Role of spinal anesthesia in obstetric practice: advantages, complications and contraindications its advantages, uses, complications and contraindications.

Spinal block or subarachnoid block  is the most commonly practiced in obstetric surgeries and can be used in vaginal delivery also. It is a type of regional analgesia in which a local anesthetic is introduced into the subarachnoid space to get the effect of analgesia.

Advantages:

 The advantages of the spinal block are,

 Compared with other procedures it is having short procedure time.

 The  onset of the block is rapid than other regional anesthesia procedures.

And it is having high success rate.

As there will be  smaller subarachnoid space during pregnancy because of engorgement of the internal vertebral venous plexus, less amount of anesthetic agent is needed. Compared with nonpregnant women same amount of anesthetic agent in the same volume of solution produces a much higher blockade in parturients.

Uses:

In vaginal delivery:

For instrumental delivery, i.e.  for forceps or vacuum delivery,  low spinal block is used popularly.

In it the level of analgesia will extend to the T10 dermatome, which corresponds to the level of the umbilicus. Blockade to this level provides excellent relief from the pain of uterine contractions.

Many  local anesthetic agents have been used for spinal analgesia.

Among them lidocaine given in a hyperbaric solution produces excellent analgesia and has the advantage of a rapid onset and relatively short duration of action.

 And also bupivacaine in a dose of 10 to 12 mg in an 8.5-percent dextrose solution provides satisfactory anesthesia to the lower vagina and the perineum for more than 1 hour.

But none of these two should be administered until the cervix is fully dilated and all other criteria for safe forceps delivery have been fulfilled.

Hypotension is a common side effect, it can be prevented by preanalgesic intravenous hydration with 1 lit of crystalloid solution.

In cesarean delivery.

For caesarean delivery the level of sensory blockade should extend up to the T4 dermatome.

The dosage of local anesthetics used in caesarean delivery  depends on maternal size.

Normally  10 to 12 mg of hyperbaric bupivacaine or 50 to 75 mg of hyperbaric lidocaine are

administered. To increase the rapidity of onset and to block shivering 20 to 25 µg of fentanyl can be added.

Along with this if 0.2 mg of morphine is added it will improve the  pain control during delivery and postoperatively.

Complications:

Hypotension :.

 This is the  common complication of spinal anesthesia and it may develop soon after injection of the local anesthetic agent  due to vasodilatation from sympathetic blockade compounded by obstructed venous return from uterine compression of the vena cava and adjacent large veins.

It mainly affects the placental blood flow. It can be noticed as  in the supine position though  there is no maternal hypotension as measured in the brachial artery, placental blood flow may still be significantly reduced.

Treatment of spinal block induced hypotension:

Treatment includes uterine displacement by moving the patient to lateral side, intravenous hydration by giving crystalloids of 1 lit  and intravenous bolus injections of ephedrine or phenylephrine.

The ephedrine raises  the blood pressure by increasing cardiac output rather than

vasoconstriction. Phenylephrine is known to have potential adverse effects on uterine blood flow. But according to some studies the safety profiles of ephedrine and phenylephrine are comparable.

By infusing of 1000 mL of ringer lactate in a period of 20 minutes before spinal injection and 5-mg boluses of ephedrine will maintain normal blood pressure and resulted in a mean umbilical artery blood pH of 7.26.

But if prophylactic infusions containing diluted ephedrine are given in some cases, they led significant fetal acidemia  with the mean pH of about 7.12. So, it is controversial whether routine prophylactic ephedrine is needed or not.

High spinal blockade:

 Sometimes complete spinal blockade may occur as a  consequence of administration of an excessive dose of local anesthetic agent.

But this is always not due to excessive dose, accidental total spinal block may even occur following an epidural test dose.

 In complete spinal block, hypotension and apnea promptly develop and must be immediately treated to prevent cardiac arrest.

 Treatment:

 In the undelivered woman by positioning her laterally, there by  uterus  immediately displaces to lateral side and  aortocaval compression decreases.

 Effective ventilation to be established preferably by tracheal intubation.

 And to correct hypotension intravenous fluids and ephedrine are to be given.

