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CJRT RCTR
Canadian Journal of Respiratory Therapy | Journal canadien de la thérapie respiratoire
The journal for respiratory health professionals in Canada Summer | Été 2011
Le journal des professionnels de la santé respiratoire au Canada Volume | Numéro 47.2
FROM THE EDITOR IN CHIEF | MESSAGE DE LA RÉDACTRICE EN CHEF
4... Amy Reid
ORIGINAL ARTICLES | ARTICLES ORIGINAUX (En anglais seulement)
6... Understanding Draw-over Anesthesia
Dale Morrison / Daniel Cashen / Thomas Coonan
11... The Association of Body Mass Index with Airway Obstruction in Non-Asthmatics: Implications for the Inaccurate
Differential Diagnosis of Asthma in Obesity
Andrew J. West / Debbie Burton / Ali Bell
23... Characterizing Obstructive Sleep Apnea and its Management in Paediatric and Adolescent Patients Hospitalized in Canada
Kathy F Spurr / Debra L Morrison / Michael A Graven / Adam Webber / Robert W Gilbert
DIRECTED READING ARTICLE | LECTURE DIRIGÉE (En anglais seulement)
29... Update in Neonatal and Pediatric Mechanical Ventilation: Patient Ventilator Interactions
Mark J Heulitt
ABSTRACTS FROM POSTER PRESENTATIONS | RÉSUMÉS DES PRÉSENTATIONS D’AFFICHES
41... Traumatic Brain Injury: Alternative Management Options | Jessika Beaulieu
Raising a Critical Consciousness for the Reformation of Health Care Culture | Andria Darlington
Comparison of differents gas humidification devices during high frequency oscillatory ventilation (HFOV) | Stéphane Delisle
The Implementation of CASS Endotracheal Tubes at University Health Network (UHN) | Tara Fowler
2009 H1N1 Pandemic: an Evaluation of Planning and Management Strategies | Thomas S. Fudge
Lessons Learned in Rehab: The Evolution of Respiratory Education in Pulmonary Rehabilitation at St. Clare’s | Susan Haskell
Securing endotracheal tubes in neonates: an audit after modification of practice | Julia Infantino
Early Implementation of Non-Invasive Positive Pressure Ventilation in Cardiogenic Pulmonary Edema:
the Effects on Quality of Life, Mechanical Ventilation and Mortality | Kayla Jensen
An Alternative to the Standard Tracheotomy Tube | Marianne MacKenzie
Identifying the Barriers to Clinical Practice for Tracheotomy Weaning and Decannulation of Patients | Marianne Ng
Surgical Care During Recent Crises: What Do The Data Tell Us? | Jason W. Nickerson
Proportional Assist Ventilation (PAV) / Ventilation assistée proportionnelle (VAP) | Misbah Quraishi
The Association of Body Mass Index with Airway Obstruction: Implications for the Inaccurate Differential
Diagnosis of Asthma in Obesity | Andrew West
OFFICIAL JOURNAL OF THE CSRT | SUMMER 2011, VOLUME 47.2
Marketing and Advertising Sales Editor in Chief
For advertising rates and information contact Amy Reid, RRT, FCSRT, CRE
Rita Hansen, Suite 400-331 Cooper St., Ottawa ON, K2P OG5; Hotel Dieu Grace Hospital, Asthma Research Group Inc., Cottam, ON
800-267-3422, ex 223; Fax 613-521-4314; rhansen@csrt.com;
or visit our website at www.csrt.com under “Publications” Associate Editor
Jason Nickerson, RRT, FCSRT, PhD(c), PhD Candidate,
Centre for Global Health, Institute of Population Health,
Subscriptions University of Ottawa, Ottawa ON
CJRT is published four times a year (Spring, Summer, Fall and Winter)
Editorial Board Members
Annual subscriptions are included in annual membership to the CSRT. Wrae Hill, MSc, RRT, FCSRT, BSc
Subscription rate for 2010 for other individuals and institutions within Corporate Director - Quality Improvement & Patient Safety (QIPS),
Canada is $50. International orders are $60 Cdn. All Canadian orders are Interior Health, Canadian Patient Safety Officer - CPSI, Kelowna, BC
subject to 13% HST. Requests for subscriptions and changes of address:
Peter J. Papadakos, MD, FCCM
Membership, CSRT, Suite 400 - rue 331 Cooper St., Ottawa, ON K2P 0G5.
Director, Critical Care Medicine
Professor, Departments Anesthesiology, Surgery and Neurosurgery,
Once published, an article becomes the permanent property of The
University of Rochester, Rochester, New York
Canadian Journal of Respiratory Therapy and may not be published
elsewhere, in whole or in part, without written permission from the Norman H. Tiffin, BSc, RRT, MSA
Canadian Society of Respiratory Therapists. All editorial matter in President, Tiffin Consulting, Chesterfield VA
CJRT represents the opinions of the authors and not necessarily those of Andrea White Markham, RRT, CRE,
The Canadian Journal of Respiratory Therapy, the editors, Editorial Faculty, Respiratory Therapy, Adjunct Lecturer Dalhousie University
Board, the publisher of the journal, or the CSRT. The Canadian Journal of Coordinator PLA, The Michener Institute, Toronto ON
Respiratory Therapy assumes no responsibility or liability for damages
arising from any error or omission of from the use of any information or
advice contained in the CJRT including editorials, articles, reports, book CSRT Board Representative
and video reviews letters and advertisements. Christina Dolgowicz, RRT, FCSRT, CRE, Smiths Falls ON
CSRT Executive Director
Christiane Ménard, Ottawa ON
Managing Editor
Rita Hansen, Ottawa ON
CSRT Board of Directors 2011-2012
President, James McCormick, Ontario
Past-President, Michael Lemphers, British Columbia
President-Elect, Angela Coxe, Ontario
Publications Mail Agreement | No. 40012961
Treasurer, Jeff Dmytrowich, Saskatchewan
Registration No. | 09846
ISSN 0831-2478 BOARD MEMBERS
Return undeliverable Canadian addresses to: Dennis Hunter, Ontario
Suite 400 - 331 Cooper St., Ottawa ON K2P 0G5 Christina Dolgowicz, Ontario
cjrt@csrt.com Cynthia Welton, Ontario
© 2011 Canadian Journal of Respiratory Therapy – all rights reserved Krystle Hong, Alberta
Canadian Journal of Respiratory Therapy SUMMER | ÉTÉ 2011 1
Journal canadien de La thérapie respiratoire Volume | Numéro 47.2
Journal OFFICIEL DE LA SCTR | ÉTÉ 2011, NUMÉRO 47.2
Marketing et publicité / Annonces classées Rédacteur-en-Chef
Rita Hansen, Suite 400- rue 331 Cooper., Ottawa ON, K2P 0G5; Amy Reid, RRT, FCSRT, CRE
800-267-3422, poste 223; Courriel 613-521-4314; rhansen@csrt.com; ou Hôpital Hôtel Dieu Grace, Asthma Research Group Inc., Cottam (Ont.)
visitez notre site Web: www.csrt.com sous « Publications »
Rédacteur adjoint
Abonnements Jason Nickerson, RRT, FCSRT, PhD(c), candidat au doctorat,
La RCTR paraît 4 fois l’an (en printemps, été, automne et hiver). Institut de recherche sur la santé des populations
Université d’Ottawa, Ottawa (Ont.)
