Conference Lectures

Labour Analgesia, an Update

Dr. Ketan S. Parikh
Consultant Anesthesiologist,
Breach Candy Hospital,
Bombay Hospital and Medical Research Center
 

 


INTRODUCTION:

On 14 June 1998, the Los Angeles Times published an article detailing a lawsuit filed by a patient alleging that she had been denied labour epidural analgesia by the anesthesiologist….the now famous 'Northridge case.'  There are no other circumstances where it is considered acceptable for a person to experience severe pain, amenable to safe intervention, while under a physician's care. Maternal request is sufficient enough justification for pain relief during labour. This strong affirmation of the basic human right to receive pain relief during labour could be considered as a landmark for our specialty.

HISTORY:

Since it's introduction, in 1847, when Queen Victoria set the ball rolling, pain relief in labour, has witnessed strong opposition from church, obstetricians and by women themselves. At the turn of millennium, a change of attitude from 'no pain no gain' to 'pain relief is a basic human right' is the corner stone of our success.

GOLD STANDARD:

Intramuscular Pethedine, inhalation of Entonox and continuous epidural with on demand boluses of local anesthetics have been the standard practice. The last decade or so, has seen marked changes in the conventional modalities of pain relief in labour. The updates can be divided into scientific updates and supportive updates.

SCIENTIFIC UPDATES:

REGIONAL ROUTE: Of all possible methods for pain relief in labour, central neuroaxial blockade provides safe, most effective and least depressant analgesia.

PHARMACOLOGICAL UPDATES:

LOCAL ANAESTHETICS:

ROPIVACAINE:

Ropivacaine was developed to provide a long acting local anaesthetic with similar therapeutic profile to bupivacaine with less cardiotoxicity. Selective sensory block & limited motor block is an added advantage. Ropivacaine is an amino amide class of local anaesthetic and is supplied as pure S (-) enantiomer. A prospective meta-analysis has shown a significantly reduced rate of instrumental deliveries and lower incidence of motor blockade. However, the use of Low dose mixtures with minimal risk of CVS toxicity nullifies this potential benefits of Ropivacaine.

L-BUPIVACAINE:

A new amide local anaesthetic, l-isomer of racemic mixture of bupivacaine with significantly reduced cardiotoxic potential and reduced stimulatory effects on Central Nervous System but with same local anaesthetic potency. Studies from a couple of centers in UK, have concluded that l-bupivacaine provide comparable analgesia during labour.
OPIOID:

Morphine and Pethedine have been used for epidural pain relief but with delayed side effect. The emphasis is on short or ultra short acting highly lipid soluble narcotics for quick onset and rapid recovery.

FENTANYL OR SUFENTANIL?
The duration and quality of analgesia between the two drugs is not significantly different. Incidence of side effects especially pruritus is less with fentanyl. Fentanyl is more cost effective. Fentanyl, 2ug/ml, has become a standard addition to the epidural mixture for labor analgesia.

IS AN OPIOID SAFE?

Along with the usual side effects of IT narcotics like pruritus, nausea, vomiting, hypotension & urinary retention, a particular concern for an obstetric anaesthetist are maternal respiratory depression, uterine hyperstimulation and fetal bradycardia.

  • Maternal Depression:            Although it is rare, central respiratory depression has been reported with both fentanyl as well as sufentanil. Some of the reported cases might have resulted due to potentiation of respiratory depressant effect by parentally administered opioid. Hence patients receiving CSE must be monitored for this complication for at least 20 minutes following IT opioids.
  • Uterine hyperstimulation & fetal bradycardia: Severe fetal bradycardia with CSE is reported, but are usually transient. This may be due to reduction in maternal catecholamines precipitating uterine hypertonicity and fetal bradycardia. Several recent reports have evaluated the incidence of fetal bradycardia and increase in emergency LSCS, but have failed to show an association.

OPIOID WITH LOCAL ANAESTHETICS:

The concept is to make the best of both, Make 1+ 1=3. Opioids are known for their dose sparing effects on local anaesthetic agents. A study from The University of Michigan Medical Center, by Polley & others have shown 37.5 fold reduction in MLAC by addition of sufentanil 1.5 ug/ml.

