Identification of the Risk Factors Associated with ICU Mortality

Transcription

1 Bomtrcs & Bostatstcs Intrnatonal Journal Idntfcaton of th Rsk Factors Assocatd wth ICU Mortalty Abstract Th objctv of ths study s to dntfy th rsk factors that nflunc th surgcal and mdcal Intnsv Car Unt (ICU) mortalty. W consdrd data that was collctd at Bay Stat Mdcal Cntr n Sprngfld, Massachustts []. W dvlopd statstcal modls that dntfy th rsk factors assocat wth ICU mortalty. In ordr to dntfy th rsk factors wthout subjctv bas, w xplord multpl varabl slcton mthods. W xplord svral mthods ncludng what w call manually pckd bst modl, forward slcton, backward lmnaton, and th last absolut shrnkag and slcton oprator (LASSO). W appld 5-fold cross valdaton on th fnal modl of manually pckd bst modl, forward slcton and backward lmnaton and appld both valdaton st approach and 5-fold cross valdaton on LASSO to crat confuson matrcs and calculat th rror rat of ach mthod. Fnally, w rcommndd th modl for prdctng ICU mortalty wth lowst msclassfcaton rror rat. Volum 6 Issu Nassr Abdullah K Alghamd and Munn Bgum 2 * Mathmatcs dpartmnt, Albaha unvrsty, Saud Araba 2 Dpartmnt of Mathmatcal Scncs, Ball Stat Unvrsty, USA Rsarch Artcl *Corrspondng author: Munn Bgum, Dpartmnt of Mathmatcal Scncs, Ball Stat Unvrsty, Munc, IN 47306, USA, Tl: ; Emal: Rcvd: May 2, 206 Publshd: Jun 5, 207 Introducton Th car and tratmnt of crtcally ll patnts n spcal rooms wth lf-savng tchnology s th major componnt of modrn mdcal scnc. Th dagnoss and tratmnt of th patnts n crtcal condtons s hghly dpndnt on nvasv dagnostc as wll as thraputc procdurs. Howvr, th man dsrupton of host dfns mchansms coms from th lf support systms. Accordng to Morand, Jackson, and Wsly [2], thr ar ICUacqurd nfctons that s rsponsbl for th hgh mortalty rat of th ICU patnts. Th rsarchrs study offrs a usful nformaton concrnng th topc. Th am of thr study was to dtrmn th pdmology as wll as th rsk factors for nosocomal nfctons and th mortalty rat n th ICU. Du to th varatons of th study mthods, th nfcton rats from dffrnt ICUs ar dffcult to compar. Grard, Pandharpand, & Ely [3] show that dlrum, a fluctuatng dsturbanc of cognton, s a sgn of acut bran dysfuncton n th patnts wth crtcal llnsss n th ICU. Th patnts wth crtcal llnsss ar mor lkly to hav dlrum. Also, Morand, Jackson, & Wsly Ely [2] show that dlrum can b rlatd to th cogntv mparmnt that prssts for an xtndd prod aftr dscharg. Tchnqus of tratng dlrum at th ICU has bn th subjct of nvstgatons n th rcnt past. Ag s also suggstd as on of th prdctors of mortalty n th ICU. Th numbr of ldrly patnts who ar bng admttd to th ICU has bn ncrasd, not only n th USA but also ntrnatonally (Blayach t al. [4]). Thr ar fw studs that hav bn conductd to lnk old ag wth th ICU mortalty rat. Th currnt rsarch ncluds ag as on of th rsk factors for ICU mortalty. Background Th ICU mortalty rat n any hosptal s th hghst compard to othr unts. Th Untd Stats of Amrca has an approxmat 4 mllon ICU admssons annually and th mortalty rat of 500,000 daths vry yar. Th mdcal rrors occur n any unt of th hosptal, but t mor lkly to occur n th ICU snc th ICU patnts undrgo complx