L’abonnement annuel est compris dans la cotisation des membres de
la SCTR. Le tarif annuel d’abonnement pour les non-membres et les Comité de Rédaction
établissements au Canada est de 50 $. Les commandes internationales sont Wrae Hill, MSc, RRT, FCSRT, BSc
60 $ Canadien. La TVH de 13% est ajoutée aux commandes canadiennes. Directeur – Amélioration de la qualité et de la sécurité des patients,
Veuillez faire parvenir les demandes d’abonnement et les changements Interior Health, Agent de la sécurité des patients canadiens
d’adresse à l’adresse suivante: Centre des services aux membres, Institut canadien pour la sécurité des patients, Kelowna (C.-B.)
SCTR, Suite 400 - rue 331 Cooper, Ottawa ON K2P 0G5.
Peter J. Papadakos, MD, FCCM
Dès qu’un article est publié, il devient propriété permanente de Directeur, Médecine des soins intensifs
The Canadian Journal of Respiratory Therapy, et ne peut être publié ail- Professeur, Départements d’anesthésiologie,
leurs, en totalité ou en partie, sans la permission de la Société canadienne de chirurgie et de neurochirurgie,
des thérapeutes respiratoires. Tous les articles à caractère éditorial dans Université de Rochester, Rochester (New York)
le RCTR représentent les opinions de leurs auteurs et n’engagent ni le Norman H. Tiffin, BSc, RRT
Canadian Journal of Respiratory Therapy, ni les rédacteurs ou l’éditeur Président, Tiffin Consulting, Chesterfield VA
de la revue, ni la SCTR. La Revue canadienne de la thérapie respiratoire
décline toute responsabilité civile ou autre quant à toute erreur ou omis- Andrea White Markham, RRT
sion, ou à l’usage de tout conseil ou information fi gurant dans le RCTR et Membre du corps professoral, Thérapie respiratoire,
les éditoriaux, articles, rapports, recensions de livres et de vidéos, lettres et Chargée de cours associée à l’Université de Dalhousie,
publicités y paraissant. Coordinatrice de l’ERA, The Michener Institute, Toronto (Ont.)
Concernant l’adhésion à la SCTR : Représentant du Conseil d’administration de la SCTR
Suite 400 - rue 331 Cooper, Ottawa ON K2P 0G5 Christina Dolgowicz, RRT, FCSRT, CRE, Smiths Falls (Ont.)
800-267-3422 poste 223
Directrice générale de la SCTR
Christiane Ménard, Ottawa (Ont.)
Directrice de la rédaction
Rita Hansen, Ottawa (Ont.)
Conseil d’administration – De mai 2011 à mai 2012
Président, James McCormick, (Ont.)
Courrier de publications | No. 40012961 Ancien président, Michael Lemphers, (C.-B.)
Président désigné, Angela Coxe, (Ont.)
No d’enregistrement | 09846 Trésorier, Jeff Dmytrowich, (Sk.)
ISSN 0831-2478
Retourner toute correspondence ne pouvant être livrée au : Membre du conseil
Suite 400 - rue 331 Cooper, Ottawa ON K2P 0G5 Dennis Hunter, (Ont.)
cjrt@csrt.com
Christina Dolgowicz, (Ont.)
(© 2011 Revue canadienne de thérapie respiratoire – tous droits réservés) Cynthia Welton, (Ont.)
Krystle Hong, (Alb.)
SUMMER | ÉTÉ 2011 Canadian Journal of Respiratory Therapy
2 Volume | Numéro 47.2 Journal canadien de LA thérapie respiratoire
CSRT/CAREstream Student Excellence Award Winners 2011
The CSRT is proud to partner with CAREstream Medical Limited, to provide recognition
to students in the twenty educational programs across Canada. This award recognizes
students in each respiratory therapy program (accredited through the Council on
Accreditation for Respiratory Education) who have successfully completed the
certification examination and have made a substantial achievement as a student.
Congratulations to our winners!
Melissa Field - College of the North Atlantic, NL
Sara Kristin Kohler - New Brunswick Community College (NBCC) - Saint John, NB
Jenny Macdonald - College communautaire du Nouveau-Brunswick (C.C.N.B.), campus Dieppe, NB
Lisa Marie Bates - QEII/Dalhousie School of Health Sciences, NS
Shaun Edgar Lockhart - Vanier College, QC
Nathalie Roberge - Le Collège de Rosemont, QC
Myriam De Serres - Le Cegep de Ste-Foy, QC
Pascal Daigle - Le Cegep de Sherbrooke, QC
Pierre-Marc Doyon - Collège Ellis, QC
Kathleen Larouche - Cegep de Chicoutimi, QC
Ileana Diaz - Algonquin College of Applied Arts and Technology, ON
Pierre Tétrault - La Cite Collegiale-College d’arts appliques et de technologie, ON
Alexandra Brazeau - Canadore College of Applied Arts and Technology, ON
Cindy Hook - Fanshawe College of Applied Arts and Technology, ON
Kyla M. Rubenstein - Conestoga College Institute of Technology and Advanced Learning, ON
John Michaels - The Michener Institute for Applied Health Sciences, ON
Mr. Phucquoc Mai - University of Manitoba-School of Medical Rehabilitation, ON
Calvin Loewen - Northern Alberta Institute of Technology, AB
Chelsea Francis - Southern Alberta Institute of Technology, AB
Emily Chiu - Thompson Rivers University, BC
Message from the Editor-in-Chief
Amy Reid, RRT, FCSRT, CRE
A
s I reflect on the scope and in Paediatric and Adolescent Patients
diversity of presentations at Hospitalized in Canada and reviews the
the CSRT annual Education need for accurate and complete data in
Conference, held in June in Quebec the management of obstructive sleep
City, I was impressed the quality of apena. Dr. Mark Heulitt has prepared a
presentations by respiratory therapists. directed reading on Update in Neonatal
Each year the number of RTs and Pediatric Mechanical Ventilation:
presenting pertinent and progressive Patient Ventilator Interaction. Dr. Heulitt
information grows – a sure sign that provides information to readers on
the respiratory profession is coming the relationship between the two
into its own. controllers involved in patients breathing
As well, we had an outstanding spontaneously on mechanical ventilation,
number of posters presented in two as well as identifying the different types
categories – RT and Student. The of patient-ventilator asynchrony.
