For several decades, epidural analgesia suffered from the perception that it prolongs labor and increases the incidence of instrumental and operative deliveries. Numerous independent maternal, fetal, obstetric and anesthetic factors influence obstetric outcome, however.
The majority of studies over 10 years old addressing this issue are complicated by retrospective analysis, selection bias, a lack of rand- omization, the inability to blind participants, crossover, and ethical issues related to withholding treatment. In addition, women request- ing epidural analgesia may be inherently different from those who do not (Table 3.14 ). Intense pain may actually be a marker for abnor- mal or dysfunctional labor, which in itself results in longer labors and increases not only the likelihood of instrumental or operative delivery, but also the probability the parturient will request epidural analgesia.
Despite limitations with any study design, the vast majority of sentinel event or “catastrophe” model (sudden offering of an epidural service, for example) studies suggest that epidural analgesia has no clinically signifi cant effect on the progress of labor or the incidence of cesarean section . A recent series of 750 parturients randomized to either CSE labor analgesia or systemic IV opioid analgesia in early labor (<4 cm cervical dilatation) found that patients in the CSE group had shorter fi rst and second stages of labor. There was no differ- ence between groups in cesarean delivery rate and, of course, the CSE patients had much lower pain scores than the systemic analgesia group.
Table 3.14 Characteristics of Parturients Requesting Epidural Analgesia
1. Frequently nulliparous
2. Earlier stages of labor and with higher fetal station 3. Slower cervical dilatation prior to requesting analgesia 4. More likely to be receiving oxytocin
5. Deliver larger babies 6. Have smaller pelvic outlets
7. Greater pain of labor (dysfunctional labor)
8. Higher risk of operative delivery (poor fetal status or maternal disease)
Obstetric Anesthesia69
Systemic and Alternative Analgesia for Labor
General Considerations and Alternatives
Attitudes toward analgesia for labor and analgesic methods are diverse. Despite the justifi able enthusiasm of obstetric anesthesiolo- gists for epidural analgesia, pain during labor and delivery is contextu- ally unique and individual-specifi c.
Globally, the vast majority of pregnant women have no access to
•
epidural analgesia (or any form of pharmacological pain relief).
In developed countries, many parturients manage very well without
•
epidural analgesia but most request some method of pain relief.
If ready access to epidural analgesia is available, 50
• % –90 % of
women will use it.
The popularity of non-epidural methods varies with cultural, regional and local influences (Table 3.15 ). For example, transcutaneous electrical nerve stimulation (TENS; Figure 3.4 ) and “water blocks”
(Figure 3.5 ) appear more widely used in Scandinavia; ketamine in India;
nitrous oxide inhalation in the UK and Australia; and intramuscular opioids in much of Europe.
Nitrous Oxide
Nitrous oxide was described as an analgesic for labor pain in 1880, and became popular after the manufacture of the Minnitt apparatus for self-inhalation of mixtures with air. This was followed by Entonox, a 50:50 mix with oxygen (Figure 3.6 ).
Nitrous oxide has very rapid onset and offset due to low blood-gas solubility. The parturient inhales in conjunction with each contraction via a mouthpiece or face mask.
Concentrations of 30
• % –70 % provide modest analgesia for
10 % –40 % of parturients.
Side effects include drowsiness, reduced awareness, and occasion-
•
ally nausea.
Risks include oversedation, dizziness, hyperventilation-induced
•
hypocarbia and tetany, and compensatory hypoventilation between contractions that leads to maternal and fetal hypoxemia. This is more likely after opioid analgesia or in the obese parturient.
Atmospheric pollution in the delivery unit to 300 ppm has been
•
measured, and is beyond the recommended limits of 25–100 ppm.
This raises concerns about abortion and bone marrow effects among staff working in the unit.
70Pain Relief for Labor and Delivery
Other inhalational agents can also be used.
Inhalational of subhypnotic concentrations of various inhalational
•
anesthetic drugs (e.g., 0.25 % isofl urane or 1 % –4.5 % desfl urane with 50 % nitrous oxide and oxygen) has shown modest effi cacy.
Such techniques are not popular because of practical problems with
•
drug delivery.
