Pudendal Nerve Block

First reported by King in 1916 for pain control during the second stage of labor, pudendal nerve block is commonly performed by obstetrician in patients without spinal or epidural analgesia.
The pudendal nerve carries somatic nerve fibres from the anterior primary divisions of the second, third and fourth sacral nerves.
The technique aims at blocking the nerve distal to its formation but proximal to its division into its terminal branches (i.e., dorsal nerve of the clitoris, perineal nerve and inferior haemorrhoidal nerve) .
The technique is based on bilateral injection of 10 ml of local Anesthetic solution medial and posterior to the ischael spine after introducing the needle through vaginal mucosa and sacrospinous ligament.
Another percutaneous approach has been described but it is less commonly applied.
Careful aspiration is a must as pudendal artery lies in close proximity to the nerve1.
Complications include systemic toxicity, laceration of vaginal mucosa, vaginal and ischeorectal haematoma and subgluteal abscess.
As paracervical block, direct injection into foetal tissues and needle-stick injuries are a potential risk.
Pudendal nerve block may provide satisfactory analgesia for spontaneous vaginal delivery an outlet forceps delivery but it is entirely inadequate for mid forceps delivery, cervical repair and manual examination of the uterus .

Effects of Regional Blockade on Materno-Fetal Physiology

# Pain relief leads to a reduction in serum catecholamines by decreasing physical stress or by denervating the adrenal medulla with subsequent enhancement of uterine blood flow.
# Hypotension occurring secondary to central blockade decreases uterine blood flow as uterine perfusion pressure is dependent on maternal mean arterial pressure with minimum capacity for autoregulation.
# Avoidance of maternal hypotension prevents any derangement of umbilical artery blood flow .
# Aortocaval compression is compensated for by sympathetic hyperactivity. Regional blockade may diminish this reflex but on the other hand venous dilatation of vertebral and paraspinous veins draining into the azygous compensates for minor degree of aortocaval compression. Provided prolonged hypotension is avoided, improved foetal outcomes with epidurals are known to occur secondary to improved placental haemodynamics.
# Reduced perioperative blood loss is associated with regional anesthesia (e.g. for placenta previa) . This has been attributed to avoidance of inhalational agents (all have uterine relaxant effects to a varying degree) and reduced pelvic venous plexuses pressures due to venodilatation.
# Early ambulation is another documented benefit of regional techniques which is caused by both direct effects (avoidance of depressant effects of general anesthesia) and indirect causes (elimination of stress response by the pre-emptive effect of regional blockades).
# Pain scores postoperatively are much lower postoperatively when a regional technique is used. This is reflected as a decrease in opioid requirements which leads to better somatosensory profiles for the mother and baby .
# Avoidance of general anesthetic effects on the baby is reflected as less postpartum interventions and early feeding. This is of particular value when a long predelivery phase (e.g. patients who had previous CS) is expected.
# Epidural improves incoordinate uterine activity unless severe hypotension ensues .

Minimum anesthetic machine check under life-threatening conditions

situations do arise in anesthesia for trauma or emergency cesarean section where there is neither time nor opportunity to fully check the anesthesia gas machine. The following checklist is suggested for these situations. It requires little if any additional time, and can add greatly to safety, and hence, peace of mind.

1. High pressure test of the breathing circuit
   • Ensures there are no leaks distal to common gas outlet
2. Check suction
3. Observe and/or palpate breathing bag during preoxygenation
   Ensures
   • Adequate flow of oxygen
   • Good mask fit (very important)
   • The patient is breathing
   • The Bag/Vent switch is on "Bag" not "Vent"

With all new machines, the electronic checklist can be bypassed in emergencies. Whether this 30 second process is acceptable must be determined by each clinical practice.