judging panel had some lively debates We also present the abstracts from
as we worked towards picking our all 13 poster presentations at the CSRT
winners. Not an easy task with so Education conference, held in Quebec
many high-quality submissions. All posters abstracts are City in June. Congratulations to our two winners – Julia
included in this issue of the CJRT. Infantino for the best RT Poster - Securing Endotracheal
The ever-increasing participation of RTs at this Tubes in Neonates: An Audit After Modification of Practice;
conference is one of the ways we advance our profession. and Thomas Fudge for his Student RT Poster - 2009 H1N1
By actively participating in professional development Pandemic: an Evaluation of Planning and Management
activities we highlight our skills, knowledge and expertise Strategies.
to our peers, other professionals and the public. With yet another successful and informative
I encourage respiratory therapists who presented at conference behind us, we are calling on more respiratory
conference to consider submitting their work to the journal therapists to step into the spotlight. Consider presenting
in the form of a case presentation, literature review or as at the Education Conference next year in Vancouver.
basic research. I would also like to draw your attention The CSRT is issuing a special invitation to respiratory
to the Call for Papers for a special edition of the CJRT. therapists to submit an abstract of a presentation for
Associate Editor, Jason Nickerson will be spear-heading consideration by the program committee. The goal is to
a special issue that will focus on how respiratory therapy have the majority of presentations delivered by respiratory
services are delivered to different patient populations or therapists. We wish to cover all areas of practice and you
in unique settings or circumstances. Details can be found may submit more than one abstract. The deadline is
on page 39. October 31st, 2011. Details can be found on the CSRT
In this issue, Dan Cashen has written a paper, Drawover website. Why not share your expertise and build on your
Anesthesia, where he reviews the challenges of anesthesia in own professional development activities?
unresourced and difficult environments. The Association of As always, I encourage you to submit your manuscripts
Body Mass Index and Airways Obstruction is presented by to the journal for consideration. We have a dynamic tool
Andrew West where he discusses the association between available to disseminate knowledge and provide RTs with
obesity and asthma. Kathy Spurr presents her paper a vehicle to publish their papers. Please feel free to contact
Characterizing Obstructive Sleep Apnea and its Management me at amy.cjrt@gmail.com.
SUMMER | ÉTÉ 2011 Canadian Journal of Respiratory Therapy
4 Volume | Numéro 47.2 Journal canadien de LA thérapie respiratoire
Message de la rédactrice en chef
Amy Reid, RRT, FCSRT, CRE
J
e suis fortement impressionnée par Sleep Apnea and its Management in
la qualité, la portée et la diversité Paediatric and Adolescent Patients
des exposés entendus au congrès Hospitalized in Canada où elle aborde
éducatif annuel tenu cette année à la nécessité de données précises et
Québec en juin. D’année en année, nous complètes pour la gestion de l’apnée
assistons à la croissance du nombre de obstructive du sommeil. Le Dr Mark
thérapeutes respiratoires qui présentent Heulitt a préparé la lecture dirigée
de l’information percutante et évolutive, Update in Neonatal and Pediatric
un signe évident de la maturité de notre Mechanical Ventilation: Patient
profession. Ventilator Interaction. Il fournit au lecteur
En outre, nous avons eu un grand de l’information sur la relation entre
nombre d’affiches provenant des les deux contrôleurs en action dans
thérapeutes respiratoires et des étudiants. la respiration spontanée des patients
Leur évaluation par les juges et le choix soumis à la ventilation mécanique
des lauréats ont certainement suscité un et il présente les différents types
débat animé. La tâche n’a pas été facile d’asynchronisme patient-ventilateur.
devant des présentations d’une si grande Vous pourrez également consulter
qualité. Vous pourrez consulter les résumés des affiches les 13 résumés des affiches qui ont été vues au congrès
dans le présent numéro du JCTR. éducatif de Québec en juin. Nous félicitons les deux
Le nombre croissant de thérapeutes respiratoires lauréats– Julia Infantino pour la meilleure affiches des
participant au congrès nous permet de faire avancer thérapeutes respiratoires - Securing Endotracheal Tubes
la profession. C’est en prenant part aux activités de in Neonates: An Audit After Modification of Practice; et
perfectionnement professionnel que nous mettons en Thomas Fudge pour la meilleure affiche étudiante -
évidence nos aptitudes, nos connaissances et notre expertise 2009 H1N1 Pandemic: an Evaluation of Planning and
à l’intention de nos collègues, des autres spécialistes de la Management Strategies.
santé et du grand public. Au terme d’un autre congrès informatif et réussi,
J’invite les thérapeutes respiratoires qui ont présenté nous faisons appel aux thérapeutes respiratoires : songez
des exposés au congrès à soumettre leur travail au Journal à faire une présentation dans le cadre du Congrès éducatif
sous forme d’un cas, d’une analyse documentaire ou d’une à Vancouver l’an prochain. La SCTR lance une invitation
recherche. Je tiens également à attirer votre attention sur spéciale aux thérapeutes respiratoires, les incitant à
l’invitation à présenter des communications lancée pour un soumettre un résumé d’une présentation aux fins
numéro spécial du Journal. En effet, le rédacteur adjoint d’évaluation par le Comité du programme. Le but consiste
Jason Nickerson s’est chargé d’un numéro qui portera à ce que la majorité des présentations soient données par
sur la façon dont les services de thérapie respiratoire sont des thérapeutes respiratoires. Tous les domaines d’exercice
fournis à différentes populations dans des endroits uniques doivent être abordés et il est possible de soumettre plus
ou des circonstances particulières. Pour de plus amples d’un résumé. La date limite est le 31 octobre 2011. Les
détails, voir la page 40. détails sont affichés sur le site Web de la SCTR. Pourquoi
Dans le présent numéro, Dan Cashen nous présente ne pas partager votre expertise et étoffer l’ampleur de vos
Drawover Anesthesia où il passe en revue les défis de activités de perfectionnement professionnel?
