Retrospective study of the prevalence of postanaesthetic hypothermia in dogs

Abstract

The anaesthetic records of 1525 dogs were examined to determine the prevalence of postanaesthetic hypothermia, its clinical predictors and consequences. Temperature was recorded throughout the anaesthesia. At the end of the procedure, details coded in were: hyperthermia (>39.50°C), normothermia (38.50°C-39.50°C), slight (38.49°C-36.50°C), moderate (36.49°C-34.00°C) and severe hypothermia (<34.00°C). Statistical analysis consisted of multiple regression to identify the factors that are associated with the temperature at the end of the procedure. Before premedication, the temperature was 38.7 ± 0.6°C (mean ± sd). At 60, 120 and 180 minutes from induction, the temperature was 36.7 ± 1.3°C, 36.1 ± 1.4°C and 35.8 ± 1.5°C, respectively. The prevalence of hypothermia was: slight, 51.5 per cent (95 per cent CI 49.0 to 54.0 per cent); moderate, 29.3 per cent (27.1-31.7 per cent) and severe: 2.8% (2.0-3.7%). The variables that associated with a decrease in the temperature recorded at the end of the anaesthesia were: duration of the preanesthetic time, duration of the anaesthesia, physical condition (ASA III and ASA IV dogs showed lower temperatures than ASA I dogs), the reason for anaesthesia (anaesthesia for diagnostic procedures or thoracic surgery reduce the temperature when compared with minor procedures), and the recumbency during the procedure (sternal and dorsal recumbencies showed lower temperatures than lateral recumbency). The temperature before premedication and the body surface (BS) were associated with a higher temperature at the end of the anaesthesia, and would be considered as protective factors.

A clinical audit cycle of post-operative hypothermia in dogs

“…Our,findings,support,previous,observa=ons,that,post;opera=ve,hypothermia,is,extremely,common, (Redondo,et,al.,2012a;,Redondo,et,al.,2012b;,Waterman,1975)., Comparisons,between,studies,are, limited,by,the,varying,defini=ons,of,hypothermia,applied.,For,example,,Redondo,et,al.,(2012),reported, 83.6%,of,dogs,as,hypothermic, (Redondo,et,al.,2012b).,The,slightly,higher,incidence,we,observed,(88.9%), could,be,explained,by,the,difference,in,cut;off,values,for,iden=fying,hypothermia,(37.5˚C,versus,36.5˚C). It,is,unlikely,that,the,high,prevalence,of,epidural,anaesthesia,in,the,study,popula=on,contributed, substan=ally,to,the,magnitude,or,=me,course,of,intra;opera=ve,hypothermia,observed,but,may,have, contributed,to,prolonga=on,of,post;opera=ve,hypothermia.,Epidural,and,spinal,anaesthesia,widen,the, interthreshold,range,but,to,a,lesser,extent,than,general,anaesthe=cs,(Emerick,et,al.,1994; However,the,con=nued,presence,of,epidural,anaesthesia,in,the,recovery,period,and,consequent, depression,of,thermoregulatory,control,and,peripheral,vasodila=on,may,have,offset,aoempts,to,warm, our,pa=ents. In,dogs,,the,defini=on,of,periopera=ve,hypothermia,and,subsequent,classifica=on,(typically,,mild,, moderate,,severe),is,highly,variable,and,somewhat,arbitrary, (Armstrong,et,al.,2005;,Oncken,et,al.,2001)., It,would,seem,more,appropriate,to,base,a,defini=on,on,an,important,outcome.,Unfortunately,,this, approach,is,limited,by,the,current,evidence,base,available,for,important,outcomes,in,dogs.,With,this, current,gap,,we,would,suggest,applying,the,well;established,human,range,for,mild,hypothermia,,a, decrease,in,core,body,temperature,of,1;3˚C,below,normal,,which,is,based,on,numerous,nega=ve, outcomes, (Alexander,et,al.,2008;,Kurz,2008;,Scoo,and,Buckland,2006;,Sessler,2001;,Torossian,2008)., With,a,mean,normal,temperature,of,37˚C,in,adult,humans,,this,range,represents,a,2.7;8%,decrease., Applying,this,percentage,decrease,to,reported,mean,rectal,temperatures,in,dogs,,suggests,a, temperature,range,of,35.4,to,37.9˚C,may,be,clinically,important, (Table,3).…”

“…The, development,of,hypothermia,during,anaesthesia,is,a,common,occurrence,in,both,humans,and, animals,and,has,been,associated,with,numerous,side,effects,(Sessler,1997;,Sessler,2001;,Torossian,2008;, Pome,et,al.,2007;,Redondo,et,al.,2012a;,Redondo,et,al.,2012b;,Waterman,1975;,Evans,et,al.,1973)., In,humans,,a,temperature,drop,as,small,as,1˚C,results,in,clinically,important,consequences.,Hypothermia, is,associated,with,prolonged,anaesthe=c,recovery,,prolonged,hospitalisa=on,,increased,surgical,site, infec=on,,increased,bleeding,,impaired,immunity,,postopera=ve,shivering,and,thermal,discomfort,(Scoo, and,Buckland,2006;,Sessler,2001;,Torossian,2008;,Kurz,2008;,Kurz,et,al.,1995)., Limited,inves=ga=ons,in, veterinary,medicine,have,iden=fied,delayed,anaesthe=c,recovery,as,consequences,of,post;opera=ve, hypothermia, (Pome,et,al.,2007;,Redondo,et,al.,2012b).,The,rela=onship,between,hypothermia,and, wound,infec=on,rate,remains,unclear, (Beal,et,al.,2000).…”

