Anesthetic Management of the Obese Surgical Patient Anesthetic Management of the Obese Surgical Patient Jay B. Brodsky, MD Professor,DepartmentofAnesthesiaandMedicalDirector,PerioperativeServices,StanfordUniversityMedicalCenter, Stanford,CA,USA Hendrikus J.M. Lemmens, MD, PhD ProfessorandAssociateChairforClinicalAffairs,Chief:Multi-SpecialtyDivision,DepartmentofAnesthesia, StanfordUniversitySchoolofMedicine,Stanford,CA,USA CAMBRIDGE UNIVERSITY PRESS Cambridge,NewYork,Melbourne,Madrid,CapeTown, Singapore,SãoPaulo,Delhi,Tokyo,MexicoCity CambridgeUniversityPress TheEdinburghBuilding,CambridgeCB28RU,UK PublishedintheUnitedStatesofAmericaby CambridgeUniversityPress,NewYork www.cambridge.org Informationonthistitle:www.cambridge.org/9781107603332 #JayB.BrodskyandHendrikusJ.M.Lemmens2012 Thispublicationisincopyright.Subjecttostatutoryexception andtotheprovisionsofrelevantcollectivelicensingagreements, noreproductionofanypartmaytakeplacewithout thewrittenpermissionofCambridgeUniversityPress. Firstpublished2012 PrintedintheUnitedKingdomattheUniversityPress,Cambridge AcataloguerecordforthispublicationisavailablefromtheBritishLibrary LibraryofCongressCataloging-in-PublicationData Brodsky,JayB. Anestheticmanagementoftheobesesurgicalpatient/ JayB.Brodsky,HarryJ.M.Lemmens. p. ; cm. Includesbibliographicalreferencesandindex. ISBN978-1-107-60333-2(Paperback) 1. Anesthesia–Complications. 2. Obesity–Surgery. I. Lemmens,HarryJ.M. II. Title. [DNLM: 1. Anesthesia–methods. 2. Obesity–complications. 3. PatientPositioning. 4. SurgicalProcedures,Operative. WO200] RD82.5.B762012 617.403–dc23 2011024206 ISBN978-1-107-60333-2Paperback CambridgeUniversityPresshasnoresponsibilityforthepersistenceor accuracyofURLsforexternalorthird-partyinternetwebsitesreferredto inthispublication,anddoesnotguaranteethatanycontentonsuch websitesis,orwillremain,accurateorappropriate. Everyefforthasbeenmadeinpreparingthisbooktoprovideaccurateand up-to-dateinformationwhichisinaccordwithacceptedstandardsand practiceatthetimeofpublication.Althoughcasehistoriesaredrawnfrom actualcases,everyefforthasbeenmadetodisguisetheidentitiesofthe individualsinvolved.Nevertheless,theauthors,editorsandpublisherscan makenowarrantiesthattheinformationcontainedhereinistotallyfree fromerror,notleastbecauseclinicalstandardsareconstantlychanging throughresearchandregulation.Theauthors,editorsandpublishers thereforedisclaimallliabilityfordirectorconsequentialdamages resultingfromtheuseofmaterialcontainedinthisbook.Readersare stronglyadvisedtopaycarefulattentiontoinformationprovidedbythe manufacturerofanydrugsorequipmentthattheyplantouse. Contents Preface vii Section 1 – General 10 Anesthesia, obesityand orthopedic considerations surgery 87 11 Anesthesia, obesityand oral, 1 Introduction toobesity 1 head andneck surgery 2 Pre-operative considerations 12 (OHNS) 94 3 Intra-operative management 24 12 Anesthesia, obesityand plasticand reconstructive 4 Pharmacologicconsiderations 36 surgery 98 5 Post-operative management 43 13 Anesthesia, obesityand ophthalmic surgery 103 Section 2 – Anesthesia for 14 Anesthesia, obesityand specific procedures obstetrics 107 6 Anesthesia, obesityand abdominal 15 Anesthesia, obesityand ambulatory and pelvic operations 57 surgery 115 7 Anesthesia, obesityand 16 Anesthesia, obesityand out-of-OR cardiovascular surgery 68 procedures 124 8 Anesthesia, obesityand thoracic surgery 73 Index 130 9 Anesthesia, obesityand neurosurgery 81 v Preface Aseveryanesthesiologist nowrecognizes, obesity hasbecome anever-growing,worldwide problem of epidemic proportions (see Figure below). Today in the United States a two- thirds majority of adults are “overweight” and more than 30% are “obese.” It is estimated that by the year 2025 the number of obese Americans will exceed 40% of the population. It is not uncommon for anesthesiologists to encounter extremely obese patients daily, whetherinanambulatory surgerycenter,obstetricalsuite,painclinic,ataninterventional radiologyor endoscopy site, as well as in the operatingroom. Figure Adultobesityratesinselectedcountries.Obesityhasbecomeaworldwideproblemofepidemic proportions. vii viii Preface Our companion book Morbid Obesity – Peri-operative Management (Second edition) (Cambridge University Press, 2010) considers