ntrvntons. A study on th mortalty rsk factors and valdaton of svrty scorng systms n th crtcally ll patnts wth acut rnal falur was conductd to dntfy th dtrmnants for mprovng patnt car. Rnal falur has a hgh prvalnc n th ICU and assocatd wth hgh mortalty rats. Idntfcaton of th mortalty rsk factors hlps to addrss ntrvnton to ths rsk factors and mprovs patnt car (Lma, Zantta, Castro & Yu [5]). Iwuafor, t al. [6] conductd a study sought to dtrmn th prvalnc, rsk factors, clncal outcom, and th mcrobologcal profl of th hosptal-acqurd nfctons n th ICU of a Ngran hosptal. Infctons commonly affct crtcally ll patnts and hav a hgh assocaton wth mortalty. Th study dntfd blood stram nfctons and th urnary tract nfctons as a sgnfcant rsk factors assocatd wth th ICU mortalty. Data and Varabl dscrpton W consdrd data collctd at Bay Stat Mdcal Cntr n Sprngfld, Massachustts that can b downloadd from Unvrsty of Massachustts, Amhrst wbst []. Th datast conssts of 200 obsrvatons wth 20 varabls. Th rspons varabl (STA), vtal status s catgorcal. Th othr catgorcal prdctor varabls ar: Gndr, Rac, SER (Srvc at ICU Admsson), CAN (Cancr Part of Prsnt Problm), CRN (Hstory of Submt Manuscrpt Bom Bostat Int J 207, 6(): 0057

2 Copyrght: Idntfcaton of th Rsk Factors Assocatd wth ICU Mortalty 207 Alghamd t al. 2/0 Chronc Rnal Falur), INF (Infcton Probabl at ICU Admsson), CPR (CPR Pror to ICU Admsson), PRE (Prvous Admsson to an ICU wthn 6 Months), TYP (typ of admsson), FRA (Long Bon, Multpl, Nck, Sngl Ara, or Hp Fractur), PO2 (PO2 from Intal Blood Gass), PH (PH from Intal Blood Gass), PCO (PCO2 from ntal Blood Gass), BIC (Bcarbonat from Intal Blood Gass), CRE (Cratnn from Intal Blood Gass) and LOC (Lvl of Conscousnss at ICU Admsson). Th contnuous prdctor varabls ar Ag, SYS (Systolc Blood Prssur at ICU Admsson) and HRA (Hart Rat at ICU Admsson). Tabl shows th total numbr of ICU patnts accordng to vtal status. It shows 80% of patnts survvd and 20% dd. Fgur shows th graphcal rprsntaton of ths statstcs. Tabl : Vtal Status of ICU Patnts. Status Frquncy Status Prcntag Survvd Dd Total Survvd (%) Dd (%) Total (%) Fgur : Numbr of ICU patnts accordng to Vtal Status. Th tabl abov shows that, 24 mals dd (2%) out of 24 total mals and 6 fmals dd (8%) out of 76 fmals at th ICU. From ths rsults, t clarly dmonstrats that mals ar mor vulnrabl to th ICU mortalty as compard to fmals. Th study also sought to dtrmn whthr thncty s assocatd wth mortalty. From th tabl abov, 37 (8.5%) of 75 Whts dd, (0.5%) out of 5 Blacks dd, and 2 (%) out of 0 othrs dd. Th survval rat for th black patnts and othr racs was lss (7% and 4% rspctvly) compard to that of th wht patnts (69%). Howvr, thr wasn t suffcnt data n th Black and Othr catgory to mak dcsv comparson. W can s 46.5% of patnts wr mdcally tratd at ICU compard to 53.5% of patnts who wr tratd surgcally. Thr was no ncdnc of cancr n 90% of ICU patnts. Out of thos, 8% dd. In addton, 2% of patnts who had cancr dd. Th abov rsults dmonstrat that th cancr s a low prdctor of ICU mortalty for th crtcally ll patnts admttd to th ICU. Accordng to ths rsults, th prsnc of cancr can lad to th survval of th patnt n th ICU. W