Comparison of the Effectiveness of Two-Handed Mask Ventilation Techniques (C-E versus V-E) in Obese Patients Requiring General Anesthesia in an Indian Population.

Background: Two-handed mask ventilation techniques are often used in cases of difficult mask ventilation scenarios. A comparison of two methods of two-handed techniques in terms of tidal volume was undertaken in the context of the obese population. Aims and
Objectives: To determine and compare the effectiveness of mask ventilation in obese Indian adult subjects by using either the C-E technique or the V-E technique after induction of general anaesthesia. Material and
Methods: This was a randomised interventional study conducted on eighty obese patients. They were randomized into Group A ventilated with C-E technique and Group B with V-E technique. Expired tidal volume (VTe), Peak inspiratory pressure (PIP), SpO2, EtCO2 and vital signs were noted.
Results: The BMI and hemodynamic parameters were comparable between the two groups. The expired tidal volume of 702 ± 77 mL with the V-E technique was significantly more than the C-E technique, which was 492 ± 71 mL. The ventilatory failure rate with the C-E technique was 15% and 0% with the V-E technique. There was no significant difference between the peak airway pressures for the two techniques: 20.3 ± 1.5 mm H2O for Group A and 20.5 ± 1.2 mm H2O for Group B. Conclusions: Mask ventilation with the two-handed V-E technique is associated with better tidal volumes and reduced failure rates in the obese population. So the V-E technique should be attempted first as a rescue measure in obese adult patients if the return of spontaneous breathing and tracheal intubation is impossible. Copyright:

INTRODUCTION

Mask ventilation is a fundamental technique in airway management that plays a crucial role in saving the life of the patient. It remains an important bridge to a definitive airway in cases of difficult intubation.

Mask ventilation is performed in apneic patients in both elective and emergent conditions to oxygenate and facilitate an airway. The predictors of difficult mask ventilation include increased body mass index (BMI), history of snoring/sleep apnea, presence of beard, lack of teeth, aged over 55 years, Mallampati III or IV, limited mandibular protrusion, male gender, and airway masses/tumors.[123] Signs of inadequate face mask ventilation include, but are not limited to, absent or inadequate chest movement, absent or inadequate breath sounds, auscultatory signs of severe obstruction, cyanosis, gastric air entry or dilatation, decreasing or inadequate SpO2, absent or inadequate exhaled carbon dioxide, and absent or inadequate spirometric measures.[4]

Obesity is one of the predictors of difficult mask ventilation. Obese patients have excess fatty tissue on the breast, neck, thoracic wall, abdomen, mouth, and pharynx.[5] The deposition of adipose tissue in pharyngeal and parapharyngeal area results in decreased patency of the pharynx. Obese patients tend to have a higher metabolic demand, decreased functional residual capacity, and increased ventilation-perfusion mismatch, which results in greater impairment of lung function compared to patients with normal BMI during ventilation.[6] A significant negative linear correlation between time to desaturation and obesity has been shown during anesthesia induction despite adequate preoxygenation.[7] Hence, effective mask ventilation is of vital importance.

There are multiple approaches for hand positioning during mask ventilation, one-handed and two-handed techniques. Two-handed techniques are reserved for difficult mask ventilation situations as they provide a better mask to face seal[89] and produce greater tidal volumes.[1011]

Frequently used techniques of two-handed mask ventilation are the C-E technique and the V-E technique. The C-E technique applies the mask by forming a “C” shape with the thumb and index finger over each side of the mask while the third, fourth, and fifth fingers of both hands lift the mandible toward the mask in a three-fingered “E” shape [Figure 1]. The V-E technique uses the thumb and the eminence of each hand placed over each side of the mask, while the second to fifth digits pull the jaw upward, again forming an “E” shape [Figure 2].[12]

Figure 1

C-E technique

Figure 2

V-E technique

Despite the importance of this skill, limited studies are comparing the effectiveness of these (C-E vs. V-E) techniques in obese adults. Due to the significance of mask ventilation, it is important to be able to objectively measure the outcome of this procedure. With this background, we aim to compare the effectiveness of the two-handed mask ventilation techniques (C-E vs. V-E) in obese patients requiring general anesthesia.

