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* From the Departments of Anesthesiology, Weill Medical College of Cornell University, New York, NY; and
Women and Infants’ Hospital, Providence, RI, USA.
Address correspondence to: Dr. Farida Gadalla, Department of Anesthesiology, Weill Medical College of Cornell University, 525 East 68th Street, New York, NY 10021, USA. Phone: 212-746-2795; Fax: 212-746-8563; E-mail: fgadalla{at}med.cornell.edu
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Abstract |
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Methods: One hundred healthy women requesting CSE labour analgesia with either fentanyl 20 µg or sufentanil 10 µg were prospectively randomized to receive either no epidural injection (dry group, n = 50) or epidural 10 mL saline injection (saline group, n = 50) before epidural catheter placement. A nylon multiport catheter was then threaded 3–5 cm into the epidural space and the needle was removed. We diagnosed iv catheter placement if blood was freely aspirated, if the mother became tachycardic after injection of epinephrine 15 µg, or if intracardiac air was heard (using ultrasound) after injection of air 1.5 mL.
Results: Intravenous epidural catheter placement occurred in one saline and ten dry group patients (P < 0.01). No complications of excessive cephalad intrathecal opioid spread (i.e., difficulty swallowing, hypoxemia, or respiratory arrest) occurred.
Conclusions: Injecting 10 mL or saline through the epidural needle after intrathecal opioid injection and before threading the catheter significantly decreased accidental venous catheter placement without any apparent increase in complications from excessive cephalad intrathecal opioid spread.
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Introduction |
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Injection of a sufficiently large volume of epidural fluid before catheter threading decreases the incidence of accidental venous catheter placement during epidural anesthesia. The accidental iv epidural catheter placement rate decreases significantly after injection of 10 mL of 0.5% bupivacaine (9% vs 3%, P = 0.05) or saline (16% vs 0%, P < 0.01) through the epidural needle but not after injection of saline 3 mL (13% vs 16%, P = NS).1–3 Saline 5 mL produced a decrease in the iv epidural catheter incidence that was significant in one of two studies (16% vs 9%, P < 0.05; 12% vs 6%, P = NS).5,A
It is not known whether injecting fluid through the epidural needle [pre-cannulation epidural fluid injection (PEFI)] is safe or effective during CSE anesthesia. During surgical anesthesia, injection of 5–10 mL saline through an epidural catheter five to 20 min after spinal hyperbaric bupivacaine injection increases the sensory anesthetic level by 1–4 dermatomes.6–9 Even without epidural saline injection, intrathecal fentanyl or sufentanil labour analgesia can produce difficulty swallowing or respiratory arrest.10,11 Therefore, in this study, in addition to determining whether injecting saline through the epidural needle would decrease the incidence of intravascular epidural catheter placement, we assessed each case for symptoms of excessive cephalad intrathecal opioid spread.
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Methods |
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Each CSE was done with the patient in the sitting position after receiving 1 L lactated Ringer’s solution intravenously. We recorded pulse oximetry continuously and blood pressure intermittently during and 30 min following CSE placement. We identified the midline epidural space by loss of resistance to air at the L2-3 or L3-4 interspace with a 17-gauge, 9 cm Hustead epidural needle. If the dura was punctured with the epidural needle, no further study procedures were performed. A 12.5 cm Whitacre spinal needle was inserted through the epidural needle, fentanyl 20 µg (n = 97) or sufentanil 10 µg (n = 3) were injected intrathecally, and the Whitacre needle was removed. In the dry group, a 20-gauge closed-tip, nylon, multiport epidural catheter (Sims Portex, Inc., Keene, NH, USA) was inserted 3–5 cm into the epidural space without prior fluid injection. In the saline group, 10 mL preservative-free normal saline was rapidly, in less than ten seconds, injected through the epidural needle before the epidural catheter was inserted 3–5 cm into the epidural space. The epidural needle was then removed and the catheter taped to the patient’s back.
All catheters were observed for spontaneous fluid return and aspirated with a 3-mL syringe. If clear fluid could be freely aspirated, we assumed that the fluid was cerebrospinal fluid (CSF), ended the study, and treated the patient as clinically appropriate. We obtained no wet taps and no profound motor block. If freely flowing blood appeared, iv catheter placement was diagnosed. If no blood or CSF were aspirated, we injected 3 mL lidocaine 2% plus epinephrine 15 µg and observed the pulse oximeter for a tachycardic response to epinephrine (either a 25 beats•min-1 maternal heart rate increase or a 10 beats•min-1 increase in the maximum maternal heart rate during a contraction).12 If the aspiration and epinephrine test results were negative, we injected 1.5 mL air while listening for a mill-wheel murmur using a Doppler external fetal heart rate probe placed over the maternal precordium.13 Aspiration for blood was attempted again if initial aspiration was negative and either the epinephrine or air tests indicated iv catheter location. If any of these tests were positive, these catheters were removed and replaced. Intrathecal catheter location was diagnosed and no further data were collected if the patient developed profound motor block three to five minutes after the lidocaine-epinephrine injection.
