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Natwara Asanathong, M.D.*, Natticha Jiamjira-anon, M.D.**, Jatuporn Eiamcharoenwit (onsontia), M.D.
***, Sumon Mantaga, Nsc. ****, Chayanan anakiattiwibun, Msc. *****,
Arunotai Siriussawakul, M.D.*****,
******,
Nonthida Rojanapithayakorn, M.D.******
* Sisaket Hospital, Sisaket, 33000 ailand, ** Sawang Daen Din Crown Prince Hospital, Sakon Nakhon, 47110 ailand, *** Anesthesiology Department,
Prasat Neurological Institute, Bangkok, 10400 ailand, **** Department of Nurse Anesthetists, Ratchaburi Hospital, Ratchaburi, 77000 ailand,
***** Integrated Perioperative Geriatric Excellent Research Center, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, 10700 ailand,
****** Department of Anesthesiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, 10700 ailand.
Incidence of Adverse Perioperative Airway
Complications in Obese Non-Pregnant and Pregnant
Patients Undergoing General Anesthesia
ABSTRACT
Objective: Airway complications in obese patients are a major concern during surgical operation. is study
aimed to determine the incidence of airway- and respiratory-related anesthetic complications for obese (including
maternal) patients undergoing general anesthesia.
Materials and Methods: is multicenter, retrospective, observational study evaluated obese female patients (BMI
≥ 30 kg/m
2
), both non-pregnant and pregnant, undergoing general anesthesia in 5 hospitals across ailand during
May 2013 - August 2016. e primary observation was anesthesia-related airway complications (dicult and failed
intubations, aspiration, desaturation, and airway injuries) detected during anesthesia. An analysis was performed
to compare the incidents of the adverse events and to determine the risk factors for airway-related adverse events
in both groups.
Results: ere were 1,347 obese patients enrolled (777 non-pregnant and 570 pregnant). e overall incidence of
airway and respiratory complications was observed in 129 patients (9.6%), with a higher rate in pregnant patients
(12.5% vs. 7.5%; p<0.05). e most common complications were desaturation (5.6%) followed by airway injuries
(3.6%) and dicult intubation (1.5%). e factors signicantly associated with adverse airway-related events were
obesity class II (OR=1.63 [1.05–2.54]), obesity class III (OR=2.25 [1.19–4.25]), pregnancy (OR=1.73 [1.18–2.54]),
Mallampati classications III–IV (OR=1.69 [1.16–2.48]), and neck circumference <43 cm (OR=3.33 [1.02-10.81]),
p<0.05).
Conclusion: e incidence of the anesthesia-related airway and respiratory complications was 9.6%, with a higher
rate in pregnant patients. e most common adverse airway event was desaturation. However, the frequency of
serious airway events was low.
Keywords: Airway; obesity; perioperative; complication (Siriraj Med J 2022; 74: 178-184)
Corresponding author: Nonthida Rojanapithayakorn
E-mail: nonthida.roj@mahidol.ac.th
Received 19 December 2021 Revised 21 January 2022 Accepted 25 January 2022
ORCID ID: https://orcid.org/0000-0002-0305-0316
http://dx.doi.org/10.33192/Smj.2022.22
All material is licensed under terms of
the Creative Commons Attribution 4.0
International (CC-BY-NC-ND 4.0)
license unless otherwise stated.
Rojanapithayakorn et al.
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Original Article
SMJ
INTRODUCTION
Obesity is a major risk factor of various diseases
and associated with an increase in all-cause mortality.
1
According to the World Health Organization, obesity
rates have almost tripled worldwide since 1975. In 2016,
39.8% of adults in the USA were overweight,
2
and during
2013-2014, 7.7% of adults in the USA were extremely
obese.
3
Performing general anesthesia in obese patients is
challenging, beginning from induction to immediate
post operation. e airway and respiratory system are
the most common area in which complications occur
in obese patients, accounting for more than 80% of all
events.
4
e incidence of dicult intubation in obesity
varies from 4% to 15%
5
, depending on the population and
the denition of dicult intubation utilized by studies.
e incidence of dicult airway in obese patients was 3
times that of non-obese patients.
6
Moreover, it is a risk
factor for aspiration, which is one of the main causes of
airway-related mortality in anesthesia.
7
Anesthesia is one of the leading cause of maternal
mortality. Of all the causes of maternal complication
from anesthesia, dicult intubation and aspiration is
the second only to high spinal block in frequency.
