Abg Analysis Alpha a Vs Ph Stat

Cerebralbloodflow(CBF) isautorsgulatedoverarangeofmeanarterialprss-sures (MAP) 60-150 mm Hg. This is accomplishedby maintainingtight regional/ metabolism coupling:

J temp = ┬┐metabolism = JCBF Uncoupling oftheautoregulation mechanismoccurs with intracerebralpa-thology and CO 2.

1. pH stat exogenous CO 2 is added =passive cerebralvasodilation occurs overridingthe usualautoregulation mechanism.

(+) CBF canbemaintainedatlowerperfusionpressure,luxurycei^bralperfu-sion can occur

(-) steal from stenosed cerebral arteries, f delivery ofembolito cerebral creuMon

2. a stat: as temperature falls ^pCO2 J ^ cerebral blood flow J, but maintain cerebral autoregulation and flow/metabolism coupling and enables brain to adjust CBF in response to metabolic demands (+) maybe more physiologic, lessen RBChemolysis (-) may maintain adequate regional CBF, despite overall J CBF

Theories aside and in the absence ofoverwhelming evidence (outcome studies) the practicalityis that in the U.S. there is still a50:50split between either management strategy. At TTH, astat is the predominant ABG management.

Selected Readings

1. Cardiopulmonary Bypass: Principles and Practice, Gravalee, Davis and Utley editors: Williams and Wilkins (1992).

2. Murkin JM. Con: Blood gases should be corrected for temperature during hypo-thermic cardiopulmonary bypass. J Cardiothorac Vasc Anes 1988; 2:701-707.

3. Hornick P, Taylor K. Pulsatile and nonpulsatile perfusion: The continuing controversy. J Cardiothorac Vasc Anes 1997; 11:310-315.

4. Bert AA, Stearns GT, Feng W et al. Normothermic cardiopulmonary bypass. J Cardiothorac Vasc Anes 1997; 11:91-99.

5. Tallman RD Jr. Acid base regulation, Alpha stat, and the Emperor's New Clothes. J Cardiothorac Vasc Anes 1997; 11:282-288.

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