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Marie T. Pavini

Richard S. Irwin


T?ng quan v? k? thu?t

- Phn tch kh mu ??ng m?ch (ABG) c?n m?t m?u mu ??ng m?ch ?? lm xt nghi?m ?o pH, p l?c ring ph?n CO2 (PaCO2), p l?c ring ph?n Oxy (PaO2), bicarbonat (HCO3) v ph?n tr?m bo ha oxy mu (SaO2) ?? ?nh gi tnh tr?ng h h?p, chuy?n ha v toan ki?m c?a b?nh nhn.

- D?a vo hnh d?ng ???ng cong phn ly oxy hemoglobin cho th?y vi?c ?o l??ng ?? bo ha oxy mu (SaO2) c th? khng ph?n nh ?ng l??ng oxy mu ??ng m?ch v p l?c ring ph?n Oxy gi?m th?p ?ng k? tr??c khi gi?m ?? bo ha oxy mu ??ng m?ch. M?t khc vi?c xc ??nh ?? bo ha Oxy mu ??ng m?ch (SaO2) qua Oximetry c th? chnh xc h?n khi tnh SaO2 t? kh mu.

- HCO3- trong k?t qu? kh mu ??ng m?ch ???c tnh c s? khc bi?t so v?i HCO3- ???c ?o trong mu t?nh m?ch.

D?ng c?

- D?ng c? l?y m?u kh mu chu?n l m?t syring th?y tinh. Syring ???c n?i v?i kim, v?i m?t kim ?? l?n c th? cho php mu ??ng m?ch t? ??y ln qua kim v vo trong syring m khng c?n ph?i ht.

- C r?t nhi?u lo?i kt l?y m?u kh mu ??ng m?ch v?i syring chuyn bi?t ring cho t?ng b? kt (xem thm ph?n IV.A)

Cc l?a ch?n khc

- B?ng vi?c s? d?ng cc gi tr? hi?u ch?nh, k?t qu? kh mu t?nh m?ch l h?u ch khi khng c nghi ng? v? r?i lo?n oxy ha mu (trong cc tr??ng h?p kh mu ??ng m?ch c s? t??ng ??ng t?t v?i ?? bo ha oxy mu, khi ? khng c thay ??i ?ng k? no v? qu trnh oxy ha mu).

- ??t catheter ??ng m?ch l c?n thi?t ? cc b?nh nhn c?n xt nghi?m kh mu ??ng m?ch nhi?u l?n.

CH? ??NH

Ch?n ?on

- Cc r?i lo?n th?ng b?ng toan ki?m v oxy ha mu c th? nhanh chng d?n ??n cc r?i lo?n nh?p tim n?ng, khng ?p ?ng, th?m ch t? vong v gip ng??i bc s? nh?n ra ???c nguyn nhn c?a cc r?i lo?n nh? gi?m t??i mu m, r?i lo?n chuy?n ha, r?i lo?n h h?p.

- C?n lm xt nghi?m kh mu ??ng m?ch trong cc tr??ng h?p r?i lo?n th?c khng r nguyn nhn, cc r?i lo?n v? h hp, kh?ng ??nh cc r?i lo?n gi?m oxy ha mu ho?c cc b?t th??ng HCO3-

- S? khc bi?t gi?a SaO2 v PaO2 trn kh mu ??ng m?ch c th? g?i ch?n ?on carboxyhemoglobinemia v methemoglobinemia.

- PaO2 trn kh mu ??ng m?ch l c?n thi?t ?? tnh chnh p oxy ph? nang mao m?ch trong vi?c xc ??nh nguyn nhn toan h hp v ki?m h h?p.

- Cc gi tr? trong kh mu ??ng m?ch l c?n thi?t ?? ?nh gi t?ng l??ng oxy mu ??ng m?ch (CaO2), oxy phn ly (DO2) v oxy tiu th? (VO2).


Vi?c ch?c kim vo m?t ??ng m?ch ???c t?o hnh nh? ph?u thu?t c th?:

- Gy ra m?t gi? phnh ??ng m?ch

- Lm m?t tnh ton v?n c?a m?nh ghp

- Lm lan truy?n ? nhi?m khu?n.


Th?n tr?ng

- N?u s? d?ng m?t syring plastic c?n l?u m?t s? l?i sau:
+ PaO2 c?ng nh? Oxy c th? b? th?p gi? t?o do b? l?i p su?t khi PaO2 trong m?u v??t qu 221 mmHg.
+ Syring plastic c t? l? di?n tch b? m?t l?n lm thay ??i tnh th?m c?a kh khi so snh v?i syring 3 ml. V l do ny cc b? kt v?i kim b??m n?i v?i ?ng di khng nn s? d?ng
+ S? d?ng Syring plastic c th? t?o nhi?u b?t kh c?ng nh? kh lo?i b? chng.
+ Khi dng Syring plastic ph?i ko pittng, ?i?u ny c th? ht ph?i mu t?nh m?ch p l?c th?p d?n t?i phn tch m?u mu t?nh m?ch.
+ Khi ko pittng ?? ht mu, b?t kh c th? b? ko theo vo m?u. N?u b?t kh nhi?u c th? lm k?t qu? PaO2 v PaCO2 th?p gi? t?o.

