The New England journal of medicine
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We prospectively measured the end-tidal carbon dioxide concentration during 13 episodes of cardiac arrest in 10 critically ill patients receiving mechanical ventilation, to evaluate its usefulness as an indicator of circulatory status during cardiac arrest and resuscitation. The end-tidal carbon dioxide concentration decreased from a mean (+/- SD) of 1.4 +/- 0.9 to 0.4 +/- 0.4 percent after the onset of cardiac arrest. During precordial compression, it increased to 1.0 +/- 0.5 percent. ⋯ However, it remained 0.7 +/- 0.4 percent in six patients in whom resuscitative efforts failed to restore spontaneous circulation. These observations are consistent with experimental studies of cardiopulmonary resuscitation in pigs, in which the end-tidal carbon dioxide concentration varied directly with the cardiac output produced by precordial compression. We therefore propose that measurement of the end-tidal carbon dioxide concentration may be a practical, non-invasive method for monitoring blood flow generated by precordial compression during cardiopulmonary resuscitation and an almost immediate indicator of successful resuscitation.
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We evaluated the use of the urinary anion gap (sodium plus potassium minus chloride) in assessing hyperchloremic metabolic acidosis in 38 patients with altered distal urinary acidification and in 8 patients with diarrhea. In seven normal subjects given ammonium chloride for three days, the anion gap was negative (-27 +/- 9.8 mmol per liter) and the urinary pH under 5.3 (4.9 +/- 0.03). In the eight patients with diarrhea the anion gap was also negative (-20 +/- 5.7 mmol per liter), even though the urinary pH was above 5.3 (5.64 +/- 0.14). ⋯ When the data on all subjects studied were pooled, a negative correlation was found between the urinary ammonium level and the urinary anion gap. We conclude that the use of the urinary anion gap, as a rough index of urinary ammonium, may be helpful in the initial evaluation of hyperchloremic metabolic acidosis. A negative anion gap suggests gastrointestinal loss of bicarbonate, whereas a positive anion gap suggests the presence of altered distal urinary acidification.