Metabolic acidosis is one of the most common complications of chronic kidney disease (CKD). It is associated with the progression of CKD, and many other functional impairments. Until recently, only serum bicarbonate levels have been used to evaluate acid-base changes in patients with reduced kidney function. However, recent emerging evidence suggests that nephrologists should reevaluate the clinical approach for diagnosing metabolic acidosis in patients with CKD based on two perspectives; pH and anion gap. Biochemistry and physiology textbooks clearly indicate that blood pH is the most important acid-base parameter for cellular function. Therefore, it is important to determine if the prognostic impact of hypobicarbonatemia varies according to pH level. A recent cohort study of CKD patients showed that venous pH modified the association between a low bicarbonate level and the progression of CKD. Furthermore, acidosis with a high anion gap has recently been recognized as an important prognostic factor, because veverimer, a nonabsorbable hydrochloride-binding polymer, has been shown to improve kidney function and decrease the anion gap. Acidosis with high anion gap frequently develops in later stages of CKD. Therefore, the anion gap is a time-varying factor and renal function (estimated glomerular filtration rate) is a time-dependent confounder for the anion gap and renal outcomes. Recent analyses using marginal structural models showed that acidosis with a high anion gap was associated with a high risk of CKD. Based on these observations, reconsideration of the clinical approach to diagnosing and treating metabolic acidosis in CKD may be warranted.

A 65-year-old woman who had been diagnosed with a thoracic aneurysm was admitted to our hospital because of loss of consciousness. Brain CT revealed that the left corticomedullary junction is obscured. Contrast-enhanced CT demonstrated an acute type A aortic dissection with right internal carotid artery occlusion, left internal carotid artery stenosis, and severe pectus excavatum. Although the consciousness level at the time of admission was JCS200, it gradually improved and she regained spontaneous movement of the right side of her body. Repair of the acute type A dissection was indicated because her neurological deficit had improved. The surgery was performed via an L-shaped approach consisting of a median sternotomy and a left 5th intercostal thoracotomy with moderate hypothermic circulatory arrest and selective cerebral perfusion. An entry was found in the aortic arch between the origins of the brachiocephalic artery and the left common carotid artery, and a partial arch replacement was performed using a four-branched artificial graft. Although the right hemiparesis remained, she recovered well and was transferred to a rehabilitation hospital at 45 days postoperatively. The L-incision approach obtained a good surgical field in a patient with a type A dissection and severe pectus excavatum.