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Obstetrics Anesthesia By Dr. Mahmoud Abdelkhalek Physiological changes of pregnancy Physiologic and anatomic changes develop across many organ systems during pregnancy and the postpartum period The Metabolic, hormonal and physical changes all have impact on anesthetic management To the anesthesiologist, the most important changes are those that affect the respiratory and circulatory systems. Respiratory system There is an increased risk of difficult or failed intubation in the parturient. This is primarily due mucosal vascular engorgement which leads to airway edema and friability. Laryngoscopy can be further impeded by the presence of large breasts. Increased risk of pulmonary aspiration of stomach contents due to: – Upward displacement of the stomach – Decreased gastric motility and increased gastric secretions – Incompetent gastro-esophageal junction Respiratory system In fact, airway complications (difficult intubation, aspiration) are the most common anesthetic cause of maternal mortality The best means of avoiding this outcome is to avoid general anesthesia (by using a regional technique) If a general anesthetic is required, NPO status for eight hours is preferred although not achievable in an emergency situation Pretreatment of all parturients with a non-particulate antacid (30 cc sodium citrate p.o.) as well as with a histamine blocker (ranitidine 50 mg IV) is important. Finally, a rapid sequence induction with cricoid pressure is mandatory Respiratory system With the apnea that occurs at induction of anesthesia, the parturient becomes hypoxic much more rapidly than the non-pregnant patient due to 2 main reasons: – Oxygen requirement has increased by 20% by term – Decrease of FRC, which serves as an “oxygen reserve” by 20% due to upward displacement of the diaphragm Minute ventilation increases to 150% of baseline leading to a decrease in PaCO2 (32 mmHg) The concomitant rightward shift in the oxyhemoglobin dissociation curve allows increased fetal transfer of O2 CVS Blood volume increases by 40% during pregnancy in preparation for the anticipated 500-1000 cc average blood loss during vaginal or Caesarian delivery, respectively. The increase of intravascular volume may not be tolerated by parturients with concomitant cardiovascular disease, such as mitral stenosis When the pregnant patient is in the supine position, the heavy gravid uterus compresses the major vessels in the abdomen leading to maternal hypotension and fetal distress (supine hypotensive syndrome) Left lateral tilt, usually achieved with a pillow under the woman’s right hip, is an important positioning maneuver Stages of normal labour The 1st stage of labour – Cervix effaces then cervical dilatation begins – Rate of cervical dilatation: Primigravida: 1 cm/ hour Multigravida: 2 cm/ hour – Routine observations: Fetal HR every 15 minutes Maternal pulse and BP every 30 minutes Temperature 4-hourly Urine analysis at each emptying of bladder Stages of normal labour The 2nd stage of labour – Commences at full dilatation of the cervix and terminates at the delivery of the baby – If prolonged more than 1 hour the fetus may become acidotic – At the delivery of anterior shoulder, IM oxytocin is given to hasten the delivery of the placenta and to stimulate the uterine contraction Stages of normal labour The 3rd stage of labour – The complete delivery of the placenta& membranes& contraction of the uterus – Placental blood flow (15% of CO) redistribute to maternal circulation and may precipitate heart failure immediately postpartum in women with cardiac disease Analgesia for labour The three most commonly used types of analgesic agents in labour are: 1. Inhaled N2O 2. Opioids 3. Regional techniques N2O/O2 (Entonox®) is the most commonly used inhalational agent and may be slightly more efficacious than pethidine, but complete analgesia is never attained Analgesia for labour Worldwide, pethidine remains one of the most popular opioids for labour analgesia Drawbacks: – Has a long half-life in the fetus (18–23hr) – Known to reduce fetal heart rate variability in labour – Associated with changes in neonatal neurobehaviour, including an effect on breastfeeding When regional analgesia is contraindicated, fentanyl or remifentanil PCA may be more Beneficial Diamorphine has also been advocated, although it may prolong labour by >1hr Analgesia for labour Uterine pain is transmitted in sensory fibres, which accompany sympathetic nerves and end in the dorsal horns of T10–L1 Vaginal pain is transmitted via the S2–S4 nerve roots (the pudendal nerve) Neuraxial