Table 3.15 Features of Nonpharmacological Methods of Labor Analgesia
In general
Aid relaxation and ability to cope with pain no or minimal pain reduction
•
High levels of maternal satisfaction especially if patient-controlled
•
Popular and widely available
useful alone or as adjuncts to other methods
•
Excellent safety record
avoid hyperventilation during breathing exercises if the fetus is
•
compromised Specifi c techniques Water baths/massage
readily available; no antenatal preparation required
•
Learned relaxation techniques/biofeedback/hypnosis motivation or investment of time or money essential
•
Transcutaneous electrical nerve stimulation (TENS)/acupuncture mainly a placebo analgesic effect
•
safe, but may limit mobility
•
Water block
painful injection may need repetition
•
modest effi cacy and short duration
•
Figure 3.4 Position of TENS electrodes for labor.
Obstetric Anesthesia71
Opioid Analgesia
Morphine and scopolamine injection were introduced for labor pain in 1902, but little systematic evaluation of neonatal effects was attempted until Virginia Apgar developed her simple scoring system in 1953. Meperidine (pethidine) was introduced in the 1940s and was promoted as having minimal respiratory depressant effects.
Morphine has more favorable kinetics, the neonatal half-life is
•
shorter, and plasma levels remain low or undetectable.
In Europe and the United States, partial
• μ - or κ -opioid receptor
agonists (e.g., meptazinol, pentazocine, nalbuphine, butorphanol) and tramadol (a mixed μ -opioid, serotonergic and α 2 -adrenergic agonist) are also available. Administration of some opioids by midwives is permitted in some countries, including the UK and Australia.
10
8
6
4
2
0
Water block
Meperidine (I.M.)
Paracervical block
Epidural block Nitrous
oxide
Mean visual analog pain score
Figure 3.5 Visual pain scores (0–10) before and after pain management in the fi rst stage of labor in the various pain relief groups. Minimum, lower (25th) quartile, median, upper (75th) quartile, maximum. Reprinted with permission from Ranta P, Jouppila P, et al. Parturient’s assessment of water blocks, pethidine, nitrous oxide, paracervical and epidural blocks in labour.
Int. J Obstet Anesth. 1994;3(4):196.
72Pain Relief for Labor and Delivery
• κ -opioid agonists are particularly effective at polymodal visceral nociceptors sensitized by chemical or thermal stimuli, and females are more sensitive to their effect, so these drugs show some exper- imental promise.
Conventional Systemic Opioid Administration
Over the course of a labor, intramuscular [IM] or intravenous [IV]
opioids (morphine or meperidine) are usually restricted to one or two injections.
Opioids delay gastric emptying.
•
Normeperidine, a metabolite of meperidine, is proconvulsant.
•
Both meperidine and morphine cross the placenta rapidly due to
•
their low molecular weights and lipid solubility. This may diminish fetal heart rate variability.
Exhalation valve
Safety valve Face mask
Spring Diaphragm
Non- interchangeable cylinder valve and yoke Gas cylinder Filter
1st stage valve 2nd stage
(tilting type) valve 2nd stage pressure reduction (atmosphere)
Sensing diaphragm
Corrugated hose
1st stage reduction
Figure 3.6 The Entonox nitrous oxide/oxygen analgesic apparatus (British oxygen). Reprinted with permission from Crawford JS, Principles and Practice of Obstetric Anaesthesia 5 th ed . 1984, Wiley-Blackwell.
Obstetric Anesthesia73
Although dose-related, even a single dose of opioid can cause neo-
•
natal respiratory depression (Figure 3.7 ); this is maximal 2–3 hours after IM administration.
The long elimination half-lives in newborns (compared with adults)
•
of both meperidine (13–23 hours) and its active metabolite, normeperidine (60 hours) depress newborn sucking behavior for up to 4 days.
Opioids generally result in poor pain relief, with only 25 % –40 % of women reporting benefi t. Most women report no reduction, or only a small reduction, of pain scores, but benefit from eu- phoria and relaxation. Opioids also commonly cause confusion, reduced awareness and nausea, and are associated with low maternal satisfaction.
Percent 0 – 6 scores
35
30
0
1 2 3 4
15 50 mg
75–100 mg
197 cases 453 cases Meperidine
49 25
74 153
68
89 177
Hour of administration before birth 25
20
15
10
5
Figure 3.7 Percentage of low neonatal Apgar scores in relation to timing of intramuscular meperidine administration before delivery. This article was published in the American Journal of Obstetrics and Gynecology, Vol. 89, Shnider SM and Moya F, Effects of meperidine on the newborn infant, pg. 1011, Copyright Elsevier (1964).
74Pain Relief for Labor and Delivery
Non-opioid systemic analgesia with ketamine is employed in some countries because the drug is cheap and readily available.