l’anesthésie dans les milieux particuliers où les ressources Comme toujours, je vous encourage à soumettre vos
sont déficientes. Andrew West quant à lui nous propose manuscrits au Journal. C’est un outil puissant de diffusion
The Association of Body Mass Index and Airways Obstruction des connaissances et de publication des articles des
où il examine le lient entre l’obésité et l’asthme. Kathy thérapeutes respiratoires. Si vous avez des commentaires,
Spurr nous offre son article Characterizing Obstructive veuillez communiquer avec moi -amy.cjrt@gmail.com
Canadian Journal of Respiratory Therapy SUMMER | ÉTÉ 2011 5
Journal canadien de La thérapie respiratoire Volume | Numéro 47.2
Original Article
Understanding Draw-over Anesthesia
Dale Morrison, RRT, AA
Daniel Cashen, RRT*
Thomas Coonan, MD, FRCPC
Queen Elizabeth II Health Sciences Centre, Department of Anesthesia, Halifax, Nova Scotia
Abstract Résumé
In the face of recent natural disasters happening around Face à la série de désastres naturels qui ont frappé
the world, the realities of field anesthesia during war time, le monde au cours des dernières années, aux réalités de
and the challenges of anesthesia in unresourced, difficult l’anesthésie en zone de guerre et aux défis de l’anesthésie dans
environments, anesthesia practitioners and respiratory les zones difficiles et faibles en ressources, les praticiens de
therapists face constant challenge. More than ever, health l’anesthésie et les thérapeutes respiratoires sont confrontés
care professionals need to know and understand the à des défis incessants. Plus que jamais, les professionnels de
capabilities and limitations of the equipment needed to la santé doivent connaître et comprendre les capacités et
safely administer an anesthetic. Draw-over anesthesia can les limitations de l’équipement utilisé pour administrer en
be performed without O2, or electricity, and this technology toute sécurité les anesthésiques. L’anesthésie à l’aide d’un
warrants attention and development. vaporisateur de type « draw-over » peut se faire sans O2 ou
sans électricité : cette technologie mérite d’être étudiée et
développée.
Keywords: Draw-over vaporizer, Draw-over anesthesia, Plenum vaporizer, Mots-clés : Évaporateur par les gaz inspirés, Anesthésie par les gaz inspirés,
Oxygen economizer tube, breathing circuit, FiO2 concentration, Non-re- Vaporisateur soufflant, Tube économiseur d’oxygène, circuit respiratoire,
breathing valves. Concentration de FiO2, Valves sans réinspiration.
Introduction the patient. The tubing proximal (upstream) of the vaporizer is
O
verwhelming challenges will confront an anesthesia used to supply a reservoir to which oxygen can be added. The
provider in many developing countries, during delivery tubing distal to the vaporizer transports the mixed
routine operative care, natural disasters, or war. There gas (carrier gas and agent) to the patient. A non-rebreathing
will be no oxygen, no electricity and primitive unserviced valve, fitted to the patient end, allows the patient to inspire
equipment on site. and expire without any rebreathing of carbon dioxide.
Draw-over anesthesia is simply the act of drawing a The common vaporizers used for draw-over anesthesia
carrier gas through a vaporizer and over a volatile liquid, for are the PAC (Portable Anesthesia Complete), EMO (Epstein
the purpose of providing anesthesia. Draw-over anesthesia is Macintosh,Oxford), OMV (Oxford Miniature Vaporizer )
not a new concept: William T.G. Morton used ether and a (Figure 3), and more recently the DDV (Diamedica Draw-
draw-over vaporizer on October 16, 1846, in the first public over Vaporizer). All these systems are still available, however,
demonstration of volatile agent anesthesia.1 Ether was widely all but the DDV are crafted one order at a time. Airflow,
used as a volatile anesthetic in the military from 1846 until drawn through the vaporizer, is determined by the patient’s
the end of World War II, in both plenum (push –over) and tidal volume and respiratory rate. Since anesthesia is
draw-over (pull-over)systems, and a draw-over anesthesia kit maintained by the patient’s efforts, all draw-over vaporizers
can be invaluable as a primary or back up device. Indeed, need to have a low resistance, to accommodate intermittent
many experienced anesthesia volunteers take portable draw- gas flow and large variations in gas flow through the vaporizer.
over epuipment on missions, in anticipation that ingenious The resistance of these vaporizers range from 0.5 – 2 cwp at
technology may fail. 30 L/min. To put this in perspective, a regular continuous
A modern draw-over system consists of a reservoir flow plenum vaporizer (modern day pushover) resistance is
tube, a vaporizer, an oxygen inlet, a delivery tube and a approximately 4cwp/L/min.3
non-rebreathing valve.2 (See Figure 1). Ambient air enters These draw-over vaporizers weigh approximately
the system from the atmosphere due to negative pressure 1.6 – 2.6 Kg, with the exception of the EMO which is
generated by a patients’ spontaneous efforts and is then drawn approximately 10Kg. They maintain their stated accuracy
over the vaporizer to collect anesthetic agent and deliver it to from 1°C, to as high as 50ºC. Most have thermal buffering,
SUMMER | ÉTÉ 2011 Canadian Journal of Respiratory Therapy
6 Volume | Numéro 47.2 Journal canadien de LA thérapie respiratoire
Figure 1: from Eales M, Rowe P, and Tully R, Improving the concentrations are independent of the pattern of ventilation
efficiency of the drawover anaesthetic breathing system, with the OET in place. Without an OET, the performance
Anaesthesia, 2007, 62, pages 1171-1174
of the system is considerably impaired and the final FiO2
concentration depends on flow of O2, minute volume, and
pattern of ventilation.
Using a one metre length of tubing (internal volume of
415 ml) will produce an inspired oxygen concentration of
at least 30% with an O2 inflow rate of 1.0 l/min, and 60%
with 4 l/min, at normal adult ventilation.9 Using a larger
inflow reservoir can be cumbersome. Eales, Rowe and Tully
described a modified reservoir employing a bag (rather than
a tube) to increase the internal volume of the reservoir. They
also added a one-way valve at the inlet of the bag, to prevent
spillage of O2 when using high flow rates, and an adjustable
pressure limiting APL valve (5cwp continuous positive airway
pressure) to prevent excessive pressure developing. (Figure 2)
Such a reservoir permits a predictably high FiO2 when high
minute ventilation is required.2
and the PAC and EMO have thermal compensation.4 These Figure 2: from Eales M, Rowe P, and Tully R, Improving the
are all are acceptable for use as plenum/pushover vaporizers efficiency of the drawover anaesthetic breathing system,
except for the PAC, since it becomes inaccurate when Anaesthesia, 2007, 62, pages 1171-1174
used as a plenum. It is common to use such methodology in
small children.4
When air is mixed with vapour from the vaporizer, it
allows for a potentially “hypoxic mixture” to be delivered
to the patient. This is a theoretical problem rather than a
practical one, as the vapour concentration is small, and it is
unlikely that the inspired oxygen concentration would fall
below 18%, the international standard for oxygen analyser
alarms. This fact notwithstanding, a hypoxic mixture could
ensue as vaporizers are developed to deliver a 7% sevoflurane
mixture. It is far more important to consider the negative
respiratory physiological effects of general anesthesia (with
agents other than diethyl ether), which tend to reduce
ventilation and increase shunting of blood within the lung
(V/Q mismatch). Accordingly, supplemental oxygen should
be included in draw over circuits whenever possible.5 While
there is evidence that normoxia can be maintained in healthy
patients in the presence of controlled ventilation, clinical
anesthesia can cause significant hypoxemia with spontaneous
ventilation (pFigure 3: From Anaesthesia at the District Hospital, 2nd edition, The OIB was designed in the era when Heidbrink – type
Michael B. Dobson, World Health Organization Pg 63 Adjustable Pressure Limiting Valves (APL) were generally
used for anesthesia circuits, rather than non-rebreathing
Clinical use of anaesthetic equipment
valves, and the one way valve (Outlet Valve) that is on the
patient side of the OIB was built into the device to prevent
expired gases from being aspirated retrograde into the bellows.
