◊ 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 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.

◊ Reviewed by M. Van De Velde, MD, PhD,
Department of Anaesthesiology,
UZ Leuven, Belgium

The present paper reports on a well performed systematic review by distinguished obstetric anesthetists evaluating seven different strategies to reduce the risk of accidental epidural vein cannulation in obstetric patients and in pregnant women in particular:

1. lateral positioning versus sitting;
2. paramedian versus midline approach;
3. smaller epidural needles or catheters;
4. injecting saline through the epidural needle before catheter insertion;
5. using a single versus multiple orifice catheter;
6. wire-embedded polyurethane catheters;
7. limiting insertion depth.

The authors reviewed 90 trials and included 30 randomized controlled trials in their analysis. Overall incidence of epidural vein cannulation was 6.2%. Five interventions were found to decrease this incidence:

1. Placing the epidural catheter in the lateral position
2. Distention of the epidural space using saline before epidural catheter placement
3. Use of single-orifice catheters
4. Wire-embedded polyurethane catheters
5. Insertion depth of the catheter of 6 cm or less

The authors stated that limitations in the design and quality of studies weakened the conclusions. They also correctly note that the interaction between various interventions might alter results. It is noteworthy that various interventions while they reduce the risk of vein cannulation may increase the risk of other complications.