A chin-lift mask produces a patent airway more effectively than an oropharyngeal airway using the EC-clamp technique in obese patients

Abstract

Objective

To evaluate the efficiency of ventilation using a novel chin-lift mask compared with an oropharyngeal airway (OPA) with EC-clamp technique in obese patients.

Methods

Obese patients scheduled for cholecystectomy under general anaesthesia were divided into two groups: the OPA group, in which a standard mask and OPA with the EC-clamp technique were used; the CL group, in which the chin-lift mask was used. Respiratory data were compared.

Results

One hundred patients were recruited and assigned to the OPA (n = 50) and CL (n = 50) groups. Compared with the OPA group, expired tidal volume, peripheral oxygen saturation (S_pO₂), tidal volume/peak inspiratory pressure ratio and end-tidal carbon dioxide were higher, and the peak and mean inspiratory pressures were lower, in the CL group. In the CL group, no patient had an S_pO₂ ≤95% and the lowest S_pO₂ was 99%, whereas in the OPA group, 23 patients had an S_pO₂ ≤95% and the lowest S_pO₂ was 92%. Difficult mask ventilation occurred in eight patients in the OPA group but in none in the CL group.

Conclusion

The chin-lift mask provided a patent airway and better quality mask ventilation than an OPA with EC-clamp technique in obese patients.

Keywords

Mask ventilation bag-valve mask EC-clamp technique

Introduction

The effective provision of artificial ventilation to unconscious and apnoeic patients via a mask is an important basic skill for emergency physicians and anaesthetists.¹ Sufficient oxygenation is required for induction; otherwise, brain damage or death can result.² Almost 30% of anaesthesia deaths result from difficult airway management and a failure of bag-valve mask ventilation.³ However, performing face-mask ventilation is particularly challenging in obese patients.⁴

In the EC-clamp technique, as described in the American Heart Association guidelines for emergency cardiac care,⁵ the thumb and forefinger form a ‘C’ shape over the mask and exert downward pressure on the mask, while the third, fourth and fifth finger (forming an ‘E’) are positioned along the jaw to maintain the jaw thrust. In practice, the jaw is not only pulled forward by the fifth finger but is also held in position by a backward pull towards the upper jaw, which requires the operator’s fingers to have enough strength to maintain the airway. If the operator’s hand becomes fatigued, which may particularly occur when the position is held for a long period of time or in obese patients, the airway may become partly obstructed, reducing the efficiency of the ventilation. The main difficulty in keeping the airway unblocked in obese patients (or in difficult mask ventilation situations) is maintaining the advancement of the mandible. To solve this problem, a chin-lift mask was devised; this customized, manually adjustable intraoral appliance lifts the tip of the jaw effectively and consistently. The present study evaluated respiratory data obtained during anaesthesia induction using the novel chin-lift mask, compared with an oropharyngeal airway (OPA) with the EC-clamp technique.

Patients and methods

People with American Society of Anesthesiologists physical status I–II and a body mass index >30 who had cholecystitis and were scheduled for cholecystectomy under general anaesthesia at the Tianjin Union Medicine Centre, Tianjin, China, between March 2012 and October 2012 were recruited sequentially to the study. Patients underwent physical assessments including history of snoring or sleep apnoea, and other assessments to predict ease of intubation. Patients with upper-airway abnormalities, facial hair, facial anatomical abnormalities, hiatus hernia, gastro-oesophageal reflux, ischaemic or congenital heart disease, or severe acute or chronic lung disease were excluded. After enrolment, patients were randomly assigned using a computerized random-number generator list to two groups: the OPA group, in which a standard mask and OPA with the EC-clamp technique were used, and the CL group, in which the chin-lift mask was used.

Written informed consent was obtained from all study participants. The study protocol was approved by the Institutional Review Board of Tianjin Union Medicine Centre, Tianjin, China.

Anaesthesia

Patients fasted from midnight before the operation; no premedication was administered. After placement of routine monitoring devices and capnography monitors, and preoxygenation with 100% oxygen for 3 min administered via a standard mask in the OPA group and via the chin-lift mask in the CL group, anaesthesia was induced with intravenous 0.05 mg/kg midazolam, 2.0 µg/kg fentanyl, 2 mg/kg propofol and 0.5 mg/kg atracurium. A total fresh gas flow of 3 l/min oxygen was delivered via the standard mask or the chin-lift mask. The ventilation parameters were initially set at a tidal volume of 10 ml/kg at a rate of 12 breaths/min. The adjustable pressure limiting valve was set at 30 cmH₂O. A standard circle circuit and 2-l bags were used.