techniques; spinal, combined spinal/epidural (CSE)& epidural; can be expected to provide effective analgesia in over 85% of women Remember that acceptable analgesia for women in labour does not mean a complete absence of sensation Analgesia for labour However, neuraxial analgesia was associated with: – Hypotension – Increased oxytocin use – An increased incidence of maternal pyrexia – A 40% increase in the incidence of instrumental deliveries, although techniques, such as using low concentrations of LA, can reduce this effect Fetal umbilical pH was marginally improved with epidural analgesia Regional labour analgesia Indications – Maternal request. – Expectation of operative delivery (e.g. multiple pregnancy, malpresentation) – Obstetric disease (e.g. pre-eclampsia) – Maternal disease: in particular, conditions in which sympathetic stimulation may cause deterioration in maternal or fetal condition – Specific CVS disease (e.g. regurgitant valvular lesions) – Severe respiratory disease (e.g. cystic fibrosis) – Specific neurological disease (intracranial A–V malformations, spinal cord injury etc.) – Conditions in which GA may be life-threatening (e.g. morbid obesity) Regional labour analgesia Contraindications – Allergy (true allergy to amide LAs is rare) – Local infection – Uncorrected hypovolemia – Raised ICP – Coagulopathy: Spinal analgesia is probably safer than epidural analgesia Tests of coagulation and the platelet count should be within 6hr of the time of the procedure, but, especially with pre-eclampsia, it is also important to consider the rate at which the platelet count is falling Relative contraindications Expectation of significant hemorrhage Untreated systemic infection (risk of ‘seeding’ infection into the epidural space) Specific cardiac disease (e.g. severe valvular stenosis, Eisenmenger’s syndrome, peripartum cardiomyopathy (rapid changes in BP, preload, and afterload of the heart) ‘Bad backs’ and previous back surgery do not contraindicate regional analgesia/anesthesia, but scarring of the epidural space may limit the effectiveness of epidural analgesia and increase the risk of inadvertent dural puncture. Intrathecal techniques can be expected to work normally Consent Most UK anesthetists do not take written consent before inserting an epidural for labour analgesia, but ‘appropriate’ explanation must be given The Obstetric Anesthetists’ Association has produced an information leaflet for mothers which includes a quantitative estimate of the incidence of a variety of potential complications, including neurological injury The explanation and, in particular, the possible hazards discussed must be documented, as many women do not accurately recall information given in labour Information about labour analgesia should always be available antenatally Epidural analgesia for labour Competent assistant should be available Scrupulous attention to sterile technique is required. A mask, hat, gown, and gloves should be worn Establish IV access Fluid preload may help with subsequent hypotension Position in either a full lateral or sitting position – Finding the midline in the obese may be easier in the sitting position – Accidental dural puncture may be slightly lower in the lateral position Fetal HR should be recorded before and during the establishment of analgesia Epidural analgesia for labour Skin sterilization with 0.5% chlorhexidine is common in the UK: – most sterilizing solutions, including chlorhexidine, are neurotoxic, so great care must be taken to avoid contamination of the neuraxial equipment or the anesthetist’s gloves – It is recommended that chlorhexidine is never on the sterile work surface, and it is sensible to complete skin sterilization before the neuraxial equipment is unwrapped – Chlorhexidine must be allowed to dry before the skin is touched Locate the epidural space: – Loss of resistance to saline may have slight advantages in both the reduced incidence of accidental dural puncture and reduced incidence of ‘missed segments’, compared with loss of resistance to air). – The incidence of puncturing a blood vessel with the epidural catheter is reduced if 10mL of saline is flushed into the epidural space before the catheter is inserted Epidural analgesia for labour Always insert the catheter as gently as possible Introduce 4–5cm of the catheter into the epidural space: – Longer has an increased incidence of unilateral block, and shorter increases the chance that the catheter pulls out of the space – Multihole catheters have a lower incidence of unsatisfactory blocks Check for blood/CSF: – If blood is aspirated, see if the catheter