8
e
pregnancy-related anatomical and physiological changes
heighten the risk of airway and respiratory problems
occurring during general anesthesia. us, it is important
to be aware of the risks of complications associated with
general anesthesia in obese patients. Furthermore, it is
very likely that the risk would be even higher in obese
patients with pregnancy.
e main aims of the present study were to determine
the incidences of airway- and respiratory-related anesthetic
complications in female obese patients, and to ascertain
the resulting airway management outcomes. e secondary
objectives were to compare the airway-complication
incidences between obese non-pregnant patients and
obese pregnant patients, and to assess the characteristics
of the patients in order to identify factors associated with
the occurrence of such complications.
MATERIALS AND METHODS
This retrospective analysis evaluated on obese
non-pregnant and pregnant female patients undergoing
general anesthesia during May 2013 to August 2016
from a university hospital (Siriraj Hospital, Bangkok)
and 4 tertiary hospitals across ailand (Taksin hospital,
Bangkok; Surat ani Hospitals, Surat ani Province;
Phaholpolpayuhasena Hospital, Kanchanaburi Province;
and Maharat Nakhon Ratchasima Hospital, Nakhon
Ratchasima Province).
e inclusion criteria were female patients, aged
≥18 years old, having undergone surgery under general
anesthesia with conventional endotracheal tube intubation,
a BMI of ≥30 kg/m
2
, and gestational age of 34-42 weeks
for obese pregnant patients. Exclusion criteria included
patients who had a signicant orofacial pathology likely to
disturb intubation; having a history of dicult intubation;
having a condition leading to an abnormally increased
BMI (such as a huge intra-abdominal tumor, massive
ascites, or a patient with a full stomach).
Data collected were extracted by an anesthesiologist
from each hospital. e details were compiled on a
standardized data collection form and comprised each
patient’s demographic prole (sex, age, body weight,
and height), ASA physical status, diagnosis, type of
operation, and airway assessment parameters. In this
study, the airway and respiratory adverse events during
anesthesia were (1) dicult intubation, (2) desaturation,
(3) aspiration, (4) failed intubation and (5) airway injury.
Dicult intubation was dened and classied according
to the Intubation Diculty Scale,
9
a score of > 5 indicates
dicult intubation. Desaturation was dened as having at
least one episode of oxygen saturation (SpO
2
) below 90%
for more than 10 seconds intra-operatively.
10
Aspiration
was dened as the entry of liquid or solid material into
the trachea and/or lungs.
11
An airway injury included
various levels of injury, ranging from a sore throat; lip,
gum, or tongue trauma; palate and tonsil abrasion; to
tooth mobility or tooth extraction. e postponement
of the operation; remaining on endotracheal intubation
to the post anesthesia care unit as a result of an airway
or respiratory event; an unplanned, intensive-care-unit
admission; brain damage; and an in-hospital, anesthesia-
related death were also recorded.
Statistical analysis
Using the estimated prevalence of 3% and a 1% error,
a minimum sample size of 1,118 cases was obtained. To
compensate for a 20% dropout for unforeseen reason, the
size was adjusted to 1,342 cases. Demographic variables
were presented as median and interquartile range for
continuous data, and frequency and percentage for
categorical data. Comparison of the categorical data
were performed using Chi-square or Fisher’s exact test.
Comparison of the continuous data were performed using
T-test or Mann-Whitney U test. e characters associated
with the adverse airway events were identied using
logistic regression. Risk factors with a univariable p–value
of < 0.2 were entered into a multiple logistic regression
model. Crude odds ratio (OR) and adjusted odds ratios,
with their respective 95% condence intervals, were
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180
reported. e data were analyzed using SPSS Statistics
for Windows, version 18 (SPSS Inc., Chicago, IL, USA).
RESULTS
e study included a total of 1,347 obese patients
(777 not pregnant, and 570 pregnant) who had undergone
surgery under general anesthesia using conventional
endotracheal intubation. e median age of the patients
was 37 years old. eir average BMI was 33.1 kg/m
2
; the
majority were in obesity class I under World Health
Organization criteria (66.5%), with about 8.3% being
morbidly obese. As to ASA status, 69.0% were class
II due to obesity or pregnancy (Table 1). The most
frequently performed surgical procedure types were
general surgery; gynecological; head, neck, and breast
surgery; and cesarean sections. Mallampati classication
III or IV was recorded in 30.5% of the patients. e
median mentosternal distance and neck circumference
were 16.0 and 37.0 cm, respectively. Almost all patients
were successfully intubated on the rst attempt by the
rst operator, with the initial technique being applied
without the need for a high liing eort or external
laryngeal pressure. Most patients had a laryngoscopic-
view grade of I or II (66.1% and 28.5%, respectively).
e incidence of anesthesia-related airway and
respiratory complications was observed in 129 patients
(9.6%), with a higher incidence occurring among pregnant
than non-pregnant patients (12.5% vs. 7.5%; p=0.002)
(Table 2). Among them, there were over all 147 airway-
related complications. e most common was a briey
sustained, oxygen desaturation below 90% (5.6%), with
a signicantly greater incidence for the pregnancy group
than the non-pregnancy group (11.6% vs. 1.3%; p<0.001).
e second most common event was airway injury (3.6%),
followed by dicult intubation (1.5%). ere was no
patients experiencing aspiration or a failed intubation.
