- DDi vdi mot sDthuDc chi sau khi chuyen hoa mdi cotac dung hoac tang dQc tinh thi cam ling enzym lam tang tac dung hoac tang dQc tinh cua thuoc.
2. THUne GAy ME DU'dNG HO HAP
2.1. D~c di~m chung
2.1.1. Chuyi'n vgn cua thutk: gay me
Cac thuoc gay me duong' ho hap la cac chat khi hoac chat long bay hoi. Khi hit vao, thuoc gay me qua mui tdi ph6i, khuech tan vao mau r6i den than kinh trung uong va gay tac dung uc che. Khi nong de?thuoc gay me d than kinh trung uong dat tdi ngudng, trang thai me se xu at hien.
S1jxam nhap thu6c gay me vao ph6i phu thuoc vao n6ng de?thuOc gay me trong khong khi hit vao va s1jthong khi d ph6i.
S1j xam nh~p cua thu6c gay me tit ph6i vao mau ph\l thue?cvao s1j chenh l~ch n6ng de?gifia ph6i va mau, tinh tham cua mang phe nang va d~c bi~t la tinh hoa tan cua thu6c gay me trong mau. Trong d6, tinh hoa tan cua thu6c gay me trong mau la yeu to' quan tr9ng nhat, dUQcbi~u thi b&ngh~ so'phan bo'maul
khi. Cac thuo'c gay me it tan trong mau c6 h~ so'phan b6 maul khi nho, ap suat de?ngmlilchtang nhanh, nen dliltcan b&ngd nao nhanh, thdi gian ti~m tang se nglin va nguQc llili.Vi d\l: h~ s6 phan b6 maul khi cua nitrogen oxyd, halothan va methoxyfluran Illn lUQtla 0,47- 2,3- 12 nen nitrogen oxyd gay me nhanh nhat con methoxyfluran gay me ch~m (xem bang 3.2).
Bang 3.2. M¢tsod~e tfnh ella thuec gay me dllong he hap
Ten thuoc MAC* (ty I~ %) H~ so philn bo maulkhi Chuy~n h6a (ty I~ %)
Nitrogen oxyd 105 0,47 0 Halothan 0,75 2,3 > 40 Enfluran 1,7 1,8 8 Isofluran 1,4 1,4 <2 Methoxyfluran 0,16 12 >70 Sevofluran 2,0 0,69 2- 5 Desfluran 6- 7 0,42 < 0,05
(*)MAC (Minimum Alveolar Concentration): n6ng dQto'i thie'u cancoCllathuoc trong ph€' nang.
M(>tphan cac thuoc gay me h6 hap duoc chuyen hoa d gan (nhu halothan chuyen hoa thanh clorotrifluoroetyl) gay d(>cvdi gan.
Cac thuoc gay me duong he hap chu ye'u duoc thai trir qua duong he hap, mot phan thai tru qua than nen co th~ gay d(>cvdi than, Vi du: cac thu6c co chua halogen nhat la methoxyfluran khi chuyen hoa d gan giai phong ra halogen. Cac halogen nay thai trir qua than, gay d(>ccho than,
2.1.2. Tac d¥ng
• Ttic dung gay me
Hoat tinh gay me cua thu6c duoc xac dinh dua VaGn6ng d(>t6i thi~u cua thuoc trong phe' nang (Minimum Alveolar Concentration- MAC) lam mat van d(>ngtren 50% benh nhan d6i vdi m(>tkich thich dau chuan. Thu6c gay me co MAC cang thap thi hO:,lttinh gay me cang m:,lnh. Gia trj MAC co th~ giam d ngudi cao tu6i.
• Tac dung tren cae cd quan
- Tren h6 hap: hllu he't thu5c gay me ho hap deu gay uc che' ho hap d cac muc d(> khac nhau, trong do gay uc che' m~nh nhat la isofluran va. enfluran.
- Tren nao: lam giam chuy~n hoa d nao nhung tang luu luqng mau nao nen tang ap l\iC S9 nao (nhat la d ngtidi bi chan thudng vung dllu hay u nao). Trong do, nitrogen oxydit gay tang ap l\iCS9nao nhat.
- Tren h~ tim m~ch: n6i chung, thuO'c gay me (halothan) uc che'tim, gian m:,lch va h:,l huye't ap. Tuy nhien, m(>t so' thu6c nhu isofluran, methoxyfluran va enfluran co th~ lam tang nhip tim (thong qua phan X:,l cUdnggiao cam).
- Tren cd: hllu he't cac thu6c gay me ho hap deu co tac d\lng gian cd.
- Tren th?n: tat ca cac thu6c gay me deu lam giam t6c d(>19Ccllu th?n va luu luqng mau qua th?n do tang suc can m~ch th?n, tuy nhien muc d(>anh hUdng khac nhau.
2.1.3. Cac thai kj gay me
Dua vao d9 nhay cam cua than kinh trung uong doi vdi thuoc gay me theo thu tv tu vo nao xuong dudi vo va dua vao dau hieu lam sang, Arthur Credel (1920) da chia tac dung cua thuoc gay me ho ha'p thanh 4 giai doan tuong ung
vdi 4 thoi ky gay me.
