INTRODUCTION
Mask ventilation is a basic skill required for management of airway in anesthesiology. The most commonly used technique is the single-handed “CE” technique. Jaw thrust (JT) is ideally used for difficult mask ventilation cases. In CE technique , usually a nondominant hand is used. The thumb and index fingers are used to create a C-shaped seal around the neck of the mask. Rest of the fingers are used to perform chin lift while JT is provided by the weak little finger.
CE technique has not been validated as an effective technique for mask ventilation in terms of expired tidal volume (TV). There are few studies that demonstrate whether CE technique can generate or maintain triple airway maneuver by itself and fewer have compared CE technique with two-handed mask holding technique.[1 CE technique and two-handed JT technique.[2 CE technique and JT technique during pressure-controlled ventilation (PCV) by the mean of returned TV.
METHODS
This prospective, randomized, cross-over study was conducted over 1 year from September 2017 to December 2018 in a tertiary care hospital. The study received Ethical Committee approval from our institution (ss-1/EC 049/2017) and was registered in Clinical Trials Registry of India (CTRI/2018/04/012958). Written and informed consent was obtained for the participation in the study and use of patient data for research and educational purposes. The study protocol conformed to the ethical principles of medical research of the Helsinki Declaration 2013.
Sixty-five adult patients undergoing elective surgeries under general anesthesia were enrolled.
Inclusion criteria were patients aged 18-70 years and American Society of Anesthesiologists physical status classes I and II.
Exclusion criteria were anticipated difficult airway/difficult mask ventilation (dental or facial abnormality), need of rapid sequence induction, edentulous, pregnancy, body mass index >30 kg.m−2 , presence of nasogastric tube, and history of obstructive sleep apnea. Difficult airway was assessed by mouth opening/interincisor gap <3.5 cm, Mallampati score 3 and 4, temporomandibular joint mobility by upper lip bite test, and jaw protrusion. Both the techniques were performed on each patient, hence a cross-over study design. The sequence of the technique was divided into CE-JT technique and JT-CE technique .
Patients were randomly allocated to start with either CE-JT technique or JT-CE technique using coin flip method.
The operators performing the study had to have two years of experience in mask ventilation .
An adequate size face mask was selected and held over the bridge of the nose and mouth. In CE technique , thumb and index fingers were used to create an anterior seal around the mask, while the rest of the fingers were used to lift the chin [Figure 1 ].
Figure 1: CE technique
In the JT technique, both thumbs were used to create an anterior seal on the mask and JT maneuver was performed mainly by the index and second fingers [Figure 2 ].
Figure 2: Jaw thrust technique
The anesthesia machine (Datex Ohmeda Aestiva ®-General Electric, Chicago, IL, USA) was checked and calibrated. As per hospital protocol, all patients received premedication. Patients were shifted to the operative room, and standard monitors including pulse oximetry, electrocardiography, noninvasive arterial blood pressure, and capnography were connected to all patients. Patient's head was positioned on a standard pillow. Preoxygenation was carried with 6 L of 100% oxygen for 3 min by primary anesthesia care team who were not involved in the study. Anesthesia induction was done with intravenous (i.v.) fentanyl 2 μg.kg−1 and propofol 2 mg.kg−1 . After patient was induced, the ability to ventilate was checked as shown by chest rise and end-tidal carbon dioxide detection. Patients who required an oropharyngeal airway and inability to ventilate with single hand were excluded from the study. Once face mask ventilation was confirmed, i.v. atracurium 0.5 mg.kg−1 was given. Patient was manually ventilated for 3 min with oxygen and isoflurane 1%. Patients were handed over to the study operator to conduct study. At the start of the study, the operator was told which technique to perform first. The operator performed the given technique and once ready informed the investigator. The mechanical ventilator was then started with pressure control mode with frequency of 15 breaths/min and inspiratory to expiratory time I:E ratio of 1:2. Each breath was given with peak inspiratory pressure of 15 cm H2 O with no PEEP. The operator was blinded to the ventilator data as it was placed behind his/her back. The patients were ventilated with either CE technique followed by JT technique or with reverse sequence. Each technique was performed for 1 min and the expired TVs for last 12 breaths were recorded by an investigator [Figure 3 ]. Mask repositioning was not allowed during the 1 min study period. In between the two techniques, the operator was allowed to place the mask in the described way and do JT/finger positioning as required. Once the operator confirms the position, the PCV is started. The investigator assessed mask leak as audible or not. The epigastrium was auscultated with a stethoscope continuously by an assistant to note whether gastric insufflation was heard with each breath. The assistant was blinded to the technique and ventilator data by standing facing the foot end of the patient. Other parameters such as heart rate, blood pressure, oxygen saturation, and end-tidal carbon dioxide were monitored. After the study, the operator's preference as to which method they were more comfortable with was noted. Any adverse events such as hypoxia or bradycardia were noted. The mean of returned TV of each technique was calculated and compared. Demographic data of the subjects of the study such as age, sex, height, weight, BMI, and Mallampati score were compared.
