ORIGINAL PAPER
Nagoya J. Med. Sci. 83. 801–810, 2021
doi:10.18999/nagjms.83.4.801

Evaluation of predictive factors related to the presence orabsence of supplemental oxygen therapy and comparison ofphysical functions after video-assisted thoracic surgery
Kohji Iwai1, Ryo Komada1, Yasuhiko Ohshio2 and Jun Hanaoka2
Division of Physical Therapy, Rehabilitation Units, Shiga University of Medical Science, Otsu, Japan2
Department of Thoracic Surgery, Shiga University of Medical Science, Otsu, Japan

1

ABSTRACT
We performed a retrospective study of 102 individuals to evaluate predictive factors for needing
supplemental oxygen therapy following video-assisted thoracic surgery (VATS) and to compare patients’physical functions before and after surgery. Prior to surgery, we evaluated quadriceps torque, 6-minute
walk distance (6MWD), timed up and go test, and grip strength. During the 6MWD, patients’ oxygen
saturation was recorded every minute. Quadriceps torque and 6MWD were evaluated again following
surgery. The indication for supplemental oxygen therapy was determined based on desaturation (<85%)
during the 6MWD in room air. A total of 14 patients needed oxygen therapy at discharge (group A), while
88 patients did not need oxygen therapy (group B). In group A, the postoperative 6MWD was repeatedwith supplemental oxygen. Compared with the same parameters in group B, in group A the percentage
diffusing capacity for carbon monoxide was significantly lower (p=0.011), while a history of smoking(p=0.016), exercise-induced hypoxemia (EIH, p<0.001), chronic obstructive pulmonary disease (p<0.001),
and interstitial pneumonia (p=0.008) were significantly higher. Logistic regression analysis showed that
EIH was an independent risk factor for requiring supplemental oxygen therapy following surgery (oddsratio: 46.2, 95% CI: 9–237.1; p<0.001). In group A, patients’ minimum oxygen saturation was significantly
improved by oxygen administration (83.4±3.4 vs. 87.7±3.3, p=0.002), but there was no difference in walking
distance (359.5±64.2 vs. 353.6±41.6, p=0.482). Our data indicate that patients should be preoperatively
evaluated to predict postoperative hypoxemia and that this evaluation could complement the prediction of
postoperative need for oxygen therapy.
Keywords: VATS, supplemental oxygen therapy, physical function, rehabilitation
Abbreviations:
VATS: video-assisted thoracic surgery
6MWD: 6-minute walk distance
EIH: exercise-induced hypoxemia
ANOVA: analysis of varianceThis is an Open Access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
License. To view the details of this license, please visit (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Received: January 29, 2021; accepted: April 6, 2021
Corresponding Author: Kohji Iwai, PT, PhD
Division of Physical Therapy, Rehabilitation Units, Shiga University of Medical Science, Seta Tsukinowa-cho,
Otsu 520-2192, Japan
Tel: +81-77-548-2670, E-mail: kojin@belle.shiga-med.ac.jp
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INTRODUCTION
Although the advances made in lung cancer diagnosis and treatment techniques have been
impressive, lung cancer remains a leading cause of cancer-related death.1 Lung resection is themost effective treatment for early-stage lung cancer and is commonly performed via minimallyinvasive video-assisted thoracic surgery (VATS) lobectomy.2,3 VATS is superior to thoracotomy
in terms of perioperative morbidity and a reduced length of hospital stay.4,5 Many patients withlung cancer are elderly, have a history of smoking, and often have chronic respiratory disease;
the increased use of VATS has enabled curative therapy for such patients, ie, those who areelderly or have poor lung function.6,7 However, in some cases, postoperative hypoxemia occurs following lung resection, and supplemental oxygen therapy might be necessary. For thisreason, it is useful to predict, prior to surgery, the characteristics of patients who may needpostoperative supplemental oxygen therapy. In general, the range of resected lung is predictiveof the postoperative decline in lung function.8 However, predicting the need for postoperativeoxygen therapy based on preoperative physical function has not been evaluated. Furthermore,
the difference in postoperative physical function with or without supplemental oxygen therapy
has not been sufficiently studied.
The aim of this study was to observe the postoperative course of patients who underwent
VATS and for whom a preoperative evaluation was performed, to identify predictive factors related
to the presence or absence of supplemental oxygen therapy, and to compare patients’ physicalfunctions before and after surgery.