the whole spectrum of the peri-operative managementofmorbidlyobesepatientsfromtheperspectivesoftheentireteam–surgeon, anesthesiologist, nurses, nutritionists, psychologist and others. Although we covered the major concerns important for the anesthesiologist in that book, space did not allow for discussion of specific anesthetic considerations by surgical specialty and for the other interventions for which an anesthesiologist is likely to encounter an obese patient. As our specialtyawakestothespecialneedsofmorbidlyobesepatientsmoreandmoreliteratureis becoming available. This book is specifically intended as a supplement for anesthesia-care providers. We review the data currently available by surgical specialty as that information pertainstotheobesepatientundergoinganestheticcare.Unfortunately,despitetheobesity epidemicofthepasttwodecades,theanesthesialiteratureisrelativelysparseontheneedsof obese patients under special circumstances. We have tried to include the information currently available. We predict that future editions of this book will be significantly expanded as experience with the anesthetic management of obese patients continues to accumulate and as pertinentclinical studies are published. Jay B. Brodsky, MD Hendrikus J.M.Lemmens, MD, PhD Departmentof Anesthesia Stanford University School of Medicine Generalconsiderations Section1 Chapter Introduction to obesity 1 Obesity is a metabolic disease in which adipose tissue comprises a greater than normal proportion of body tissue. There is really no precise definition of when obesity actually begins.Dictionarydefinitionsof“obesity”includedescriptionslike“thestateofbeingwell above one’s normal weight” or “an excess of subcutaneous fat in proportion to lean body mass.”Anindividualcanbeconsideredtobeobesewhentheamountofbodyfatincreases beyond the point where their health begins to deteriorate. Extreme obesity is often associated with a shortened life expectancy. The precursors of obesity include gender, genetic and environmental effects (such as changes in dietary habits and lack of exercise), ethnicity, education and socio-economic status. In industrialized countries obesity was once more common in the lower socio-economic groups, while in developing countries it was usually associated with affluence. As the worldwide epidemic of obesity (globesity) spreads, patients in every socio-economic group in all countries are becoming obese (Figure 1.1a, b). [1] Overweight has been defined as an excess of total or expected “normal” body weight, including all tissue components (muscle, bone, water and fat) of body composition. In practice,thetermsobesityandoverweightareoftenusedinterchangeablytorefertoexcess body fat, but ideally an index of obesity should reflect only excess adipose tissue and be independent of height,bodyfluids, and muscle and skeletal mass. Bodymassindex(BMI)isnowthestandardmeasurefordescribingdifferentcategories ofobesity.ItmustalwaysberememberedthatBMIisanindirectmeasureofobesitysinceit onlyconsidersheightandweight,irrespectiveofthesourceofanyadditionalweight.BMIis calculatedbydividingpatientweight(kilograms,kg)bythesquareoftheirheight(meters,m); BMI ¼ kg/m2. An increased BMI can be present from any cause of excess weight (body building,ascites,verylargetumor)evenintheabsenceofadditionalfat. IntheUnitedStatesandinmostindustrializednationsanindividualwithaBMI18–25 kg/m2 is considered to be normal weight, and are “overweight” if their BMI is > 25 but <30kg/m2.AnyonewithaBMI(cid:2)30kg/m2isdescribedas“obese.”Morbidobesity(MO) isatermforadegreeofobesitythat,ifuntreated,willsignificantlyshortenlifeexpectancy. Morbid obesity has been defined as a doubling of ideal body weight (IBW) or as IBW þ 100 kg. Today a patient with a BMI (cid:2) 40 kg/m2 is considered to be morbidly obese. As patientscontinuetoincreaseinsize,newdefinitionsarebeingadoptedintomedicaljargon. AnyonewithaBMI>50kg/m2isnowdescribedassuper-obeseandanindividualwitha BMI >60 kg/m2 is super-superobese (Table 1.1). Definitions of obesity based on BMI differ depending on geographic location and cultural norms. For example, in Japan a patient with a BMI (cid:2) 25 kg/m2 is “obese” and in ChinaobesityisdefinedasaBMI(cid:2)28kg/m2;whileapatientwiththesesamevalueswould 1