Multiport epidural catheters - Does the air test work?

Background: Multiport epidural catheters are popular; however, the reliabil ity of the air test has not been evaluated with this catheter design. The a uthors determined the effectiveness of aspirating for blood and the air tes t in detecting intravascular multiorifice epidural catheters. Methods: Three hundred women in labor underwent placement of a blunt-tip, t hree-hole, 20-gauge, lumbar epidural catheter, If there were no signs of sp inal anesthesia, 3 mi lidocaine or bupivacaine was injected and the patient was observed for signs of spinal anesthesia. If there were no signs of spi nal anesthesia, the authors injected 1 mi air through the epidural catheter while listening to the maternal precordium using a Doppler fetal heart rat e monitor. Catheters through which blood was aspirated were air-tested and replaced. Patients with air-test-positive, blood-aspiration-negative cathet ers received 100 mg lidocaine through the catheter and mere questioned abou t toxicity symptoms, The authors injected bupivacaine-fentanyl through aspi ration-negative,air-test-negative catheters and recorded the sensory analge sic level 20 min later. Results: The authors aspirated cerebrospinal fluid through one catheter and documented intravascular placement in 11 catheters. Results of the air tes t and blood aspiration were positive for eight catheters. Blood could not b e aspirated from one air-test-positive catheter; perioral numbness develope d in the patient after lidocaine injection. Blood was freely aspirated from two air-test-negative catheters, In the remaining 288 catheters, bupivacai ne-fentanyl injection produced epidural analgesia in 279 patients and no ef fect in 9 patients. Conclusions: The authors obtained false-negative results with both catheter aspiration and the air test. Fractionating the local anesthetic dose is im portant when using multiorifice epidural catheters.