Renal fluoride excretion and plasma fluoride levels during and after enflurane anesthesia are dependent on urinary pH

To determine the effects of urinary pH on fluoride ion excretion and the resulting plasma fluoride concentration during and after enflurane anesthesia, renal function, plasma inorganic fluoride levels, and fluoride excretion were studied in two groups of patients pretreated with either NH4Cl or acetazolamide to produce acidic or alkaline urine, respectively. During anesthesia, urinary flow rate, inulin clearance (Cin) and para-aminohippurate (PAH) clearance (CPAH) were 7, 61, and 43 per cent of control values in the acidic-urine group and 22, 74, and 57 per cent of control values in the alkaline-urine group, respectively. Fractional fluoride clearances (CF/CIN) during anesthesia and operation were 0.06 +/- 0.05 in the acidic-urine group (urinary pH 5.08) and 0.68 +/- 0.23 in the alkaline-urine group (urinary pH 8.16). Values of total fluoride excretion during the same period were 0.06 +/- 0.04 mg and 0.87 +/- 0.29 mg, respectively. Mean maximal plasma levels of fluoride were 26.3 +/- 7.3 microM in the acidic-urine group and 13.5 +/- 2.4 microM in the alkaline-urine group. The differences between groups in fluoride clearance, fluoride excretion, and plasma fluoride levels were all statistically significant. The data clearly show that renal fluoride clearance is closely related to urinary pH.