can be withdrawn further (leave a minimum of 3cm in the space) – If blood is still present, remove the catheter, and reinsert Epidural analgesia for labour Give an appropriate test dose – An ‘appropriate’ test remains controversial – Using 0.5% bupivacaine significantly increases motor block – Using 1:200 000 adrenaline to detect IV placement of a catheter has both high false positive and false negative rates – Many anesthetists will use 8–15mL of 0.1% bupivacaine with a dilute opioid (2 micrograms/mL fentanyl) as both the test and main doses – This will exclude intrathecal placement but may not exclude intravascular placement – However, the complete absence of a detectable block after a normal labour analgesia loading dose is a warning sign of possible IV cannulation – Remember every dose is a ‘test dose’! Epidural analgesia for labour If required, give further LA to establish analgesia: – There should be no need to use concentrations >0.25% bupivacaine Measure maternal BP every 5min for at least 20min after every bolus dose of LA Once the epidural is functioning, it can be maintained by one of three methods: 1. Intermittent top-ups of LA administered by a PCEA: In general, larger volumes of low-concentration bupivacaine with opioid produce more effective analgesia A common regimen would be 5–10mL boluses of 0.0625– 0.1% bupivacaine with 2 micrograms/mL fentanyl and a 15– 20min lockout period Epidural analgesia for labour 2. A continuous infusion of LA (5–12mL/hr of 0.0625–0.1% bupivacaine with 2 micrograms/mL fentanyl) 3. Intermittent top-ups of LA administered by midwives: – this is now rare in the UK – Historically, boluses of 5–10mL of 0.25% bupivacaine were used, but a more modern approach would be to use a larger volume of a lower concentration such as 10–15mL of 0.1% bupivacaine with 2 micrograms/mL fentanyl Combined spinal/epidural analgesia for labour A combination of low-dose subarachnoid LA and/or opioid, together with subsequent top-ups of weak epidural LA, produces a rapid onset of analgesia with minimal motor block An epidural technique alone can produce a similar degree of analgesia and motor block but may take 10–15min longer to establish Indications for CSEs include establishing rapid analgesia in women who are unable to cope with labour pain, re-establishing analgesia for women who have had a failed epidural, and preservation of leg strength for women who want to walk in labour In some centres, CSEs are used routinely because of the rapid speed of onset, the reliable initial analgesia, together with some evidence of improved epidural analgesia after the initial spinal analgesia has receded Combined spinal/epidural analgesia for labour CSE can be performed as a needle-through-needle technique or as separate injections in the same, or in different, intervertebral spaces: Either: – Locate the epidural space at the L3/4 interspace or below with a Tuohy needle (The level of the iliac crests usually corresponds to the spinous process of L4 (Tuffier’s line), although there is variation between individuals) – Pass a 25–27G pencil-point needle through the Tuohy needle to locate the subarachnoid space – Inject the subarachnoid solution (e.g. 0.5–1.0mL of 0.25% bupivacaine – with 5–25 micrograms of fentanyl or the equivalent dose in mg) – Without rotating the epidural needle, insert an epidural catheter Combined spinal/epidural analgesia for labour Or: – Perform the spinal at L3/4 or below with a 25–27G pencil-point needle – Inject the spinal solution – Insert an epidural catheter at a different interspace – This technique is particularly helpful when women are unable to stay still because of pain – The spinal is usually quick and relatively easy, and, once analgesia has been established, an epidural can be performed with a more cooperative patient – After 15min, once the analgesia from the spinal solution is established, – check the degree of motor and sensory block, and then administer an epidural test dose. If this dose is given accidentally intrathecally, the block would be expected to change significantly within 5min – Further management of the epidural is the same as for epidural analgesia alone. ‘Walking’ epidurals Effective analgesia with minimal motor block of the lower limbs can be readily produced with low doses of an epidural or intrathecal LA, usually in combination with an opioid, e.g. subarachnoid injection of 1–2.5mg of bupivacaine with 10–25micrograms of fentanyl or an epidural bolus of 15– 20mL of 0.1% bupivacaine with 2 micrograms/mL fentanyl, and subsequent epidural top-ups of 15mL of the same solution, as required. In some