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Physiological Measurement
PAPER • OPEN ACCESS
A randomised trial evaluating mask ventilation
using electrical impedance tomography during
anesthetic induction: one-handed technique
versus two-handed technique
To cite this article: Lingling Gao et al 2022 Physiol. Meas. 43 064004
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Physiol. Meas. 43 (2022)064004 https://doi.org/10.1088/1361-6579/ac70a3
PAPER
A randomised trial evaluating mask ventilation using electrical
impedance tomography during anesthetic induction: one-handed
technique versus two-handed technique
Lingling Gao
1,2,5
, Yun Zhu
1,2,5
, Congxia Pan
1,2
, Yuehao Yin
1,2
, Zhanqi Zhao
3,4
, Li Yang
1,2,∗
and
Jun Zhang
1,2,∗
1
Department of Anesthesiology, Fudan University Shanghai Cancer Center, Fudan University, Shanghai, People’s Republic of China
2
Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, People’s Republic of China
3
Department of Biomedical Engineering, Fourth Military Medical University, Xi’an, People’s Republic of China
4
Institute of Technical Medicine, Furtwangen University, Villingen-Schwenningen, Germany
5
These authors contributed equally to this work.
∗
Authors to whom any correspondence should be addressed.
E-mail: snapzhang@aliyun.com and liyangmagic@sina.com
Keywords: mask ventilation, one-handed technique, two-handed technique, pulmonary ventilation distribution, electrical impedance
tomography
Abstract
Objective. Mask positive-pressure ventilation could lead to lung ventilation inhomogeneity,
potentially inducing lung function impairments, when compared with spontaneous breathing. Lung
ventilation inhomogeneity can be monitored by chest electrical impedance tomography (EIT), which
could increase our understanding of mask ventilation-derived respiratory mechanics. We hypothe-
sized that the two-handed mask holding ventilation technique resulted in better lung ventilation,
reflected by respiratory mechanics, when compared with the one-handed mask holding technique.
Approach. Elective surgical patients with healthy lungs were randomly assigned to receive either one-
handed mask holding (one-handed group)or two-handed mask holding (two-handed group)
ventilation. Mask ventilation was performed by certified registered anesthesiologists, during which
the patients were mechanically ventilated using the pressure-controlled mode. EIT was used to assess
respiratory mechanics, including ventilation distribution, global and regional respiratory system
compliance (C
RS
), expiratory tidal volume (TVe)and minute ventilation volume. Hemodynamic
parameters and the PaO
2
-FiO
2
ratio were also recorded. Main results. Eighty adult patients were
included in this study. Compared with spontaneous ventilation, mask positive-pressure ventilation
caused lung ventilation inhomogeneity with both one-handed(global inhomogeneity index:
0.40±0.07 versus 0.50±0.15; P<0.001)and two-handed mask holding (0.40±0.08 versus
0.50±0.13; P<0.001). There were no differences in the global inhomogeneity index (P=0.948)
between the one-handed and two-handed mask holding. Compared with the one-handed mask
holding, the two-handed mask holding was associated with higher TVe (552.6±184.2 ml versus
672.9±156.6 ml, P=0.002)and higher global C
RS
(46.5±16.4 ml/cmH
2
O versus
53.5±14.5 ml/cmH
2
O, P=0.049). No difference in PaO
2
-FiO
2
ratio was found between both
holding techniques (P=0.743).Significance. The two-handed mask holding technique could not
improve the inhomogeneity of lung ventilation when monitored by EIT during mask ventilation
although it obtained larger expiratory tidal volumes than the one-handed mask holding technique.
Abbreviations
ASA American Society of Anesthesiologists
BMI body mass index
OPEN ACCESS
RECEIVED
14 March 2022
REVISED
10 May 2022
ACCEPTED FOR PUBLICATION
17 May 2022
PUBLISHED
28 June 2022
Original content from this
work may be used under
the terms of the Creative
Commons Attribution 4.0
licence.
Any further distribution of
this work must maintain
attribution to the
author(s)and the title of
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and DOI.
