Pupendal block

TABLE P-2  Indications and precautions for pudendal block

• Review general care principles.

• Prepare 40 mL 0.5% lignocaine solution without adrenaline.

Note: It is best to limit the pudendal block to 30 mL of solution so that a maximum of 10 mL of additional solution may be injected into the perineum during repair of tears, if needed.

• Use a 15 cm, 22-gauge needle to inject the lignocaine.

The target is the pudendal nerve as it passes through the lesser sciatic notch. There are two approaches:

• through the perineum;

• through the vagina. 

The perineal approach requires no special instrument. For the vaginal approach, a special needle guide (“trumpet”), if available, provides protection for the provider’s fingers.

PERINEAL APPROACH

• Infiltrate the perineal skin on both sides of the vagina using 10 mL of lignocaine solution.

Note: Aspirate (pull back on the plunger) to be sure that no vessel has been penetrated. If blood is returned in the syringe with aspiration, remove the needle. Recheck the position carefully and try again. Never inject if blood is aspirated. The woman can suffer convulsions and death if IV injection of lignocaine occurs.

• Wearing high-level disinfected gloves, place two fingers in the vagina and guide the needle through the perineal tissue to the tip of the woman’s left ischial spine (Fig P-2).

Figure P-2

Perineal approach

• Inject 10 mL of lignocaine solution in the angle between the ischial spine and the ischial tuberosity.

• Pass the needle through the sacrospinous ligament and inject another 10 mL of lignocaine solution.

• Repeat the procedure on the opposite side.

• If an episiotomy is to be performed, infiltrate the episiotomy site in the usual manner at this time.

• At the conclusion of the set of injections, wait 2 minutes and then pinch the area with forceps. If the woman can feel the pinch, wait 2 more minutes and then retest.  

Anaesthetize early to provide sufficient time for effect. 

VAGINAL APPROACH

• Wearing high-level disinfected gloves, use the left index finger to palpate the woman’s left ischial spine through the vaginal wall (Fig P-3).

Figure P-3

 Vaginal approach without a needle guide 

• Use the right hand to advance the needle guide (“trumpet”) towards the left spine, keeping the left fingertip at the end of the needle guide.

• Place the needle guide just below the tip of the ischial spine.

Remember to keep the fingertip near the end of the needle guide. Do not place the fingertip beyond the end of the needle guide as needle-stick injury can easily occur. 

• Advance a 15 cm, 22-gauge needle with attached syringe through the guide. 

• Penetrate the vaginal mucosa until the needle pierces the sacrospinous ligament.

Note: Aspirate (pull back on the plunger) to be sure that no vessel has been penetrated. If blood is returned in the syringe with aspiration, remove the needle. Recheck the position carefully and try again. Never inject if blood is aspirated. The woman can suffer convulsions and death if IV injection of lignocaine occurs.

• Inject 10 mL of lignocaine solution.

• Withdraw the needle into the guide and reposition the guide to just above the ischial spine.

• Penetrate the vaginal mucosa and aspirate again to be sure that no vessel has been penetrated. 

• Inject another 5 mL of lignocaine solution.

• Repeat the procedure on the other side, using the right index finger to palpate the woman’s right ischial spine. Use the left hand to advance the needle and needle guide and inject the lignocaine solution. 

• If an episiotomy is to be performed, infiltrate the episiotomy site in the usual manner at this time.

• At the conclusion of the set of injections, wait 2 minutes and then pinch the area with forceps. If the woman can feel the pinch, wait 2 more minutes and then retest.

Anaesthetize early to provide sufficient time for effect.

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