Spinal  (postdural puncture) headache:

Some women complain of headache after spinal anesthesia, the factor though to be responsible is  leakage of cerebrospinal fluid from the site of puncture of the meninges. And  when the woman sits or stands, the diminished volume of cerebrospinal fluid allows traction on pain-sensitive central nervous system structures.

Prevention:

By  using a small-gauge spinal needle.

And  avoiding multiple punctures.

 Sprotte and Whitacre needles had the lowest risks of postdural puncture headaches.

By  placing the woman absolutely flat on her back for several hours is effective in preventing headache.

Treatment:

By giving vigorous hydration spinal headache may be reduced, but lacking  evidence to support its use.

In some studies administration of caffeine which is a cerebral vasoconstrictor, has been shown  to give some temporary relief.

In case of severe headache, an epidural blood patch is effective. In this a few millilitres of autologous blood should be taken  aseptically by venipuncture without using anticoagulant and this should be injected into the epidural space at the site of the dural puncture. With  this  relief is immediate and complications are uncommon.

 If the headache persists despite treatment with a blood patch and does not show the pathognomonic postural characteristics then other diagnoses should be considered and appropriate testing to be performed.

As sometimes a case of superior sagittal sinus thrombosis may manifest as a postural headache.

Sometimes  persistent cerebrospinal fluid leak is seen in some women.

Convulsions :

In very rare cases, postdural puncture cephalgia is associated with blindness and convulsions.

The incidence is very low as eight  such cases associated with 19,000 regional analgesic procedures in one study.

 It is thought to be caused because of cerebrospinal fluid hypotension.

Bladder  dysfunction:

For the  few hours after the procedure  with spinal analgesia, bladder sensation decreases  and bladder emptying  becomes impaired. So , bladder distension occurs  in the  postpartum period  especially if appreciable volumes of intravenous fluid are given.

This can be managed by catheterizing the bladder with foley’s catheter.

Oxytocics  and hypertension:

Though hypotension is common after spinal anesthesia, paradoxically, hypertension occurs commonly after injecting ergonovine or methylergonovine following

delivery  in women who have received a spinal or epidural block.

Arachnoiditis  and meningitis:

These complications were common in the past as at that time  local anesthetics are preserved in alcohol, formalin, or other toxic solutes.

As nowadays these are not used and disposable equipment is being used by most with aseptic technique meningitis and arachnoiditis have become rarities. But  these complications are occurring occasionally.

Other complications are obese women having significant impaired ventilation and needing

close clinical monitoring, pruritis, failed regional block needing general anaesthesia, formation of epidural abscess or hematoma etc.

Contraindications:

 The absolute contraindications to spinal analgesia are:

Refractory maternal hypotension:

Some of the obstetrical complications can also lead to maternal hypovolemia and hypotension such as severe hemorrhage are contraindications to the use of spinal

block.

The cardiovascular effects of spinal block in the presence of acute blood loss, but in the absence of the hemodynamic effects of pregnancy.

Maternal coagulopathy:

Disorders of coagulation and defective hemostasis also preclude the use of

spinal analgesia.

If the woman have received once daily dose of low molecular weight heparin within 12 hours spinal anesthesia should not be given.

Untreated bacteremia:

If patient having generalized bacterial infection better not to give spinal anesthesia.

Infection over the site of needle placement:

 Subarachnoid  puncture is contraindicated when the skin or underlying tissue at the site of needle entry is infected.

Neurological disorders:

These disorders  are considered to be contraindications as they may sometimes become

exacerbated because of  anesthetic agent.

Presence of any mass lesion causing increased intracranial pressure is also contraindication for spinal anesthesia.

Also if patient undergone any spinal surgery previously like laminectomy to be enquired before  proceeding as it may cause problem in giving anesthesia.

Other maternal conditions:

Significant  aortic stenosis or pulmonary hypertension are also relative contraindications to the use of spinal analgesia.

Preeclampsia:

If patient is having  severe preeclampsia if it become further complicated with significant hemorrhage there occurs markedly decreased blood pressure  when subarachnoid analgesia is used.

The conclusion is that with severe preeclampsia, epidural analgesia is preferable than subarachnoid block and general anesthesia. The general anesthesia especially is having inherent risks of difficult intubation due to airway edema and cerebrovascular accidents due to increased blood pressure.