ArticlePDF Available

A randomised trial evaluating mask ventilation using electrical impedance tomography during anesthetic induction: One-handed technique versus two-handed technique


Abstract and Figures

Objective: Mask positive pressure ventilation could lead to inhomogeneity of lung ventilation, potentially inducing lung function impairments, when compared with spontaneous breathing. The inhomogeneity of lung ventilation can be monitored by chest electrical impedance tomography (EIT), which could increase our understanding of mask ventilation-derived respiratory mechanics. We hypothesized that two-handed mask holding ventilation technique had better lung ventilation reflected by respiratory mechanics when compared with 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 with pressure-controlled mode. EIT was used to assess respiratory mechanics including: ventilation distribution, global and regional respiratory system compliance (CRS), expiratory tidal volume (TVe) and minute ventilation volume. Besides, hemodynamic parameters and PaO2-FiO2-ratio were also recorded. Main results: Eighty adult patients were included in this study. Compared with spontaneous ventilation, mask positive pressure ventilation caused inhomogeneity of lung ventilation in both one-handed group (global inhomogeneity index: 0.40±0.07 vs. 0.50±0.15; P<0.001) and two-handed group (0.40±0.08 vs. 0.50±0.13; P<0.001). There were no differences of global inhomogeneity index (P = 0.948) between the one-handed group and two-handed group. Compared with one-handed group, two-handed group was associated with higher TVe (552.6±184.2 ml vs. 672.9±156.6 ml, P=0.002) and higher global CRS (46.5±16.4 ml/cmH2O vs. 53.5±14.5 ml/cmH2O, P=0.049). No difference of PaO2-FiO2-ratio was found between two groups (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 one-handed mask holding technique.
Content may be subject to copyright.
Physiological Measurement
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
View the article online for updates and enhancements.
You may also like
Unilateral empyema impacts the
assessment of regional lung ventilation by
electrical impedance tomography
D Bläser, S Pulletz, T Becher et al.
Portable multi-parameter electrical
impedance tomography for sleep apnea
and hypoventilation monitoring: feasibility
Min Hyoung Lee, Geuk Young Jang,
Young Eun Kim et al.
Biomedical imaging with hyperpolarized
noble gases
Kai Ruppert
This content was downloaded from IP address on 24/11/2022 at 09:49
Physiol. Meas. 43 (2022)064004
A randomised trial evaluating mask ventilation using electrical
impedance tomography during anesthetic induction: one-handed
technique versus two-handed technique
Lingling Gao
, Yun Zhu
, Congxia Pan
, Yuehao Yin
, Zhanqi Zhao
, Li Yang
Jun Zhang
Department of Anesthesiology, Fudan University Shanghai Cancer Center, Fudan University, Shanghai, Peoples Republic of China
Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, Peoples Republic of China
Department of Biomedical Engineering, Fourth Military Medical University, Xian, Peoples Republic of China
Institute of Technical Medicine, Furtwangen University, Villingen-Schwenningen, Germany
These authors contributed equally to this work.
Authors to whom any correspondence should be addressed.
E-mail: and
Keywords: mask ventilation, one-handed technique, two-handed technique, pulmonary ventilation distribution, electrical impedance
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,
reected 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 certied 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
), expiratory tidal volume (TVe)and minute ventilation volume. Hemodynamic
parameters and the PaO
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
(46.5±16.4 ml/cmH
O versus
53.5±14.5 ml/cmH
O, P=0.049). No difference in PaO
ratio was found between both
holding techniques (P=0.743).Signicance. 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.
ASA American Society of Anesthesiologists
BMI body mass index
14 March 2022
10 May 2022
17 May 2022
28 June 2022
Original content from this
work may be used under
the terms of the Creative
Commons Attribution 4.0
Any further distribution of
this work must maintain
attribution to the
author(s)and the title of
the work, journal citation
and DOI.
© 2022 The Author(s). Published on behalf of Institute of Physics and Engineering in Medicine by IOP Publishing Ltd
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
regional ventilation delays standard deviation
TVe expiratory tidal volume
ΔEELV changes in end-expiratory lung volume
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 averagingopposite 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 inuence 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
), expiratory tidal volume
(TVe)and the PaO
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
(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
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 reux and aspiration; (iv)requirement of
awake intubation; (v)facial and thoracic deformities; (vi)implants in the body, such as cardiac pacemakers, and
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 ow rate of 6 l min
of 100% O
for three minutes under spontaneous breathing.