On the other hand, in present times, when non-rebreathing
valves are employed at the patient end of the circuit, a magnet
must be used to keep the OIB outlet valve open. This is to
allow the pressure on the inlet side of the non-rebreathing
valve to return to atmospheric pressure with the rise of the
bellows, and allow the patient to exhale through the non-
rebreathing valve, out to atmosphere. If a non-rebreathing
valve is used, and the integral one way outlet valve is NOT
disabled by using a magnet, the positive pressure remains on
the inspired side of the nonrebreathing valve and prevents
the patient from exhaling. With each successive inspiration,
pressure within the breathing system increases, eventually
possibly causing barotraumas.12
Laerdal IV, Ambu E1 and Ruben valves, can be used
effectively at the patient end of the draw-over circuit. (See
Fig 4) These valves may become soiled and inoperable during
use. If the inspiratory side sticks open, the patient may be
Figure 4: From Anaesthesia at the District Hospital, 2nd edition,
Fig. 7.7. Breathing systems (OIB, Oxford inflating bellows). Michael B. Dobson, World Health Organization pg 58
an EMO are so rapidly corroded by halothane that a single
filling of an EMO with halothane will destroy the vaporizer.4
The output of sevoflurane from a PAC vaporizer is
between 0.1 and 3.6% (v/v), which would be sufficient for
anesthestic maintenance but inadequate for routine inhalation
induction.10 Two OMV vaporizers in series will deliver from
0.5% to 5.9 %, sevoflurane and this dynamic would seem
a feasible technique for induction and maintenance of
sevoflurane anesthesia.11 Recently, a new Diamedica vaporizer
has been developed that delivers an adequate concentration
(8%) of Sevoflurane.
The introduction of a self inflating bag or bellows,
downstream from the vaporizer, allows for intermittent
positive pressure ventilation. (Fig 3) A one way valve must be
present on the upstream proximal side of the bag, and distal
to the vaporizer, to prevent gas from flowing retrograde into
the vaporizer.
Special mention should be made of the Oxford Inflating
Bellows (OIB). This device remains in widespread use and
consists of a rubber concertina bellows mounted between two
one-way valves, an upstream (inlet) valve and a downstream
(outlet) valve (See figure 3 top schematic). When the bellows
is manually compressed, the inlet valve closes to prevent
retroflow into the vaporizer, and the outlet valve opens to
direct the anesthetic gases towards the patient. On the next
cycle, the bellows is lifted and draws in gas through the inlet valve.
Fig. 2.9. Universal breathing valves.
SUMMER | ÉTÉ 2011 Canadian Journal of Respiratory Therapy
8 Volume | Numéro 47.2 Journal canadien de LA thérapie respiratoireprevented from exhaling therefore leading to increased The Ayres “T” piece, is ideal for children under 20Kg. A
pressure build up in the lung. If the expiratory side of the version commonly used is a Jackson-Rees modification, which
valve sticks open, the patient may draw from room air rather has an open bag attached to the expiratory limb (Mapleson F).
than the circuit. A PEEP apparatus can be used with the It is recommended that a FGF 2-3 times the minute volume
Laerdal valve, but not with the other non-rebreathing valves. is required to prevent rebreathing of CO2 and the minimum
Non-rebreathing valves may stick with prolonged use without flow should be >3L/min. The minimum minute ventilation
cleaning and proper maintenance. Inspection and testing are should be 150 ml/kg/min.
required to ensure functional operation of the valves and safe In conclussion, the attraction of Draw-Over lies in the
use with patients.13 fact that it is fundamentally simple, robust, easily portable
Pediatrics can be a large percentage of the cases seen and can function without compressed gases and even without
in the developing world. Three physiological parameters to supplementary oxygen, when absolutely mecessary. A failure
consider are apparatus dead space, resistance, and work of of the oxygen supply will result in a default to room air and
breathing. In pediatrics, two types of circuits are commonly this will be adequate (though not desirable) for most patients.