- N?u s? d?ng qu nhi?u heparin s? lm thay ??i n?ng ?? cc kh ha tan (do trong heparin ? c s?n PO2 150 mm Hg; PCO2 <0.3 mm Hg ? nhi?t ?? phng). Ch? c kho?ng 4% tr??ng h?p x?y ra l?i ny khi dng 0.2 ml heparin cho 3 5 ml mu. Ng??c l?i n?u dng t heparin c nguy c? t?o c?c mu ?ng trong m?u. N?u dng heparin tinh th? lm gi?m nguy c? pha long nh?ng t?ng nguy c? t?o c?c mu ?ng.

- N?u m?u mu khng ???c xt nghi?m trong vng 1 pht ho?c khng ???c lm l?nh ? 2 C, PO2 v pH s? th?p, PCO2 t?ng l do t?ng h h?p t? bo v t?ng tiu th? O2 b?i t? bo b?ch c?u v ti?u c?u. ?i?u ny l ?ng k? n?u c t?ng b?ch c?u > 40 109/L ho?c t?ng ti?u c?u 1,000 109/L.

- Cc m?u mu c l?n mu t?nh m?ch s? c k?t qu? PO2 th?p.

- ? m?t ng??i bnh th??ng n?u nh?n th? trong 35 giy s? cho k?t qu? PaO2 gi?m xu?ng 50 mm Hg, pH gi?m 0.07 v t?ng PaCO2 10 mm Hg.

V? tr l?y m?u

- V? tr t?t nh?t l ? ??ng m?ch c h? th?ng tu?n hon bng h? t?t ?? khng b? gi?m t??i mu trong tr??ng h?p co th?t m?ch ho?c c c?c mu ?ng. V? tr ??ng m?ch ? nng st b? m?t da gip ti?p c?n ??ng m?ch d? dng v ?? ?au. ??ng m?ch quay l v? tr ???c ?a thch do h?i ?? cc y?u t? trn. ??ng m?ch tr? cung c?p ?? tu?n hon bng h? ? kho?ng 92% ng??i l?n. Ti?n hnh test Allen th??ng quy khi ch?c kh mu l ?i?u khng c?n thi?t.

- N?u khng ti?p c?n ???c ??ng m?ch quay, ??ng m?ch mu chn, ??ng m?ch chy sau, ??ng m?ch thi d??ng nng (? tr? em), ??ng m?ch cnh tay, ??ng m?ch ?i c th? ???c l?a ch?n thay th?.

- ??ng m?ch cnh tay, ??ng m?ch ?i khng ???c l?a ch?n ? cc b?nh nhn c r?i lo?n ?ng mu v nguy c? ch?y mu gy chn p m?ch c th? x?y ra.

- B?t k? m?ch mu no ? ???c can thi?p ngo?i khoa ??u khng nn lm th? thu?t.

K? thu?t

- ?nh gi k? ton tr?ng b?nh nhn.

- B?c l? b? m?t ??ng m?ch ???c ti?p c?n. N?u ti?p c?n ??ng m?ch quay, l?t ng?a bn tay, g?p nh? c? tay, s? ??ng m?ch. C? ??nh tay c?a b?nh nhn b?ng b?ng dnh ? v? tr ny.

- Lm s?ch v? tr ti?p c?n b?ng dung d?ch alcohol ho?c dung d?ch h?n h?p chlorhexidine/alcohol.

- Tim lidocain 1% trong da t?o n?t s?n nh? b?ng kim 25G t?i v? tr d? ??nh s? ch?c kim catheter.

- N?i kim 22G ho?c m?t kim l?n h?n v?i m?t syring th?y tinh c th? ch?a 5 ml mu. Trng kim v syring b?ng dung d?ch mu?i heparin (1000UI/ml) ho?c s? d?ng b? kt kh mu c s?n.

- Ch?c kim vo ??ng m?ch t?o m?t gc 30 so v?i m?t da d?c theo ???ng ?i c?a m?ch mu ?? trnh ch?c vo mng x??ng n?m d??i ??ng m?ch.

- Khi ? ti?p c?n ???c vo trong lng ??ng m?ch v l?y ???c mu vo trong syring th?y tinh, l?y kho?ng 3 ml mu ho?c s? l??ng ty theo khuy?n co c?a t?ng b? kt kh mu c? th?.