Intravenous or subcutaneous ketamine infusion (250 mcg/kg/h),
•
after a bolus of 0.25 mg/kg, reduces labor pain scores.
Small intravenous doses result in 3–5 minutes of analgesia in late
•
labor or at delivery.
Maternal amnesia and aspiration are recognized hazards.
•
Patient-Controlled Intravenous Analgesia (PCIA)
Contraction pain scores diminish very little after systemic opioids (Figure 3.8 ), with the exception of the potent μ -opioid receptor agonist remifentanil. Patient-controlled intravenous analgesia (PCIA) with fenta- nyl results in modest analgesia but total doses > 600 mcg are likely to cause neonatal depression and require reversal at birth with naloxone.
Mean visual analog pain score
50
40
30
20
10
0
First dose
Before Second dose
Figure 3.8 Pain intensity before and following intravenous morphine (dose 0.05 mg/kg body weight) or meperidine (dose 0.5 mg/kg body weight).
Values are presented in box plot (median with interquartile range). No signifi cant effect was found after each dose. _, morphine;_, meperidine (pethidine). Reprinted with permission from Olofsson C, et al. Lack of analgesic effect of systemically administered morphine or pethidine on labour pain. Br J Obstet Gyenaecol . 1996;103:969.
Obstetric Anesthesia75 Although usually reserved for specifi c indications (such as a contrain- dication to requested epidural analgesia), the potent ultra-short acting opioid remifentanil is being used for PCIA in many countries, despite use during labor being “off-label.”
Remifentanil—
Reaches peak effect site concentration within 2–3 minutes of
•
IV administration.
Has a very short, 3-minute, context-sensitive half-life (i.e., the time
•
for plasma concentration to fall by 50 % from a steady-state level during drug infusion), independent of the duration of infusion, due to tissue and blood esterase metabolism.
Shows very rapid placental transfer, but is rapidly metabolized by
•
the fetus; neonates rarely appear affected after remifentanil in labor.
Remifentail often causes maternal drowsiness and hypoxemia, requir- ing oxygen therapy in approximately 15 % of parturients. It can cause profound respiratory depression, muscle rigidity and severe hypox- emia after a rapid bolus or accidental injection of very small volumes of drug, so protocol-based monitoring and application of safety guide- lines are essential (Table 3.16 ).
Remifentanil PCIA is not as effective as epidural analgesia, but is a valid option when epidural techniques cannot be employed (Table 3.17 for a potential regimen).
The optimum dosing regimen is unclear, but titration of bolus doses
•
(0.1–0.5 mcg/kg) over 1 minute, or adjustment of infusion, is fre- quently required to optimize outcomes.
Short lockout intervals (1–3 minutes) are used to allow frequent
•
repeated dosing, despite peak effect site concentrations usually occurring after the contraction.
Alternative regimens provide fi xed bolus doses but a titrated con-
•
tinuous infusion or an infusion alone. In one study, an infusion of 0.025–0.15 mcg/kg/min (mean infusion rate 0.075–0.1 mcg/kg/min) resulted in analgesia that was not as good as neuraxial analgesia for labor, but lower pain scores than those reported in most series of remifentanil PCIA. Mild sedation occurred in 4% but no respiratory depression or fetal heart rate effects were reported.
Alternative Techniques
When using “alternative techniques” for labor analgesia, several points should be considered.
76Pain Relief for Labor and Delivery
For some patients, use of a holistic approach to preparation for
•
labor is important. Patient education is very helpful, and anesthesi- ologists as well as midwives can play an important role.
Women accompanied by a duola (support person) or using relaxa-
•
tion, breathing exercises, psychological support and physical thera- pies such as water baths or counter-irritation by back rubbing, experience modest reductions in pain and are more likely to express that labor was a positive experience.