notc that only 9.5% of patnts had chronc rnal falur compard to 95.5% who dd not hav that falur. Th rsults abov show that th hstory of chronc rnal dsas s not a rsk factor for mortalty of th crtcally ll patnts admttd to th ICU. For th patnts wth a hstory of chronc rnal falur, th mortalty was 4%, whch s four tms lowr compard to thos who dd not hav a hstory of chronc rnal falur whch was 6%. W notc that 2% of patnts who had nfcton at ICU admsson dd compard to 8% wthout nfcton who dd. Infcton at ICU admsson s a usful prdctor of mortalty n th ntnsv car unt wth thos nfctd havng a hghr lklhood of dath compard to th unnfctd ons. Also 6.5% of ICU patnts had CPR pror to ICU admsson. Th prcntag of patnts wth CPR pror to th ICU admsson who dd s low compard to th prcntag of patnts wthout CPR. It can b sn 5% of patnts had prvous admsson to an ICU wthn 6 months. Th prvous admsson to th ntnsv car unt s not a prdctv factor for th mortalty rat n th ICU. Th prcntag of popl wth prvous admssons to th ICU who dd s low compard to thos who had not bn admttd bfor. W can s that thr ar mor daths assocatd wth mrgncy admsson compard to th lctv admsson. From th abov rsults, w can s that th mortalty rat s 9% for th mrgncy admsson as compard to th % of lctv admsson. Th only 5 patnts had fractur and 3 of thm dd. In contrast 37 patnts out of 85 who dd not hav fractur dd. Th majorty of patnts at ICU had PO2 from ntal blood gass gratr than 60. Th mortalty rat for patnts whos PO2 s gratr than 60 s 7.5%. Patnts whos ntal blood gass PH was hghr than 7.25 showd hghr mortalty rat that was twc that of th patnts whos ntal blood gass PH was blow In addton, th mortalty rat for patnts whos PCO2 from ntal blood gass lss than 45 s hghr than thos whos PCO2 s gratr than 45. Th mortalty rat of patnts whos Bcarbonat from ntal blood gass was gratr than 8 s svn tms th mortalty rat of patnts whos Bcarbonat from ntal blood gass was lss than 8. It can b sn th ICU patnts whos cratnn lvl from ntal blood gass was gratr than 2.0 hav a hghr mortalty rat. Th rsults abov show that th mortalty rat of ICU patnts who had dp stupor or coma was hgh. Patnts who had no coma survvd wth a probablty of mor than 85%. Th rsults n Tabl 3 dmonstrat that ag plays a sgnfcant rol n th admsson of patnts to th ICU. Tabl 3 and Fgur 2 show that patnts ag s btwn 6 92 yars old and th majorty of ICU patnts ar btwn yars old. In addton, th boxplot shows th man ag of dd patnts s 70. Fgur 3 shows that th majorty of patnts wr at rsk who had systolc blood prssur btwn 20 to 40. Th man of systolc blood prssur of th patnts at ICU s 32.3 mmhg. Th boxplot shows a patnt who had 256 mmhg dd. Fgur 4 shows th admsson to th ICU s hghr for th patnts wth hgh hart rat wth th man hart rat durng th frst day of admsson bng 98/mn. Th hart rat, howvr, dpnds on varous factors such as th patnt s mood, body tmpratur, physcal actvts, tc. Ctaton: Alghamd NAK, Bgum M (207) Idntfcaton of th Rsk Factors Assocatd wth ICU Mortalty. Bom Bostat Int J 6(): DOI: /bbj

