anaesthesia and obesity in caesarean elective

7/28/2019 Anaesthesia and Obesity in Caesarean Elective

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Impact of spinal anaesthesia and obesity on maternal

respiratory function during elective Caesarean section*

B. S. von Ungern-Sternberg,1

A. Regli,1

E. Bucher,1

A. Reber2

and M. C. Schneider3

1 Senior Registrar, 3 Associate Professor & Head of Obstetric Anaesthesia, Department of Anaesthesia, University of

BaselKantonsspital, CH 4031 Basel, Switzerland

2 Associate Professor & Head, Department of Anaesthesia and Intensive Care Medicine, Hospital of Zollikerberg,

CH 8125 Zollikerberg, Switzerland

Summary

Spinal anaesthesia for Caesarean section has gained widespread acceptance. We assessed the impact

of spinal anaesthesia and body mass index (BMI) on spirometric performance. In this prospective

study, we consecutively assessed 71 consenting parturients receiving spinal anaesthesia with hyp-

erbaric bupivacaine and fentanyl for elective Caesarean section. We performed spirometry during

the antepartum visit (baseline), immediately after spinal anaesthesia, 1020 min, 1 h, 2 h after the

operation, and after mobilisation (3 h). Baseline values were within normal ranges. There was a

significant decrease in all spirometric parameters after effective spinal anaesthesia that persisted

throughout the study period. The decrease in respiratory function was significantly greater in obese

(BMI > 30 kg.m)2) than in normal-weight parturients (BMI < 25 kg.m)2), e.g. median (IQR)

vital capacity directly after spinal anaesthesia; )24 ()16 to )31)% vs. )11 ()6 to )16)%, p < 0.001

and recovery was significantly slower. We conclude that both spinal anaesthesia and obesity

significantly impair respiratory function in parturients.

Keywords Anaesthesia; obstetric. Anaesthesia, spinal. Complications; obesity.

Respiratory physiology.

........................................................................................................

Correspondence to: Dr Britta von Ungern-Sternberg

E-mail: [email protected]*Presented in part at the European Society of Anaesthesiologists

Annual Meeting, Glasgow; June, 2003.

Accepted: 7 April 2004

For the majority of anaesthetists, spinal anaesthesia (SA)

has become the preferred anaesthetic technique for

elective Caesarean section. SA has a higher anaesthetic

success rate than epidural anaesthesia [1] and reduces the

potential for maternal morbidity and mortality related to

airway complications associated with general anaesthesia

[2]. Despite some degree of motor blockade, SA has onlya slight effect on spirometric volumes in normal weight,

non-pregnant patients because of diaphragmatic compen-

sation acting as a counterbalancing mechanism; SA is

associated with a slight decrease in vital capacity (VC) of

about 10% in normal weight patients [3, 4]. However,

this may differ in obese individuals, as SA tends to

decrease lung volumes to a greater extent in these

individuals than in normal weight, non-pregnant patients

[5]. Furthermore, obesity has a significant impact on the

respiratory function of non-pregnant patients undergoing

breast surgery or lower abdominal laparotomy, as indica-

ted by a mean decrease in VC of 40% (SD 19%) in obese

(BMI > 30 kg.m)2) vs. 12% (SD 7%) in normal weight

(BMI < 25 kg.m)2) patients following general anaesthesia

[6]. In industrial countries, there has been an increase in

the prevalence of obesity in the general population as wellas in pregnant women [7]. As pregnancy itself is associated

with many changes in respiration that also impinge on

respiratory function [8], obese pregnant women are

likely to be at an increased risk of impaired respiratory

function. In particular, the cephalic shift of the diaphragm

caused by the expanding uterus is enhanced in the

presence of obesity and jeopardises pulmonary gas

exchange by a marked reduction in functional residual

capacity [9] and a simultaneous rise in closing volume that

Anaesthesia, 2004, 59, pages 743749.....................................................................................................................................................................................................................

2004 Blackwell Publishing Ltd 743


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may exceed functional residual capacity in about 50% of

pregnant women. This predisposes to airway closure in

the normal tidal volume breathing range [10]. Therefore,

we hypothesised that obese parturients would have a

significantly greater decrease in spirometric volumes than

normal weight parturients following SA and a slower

recovery of respiratory function.

