The effects of hypercapnea on bp in rats

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Edward M. Omron MD, MPH

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The effects of hypercapnea on bp in rats

  1. 1. 5 Al-Delaimy WK. Hair as a biomarker for exposure to tobacco CHEST (May 2007),1 and we certainly agree that our observations smoke. Tob Control 2002; 11:176 –182 regarding changes in baseline strong ion difference (SID) in anal- buminemic rats have “practical implications for intensivists who apply physicochemical analysis at the bedside.” However, we are surprised that Dr. Omron has interpreted our comments to suggestEffects of Hypercapnea on BP in Rats that hypoalbuminemia can directly alter SID. Instead, we stated that “we speculate that the normal physiologic response to hypoalbumin-To the Editor: emia is to lower the SIDa [apparent SID] . . . .” Indeed, these physiologic responses, or “secondary physiologic adaptations” as Dr. I read with great interest the recent article in CHEST (May Omron refers to them, would necessarily involve changes in2007) by Gomez et al,1 who investigated the effects of hypercap- ´ strong ions most likely via the action of the kidney. Changes innea on BP in hypoalbuminemic and analbuminemic rats. I SID are well known to occur as a result of long-term changescongratulate the authors on an intriguing exploration of physico- in Pco2 but have not been described as a consequence of changes inchemical principles, but I disagree with one of their main weak acids such as albumin. Importantly, the metabolic componentconclusions that “the presence of a lower SIDa [apparent strong of acid-base balance, quantified by base excess, comprises both SIDion difference] in the NAR [Nagase analbuminemic mutant and total weak acids2; thus, as opposed to Dr. Omron’s assertion,Sprague-Dawley] rats. . . is consistent with a reduction in the ‘set hypoalbuminemia per se does significantly change the base excesspoint’ for SIDa to maintain acid-base equilibrium in the face of a (for every gram-per-deciliter change in albumin level, base excessreduced weak acid content.” This simple statement has immense changes by approximately 3 mEq).2,3 This has important “practicalpractical implications for intensivists who apply physicochemical implications” because if one considers these changes in SID to beanalysis at the bedside. Hypoalbuminemia per se does indeed “pathologic” instead of “physiologic,” one will be tempted to treatchange the buffering capacity2 but cannot significantly reduce or them. Our study did not and could not address therapy but wechange the plasma buffer base or effective strong ion difference cannot share Dr. Omron’s certainty that changes in SID in the(the more relevant physicochemical parameters), contrary to the critically ill should always be treated. Instead, we would only offerauthors’ suggestion. A primary change of one independent the time-honored clinical advice that we should treat patients, theirvariable (albumin) will not affect the other independent variables diseases, and symptoms, and not merely numbers.(plasma buffer base or Pco2) in a physicochemical system.3 Tochange any of the independent variables, an intervention must beintroduced from outside the system (ie, altering the minute John A. Kellum, MD, FCCPventilation, renal intervention, or the accumulation of unmea- University of Pittsburghsured acids). These are secondary physiologic adaptations and not Pittsburgh, PAconsequences of the “laws of chemistry.” Each of these possibil- Jose Gomez, MD ´ities may explain the lower baseline SIDa and effective strong ion Yale Universitydifference in NAR rats. In the special case of analbuminemic rats, New Haven, CTat baseline conditions the reduction in SIDa represents a com-pensated but markedly deranged metabolic acid-base status. The The authors have reported to the ACCP that no significantquestion is not whether the clinician calls this state a mixed conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.acid-base disorder or normal compensation, but whether an Reproduction of this article is prohibited without written permissionintervention is necessary to restore standard-state conditions. In from the American College of Chest Physicians (www.chestjournal.the NAR rats, the answer is obviously no, but in a critically ill org/misc/reprints.shtml).patient with lactic acidosis, hypoalbuminemia, hyperchloremia, Correspondence to: John A. Kellum, MD, FCCP, University ofand hyponatremia the answer is yes. Pittsburgh, Critical Care Medicine, 608 Scaife Hall, 3550 Terrace St, Pittsburgh, PA 15261; e-mail: kellumja@ccm.upmc.edu Edward M. Omron, MD, MPH, FCCP DOI: 10.1378/chest.07-1761 Novi, MI ReferencesThe author has no conflict of interest to disclose. 1 Gomez JL, Gunnerson KJ, Song M, et al. Effects of hyper- ´Reproduction of this article is prohibited without written permission capnea on BP in hypoalbuminemic and Nagase analbumin-from the American College of Chest Physicians (www.chestjournal. emic rats. Chest 2007; 131:1295–1300org/misc/reprints.shtml). 2 Kellum JA. Clinical review: reunification of acid-base physi-Correspondence to: Edward M. Omron, MD, MPH, FCCP, ology. Crit Care 2005; 9:500 –507Pulmonary and Critical Care Specialists, 39650 Orchard Hill 3 Wooten EW. Calculation of physiological acid-base parame-Place, Suite 100, 48375-5331; e-mail: edofiron@gmail.com ters in multicompartment systems with application to humanDOI: 10.1378/chest.07-1247 blood. J Appl Physiol 2003; 95:2333–2344 References 1 Gomez JL, Gunnerson KJ, Song M, et al. Effects of hyper- ´ Genetical Analbuminemia Is capnea on BP in hypoalbuminemic and Nagase analbumin- emic rats. Chest 2007; 131:1295–1300 Not an Appropriate Model for 2 Fencl V, Jabor A, Kazda A, et al. Diagnosis of metabolic Hypoalbuminemia in Critically acid-base disturbances in critically ill patients. Am J Respir Crit Care Med 2000; 162:2246 –2251 Ill Patients 3 Fencl V, Leith DE. Stewart’s quantitative acid-base chemis- try: applications in biology and medicine. Respir Physiol 1993; To the Editor: 91:1–16 The article presented by Gomez and colleagues1 is very ´ interesting and well documented, stating that analbuminemic ratsResponse are not more susceptible to hypercapnia-induced hemodynamic instability or changes of pH. This can be interpreted as a clearTo the Editor: contradiction to the classical acid-base analysis in which albumin We thank Dr. Omron for his letter regarding our recent article in constitutes a buffer. One would have expected the albumin groupwww.chestjournal.org CHEST / 132 / 5 / NOVEMBER, 2007 1717

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