We recorded maternal demographics, the amount of air injected during identification of the epidural space, the catheter insertion depth, the ease of catheter threading, the time interval from saline injection to catheter insertion, and any spontaneous maternal complaints of difficulty swallowing. We monitored maternal oxygen saturation continuously for 30 min after CSE initiation and recorded any instances of oxygen saturation < 95%. We recorded whether or not iv or intrathecal catheter migration was subsequently diagnosed by blood or CSF aspiration.
Statistics
In order to calculate sample size, we assumed an incidence of iv cannulation of 15% in the dry group and 0.1% in the saline group. At a significance level of 0.05 and power of 0.8, the estimated sample size was 49 patients per group.
Data were analyzed using Student’s t test, Fisher’s exact test, or the Mann Whitney test, where applicable. P < 0.05 indicated statistical significance.
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Results |
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). All catheters were easily inserted. In the saline group, catheter insertion took place 18 ± 8 sec after saline injection. We identified iv catheter placement in 1/50 saline group and 10/50 dry group patients (2% vs 20%, P < 0.01). Intravenous catheter placement was identified by initial blood aspiration (one saline, four dry group patients), epinephrine injection (one dry group patient), or by the air test (five dry group patients). Blood was subsequently aspirated from four of the five iv catheters identified by the air test. No anesthetic complications occurred, including hypoxemia, patient complaint of difficulty swallowing, intrathecal catheter placement, respiratory arrest, or subsequent iv or intrathecal catheter migration.
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Discussion |
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The fact that we encountered no untoward side effects in this study suggests but does not prove the safety of injecting saline through the epidural needle in the context of CSE for labour. With no events in a 50-patient series, one can say with 95% confidence that the true event incidence is 
6%.14 Our safety results should be verified in a larger case series.
The rapid onset of spinally administered drugs in parturients makes swift, accurate epidural catheter threading essential during CSE labour analgesia. Respiratory arrest has been reported four minutes after intrathecal sufentanil injection in a parturient.10 Intravenous catheter threading forces the anesthesiologist either to replace the epidural catheter quickly or to postpone or abandon epidural catheterization. Thus CSE placement techniques should minimize iv threading of epidural catheters.
Test doses and aspiration cannot reliably detect intravenously located multiport epidural catheters. Injected test doses lack sensitivity with partially iv multiport catheters, for injectates preferentially exit the proximal hole while the distal hole is the one most likely to be located intravenously.15 Aspiration-negative but intravenously-located multiport epidural catheters have been reported.4,13 The problems of testing epidural catheter location re-emphasize the need to avoid venous cannulation.
Accidental intrathecal catheter threading, in the absence of dural puncture by the epidural needle, occurs so rarely during CSE labour analgesia (0.13%–0.4% incidence) that it is unlikely that PEFI will affect this potential complication.11,16 Cadaveric and in vitro studies have shown that it is very difficult to force an 18- or 20-gauge epidural catheter through dura punctured by a 25-gauge spinal needle.17,18
Using an Arrow Flex-Tip (Arrow International, Reading, PA, USA) epidural catheter is an alternative way to minimize the incidence of venous cannulation. In parturients, the incidence of venous cannulation is lower with the softer, uniport Flex-Tip Arrow® than with the harder, multiport Portex® (Sims Portex Inc., Keene, NH, USA) epidural catheter (1.1% vs 5.7%, P < 0.001).16 However, the primary advantage of multiport catheters, the low incidence of one-sided and patchy epidural blocks, could be lost by using uniport epidural catheters.19
One limitation of our study is the high incidence of venous cannulation in the dry group. Other centres, using different epidural needles, catheters, or placement techniques, may have a lower baseline incidence of venous cannulation. In addition, the anesthesiologist who tested the catheter for iv placement knew the patient’s group assignment. We attempted to compensate for this logistically necessary design flaw by establishing strict criteria for the diagnosis of iv catheter placement.
Our study does not address the safety or efficacy of PEFI during CSE anesthesia for Cesarean delivery. Intrathecal bupivacaine injection creates a situation similar to that of the non-obstetric studies in which epidural fluid injection increased the spinal sensory anesthetic level 1–4 dermatomes.6–9 Since large bupivacaine doses are commonly used for Cesarean delivery, PEFI might lead to unacceptably high levels of spinal anesthesia.
