Respuestas Compensadoras JASN 2010

Secondary Responses to Altered Acid-Base Status: The Rules of Engagement Horacio J. Ad rogue ´ * †‡ and Nicolaos E. Madias § *Department of Medicine, Baylor College of Medicine, Houston, Texas; † Department of Medicine, Methodist Hospital, Houston, Texas; ‡ Renal Section, Veterans Affairs Medical Center, Houston, Texas; § Department of Medicine, Tufts University School of Medicine, Boston, Massachusetts; and Department of Medicine, Division of Nephrology, St. Elizabeth’s Medical Center, Boston, Massachusetts The phys iolo gic appro ach to acid -basedisor- ders views blood pH as determined by the pre vai li ng lev el s of car bon ic aci d (Pa CO 2 , t he respiratory component) and plasma bicar- bonat e conce ntrat ion ([HC O 3 ] , th e met a- bolic component), as stipulated by the Hende rson equa tion, [H ] 24 PaCO 2 /[HCO 3 ]. 1 The fou r can oni cal aci d- base disorders include the respi rator y dis orders (acido sis andalkalosis) and the metab olic disorders (acid osis and alka lo- sis). Whereas the respiratory disorders ar e expr esse d as pr imar y change s in PaCO 2 , the metabolic disorders are ex- pressed as primary changes in plasma [HCO 3 ]. 2,3 Each primary change in either the respiratory or the metabolic component elicits in vivo a secondary response in the countervailing component that is directional and proportional to the primary change, albeit fractionally smaller, thus tending to minimize the change in body acidity. These secondary responses orig- inate from physi cochemical buffe ring and change in ventilation, organic-acid met abolism, and ren al aci dif ication. The y ha ve be en qu ant if ied in dog s and hu - mans, are consistent in presence and pre- dict abl e in magn itud e, andare view ed as an integral part of each canonical disorder. Absence of an appropriate secondary re- spons e de not es th e coe xis te nce of an ad di - tional acid-bas e disturbance. 1–3 A popular, alternative epithet of the secon dary resp onses is compe nsat ory. We discourage use of this term, because it evo kes confus ing pronouncements about parti al versus compl ete compensa- tion; secon daryresponses genera lly ame- liorate the impact of primary changes on blood acidity but never completely re- sto re blo od aci dit y to control lev els . Moreover, under certain circumstances, secondary responses yield a maladaptive effect on blood pH (see next section). 1,3 We term the secondary responses to respiratory acidosis (primary increase in PaCO 2 ) and respiratory alk alo sis (pr i- mary decrease in Pa CO 2 ) secondary hy- perbicarbonatemia and secondary hypo - bica rbonat emia , resp ectiv ely. The alte rnati ve terms secondary or compensatory metabolic alkalosis and secondary or compensatory metabolic acidosis, respectively, are als o conf usi ng and obje ctio nabl e. Simi- larl y, the sec onda ry responses to meta bol ic acido si s (p rimary de cre as e in pl as ma [HCO 3 ]) and met abol ic alk alos is (pri - mary increa se in pla sma [HCO 3 ]) are term ed sec onda ry hyp ocap niaand sec ondary hypercapnia, respectively ; we discourage use of the alternative terms secondary or compensa tory respiratory alkalosis and seconda ry or comp ens ator y res pira toryac- idosis , respecti vely. 3 MAGNITUDE AND TIME COURSE OF THE SECONDARY RESPONSES Here we examine the mean slope of the secondary response to each cardinal acid- base disorder (Table 1) and the time in- terval required for each secondary re- spo nse to rea ch comple tion. Toward thi s end, we revie wed all avail able human Published online ahead of print. Publication date available at www.jasn.org. Correspondence: Dr. Nicolaos E. Madias, Depart- ment of Medicine, St. Elizabeth’s Medical Center, 736 Cambridge Street, Boston, MA 02135. Phone: 617-562-7502; Fax: 617-562-7797; E-mail: nicolaos. [email protected] Copyri ght © 2010 by the Ameri can Society of Nephrology ABSTRACT Each of the four canonical acid-base disorders expresses as a primary change in carbon dioxide tension or plasma bicarbonate concentration followed by a secondary response in the countervailing variable. Quantified empirically, these secondary responses are directional and proportional to the primary changes, run a variable time course, and tend to minimize the impact on body acidity engendered by the primary changes. Absence of an appropriate secondary response denotes the coexistence of an additional acid-base disorder. Here we address the expected magnitude of the sec ondary response to each cardinal acid-base disorder in humans and offer caveats for jud ging the appropriat ene ss of each sec ondary response. J Am Soc Nephrol 21: 920–923, 2010. doi: 10.1681/ASN.2009121211 SCIENCE IN RENAL MEDICINE www.jasn.org 920 ISSN : 1046-6673/2106-920 J Am Soc Nephrol 21: 920–923, 2010

Respuestas Compensadoras JASN 2010

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