 

ADDITIVES:

  • Clonidine:  Low dose of clonidine is associated with improved analgesic efficacy of Local anaesthetic and/or opioid. But clonidine induced hypotension is worsened by combining it in this situation making it useless in labor analgesia.
  • Neostigmine: Intrathecal neostigmine causes analgesia in both animal as well as humans. A study from Nelson et al (Anesthesiology, 1999; 91: 1293-8) did not find analgesic usefulness but noticed 25% reduction in ED50 of sufentanil, by shifting its Dose Response curve to left. In another study, dose related nausea was reported in 55% of cases. However it causes nausea and its use in labor is yet to be approved.
  • Adrenaline: Apart from the vasoconstrictive effect, prolonging the duration of action of the local anaesthetics, epinephrine by its weak agonistic action on the alpha 2 receptors is an excellent additive to improve the quality of pain relief, when not contraindicated.

 

TECHNICAL UPDATES:

Epidural route:

Improvement on intermittent epidural top ups is necessary due to following
Problems:  Operator dependent                                        Solution:   Epidural Infusions CEI
Systemic upsets, bolus effect                                          Epidural PCAs
Windows of pain                                                            alone or with background infusion      

 

Advantages of CEI:                                             Advantage of EPCA

  • Continuous analgesia                                     mothers assume active role in her own pain relief
  • more even level of block                               larger degree of control over sensation experienced
  • increased safety                                           greater satisfaction
  • stable vital signs
  • reduced motor block

 

 

Intrathecal route:

Various combinations of local anaesthetics & opioid either alone or in tandem have been tried. The best to date is combination of 25 mcg of fentanyl or 10 mcg of sufentanil with 2.5 mg of bupivacaine. Problem with single dose is that the duration of analgesia of approximately 110 to 125 mins, though acceptable for multiparous or the last hour of first stage of labour, is useless in nulliparous and in early labour.

Solution:            a).    Continuous spinal analgesia, (CSA)

  •  Combined Spinal Epidural, (CSE)… walking epidural

CONTINUOUS SPINAL ANALGESIA, ARE SPINAL CATHETERS BACK?

In 1991, four cases of cauda equina syndrome, in non-obstetric patients, were associated with CSA. It was likely that the small flow rate through micro catheter contributed to pooling of hyperbaric, high concentration drug in the sacral area resulting in neurological injury. There are no cases associated with opioids used in similar manner. As the picture became more clear, it was concluded that the catheter themselves are not inherently dangerous.

In 1996, FDA granted an approval for a multi center study of safety and efficacy of CSA in parturient.  The study will enroll 400 patients, 100 each in four institute. 75 will receive CSA & 25 CEA.  The drugs used will be a combination of sufentanil & bupivacaine. The preliminary report of the trial as on Jan 1999 is, to date continuous spinal labour analgesia with 28-G catheter using sufentanil & bupivacaine appears to be safe and efficacious. The final results of the trial were able to rule out the association of this technique with neurologic injury. The study concluded that providing intrathecal labour analgesia with sufentanil and bupivacaine via a 28-gauge catheter has an incidence of neurologic complication <1% and that it produces better initial pain relief and higher maternal satisfaction, but is associated with more technical difficulties and catheter failures compared with epidural analgesia. Also, the CSEA kit is more expensive and hence is not routinely recommended

COMBINED SPINAL EPIDURAL; 'THE WALKING OR MOBILE EPIDURAL'

CSE provides the advantage of spinal i.e. speed of onset and lack of motor block with additional flexibility of renewal and extensibility with an epidural catheter. CSE can be safely used to provide labour analgesia in any patient requesting pain relief. However there are specific patients who will greatly benefit from this technique.

  • Patients in early labour: The initial dose of IT opioid alone will make them very comfortable for app.2-3 hrs, without any motor block allowing them to ambulate. And thus the name Walking or mobile epidural!
  • In late labour: IT opioids will provide almost immediate pain relief. Though, in imminent second stage of labour, opioid alone may fail to provide adequate analgesia, may be due to thicker sacral roots involvement, IT combination of LA + Opioid must be considered.