© 2022 The Author(s). Published on behalf of Institute of Physics and Engineering in Medicine by IOP Publishing Ltd
C
RS
respiratory system compliance
EIT electrical impedance tomography
GI global inhomogeneity index
PBW predicted body weight, for men=50+0.9 [height (cm): 152.4], and for women=45.5+0.9
[height (cm): 152.4]
ROI regional lungs of interest
RVD
SD
regional ventilation delays standard deviation
TVe expiratory tidal volume
ΔEELV changes in end-expiratory lung volume
Introduction
Mask ventilation, an essential skill for practitioners engaged in airway management (Lim and Nielsen 2016), has
been shown to cause regional distributions of ventilation shifts towards ventral lung areas in the supine position
(Ukere et al 2016, Lumb et al 2020), leading to lung ventilation inhomogeneity (Ukere et al 2016). This impairs
carbon dioxide removal and oxygen uptake (Rothen et al 1998, Lumb et al 2020). Therefore, it is necessary to
improve the inhomogeneity of lung ventilation when using mask ventilation in several clinical scenarios in order
to improve oxygenation, for instance, for obesity patients. However, the reasons for lung ventilation
inhomogeneity during mask ventilation remains elusive, and methods to improve this remain to be investigated.
Global measures such as oxygenation or respiratory system mechanics are traditionally used to evaluate the
effects of mask ventilation (Joffe et al 2010, Fei et al 2017, Itagaki et al 2017). Misleading information may be
produced by ‘averaging’opposite pathological phenomena in different lung units (Frerichs et al 2017). This
underlines the need for regional lung monitoring. Conventional radiological methods such as chest
radiography, computed tomography, and magnetic resonance imaging, generate static information on the
structural changes of the pulmonary tissue. However, these methods are not practical for evaluating the dynamic
changes of mask ventilation, especially in the operating room. Electrical impedance tomography (EIT),asa
noninvasive, nonradiological medical imaging method (Frerichs et al 2017), can be used for bedside monitoring
of the lung, both globally and regionally, even under dynamic lung ventilation. Lung impedance changes are
highly correlated to the global volume changes measured at the airway opening (Ngo et al 2017, Zhao et al 2017).
Recent clinical studies (Zhao et al 2019, Lumb et al 2020, Zhang et al 2020, Bayford et al 2022)imply the potential
of EIT to assess the heterogeneous behavior of regional lung tissue from various conditions, including mask
ventilation (Lumb et al 2020). The heterogeneity estimation provided by EIT includes not only spatial but also
the temporal distribution of lung function measures (e.g. Lasarow et al 2021).
Despite the knowledge that the two-handed mask holding technique is superior to the one-handed mask
holding technique for providing higher tidal volume (Joffe et al 2010, Fei et al 2017), the influence of these two
mask ventilation techniques on regional ventilation mechanics remains unknown. Understanding the
ventilation-derived respiratory mechanics via EIT monitoring may be helpful in improving our mask ventilation
performance. The aim of the present study was to determine the effects of the two mask holding ventilation
techniques on global and regional lung ventilation during anesthetic induction. We hypothesized that two-
handed mask holding ventilation improves the lung ventilation inhomogeneity monitored by EIT. The primary
outcome was the global inhomogeneity index (GI). The secondary outcomes were other respiratory metrics
including centre of ventilation, regional ventilation delays standard deviation (RVD
SD
), expiratory tidal volume
(TVe)and the PaO
2
-FiO
2
ratio.
Methods
Ethics approval
This clinical trial was a single center, randomized clinical study performed in Fudan university Shanghai Cancer
Center and approved by the Ethics Committee (IRB2010225-10). This study was registered on ClinicalTrial.gov
(NCT04617665)and written informed consents were obtained from all participating patients before
enrollment. An investigator assessed patients for eligibility the day before surgery.
Inclusion and exclusion criteria
From November to December 2020, adult patients with American Society of Anesthesiologists (ASA)physical
status I-II scheduled for elective surgery under general anesthesia were screened for this study. The exclusion
2
Physiol. Meas. 43 (2022)064004 L Gao et al
criteria included: (i)acute and chronic respiratory disorders, including chronic obstructive pulmonary disease
(COPD)and asthma; (ii)a history of lung surgery; (iii)high risk of reflux and aspiration; (iv)requirement of
awake intubation; (v)facial and thoracic deformities; (vi)implants in the body, such as cardiac pacemakers, and
(vii)pregnancy.
