General Anaesthesia – the Reducing Atelectasis during

60 Pages·2013·1.11 MB·English

by  Jesper Andersson

Digital Comprehensive Summaries of Uppsala Dissertations
from the Faculty of Medicine 954
Reducing Atelectasis during
General Anaesthesia – the
Importance of Oxygen
Concentration, End-Expiratory
Pressure and Patient Factors
A Clinical Study Exploring the Prevention
of Atelectasis in Adults
LENNART EDMARK
ACTA
UNIVERSITATIS
ISSN 1651-6206
UPSALIENSIS
ISBN 978-91-554-8808-6
UPPSALA
urn:nbn:se:uu:diva-209714
2013
Dissertation presented at Uppsala University to be publicly examined in Vårdskolans aula,
Ingång 21, Västmanlands sjukhus Västerås, Västerås, Wednesday, 18 December 2013 at
13:00 for the degree of Doctor of Philosophy (Faculty of Medicine). The examination will
be conducted in Swedish. Faculty examiner: Professor emeritus Sten Lindahl (Karolinska
institutet, Institutionen för fysiologi och farmakologi).
Abstract
Edmark, L. 2013. Reducing Atelectasis during General Anaesthesia – the Importance of
Oxygen Concentration, End-Expiratory Pressure and Patient Factors. A Clinical Study
Exploring the Prevention of Atelectasis in Adults. Digital Comprehensive Summaries of
Uppsala Dissertations from the Faculty of Medicine 954. 59 pp. Uppsala: Acta Universitatis
Upsaliensis. ISBN 978-91-554-8808-6.
Background: The use of pure oxygen during preoxygenation and induction of general
anaesthesia is a major cause of atelectasis. The interaction between reduced lung volume,
resulting in airway closure, and varying inspiratory fractions of oxygen (FO) in determining
I 2
the risk of developing atelectasis is still obscure.
Methods: In this thesis, computed tomography (in studies I and II during anaesthesia, in
studies III and IV postoperatively) was used to investigate the area of atelectasis in relation
to FO and varying levels of continuous positive airway pressure (CPAP) or positive end-
I 2
expiratory pressure (PEEP).
Study I investigated the short-term influence of reducing FO during preoxygenation and
I 2
induction of general anaesthesia, and the time to hypoxia during apnoea.
Study II focused on the long-term effect of an FO of 0.8 for preoxygenation.
I 2
Study III applied CPAP/PEEP with an FO of 1.0 or 0.8 for pre- and postoxygenation until
I 2
extubation. After extubation, CPAP with an FO of 0.3 was applied before the end of mask
I 2
ventilation.
Study IV compared two groups given CPAP/PEEP during anaesthesia and an FO of 1.0 or
I 2
0.3 during postoxygenation, but without CPAP after extubation.
Results: Study I showed a reduction in atelectasis with an FO of 0.8 or 0.6, compared
I 2
with 1.0, but the time to hypoxia decreased. In study II, atelectasis evolved gradually after
preoxygenation. In study III, atelectasis was reduced with an FO of 1.0 and CPAP/PEEP
I 2
compared with an FO of 1.0 without CPAP/PEEP. The intervention failed in the group given
I 2
an FO of 0.8, this group had more smokers. Atelectasis and age were correlated. In study IV,
I 2
no difference was found between the groups. Post hoc analysis showed that smoking and ASA
class increased the risk for atelectasis.
Conclusion, the effect of reducing FO during preoxygenation to prevent atelectasis might
I 2
be short-lived. A lower FO shortened the time to the appearance of hypoxia. Increasing lung
I 2
volume by using CPAP/PEEP also decreased the risk of atelectasis, but the method might fail;
for example in patients who are heavy smokers. In older patients care must be taken to reduce
a high FO before ending CPAP.
I 2
Keywords: Anaesthesia, general. Lung: Atelectasis; CPAP; Oxygen; PEEP; Ventilation,
mechanical; Tomography, X-ray computed.
Lennart Edmark, Centre for Clinical Research, County of Västmanland, Centrallasarettet,
Uppsala University, SE-72189 Västerås, Sweden. Department of Medical Sciences, Clinical
Physiology, Akademiska sjukhuset, Uppsala University, SE-75185 Uppsala, Sweden.
© Lennart Edmark 2013
ISSN 1651-6206
ISBN 978-91-554-8808-6
urn:nbn:se:uu:diva-209714 (http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-209714)
To my parents Roland and Bergljot
And to my daughter Emma

List of Papers
This thesis is based on the following papers, which are referred to in the text
by their Roman numerals.

I. Edmark, L., Kostova-Aherdan, K., Enlund, M., Hedenstierna, G. (2003)
Optimal oxygen concentration during induction of general anesthesia.
Anesthesiology, 98:28-33.