used: a regular draw-over circuit, preferably with a pedi-valve; Understanding the limitations of all aspects of equipment
and an Ayres “T” piece (Mapleson E circuit). The same draw- is important for safe operation. A thorough understanding
over vaporizers can be used, as with adults. However, most of the operation of these circuits and the completion of a
practitioners will opt for an Ayres “T” piece in children less checkout procedure is a vital component to ensuring safety
than 10-15 kg, in consideration of the limitation for air flow for the staff and patients. Assessing the situation with regard
generation in small children. Provided the inflow rates are to patient’s age, size, procedure, availability of equipment and
above 4l/min, the accuracy of draw-over vaporizers, in this personnel, and obtaining the proper kit is essential for patient
plenum mode, are adequate to be used as a fresh gas source safety. (see Table 1)
for the “T” piece.14
Table 1
Advantages Disadvantages
Simplicity of concept and assembly Decreasing familiarity with the technique and equipment
No need for pressurized gas supply, regulators and flow meters Vaporizer limitations
Minimum FiO2 is ~18-21% Filling systems not agent specific (potential advantage)
Robust, reliable, easily serviced equipment Basic temperature compensation, affecting performance
at extremes
Low cost (purchase and maintenance) Less easy to observe spontaneous ventilation with self
inflating bag
Portable, suitable for field anesthesia (easy to transport Cumbersome in pediatric use, unless lightweight tubing
and set-up) is available
Easy to service by locally trained staff
*Corresponding Author
Queen Elizabeth II Health Sciences Centre, Department of Anesthesia, 1796 Summer Street,
Halifax, Nova Scotia B3H 3A7
Telephone 902-473-5411 Fax 902-473-3820 dan.cashen@cdha.nshealth.ca
Canadian Journal of Respiratory Therapy SUMMER | ÉTÉ 2011 9
Journal canadien de La thérapie respiratoire Volume | Numéro 47.2References
1. World Anaesthesia; update in anaesthesia, Issue 15 (200) Article 6, 9. Mackie AM. Drawover anaesthesia systems; factors determining the
Dr. Simpson, Dr. Wilson inspired oxygen concentration. Anesthesia 1987; 42:299-304
2. Eales M, Rowe P, Tully R. Improving the efficiency of the drawover 10. Pylman ML, Teiken PJ. Sevoflurane concentration available from
anaesthetic breathing system. Anaesthesia 2007; 62:1171-1174 the universal drawover vaporizer. Mil Med 1997; 162(6):405-406
3. Fundamentals of Anaesthesia, Third Edition, 2009, Smith T et al, 11. Lui EH, Dhara SS. Sevoflurane output from the OMV in drawover
page 838 mode. Anesthesia Intensive Care 2000; 28(5):532-536
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Anesthesia Analgesia 1995; 80:424-426
6. Tighe SQM, et al, Minimum oxygen requirements during
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1991; 46:52-56 CAS Annual Meeting. Paul Brousseau RRT (AA), QEII Health
Science Centre, Halifax, NS
7. Dobson MB. Oxygen concentrators offer cost savings for
developing countries. Anaesthesia 1991; 46:217-219 14. Paediatric Anesthesia Review 1988; 8:6
8. Jarvis DA, Brock-Utne JG. Use of an oxygen concentrator
linked to a draw-over vaporizer (Anesthesia Delivery System for
Underdeveloped Nations). Anesth Analg 1991; 72:805-810
SUMMER | ÉTÉ 2011 Canadian Journal of Respiratory Therapy
10 Volume | Numéro 47.2 Journal canadien de LA thérapie respiratoireOriginal Article
The Association of Body Mass Index with Airway Obstruction in Non-Asthmatics:
Implications for the Inaccurate Differential Diagnosis of Asthma in Obesity
Andrew J. West MAppSc, RRT 1,2, Debbie Burton PhD 3, Ali Bell MSc 2
1. School of Medical Rehabilitation, Faculty of Medicine, University of Manitoba, Winnipeg, Manitoba
2. Research and Performance Support, Regina Qu’Appelle Heath Region, Regina, Saskatchewan
3. School of Biomedical Sciences, Charles Sturt University, New South Wales, Australia
Abstract Résumé
Introduction: An association between obesity and asthma has Introduction : Certains chercheurs ont signalé une association
been reported, with disparity between males and females in this entre l’obésité et l’asthme, avec des disparités entre les hommes
association that is not fully explained. Studies investigating the et les femmes dans cette association qui n’ont pas été entière-
association typically have not identified asthma using accepted ment expliquées. Les études portant sur cette association n’ont
objective diagnostic methods, possibly leading to the inaccurate généralement pas relevé l’asthme selon des méthodes diagnos-
diagnosis and management of asthma in those with obesity. tiques objectives acceptées, ce qui peut avoir mené à des erreurs
de diagnostic et de gestion de l’asthme chez les personnes obèses.
Objective: This study investigated the association, including
gender differences, between obesity and airway obstruction in Objectif : Cette étude a examiné les liens, incluant les différenc-
non-asthmatics identified by spirometric protocols. es liées au sexe, entre l’obésité et l’obstruction des voies respi-
ratoires chez les personnes non asthmatiques identifiées par les
Methods: The pulmonary function test results of non-asthmat- protocoles spirométriques.
ic subjects were reviewed. Statistical analyses were employed to
determine the association between pulmonary function measures Méthodologie : Les résultats des tests de fonction pulmonaire
and BMI. pour les sujets non asthmatiques ont été examinés. L’analyse
statistique a été utilisée pour déterminer l’association entre les
Results: Significant differences in the pulmonary function values, mesures de fonction pulmonaire et l’IMC.
measured as a percentage of predicted, existed between BMI
ranges including FVC (p < 0.001), FEV1/FVC (p < 0.001), Résultats : Des écarts significatifs, en pourcentage des prévi-
and FEF50% (p < 0.02). Gender differences were evident in sions, ont été mesurés dans les valeurs de fonction pulmonaire
FVC, FEV1, FEV1/FVC, FEF25% , and FEF50% (all p < 0.001). entre les plages d’IMC, incluant FVC (p < 0,001), FEV1/FVC
When age and smoking were controlled for, gender differences (p < 0,001), et FEF50% (p < 0,02). Des écarts entre les sexes ap-
remained in the pattern of the effect of BMI on FVC. FVC was paraissent dans FVC, FEV1, FEV1/FVC, FEF25% et FEF50%(dans
progressively compromised for females as BMI increased above tous les cas, p < 0,001). Lorsqu’on tient compte de l’âge et du
normal range ( ≥ 25 kg/m2), and was diminished in males with statut de fumeur, les différences entre les sexes subsistent dans la
a BMI ≥ 30 kg/m2. distribution des effets de l’IMC sur la FVC. La FVC est pro-
gressivement compromise chez les sujets féminins à mesure que
Conclusions: Clear association was not found between indices l’IMC augmente au-delà de la plage normale (≥ 25 kg/m2) et
of airway obstruction and increasing BMI in this non-asthmatic diminue chez les sujets masculins présentant un IMC de ≥ 30
group. The study findings suggest a restrictive pulmonary function kg/m2.
profile in obesity which is specific to non-asthmatics and
unique to each gender. The compromising effects of increasing Conclusions : Aucune association claire n’a été établie entre les
adiposity on FVC may be experienced at a lower BMI in females indices d’obstruction des voies respiratoires et l’augmentation
than in males. de l’IMC dans ce groupe de non asthmatiques. Les conclu-
sions de l’étude semblent présenter un profil de restriction de la
fonction respiratoire chez les personnes obèses propre aux non
asthmatiques et unique à chaque sexe. Les effets négatifs de
l’augmentation de l’adiposité sur la FVC peuvent apparaître à un
IMC plus faible chez la femme que chez l’homme.