Then anesthetic induction was conducted with intravenous target control infusion propofol (Marsh mode)
(Thomson et al 2014), sufentanil 0.3 μgkg
, and rocuronium 0.6 mg kg
. After the patients 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
O, and positive end-expiratory pressure (PEEP)=0 cmH
The operators performing mask ventilation were certied registered anesthesiologists (gure 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 difcult 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 ve 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
)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 nger form a C,providing anterior pressure over the mask, while the third, fourth, and fth ngers form an Eto
lift the jaw. For the two-handed technique, the providers 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 fth 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.
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 fth intercostal space, and a reference electrode was
placed on the right thorax (Spinelli et al 2019). Customized software was used to quantitatively analyze the
ofine 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
, 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
was determined as ((fraction of ROI)×TVe)/driving pressure.
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 αsignicance 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 Fishers exact test. Quantitative variables
between the groups were analyzed using Studentsttest or the MannWhitney U test. The primary outcome GI
was analyzed by an unpaired ttest. Statistical signicance was dened as P<0.05, and all Pvalues were two-
sided. The clinical data were analyzed using SPSS 19.0 (SPSS, Inc., Chicago, IL, USA).
A total of 119 consecutive patients were screened in the study period. 39 patients were excluded due to various
causes (gure 2). All patients were successfully intubated at the rst attempt. There were no anaesthesia-related
adverse events in either group. The data of 80 patients were included in the nal 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 signicant 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)(gure 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 signicant 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
(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
versus 9.8±2.3 l min
,P=0.010, table 3)and global C
(46.5±16.4 ml/cmH
O versus 53.5±14.5 ml/cmH
O, P=0.049)(table 2). However, there were no
signicant differences in regional C
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
ratio were compatible between the two holding techniques during anaesthetic
induction (table 3).
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 (1976)55.4 (2883)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
)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
7.0 (6.08.75)7.0 (6.09.0)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
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
=regional ventilation delays standard deviation; ROI=regional of interest.
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
Table 2. Parameters of regional ventilation distribution of one-handed mask holding ventilation versus two-handed mask holding
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
5.5 (4.07.0)4.0 (3.05.0)0.032
Global C
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 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 (24.054.8)44.5 (20.075.8)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
: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
)8.2±2.9 9.8±2.3 0.010
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
ratio 390.3±92.0 383.1±104.1 0.743
Data are presented as mean±SD. TVe: expiratory tidal volume.
Physiol. Meas. 43 (2022)064004 L Gao et al
Our study examined regional ventilation with two mask-holding ventilation techniques during anesthetic
induction in lung-healthy surgical patients. The protocol was designed to reect clinical decision-making for
anesthesiologists regarding the choice of one-handed or two-handed mask holding ventilation for healthy lungs.
The EIT method conrmed 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
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 nding 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 articial 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
body weight TV and 5 cmH
O PEEP. Increasing TV from 5 to 10 ml kg
body weight led to a small
but signicant redistribution of ventilation in favor of the dependent lung regions. The geometrical centre of
ventilation moved slightly but signicantly towards dependent regions. We suspected that such redistribution
via increasing TV might indicate rather tidal recruitment/derecruitment. Therefore, RVD
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
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 ndings of increased global C
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
analysis, though there were no statistical differences, all the absolute values of four ROI C
bigger in the two-handed group than in the one-handed group. These results indicated that there was elevated
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
It had been found that hyperventilation could be inferred from decreased C
using different TV (Zick et al
2013). The studies demonstrated that high TV with PEEP was associated with increased regional C
in the
dependent lung regions and decreased regional C
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 xes the mask tightly onto the patients 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 airways 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 difcult 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 electrodeskin 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 difcult 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
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.
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.
The authors would like to thank colleagues for their assistance in carrying out the study, by performing the
specied 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.
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 signicantly 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 nal
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
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).