In conclusion, injecting saline 10 mL through the epidural needle after intrathecal opioid injection and before threading of the nylon, multiport, epidural catheter greatly decreased the venous catheter placement rate. We postulate that this is due to widening the space and pushing blood vessels away from the epidural needle tip. In this series of 100 labouring women requesting CSE, no evidence of excess intrathecal opioid effect (respiratory depression, hypoxemia, or dysphagia) was seen. Given our sample size and the low incidence of these complications, however, this study does not establish the safety of this technique. PEFI may be a useful way to decrease the incidence of iv epidural catheter placement during CSE labour analgesia.
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Footnotes |
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A
Ahn NN, Ung DA, DeFay S, et al. Blood vessel puncture with epidural catheters. Anesthesiology 1989; 71: A916. 
Revision received December 13, 2002. Accepted for publication September 30, 2002.
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2 Mannion D, Walker R, Clayton K. Extradural vein puncture–an avoidable complication. Anaesthesia 1991; 46: 585–7.[Medline]
3 Rolbin SH, Halpern SH, Braude BM, Kapala D, Unger R, Radhakrisnan S. Fluid through the epidural needle does not reduce complications of epidural catheter insertion. Can J Anaesth 1990; 37: 337–40.
4 Norris MC, Fogel ST, Dalman H, Borrenpohl S, Hoppe W, Riley A. Labor epidural analgesia without an intravascular "test dose". Anesthesiology 1998; 88: 1495–501.[Medline]
5 Scott DA, Beilby DS. Epidural catheter insertion: the effect of saline prior to threading in non-obstetric patients. Anaesth Intensive Care 1993; 21: 284–7.[Medline]
6 Blumgart CH, Ryall D, Dennison B, Thompson-Hill LM. Mechanism of extension of spinal anaesthesia by extradural injection of local anaesthetic. Br J Anaesth 1992; 69: 457–60.
7 Stienstra R, Dahan A, Alhadi BZ, van Kleef JW, Burm AG. Mechanism of action of an epidural top-up in combined spinal epidural anesthesia. Anesth Analg 1996; 83: 382–6.[Abstract]
8 Stienstra R, Dilrosun-Alhadi BZ, Dahan A, van Kleef JW, Veering BT, Burm AG. The epidural "top-up" in combined spinal-epidural anesthesia: the effect of volume versus dose. Anesth Analg 1999; 88: 810–4.
9 Takiguchi T, Okano T, Egawa H, Okubo Y, Saito K, Kitajima T. The effect of epidural saline injection on analgesic level during combined spinal and epidural anesthesia assessed clinically and myelographically. Anesth Analg 1997; 85: 1097–100.[Abstract]
10 Ferouz F, Norris MC, Leighton BL. Risk of respiratory arrest after intrathecal sufentanil. Anesth Analg 1997; 85: 1088–90.[Medline]
11 Albright GA, Forster RM. The safety and efficacy of combined spinal and epidural analgesia/anesthesia (6,002 blocks) in a community hospital. Reg Anesth Pain Med 1999; 24: 117–25.[Medline]
12 Leighton BL, Norris MC, Sosis M, Epstein R, Chayen B, Larijani GE. Limitations of epinephrine as a marker of intravascular injection in laboring women. Anesthesiology 1987; 66: 688–91.[Medline]
13 Leighton BL, Topkis WG, Gross JB, et al. Multiport epidural catheters. Does the air test work? Anesthesiology 2000; 92: 1617–20.[Medline]
14 Grayzel J. A statistic for inferences based upon negative results (Letter). Anesthesiology 1989; 71: 320–1.[Medline]
15 Leighton BL, Katsiris SE, Halpern SH, Wilson DB, Kronberg JE. Multiport epidural catheters: can orifice location be tested? Anesthesiology 2000; 92: 1840–2.[Medline]
16 Jaime F, Mandell GL, Vallejo MC, Ramanathan S. Uniport soft-tip, open-ended catheters versus multiport firm-tipped close-ended catheters for epidural labor analgesia: a quality assurance study. J Clin Anesth 2000; 12: 89–93.[Medline]
17 Holmstrom B, Rawal N, Axelsson K, Nydahl PA. Risk of catheter migration during combined spinal epidural block: percutaneous epiduroscopy study. Anesth Analg 1995; 80: 747–53.[Abstract]
18 Angle PJ, Kronberg JE, Thompson DEA. In-vitro investigation of epidural catheter penetration of human dural tissue. Anesthesiology 2001; 95: A1070 (abstract).
19 Dickson MA, Moores C, McClure JH. Comparison of single, end-holed and multi-orifice extradural catheters when used for continuous infusion of local anaesthetic during labour. Br J Anaesth 1997; 79: 297–300.
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