3 Copyrght: Idntfcaton of th Rsk Factors Assocatd wth ICU Mortalty 207 Alghamd t al. 3/0 Tabl 2: Catgorcal varabls and Vtal Status of ICU Patnts. Status Frquncy Status Prcntag Survvd Dd Total Survvd (%) Dd (%) Total (%) Gndr Mal Fmal Wht Rac Black Othr Srvc Cancr Chronc Infcton CPR PRE Typ Fractur PO2 PH PCO2 BIC CRE Mdcal Surgcal No Ys No Ys No Ys No Ys No Ys Elctv Emrgncy No Ys > < > < < > > < < > No coma LOC Dp stupor Coma Ctaton: Alghamd NAK, Bgum M (207) Idntfcaton of th Rsk Factors Assocatd wth ICU Mortalty. Bom Bostat Int J 6(): DOI: /bbj

4 Copyrght: Idntfcaton of th Rsk Factors Assocatd wth ICU Mortalty 207 Alghamd t al. 4/0 Tabl 3: Contnuous varabls summary. Summary Mn. st Qu. Mdan Man 3rd Qu. Max. Ag Systolc Blood Prssur Hart Rat Fgur 3: Systolc Blood Prssur and Vtal Status. Objctv Idntfcaton of Rsk Factors of ICU Mortalty Snc th rspons varabl n our data (vtal status) s bnary, bnary logstc rgrsson s an approprat modl to consdr. Logstc rgrsson s a prdctv analyss tchnqu usd to llustrat th rlatonshp btwn a bnary rspons varabl and th prdctors usng th rgrsson on th logarthm of th odds of havng a rspons [7,8]: Lt Y b th bnary rspons varabl for Y = 0, th patnt survvd Y =, th patnt dd π thn, logt ( π ) = log π th patnt, wth Fgur 2: Ag and Vtal Status. β + β x + + β x 0 k k Ctaton: Alghamd NAK, Bgum M (207) Idntfcaton of th Rsk Factors Assocatd wth ICU Mortalty. Bom Bostat Int J 6(): DOI: /bbj

5 Copyrght: Idntfcaton of th Rsk Factors Assocatd wth ICU Mortalty 207 Alghamd t al. 5/0 Whr, π = W consdr multpl varabl slcton mthods n ordr to dntfy rsk factors n an objctv mannr. Ths ar manually pckd bst modl, forward slcton, backward lmnaton and last absolut shrnkag and slcton oprator (LASSO). W dscuss ths mthods brfly as follows. <.0) manually and rmov all th factors whch ar nsgnfcant. W thn rft th modl wth all th sgnfcant varabls n th modl. Forward slcton For forward slcton, a null modl (a modl wth no prdctors), srvs as th startng pont. W add on varabl at a tm to th null modl and rfttd th modl ncludng th addd varabls. Th da was to kp t f th varabl that had bn addd was sgnfcant and thn add th nxt varabl. If not, w lmnatd t and addd th nxt varabl. W rfttd th modl usng th sam procdur untl th stoppng rul was satsfd (all th varabls n th modl ar sgnfcant). Backward slcton Backward lmnaton mthod starts wth a full modl that contans all th prdctors n th modl. Th last sgnfcant rsk factors; that s, th ons havng th largst P valu (gratr than 0%) ar lmnatd, and th modl s thn rfttd. Each stp rmovs th last sgnfcant varabl from th modl untl th rmanng varabls hav thr P valus smallr than th spcfd 0.0. Last Absolut Shrnkag and Slcton Oprator (LASSO) Wth ths mthod, thr s an automatc slcton of prdctors of th targt varabl from th larg st of potntal prdctors. By dong so, th mthod wll rturn th coffcnts of th rrlvant varabls to zro thrby prformng an automatc slcton of varabls. Th LASSO formulats a curv fttng as a quadratc programmng problm wth th objctv functon that pnalzs th absolut sz of th coffcnts basd on a valu of a tunng paramtr, say. Th mthod, thrfor, shrnks th sz of th nonzro coffcnts and nds up wth th most usful varabls. π logt ( π ) = log π β0 + βx + + βkx + LASSO pnalty k + LASSO pnalty Fgur 4: Hart Rat at ICU Admsson and Vtal Status. Manually