The characteristics of the patients with airway
and respiratory complications are listed in Table 3.
Compared with patients without any complications,
those with complications had a higher frequency of
Mallampati classications III and IV (39.5.% vs. 28.2%).
Patients with obesity class III had a higher incidence of
complications (15.2%) than those with obesity class I
(7.9%), and II (12.1%). In the multivariate analysis, the
independent risk factors for adverse airway-related events
were determined to be obesity class II (OR=1.63 [1.05–
2.54]; p=0.031), obesity class III (OR=2.25 [1.19–4.25];
p=0.012); pregnancy (OR=1.73 [1.18–2.54]; p=0.005); and
Mallampati classications III–IV (OR= 1.69 [1.16–2.48];
p=0.007). Neck circumference > 42 cm had adjusted
odds ratio of 0.30 [0.09–0.98]; p=0.046).
Only 1 patient remained on endotracheal intubation
upon transferred to the post anesthesia care unit. No
operation postponement, unplanned intensive care unit
admission, brain death, or in hospital mortality occurred.
DISCUSSION
Obesity can have a profound impact on anesthesia-
related morbidity and mortality, particularly the airway
and respiratory system. In the current research, the
incidence of airway and respiratory complications was
9.6% (7.5% for the non-pregnancy group, and 12.5% for
the pregnancy group; p=0.002), which was higher than
the overall incidence of airway-related events in the ai
general population previously reported (0.61%).
12
Dicult intubation and airway injuries occur in
the presence of the excess fatty tissue.
13
Physiological
changes that arise during pregnancy can cause dicult
intubation through both capillary engorgement and
enlarged breasts.
14
Additionally, obesity causes reduced
functional residual capacity; atelectasis; greater work of
breathing; and worsened ventilation-perfusion mismatch.
All of these resultant conditions cause rapid desaturation
in obese patients relative to non-obese patients, and they
are aggravated during pregnancy.
15
In the current research, desaturation was found to
be the most common adverse event among obese patients
(5.6%), and its incidence was signicantly higher among
the obese pregnant patients than the non-pregnant
patients (11.6% vs. 1.3%; p<0.001). A total of 66 out of 78
events (84.6%) in the pregnancy group involved oxygen
desaturation. In 2 studies reporting anesthesia-related
events in ailand
16,17
, the most common adverse event
during cesarean delivery was desaturation (13.8%–17.39%
of all adverse events).
More than half of the patients in our study were
easily intubated (60.3%). The incidence of difficult
intubation was 1.5%, which was higher than the gure
of 0.08% reported for general patients by the Perioperative
Anesthetic Adverse Events in ailand Study.
4
A meta-
analysis has found the incidences of dicult intubation
for obese patients to be 4.2%-4.3%.
5
As for the current
research, the low incidence of dicult intubation relative
to other studies could result from 3 factors. Firstly, the
majority of the patients were of class I obesity status
(which carries a lower risk for dicult intubation than
the higher obesity classes). Secondly, the population in
the current study were female patients; fat in females
tends to be localized to the hips and buttocks, where it
has a negligible eect on intubation diculty. irdly, the
present study was undertaken at tertiary hospitals, where
the anesthesiologists are likely to have had considerable
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Original Article
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TABLE 1. Demographic and airway management data.