Giai doan 1:Thdi ky guim dau
Thuoc gay me uc che trung tam cao cap d vo nao lam nguoi benh mat dan linh cam, cam giac k~ ca cam giac dau, cam giac nong va cam giac lanh.
Giai doon 2:Thai ky kich thich
Thuoc gay me uc che' trung tam van d9ng d vo nao lam trung tam van d9ng dudi vo nao thoat uc che, benh nhan d trang thai kich thich: la het, gi~y dua, non, ho, tang tiet dom, co th~ gay co th!1t khi phe' quan, ho ha'p khong deu, nhip tim khong deu, huyet ap tang ... Thdi ky kich thich chi keo dai 1- 2 phut nhung la thdi ky d~ gay tai bien, vi v~y phai phoi hqp thuoc d~ lam giam ho?c ma't thdi ky nay.
Giai dogn 3:Thdi ky phdu thu~t
Thuoc gay me uc che xuong vling duoi vo va tllY song gay mat y thuc, mat phan x:;t"gian cd. Thdi ky nay phli hqp cho cac ph~u thu~t.
Giai dogn 4:Thdi ky li¢t hanh tily
Thuoc gay me uc che vao trung tam ho hap va v~n m:;t,chd hanh nao, lam tim d~p ch~m, yeu, m:;t,chyeu, roi lo:;t,nho hap, co th~ gay ngung tim, ngung ho hap. Neu khong cap cuu kip thdi b~nh nhan se chet sau 3 - 4 phut. Vi v~y, khong duqc gay me vuqt qua giai do:;t,n3.
Khi ngung si't d1,lngthuoc gay me, ho:;t,td9ng clla cac trung khu th~n kinh duqc h6i ph1,lcd~n d~n theo thu tv ngtiqc l:;t,i.
2.2. Ether
Dij,c diem
La chat long khong mau, mlii thdm d?c bi~t, rat d~ chay nt), khi g?P khong khi, anh sang chuy~n thanh peroxyt ethyl rat d9c.
Dztf/c di}ng h(Jc
Cac thuoc gay me ho hap noi chung va ether noi rieng, sau khi duqc hap thu vao mau se ph an bo d~u tien vao cac cd quan co luu luqng mau cao (nhu nao, tim, gan, th~n) sau do vao cac cd quan it duqc tuoi mau nhu cd, rna. Khoang 2 - 3% thuoc duqc chuy~n hoa d gan thanh acetaldehyd, alcol, acid acetic ... khoang 85-90% thuoc thai tru qua dUdng ho hap d d:;t,ngchua chuy~n hoa. Cac chat da chuy~n hoa qua gan duqc thai tru qua nuoc ti~u.
Tcic dung
_ Gay me: ether c6 tac dung gay me manh, giam dau va gian co teSt.Nhung do ether c6 h~ s6 phan b6 maul khi Ion nen thoi ky khdi me keo dai va d~ gay kich thich.
_ Tren tim mach va huyet ap: d lieu gay me, thuoc kich thich nhe than kinh giao cam lam giai ph6ng cac catecholamin nen gay tang nhe nhip tim va huyet ap,Thu6c gay gian mach nao, tang ap luc SQnao.
_ Tren ho hap: gay gian nhe khi quan nhung kich thich manh niem mac ho hap gay tang tiet dom dai, gay phan xa co thit thanh quan, gay non.
_ Covan: c6 tac dung gian co van do uc che tuy s6ng, b6 thap va uc che d~n truyen van dQng,c6 tac dung hiep d6ng vdi cac thuoc gian co nhu cac thu6c gian co loai cur a ch6ng khli C\tc, cac khang sinh c6 tac d\lng gian cd nhu khang sinh nh6m aminosid, lincosamid.
Tcic dung khong mong mu{/n
Kh6 duy tri sl;ib6c hdi 6n dinh (do binh chua l~nh d~n), d~ chay n6, khdi me dai, d~ gay non va kich thich nen hi~n nay rat it dung.
Chong chi dinh
- Tang ap ll;iCSQnao. - B~nh ti~u dudng.
- Suy gan, suy th~n n~ng. - SeStcao.
Lie'u dung
Trung binh 12D-150mU l~n gay me. LQ120mL.
2.3. Halothan
Dij,c die"'m
Halothan la chat long khong mau, d~ bay hdi, mui thdm d~ chiu, khong chay n6, g~p anh sang d~ chuy~n thanh acid bay hdi, an mon kim lo:;ti(tru crom va k~n), hoa tan cao su, chat deo (tru polyethylen), khong bi voi soda phan hUY.
Tcic dlfng
_ Gay me: ho:;tttinh gay me tudng d6i cao, xu~t hi~n tac d\lng gay me tudng d6i nhanh, em diu, dnh nhanh, khong gay kich thich nhung gian cd va giam dau kern nen thudng phai ph6i hqp them voi cac thu6c giam dau va gian cd.
_ Tren ho hap: thu6c gay uc che ho hap, lam giam luu luqng ho hap. Neu gay me sau d~ gay thieu oxy cho mo, gay toan mau va ngung thd nen thudng phai h6 trq thd oxy. Thu6c khong gay kich thich niem m:;tcho hap, khong lam tang tiet dich va c6 tac d\lng gian cd trdn khi quan.