MATERIALS AND METHODSThis retrospective study was conducted between April 2015 and December 2017 in patients
who underwent VATS at Shiga University of Medical Science Hospital, Otsu, Japan. Although 207
patients were initially enrolled except for 3 who were transferred, data in the hospital databasewere incomplete for 80 patients, and 25 patients had no preoperative prescription. Therefore, atotal of 102 patients were eventually recruited. All patients lived independently and none of thepatients had received supplemental oxygen therapy prior to undergoing VATS.
According to our protocol, on the day prior to their surgery, all participants were informed
about the role and contents of a structured, postoperative pulmonary rehabilitation program, which
was to be performed by physical therapists. For the preoperative evaluation of participants, thetimed up and go test (TUG) and grip strength were measured, in addition to their quadriceps
torque and 6-minute walk distance (6MWD). The 6MWD was performed according to thestandardized procedure of the American Thoracic Society (ATS).9 During the 6MWD, participants’
oxygen saturation value was recorded every minute (PALSOX-300, KONICA MINOLTA Co.,Tokyo, Japan), and their exercise-induced hypoxemia (EIH) was determined when their oxygen
saturation reached 90% or less.10 Isometric quadriceps torque was measured using an isometricdynamometer (Isoforce GT-360, OG Wellness Co., Okayama, Japan). The quadriceps torquewas divided by the length of the lower limb (Nm). TUG was measured from an initial position
seated on a 40 cm-high armrest chair; the patient rose at a signal, walked around a pole 3-maway, and returned to their seat.11 Grip strength was measured using a digital grip force meter
manufactured by Takei Instrumentation Industry (Tokyo, Japan). Patients’ basic information at
hospital admission, including preoperative lung function and comorbidities, was collected fromtheir medical records (Table 1).
All patients underwent scheduled surgeries. As soon as the participants were clinically stable

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Indication of oxygen therapy after VATS

and adequate pain control was confirmed, early postoperative rehabilitation in the ward wasstarted on postoperative day 1. From postoperative day 2, participants with no complications
were started on postoperative aerobic exercise training and quadriceps resistance training in the
rehabilitation room. This training continued until the time they were discharged from hospital.
Patients’ postoperative evaluation (quadriceps torque and 6MWD) was performed one or twodays before their scheduled discharge. Quadriceps torque and the 6MWD were selected for
postoperative revaluation, which were useful and effective evaluation methods for VATS cases.12
When hypoxemia was exacerbated following surgery, we discussed indications for oxygentherapy. The criterion for oxygen supplementation used by our hospital is an oxygen saturationof less than 85% during the 6MWD in room air, which is based on the Japanese standards.13
An oxygen saturation of between 85% and 90% during the 6MWD test was comprehensively
determined based on a patient’s background and their degree of comorbidities. Participants weredivided into two groups: 14 patients who received supplemental oxygen therapy (group A) and88 patients who did not receive supplemental oxygen therapy (group B) at discharge. Patientsin group A were considered to need supplemental oxygen therapy, so their 6MWD the next day
was performed with the amount of oxygen prescribed by the doctor (oxygen flow rate 2.2±0.9
L). The physical therapist performed evaluation by oxygen saturation to ensure their safety andthe 6MWD was discontinued when a patient demonstrated exacerbation of clinical symptoms.
The study protocol conformed to the ethical guidelines of the 1975 Declaration of Helsinki, as
reflected in a priori approval by the clinical research ethical committee of our hospital (approval
number: 29-286). Participants’ informed consent was obtained in the form of opt-out.
Statistical analysis
Statistical analysis was performed using IBM SPSS Statistics 22 (IBM, New York, NY, USA).
Results were considered statistically significant if the two-tailed P-value was less than 0.05. Data
are shown as means ± standard deviation (SD), except for non-normally distributed variables,
which are shown as medians. Based on whether supplemental oxygen therapy was provided,baseline comparisons between patient information, comorbidities, lung function (vital capacity andforced expiratory volume in 1 second using predicted values to adjust for disproportionate physique), and physical function were performed using the Mann–Whitney U test or the chi-square
test after examining normally distributed variables using the Shapiro–Wilk test. Range of resection and surgical procedures were performed chi-square test after cross-tabulation. The oxygen
saturation values recorded every minute during the 6MWD were examined by repeated one-way
analysis of variance (ANOVA) and the Bonferroni test. Following adjustments for the range ofresection and surgical procedures, a logistic regression analysis using independent variables withsignificant differences (percentage diffusing capacity for carbon monoxide, %DLCO; EIH; historyof smoking; chronic obstructive pulmonary disease, COPD; and interstitial pneumonia, IP) was
taken as a comparison between groups involved in supplemental oxygen therapy and to estimate
odds ratios and their 95% confidence intervals. Preoperative and postoperative changes in 6MWD
and isometric quadriceps torque were determined using a two-way ANOVA to determine themain effects and interactions (period, before and after surgery; group, presence or absence of
supplemental oxygen therapy). Finally, we performed 6MWD using supplemental oxygen therapy
for patients who were decided to introduce supplemental oxygen therapy and compared theirminimum oxygen saturation and walking distance using a paired t-test.