Methods

Following approval by the Ethics Committee of the

University of Basel, Switzerland, and after obtaining

written informed consent, we consecutively assessed 71

healthy (ASA physical status III) parturients with term

pregnancies (3642 weeks gestation) in this prospective

study. Exclusion criteria were bronchial asthma requiring

regular therapy, cardiac problems associated with dys-

pnoea or severe psychiatric disorder. Parturients had to be

free of pain to be included in this study. This was definedas a score of 20 mm on a 100 mm visual analogue

scale (VAS, where 0 mm represented no pain and

100 mm the worst possible pain).

For spirometric measurements, we used a Vitalograph

2120 (Vitalograph, Hamburg, Germany). We standard-

ised the spirometric assessments with each parturient in

a 30 head-up position and in the absence of pain

(VAS 20 mm). After a thorough demonstration of the

correct usage of the device, we measured VC, forced vital

capacity (FVC), forced expiratory volume in 1 s (FEV1),

peak expiratory flow rate (PEFR) and mid-expiratory

flow (MEF25)75) and calculated the FEV1FVC ratio. We

performed spirometry at least three times to meet the

criteria of reproducibility as defined by the European

Respiratory Society [11] and recorded the best measure-

ment for further analysis. At the antepartum assessment,

we measured the weight and height of each parturient to

obtain their BMI. The antepartum spirometric assessment

was used as baseline value (M0).

Patients received intravenous ranitidine 50 mg and

metoclopramide 10 mg 60 min before the operation and

30 ml 0.3 M oral sodium citrate immediately before

transfer to the operating theatre. We performed SA

according to our routine using a 25-G pencil point

needle. After identifying the subarachnoid space at theL3L4 or L2L3 interspace with the parturient lying in the

right lateral position, we administered 0.5% hyperbaric

bupivacaine 12.5 mg with fentanyl 10 lg. Thereafter, the

parturient was turned on her back and left lateral uterine

displacement was achieved by a wedge placed under the

right hip and a 10 tilt of the operating table to the left.

We assessed the level of sensory blockade using an ethyl

chloride spray. As soon as the sensory level was above T5,

we passively moved the parturient into a 30 head-up

position in order to prevent cephalic spread of local

anaesthetic and performed the second spirometric assess-

ment (M1).

For postoperative pain relief, we gave intravenous

increments of methadone 2 mg to achieve a VAS pain

score of 20 mm while coughing. The total dose of

methadone given to each patient was neither limited nor

weight adjusted. Basic analgesia consisted of paracetamol

1000 mg rectally directly after the operation. We did not

administer any local anaesthetic into the wound.

As soon as a VAS pain score of 20 mm was

achieved, spirometry was performed for the third time

(about 1020 min after the operation, M2). Spirometric

measurements were repeated 1 h (M3), 2 h (M4) and 3 h

(after mobilisation, M5) after the operation and the

cumulative methadone requirement was recorded at each

assessment. Prior to the last measurement (M5), the

parturients were mobilised out of bed and encouraged to

walk a few steps in the recovery area (all about 5 min).We performed the last spirometric assessment (M 5) again

i n a 30 head-up position to assess the influence of

mobilisation on spirometric volumes. However, we did

not measure spirometric volumes directly before and after

mobilisation in order not to interfere disproportionately

with the process of early bonding between the mother

and her newborn.

To allow comparison of the parturients, the spirometric

values were calculated as percentage change from the

baseline value measured pre-operatively (M0). For statis-

tical analysis, a repeated-measures analysis of variance

(ANOVA) was used. We used a Wilcoxon rank sum test to

compare measurements between the BMI groups

(BMI < 25, 2530, > 30 kg.m)2). For post hoc compar-

isons, a Bonferroni test was used. The Spearman rank

correlation test was used to assess the relationship between

spirometric measurements and BMI. A p-value of < 0.05

was considered significant. For statistical calculations, we

used STAT VIEW FOR WINDOWS (SAS Institute Inc., Cary,

NC, Version 5.0.1).

