STEFAN SCHEINGRABER, LARS HEITMANN, WERNER WEBER AND UDILO FINSTERER
Clinic of Anesthesiology, Ludwig Maxmilians University, Klinikum Grosshadern, Munich, Germany
Anesth. Analg., 90: 946–950, 2000
Acid base status during transurethral resection of the prostate (TURP) has been virtually neglected. In this study, the acid base status was measured and interpreted according to the Stewart approach, which focuses more on the influence of serum electrolyte concentrations on acid base changes than does the conventional Henderson-Hasselbalch approach. The following variables were ascertained in 20 patients undergoing TURP: PaO2, Paco2, pHa, actual bicarbonate, standard base excess, serum concentration of sodium, potassium, chloride, lactate, and total protein. A study group (n = 11) and a control group (n = 9) were constructed, depending on the maximal amount of fluid absorption estimated using ethanol concentration monitoring in the expired gas. Those in the study group developed a mild acidosis with a decrease in pH from 7.41 to 7.37, compared with a very discrete pH decrease from 7.44 to 7.42 in the controls. Moderate irrigant absorption during TURP was found to lead to a specific acidosis. Because the constellation of independently pH-regulating variables appears to be typical of TURP, this acidosis could be called “TURP-acidosis.”
The authors contend that during TURP, absorption of irrigating solution results in a modest metabolic acidosis. The pH decrease in the control (low irrigant absorption) group was 0.022 units, while in the study (high absorption) group pH decreased by 0.045 units, a significantly greater effect. The difference in pH was entirely “metabolic” in origin, since Paco2 remained stable in both groups. These findings can be partially explained by the fact that patients in the study group received about 50% more intravenous Ringer’s lactate (789 ml) than those in the control group (524 ml). Because this solution is slightly hyperchloremic ([CI−] = 112 mEq/l) and hyponatremic ([Na+] = 130 mEq/l), its administration would be expected to decrease the difference between serum Na+ and Cl− concentrations (and hence the “anion gap”). Although concentrations of both Na+ and Cl− decreased in both groups because irrigating solution was absorbed, the anion gap ([Na+] + [K+] − [Cl−]) decreased more in the study group (−2.8 mEq/l) than in the control group (–0.8 mEq/l). So we are primarily dealing with a nongap acidosis resulting from relative hyperchloremia, which was greater in the study group than in the controls. The remainder of the acidosis can be accounted for by the fact that serum lactate increased more in the study group (1.1 mEq/l) than in the control group (0. 5 mEq/l). I believe that before the authors coin a new term, “TURP acidosis,” they should determine whether similar changes in acid base status are observed in patients undergoing minor, nonurologic surgery who receive different volumes of lactated Ringer’s solution without absorbing irrigating solution.
Jeffrey D. Gross M.D.