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Table 1Baseline characteristics of the patients at the time of hospitalization

All patients (n=102)
Age (years)

72.4 ± 8.4

Sex (Men, %)73 (71.6)

Height (cm)

161.8 ± 8.5

Weight (kg)58.9 ± 10.4

Body mass index (kg/m )22.5 ± 3.4

2

Pulmonary function
VC (L)

3.2 ± 0.7

%VC (%)

99.4± 15.1

FEV1 (L)

2.2 ± 0.6

%FEV1 (%)

88.1 ± 19.7

FEV1/FVC (%)

70.5 ± 12.1

%DLCO (%)

95.5 ±30.2

Physical function
6MWD (m)463.4 ± 81.0

Quadriceps torque (Nm)

94.9 ± 34.1

Grip strength (kg)29.4 ± 7.5

TUG (seconds)

7.6 ± 2.1

Comorbidities
Diabetes (n, %)30 (29.4)

Hypertension (n, %)46 (45.1)

COPD (n, %)16 (15.7)

IP (n, %)6 (5.9)Characteristics of participants are shown as mean ± SD for parametric data.
FVC: forced vital capacity
VC: vital capacity
FEV: forced expiratory volume
DLCO: diffusing capacity for carbon monoxide
6MWD: 6-minutes walk distance
TUG: timed up and go test
COPD: chronic obstructive pulmonary disease
IP: interstitial pneumonia

RESULTS
Surgical and oncological data, postoperative complications, surgery time, and postoperative
hospital stay are shown in Table 2. There was no exacerbation of clinical symptoms during the
6MWD for any patients. For the trend of oxygen saturation during the 6MWD, patients in bothgroups A and B showed a significant decrease in oxygen saturation during the 6MWD at every
1-minute interval compared with when they were at rest. However, it was noteworthy during
the 6MWD of the preoperative evaluation, the group that received supplemental oxygen therapy

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Indication of oxygen therapy after VATS

showed a significant decrease in oxygen saturation within 2 minutes of the start of the test, andthis tendency became even more marked following surgery (Fig. 1).
The %DLCO was significantly lower in group A than in group B (p=0.011). EIH (p<0.001),
a history of smoking (p=0.016), COPD (p<0.001), and IP (p=0.008) were significantly higher
in group A than in group B (Table 3). Logistic regression analysis showed that EIH was anindependent risk factor for requiring supplemental oxygen therapy following surgery (odds ratio
46.2, 95% CI: 9–237.1; p<0.001). Based on the two-way ANOVA, 6MWD showed a main
effect, but interaction did not show. Quadriceps torque did not show either a main effect or any
interactions (Table 4). Following surgery, 6MWD was performed with or without oxygen therapy
in patients in group A, and their minimum oxygen saturation was significantly improved following
oxygen administration (83.4±3.4 vs. 87.7±3.3, p=0.002); however, there was no difference in their
walking distance (359.5±64.2 vs. 353.6±41.6, p=0.482, Fig. 2).

Table 2

Characteristics of video-assisted thoracic surgery (VATS) and post-surgery information for patientswith lung cancer

All patients (n=102)
Stage of lung cancer (n)IA/IB/IIA/IIB/IIIA/IIIB

65/16/9/5/6/1

surgical procedures (n, %)RUL

36 (35.3)

RML

7 (6.9)RLL

16 (15.7)

LUL

26 (25.5)

LLL

17 (16.7)

Range of resection (n, %)Wedge resection

18 (17.6)

Segmentectomy

10 (9.8)

Lobectomy

74 (72.5)

Surgery time (minutes)

271.5 ± 120.1

Postoperative complications
Paf (n, %)15 (14.7)

Pneumonia (n, %)4 (3.9)

Postoperative hospital stay (day)Median (IQR)

8.0 (6.0–10.0)

Characteristics of the participants are shown as mean ± SD for parametric data, and median for
non-parametric data.
RUL: right upper lobectomy
RML: right middle lobectomy
RLL: right lower lobectomy
LUL: left upper lobectomy
LLL: left lower lobectomy
Paf: paroxysmal atrial fibrillation
IQR: interquartile range

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Fig. 1

Changes in oxygen saturation during 6-minute walk distance in patients with orwithout supplemental oxygen therapy
The left vertical axis represents oxygen saturation (%) accordingly. The left figure; patients with supplemental
oxygen therapy (group A, n=14). The right figure; patients without supplemental oxygen therapy (group B, n=88).