MATERIALS AND METHODS

After obtaining institutional ethics committee approval and written informed consent, 80 American Society of Anesthesiologists PS Status classes I, II, and III patients of either sex aged between 20 and 50 years with BMI 25–35 kg.m−2 undergoing elective surgeries under general anesthesia were included in this hospital-based randomized interventional study. Patients with acute and chronic respiratory disorders, presence of beard, temporomandibular jaw abnormality, edentulous patients, limited mandibular protrusion, presence of airway mass or tumor, patients requiring rapid sequence induction or awake intubation, and pregnant patients were excluded from the study. After computer-generated randomization, the patients were allocated into two groups of 40 patients each. In Group A, patients received ventilation with the C-E ventilation technique, while in Group B, patients received ventilation with the V-E technique after induction of general anesthesia.

Preanesthetic evaluation included history, complete physical examination, blood biochemistry, ECG, and chest X-ray. Informed written consent was obtained after providing a complete explanation regarding the study protocol and the procedure. Patients were NPO for 8 h before surgery. Intravenous (i.v.) access was obtained using 20G i.v. cannula, and Ringer's lactate was started. Intraoperative monitoring included ECG, SPO2, NIBP, and EtCO2.

Anesthesia was administered by a uniform technique in all patients. Anesthesia resident doctors skilled in the technique of bag-valve-mask ventilation performed mask ventilation in all the cases and they were not part of the study team.

The patient was placed in the supine position on the OT table with head in the neutral position on a pillow of 10 cm height. Preoxygenation through a mask with a flow rate of 10 L.min−1 of 100% O2. The patient was premedicated with glycopyrrolate 0.2 mg (i.v.), midazolam 0.2 mg.kg−1 (i.v.). bolus of fentanyl 2 μg.kg−1 (i.v.) was given before induction. Anesthesia was induced with i.v. propofol (2–2.5 mg.kg−1) titrating to achieve an appropriate level of sedation based on clinical assessment.

Once apnea occurred after induction, the patient was ventilated with one of the two techniques either the two-handed C-E or V-E technique. Ventilation was achieved using pressure control mode at the rate of 10 bpm, inspiratory to expiratory time ratio of 1:2, peak inspiratory pressure (PIP) of 20 cm H2O, and no PEEP.

If the subjects were adequately ventilated as defined by perceivable chest movement and carbon dioxide measured during exhalation (EtCO2) at least for three breaths, ventilation was continued by the same method until the completion of 10 breaths. If ventilation failed with the C-E technique for all the first three consecutive breaths, then patients were ventilated by inserting an oropharyngeal airway. If ventilation was adequate, the ventilation method was continued till the completion of 10 breaths.

In Group B, patients were ventilated with the V-E technique and the same protocol was followed. In cases, we were unable to ventilate even after insertion of an oropharyngeal airway, a laryngeal mask airway or tracheal intubation was used for airway management as a backup, and the study was terminated.

All ventilator settings and measured parameters displayed on the ventilator and monitor (Dräger Fabius® GS premium) including expired tidal volume (VTe), PIP, SpO2, EtCO2, and vital signs were noted. The target number for ventilation was 10 breaths for both C-E and V-E techniques. The last five breaths were used for the final analysis to calculate VTe and PIP.

The mean of the last five breaths was used as a single data point. Attempted mask ventilation was considered a failure if VTe 13]

The formula for predicted body weight (PBW) for men = 50 + 0.9 (height [in centimeters] −152.4) and women = 45.5 + 0.9 (Height [in centimeters] −152.4). Considering the fact that Indians exhibit unique features of obesity which are different from the western population, here we define obesity according to “Consensus Statement for Diagnosis of Obesity” published in the Journal of the Association of Physicians of India:[14] Normal: 18.0–22.9 kg.m−2, overweight: 23.0–24.9 kg.m−2, and obese: 25 kg.m−2 and above.

