Multiport epidural catheters: Does the air test work?

Background: Multiport epidural catheters are popular; however, the reliability of the air test has not been evaluated with this catheter design. The authors determined the effectiveness of aspirating for blood and the air test in detecting intravascular multi-orifice epidural catheters. Methods: Three hundred women in labor underwent placement of a blunt-tip, three-hole, 20-gauge, lumbar epidural catheter. If there were no signs of spinal anesthesia, 3 ml lidocaine or bupivacaine was injected and the patient was observed for signs of spinal anesthesia. If there were no signs of spinal anesthesia, the authors injected 1 ml air through the epidural catheter while listening to the maternal precordium using a Doppler fetal heart rate monitor. Catheters through which blood was aspirated were air-tested and replaced. Patients with air-test-positive, blood-aspiration-negative catheters received 100 mg lidocaine through the catheter and were questioned about toxicity symptoms. The authors injected bupivacaine-fentanyl through aspiration-negative, air-test-negative catheters and recorded the sensory analgesic level 20 min later. Results: The authors aspirated cerebrospinal fluid through one catheter and documented intravascular placement in 11 catheters. Results of the air test and blood aspiration were positive for eight catheters. Blood could not be aspirated from one air-test-positive catheter; perioral numbness developed in the patient after lidocaine injection. Blood was freely aspirated from two air-test-negative catheters. In the remaining 288 catheters, bupivacaine-fentanyl injection produced epidural analgesia in 279 patients and no effect in 9 patients. Conclusions: The authors obtained false-negative results with both catheter aspiration and the air test. Fractionating the local anesthetic dose is important when using multi-orifice epidural catheters.