pckd bst modl In ordr to dntfy th rsk factors for th vtal status at ICU, whch s a bnary rspons varabl, w startd wth th procss of manually pckd bst modl. To corrctly lvrag ths mthod, w bgn wth bnary logstc rgrsson modl. Frst, w ft a modl wth all prdctor varabls. Nxt w pck th sgnfcant varabls (n ths cas rsk factors) wth th smallst P-valu (P Whr, π = LASSO pnalty = λ β + λ p j= + λ π > 0.5, y = β p j= j β j ( dad ) p j= Wth th prdctd probablty of th bnary rspons, can prdct th rspons tslf usng th abov cut pont. Thus, f th prdctd probablty of dyng s gratr than 0.5, w codd th prdctd rspons as (dd) and 0 (survvd) othrws. j w Ctaton: Alghamd NAK, Bgum M (207) Idntfcaton of th Rsk Factors Assocatd wth ICU Mortalty. Bom Bostat Int J 6(): DOI: /bbj

6 Copyrght: Idntfcaton of th Rsk Factors Assocatd wth ICU Mortalty 207 Alghamd t al. 6/0 Valdaton and k-fold cross valdaton approach Valdaton/cross valdaton approach s an objctv mthodology to slct an optmal stratgy. To slct th bst modl from th varabl slcton modls slctd by four stratgs, w mplmnt valdaton and cross valdaton. W appld k-fold cross valdaton approach on th fnal modl of manually pckd bst modl, forward slcton and backward lmnaton to crat th confuson matrcs and calculat th rror rat of ach mthod. Snc w hav 200 obsrvatons, w dcdd to us 5 folds whch splt th data nto two; tranng and tstng datasts. Tranng st had 60 obsrvatons and tstng st had 40 obsrvatons (total 5 sts ach havng 40 obsrvatons). k-fold cross-valdaton approach s applcabl whr th orgnal sampl s parttond at random nto k subsampls and on s lft out n vry traton stp. Lt k parts b C, C., C, whr C dnots th ndcs 2 K of th obsrvatons n part. W hav th followng formula to stmat rror rat: K n CV = ( MSE ) n = Whr MSE = y y / n k, C obsrvaton, and n 2 y s th ft for = n K. For ths study, n=200, K= 5. So, thr ar 200/5 parts of 40. Th data s splt to two groups of tstng and tranng: tstng = 40 and tranng = 60. W ft logstc modls on th tranng data sts and calculat msclassfcaton rror rat on th tst data. In addton, w conductd k- fold cross valdaton and valdaton st on LASSO and compard th rsults of ach mthod. Snc w hav 200 obsrvatons, w dcdd to us valdaton st whch splt th data nto two; tranng and tstng datasts. Tranng st had 00 obsrvatons and tstng st had 00 obsrvatons (total 2 sts ach havng 00 obsrvatons). Th valdaton st rror rat s dtrmnd usng: n CV = n h = 2 Whr s th rsdual obtand from fttng a modl to all th n obsrvatons. Rsults and Dscusson Manually pckd bst modl In ths mthod, w ft a modl wth all prdctor varabls. W pck th sgnfcant varabls (n ths cas rsk factors) wth th smallst P-valu (P < 0.0) manually and rmov all th factors whch ar nsgnfcant. W thn rft th modl wth all th sgnfcant varabls n th modl. Tabl 4 shows th sgnfcant and nsgnfcant prdctors of th manually pckd bst modl. Tabl 4: Modl (All varabls). Estmat Std. Error z valu P-valu Sgnfcanc (Intrcpt) AGE Sgnfcant GENDER RACE SER CAN Sgnfcant CRN INF CPR SYS HRA PRE TYP Sgnfcant FRA PO PH Sgnfcant PCO Sgnfcant BIC CRE LOC Sgnfcant Ctaton: Alghamd NAK, Bgum M (207) Idntfcaton of th Rsk Factors Assocatd wth ICU Mortalty. Bom Bostat Int J 6(): DOI: /bbj