The primary objective of the study was to determine the difference in mean VTe between the two groups (C-E vs. V-E) after induction of general anesthesia. Secondary objectives included the difference in peak airway pressure (PIP), VTe/actual weight, VTe/PBW between the two groups, to determine the failure rates of mask ventilation and the difference in the percentage of cases requiring oropharyngeal airway due to failure of ventilation between the two groups. The sample size was calculated to be 36 subjects for each of the two groups at 95% confidence interval and 80% power. This sample size is also adequate to cover all other study variables. For our study purpose, 40 patients were taken into each group.

Statistical analysis

All the data were entered onto a Microsoft Excel spreadsheet and were analyzed statistically using STATA SE (version 17.0) software (StataCorp LLC, College Station, TX, USA). All the quantitative data were summarized in the form of mean ± standard deviation. The difference between the mean value of both groups was analyzed using the Student's t-test. All the qualitative data were summarized in the form of numbers and percentages. The differences between proportions were analyzed using Fisher's exact test and Chi square test. The levels of significance and α-error were kept at 95% and 5%, respectively, for all statistical analyses. Probability was significant if P < 0.05 and nonsignificant if more than 0.05.

RESULTS

Eighty patients were taken up for the study and there were no dropouts. There were no statistically significant differences between the two groups in terms of the demographic profile including age, sex, height, weight, BMI, and physical status [Table 1].

Table 1

Demographic characteristics of patients

Characteristic	C-E technique	V-E technique	P
Age (years), mean±SD	37.3±8.7	34.4±9.3	0.154*
Gender, n (%)
Male	17 (42.5)	16 (40.0)	0.820^
Female	23 (57.5)	24 (60.0)
Height (cm), mean±SD	163.2±6.7	163.6±5.2	0.766*
Weight (kg), mean±SD	75.9±6.9	77.8±5.9	0.195*
BMI (kg/m2), mean±SD	28.4±1.4	29.0±1.6	0.078*
ASA grade, n (%)
I	35 (87.5)	33 (82.5)	0.755#
II	5 (12.5)	6 (15.0)
III		1 (2.5)

*Student’s t-test, ^Chi-square test, #Fischer’s exact test. SD=Standard deviation, BMI=Body mass index, ASA=American Society of Anesthesiologists

The hemodynamic parameters such as heart rate, systolic blood pressure (SBP), and diastolic blood pressure (DBP) were recorded preoperatively. No statistically significant difference was found between the two groups in mean heart rate, mean SBP, and mean DBP. All 80 subjects achieved target peak airway pressure. The PIP of the last five breaths of Group A was 20.3 ± 1.5 cm of H2O and Group B was 20.5 ± 1.2 cm of H2O (P = 0.536). No statistically significant difference was found in EtCO2 and SpO2 between the two groups (P > 0.05). Mean VTe was found to be 492.2 ± 71.7 ml for the C-E technique and 702.0 ± 77.2 ml for the V-E technique [Figure 3]. A statistically significant difference was found in the mean VTe between the study groups (P ≤ 0.001) [Table 2]. Mean VTe/actual weight was 6.5 ± 0.9 ml/kg and 9.0 ± 0.9 mL.kg− 1 in C-E and V-E techniques, respectively (P ≤ 0.001). Mean VTe/PBW was 8.7 ± 1.5 mL.kg−1 in Group A and 12.3 ± 1.9 mL.kg−1 in Group B (P ≤ 0.001) [Table 2]. There were six (15%) instances of failure of ventilation [Figure 4] and oropharyngeal airway usage [Figure 5] with the C-E technique, while none was recorded with the V-E technique (P = 0.026).