“…Despite,clear,evidence,of,nega=ve,outcomes,associated,with,hypothermia,in,humans,,the,reported, incidence,of,post;opera=ve,hypothermia,is,high,,ranging,between,53%;85%.,However,,the,recent, development,and,implementa=on,of,hypothermia,management,guidelines,has,created,a,mechanism,for, improvement, (Sessler,2009;,Torossian,2007;,Alexander,et,al.,2008;,Slotman,et,al.,1985;,Vaughan,et,al., 1981;,Stewart,et,al.,1987)., In,veterinary,medicine,,two,large,scale,studies,(n=,275,cats,and,1525,dogs), reported,an,incidence,of,post;opera=ve,hypothermia,(defined,as,an,oesophageal,temperature,less,than, 38.5°C),of,83.6%,of,dogs,and,96.7%,of,cats, (Redondo,et,al.,2012a;,Redondo,et,al.,2012b)., There,are, currently,no,management,guidelines,or,standards,of,care,for,peri;opera=ve,hypothermia. Clinical,audit,is,a,quality,improvement,tool,for,evalua=ng,and,improving,pa=ent,care, (Rose,et,al.,2016;, Burgess,2011;,Mosedale,1998)., As,a,standard,of,care,in,human,medicine,,clinical,audit,has,been, successful,in,genera=ng,con=nued,improvements,in,pa=ent,care,though,its,applica=on,in,veterinary, medicine,is,currently,limited, (Patel,et,al.,2013;,Shonfeld,et,al.,2011;,;,Rose,et,al.,2016). In,light,of,the,evidence,of,adverse,effects,associated,with,post;opera=ve,hypothermia,,and,the, suspected,incidence,of,prolonged,hypothermia,in,our,clinic,,we,sought,to,quan=fy,and,reduce,the, incidence,of,post;opera=ve,hypothermia,by,performing,a,clinical,audit., ,prospec=ve,clinical,audit,was,conducted,at,a,small,animal,veterinary,referral,hospital.,Client,consent,…”

A clinical audit cycle of post-operative hypothermia in dogs

“…The,mechanism,of,anaesthesia;induced,hypothermia,is,well,described, (Matsukawa,et,al.,1995b;,Sessler, 1997).,Essen=ally,,anaesthe=cs,allow,an,increased,devia=on,in,temperature,from,normothermia,before, a,thermoregulatory,response,is,triggered,(increased,interthreshold,range), (Matsukawa,et,al.,1995a;, Xiong,et,al.,1996).,In,conscious,adult,humans,,the,interthreshold,range,is,usually,0.2˚C.,During,general, anaesthesia,(vola=le,and,injectable,agents),the,interthreshold,range,increases,to,approximately,4˚C, allowing,a,substan=al,decrease,in,core,temperature,before,a,thermoregulatory,response,occurs.,The, increase,in,interthreshold,range,results,in,vasodila=on,,leading,to,the,redistribu=on,of,heat,from,the, core,to,the,periphery,,with,a,rapid,narrowing,of,the,core,to,periphery,temperature,gradient,as,core, temperature,decreases.,This,heat,redistribu=on,accounts,for,the,majority,(approximately,80%),of, hypothermia,occurring,over,the,first,1;3,hours,of,general,anaesthesia, (Matsukawa,et,al.,1995b).,The, next,phase,of,hypothermia,is,a,more,gradual,decrease,in,temperature,as,metabolic,heat,produc=on, does,not,compensate,for,heat,loss,to,the,environment.,This,results,from,a,decrease,in,the,basal, metabolic,rate,by,30;40%,and,a,reduc=on,in,muscle,ac=vity.,Finally,,if,anaesthesia,is,sufficiently,long,(>, 3;5,hours),,a,steady,state,is,achieved,between,heat,produc=on,and,heat,loss,,which,may,result,from,a, combina=on,of,external,warming/,insula=on,or,ac=va=on,of,vasoconstric=on,,or,both.,These,three, phases,of,hypothermia,have,been,observed,in,veterinary,medicine, (Redondo,et,al.,2012a;,Redondo,et, al.,2012b).,Our,data,support,these,findings,,showing,the,biggest,temperature,drop,occurring,in,the,hour, or,so,following,the,induc=on,of,general,anaesthesia,(between,pre;induc=on,and,pre;incision),,with,the, magnitude,of,decrease,(1.6˚C),reflec=ng,that,reported,in,humans,and,dogs, (Cabell,et,al.,1997;, Matsukawa,et,al.,1995b;,Redondo,et,al.,2012b).,Addi=onally,,we,iden=fied,a,modest,decrease,in, temperature,associated,with,premedica=on,and,speculate,that,this,resulted,from,decreased,ac=vity., Redondo,et,al.,(2012),found,that,a,longer,pre;anaesthe=c,period,,the,=me,from,premedica=on,to, induc=on,of,anaesthesia,,was,associated,with,lower,core,body,temperatures,at,the,end,of,anaesthesia, (Redondo,et,al.,2012b).,Considered,together,,this,makes,a,case,for,avoiding,extended,pre;anaesthe=c, periods,,once,the,desired,effect(s),of,premedica=on,has,been,achieved.…”

The Association of Shelter Veterinarians’ 2016 Veterinary Medical Care Guidelines for Spay-Neuter Programs

“…Therefore, efforts to maintain normal body temperature should be made from the time of patient admission until discharge. 62 Prior to premedication and induction of anesthesia, ambient temperature and humidity should be controlled to keep animals comfortable. Drafts should be avoided, and animals should be kept dry.…”