7 Copyrght: Idntfcaton of th Rsk Factors Assocatd wth ICU Mortalty 207 Alghamd t al. 7/0 W rft th modl wth th sgnfcant prdctors (rsk factors n ths cas) and lmnat th nsgnfcant prdctors all togthr. Tabl 5 blow shows th fnal modl wth all sgnfcant varabls. It shows that th rsk factors ag, cancr part of prsnt problm, typ of admsson, PH from Intal blood gass, PCO2 from ntal blood gass and Lvl of conscousnss at ICU admsson as th rsk factors [9,0]. From tabl 5, our modl quaton can b wrttn as: π logt ( π ) = log π = β + β x + β x β x + β x + β x + β x ( ) = AGE CAN TYP PH PCO LOC β Tabl 5: Modl 2 (fnal modl of manually pckd bst modl). Estmat Std. Error z valu P-valu Sgnfcanc (Intrcpt) E-07 AGE Sgnfcant CAN Sgnfcant TYP Sgnfcant PH Sgnfcant PCO Sgnfcant LOC E-05 Sgnfcant π = Consdrng th mdan ag =63, prsnc of cancr =, typ of admsson was lctv =0, had no coma or stupor =0, and kp th rst factors fxd, w found: π =.2% β = chanc of mortalty. + Consdrng th sam as abov xcpt th typ of admsson was mrgncy =, w found: π = 67.8% β = chanc of + mortalty. In addton, f typ of admsson s mrgncy =, had coma =2, and kp th rmanng factors fxd w found th chanc of mortalty ncrasd from 67.8% to 99.5%. Forward slcton modl For forward slcton, a null modl (a modl contans no prdctors), srvd as th startng pont. W addd on varabl at a tm to th null modl and rfttd th modl ncludng th addd varabls. Th da was to kp t f th varabl that had bn addd was sgnfcant and thn add th nxt varabl. If not, w lmnatd t and addd th nxt varabl. W rfttd th modl usng th sam procdur untl th stoppng rul was satsfd (all th varabls n th modl ar sgnfcant mtng th lvl of 0%). Th tabl abov shows th fnal modl of forward slcton mthod. It shows that th rsk factors ag, typ of admsson and lvl of conscousnss at ICU admsson statstcally sgnfcant for th ICU status. From tabl 6, our modl quaton can b wrttn as: π logt ( π ) = log π = β + β x + β x + β x = AGE TYP LOC Consdrng th mdan ag =63, typ of admsson was lctv=0, had no coma or stupor=0, and kp th rst factors fxd, w found: π = 3.09% β = chanc of mortalty. + Consdrng th sam as abov xcpt th typ of admsson was mrgncy =, w found: π = = 22.2% chanc of mortalty. Backward lmnaton modl In ths mthod, w bgan wth th full modl whch ncluds all prdctors n th modl and lmnat varabls on at a tm. Th last sgnfcant rsk factors; that s, th ons havng th largst P Ctaton: Alghamd NAK, Bgum M (207) Idntfcaton of th Rsk Factors Assocatd wth ICU Mortalty. Bom Bostat Int J 6(): DOI: /bbj

8 Copyrght: Idntfcaton of th Rsk Factors Assocatd wth ICU Mortalty 207 Alghamd t al. 8/0 valu (gratr than 0%) ar lmnatd, and th modl s thn rfttd. Tabl 7 shows th fnal modl of backward lmnaton mthod. It shows that th rsk factors ag, cancr part of prsnt problm, systolc blood prssur at ICU admsson, typ of admsson, PH from ntal blood gass, PCO2 from ntal blood gass, and lvl of conscousnss at ICU admsson statstcally sgnfcant for th ICU status. From tabl 7, backward lmnaton modl quaton can b wrttn as: π logt ( π ) = log π = β + β x + β x + β x + β x + β x + β x + β x ( ) ( ) = AGE CAN SYS TYP PH PCO LOC Tabl 6: Fnal modl of Forward slcton. Estmat Std. Error z valu