The patient’s position for induction was supine, with the extremities resting comfortably on padded surfaces in a neutral anatomical position. The head was rested comfortably on a standard pillow that was raised in a ‘sniff’ position. When the train-of-four count fell to <2, either an OPA and standard mask was held in place using the EC-clamp technique or the chin-lift mask was put in position. The latex-free chin-lift mask was designed for single use in adults, and is based on the standard mask. The chin-lift mask is constructed from polyvinylchloride approved by the International Organization for Standardization (ISO 10993), which is nontoxic, hypoallergenic, noncarcinogenic and generally well tolerated. At the bottom of the mask, there is a matrix column with a J-shaped slide that holds a moveable insert (Figure 1A and 1B). The straight section is 12.5 cm long and the curved section is 5 cm long. The thickness of the J-shaped slide is 2 mm. The radius of the curved section is similar to that of a laryngoscope blade. The proximal end of the slide contains 15 holes. When the slide is adjusted maximally upwards, the tip of the slide returns to the inside of the air cushion, so the device can be used for both preoxygenation and provision of oxygen (Figure 1C). The button at the front of the cylindrical matrix column is pressed to adjust the length of the J-shaped slide until the tip of the slide maximally lifts the jaw. The adjustable vertical range is 4 cm (Figure 1D). As soon as the operator releases the button, the interior card slot in the matrix column is locked into one of the slide holes and the tip of the J-shaped slide fits on the surface of the oral mucosa of the lower jaw, so the chin is held in a forward position relative to the stationary maxilla. This procedure takes 5–10 s. With the tip of the slide acting as a fulcrum, the operator places a thumb on the top portion of the mask and the fingers on the matrix column. The chin-lift mask allows the operator to lift the jaw upwards and simultaneously to extend the atlanto-occipital joint while applying enough downward pressure to create an airtight seal (Figures 2 and 3). The dominant hand can then ventilate the patient using a bag-valve device.

Figure 1.

The chin-lift mask: (A) front view, (B) side view, (C) slide adjusted maximally upwards, (D) slide adjusted minimally upwards.

Figure 2.

Use of the chin-lift mask for ventilation.

Figure 3.

Diagrammatic representation of the position of the chin-lift mask.

The same anaesthetist performed all the induction procedures. He had been trained to use the chin-lift mask using mannequins prior to the study and had >10 years’ clinical experience.

After induction using the two types of mask, an endotracheal tube was inserted by an experienced anaesthesiologist.

Patient assessment

Mean expired tidal volume (Vt), peak inspiratory pressure (PIP), mean inspiratory pressure (MIP), tidal volume/peak inspiratory pressure ratio (Vt/PIP), end-tidal carbon dioxide (EtCO₂) level and peripheral oxygen saturation (S_pO₂) were recorded during anaesthesia induction. All data were collected by a single observer,positioned in a manner that was blinded to the type of mask being used.

Patients with more than one of the following criteria were defined as experiencing difficult mask ventilation: (1) inability to maintain an S_pO₂ >92%; (2) ‘significant’ gas leakage beneath the face mask; (3) need to increase the gas flow to >6 l/min; (4) no perceptible chest movement; (5) two-handed mask ventilation requiring assistance by an anaesthesiologist; (6) more than two oxygen flushes needed.⁶ A reduction in S_pO₂ to <95% was considered to be a failure of ventilation; in these circumstances, the study could be terminated, a potential effective alternative to the ‘four hand/two person skill’ was provided or immediate tracheal intubation was performed. This S_pO₂ threshold was chosen because the more usual threshold of 90% might have posed an unacceptable risk in obese patients.

Statistical analyses

All numerical data were presented as mean ± SD and were compared using Student’s independent two-sample t-test. The Pearson χ²-test or the Fisher’s exact test was used to compare nominal variables. A P-value <0.05 was considered to be statistically significant. Assuming a 100 ml Vt difference between the groups and a standard deviation of 100 ml, a study group size of 50 individuals was calculated to be necessary to achieve a significant difference between the groups with a power of 0.9.⁷ All statistical analyses were performed using SPSS® software, version 15.0 (SPSS Inc., Chicago, IL, USA).

Results

A total of 100 patients aged 22–64 years (14 female; 86 male) were included in this study, of whom 50 were assigned to the OPA group and 50 to the CL group. Patient demographic and clinical characteristics are shown in Table 1.

Table 1.

Demographic and clinical characteristics of obese patients undergoing general anaesthesia induction using either a standard mask and oropharyngeal airway with the EC-clamp technique (OPA group) or a novel chin-lift mask (CL group).