Results

Seventy-one parturients were included in this study: of

these, six (9%) declined to continue and 65 successfullycompleted the study. Seven parturients (11%) were occa-

sional to moderate smokers (< 10 cigarettes per day) and

three (5%) were ex-smokers who stopped smoking before

becoming pregnant. The majority of parturients (n = 55;

85%) had been non-smokers all their lives. Patient char-

acteristics and obstetric details are summarised in Table 1.

Surgical anaesthesia was achieved in all parturients with

a median (IQR [range]) upper sensory level of T4 (T3T5[T2T5] ) a t M1. Postoperatively, the assessed median

B. S. von Ungern-Sternberg et al. Spin al anaes th es ia and o besity in Caesarean s ecti on An aesthesi a, 20 04, 59, pages 743749......................................................................................................................................................................................................................

744 2004 Blackwell Publishing Ltd


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upper sensory levels for different times of spirometry were

as follows: T5 (T3T7 [T2T12]), T8 (T5T11 [T3L5])

and T12 (T9L3 [T6none]) 20 min (M2), 1 h (M3) and

2 h (M4), respectively, after Caesarean section. There was

no residual sensory level 3 h after the operation (after

mobilisation, M5). The mean duration of surgery was 53

(SD 10) min.

In all parturients, spirometric values were all within

normal ranges. However, there was a significant

decrease in all spirometric parameters after effective

SA (Table 2). VC decreased significantly more in the

obese (BMI > 30 kg.m)2) than in normal-weight par-

turients (BMI < 25 kg.m)2) (Table 3). This decrease

persisted over the whole observation period. FVC and

FEV1 changed in parallel with VC, but both PEFR and

MEF25-75 showed a significantly greater reduction and

slower recovery than the other parameters (Table 2).

The FEV1FVC ratio was not affected by SA and

remained unchanged throughout the observation per-

iod. Three hours after the operation and after patient

mobilisation, baseline conditions of spirometric values

had not been re-established in any of the BMI groups

of parturients (Tables 3 and 4). At each assessment

following SA and Caesarean section, there was a

significant negative correlation between BMI and the

spirometric parameters (Table 5).

No intravenous methadone was necessary for any

parturient during or directly after the operation. The

amount of methadone (median (IQR [range])), given

Table 1 Characteristics of parturients (n = 65). Values aremedian (interquartile range [range]) or number (%).

Age; year 32 (2539 [2040])

Body mass index

Before pregnancy 24 (1830 [1741])

Term pregnancy 30 (2338 [2150])

Gestation; weeks 39 (3840 [3642])Primigravida multigravida 28 (43%) 37 (57%)

Table 2 Results of spirometry in parturients receiving spinal anaesthesia for elective caesarean section. Absolute values and changes ofvital capacity (VC), forced vital capacity (FVC), forced expiratory volumes in 1 s (FEV 1, peak expiratory flow rate (PEFR) and mid-expiratory flow (MEF25)75). Values are median (IQR) or % decrease of preoperative value. All changes were statistically significantcompared with baseline values (repeated measure ANOVA, p < 0.001).

Parameters

VC [I] FVC [I] FEV1 [I] PEFR [I.min)1] MEF25)75[I.s)1]

Pre-operative; M0 3.4 (2.74.1) 3.2 (2.53.9) 2.9 (2.33.6) 389 (326452) 4.1 (3.54.7)

After SA; M1 2.8 (2.23.4) 2.7 (2.03.4) 2.4 (1.82.9) 266 (201332) 2.9 (2.23.5)

% decrease from M0 18 (727) 17 (727) 18 (630) 30 (1743) 29 (1643)

After surgery; M2 2.7 (2.03.4) 2.6 (1.93.3) 2.4 (1.73.0) 276 (207346) 2.9 (2.13.7)% decrease from M0 18 (333) 17 (233) 18 (334) 28 (1641) 28 (1541)

1 h; M3 2.8 (2.03.6) 2.6 (1.83.4) 2.3 (1.63.1) 271 (200341) 2.9 (2.23.6)

% decrease from M0 17 (034) 18 (035) 19 (038) 29 (1641) 29 (1641)

2 h; M4 2.7 (2.03.5) 2.7 (1.93.4) 2.4 (1.73.0) 278 (210347) 2.9 (2.23.6)

