Elevated serum
sodium and
potassium levels were recently observed when sampled through a
heparin-bonded umbilical
catheter and measured with certain
ion-selective electrodes. The cationic
surfactant,
benzalkonium chloride (BZC), is known to falsely elevate those
cations in serum. Inasmuch as most
heparin-bonded umbilical
catheters use BZC during the bonding process, an in vitro study was performed to estimate the quantity of BZC released and the duration of
sodium and
potassium elevations during pooled sera infusion. Three
heparin-bonded umbilical
catheters and 3
silastic umbilical
catheters were first flushed with 0.3 mL of
normal saline and then perfused with pooled sera (
sodium, 142 mEq/L;
potassium, 4.6 mEq/L) at 2.5 microL/h. Effluent samples were collected from 0 to 8 hours and analyzed by
ion-selective electrodes. Elevated serum
sodium concentrations from 160 to greater than or equal to 250 mEq/L and
potassium concentrations from 6.0 to greater than or equal to 9.6 mEq/L were observed. The BZC concentration in the
catheter effluent was measured by mass spectrometry, with peak values of 10 micrograms/mL detected by this method. When varying concentrations of BZC (1 to 100 micrograms/mL) were added directly to pooled serum, a dose-dependent increase in serum
sodium was observed. These data demonstrate that BZC released from
heparin-bonded umbilical
catheters elevates serum
electrolyte values measured with some
ion-selective electrodes. The observed increase in
sodium and
potassium concentrations may lead to clinical errors in management.
Benzalkonium chloride is associated with myriad of linical symptomatology. Whether this amount of BZC is toxic in the small premature neonate is presently unknown.