Figure 3: Flowchart of methodology
If inadequate mask ventilation was observed, i.e., returned TV <4 mL. kg−1 associated with inadequate chest rise or oxygen saturation <90%, the study was discontinued.
Outcome
The primary outcome was mean expired TV. The secondary outcome was to assess mask leak, gastric insufflation , and operator's satisfaction with each technique.
Statistical analysis
Based on a previous study conducted by Joffe A M et al .,[2 −1 predicted body weight (PBW) with CE technique and 8.60 ± 2.31 mL.kg−1 PBW with JT technique.[2
n = sample size in case group
r = ratio of controls to cases
σ2 = standard deviation (SD) of the outcome variable
Zβ = desired power (typically 0.84 for 80% power)
Zα/2 = desired level of statistical significance (typically 1.96)
Difference = effect size (the difference of means)
Statistical software namely IBM SPSS 22.0 and R environment version 3.2.2 were used for data analysis. Microsoft Excel was used to generate graphs and tables.
Data were expressed as mean ± SD for continuous variables and number (%) for categorical variables. Student's t -test (two tailed, independent) was used to find the significance of the study parameters on a continuous scale between the two groups (inter group analysis) on metric parameters. Leven's test for homogeneity of variance was performed to assess the homogeneity of variance.
Student's t -test (two tailed, dependent) was used to find the significance of the study parameters on a continuous scale within each group. P < 0.05 was considered statistically significant.
Chi-square/Fisher's exact test was used to find the significance of the study parameters on a categorical scale between two or more groups, Nonparametric setting was used for qualitative data analysis.
RESULTS
Sixty five patients who met inclusion criteria were enrolled in the study. Three patients (4.6%) could not be adequately ventilated by primary anaesthesia care team and oral airway was used. Hence they were excluded from the study. 62 patients were considered for analysis [Figure 4 ]. Demographic and baseline characteristics are presented in Table 1 .
Figure 4: CONSORT flow diagram
Table 1: Demographic parameters
There was a significant increase in mean TV generated by JT technique over CE technique (591.46 ± 140.27 mL vs. 544.59 ± 159.08 mL; P < 0.001) [Table 2 ]. Gastric insufflation (12.9% vs. 14.5%) and mask leak (11.3% vs. 38.7%) were more in CE technique than JT technique. Operator comfort (79% vs. 19.4%) was more in JT technique [Table 3 ].
Table 2: Comparison of mean tidal volume between CE technique and jaw thrust technique
Table 3: Comparison of incidence - Gastric insufflation , audible mask leak, operator comfort in CE and jaw thrust technique in percentage (%)
All the patients had both the techniques performed, hence were comparable as this was a cross-over study. A total of 10 operators with 2 years of experience in mask ventilation participated. Out of the 10 operators, 6 operators were male and four were female. None of the patients had any adverse event such as hypoxia or bradycardia.
DISCUSSION
The findings in our study showed that JT technique was superior to single-hand CE technique in terms of returned TV in apneic adult patients on PCV. The incidence of gastric insufflation and audible mask leak was more in CE technique compared to that of JT technique. Majority of the operators in the study were more comfortable with the JT technique than CE technique .
Successful mask ventilation involves flow of gas along a path of low resistance. Upper airway patency is best judged by exhaled TV measurement on PCV. Inadequate ventilation with 25 cm H2 O must rule out upper airway obstruction.[3 mask ventilation are directed to relieve the resistance to flow of gas in airway. In literature, the most described and well-known method is one-handed CE technique . As trainees, this method is taught and mastered first. The American Heart Association 2015 guidelines recommends one-handed CE technique for mask ventilation .[4
Even for the experienced anesthetist, it is not always possible to obtain a good seal, while keeping the airway open, with one hand. Most of the operators use the nondominant hand to hold the mask. It is tiring for one person to maintain this hand position. It can be difficult for people with small hand span to reach behind the angle of the jaw, thus effectively unable to perform the mandibular advancement. It may also depend on the individual. Some people perform better with one technique and the others do not. This variability may be due to the experience, grip strength, bias, hand span, and size of face mask they prefer. CE technique requires skill as one hand ensures both mask seal and neck extension. The triple airway maneuver of head tilt, chin lift, and JT is proved to improve airway patency. However, the weaker little finger in CE technique may not generate JT, i.e., it is unable to pull the mandible upward to prevent collapse of the upper airway.[1 5 mask ventilation .[6 CE technique holds the mandible body, closes the mouth, and tends to push the submandibular region. Any pressure on sub-mandibular soft tissues may occlude the airway. As the hand is placed on one side of the mask, the gases tend to leak from the other side. JT technique opens the mouth. The two-handed JT method principally includes the triple airway maneuvers (mandibular advancement, head extension, and mouth opening). As tongue base is directly attached to mandible, the forward JT moves it away and increases retroglossal space. JT widens oropharynx and velopharynx.[7 mask ventilation . Uzun et al . observed that obstruction was at tongue base level in anesthetized patients.[8
Joffe A M et al . used an oropharyngeal airway in obese patients which bypassed the velopharynx, the narrowest part of airway and improved airway patency.[2 CE technique . The retroglossal airway collapse occurs in obese and nonobese patients. Mandibular advancement lifts epiglottis from the posterior pharyngeal wall and thus enhances the area of laryngeal inlet. Only mandibular advancement with or without continuous positive airway pressure relieves the obstruction at the retroglossal site. Their results are comparable to our study and are due to the maintenance of anatomical balance in pharynx due to longitudinal traction forces.