centres, women with minimal motor blockade are encouraged to mobilize The possible advantages of these techniques include: – Minimal motor block associated with these techniques increases maternal satisfaction scores – Intrathecal, as opposed to epidural, techniques produce a more rapid onset of analgesia Mobilization Mobilization has been criticized, because: – Leg strength may be compromised, and this becomes increasingly likely with repeated doses of epidural LA – Impaired proprioception may make walking dangerous, even when leg strength has been maintained. While dynamic posturography suggests that, following an initial intrathecal dose of 2.5mg of bupivacaine and 10 micrograms of fentanyl, proprioception is adequate for safe walking, this may no longer be true after repeated epidural top-ups – Intrathecal opioid may cause temporary fetal bradycardia, probably by altering uterine blood flow through a change in maternal spinal reflexes – Assessing the fetal condition is difficult when the mother is mobile – In practice, even when a technique is used that could allow walking, only ~50% of women actually choose to do so. Despite this, most women prefer the added sense of control engendered by retaining leg strength Mobilization – If women are to be allowed to walk, always wait at least 30min from the initiation of the block before attempting mobilization – Then: Check the strength of straight leg-raising in bed Ask the woman if she feels able to stand When the woman first stands, have two assistants ready to offer support, if required Perform a knee bend Ask the woman if she feels safe Allow full mobilization After each top-up, the same sequence must be repeated The poorly functioning epidural Look for the pattern of failure (Table 33.3) Remember that a full bladder may cause breakthrough pain, ask the midwife if a full bladder is likely Carefully assess the spread of the block It is important to be confident that the epidural could be topped up for a Caesarean section, if required Therefore, if in doubt, re-site the epidural The poorly functioning epidural Complications of epidural analgesia Hypotension: – In the absence of fetal distress, a fall in systolic BP of 20% or to 100mmHg (whichever is higher) is acceptable – However, uterine blood flow is not autoregulated, and prolonged or severe hypotension will cause fetal compromise – IV fluid loading is not routinely required when using low doses of LA, but patients should not be hypovolemic before instituting regional analgesia – When hypotension or fetal distress is detected, it should be treated quickly – Avoid aortocaval occlusion—make sure that the patient is in the full lateral position. (Remember that, in the lateral position, BP should be measured in the dependent arm—there is often a 10mmHg difference between the upper and lower limbs) Complications of epidural analgesia – Give an IV fluid bolus of crystalloid solution and, if the fetus is distressed, mask O2 supplementation – Give 6mg IV ephedrine, and repeat as necessary – If the fetus is distressed, call the obstetricians – Remember that brachial artery pressure may not reflect uterine artery blood flow – If fetal distress is detected and is chronologically related to a regional anesthetic procedure, treat as above, even in the absence of overt hypotension Subdural block Subdural block occurs when the epidural catheter is misplaced between the dura mater and arachnoid mater In obstetric practice, the incidence of clinically recognized subdural block is <1:1000 epidurals However, subdural blocks may be clinically indistinguishable from epidural blocks Definitive diagnosis is radiological Subdural block The classical characteristics of a subdural block are: – A slow onset (20–30min) of a block that is inappropriately extensive for the volume of LA injected – The block may extend to the cervical dermatomes, and Horner’s syndrome may develop – The block is often patchy and asymmetrical – Sparing of motor fibres to the lower limbs may occur – A total spinal may occur with top-up doses. This is probably due to an increase in volume, causing the arachnoid mater to rupture – If a subdural is suspected, re-site the epidural catheter Total spinal The incidence of unexpected high or total spinal is variously reported to be 1:1500 to 1:4500 epidurals Usually the onset is rapid, although delays of 30min or more have been reported Delayed onset may be related to a change in the maternal position or a subdural catheter placement Symptoms are of a rapidly rising block Initially, difficulty in coughing may be noted (which is commonly seen during regional