% decrease from M0 17 (233) 17 (231) 18 (235) 27 (1637) 25 (1436)

After mobilisation/3 h; M5 2.8 (2.13.6) 2.8 (2.03.5) 2.4 (1.73.1) 281 (210350) 3.0 (2.23.8)

% decrease from M0 14 (029) 16 (131) 17 (133) 26 (1239) 25 (1040)

Table 3 Results of vital capacity inparturients receiving spinal anaesthesiafor elective caesarean section accordingto body mass index (BMI). Values aremedian (IQR) or % decrease of pre-

operative value. All changes to baselinewere significant (repeated measureANOVA), the significances of all valuesbetween BMI < 25 and >30 (Wilcoxonsigned rank test) are indicated(* = significant, n.s. = not significant),p < 0.001.

BMI; kg.m)2

Vital capacity

30 (n = 34) 30

Pre-operative M0

3.4 (3.03.7) 3.4 (2.84.0) 3.3 (2.54.1) n.s.After SA*; M1 3.0 (2.93.1) 2.8 (2.33.3) 2.5 (1.93.1) *

% decrease from M0 11 (616) 15 (1120) 24 (1631) *

After surgery; M2 3.1 (2.73.4) 2.9 (2.53.3) 2.5 (1.93.0) *

% decrease from M0 8 (218) 15 (821) 27 (1540) *

l h; M3 3.1 (2.93.4) 2.9 (2.43.4) 2.4 (1.83.0) *

% decrease from M0 9 (315) 14 (820) 28 (1541) *

2 h; M4 3.2 (2.93.6) 3 (2.53 .4) 2.4 (1.83.0) *

% decrease from M0 6 (310) 14 (920) 27 (1639) *

After mobilisation (3 h); M5 3.3 (3.03.6) 3 (2.43 .7) 2.5 (2.03.0) *

% decrease from M0 4 (29) 12 (717) 23 (1135) *

*SA, spinal anaesthesia.

Anaesthesia, 2004, 59, pages 743749 B. S. von Ungern-Sternberg et al. Spinal anaesthesia and obesity in Caesarean section......................................................................................................................................................................................................................



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intravenously was 0 (00 [04]) mg during the first hour

after the operation, 6 (210 [210]) mg between the first

and second hour, and 6 (3.58.5 [412]) mg between the

second and third hour. This added up to a total dose of

methadone of 12 (816 [820]) mg over the entire

observation period. All parturients maintained an arterial

oxygen saturation of 97%.

Discussion

Obese parturients presenting for Caesarean section have a

high risk of anaesthetic and obstetric complications that

contribute to peri-operative morbidity and mortality.

Although these parturients are particularly at risk forpulmonary complications resulting from changes induced

by pregnancy and obesity, there are no reported

controlled trials on the impairment of peri-operative

respiratory function in this subgroup. There are some

reports on the respiratory effects of SA and epidural

anaesthesia for Caesarean section in normal weight

parturients [1216], and only a small study on the effect

of SA in obese, albeit non-pregnant, patients [5]. Thus,

the present prospective study was designed to evaluate

both normal weight and obese parturients scheduled for

elective Caesarean section.

In our study, baseline spirometric values were all

within normal ranges for normal weight as well as obese

parturients. Not unexpectedly, there were no signs of

airway obstruction during the whole study period, as the

FEV1FVC ratio is not or only minimally influenced byobesity [6] and apparently by SA. Following institution of

SA, the decrease in VC observed in parturients with a

normal BMI was comparable to findings reported in

other studies [3, 4, 1214], whereas VC values were

significantly lower in those with a BMI > 30 kg.m)2

()11% vs. )24%) (Table 3). A significant negative

correlation between spirometric parameters and the

BMI persisted throughout the study (Table 5). Any

calculation of BMI values in parturients is somewhat

arbitrary, as the overweight of a parturient is partly

attributable to surplus body water content, the weight of

the foetus plus the hydramnion, and not solely due to

excess adipose tissue. This puts intrinsic limitations on

any straightforward comparison with non-pregnant obese

individuals. Nevertheless, we used the common BMI

categories as we still consider this parameter to be the

most reliable for evaluating the influence of body

configuration, even those of parturients, on respiratory

mechanics.