Study procedure
After entering the operating room, patients were placed in the supine position with the head in a neutral position
on a pillow and elevated 10 cm. The baseline clinical characteristics of patients were collected by a nurse,
including age, gender, height, weight, body mass index (BMI)and ASA physical status. Additionally, airway
assessments such as Mallampati scores, thyromental distance, mouth opening, lack of dentition, presence of
beard, history of sleep apnea, upper lip bite test and laryngoscope grade were also recorded.
Standard monitoring protocols were applied, including ECG, pulse oximetry, and capnography, and an
arterial line was established for invasive arterial pressure monitoring and arterial blood gas analysis.
Preoxygenation, via a suitable plastic mask (PAIM, AM0031 (5316), Congren Medical Device Co., LTD,
Xiamen, China)placed over the bridge of the nose and chin to achieve an air-tight seal, was performed before
anaesthetic induction with a flow rate of 6 l min
−1
of 100% O
2
for three minutes under spontaneous breathing.
Then anesthetic induction was conducted with intravenous target control infusion propofol (Marsh mode)
4μgml
−1
(Thomson et al 2014), sufentanil 0.3 μgkg
−1
, and rocuronium 0.6 mg kg
−1
. After the patient’s loss of
consciousness, spontaneous breathing disappeared gradually. Twenty seconds after the injection of
rocuronium, mechanical ventilation was delivered by the anaesthetic machine in pressure control mode (Fei et al
2017). The ventilation parameters were set as respiratory frequency=15 bpm, inspiratory-to-expiratory time
ratio=1:2, peak inspiratory pressure=15 cmH
2
O, and positive end-expiratory pressure (PEEP)=0 cmH
2
O.
The operators performing mask ventilation were certified registered anesthesiologists (figure 1). To achieve an
air-tight seal, the face mask leak was checked through the monitoring of the ventilation pressure and
capnography waveform. Endotracheal intubation was performed ninety seconds after rocuronium
administration. Throughout the whole procedure, further airway management was initiated if oxygen
saturation was 90% during mask ventilation, or for safety reasons based on the judgment of study team. Those
patients with unexpected difficult mask ventilation would be excluded from the study.
The whole procedure of anaesthetic induction, including the dynamical parameters (e.g. TV, respiratory
rate)showed in the anaesthesia monitor and machine, was recorded by a video recorder for data revisiting and
further analysis. Only the person who conducted the statistical analysis was blinded to the randomization. The
revisited parameters included TVe (the average TVe value of the last five breaths during mask ventilation),
minute ventilation volume (value immediately before intubation), driving pressure, heart rates (immediately
before induction and intubation), and systolic blood pressure (immediately before induction and intubation).
The globe respiratory system compliances (C
RS
)were calculated as TVe/driving pressure. Immediately before
anaesthetic induction and endotracheal intubation, arterial blood gas analysis (GEM3500; Instrumentation
Laboratory, USA)was performed twice.
Figure 1. One-handed and two-handed mask holding ventilation techniques. (a)One-handed mask holding technique. (b)Two-
handed mask holding technique. For the one-handed technique, only one hand can be used to achieve the face mask seal. The left
thumb and index finger form a ‘C,’providing anterior pressure over the mask, while the third, fourth, and fifth fingers form an ‘E’to
lift the jaw. For the two-handed technique, the provider’s thumb and thenar eminence of each hand are held parallel, adjacent to the
mask connector, and depress each side of the mask. The second through fifth digits wrap around and elevate the mandible to draw it
anteriorly into the mask, establishing both a jaw-thrust and chin-lift maneuver when appropriate.