Characteristic	OPA group n = 50	CL group n = 50
Age, years	44.3 ± 7.7	43.5 ± 8.2
Age >55 years	4 (8)	4 (8)
Sex
Female	8 (16)	6 (12)
Male	42 (84)	44 (88)
ASA physical status
I	31 (62)	32 (64)
II	19 (38)	18 (36)
Height, cm	171.9 ± 6.2	172.5 ± 5.4
Weight, kg	93.0 ± 8.2	95.1 ± 8.0
Body mass index, kg/m²	31.4 ± 2.0	31.9 ± 1.3
History of snoring or obstructive sleep apnoea	29 (58)	26 (52)
Cannot protrude lower teeth past upper teeth	17 (34)	15 (30)
Mallampati score²⁰
I	7 (14)	8 (16)
II	18 (36)	20 (40)
III	22 (44)	19 (38)
IV	3 (6)	3 (6)

Data presented as mean ± SD or number (%) of patients.

ASA, American Society of Anesthesiologists.

No statistically significant between-group differences (P ≥ 0.05) using Student’s independent two-sample t-test for numerical data and Pearson χ²-test or Fisher’s exact test for nominal variables.

Ventilation indices in the two groups are shown in Table 2. The chin-lift mask provided more effective ventilation than an OPA plus EC-clamp technique. The Vt, Vt/PIP ratio and EtCO₂ were significantly higher and the PIP and MIP significantly lower in the CL group than in the OPA group (P < 0.001). In addition, in the CL group, no patient had an S_pO₂ ≤95% and the lowest S_pO₂ was 99%, whereas in the OPA group, 23 patients had an S_pO₂ ≤95% and the lowest S_pO₂ was 92% (P = 0.003). Eight patients in the OPA group were defined as having difficult mask ventilation and were ventilated by a two-handed technique by a second anaesthesiologist. In contrast, no cases of difficult mask ventilation occurred in the CL group. No airway injuries (such as lip laceration or haematoma, dental injury, tongue laceration, pharyngeal laceration or laryngeal laceration) were observed in either group. No patients experienced vomiting or aspiration.

Table 2.

Ventilation indices in obese patients undergoing general anaesthesia induction using either a standard mask and oropharyngeal airway with the EC-clamp technique (OPA group) or a novel chin-lift mask (CL group).

Index	OPA group n = 50	CL group n = 50	T	Statistical significance	95% confidence intervals
Vt, ml	469 ± 26	804 ± 138^a	−16.85	P < 0.001	−375.36, −296.24
PIP, cmH₂O	12.5 ± 2.5	8.6 ± 1.1^a	10.02	P < 0.001	3.06, 4.58
MIP, cmH₂O	8.7 ± 1.1	5.5 ± 0.9^a	21.82	P < 0.001	−12.55, −10.45
VT/PIP ratio	39.0 ± 7.5	94.2 ± 20.0^a	−18.31	P < 0.001	−61.23, −49.26
S_pO_2, %	95.7 ± 1.32	99.5 ± 0.5^a	−19.06	P < 0.001	−4.12, −3.40
EtCO₂, mmHg	31.8 ± 1.9	43.3 ± 3.2^a	16.12	P < 0.001	2.84, 3.64

Data presented as mean ± SD.

Vt, expired tidal volume; PIP, peak inspiratory pressure; MIP, mean inspiratory pressure; S_pO₂, peripheral oxygen saturation; EtCO_2, end-tidal carbon dioxide.

P < 0.05 compared with the OPA group using Student’s independent two-sample t-test.

Discussion

In the present study, the chin-lift mask offered advantages in most technical aspects of airway management in obese patients. The chin-lift mask effectively lifted the jaw, produced a patent airway and helped the operator successfully perform one-handed bag mask ventilation during the induction of anaesthesia.

