Simple test confirms correct catheter placement

By Eleanor McDermid, Senior medwireNews Reporter

Injecting sodium bicarbonate into a peripheral intravenous (iv) catheter is a straightforward means of testing its placement and patency in mechanically ventilated children, say researchers.

If the catheter is properly placed, the procedure causes a marked increase in exhaled carbon dioxide concentration within three breaths of the injection, report Erez Ben-Menachem (Sheba Medical Center, Ramat Gan, Israel) and colleagues in Anesthesia and Analgesia.

But they caution: "Care should be taken if testing an IV cannula previously or concurrently being used for medications, because sodium bicarbonate may be incompatible with certain drugs, including epinephrine, norepinephrine, dobutamine, midazolam, calcium salts, and magnesium salts."

The team injected sodium bicarbonate 2.10% or 1.05%, or saline 0.90%, in a random order, into the iv catheters of 18 children who were mechanically ventilated. Sodium bicarbonate 2.10% caused end-tidal carbon dioxide levels to rise from an average of 32.8 to 39.0 mmHg within three breaths, and sodium bicarbonate 1.05% caused a smaller but still significant rise, from 33.4 to 36.3 mmHg.

Saline caused no change (average increase 0.06 mmHg) and anesthesiologists who were blinded to the treatment could easily distinguish between sodium bicarbonate and saline injections based on end-tidal carbon dioxide.

Ben-Menachem et al previously tested the technique in adult patients, finding that exhaled carbon dioxide levels peaked at the seventh breath after injection. They say that the earlier increase seen in the present study is likely "the result of the higher relative cardiac output and faster circulation time seen in children."

The researchers recommend using sodium bicarbonate 2.1% and add: "Reassuringly, the 2.1% sodium bicarbonate bolus (0.25 mEq/kg), even if repeated several times a day, is well below the recommended 8 mEq/kg/day sodium bicarbonate dose limit for children younger than 2 years of age."

However, they would avoid the procedure in premature babies and children with elevated intracranial pressure.

The team says that the technique should now be tested with central venous catheters. About half of all claims relating to peripheral catheters are caused by extravasation of drugs or fluid, but the researchers note that "the consequences of misplaced or migrated central vascular access can be catastrophic with the potential for infusion of fluids into the pleural or abdominal cavity."

They add: "Cardiovascular collapse could potentially occur should inotropic infusions be given through a catheter not positioned intravascularly."

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