3
Physiol. Meas. 43 (2022)064004 L Gao et al
EIT monitoring and analysis
The global and regional lung ventilation were continuously monitored and recorded by EIT (PulmoVista500,
Draeger Medical, Luebeck, Germany). In the present study, an EIT electrode belt, which carries 16 electrodes
with a width of 40 mm, was placed around the thorax in the fifth intercostal space, and a reference electrode was
placed on the right thorax (Spinelli et al 2019). Customized software was used to quantitatively analyze the
offline EIT data. During mask ventilation, results were derived from the mean of all the breaths occurring in the
1 min before intubation (Lumb et al 2020). The following variables were calculated (Frerichs et al 2017): GI,
centre of ventilation, RVD
SD
, compliance win and loss of mask ventilation compared with spontaneous lung
ventilation. Changes in end-expiratory lung volume between mask ventilation and spontaneous lung ventilation
were analyzed by calculating the differences between the minimum (end-expiratory)values of tidal volume
relative impedance change (Hinz et al 2003, Zick et al 2013). The EIT image was divided into quadrants (four
regions of interest, ROIs). Regional C
RS
was determined as ((fraction of ROI)×TVe)/driving pressure.
Randomization
The patients were randomly divided into two groups: the one-handed mask holding ventilation group (one-
handed group)and the two-handed mask holding ventilation group (two-handed group)immediately after the
EIT electrode belt was placed. Randomization was accomplished using the series of envelopes method (Itagaki
et al 2017). 80 envelopes each contained a sheet of paper with one of 80 sequential numbers written on it,
ensuring that 40 participants were allocated to the one-handed group and another 40 to the two-handed group.
The operators participating in the study were blinded to the group assignment until the induction of general
anesthesia, when the envelopes were opened.
Statistical analyses
As GI was reported to be 0.43±0.04 during bag-mask ventilation (Lumb et al 2020), we assumed that there was
a 0.025 difference between one-handed mask holding ventilation and two-handed mask holding ventilation,
and the variance was 0.04. And with a statistical power of 80%, a two-sided αsignificance level of 0.05, a sample
size of 40 patients in each group would be enrolled. Considering a dropout rate of 30%, a total of 114 patients
would be enrolled at least.
Continuous variables were presented as mean±standard deviation, or median with the interquartile range
depending on the normality of the distribution. Categorical variables were presented as numbers and
proportions. Binary variables were analyzed using a chi-square test or a Fisher’s exact test. Quantitative variables
between the groups were analyzed using Student’sttest or the Mann–Whitney U test. The primary outcome GI
was analyzed by an unpaired ttest. Statistical significance was defined as P<0.05, and all Pvalues were two-
sided. The clinical data were analyzed using SPSS 19.0 (SPSS, Inc., Chicago, IL, USA).
Results
A total of 119 consecutive patients were screened in the study period. 39 patients were excluded due to various
causes (figure 2). All patients were successfully intubated at the first attempt. There were no anaesthesia-related
adverse events in either group. The data of 80 patients were included in the final analysis, in which 40 patients
were allocated to the one-handed group and 40 patients to the two-handed group. Their clinical characteristics
are listed in table 1.
As compared with spontaneous ventilation, mask positive-pressure ventilation during anaesthetic induction
caused significant lung ventilation inhomogeneity, both with one-handed (GI: 0.40±0.07 versus 0.50±0.15;
P<0.001)and two-handed mask holding (0.40±0.08 versus 0.50±0.13; P<0.001)(figure 3). However,
there were no differences in GI (P=0.948, table 2)between the one-handed and two-handed mask holding, as
well as the parameter centre of ventilation (P=0.438, table 2). There were no significant differences in the
ventilation distribution of the four ROIs (P>0.05, table 2)between both holding techniques. In contrast,
compared with the one-handed mask holding technique, the two-handed mask holding technique decreased the
RVD
SD
(P=0.032, table 2).
Compared with the one-handed mask holding technique, the two-handed mask holding technique was
associated with higher TVe (552.6±184.2 ml versus 672.9±156.6 ml, P=0.002, table 3), minute ventilation
volume (8.2±2.9 l min
−1
versus 9.8±2.3 l min
−1
,P=0.010, table 3)and global C
RS
(46.5±16.4 ml/cmH
2
O versus 53.5±14.5 ml/cmH
2
O, P=0.049)(table 2). However, there were no
significant differences in regional C
RS
between both holding techniques (P>0.05, table 2).