P-valu Sgnfcanc (Intrcpt) E-07 AGE Sgnfcant TYP Sgnfcant LOC Sgnfcant Tabl 7: Fnal modl of backward lmnaton mthod. Estmat Std. Error z valu P-valu Sgnfcanc (Intrcpt) AGE Sgnfcant CAN Sgnfcant SYS Sgnfcant TYP Sgnfcant PH Sgnfcant PCO Sgnfcant LOC Sgnfcant Consdrng th mdan ag =63, prsnc of cancr =, mdan systolc blood prssur =30, typ of admsson s lctv =0, had no coma or stupor=0, and kp th rst factors fxd, w found: π = =.96% chanc of mortalty. Consdrng th sam as abov xcpt th typ of admsson was mrgncy =, w found: π = = 68.06% chanc of mortalty. Last Absolut Shrnkag and Slcton Oprator (LASSO) W ft LASSO wth valdaton st approach. Th rsults ar prsntd n Tabl 8. Tabl 8 shows th fnal modl of LASSO (valdaton st). W can s typ of admsson, and lvl of conscousnss at ICU admsson as th rsk factors. W also fttd LASSO wth applyng 5-fold cross valdaton approach. Tabl 9 has th rsults of ths approach. Tabl 9 shows th fnal modl of LASSO (5-fold cross valdaton). Cancr part of prsnt problm, prvous admsson to an ICU wthn 6 months, typ of admsson, PH from ntal blood gass, PCO2 from ntal blood gass, and lvl of conscousnss at ICU admsson ar dntfd as th rsk factors by ths approach. Msclassfcaton rror rat Th cross-valdaton approach allows to comput msclassfcaton rror rat by calculatng th confuson matrx. Tabls 0 4 prsnt confuson matrcs for manually pckd Ctaton: Alghamd NAK, Bgum M (207) Idntfcaton of th Rsk Factors Assocatd wth ICU Mortalty. Bom Bostat Int J 6(): DOI: /bbj

9 Copyrght: Idntfcaton of th Rsk Factors Assocatd wth ICU Mortalty 207 Alghamd t al. 9/0 bst modl, forward slcton modl, backward lmnaton and LASSO. Tabl 8: Fnal modl of LASSO (valdaton st). Coffcnt (Intrcpt) AGE GENDER RACE SER CAN CRN INF CPR SYS HRA PRE TYP FRA PO2 PH PCO BIC CRE LOC Tabl 9: Fnal modl of LASSO (5-fold cross valdaton). coffcnt (Intrcpt) AGE GENDER RACE SER CAN CRN INF CPR SYS HRA PRE TYP FRA PO PH PCO BIC CRE LOC From th confuson matrx n tabl 0, w calculat th msclassfcaton rror rat of manually pckd bst modl as *00 = 37.5%. 200 Tabl 0: Manually pckd bst modl confuson matrx. Actual Prdctd From th confuson matrx n tabl, w calculat th msclassfcaton rror rat of forward slcton modl as *00 = 42.0%. 200 Tabl : Forward slcton confuson matrx. Actual Prdctd From th confuson matrx n tabl 2, w calculat th msclassfcaton rror rat of backward lmnaton modl as *00 = 37.5%. 200 Tabl 2: Backward lmnaton confuson matrx. Actual Prdctd From th confuson matrx n tabl 3, w calculat th msclassfcaton rror rat of LASSO undr valdaton st Ctaton: Alghamd NAK, Bgum M (207) Idntfcaton of th Rsk Factors Assocatd wth ICU Mortalty. Bom Bostat Int J 6(): DOI: /bbj

10 Copyrght: Idntfcaton of th Rsk Factors Assocatd wth ICU Mortalty 207 Alghamd t al. 0/ approach as *00 = 6.0%. 200 Tabl 3: LASSO confuson matrx valdaton st. Actual Prdctd From th confuson matrx n tabl 4, w calculat th msclassfcaton rror rat of LASSO undr 5-fold cross-valdaton as *00 = 4.5%. 