Total
Obesity Obesity
Characteristic
(n = 1347)
without pregnancy with pregnancy p-value
(n=777) (n=570)
Age (years) 37.0 (29.0, 51.0) 49.0 (38.0, 59.0) 29.0 (25.0, 34.0) <0.001
Body mass index (kg/m
2
) 33.1 (31.2, 36.1) 33.0 (31.2, 36.1) 33.2 (31.2, 36.0) 0.405
Obesity (kg/m
2
) 0.977
Obesity class I (30–34.9) 896 (66.5) 515 (66.3) 381 (66.8)
Obesity class II (35–39.9) 339 (25.2) 197 (25.4) 142 (24.9)
Obesity class III (≥ 40) 112 (8.3) 65 (8.4) 47 (8.2)
ASA classication <0.001
II 929 (69.0) 599 (77.1) 330 (57.9)
III 414 (30.7) 178 (22.9) 236 (41.4)
IV 4 (0.3) 0 4 (0.7)
Operation <0.001
Cesarean section 570 (42.3) 0 570 (100)
General surgery 237 (17.6) 237 (30.5) 0
Gynecology 175 (13) 175 (22.5) 0
Head-neck and breast 131 (9.7) 131 (16.9) 0
Orthopedic 83 (6.2) 83 (10.7 0
Ear, nose, and throat 52 (3.9) 52 (6.7) 0
Other 99 (7.3) 99 (12.7) 0
Mallampati classication <0.001
I 315 (24.3) 250 (32.2) 65 (12.5)
II 585 (45.2) 296 (38.1) 289 (55.8)
III 305 (23.6) 150 (19.3) 155 (29.9)
IV 90 (6.9) 81 (10.4) 9 (1.7)
Sternomental distance (cm) 16 (15.0, 17.2) 16.0 (15.0, 17.5) 16.0 (15.0, 17.0) 0.038
Neck circumference (cm) 37.0 (36.0, 39.0) 37.5 (36.0, 39.5) 37.0 (35.0, 38.0) <0.001
Intubation data
First attempt successful 1325 (98.4) 756 (97.3) 569 (99.8) <0.001
First operator successful 1334 (99.0) 769 (99.0) 565 (99.1) 0.415
First technique successful 1335 (99.1) 772 (99.4) 563 (98.8) 0.099
Lifting force 0.002
Little effort 891 (66.1) 523 (67.3) 368 (64.6)
Increase lift force 384 (28.5) 201 (25.9) 183 (32.1)
Maximal lift force 72 (5.3) 53 (6.8) 19 (3.3)
No external pressure 1171 (86.9) 688 (88.5) 483 (84.7) 0.040
Cord position: Abduction 1164 (86.4) 660 (84.9) 504 (88.4) 0.066
Laryngoscopic view 0.006
I 891 (66.1) 523 (67.3) 368 (64.6)
II 384 (28.5) 201 (25.9) 183 (32.1)
III 67 (5) 49 (6.3) 18 (3.2)
IV 5 (0.4) 4 (0.5) 1 (0.2)
Data presented as n (%) or median (IQR)
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TABLE 2. Airway and respiratory system adverse events.
TABLE 3. Characteristic of patients with airway and respiratory events.
Adverse events
Total without pregnancy with pregnancy
(n = 1,347) (n = 777) (n = 570)
p-value
Patients experiencing ≥1 adverse event 129 (9.6) 58 (7.5) 71 (12.5) 0.002
Overall adverse events (n) 147 (100) 69 (46.9) 78 (53.1) 0.002
Difcult intubation 0.107
Easy (IDS score = 0) 812 (60.3) 478 (61.5) 334 (58.6)
Slight difculty (IDS score = 1-5) 515 (38.2) 291 (37.5) 224 (39.3)
Major difculty (IDS score >5) 20 (1.5) 8 (1.0) 12 (2.1)
Desaturation 76 (5.6) 10 (1.3) 66 (11.6) < 0.001
Airway injury: Patients with injury 48 (3.6) 48 (6.2) 0 < 0.001
Lip, gum, tongue injury 17 (1.2) 17 (2.2) 0
Sore throat 30 (2.2) 30 (3.9) 0
Tooth injury 3 (0.2) 3 (0.4) 0
Soft palate injury 1 (0.1) 1 (0.1) 0
Data presented as n (%), IDS = Intubation Diculty Scale
Without event With event
Crude OR
Adjusted OR
Factor (n = 1,218; (n = 129;
(95% CI)
p-value
(95% CI)
p-value
90.4%) 9.6%)
Age (years) 37 (29, 52) 35 (29, 49) 1.00 (0.98-1.01) 0.423
Obesity (kg/m
2
)
Obesity class I 825 (67.7) 71 (55.0) 1 1
Obesity class II 298 (24.5) 41 (31.8) 1.60 (1.07-2.40) 0.024 1.63 (1.05-2.54) 0.031
Obesity class III 95 (7.8) 17 (13.2) 2.08 (1.18-3.68) 0.012 2.25 (1.19-4.25) 0.012
ASA classication
II 850 (69.8) 79 (61.2) 1
III–IV 368 (30.2) 50 (38.8) 1.46 (1.01-2.13) 0.047 1.04 (0.67-1.63) 0.853
Pregnancy 499 (41.0) 71 (55.0) 1.76 (1.22-2.54) 0.002 1.73 (1.18-2.54) 0.005
Mallampati Classication
I–II 874 (71.8) 78 (60.5) 1 1
III–IV 344 (28.2) 51 (39.5) 1.66 (1.14-2.42) 0.008 1.69 (1.16–2.48) 0.007
SMD < 12 cm 62 (5.1) 6 (4.7) 0.91 (0.39-2.15) 0.829
NC < 43 cm 78 (6.4) 3 (2.3) 2.87 (0.89-9.24) 0.076 3.33 (1.02-10.81) 0.046
Data presented as n (%) or median (IQR), OR: Odds ratio; 95% CI: 95% condence interval, SMD = sternomental distance, NC = Neck
circumference
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experience in the intubation of obese patients. is is
supported by the absence of failed intubations despite
30.5% of the patients having Mallampati classications
III-IV. e neck circumference < 43 cm was a sensitive
predictor for uneventful airway intubation.