Table 3Comparison of preoperative characteristics in patients with or without supplemental oxygen therapy

Total (n=102)

Group A (n=14)Group B (n=88)

p ValueAge (years)

74.0±4.6 (73.5)

72.2±8.8 (73.0)

0.367

Height (cm)164.0±5.8 (162.9)

161.5±8.9 (161.5)

0.583

Weight (kg)58.1±7.8 (59.6)

59.0±10.7 (65.8)

0.512%VC (%)

107.0±13.4 (105.0)

98.3±15.1 (98.6)

0.054%FEV1 (%)

87.4±18.9 (91.0)

88.2±19.9 (91.3)

0.931

FEV1/FVC (%)

65.1±12.9 (66.4)

71.4±11.8 (73.6)

0.172%DLCO (%)

63.5±26.1 (58.5)

100.6±27.6 (102.1)

0.011

RUL (n, %)4 (28.6)

32 (36.4)

RML (n, %)0 (0)7 (8.0)

RLL (n, %)4 (28.6)

13 (14.8)

LUL (n, %)3 (21.4)

23 (26.1)

LLL (n, %)3 (21.4)

13 (14.8)

Wedge resection (n, %)2 (14.3)

16 (18.2)

Segmentectomy (n, %)2 (14.3)

8 (9.1)

Lobectomy (n, %)10 (71.4)

64 (72.7)

EIH (n,%)

8 (57.1)

4 (4.5)<0.001

6MWD (m)441.7±77.7 (445.0)

466.8±81.4 (470.0)

0.123

Quadriceps torque (Nm)98.6±28.2 (100.5)

94.3±35.0 (90.0)

0.673

Grip strength (kg)29.2±6.3 (31.2)

29.4±7.7 (29.6)

0.501

0.466

0.908

807
Indication of oxygen therapy after VATSTUG (second)

7.5±2.1 (7.7)

8.0±2.1 (6.7)

0.721

History of smoking (n, %)14 (100)

61 (69.3)

0.016

Diabetes (n, %)4 (28.6)

26 (29.5)

0.941

Hypertension (n, %)5 (35.7)

40 (45.5)

0.447

COPD (n, %)9 (64.3)

7 (8.0)<0.001IP (n, %)3 (21.4)

3 (3.4)0.008

Characteristics of participants are shown as mean ± SD and median.
FVC: forced vital capacity
VC: vital capacity
FEV: forced expiratory volume
DLCO: diffusing capacity for carbon monoxide
RUL: right upper lobectomy
RML: right middle lobectomy
RLL: right lower lobectomy
LUL: left upper lobectomy
LLL: left lower lobectomy
EIH: exercise-induced hypoxemia
6MWD: 6-minutes walk distance
TUG: timed up and go test
COPD: chronic obstructive pulmonary disease
IP: interstitial pneumonia

Table 4

Results of two-way analysis of variance

Group

Group A (n=14)Group B (n=88)

Main effectperiodbeforesurgery

after
surgery

beforesurgery

after
surgery

Period(p value)Group(p value)

Period ×group(p value)

6MWD (m)441.7 ±
77.7

359.5 ±
64.2

466.8 ±
81.4

421.9 ±
76.1

p<0.001

0.006

0.241

Quadriceps 98.6 ±torque (Nm) 28.2

98.3 ±
28.5

94.3 ±
35.0

91.1 ±
35.6

0.802

0.414

0.841

Group A: patients with supplemental oxygen therapy (n=14).
Group B: patients without supplemental oxygen therapy (n=88).
6MWD: 6-minutes walk distanceInteraction

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Kohji Iwai et al

Fig. 2

Minimum oxygen saturation and walk distance during 6-minute walk distance after surgery
in patients with supplemental oxygen therapy
Fig. 2A: Minimum oxygen saturation
Fig. 2B: Walk distance(Group A, n=14)

