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 multiorifice 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 multiorifice epidural catheters.

The influence of epidural needle bevel orientation on spread of sensory blockade in the laboring parturient.

UNLABELLED: Both asymmetrical sensory blockade and dural puncture are undesirable outcomes of epidural analgesia. Identifying the epidural space with the needle bevel oriented parallel to the longitudinal axis of the patient's back limits the risk of headache in the event of dural puncture. However, rotating the bevel to direct a catheter cephalad may risk dural puncture. We prospectively studied the effects of needle rotation on the success of labor epidural analgesia and on the incidence of dural puncture. One hundred sixty ASA physical status I or II laboring parturients were randomly assigned to one of four groups. The epidural space was identified with the bevel of an 18-gauge Hustead needle directed to the patient's left. It was then rotated as follows: Group 0 = no rotation, final bevel orientation left (n = 39); Group 90 = rotation 90 degrees clockwise, bevel cephalad (n = 43); Group 180 = rotation 180 degrees clockwise, bevel right (n = 36); Group 270 = rotation 270 degrees clockwise, bevel caudad (n = 42). A single-orifice catheter was inserted 3 cm, and analgesia was induced in a standardized fashion. Dural puncture was evenly distributed among the groups (4.4%). There were more dermatomal segments blocked, fewer one-sided blocks, and more patients comfortable at 30 min with the needle bevel directed cephalad. Using a catheter inserted through a needle oriented in the cephalad direction increases the success of epidural analgesia. IMPLICATIONS: This prospective study shows that an epidural catheter inserted through a needle oriented in the cephalad direction increases the success of labor analgesia in the parturient. Carefully rotating the needle cephalad does not increase the risk of dural puncture, intravascular catheters, or failed blocks.

Do patient variables influence the subarachnoid spread of hyperbaric lidocaine in the postpartum patient?

BACKGROUND AND OBJECTIVES: Age, height, weight, body mass index (weight/height2), and vertebral column length may affect the subarachnoid spread of local anesthetics. Little information exists concerning the relationship between these variables and the spread of hyperbaric lidocaine. The authors studied the influence of patient demographics on the block produced by hyperbaric lidocaine in women undergoing postpartum tubal ligation. METHODS: Within 48 hours of vaginal delivery, the authors studied 44 ASA class 1-2 women agreeing to spinal anesthesia for postpartum tubal ligation. Before induction of anesthesia, the authors weighed each patient, measured her height and vertebral column length, and calculated body mass index. In a standardized manner, the authors induced spinal anesthesia with 5% lidocaine 75 mg. An observer, blinded to the measured variables, evaluated loss-of-temperature sensation and loss-of-sensation of sharpness to pinprick bilaterally every 5 minutes for 30 minutes and again at 45 and 60 minutes. RESULTS: There was no correlation between age, weight, body mass index, vertebral column length, or time from delivery to placement of the block, and the spread of sensory block after subarachnoid injection of hyperbaric lidocaine. Only height weakly correlated with the spread of block (r2 = 0.15). CONCLUSIONS: While height may have some small influence on the spread of sensory block, the variation in spread of block within patients of the same height is large. The data suggest that adjusting the dose of local anesthetic injected based on differences in patient height would provide no clinically significant benefit.