Zhanqi Zhao
Li Yang
Bayford R, Sadleir R and Frerichs I 2022 Advances in electrical impedance tomography and bioimpedance including applications in COVID-
19 diagnosis and treatment Physiol. Meas. 43 020401
Bordes J, Goutorbe P, Cungi P J, Boghossian M C and Kaiser E 2016 Noninvasive ventilation during spontaneous breathing anesthesia: an
observational study using electrical impedance tomography J. Clin. Anesth. 34 4206
Physiol. Meas. 43 (2022)064004 L Gao et al
Fei M, Blair J L, Rice M J, Edwards D A, Liang Y, Pilla M A, Shotwell M S and Jiang Y 2017 Comparison of effectiveness of two commonly
used two-handed mask ventilation techniques on unconscious apnoeic obese adults Brit. J. Anaesth. 118 61824
Frerichs I et al 2017 Chest electrical impedance tomography examination, data analysis, terminology, clinical use and recommendations:
consensus statement of the TRanslational EIT developmeNt stuDy group Thorax. 72 8393
Hinz J, Hahn G, Neumann P, Sydow M, Mohrenweiser P, Hellige G and Burchardi H 2003 End-expiratory lung impedance change enables
bedside monitoring of end-expiratory lung volume change Intensive Care Med. 29 3743
Itagaki T, Oto J, Burns S M, Jiang Y, Kacmarek R M and Mountjoy J R 2017 The effect of head rotation on efciency of face mask ventilation
in anaesthetised apnoeic adults: a randomised, crossover study Eur. J. Anaesth. 34 43240
Joffe A M, Hetzel S and Liew E C 2010 A two-handed jaw-thrust technique is superior to the one-handed EC-clamptechnique for mask
ventilation in the apneic unconscious person Anesthesiology 113 8739
Lagier D, Velly L J, Guinard B, Bruder N, Guidon C, Vidal M M and Alessi M C 2020 Perioperative open-lung approach, regional ventilation,
and lung injury in cardiac surgery Anesthesiology 133 102945
Lasarow L, Vogt B, Zhao Z, Balke L, Weiler N and Frerichs I 2021 Regional lung function measures determined by electrical impedance
tomography during repetitive ventilation manoeuvres in patients with COPD Physiol. Meas. 42 15008
Leoni A et al 2014 Difcult mask ventilation in obese patients: analysis of predictive factors Minerva Anestesiol. 80 14957
Lim K S and Nielsen J R 2016 Objective description of mask ventilation Brit. J. Anaesth. 117 8289
Lumb A B, Savic L, Horsford M R and Hodgson S R 2020 Effects of tracheal intubation and tracheal tube position on regional lung
ventilation: an observational study Anaesthesia. 75 35965
Moon T S, Fox P E, Somasundaram A, Minhajuddin A, Gonzales M X, Pak T J and Ogunnaike B 2019 The inuence of morbid obesity on
difcult intubation and difcult mask ventilation J Anesth. 33 96102
Ngo C, Leonhardt S, Zhang T, Luken M, Misgeld B, Vollmer T, Tenbrock K and Lehmann S 2017 Linearity of electrical impedance
tomography during maximum effort breathing and forced expiration maneuvers Physiol. Meas. 38 7786
Radke O C, Schneider T, Heller A R and Koch T 2012 Spontaneous breathing during general anesthesia prevents the ventral redistribution of
ventilation as detected by electrical impedance tomography: a randomized trial Anesthesiology (Philadelphia). 116 122734
Rothen H U, Sporre B, Engberg G, Wegenius G and Hedenstierna G 1998 Airway closure, atelectasis and gas exchange during general
anaesthesia Brit. J. Anaesth. 81 6816
Schullcke B, Krueger-Ziolek S, Gong B, Mueller-Lisse U and Moeller K 2016 Compensation for large thorax excursions in EIT imaging
Physiol. Meas. 37 160523
Sinclair S E, Polissar N L and Altemeier W A 2010 Spatial distribution of sequential ventilation during mechanical ventilation of the
uninjured lung: an argument for cyclical airway collapse and expansion BMC Pulm. Med. 10 25
Spinelli E, Mauri T, Fogagnolo A, Scaramuzzo G, Rundo A, Grieco D L, Grasselli G, Volta C A and Spadaro S 2019 Electrical impedance
tomography in perioperative medicine: careful respiratory monitoring for tailored interventions BMC Anesthesiol. 19 11140
Thomson A J, Morrison G, Thomson E, Beattie C, Nimmo A F and Glen J B 2014 Induction of general anaesthesia by effect-site target-
controlled infusion of propofol: inuence of pharmacokinetic model and ke0 value Anaesthesia. 69 42935
Ukere A, März A, Wodack K H, Trepte C J, Haese A, Waldmann A D, Böhm S H and Reuter D A 2016 Perioperative assessment of regional
ventilation during changing body positions and ventilation conditions by electrical impedance tomography Brit J Anaesth. 117 22835
Zhang N et al 2020 The inuence of an electrical impedance tomography belt on lung function determined by spirometry in sitting position
Physiol. Meas. 41 44002
Zhao Z et al 2019 Detection of pulmonary oedema by electrical impedance tomography: validation of previously proposed approaches in a
clinical setting Physiol. Meas. 40 54008
Zhao Z, Peng S Y, Chang M Y, Hsu Y L, Frerichs I, Chang H T and Moller K 2017 Spontaneous breathing trials after prolonged mechanical
ventilation monitored by electrical impedance tomography: an observational study Acta Anaesthesiol. Scand. 61 116675
Zhao Z, Sang L, Li Y, Frerichs I, Moller K and Fu F 2021 Identication of lung overdistension caused by tidal volume and positive end-
expiratory pressure increases based on electrical impedance tomography Brit. J. Anaesth. 126 e16770
Zick G, Elke G, Becher T, Schädler D, Pulletz S, Freitag-Wolf S, Weiler N, Frerichs I and Morty R E 2013 Effect of PEEP and tidal volume on
ventilation distribution and end-expiratory lung volume: a prospective experimental animal and pilotclinical study PLoS One 8
Physiol. Meas. 43 (2022)064004 L Gao et al
ResearchGate has not been able to resolve any citations for this publication.