- Ngay sau khi l?y ???c m?u mu, lo?i b? cc b?t kh nh? ?? ch?c ch?n m?u mu khng c b?t kh ?? ??m b?o ?? chnh xc cho k?t qu?. Rt kim ra v ?ng n?p syring

- N?u s? d?ng syring th?y tinh c?n quay trn syring trong lng bn tay t? 5 15 giy ?? tr?n ??u heparin v?i mu.

- p ln v? tr ch?c kim trong kho?ng 5 pht (lu h?n n?u b?nh nhn c r?i lo?n ?ng mu). N?u l?y kh mu ? ??ng m?ch cnh tay c th? p m?ch mu m khng b?t ???c m?ch quay.

- Ngm syring ch?a m?u mu vo ti n??c ? (m?t s? b? kt kh mu khng c?n th?c hi?n b??c ny). V?n chuy?n m?u mu t?i phng xt nghi?m ngay l?p t?c ?? phn tch. ??m b?o r?ng m?u mu ???c dn nhn c th?i gian l?y v ?i?u ki?n thng kh (FiO2 n?u b?nh nhn khng th? my) c?ng nh? nhi?t ?? c?a b?nh nhn.


Bi?n ch?ng

- N?u l?y kh mu ? ??ng m?ch quay th??ng t g?p cc bi?n ch?ng ny. Cc bi?n ch?ng c th? g?p l:
+ C??ng ph giao c?m (hi?m g?p)
+ ?au t?i ch? l?y mu c ho?c khng km theo nn th? (lm sai l?ch k?t qu?)
+ T? mu t?i ch? (t? l? nh? < 0,58%)
+ Phnh m?ch lan r?ng (th??ng do ch?c kim nhi?u l?n)
+ R?i lo?n cc ph?n x? giao c?m (th??ng do ch?c kim nhi?u l?n)
+ Co th?t m?ch
+ Ch?y mu khng ki?m sot ???c
+ T?c m?ch v?i bi?u hi?n thi?u mu ngo?i vi

- N?u l?y kh mu ? ??ng m?ch cnh tay hay ??ng m?ch ?i l v? tr kh p c th? gy ch?y mu nhi?u kh c?m (??c bi?t ? cc b?nh nhn r?i lo?n ?ng mu)

Gi tr? bnh th??ng v hi?u ch?nh

- pH: 7.35 ??n 7.45

- PaCO2: 35 ??n 45 mm Hg

- PaO2 (trong gi?i h?n bnh th??ng, khng ht thu?c l, b?nh nhn trn 40 tu?i: 108.75 - (0.39 s? tu?i) mm Hg

- Nhi?t ??: theo quy ??c nn phn tch m?u kh mu trong ?i?u ki?n 37 C. M?c d khng c nghin c?u no cho th?y c?n ph?i ?i?u ch?nh k?t qu? kh mu theo nhi?t ?? c?a b?nh nhn. Tuy nhin khi m?u mu trn 39 C th c?n hi?u ch?nh theo nhi?t ?? v ? nhi?t ?? th?p h?n ?? ha tan c?a O2 v CO2 s? cao h?n, ?? toan h?n.

- Khi ?o l??ng ?i?n gi?i t? m?u mu ??ng m?ch, lithium ho?c cc ?i?n gi?i g?n v?i heparin c?n ???c ?i?u ch?nh. Mu?i heparin s? lm t?ng n?ng ?? Natri v gi?m n?ng ?? Kali. Cc l?i do ha long c?ng x?y ra n?u dng qu nhi?u ch?ng ?ng.

Ti li?u tham kh?o

1. Allen E. Thromboangiitis obliterans: methods of diagnosis of chronic occlusive arterial lesions distal to the wrist, with illustrative cases. Am J Med Sci 1929;178:237.
The original paper describing the classic safety maneuver before arterial puncture

2. Petty T, Bigelow B, Levine B. The simplicity and safety of arterial puncture. JAMA 1966;195:181.
A classic article describing arterial puncture

3. Raffin T. Indications for arterial blood gas analysis. Ann Intern Med 1986;105:390.
A good review of the indications for arterial puncture

4. Robinson KA, Markowitz DH, Irwin RS. Arterial puncture for blood gas analysis. In: Irwin RS, Rippe JM, Lisbon A, et al., eds. Procedures and techniques in intensive care medicine, 6th ed. Philadelphia: Lippincott Williams & Wilkins, 2008: 108.
A more detailed account of the method for arterial puncture

5. Sasse S, Berry R, Nguyen T, et al. Arterial blood gas changes during breath-holding from functional residual capacity. Chest 1996;110:958.
The arterial PO2 fell by 50 mm Hg on average after 35 seconds of breath holding

6. Schmidt C, Mullert-Plathe O. Stability of PO2, PCO2 and pH in heparinized whole blood samples: influence of storage temperature with regard to leukocyte count and syringe material. Eur J Clin Chem Clin Biochem 1992;30:767.
Storage at 22 C results in a significant reduction in PO2 compared to 4 C.

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