Keywords: Airway Obstruction; Asthma; Body Mass Index; Obesity; Mots-clés : Obstruction des voies respiratoires; Asthme; Indice de masse corpo-
Pulmonary Function Tests relle; Obésité; Examens fonctionnels respiratoires
Canadian Journal of Respiratory Therapy SUMMER | ÉTÉ 2011 11
Journal canadien de La thérapie respiratoire Volume | Numéro 47.2Introduction suggests that obesity is associated with an over-diagnosis of
The worsening global epidemic of obesity is a significant asthma, due to airflow limitation that is not associated with
contributor to morbidity and mortality (1). An estimated hyper-responsiveness, a phenomenon attributed to the lack of
59.2% of the Canadian population is either overweight or use of objective diagnostic methods. Such over diagnosis may
obese (2) with an increasing trend expected to continue into result in the overuse of costly asthma therapies (13,25).
the future (3). The magnitude of the increase in obesity has Several studies have reported the association between
been paralleled by an increase in the prevalence of asthma in asthma and obesity either to be strongest in females, or to
many global locales (1,4). Asthma now affects 8.3 % of the only be significant in females (7,11,12,15,26-28). Most of
population (5), an increase of more than 1% over the last these studies, however, defined asthma by methods that did
decade (6). The phenomenon of a concurrently increasing not include measurement of airway hyperresponsiveness.
prevalence for these two disorders may be more than Indeed, there are conflicting reports that show no significant
coincidental. A mounting body of data describes obesity as a association between BMI and airway responsiveness (as
significant risk factor for the development of asthma (7), and measured by either bronchial challenge with methacholine or
offers compelling evidence of several complex interactions bronchodilator response) in both males and females (14,24),
between the two that are worthy of careful consideration while others showed a strong relationship between increasing
(8,9). The purpose of this study was to investigate the BMI and bronchial hyperreactivity in males with only a weak
association between obesity and asthma which constitutes a relationship in females (22). One possible explanation for
growing public health concern. these various outcomes is that the increased asthma prevalence
A meta-analytical study of the dose-response effect of reported in obese females is due to an obstructive profile
elevated body mass index (BMI) on asthma incidence (10) determined from studies based on symptomatic evaluation,
determined that the likelihood of asthma was 1.51 times rather than actual airway hypersensitivity or responsiveness.
higher in subjects with a BMI ≥ 25 kg/m2 compared to those In light of the lack of objective measures used to quantify
of a normal weight (18.5-24.9 kg/m2) [Odds Ratio (OR) reported disparities between the genders, misdiagnosis of
1.51, 95% CI, 1.17-1.62]. Numerous other studies are also asthma in obese females is a likely factor.
suggestive of an increased prevalence of obesity amongst adults The obstructive effects of obesity on the pulmonary
with asthma (7,8,11), but do not adequately describe any airway (17-19), and the resultant respiratory symptomology,
cause and effect relationship between the two. These studies may lead to an unwarranted diagnosis of asthma (14,25).
have typically defined asthma status based on patient self- Identifying any disparity in the underlying pulmonary
reported symptoms, or by physician diagnosed asthma that function profile between the genders in obese non-asthmatic
was then self-reported and/or lacked control for the methods subjects would be helpful in ascertaining which factors may
used to obtain the diagnosis (8,12-15). These self reports explain the differences between males and females with respect
without objective confirmation do not ensure consistency to the reported association between obesity and asthmatic
with accepted standards for the diagnosis of asthma such symptomology. This study was developed to investigate the
as those endorsed by the Canadian Thoracic Society (16). primary mechanisms that may be responsible for the reported
Preferred diagnostic techniques include bronchodilator association between obesity and subjectively diagnosed
responsiveness as determined by spirometry, or bronchial asthma, and the disparity described between genders for that
provocation testing (16). association. It was hypothesized that there would be a positive
The restrictive effect of obesity on pulmonary function, correlation between BMI status and measures of pulmonary
including a compromised FVC, is well described (17). Various function obstruction in non-asthmatic individuals, and that
authors also report distinctly obstructive elements seen in the there would be a significantly greater effect of BMI on specific
pulmonary function profile of obese individuals [BMI ≥ 30 pulmonary function variables of females when compared to
kg/m2 (1)]. It has been shown that forced expiratory volume those of males. Any noted differences between genders in
in one second (FEV1) diminishes with increasing BMI relation to the primary pulmonary function effects of obesity
in subjects with no underlying respiratory pathology (17- might offer some insight into the etiologic basis for this
19). BMI related compromise of other indicators of airflow gender-based disparity.
obstruction such as forced expiratory flow at 25%, 50% and
75% of forced vital capacity (FEF25%, FEF50% and FEF75% METHODS
respectively), and forced expiratory flow between 25% and A retrospective analysis was conducted of spirometry
75% of forced vital capacity (FEF25-75%) has also been described results obtained between June 1, 2006 and August 31, 2007.
in the literature (20,21). A correlation between asthma and The charts of patients referred by physicians to a pulmonary
obesity, however, was not found by studies that investigated function laboratory in Regina, Saskatchewan, Canada, were
the association of obesity and airway responsiveness (22-24). reviewed with respect to their relevant history and pulmonary
Hyperresponsiveness of the airway determined by function test results. As such, participants were referred by
objective methods is a hallmark of asthma diagnosis, a variety of medical specialties including General Practice,
distinguishing the pathology from others that cause an Respirology, Oncology, Pediatrics, and Internal Medicine.
obstructive pulmonary profile (16). Mounting evidence Ethical approval was granted by both the Charles Sturt
SUMMER | ÉTÉ 2011 Canadian Journal of Respiratory Therapy
12 Volume | Numéro 47.2 Journal canadien de LA thérapie respiratoireUniversity Ethics in Human Research Committee, and the was included in the analysis in order to minimize the possible
Regina Qu’Appelle Health Region Research Ethics Board. effects of any pharmacotherapy or other treatment strategy
All measures of pulmonary function that occurred that may have been initiated before the follow up test was
in the lab were performed on a Collins GS pulmonary performed.
function apparatus (Collins Medical, Inc., Braintree, MA),
in accordance with the standards of lung function testing of
the American Thoracic Society/European Respiratory Society
Table 1: Study Inclusion and Exclusion Criteria
(ATS/ERS) (29). Post bronchodilator testing was performed
a minimum of 10 minutes after administration of salbutamol
2 puffs (200 mcg) metered dose inhaler via a spacer device Inclusion Criteria Exclusion Criteria
to determine airway responsiveness, based on laboratory
protocol. All pulmonary function testing was performed Non-Asthmatic Subjects Asthmatic Subjects or those
by a Registered Respiratory Therapist trained in the use of with Other Airway Obstruction
laboratory equipment and evaluation of test results to ATS/
< 12% improvement in ≥ 12% (and a minimum 180 ml)
ERS standards. Each pulmonary function report included a FEV1 after bronchodilator improvement in FEV1 after
record of the patient’s gender, height, weight, age, smoking administration * bronchodilator administration *
status as measured by pack years, and standard spirometric
measures including forced vital capacity (FVC), the ratio FEV1 ≥ 80% of predicted FEV1 < 80% of predicted †
of forced expiratory volume in one second to forced vital † with no bronchodilator with no bronchodilator
response testing ‡ response testing ‡
capacity (FEV1/FVC), FEV1, FEF25%, FEF50%, FEF75%, and
FEF25%-75%. Each subject’s height, weight, and smoking FEV1 < 80% of predicted † FEV1 < 80%of predicted † and
history were self-reported. Pulmonary function variables and FEV1/FVC ≥ 70% of FEV1/FVC < 70% of predicted
were recorded as a percentage of the normal value predicted predicted † with no broncho- † with no bronchodilator
based on reported height and age (30). The predicted normal dilator response testing ‡ response testing ‡
reference values for pulmonary function employed were based
Criteria were designed to control for the inclusion of non-asthmatic subjects only. *
on those derived by Knudson et al. (30). Based on Canadian Thoracic Society (CTS) guidelines for the diagnosis of asthma (16),
† predicted values for pulmonary function as proposed by Knudson et al. (30), ‡ and
Participant Selection on CTS definition of airway obstruction (31).