Full-text available
Background: Electrical impedance tomography (EIT) is a non-invasive radiation-free monitoring technique that provides images based on tissue electrical conductivity of the chest. Several investigations applied EIT in the context of perioperative medicine, which is not confined to the intraoperative period but begins with the preoperative assessment and extends to postoperative follow-up. Main body: EIT could provide careful respiratory monitoring in the preoperative assessment to improve preparation for surgery, during anaesthesia to guide optimal ventilation strategies and to monitor the hemodynamic status and in the postoperative period for early detection of respiratory complications. Moreover, EIT could further enhance care of patients undergoing perioperative diagnostic procedures. This narrative review summarizes the latest evidence on the application of this technique to the surgical patient, focusing also on possible future perspectives. Conclusions: EIT is a promising technique for the perioperative assessment of surgical patients, providing tailored adaptive respiratory and haemodynamic monitoring. Further studies are needed to address the current technological limitations, confirm the findings and evaluate which patients can benefit more from this technology.
Full-text available
Purpose To determine the influence of morbid obesity on the incidence of difficult mask ventilation and difficult intubation. Methods Over a 6-year period, all tracheal intubations in the operating room of a large tertiary teaching hospital were analyzed. A modified version of the intubation difficulty scale (mIDS) was used to define easy versus difficult intubation, where a score of two or greater was defined as difficult intubation. Difficult mask ventilation was defined as the use of one or more adjuncts to achieve successful mask ventilation. Results Of 45,447 analyzed cases, 1893 (4.2%) were classified as difficult intubations. Morbidly obese patients were not more likely to have difficult intubation [Odds Ratio (OR) = 1.131, 95% confidence interval (CI): 0.958, 1.334, p = 0.146]. Factors that were associated with difficult intubation included patient age > 46 years, male sex, Mallampati 3–4, thyromental distance < 6 cm, and the presence of intact dentition. Of 37,016 cases in which mask ventilation was attempted, 1069 (2.9%) were difficult. Morbidly obese patients were more likely to have difficult mask ventilation (OR = 3.785, 95% CI: 3.188, 4.493, p < 0.0001). Other factors associated with difficult mask ventilation included patient age > 46 years, male sex, Mallampati 3–4, and a history of obstructive sleep apnea. Having intact dentition decreased the likelihood of difficult mask ventilation. Conclusion Morbidly obese patients do not have a higher incidence of difficult intubation compared to non-morbidly obese patients. However, they have a significantly higher incidence of difficult mask ventilation. Other factors that are predictive of both difficult mask ventilation and difficult intubation include age > 46 years, male sex, and Mallampati 3–4.
Objective: Current standards for conducting spirometry examinations recommend that the ventilation manoeuvres needed in pulmonary function testing are carried out repeatedly during the sessions. Chest electrical impedance tomography (EIT) can determine the presence of ventilation heterogeneity during such manoeuvres which increases the information content derived from such examinations. The aim of this study was to characterise regional lung function in patients with chronic obstructive pulmonary disease (COPD) during repetitive forced full ventilation manoeuvres. Regional lung function measures derived from these manoeuvres were compared with quiet tidal breathing. Approach: 60 hospitalised patients were examined during up to three repeated ventilation manoeuvres. 53 patients (12 women, 41 men; age: 68±17 years (mean±SD)) exhibited acceptable spirometry manoeuvres and EIT recordings suitable for analysis. Pixel values of tidal volume, forced full inspiratory and expiratory volume in 1s, forced inspiratory and expiratory vital capacity were calculated from the EIT data. Spatial ventilation heterogeneity was assessed using the coefficient of variation, global inhomogeneity index, centres and regional fractions of ventilation. Temporal inhomogeneity was examined by pixel expiration times needed to exhale 50% and 75% of regional forced vital capacity. Main results: All EIT-derived measures of regional lung function showed reproducible results during repetitive examinations. Parameters of spatial heterogeneity obtained from quiet tidal breathing were comparable with the measures derived from the forced manoeuvres. Significance: Measures of spatial and temporal ventilation heterogeneity obtained in COPD patients by EIT provide comparable findings during repeated examinations within one testing session. Quiet tidal breathing generates similar information on ventilation heterogeneity as forced manoeuvres that require high patient effort.