During quiet breathing, the diaphragm is the principal

muscle of inspiration, whereas expiration is mainly

passive. In contrast, forced expiration depends on the

muscles of the abdominal wall and to a lesser extent on

the intercostal muscles. SA with an upper sensory level of

up to T4 for elective Caesarean section induces muscleparalysis of the abdominal and intercostal muscles.

This muscle paralysis is associated with a reduction in

abdominal resistance that allows, at least in normal-

weight, non-pregnant women, the diaphragm to move

more easily during inspiration to compensate for the loss

in lung volumes attributable to SA [3]. However, this

compensatory mechanism is not fully effective during

pregnancy and is likely to be abolished by obesity. There

is another explanation for the reduction in respiratory

Table 4 Effect of mobilisation on vitalcapacity (VC), forced vital capacity(FVC), forced expiratory volume in 1 s(FEV1), mid-expiratory flow(MEF25)75) and peak expiratory flowrate (PEFR) on parturients withBMI < 25 (n = 9) vs. BMI > 30

(n = 34). Values are % decrease ofpre-operative value, median (IQR).Statistical significance (p-value) withinthe groups as determined by repeated-measures analysis of variance.

Body mass index

30

At 2 h

At 3 h/after

mobilisation p-value At 2 h

At 3 h/after

mobilisation p-value

VC 6 (310) 4 (29) 0.0052 27 (1639) 23 (1135)


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performance that we observed in obese parturients.

Obesity predisposes to the formation of atelectasis per se

and even more so after anaesthesia [17], further contri-

buting to postoperative compromise of respiratory func-

tion. Hypothetically, the delayed recovery from the

impaired respiratory function associated with SA and

Caesarean section could be caused by recumbency,

surgical manipulations during Caesarean section, and

peri-operative volume shifts, all of which contribute to

changes brought about by pregnancy, obesity and SA

and ultimately result in a marked reduction of ventilated

lung tissue.

Interestingly, there was no significant difference

between the spirometric values obtained before and after

delivery of the baby as assessed postoperatively, although

this should have enabled the diaphragm to move more

easily. The reduction in VC measured 3 h after Caesarean

section following full recovery from SA was primarily

related to the BMI as a predictive factor for postoperativeatelectasis formation and not to other factors interfering

with spontaneous respiration, such as postoperative pain.

This study emphasises the importance of early mobil-

isation as a powerful measure to restore lung volumes;

respiratory function only improved after mobilisation.

Although this improvement might be partially due to

the natural time course, as the impairment following

SA might eventually resolve by itself, we consider

mobilisation the main cause of improvement of respir-

atory function. But to determine the exact cause of this

improvement of lung volumes, a direct comparison

between lung volumes measured immediately before

and after mobilisation would be necessary. We observed

no improvement of lung volumes following SA until the

parturients were mobilised; there was no difference in VC

values determined immediately after SA (M1) and 2 h

after Caesarean section (M4), despite quite different

sensory block levels (median T4 at M1 and T12 at M4).

Although a high sensory block (T4) might be expected to

be accompanied by a higher degree of lung volume

impairment compared with a lower sensory level (T12),

which theoretically should only minimally influence lung

volumes (especially as motor blockade tends to be even

lower than the sensory level), respiratory function did not

correlate with the level of SA in the postoperative period.Improvement of lung volumes was only achieved after

mobilisation of the parturients, especially in the obese,

in spite of the continuous regression of the motor block

during the observation period.

Out of bed mobilisation presumably resulted in

reopening of some atelectasis, thereby recruiting lung

tissue for effective gas exchange. All parturients had an

arterial oxygen saturation of 97% during the entire

observation period, while receiving oxygen 2 l.min)1 via

nasal cannula. Three hours after the operation, there was a

small but significant improvement in all spirometric

parameters with the exception of FEV1 in normal weight

parturients. This is in contrast to a previous study [12] in

which MEF25)75 decreased by a further 10% from )18%

after 2 h following Caesarean section to )28% after

4 h. This difference may be the result of variations in

postoperative pain levels that increased from a mean (SD)

of 33 (4.5) after 2 h to 47 (3.6) after 4 h, despite access to

patient controlled analgesia (PCA) morphine [12].