II. Edmark, L., Auner U., Enlund, M., Östberg E., Hedenstierna G. (2011)
Oxygen concentration and characteristics of progressive atelectasis
formation during anaesthesia. Acta Anaesthesiol Scand., 55(1):75-81.

III. Edmark L., Auner U., Hallén J., Lassinantti-Olowsson L., Hedenstierna
G., Enlund M. Reduction in postoperative atelectasis by continuous
positive airway pressure and low oxygen concentration after
endotracheal extubation. In manuscript.

IV. Edmark L., Auner U., Lindbäck J., Enlund M., Hedenstierna G.
Atelectasis after anaesthesia: a randomised trial of positive airway pres-
sure and low oxygen. Submitted.

Reprints were made with permission from the respective publishers.

Contents
Introduction ................................................................................................... 11

Aims of the studies ........................................................................................ 15

Materials and Methods .................................................................................. 17

Patients ...................................................................................................... 17

Apparatus and monitoring ........................................................................ 17

Anaesthesia ............................................................................................... 18

Ventilation ................................................................................................ 18

Duration of apnoea without desaturation (DAWD) ................................. 20

Computed Tomography of the lungs ........................................................ 20

Arterial Oxygenation ................................................................................ 21

Statistical analysis ..................................................................................... 21

Keeping track of time ............................................................................... 22

Results ........................................................................................................... 23

General ...................................................................................................... 23

Duration of apnoea without desaturation (DAWD) ................................. 24

Computed Tomography of the lungs and the area of atelectasis .............. 24

Oxygenation .............................................................................................. 28

Post hoc analysis of pooled data from studies I-IV .................................. 29

Discussion ..................................................................................................... 33

Duration of apnoea without desaturation (DAWD) ................................. 33

Methodological consideration: Why a short duration of
preoxygenation? ................................................................................... 33

Computed Tomography of the lungs and the area of atelectasis .............. 34

The area of atelectasis in the basal CT scans, general observations
from study I-II ...................................................................................... 34

How did the investigation of atelectasis and DAWD in the same
occasion in study I affect the comparisons between the early (study
I) and late 80 % group (study II)? ....................................................... 35

Is there a window of opportunity? ....................................................... 37

The area of atelectasis in the basal CT scans, general observations
from study III ........................................................................................ 38

The area of atelectasis in the basal CT scans, general observations
from study IV ........................................................................................ 39
More on the topic of lung volumes and small airway closure .................. 39

The end-expiratory lung volume and airway closure .......................... 39

The missing links .................................................................................. 40

Patient factors ........................................................................................... 41

Age and atelectasis .............................................................................. 41

Age and the duration of preoxygenation .............................................. 41

Age and CPAP/PEEP .......................................................................... 42

Smoking and atelectasis ....................................................................... 43

Comments on the post hoc analysis of pooled data from studies I-IV ..... 45

Can lessons be learned from outliers? ...................................................... 45

Oxygenation .............................................................................................. 46

SpO as an oxygenation index and correlation to atelectasis .............. 46

2
SpO as an oxygenation index perioperatively .................................... 47

2
Clinical implications ................................................................................. 49

Conclusions ................................................................................................... 51

Acknowledgements ....................................................................................... 53

References ..................................................................................................... 55
Abbreviations

ASA American Society of Anesthesiologists physical status
BMI Body mass index (calculated as weight/(height in meters)2)
CC, CV Closing capacity, closing volume
COPD Chronic obstructive pulmonary disease
CPAP Continuous positive airway pressure
CT Computed tomography
DAWD Duration of apnoea without desaturation
EELV End expiratory lung volume
ERV Expiratory reserve volume
F O Fraction of end tidal oxygen
ET 2
FO Fraction of inspired oxygen
I 2
FRC Functional residual capacity
HPV Hypoxic pulmonary vasoconstriction
HU Hounsfield unit
IBW Ideal body weight
PCV Pressure controlled ventilation
PEEP Positive end expiratory pressure
PSV Pressure support ventilation
RM Recruitment manoeuvre
RV Residual volume
SpO Peripheral arterial oxygen saturation
2
TCI Target control infusion
TIVA Total intravenous anaesthesia
V Alveolar minute ventilation
A
V /Q Alveolar ventilation/perfusion ratio
A
VCV Volume controlled ventilation
V Tidal volume
T
Q Perfusion
ZEEP Zero end expiratory pressure
Preface
The first two studies in this thesis were conceived more than ten years ago,
although the second study was published only recently. These two studies
were relevant at the time they were designed. However, when the opportuni-
ty to expand the research focus arose, the ever changing nature of science
and knowledge, as well as a little bit on a personal level, made the last two
studies turn in what might appear as quite a new direction. Therefore, it may
seem that the two parts come from different perspectives. However, from
different angles these studies tell a common story, and put together a main
theme emerges.