Retrospective study of the prevalence of postanaesthetic hypothermia in cats

Abstract

A retrospective study of 275 anaesthetic records of cats was undertaken to examine the prevalence of postanaesthetic hypothermia, its clinical predictors and consequences. Temperature was recorded throughout anaesthesia. The temperature reached at the end was classified as hyperthermia (>39.50 °C), normothermia (38.50 to 39.50 °C), slight hypothermia (38.49 to 36.50 °C), moderate hypothermia (36.49 to 34.00 °C) or severe hypothermia (<34.00 °C). Statistical analysis consisted of multiple regression to identify the factors that affect the temperature at the end of the procedure. Before premedication, the mean (sd) temperature was 38.2 (1.0) °C. At 60, 120 and 180 minutes from induction, the temperature was 35.4 (1.4) °C, 35.0 (1.5) °C and 34.6 (1.5) °C, respectively. The prevalence of hypothermia was slight 26.5 per cent (95 per cent CI 21.7 to 32.0 per cent), moderate 60.4 per cent (95 per cent CI 54.5 to 66.0 per cent) and severe 10.5 per cent (95 per cent CI 7.4 to 14.7 per cent). The variables associated with a decrease in the temperature recorded at the end of anaesthesia were the duration of anaesthesia, the reason for anaesthesia (abdominal and orthopaedic surgeries significantly reduced the temperature when compared with minor procedures) and the anaesthetic risk (high-risk cats showed lower temperatures than low-risk cats). The temperature before premedication was associated with an increase in the final temperature.

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,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.…”

“…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,…”

“…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).…”

Limiting heat loss during surgery in small animals

“…However, such an effect has not been demonstrated in dogs (Pottie and others 2007, Redondo and others 2012b), cats (Redondo and others 2012a) or people (Hooper and others 2009). In the current study, Barnes and others (2017) recognised the importance of the incision size as a potential determinant of heat loss, but did not examine the effect of body mass.…”