Because pain interferes with respiration by limiting

maximum respiratory effort, it is crucial for the parturient

to be free of pain while performing spirometry so she is as

close to pre-operative baseline conditions as possible. In

our study, there was a maximum VAS pain score of

20 mm during coughing. This difference can also be

explained by the use of a different analgesic regimen. In

our study a combination of intravenous methadone (6 mg

after 2 h), spinal fentanyl and rectal paracetamol was used,compared with PCA morphine (8 mg after 2 h), which

was used alone in the other study [12]. We cannot

exclude the possibility that mothers did not use enough

PCA for fear of adverse effects on the newborn through

breast-feeding.

Initiation of effective SA was associated with a decrease

in spirometric parameters with the greatest decrease

observed in PEFR ()30%) and MEF25)75 ()29%)

values. These findings are in line with previous studies

[3, 4, 1214]. Because MEF25)75 values do not depend on

patient co-operation and are comparable with PEFR

values, the marked decrease observed in our study was

attributable to SA and not to poor patient performance.

To produce an effective cough, the patient has to inspire

deeply, close the glottis, and increase the intrapulmonary

pressure. Functional integrity of abdominal muscles is

considered very important in cough generation [13, 18]

and PEFR is a good indicator of cough effectiveness

[15, 19]. During the entire study period of 3 h, PEFR

values were significantly decreased in all parturients and

the decrease in PEFR persisted after full resolution of SA

and patient mobilization. Three hours after Caesarean

section, the reduction in PEFR was still more pro-

nounced in parturients with a BMI of > 30 kg.m)2 than

in those with a normal weight ()

34% vs.)

17%). This isimportant, as vomiting in the supine position can lead to

aspiration even in the conscious patient with competent

laryngeal reflexes [20]. Deficiency in cough effectiveness

thus adds another dimension to the high-risk profile

observed in obese parturients presenting for Caesarean

section. Therefore, it is imperative to implement an

antacid regimen pre-operatively to reduce the risk of

pulmonary acid aspiration syndrome. In our study, no

case of aspiration was noted.




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In contrast to the above findings that indicate an

overall impairment of respiratory function following SA,

we observed in a previous study that low-dose epidural

analgesia during labour resulted in a small but significant

improvement of respiratory function after initiation

of effective epidural analgesia (VC + 7%) [21]. We

hypothesised that a reduction in abdominal wall tension

in the absence of intercostal muscle blockade would

result in a decrease of diaphragmatic strain and thus ease

breathing [21]. In the present study, however, the

density and extent of motor blockade was much greater

after SA using bupivacaine 0.5% than after epidural

analgesia using a mixture of bupivacaine 0.125% and

fentanyl. In addition, the upper sensory block level

was much higher after SA than after epidural analgesia

(T4 vs. T8).

We have also found that the BMI-dependency of

respiratory function occurred following vertical laparot-

omy while evaluating different peri-operative analgesicregimens: epidural analgesia significantly improved lung

volumes following surgery compared with systemic

opioids, especially in the obese (unpublished observa-

tions). Therefore, obese parturients might further benefit

from a combined spinal-epidural anaesthetic technique,

with epidural analgesia following Caesarean section to

further improve maternal pulmonary function during the

immediate postoperative period.

We conclude that spinal anaesthesia in parturients

scheduled for Caesarean section was associated with a

BMI-dependent decrease of lung function, which per-

sisted well into the recovery period, even longer than the

actual presence of motor blockade. Sensory levels of SA

did not correlate with lung volume impairment in the

postoperative period. Although a direct comparison of

lung volumes before and after mobilisation was not

carried out, early out of bed mobilisation was most

probably the reason for the significant improvement of

lung volumes 3 h after the operation. This beneficial

effect on the recovery of respiratory function was present

in all parturients, but even more so in the obese. In

normal weight parturients, the decrease in respiratory

function was minor and baseline values were almost

re-established 3 h after Caesarean section and mobilisa-

tion. In contrast, impairment of pulmonary functionpersisted in obese parturients for a longer period despite

mobilisation.

Acknowledgements

The authors are indebted to the recovery room nurses for

their great help. The authors also thank J. Etlinger for

editorial assistance.

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