Though a higher TVe was associated with two-handed mask holding ventilation, the heart rates, systolic
pressure, and PaO
2
-FiO
2
ratio were compatible between the two holding techniques during anaesthetic
induction (table 3).
4
Physiol. Meas. 43 (2022)064004 L Gao et al
Figure 2. Flowchart of subject enrollment. EIT: electrical impedance tomography.
Table 1. Baseline characteristics of the patients.
One-handed group (n=40)Two-handed group (n=40)Pvalue
Age (years)56.3 (19–76)55.4 (28–83)0.812
Gender (male/female)19/21 22/18 0.655
ASA status (I/II)10/30 14/26 0.465
Weight (kg)66.1±12.1 66.7±12.4 0.846
Height (cm)164.3±7.3 165.6±7.0 0.403
BMI (kg.m
−2
)24.4±3.3 24.2±3.5 0.829
PBW (kg)58.3±8.2 59.9±8.0 0.395
Mouth opening (cm)4.4±1.1 4.5±0.8 0.857
Thyromental distance (cm)7.1±1.2 7.0±1.4 0.913
Missing teeth (absent/present)30/10 30/10 1.000
Beard (absent/present)36/437/3 1.000
Snoring history (absent/present)18/22 14/26 0.494
Bite the upper lip test (I/II/III)25/13/230/9/1 0.469
Mallampati grade (I/II/III)14/17/917/17/6 0.641
Laryngoscope grade (I/II/III)21/16/323/17/0 0.210
Spontaneous lung ventilation
GI 0.40±0.07 0.40±0.08 0.917
Centre of ventilation (%)45.9±4.5 45.6±5.6 0.773
RVD
SD
7.0 (6.0–8.75)7.0 (6.0–9.0)0.583
Ventilation of regional lung of interest (proportion, %)
ROI 1 (%)29.4±6.0 28.7±7.7 0.640
ROI 2 (%)24.8±5.8 25.2±7.4 0.777
ROI 3 (%)24.3±6.2 24.0±8.2 0.854
ROI 4 (%)18.1±4.8 18.6±5.2 0.623
Basic hemodynamics
Heart rate (bmp)77.4±13.4 72.3±12.2 0.082
Systolic pressure (mmHg)163.1±26.7 154.2±23.4 0.118
Basic arterial blood gas
PaO
2
-FiO
2
ratio 425.3±58.3 414.7±46.9 0.371
Data are presented as mean±SD or median (range)unless otherwise noted. ASA=American Society of Anesthesiologists; BMI=body
mass index; PBW=predicted body weight, for men=50+0.9 [height (cm): 152.4], and for women=45.5+0.9 [Height (cm): 152.4].
GI=global inhomogeneity index; RVD
SD
=regional ventilation delays standard deviation; ROI=regional of interest.
5
Physiol. Meas. 43 (2022)064004 L Gao et al
Figure 3. GI values affected by mask positive-pressure ventilation. GI:global inhomogeneity index.
*
Compared with spontaneous
breath.
Table 2. Parameters of regional ventilation distribution of one-handed mask holding ventilation versus two-handed mask holding
ventilation.
One-handed group (n=40)Two-handed group (n=40)P value
GI 0.50±0.15 0.50±0.13 0.948
Centre of ventilation (%)39.7±5.0 38.8±4.6 0.438
RVD
SD
5.5 (4.0–7.0)4.0 (3.0–5.0)0.032
Global C
RS
(ml/cmH
2
O)46.5±16.4 53.5±14.5 0.049
!EELV (rel. !Z)−300.5±1388.1 −114.3±1445.0 0.558
Ventilation of regional lung of interest (proportion, %)
ROI 1 (%)36.6±6.7 36.4±6.6 0.893
ROI 2 (%)33.3±5.4 33.9±8.7 0.736
ROI 3 (%)14.3±4.4 14.2±4.7 0.922
ROI 4 (%)12.1±4.0 12.2±3.6 0.931
ROI C
RS
(ml/cmH
2
O)
ROI 1 16.8±6.8 19.0±4.5 0.102
ROI 2 15.4±6.2 18.0±7.4 0.099
ROI 3 6.9±3.8 8.0±3.6 0.173
ROI 4 5.7±2.9 6.7±3.1 0.142
Compliance win (%)43.0 (24.0–54.8)44.5 (20.0–75.8)0.202
Compliance loss (%)20.2±14.7 20.1±17.2 0.972
Data are presented as mean±SD or median (range)unless otherwise noted. GI:global inhomogeneity index; RVD
SD
:regional ventilation
delays standard deviation; ROI:region of interest.