Patient-controlled techniques, whether non-pharmacological, intrave-
•
nous, inhaled or epidural, should be encouraged. Maternal satisfaction with the experience of childbirth is largely determined by perception
Table 3.16 Safety Guidelines when Using Remifentanil for Labor Analgesia
Dosing regimen must be protocol-based
•
Use dedicated equipment, clearly labeled
•
Use a dedicated administration line and avoid dead space within tubing
•
or intravenous cannula
Provide continuous observation for sedation and respiratory
•
depression
Use continuous or regular, frequent intermittent pulse oximetry
•
monitoring of arterial oxyhemoglobin saturation (SpO 2 ) Encourage the woman to breathe if SpO
• 2 < 95 % but > 90 % on air
Give supplemental oxygen if SpO
• 2 remains < 95 % on air & modify the patient-controlled analgesia variables
Give naloxone 200 mcg IV and stop remifentanil administration if SpO
• 2
remains < 90 %
Table 3.17 Potential Dosing Regimen for Remifentanil PCIA during Labor
Choose a fi xed concentration of remifentanil for the protocol
•
(e.g., 20 mcg/ml)
Administer remifentanil using a dedicated pump via a dedicated
•
intravenous infusion line or limb with an anti-refl ux valve and minimal dead space
Demand bolus 0.4 mcg/kg (maximum dose 40 mcg)
•
titrate down to 0.1 mcg/kg if side effects excessive
•
Continuous infusion (either routine or as an extra if maximum bolus
•
doses prove inadequate)
0.05 mcg/kg/min, titrated to maximum 0.15 mcg/kg/min
•
Lockout interval 1 minute (1–3 min depending on pump used)
•
Obstetric Anesthesia77 of personal control, rapport with support staff, and participation in decision making.
Non-pharmacologic alternatives include acupuncture and transcuta- neous electrical nerve stimulation (TENS). These methods are rarely used in developed countries, and are not of proven effi cacy.
A technique known as “water block” is sometimes employed, especially in Scandinavian countries.
Sterile water 0.1 mL is injected intra- or subcutaneously at 4 points
•
corresponding to the sacral borders.
This is transiently painful but reduces back pain during labor for up
•
to 60 minutes.
Further Reading
1. Bloom SL , McIntire DD , Kelly MA , et al. Lack of effect of walking on labor and delivery . N Engl J Med. 1998 ; 339 : 76 - 79 .
2. Bricker L , Lavender T . Parenteral opioids for labor pain relief:
A systematic review . Am J Obstet Gynecol. 2002 ; 186 : S94 - 109 . 3. Bucklin BA , Hawkins JL , Anderson JR , et al. Obstetric
anesthesia workforce survey: twenty-year update . Anesthesiology.
2005 ; 103 : 645 - 653 .
4. D’Angelo R . New Techniques for labor analgesia: PCEA and CSE .
Clin Obstet Gynecol. 2003 ; 46 : 623 - 632 .
5. D’Onofrio P , Novelli AM , Mecacci F , et al . The effi cacy and safety of continuous intravenous administration of remifentanil for birth pain relief: An open study of 205 parturients . Anesth. Analg. 2009 ; 109 : 1922 - 1924 .
6. Halpern SH , Carvalho B . Patient-controlled epidural analgesia for labor .
Anesth Analg. 2009 ; 108 : 921 - 929 .
7. Halpern SH , Leighton BL , Ohlsson A , et al . Effect of epidural vs parenteral opioid analgesia on the progress of labor: a meta-analysis . JAMA.
1998 ; 280 : 2105 - 2110 .
8. Hawkins JL . American Society of Anesthesiologists’ practice guidelines for obstetric anesthesia: update 2006 . Int J Obstet Anesth. 2007 ; 16 : 103 - 105 .
9. Hill D , Van de Velde M . Remifentanil patient-controlled analgesia should be routinely available for use in labour . Int J Obstet Anesth.
2008 ; 17 : 336 - 342 .
10. Palmer CM . Continuous spinal anesthesia and analgesia in obstetrics . Anesth Analg . 2010 ; 111 : 1476 - 1479 .
11. Rosen M . Nitrous oxide for relief of labor pain: A systematic review . Am J Obstet Gynecol. 2002 ; 186 : S110 - 126 .
12. Rowlington JC . Lipid rescue: a step forward in patient safety? Likely so!
Anesth Analg. 2008 ; 106 : 1,333 - 336 .
78Pain Relief for Labor and Delivery
13. Wong CA , Scavone BM , Peaceman AM , et al . The risk of cesarean delivery with neuraxial analgesia given early versus late in labor . N Engl J Med. 2005 ; 352 : 655 - 665 .
14. Wong CA . Epidural and Spinal Analgesia/Anesthesia for Labor and Vaginal Delivery. Chapter 23: 429-92 . In: Chestnut DH , Polley LS , Tsen LC , Wong CA , eds. Chestnut’s Obstetric Anesthesia Principles and Practice ( 4 th Ed . ) Philadelphia, PA : Mosby Elsevier ; 2009 .
79
Chapter 4
Anesthesia for Cesarean Delivery
Michael J. Paech , FANZCA