Multiport epidural catheters: does the air test work?

A systematic review of randomized controlled trials that evaluate strategies to avoid epidural vein cannulation during obstetric epidural catheter placement

BACKGROUND

In this systematic review, we evaluated the evidence for seven strategies which have been proposed to minimize the incidence of epidural vein cannulation during lumbar epidural catheter placement in pregnant women.

METHODS

Multiple databases were searched to identify prospective, randomized, controlled trials between December 1966 and October 2007 that evaluated methods to avoid epidural vein cannulation after lumbar epidural catheter placement in pregnant women. Published trials were evaluated using a quality assessment tool, and results were combined to evaluate efficacy to prevent epidural vein cannulation.

RESULTS

Of 90 trials screened, 30 trials were included (n = 12,738 subjects). Five strategies reduce the risk of epidural vein cannulation: the lateral as opposed to sitting position (six trials, mean (sd) quality score = 35% [11%], odds ratio (OR) 0.53 [95% confidence interval (CI) 0.32-0.86]), fluid administered through the epidural needle before catheter insertion (8 trials, quality score 48% [18%], OR 0.49 [95% CI 0.25-0.97]), single rather than multiorifice catheter (5 trials, quality score 30% [6%], OR 0.64 [95% CI 0.45-0.91]), a wire-embedded polyurethane compared with polyamide epidural catheter (1 trial, 31%, plus 4 unscored abstracts, OR 0.14 [95% CI 0.06-0.30]) and catheter insertion depth < or =6 cm (2 trials, 47% [11%], OR 0.27 [95% CI 0.10-0.74]). The paramedian as opposed to midline needle approach and smaller epidural needle or catheter gauges do not reduce the risk of epidural vein cannulation.

CONCLUSION

The risk of intravascular placement of a lumbar epidural catheter in pregnancy may be reduced with the lateral patient position, fluid predistension, a single orifice catheter, a wire-embedded polyurethane epidural catheter and limiting the depth of catheter insertion to 6 cm or less. In general, low manuscript quality weakens the strength of these conclusions.

Detection of Intravascular Epidural Catheter Placement: A Review

Intravascular placement of an epidural catheter is recognised as a potentially fatal complication of epidural anaesthesia and analgesia. Up to 10% of epidural catheters may be inserted into an epidural vessel, the majority of which will be recognised; however, a proportion (1% of all epidural catheters inserted) may not be identified as lying intravascularly. Opinions differ on the optimal method for identifying intravascular catheters and no perfect method exists. Some debate the need for a test of correct location, as a lack of specificity may mean that a proportion of correctly located catheters are withdrawn and resited. This review outlines the incidence and risk factors associated with intravascular placement and aims to evaluate the detection methods that have been described, in an attempt to answer the question: “What is the optimal way of detecting intravascular placement of an epidural catheter?”

The Epidural Test Dose: A Review

This review systematically examines the literature on the ability of the classical epidural test dose and other strategies to detect intravascular, intrathecal, or subdural epidural needle/catheter misplacement. For detection of simulated intravascular misplacements, a sensitivity (S) and a positive predictive value (PPV) > or =80 demonstrated by at least two randomized controlled trials coming from two different centers were determined for the following tests and patient populations: Nonpregnant adult patients = increase in systolic blood pressure (SBP) > or =15 mm Hg (S = 80-100 and 93-100; PPV = 80-100 and 83-100) or either an increase in SBP > or =15 mm Hg or an increase in heart rate > or =10 bpm after the injection of 10 (S = 100; PPV = 83-100) or 15 microg of epinephrine (S = 100; PPV = 83-100); pregnant patients = sedation, drowsiness, or dizziness within 5 min after the injection of 100 microg of fentanyl (S = 92-100; PPV = 91-95); and children = increase in SBP > or =15 mm Hg after the injection of 0.5 microg/kg of epinephrine (S = 81-100; PPV = 100). Conversely, more studies are required to determine the best strategies to detect intrathecal and subdural epidural needle/catheter misplacements in these three patient populations.

Injecting saline through the epidural needle decreases the iv epidural catheter placement rate during combined spinal-epidural labour analgesia

PURPOSE

To determine if injecting 10 mL saline before epidural catheter threading (pre-cannulation epidural fluid injection) can decrease the incidence of iv epidural catheter placement during combined spinal-epidural (CSE) labour analgesia.

METHODS

One hundred healthy women requesting CSE labour analgesia with either fentanyl 20 microg or sufentanil 10 microg 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 microg, 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.