Table 3. The expiratory tidal volume, minute ventilation volume, hemodynamic, and ABG analysis: one-handed mask holding ventilation
versus two-handed mask holding ventilation.
One-handed group (n=40)Two-handed group (n=40)Pvalues
TVe (ml)552.6±184.2 672.9±156.6 0.002
Minute ventilation volume (l min
−1
)8.2±2.9 9.8±2.3 0.010
Hemodynamic
Heart rate (bmp)64.5±9.7 63.9±10.1 0.779
Systolic pressure (mmHg)121.0±21.4 125.0±22.4 0.409
Arterial blood gas
PaO
2
-FiO
2
ratio 390.3±92.0 383.1±104.1 0.743
Data are presented as mean±SD. TVe: expiratory tidal volume.
6
Physiol. Meas. 43 (2022)064004 L Gao et al
Discussion
Our study examined regional ventilation with two mask-holding ventilation techniques during anesthetic
induction in lung-healthy surgical patients. The protocol was designed to reflect clinical decision-making for
anesthesiologists regarding the choice of one-handed or two-handed mask holding ventilation for healthy lungs.
The EIT method confirmed that mask positive-pressure ventilation causes ventilation redistribution, but the
two-handed mask holding technique could not improve lung ventilation inhomogeneity compared to the one-
handed mask holding technique. However, two-handed mask holding ventilation provided higher TVe and
global C
RS
.
Lung ventilation inhomogeneity during anesthesia was mainly caused by the ventilation ventral shift. In the
present study, we found that ventilation was redistributed towards ventral regions regardless of which of the
mask holding ventilation techniques (one-handed or two-handed)was applied. This finding was in accordance
with other studies during intermitted positive-pressure ventilation (Lagier et al 2020, Lumb et al 2020). The
reasons for this ventral shift of ventilation may include: anesthesia (Radke et al 2012, Bordes et al 2016),
neuromuscular blockade, positive pressure ventilation, or any artificial airway used to facilitate ventilation
(Lumb et al 2020). Based on the centre of ventilation between the two techniques, we found that such a ventral
shift in lung-healthy patients may not be associated with mask ventilation holding techniques.
As expected, the present study showed that two-handed mask holding ventilation provided higher TVe and
minute ventilation volume than one-handed mask holding ventilation. In an animal study led by Zick G et al
(Zick et al 2013), EIT examinations were performed in 10 anesthetized pigs with normal lungs ventilated at 5 and
10 ml kg
−1
body weight TV and 5 cmH
2
O PEEP. Increasing TV from 5 to 10 ml kg
−1
body weight led to a small
but significant redistribution of ventilation in favor of the dependent lung regions. The geometrical centre of
ventilation moved slightly but significantly towards dependent regions. We suspected that such redistribution
via increasing TV might indicate rather tidal recruitment/derecruitment. Therefore, RVD
SD
was calculated to
assess the level of tidal recruitment/derecruitment in our study. The two-handed mask holding technique
provided higher TVe when compared with the one-handed mask holding technique. However, the extra TVe
was not enough to improve ventilation distribution. In fact, the lower RVD
SD
in the two-handed mask holding
technique might suggest that the extra TVe provided by the two-handed mask holding technique might have no
adverse effects. The zero PEEP setting in our study may also contribute to the negative result, because an
adequate PEEP level improves ventilation in the dorsal lung regions (Sinclair et al 2010, Lagier et al 2020).
