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.