200 Tabl 4: LASSO confuson matrx 5-fold. Actual Prdctd From th rsults abov w conclud that, LASSO (wth applyng 5-fold cross valdaton) s th bst modl for dntfyng th rsk factors assocatd wth th ICU mortalty wth th lowst rror rat (4.5%). W can s cancr part of prsnt problm, prvous admsson to an ICU wthn 6 months, typ of admsson, PH from ntal blood gass, PCO2 from ntal blood gass, and lvl of conscousnss at ICU admsson as th rsk factors [,2]. Concluson Th major objctv of ths study s to dntfy th rsk factors assocatd wth mdcal and surgcal ICU mortalty. In ordr to dntfy th rsk factors wthout subjctv bas, w consdrd dffrnt varabl slcton mthods and rcommndd th mthod that had th lowst msclassfcaton rror rat. Th varabl slcton mthods consdrd n ths study wr manually pckd bst modl, forward slcton, backward lmnaton and last absolut shrnkag and slcton oprator (LASSO). Cross valdaton and valdaton st approach ar appld to th fnal modl of manually pckd bst modl, forward slcton, backward lmnaton, and conductd both valdaton st and 5-fold cross valdaton on LASSO. Valdaton st and 5-fold cross valdaton approachs allow us to calculat th msclassfcaton rror rats for ach mthod and fnalz th dcson by choosng th modl wth th lowst msclassfcaton rror rat. Th procdur dtrmns a rlabl modl that would dntfy th rsk factors assocatd wth ICU mortalty, n an objctv mannr. From th rsults obtand n ths study w rcommnd LASSO (wth applyng 5-fold cross valdaton) as th bst modl that dntfs th rsk factors assocatd wth th ICU mortalty snc t has th lowst rror rat (4.5%). Th modl dntfd cancr part of prsnt problm, prvous admsson to an ICU wthn 6 months, typ of admsson, PH from ntal blood gass, PCO2 from ntal blood gass, and lvl of conscousnss at ICU admsson as th rsk factors. On lmtaton of ths study s that th mthodology s appld to a lmtd publcly avalabl data on ICU mortalty from a sngl hosptal. In ordr to confrm th rsults of ths study an laboratv study on ICU mortalty should b prformd on a randomly slctd hosptals throughout th country. Acknowldgmnt Non. Conflct of Intrst Non. Rfrncs Morand A, Jackson JC, Wsly Ely E (2009) Dlrum n th ntnsv car unt. Intrnatonal Rvw of Psychatry 2(): Grard TD, Pandharpand PP, Ely EW (2008) Dlrum n th ntnsv car unt. Crtcal Car 2(S3). 4. Blayach J, Dndan T, Madan N, Abd K, Abouqal R, t al. (202) Factors prdctng mortalty n ldrly patnts admttd to a Moroccan mdcal ntnsv car unt. Southrn Afrcan Journal of Crtcal Car 28(): Lma EQ, Zantta DMT, Castro I, Yu L (2005) Mortalty rsk factors and valdaton of svrty scorng systms n crtcally ll patnts wth acut rnal falur. Rnal falur 27(5): Iwuafor AA, Ogunsola FT, Oladl RO, Oduybo OO, Dsalu I, t al. (206) Incdnc, Clncal Outcom and Rsk Factors of Intnsv Car Unt Infctons n th Lagos Unvrsty Tachng Hosptal (LUTH), Lagos, Ngra. PLoS On, (0): Bursac Z, Gauss CH, Wllams DK, Hosmr DW (2008) Purposful slcton of varabls n logstc rgrsson. Sourc cod for bology and mdcn 3(): Hosmr DW, Lmshow S, Sturdvant RX (203) Appld Logstc Rgrsson: Thrd Edton Long IYO, Ta DYH (2002) Is Incrasng Ag Assocatd wth Mortalty n th Crtcally II Eldrly. Sngapor Md J 43(): Toufn C, Franca SA, Okamoto VN, Salg JM, Carvalho CRR (203) Infcton as an ndpndnt rsk factor for mortalty n th surgcal ntnsv car unt. Clncs 68(8): Ctaton: Alghamd NAK, Bgum M (207) Idntfcaton of th Rsk Factors Assocatd wth ICU Mortalty. Bom Bostat Int J 6(): DOI: /bbj