Our findings of increased global C
RS
and TVe in the two-handed group were in accordance with the fact that
with identical mechanical properties, an increase in ventilated volume leads to an increase in compliance. In the
regional C
RS
analysis, though there were no statistical differences, all the absolute values of four ROI C
RS
were
bigger in the two-handed group than in the one-handed group. These results indicated that there was elevated
C
RS
in both ventral and dorsal regions. When compared with one-handed mask holding ventilation, two-
handed mask holding ventilation did not cause hyperventilation in ventral regions because of the increased C
RS
.
It had been found that hyperventilation could be inferred from decreased C
RS
using different TV (Zick et al
2013). The studies demonstrated that high TV with PEEP was associated with increased regional C
RS
in the
dependent lung regions and decreased regional C
RS
in the nondependent lung regions (Zhao et al 2021).
In our daily practice, a harness, such as four headbands, was usually used to hold the mask to achieve an air-
tight seal in noninvasive positive-pressure ventilation. The harness fixes the mask tightly onto the patient’s face.
However, with the harness holding the mask there is no chin-lift and head-tilt maneuver, while this can be
performed by the two-handed technique (Joffe et al 2010). This maneuver is demonstrated to move the epiglottis
away from the posterior pharyngeal wall, which can decrease the upper airway’s resistance. So, the two-handed
technique may be associated with better ventilation results when compared with a harness holding mask,
especially for obese patients with a difficult airway. It would be interesting to carry out a study comparing the use
of a harness with the two-handed technique for mask ventilation.
There are several limitations in this study. Around 12% of the screened patients were excluded from the
analysis because of EIT data unavailability. The poor EIT signal quality occurred in some very nervous patients
with irregular deep breathing during spontaneous breathing before anesthetic induction. Large changes in chest
dimensions caused by deep inspiration may decrease the data quality (Schullcke et al 2016)and cause instability
in electrode–skin contact. To minimize this effect on data collection, we tried to calm down enrolled patients
through communications with them and then started the EIT data recording. To get better skin contact, we used
conductive gel between the elastic belt electrodes and skin for patients with bad electrode-skin contact. The
study was only performed in the operating room for anesthetized patients; whether the results are applicable to
another scenario would need to be validated further. Furthermore, there were few obese patients in our study.
Since obesity is a well-known contributing factor to difficult mask ventilation (Leoni et al 2014, Moon et al 2019),
the regional distribution of lung ventilation during mask ventilation may be different in obese patients when
7
Physiol. Meas. 43 (2022)064004 L Gao et al
compared with nonobese ones. The performances of the two techniques on the regional distribution of lung
ventilation in obese patients remains to be determined.
Conclusion
In conclusion, compared with the one-handed mask holding technique, larger TVe values were presented using
the two-handed mask holding technique. However, lung ventilation inhomogeneity could not be improved by
using the two-handed mask holding technique during mask ventilation.
Acknowledgments
The authors would like to thank colleagues for their assistance in carrying out the study, by performing the
specified mask ventilation technique on patients.
Availability of data and materials
The datasets used and/or analyzed during the current study are available from the corresponding author on
reasonable request.
Authors’contributions
GLL and ZY carried out the trial procedures, analysed the data and drafted the manuscript. YY and PC
performed the randomisation, assisted with the trial procedures, and prepared the manuscript. ZZ gave
statistical advice and significantly revised the manuscript. ZJ and YL conceived of the study, and participated in
its design and coordination and helped to revise the manuscript. All authors read and approved the final
manuscript.
Ethics approval and consent to participate
This trial was approved by the Fudan University Shanghai Cancer Center Ethics Committee (IRB2010225-10),
and written informed consents were obtained from all participating patients before enrollment. All methods
were performed in accordance with the relevant guidelines and regulations.
Competing interests
Zhanqi Zhao receives a consulting fee from Dräger Medical. Other authors declare that they have no competing
interests.
Funding
Grant from Shanghai Municipal Science and Technology Committee (to Jun Zhang, No. 20Y11906200), and
partially from the National Natural Science Foundation of China (to Zhanqi Zhao, No. 52077216)and German
Ministry for Education and Research (to Zhanqi Zhao,13FH628IX6, MOVE).
ORCID iDs
Zhanqi Zhao https://orcid.org/0000-0002-1279-2207
Li Yang https://orcid.org/0000-0003-2149-7194
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