Figure 3

Mean of the VTe of the last five breaths compared between the two groups. VTe = Expired tidal volume

Table 2

Efficiency of mask ventilation obtained with C-E versus V-E technique

Variable	C-E technique	V-E technique	P
VTe (SD) in ml	492.2±71.7	702.0±77.2	<0.001*
VTe/AW (SD) ml/kg	6.5±0.9	9.0±0.9	<0.001*
VTe/PBW (SD) ml/kg	8.7±1.5	12.3±1.9	<0.001*
Ventilatory failure, n (%)	6±15.0	0±0	0.026#

Data are summarized as mean±SD. *Student’s t-test, #Fisher’s exact test. AW=Actual body weight, PBW=Predicted body weight, VTe=Expired tidal volume, SD=Standard deviation

Figure 4

Failure of ventilation in both the groups

Figure 5

Usage of oropharyngeal airway among the two groups

DISCUSSION

Our study finds that the V-E technique yielded better VTe than the C-E technique when the two-handed mask ventilation techniques were compared. Ventilation was easier to perform with the V-E technique for longer periods of time in spite of both techniques requiring considerable muscle strength. Mask ventilation with the C-E technique led to inadvertent compression of submandibular tissue leading to lesser VTe being delivered. V-E delivered greater tidal volume without a demonstrable difference in airway pressures.

It has been demonstrated using airway-training mannequin with variable airway resistance that two-handed techniques were superior to one-handed techniques,[8] and when an unconscious individual is in the supine position, the tongue falls posteriorly.[15] We know that the velopharynx is the site causing upper airway obstruction.[16] It is suggested that reduction of pharyngeal closing pressures by airway maneuvers helps in better ventilation.[17] Triple airway maneuvers (mandible advancement, neck extension, and mouth opening) with two hands in the sniffing position decreased the pharyngeal pressures thereby helping ventilation.[17]

The two-handed jaw-thrust mask technique improves upper airway patency as measured by greater tidal volumes during pressure-controlled ventilation than a one-handed C-E technique.[6] Studies have also shown that the V-E face mask ventilation grip results in improved ventilation over the C-E grip in the hands of novice providers as well.[7]

A randomized crossover study[18] compared C-E and modified V-E techniques with mouths kept open on unconscious apneic obese adults with a mean BMI of 37 kg.m-2. The modified V-E technique generated more tidal volume compared to C-E. The study was conducted on the western population, in contrast to our study which was conducted on the Indian population. In our study, ventilatory failure was observed with 6 (15%) patients with the C-E technique, and no failures were detected with the V-E technique. These cases of ventilatory failure were effectively ventilated with the usage of an oropharyngeal airway. The higher instances of failure in the C-E technique could have been due to upper airway obstruction, as a result of a lesser degree of mandibular advancement with the C-E technique. Placement of an oropharyngeal airway may have facilitated ventilation in cases of failure due to release of upper airway obstruction.

The absence of compression on submandibular tissue resulting from the placement of the operator's fingers away from the front of the neck may contribute to the improved airway patency in the V-E technique compared with the direct compression caused by the placement of the operator's fingers on the front of the neck that occurs with the C-E technique. C-E technique pushes the submandibular tissue posteriorly causing upper airway obstruction, while in the V-E technique the submandibular tissue is pushed anteriorly by the positive pressure generated. This may be the cause of the higher tidal volumes recorded.[18] We presume that the greater volumes generated by the V-E technique are due to the lack of airway obstruction.[19]

We believe our study is the first randomized, interventional study in the Indian population comparing the effectiveness of mask ventilation in a well-controlled environment, showing the superiority of the V-E technique. This was studied in well-anesthetized patients and can be extrapolated to patients in intensive care and in need of rescue ventilation.

Our study has various limitations. This study was done under general anesthesia. We did not assess the mask leak objectively. Hence, small leaks would have gone unnoticed. Hand size variability of the provider was not accounted for. Lower airway compliance could have also played a role on the ease of ventilation. Further studies are needed if the placement of airways throughout ventilation may show different results between the two techniques.

CONCLUSION

V-E technique generated greater VTe than the C-E technique in adult obese apneic patients. Given that two-handed mask ventilation is the last rescue measure, the V-E technique should be attempted first.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.