Both fentanyl as well as sufentanil is used in combination with bupivacaine safely & effectively. In the United Kingdom, the standard regime is 'The Queen Charlotte's CSE Regime.' Spinal: 2.5 mg of bupivacaine + 25 mcg of fentanyl, followed by epidural top ups of LDM of bupivacaine 0.1% + fentanyl 2 mcg/ml i.e. 0.0002%. Across the Atlantic, in USA sufentanil in dose 2.5 to 10 mcg + 2.5 mg of bupivacaine is preferred.

Apart from the other complications of the CSE, the one that’s of interests is, do these mothers have a fall if they are allowed to walk? Buggy et al advised a caution due to an almost 70% incidences of dorsal column abnormality following the standard CSE regime. Several recent studies using somato sensory evoked potential and computerized dynamic postulography to assess dorsal column function have ruled out any abnormality and endorsed safety of this ambulatory epidural.

USE OF ULTRASOUND TO STUDY NEURAXIAL ANATOMY & LOCALIZE EPIDURAL SPACE:

Ultrasound imaging of the spine has recently been proposed to facilitate identification of the epidural space and predict difficult spine score, especially in women with abnormal lumbosacral anatomy (scoliosis) and those who are obese. Carvalho et al. in their study, found a good level of success in the ultrasound-determined insertion point and very good agreement between ultrasound depth (UD) and needle depth (ND). They also concluded that the proposed ultrasound single-screen method, using the transverse approach, can be a reliable guide to facilitate labour epidural insertion. Thus, the epidural failure rate can be minimized in patients with difficult backs.

UPDATE ON LABOUR OUTCOME:

LSCS; Does epidural increase the rate of LSCS or instrumental deliveries?

The results from University of Munich, Germany, where the obstetric practice was observed from 1979 to 1996, demonstrate that the overall rate of operative deliveries does not increase despite a marked increase in the utilization of epidural pain relief. On the contrary, they projected epidural analgesia may improve an otherwise dysfunctional labour pattern and thus save a selected group of patients from undergoing Cesarean Section.
This was followed by a retrospective review of 13,203 nulliparous women who delivered between 1989 to 1995 at St. Luke's-Roosevelt Hospital Center. Logistic analysis demonstrated that the higher risk of LSCS was associated with oxytocin induction, increased maternal age, private patient status, and precious pregnancy.

There are hundreds of articles reviewing the effect of epidural on labour outcome with contradictory results. While the retrospective studies suffer selection bias, prospective studies can not blind the obstetricians. The general consensus is that analgesic efficacy of epidural is unparalleled and is relatively safe. Restricting access will result in severe pain and dissatisfaction & is unlikely to reduce rate of LSCS significantly. Sheila Cohen of Stamford University School of medicine observes a marked increase in demand for epidural by the obstetricians, since the meta-analysis published in December 1998 JAMA clearly established that epidural analgesia in labour does not increase the cesarean section rate.

WHEN TO GIVE?

In 1987, Thorp et al published two series of retrospective studies and showed increased incidences of cesarean section in the epidural group, when given too early. They suggested delaying the epidural placement to a cervical dilatation of at least 5 cm.! A recent randomized, well designed, prospective study at the University of Iowa, by David Chestnut, looked at nulliparous in spontaneous as well as induced labour in whom epidural was given early (at 3 cm) or late (5cm). They concluded that it is unnecessary to await an arbitrary 5 cm as they fail to demonstrate any association between early i.e. before 5 cm, epidural and cesarean sections. The normal recommendation is that epidural to be given as soon as mother wants it or pain is unbearable.

IS LIGHTER BETTER?

Does the degree of motor block affect the outcome of labour (length of labour, instrumental delivery rate, cesarean delivery rate)? Obstetric factors, Fetal wellbeing, clinical judgement and decision making ability of the obstetrician are uncontrollable yet very important factors having major impact on the labour outcome. On the whole all the studies support the theory that lighter blocks are likely to improve maternal ability to push thus reducing intervention in the labour or delivery process.

AMBULATION, IS IT HELPFUL?

