for SAD insertion in morbidly obese patients. The absence of motor response correlated with excellent or good insertion conditions in 100% of cases, consistent with findings in non-obese populations. Previous studies reported variable success rates (72%–84%) using jaw thrust in normal-weight adults, but the higher success here may reflect protocol differences, such as vigorous jaw thrust application and the use of a second-generation SAD.
Comparison With Alternative Indicators
End-tidal sevoflurane concentration (ETsev) and loss of eyelash reflex are less reliable. In obese patients, Wang et al. found a 50% insertion success rate at ETsev 2.5%, whereas Siddik-Sayyid et al. reported only 46% success using eyelash reflex loss in non-obese adults. Jaw thrust’s noxious stimulus likely provides a more consistent endpoint for suppressing airway reflexes.
Clinical Implications
Morbidly obese patients are at heightened risk of airway complications. Sevoflurane inhalational induction with spontaneous breathing preserves respiratory drive, reducing “cannot intubate, cannot ventilate” scenarios. The BlockBuster™ SAD’s high sealing pressure (30 cmH₂O) and gastric drainage design further enhance safety in this population.
Study Limitations
The single-arm design precludes direct comparison with other anesthesia depth indicators. Gender imbalance (73% female) and younger age (mean 29.2 years) may limit generalizability, as airway characteristics differ between sexes and age groups. Additionally, the fixed SAD size (size 4) did not account for thyromental distance variations.
Conclusion
The jaw thrust test effectively determines adequate anesthesia depth for SAD insertion in morbidly obese patients undergoing sevoflurane inhalational induction. Its simplicity, non-invasiveness, and high success rate support its integration into clinical practice for this high-risk population. Future studies should explore its utility across diverse demographics and airway devices.
doi.org/10.1097/CM9.0000000000000403
Was this helpful?
0 / 0