Adequate mask ventilation is an important component of patient safety during induction of general anaesthesia. Anaesthesia reduces airway muscle tone and increases the collapsibility of the pharyngeal structures, thereby causing airway obstruction.⁸ Obese patients may present with difficult airways, and are more likely to desaturate than lean people.^9,10 Retraction of the mandible may contribute to the reduced airway size seen during anaesthesia.¹¹ Studies have demonstrated that manual anterior displacement of the mandible (using techniques such as the chin-lift manoeuvre) can dilate and stiffen the pharyngeal airway.^12,13 The chin-lift manoeuvre is a complex technique that requires considerable skill: the left hand lifts the chin and maintains head extension while generating the mask seal.^14,15 This technique can be effective in elevating the hyoid and epiglottis, thereby increasing the exposure of the laryngeal aperture and to some extent increasing its size, especially in the absence of tone in the geniohyoid and genioglossus muscles when a neuromuscular blocking drug has been administered.¹⁶ The manoeuvre enlarges both the laryngeal inlet and the pharynx. The chin-lift mask investigated in the present study was designed to emulate the chin-lift manoeuvre. This novel method was associated with a lower PIP, a higher Vt and S_pO₂ and less frequent difficult mask ventilation compared with an OPA with the EC-clamp technique. This suggests that lifting the jaw upward enabled fresh gas to be delivered with less upper airway obstruction. Because of its simplicity of use and efficiency, the chin-lift face mask may help to prevent poor oxygenation and to maintain pharyngeal patency in obese patients during anaesthesia induction.

Physicians and anaesthetists must be trained to use the EC-clamp technique. However, if the operator’s hand is small and the patient’s face is relatively large, uneven and inadequate downward pressure on the mask often leads to air leakage that may put the patient in danger. The EC-clamp technique requires that the operator’s fingers are strong enough to maintain mandible advancement, which can easily lead to hand fatigue, especially in obese patients. In addition, this manoeuvre requires forceful pressure on the patient’s face with the tips of the third, fourth and fifth fingers, which often causes redness and painful pressure points. One advantage of the chin-lift mask is that it allows the anaesthetist to achieve an effective seal and easy ventilation for a range of patient facial types. The tip of the J-shaped slide lifts the tip of the jaw, whereas the thumb controls the posterior part of the mask so that the air cushion closely fits the patient’s face to prevent leakage. Head extension is maintained by the torque between the tip of the slide and the pressure on the posterior part of the mask. Mouth opening, which is a component of the airway manoeuvres required for the improvement of upper airway patency, is automatically achieved by the intraoral slide of the chin-lift mask. Furthermore, by elevating the tip of the jaw as in the single-hand chin-lift manoeuvre, the chin-lift mask helps to manage an unprotected airway by ‘giving an additional hand’. An OPA elevates the hyoid or epiglottis and displaces the tongue, thereby producing a fixed-calibre channel in the retroglossal and supraglossal portions of the airway. However, insertion of an OPA is not a benign procedure. The airway can push the tongue posterior and further obstruct the oropharynx if not inserted correctly. Substantial lacerations can occur if the lips or tongue are caught between the teeth and the oral airway. The airway can force the epiglottis closed against the vocal cords if it is too long, resulting in complete airway obstruction.¹⁷ Too small an airway will force the tongue against the pharynx, also producing an obstruction.¹⁸ The J-shaped slide of the chin-lift mask has an adjustable vertical range of 4 cm and therefore does not invade the laryngeal cavity. In the present study, improved ventilation resulting in higher Vt, lower PIP and MIP and higher S_pO₂ values was observed in the CL group compared with the OPA group.

The limitations of the present study should be considered when interpreting the results. First, the study could not be performed with the anaesthetist blinded to the mask used because of the obvious appearance of the chin-lift mask; hence a bias could not be excluded. Bias was minimized by the use of a blinded observer to collect the data. Secondly, the mask was not evaluated in conscious patients. In the present study, patients were ventilated under controlled conditions in the operating room, which offered ideal conditions for airway management. However, patients who require emergency airway control often have intact reflexes, so the results cannot be extrapolated to emergency settings. Thirdly, to minimize operator bias, the same male anaesthetist performed all the procedures. It has been reported that sex is an independent risk factor for difficult mask ventilation.¹⁹ Hand size may confound the ability of operators to generate and maintain a mask seal using type of mask. Koga and Kawamoto¹⁹ reported that men had a larger hand size and were able to provide higher tidal volumes than women using both of the methods tested. Fourthly, although we did not observe any adverse effects associated with use of the chin-lift mask in this small cohort of patients, it is possible that problems may arise in a wider population or if the novel method was used for a prolonged period.

In summary, the present study demonstrated that mask ventilation performed in anaesthetized and paralysed obese patients was of better quality with the novel chin-lift mask than with an OPA using the EC-clamp technique. These results suggest that the chin-lift mask could be considered as an alternative to a standard mask plus OPA with EC-clamp technique to maintain airway patency in obese patients. The role of this intraoral mask for upper airway management during deep sedation, postanaesthesia care and general anaesthetic induction requires further evaluation.

Footnotes

Declaration of conflicting interest

The authors declare that there are no conflicts of interest.

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Acknowledgements

The authors are grateful to American Journal Experts for providing assistance with English editing.

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