When CSE was introduced, it was proposed that by maintaining the motor power and allowing the mothers to walk a reduction in cesarean rate is likely. Various studies have failed to show any significant reduction in cesarean section rate by making the patients walk during labour. Ambulation, no doubt improves maternal satisfaction tremendously.

 

PUSHING EARLY V/S PUSHING LATE (PEOPLE)

Delayed pushing has been advocated in parturient under neuraxial blockade. Passive descent should be encouraged along with delayed and monitored pushing during birth to safely and effectively increase spontaneous vaginal births, decrease instrumental or assisted deliveries and shorten the pushing time.[41] The Pushing Early or Pushing Late with Epidural (PEOPLE) Study also supported delayed pushing for a better outcome.[42]

 

UPDATES ON RELEVANT ISSUES:

Accidental dural PUNCTURE (adp):

Headache following labour epidural is the commonest cause of malpractice claim in US and litigation in the UK. Prof. Reynolds et al conducted a retrospective questionnaire survey at St. Thomas' Hospital, London to assess the incidence of ADP in labour. Though the evidences were not substantial, loss of resistance to saline was considered to be better technique than LOR to air. A careful prospective audit only, can give more proof.

Management of ADP:   a.)  Convert it into spinal, a single shot if short labour is anticipated, &
continuous spinal catheter if the labour is likely to extend beyond an hour
b)   Use a higher interspace to reattempt, this is only second best as

  • factors that lead to ADP still exists
  • fistula has been created between subarachnoid and epidural space
  • Catheter can migrate through the previous hole in dura.
  • Very careful monitoring and small incremental doses are recommended.

 

BACKACHE:

A few retrospective studies associated epidurals with increased risk of long term backache. Extensive prospective studies by Prof. Reynolds and her group at St. Thomas' Hospital, London have disputed these results and refuted any association between the two. (Russell R. et al BMJ 1993; 30:1299-1302, SOAP 1995, abstract book pg.100)

NEONATAL OUTCOME

Continuous epidural infusions of local anaesthetics with or without opioids are found to be safe. J Porter & F Reynolds compared neonates whose mothers received infusions of either 0.0625% bupivacaine with 2.5 mcg/ml of Fentanyl or plain 0.125% bupivacaine and found no abnormalities in neonatal PCO2, PO2, or NACS. There was no evidence of significant neonatal drug accumulation or adverse effects even after prolonged infusions.

MATERNAL TEMPERATURE

The low dose epidurals have less effect on thermoreceptor pathways resulting in less inappropriate heat triggering reflexes. Addition of opioid may also have direct effect on thermal control. Thus reduced fetal pyrexia during low dose epidural analgesia is unlikely to trigger unnecessary panic and neonatal sepsis workout.

Updates on SYSTEMIC ROUTE:

INTRAVENOUS: PCA opioid offer alternative to epidural analgesia for labour. Studies have compared fentanyl v/s alfentanil and found fentanyl to be more effective. But are inadequate for late first stage of labour.  It is also associated with 44% incidence of moderately depressed neonate with Apgar of<6 at 1 min.

Remifentanyl PCA has gained popularity in certain western countries. However it is associated with severe respiratory depression. It requires continuous O2 saturation monitoring of mother and a one to one supervision from midwife. Recently a death has been reported due to severe respiratory depression. It is an option to think in situation where other mode of pain relief is not possible or contraindicated.

INHALATIONAL: Entonox has been in use in the UK for past 30 years. Attempts to address the limited potency of Entonox with the addition of newer inhalational agent are made. Role of subanesthetic dose of Isoflurane 0.25% in Entonox, ISOXANE, was also evaluated.

SEVOX 0.8% with oxygen is another option being explored and practiced in some parts of the world. It practically difficult, requires specialized equipments, and need anaesthetic supervision for prection and monitoring of airway. Maternal amnesia and envirm=nmental pollution is also a concern.

 

CONCLUSION:

"The practice of obstetric anesthesia is unique in medicine in that we use an invasive and potentially hazardous procedure to provide a humanitarian service to healthy women undergoing physiological process"…. David Bogod. As newer methods are evolving, no technique can substitute extreme vigilance, utmost safety precautions and the sense of responsibility, on part of the obstetric anesthetists.