FEV1 Forced Expiratory Volume in one second; FEV1/FVC ratio of Forced Expiratory
The study sought to identify subjects who were asthma Volume in one second to Forced Vital Capacity.
free. All criteria for the objective evaluation of asthma status
and airway obstruction were based on Canadian Thoracic
Society recommendations (16,31). The inclusion and
exclusion criteria are summarized in Table 1. Criteria were
Statistical Analysis
designed to exclude those subjects who, based on pulmonary
function measures, had evidence of asthma, reversible Descriptive analyses of all pulmonary function variables
airway obstruction, or airway obstruction that could not be recorded in each BMI range for males, females, and both
differentiated from either of these based solely on the available genders combined were performed. In order to assess the two
test results. The study therefore included the results of any main hypotheses the study compared each of the recorded
initial test done as part of a pre and post bronchodilator test measures of pulmonary function to varying degrees of body
where the post test showed no significant improvement in mass index, and examined for gender differences in the
FEV1. Improvement in FEV1 was defined as an increased test relationship between BMI [weight (kg)/height (m2)] and
score ≥ 12% (and a minimum of 180 ml) above the pre-test pulmonary function. The data analysis was performed in two
(baseline). The results of tests where no post-bronchodilator unique phases. The first phase served two key purposes: (1) to
testing was performed (either pursuant to laboratory procedure allow for comparison of results to those previously reported
or for other clinical reasons) were also included when the in the literature using similar analysis techniques, and (2) to
results demonstrated a lack of airway obstruction. A lack of act as a baseline from which further analysis of data could be
airway obstruction was defined as either a FEV1 ≥ 80% of made when controlling for significant confounders. There is
predicted normal, or, a FEV1 < 80% of predicted normal with much ambiguity with regards to control for confounders in
a ratio of forced expiratory volume in one second to forced the literature, thus, the second phase of the analysis identified
vital capacity (FEV1/FVC) ≥ 70% of predicted normal. The and controlled for potential confounders. This allowed for
computerized diagnostic record database of the laboratory more accuracy in identifying differences between the genders,
was used to identify 1114 subjects whose test results met the and indicated the potential influence of these confounders on
study criteria. Of the 1114 test results recorded in the study previously reported findings. The results of the first analysis
database, 195 were excluded after review revealed testing had phase were then compared to the results of the second analysis
been repeated in the laboratory two or more times for clinical phase to examine variance between the two that could have
reasons. Only the earliest test performed on any one subject been a result of the potential confounding factors.
Canadian Journal of Respiratory Therapy SUMMER | ÉTÉ 2011 13
Journal canadien de La thérapie respiratoire Volume | Numéro 47.2First Analysis Second Analysis
Data were grouped for analysis into BMI ranges The second phase of the analysis was performed after
according to the World Health Organization classification removal of outliers and control for covariates. Multivariate
system for analysis [normal weight (BMI 18.5-24.9 kg/m2); outliers were identified in BMI, age, and smoking history,
overweight (BMI 25.0-29.9 kg/m2); obese I (BMI 30.0-34.9 using Mahalabonis distance (32). This led to the deletion
kg/m2); obese II (BMI 35.0-39.9 kg/m2); obese III (BMI ≥ of ten outliers for these variables. Multivariate analysis of
40.0 kg/m2)] (Table 2) (1). Analysis of Variance (ANOVA) covariance (MANCOVA) was then performed, and age and
was performed to examine for differences between the BMI smoking history were entered as covariates since they were
groups in all other variables. ANOVA was also performed to each found to be significantly different between BMI groups.
examine for differences in variables between genders. The covariates were further explored and extreme cases,
The distributions of the data sets of each of the pulmonary identified again by Mahalabonis distance, were removed until
function variables were skewed. A square root transformation box plots indicated that there were no remaining outliers.
was used to improve the normality of their distribution as Analysis was then performed on the remaining 904 cases.
recommended by Tabachnik and Fidell (32). The benefit of Data were then regrouped for the remainder of the
the square root transformation of data is that it improves the analysis into three BMI ranges [normal (BMI 18.5-24.9 kg/
normality of the distribution, a key assumption for parametric m2); overweight (BMI 25.0-29.9 kg/m2); obese (BMI ≥ 30.0
analysis (32). For variables that were negatively skewed (FVC, kg/m2)]. This regrouping increased group size and minimized
FEV1, FVC/FEV1, and FEF25%), the data were first “reflected” the impact of sample size on the results of further analysis.
before the square root transformation was applied (32). The To further examine the potential gender differences in the
square root transformed data was used for all further statistical pulmonary function variables, separate data files were made for
analysis of these variables, but are accompanied by the males and females, and analyses were applied independently.
non-transformed data values when presented in Tables and All statistical analyses were performed using commercially
Figures, to allow readers to conceptualize the potential trends available software (SPSS version 15.0, SPSS Inc., Chicago,
more easily. This method of data analysis and presentation Illinois). Differences were considered statistically different
has been employed by other authors in this field (33). when p < 0.05.
Table 2: Comparison of Pulmonary Function and Demographic Variables between BMI Ranges, Males and Females Combined*
* Values are presented as percentage of the No. or mean (SD) percentage of predicted values, except for FEV1/FVC which is an absolute ratio. Smoking history is measured in pack years.
† BMI grouping based on the World Health Organization classification system (1). ‡ For pulmonary function variables ‘actual’ indicates non-transformed values, √ indicates mean (SD) of
square root transformed variables. § For pulmonary function variables P indicates statistical significance between BMI categories for the square root transformations of those variables.
BMI Body Mass Index; FEF25% Forced Expiratory Flow at 25% of Forced Vital Capacity; FEF25-75% Forced Expiratory Flow between 25% and 75% of Forced Vital Capacity; FEF50% Forced
Expiratory Flow at 50% of Forced Vital Capacity; FEF75% Forced Expiratory Flow at 75% of Forced Vital Capacity; FEV1 Forced Expiratory Volume in one second; FEV1/FVC ratio of Forced
Expiratory Volume in one second to Forced Vital Capacity; FVC Forced Vital Capacity.
SUMMER | ÉTÉ 2011 Canadian Journal of Respiratory Therapy
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