Background: In the Protective Ventilation in Cardiac Surgery (PROVECS) randomized, controlled trial, an open-lung ventilation strategy did not improve postoperative respiratory outcomes after on-pump cardiac surgery. In this prespecified subanalysis, the authors aimed to assess the regional distribution of ventilation and plasma biomarkers of lung epithelial and endothelial injury produced by that strategy. Methods: Perioperative open-lung ventilation consisted of recruitment maneuvers, positive end-expiratory pressure (PEEP) = 8 cm H2O, and low-tidal volume ventilation including during cardiopulmonary bypass. Control ventilation strategy was a low-PEEP (2 cm H2O) low-tidal volume approach. Electrical impedance tomography was used serially throughout the perioperative period (n = 56) to compute the dorsal fraction of ventilation (defined as the ratio of dorsal tidal impedance variation to global tidal impedance variation). Lung injury was assessed serially using biomarkers of epithelial (soluble form of the receptor for advanced glycation end-products, sRAGE) and endothelial (angiopoietin-2) lung injury (n = 30). Results: Eighty-six patients (age = 64 ± 12 yr; EuroSCORE II = 1.65 ± 1.57%) undergoing elective on-pump cardiac surgery were studied. Induction of general anesthesia was associated with ventral redistribution of tidal volumes and higher dorsal fraction of ventilation in the open-lung than the control strategy (0.38 ± 0.07 vs. 0.30 ± 0.10; P = 0.004). No effect of the open-lung strategy on the dorsal fraction of ventilation was noted at the end of surgery after median sternotomy closure (open-lung = 0.37 ± 0.09 vs. control = 0.34 ± 0.11; P = 0.743) or in extubated patients at postoperative day 2 (open-lung = 0.63 ± 0.18 vs. control = 0.59 ± 0.11; P > 0.999). Open-lung ventilation was associated with increased intraoperative plasma sRAGE (7,677 ± 3,097 pg/ml vs. 6,125 ± 1,400 pg/ml; P = 0.037) and had no effect on angiopoietin-2 (P > 0.999). Conclusions: In cardiac surgery patients, open-lung ventilation provided larger dorsal lung ventilation early during surgery without a maintained benefit as compared with controls at the end of surgery and postoperative day 2 and was associated with higher intraoperative plasma concentration of sRAGE suggesting lung overdistension. Editor’s perspective:
Objective: The aim of the study was to examine whether electrode belt of electrical impedance tomography (EIT) changed lung function in healthy volunteers, patients with respiratory muscle weakness (RMW) and chronic obstructive pulmonary disease (COPD). Approach: In total 30 subjects were included (10 healthy volunteers, 10 subjects with RMW, maximum inspiratory pressure < 40 cmH2O, and 10 COPD, grade I - IV). Spirometry measurements were conducted in sitting position once a day at similar times on two consecutive days. Slow expiratory vital capacity (VC), forced vital capacity (FVC) and maximum voluntary ventilation (MVV) manoeuvres were performed. On day 1, spirometry was performed without the EIT electrode belt, and on day 2 the belt attached to the thorax. Main results: Lung function was not influenced by the electrode belt in healthy subjects. Test-retest reliability in the healthy group was 0.89, 0.89 and 0.85 for VC, FVC and MVV, respectively. On the other hand, all investigated parameters were significantly decreased in the RMW group (VC, 51.3±18.0 vs. 46.5±18.0 %predicted, without vs. with EIT belt, p<0.01; FVC, 51.7±19.0 vs. 45.8±18.1 %predicted, p<0.01; MVV, 41.0±20.0 vs. 38.8±19.6 %predicted, p<0.01). VC and MVV also decreased significantly in the COPD group (VC, 77.4±20.5 vs. 74.6±18.8 %predicted, p<0.05; MVV, 57.4±15.7 vs. 54.4±12.5 %predicted, p<0.05). Significance: EIT electrode belt could reduce lung volumes in subjects with pre-existing lung diseases. Comparing lung function acquired with electrode belt to corresponding values obtained without the belt should be avoided.