18
In contrast,
the current research found neck circumference < 43 cm
to be risk factor for airway complication, which could
be explained by the complication recorded in the study
were not only dicult airway but the most common
adverse event was desaturation.
Airway injuries were recorded in 3.6% of the cases,
and all were in the non-pregnancy group. Of the injuries,
the most common was a sore throat (2.0%). e absence
of airway injuries in the pregnancy group might have
resulted from the use of smaller-sized endotracheal
tubes in the pregnancy group than in the non-pregnancy
group.
e major consequences of events was very low
(0.1%). e endotracheal tube remained intubated in
only 1 patient, who had undergone a tonsillectomy with
a dicult intubation. However, the sample size in this
study does not mirror the population since the incidence
of fatal complications in the general population during
anesthesia is low (0.004%-0.006%).
e risk factors associated with adverse airway-
related events have previously been identied to be
Mallampati classication III or IV, obstructive sleep
apnea syndrome, reduced mobility of the cervical spine,
limited mouth opening, severe hypoxemia (< 80%), and
coma.
19
Some of those factors were observed in the current
research. From the multivariate analysis conducted for
this study, it was found that a higher obesity class and that
Mallampati classications III–IV were associated with
a higher frequency of adverse airway events. Pregnancy
was also determined to be associated with elevated risks
of adverse airway events, compared with that for obesity
without pregnancy.
is research compared obese female patient and
showed that difference pathophysiology associated
with obesity might contribute to difference adverse
events. Pregnant obese patients were more susceptible to
desaturation. erefore, ensuring optimum pre-oxygenation
are crucial. While non pregnant patient associated with
higher incidence of airway injury, appropriate intubation
plans and prophylaxis technique should be considered.
This study had limitation primarily due to its
retrospective design. Another limitation was that no
records of pre-pregnancy weights were available, not
possible to ascertain whether the pregnant patients were
obese before - or only during - their pregnancy. e
durations might have inuenced the pathophysiology and
consequences of the obesity. Because the present study did
not compare obese and non-obese patients, a comparison
of the incidence of adverse events with those might prove
dicult.
12
Dierences in the intubation management of
the pregnancy and non-pregnancy groups might have
provided relatively easier access for the endotracheal
tube in the pregnancy group. As well, the rapid sequence
induction employed for the pregnant patients might have
increased their susceptibility to rapid desaturation. On
the other hand, as the respective anesthesia techniques
used for the non-pregnant and pregnant patients were
standard, the incidence of adverse events would still
reect what is found in normal anesthesiological practice.
It would be benecial if a future study compared obese
non-pregnant patients and obese pregnant patients in
a controlled design. Further study is also recommended
to improve the anesthesiological procedures for patients
with dierent levels of obesity.
CONCLUSION
e incidence of anesthesia-related airway and
respiratory events was 9.6%, with a signicant higher
incidence in the pregnant than the non-pregnant patients.
Based on the ndings, patients with obesity should be closely
monitored during general anesthesia. Anesthesiologists
should be aware on the most common complication
as identied in this study so as to be well prepared to
minimize undesirable outcomes.
ACKNOWLEDGEMENTS
is research project was supported by Faculty of
Medicine Siriraj Hospital, Mahidol University, Grant
Number (IO) R016231036. e funders had no role
in study design, data collection, and analysis, decision
to publish, or preparation of the manuscript. We are
grateful to Assist. Prof. Dr. Chulaluk Komoltri for her
statistical support as well as Miss Tashita Pinsanthia and
Miss Chanita Janonsoong, research assistants, for their
invaluable help with the paperwork.
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