DISCUSSION
In our study, supplemental oxygen therapy at discharge was introduced in 14 out of 102
patients (group A, 13.7%). Nicastri et al14 suggested an oxygen therapy induction rate of
15.3%, which is supported by the results of the present study. The comorbidity rates of historyof smoking, COPD, and IP were significantly higher, and %DLCO was significantly lower, inpatients in group A. In addition, the EIH expression rate during the 6MWD prior to surgery
was significantly higher in patients in group A. In other words, in patients with poor pulmonary
function who experience hypoxemia during exertion prior to undergoing surgery, their lung function and oxygenation capacity are further reduced by resection of their lungs, and it is assumed
that there is no choice but to introduce supplemental oxygen therapy. It should be noted thatwhen EIH was observed in patients prior to surgery, the introduction of supplemental oxygentherapy was 46.2-times higher following surgery. A characteristic of oxygen saturation observed
during the 6MWD prior to surgery was that oxygen saturation tended to significantly decreasein the first 2 minutes. Following surgery, the tendency of oxygen saturation to decrease became
worse still. Ueda et al15 demonstrated the importance of preoperative evaluation of hypoxemia in
predicting early postoperative prognosis, and their findings are supported by the present study.
As Irie et al suggested,12 the evaluation of quadriceps torque and 6MWD before and after
lobectomy is important, so we also measured these values in our study. The results of the twoway ANOVA with two factors showed no major effects or interactions for quadriceps torque,but 6MWD had a major effect, although no interactions were observed. Surgical invasion andreduced lung function due to resected lungs are thought to be the cause of reduced exercise
capacity. In a previous report16 it was suggested that exercise capacity improves more rapidly
following VATS, and the reduction rate was just 10% in patients in group B in this study. Thissuggests that pulmonary rehabilitation contributes to the prevention of low exercise capacity.
Although no interactions were observed, the reduction rate was about 19% in patients in group
A; it is speculated that it was more difficult to recover postoperative exercise capacity in patients
who received supplemental oxygen therapy. At the very least, it is clear that the exacerbation of
postoperative hypoxemia is involved.
Following surgery, 6MWD was performed without oxygen inhalation. The next day, 6MWD
was performed again using a quantity of oxygen as determined by the doctor for patients ingroup A, and a comparison was made between the walking distance and the minimum oxygen809
Indication of oxygen therapy after VATS

saturation. As a result, the minimum oxygen saturation was seen to be significantly improved,
but there was no significant difference in walking distance. Walking distance and pulmonary
function during 6MWD were strictly related,17 and oxygen therapy is considered not to supplement poor lung function. For that reason, there was no significant difference in walking distance.
However, oxygen therapy is known to be a technique for supplementing oxygen deficiency,
and the improvement in the minimum oxygen saturation showed that it obtained the desired
effect. Therefore, when hypoxemia is exacerbated after surgery, supplemental oxygen therapy tosupplement oxygen deficiency should be actively introduced. In addition, estimating the predicted
lung function commensurate with the extent of lung resection is helpful in predicting postoperative oxygen therapy.8 As in the present study, preoperative evaluation to predict postoperative
hypoxemia could complement the prediction of postoperative oxygen therapy.
There are some limitations associated with the present study. First, it was performed ata single center, many cases were excluded, and open thoracotomy cases were not included.
Second, differences such as complication rates and length of hospital stay were not examined.
Additionally, the oxygen partial pressure in arterial blood could not be measured following the
introduction of supplemental oxygen therapy. The oxygen partial pressure could be estimatedfrom the oxygen saturation level, but the evaluation of arterial blood oxygen partial pressure
could be more accurate when determining whether to introduce supplemental oxygen therapy.
Third, follow-up studies were not conducted with patients in whom supplemental oxygen therapy
was introduced at the time of discharge but later withdrew from supplemental oxygen therapy.

CONCLUSION
The present study evaluated factors that could be predictive of the need for induction ofoxygen therapy and compared physical functions before and after surgery. EIH prior to surgery
was an independent risk factor for the need to introduce oxygen therapy following surgery.
Furthermore, when 6MWD was performed using oxygen inhalation, the minimum oxygen
saturation was significantly improved. Therefore, when hypoxemia is exacerbated after surgery,oxygen therapy should be introduced. Our results demonstrate that preoperative evaluation ofpatients prior to them undergoing VATS is important and could complement the prediction of
postoperative need for oxygen therapy.

CONFLICT OF INTEREST
None of the authors have any conflicts of interest to disclose.

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