Anaesthesia and positive pressure ventilation cause ventral redistribution of regional ventilation, potentially caused by the tracheal tube. We used electrical impedance tomography to map regional ventilation during anaesthesia in 10 patients with and without a tracheal tube. We recorded impedance data in subjects who were awake, during bag‐mask ventilation, with the tracheal tube positioned normally, rotated 90° to each side and advanced until in an endobronchial position. We recorded the following measurements: ventilation of the right lung (proportion, %); centre of ventilation (100% = entirely ventral); global inhomogeneity (0% = homogenous); and regional ventilation delay, an index of temporal heterogeneity. We compared the results using Student's t‐tests. Relative to subjects who were awake, anaesthesia with bag‐mask ventilation reduced right‐sided ventilation by 5.6% (p = 0.002), reduced regional ventilation delay by 1.6% (p = 0.025), and moved the centre of ventilation ventrally from 51.4% to 58.2% (p = 0.0001). Tracheal tube ventilation caused a further centre of ventilation increase of 1.3% (p = 0.009). With the tube near the carina, right‐sided ventilation increased by 3.2% (p = 0.031) and regional ventilation delay by 2.8% (p = 0.049). Tube rotation caused a 1.6% increase in right‐sided ventilation compared with normal position (p = 0.043 left and p = 0.031 right). Global inhomogeneity remained mostly unchanged. Ventral ventilation with positive pressure ventilation occurred with bag‐mask ventilation, but was exacerbated by a tracheal tube. Tube position influenced ventilation of the right and left lungs, while ventilation overall remained homogenous. Tube rotation in either direction resulted in ventilation patterns being closer to when awake than either bag‐mask ventilation or a normally positioned tube. These results suggest that even ideal tube positioning cannot avoid the ventral shift in ventilation.
Objective: The aim of the present study was to evaluate two previously proposed approaches based on electrical impedance tomography (EIT) to assess pulmonary oedema at the bedside. Approach: Fourteen patients with acute respiratory distress syndrome were included and examined prospectively. Patients were rotated laterally along their longitudinal axis from supine to 45-degree left and right tilt to induce a gravity-dependent redistribution of pulmonary oedema. After a 20 min equilibration period at each of the three positions, 2 min EIT data were recorded and analyzed. Left-to-right lung and anterior-to-posterior ventilation ratios were calculated for each posture. The slopes of the regression lines in all three postures were then determined. The same examination was performed on the consecutive day. The EIT-derived parameters were compared with transcardiopulmonary thermodilution measurements. Main results: The correlations between the EIT and transcardiopulmonary thermodilution parameters were low (correlation coefficients r < 0.4) and not significant regardless of the examination days. Significance: Despite previous clinical and experimental observations, left-to-right and anterior-to-posterior ventilation ratios derived from EIT examinations after postural changes did not reflect total extravascular lung water in our study population. Clinical trial registration: NCT02870894 Registered 17 AUG 2016 (
Background: The study objective was to examine the correlation between regional ventilation distribution measured with electrical impedance tomography (EIT) and weaning outcomes during spontaneous breathing trial (SBT). Methods: Fifteen patients received 100% automatic tube compensation (ATC) during the first and 70% during the second hour. Another 15 patients received external continuous positive airway pressure (CPAP) of 5 and 7.5 cmH2 O during the first and second hours, respectively. Regional ventilation distributions were monitored with EIT. Results: Tidal volume and tidal variation of impedance correlated significantly during assist-control ventilation and ATC in all patients (r(2) = 0.80 ± 0.18, P < 0.001). Higher support levels resulted in similar ventilation distribution and tidal volume, but higher end-expiratory lung impedance (EELI) (P < 0.05). Analysis of regional intratidal gas distribution revealed a redistribution of ventilation towards dorsal regions with lower support level in 13 of 30 patients. These patients had a higher weaning success rate (only 1 of 13 patients failed). Eight of 17 other patient failed (P < 0.05). The number of SBT days needed for weaning was significantly lower in the former group of 13 patients (13.1 ± 4.0 vs. 20.9 ± 11.2 days, P < 0.05). Conclusions: Regional ventilation distribution patterns during inspiration were associated with weaning outcomes, and they may be used to predict the success of extubation.