Fei et al . compared modified two-handed mask ventilation technique with CE technique in obese patients. They found that two-handed JT technique not only provides greater TV but also has less failure rate compared to two-handed CE technique .[9
In our study, we chose PCV. In PCV, inadequate mask ventilation is suggested by reduced TV. Compared to manual ventilation, PCV provides uniform airway pressure and flow, thus allowing changes in TV as a good marker for upper airway resistance. Because this study is a cross-over study (patient acts as their own control), the respiratory compliance was standardized. Hence, higher TV obtained from JT technique must be due to improved airway patency due to neck extension and lower JT.[10 et al . proved that the risk of gastric insufflation is least with inspiratory pressure of 15 cm H2 O in PCV with adequate mask ventilation measured by real-time ultrasonography of antral area and epigastric auscultation.[11 gastric insufflation was 0% at Pinsp 10 cm H2 O and 41% at Pinsp 25 cm H2 O. We based our protocol on a study by Brimacomb et al . where air >4 mL can be detected by stethoscope auscultation after one breath with 95% confidence.[12
In our study, we used a setting of 15 cm H2 O and epigastric auscultation was performed. We had incidence of 14.52% in CE technique and 12.9% in JT technique. The inadequate mandibular advancement in CE technique , the relaxation of pharyngeal muscle, and upper oesophageal sphincter muscle due to muscle relaxant could have contributed to higher percentage of gastric insufflation in our study. When an anesthetized paralyzed patient has difficult intubation, oxygenation is dependent on good mask ventilation . If it is unanticipated difficult airway situation, a second operator is always not available for help. So, the best attempt at mask ventilation by a single person is two-handed JT using PCV.
In our study, the operator was blinded to the ventilator data and was not allowed to readjust the mask after first breath of each technique was started. So, even if the operator heard a mask leak himself, the grip was not allowed to be changed. The ventilator alarms were turned off so that the operator would not have positive or negative feedback of his/her ventilation efficacy.
Reduced expired TV could be due to inadequate seal of mask as evidenced by audible mask leak or due to inadequate airway positioning leading to gastric insufflation as heard by epigastric auscultation. It was assessed as we wanted to know in the same patient which technique had more mask leak or gastric insufflation .
The average increase in TV of 46 mL may not bring a significant change in healthy subjects undergoing elective surgery. The basal oxygen consumption in a healthy adult is 250 mL.min−1 . So, the gain of TV of 46 mL at 12 breaths/min gives rise to 540 mL.min−1 volume which doubles the oxygen delivered to the lungs. This could be clinically significant in a hypoxic patient or patient with low oxygen reserve. Those patients who have features of difficult mask ventilation or those with limited physiologic reserve may benefit from JT technique of mask ventilation .
Strengths of the study
As it is a prospective cross-over study, there was no confounders as patient was his own control
Operators with different sized hands and training were performing both techniques and thus selection bias among operators was ruled out
Exclusion of oropharyngeal airway is unique to this study when compared with other similar studies.
Limitations of the study
Use of muscle relaxants. Muscle relaxants are known to improve mask ventilation by reducing muscle tone.[13
We excluded patients with anticipated difficult airway. Further studies should exclusively compare these techniques in these patients. Mask leak was not assessed objectively. Hence, small leak would have got unnoticed.
CONCLUSION
JT technique generates greater TV compared to CE technique . Gastric insufflation and audible mask leak were more frequent in CE technique compared to JT technique. Majority of the operators felt that the JT technique was more comfortable.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
Acknowledgment
We would like to thank our institution, department colleagues, and statistics team for their support and guidance without which this study would not be possible.
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