anesthesia for a Caesarean section), then loss of hand and arm strength, followed by difficulty with talking, breathing, and swallowing If the block is rising to a concerning height, think about the likely cause Total spinal If the block is likely to be due to a correctly sited epidural LA, but excess dose, position the patient head-up If the block is due to subarachnoid plain LA (which is hypobaric, compared to CSF), a head-up position may actually encourage the block to spread further So gently position the mother in a left lateral position, which should minimize dural compression through epidural vein engorgement (which occurs with caval occlusion), and observe very closely Sudden movements may cause CSF to move further Make sure that the equipment for ventilatory and CVS support are immediately available Respiratory paralysis, CVS depression, unconsciousness, and finally fixed dilated pupils may ensue Total spinal Unsurprisingly, total spinals are reported more often after epidural anesthesia than epidural analgesia, as larger doses of LA are employed Management of total spinal Maintain airway and ventilation; avoid aortocaval compression, and provide CVS support Even if consciousness is not lost, intubation may be required to protect the airway Careful maternal and fetal monitoring is essential and, if appropriate, delivery of the fetus In the absence of fetal distress, a Caesarean section is not an immediate requirement Ventilation is usually necessary for 1–2hr Accidental intravenous injection of local anesthetic ‘Every dose is a test dose.’ The maxim is to avoid injecting any single large bolus of LA IV The risk can be minimized by: – Meticulous attention to the technique during placement – Always check for blood in the catheter – Always being alert to symptoms of IV injection with every dose of LA, even when previous doses have been uncomplicated – Dividing all large doses of LA into aliquots – Using appropriate Las – If neurological or cardiovascular symptoms occur – Stop injecting the LA – Treat according to BLS and ALS protocols. – Administer 20% lipid emulsion Neurological damage Neurological damage does occur after childbirth, but establishing cause and effect is difficult Neurological sequelae following delivery under GA is as common as delivery under regional anesthesia, suggesting that obstetric causes of neurological problems are probably commoner than any effects from the regional technique Prolonged neurological deficit after epidural anesthesia occurs in ~1:10 000 to 1:15 000 Major neurological damage probably occurs in <1:80 000 neuraxial procedures in the obstetric population, and this group of patients probably has the lowest risk of any patient population Dural puncture When loss of CSF is greater than production, as might occur through a dural tear, CSF pressure falls, and the brain sinks, stretching the meninges This stretching is thought to cause headache Compensatory vasodilatation of intracranial vessels may further worsen symptoms The incidence of dural puncture should be <1% of epidurals All midwives, as well as obstetric and anesthetic staff, should be alert to the signs of PDPH, as symptoms may not develop for several days If untreated, headaches are not only unpleasant, but also can very rarely be life-threatening, usually as a result of intracranial hemorrhage or coning of the brainstem Management of an accidental dural puncture can be divided into immediate and late Management of dural puncture: Immediate management Management of an accidental dural puncture can be divided into immediate and late Immediate management: – The initial aim is to achieve effective analgesia without causing further complication – Either: – If a dural puncture occurs, pass the ‘epidural’ catheter into the subarachnoid space – Label the catheter clearly as an intrathecal catheter, and only allow anesthetists to perform top-ups – Give intermittent top-ups through the catheter (1.0–2.5mg of bupivacaine ± 5–25 micrograms of fentanyl – Tachyphylaxis may occur with prolonged labour Management of dural puncture – Advantages: The analgesia produced is likely to be excellent There is no possibility of performing another dural puncture on reinsertion of the epidural The unpredictable spread of the epidural solution through the dural tear is eliminated The need for an epidural blood patch (although not the incidence of PDPH) may be reduced – Disadvantages: There is a theoretical risk of introducing infection The catheter may be mistaken for an epidural catheter Management of dural puncture Or: – Remove the epidural catheter – Reinsert the epidural at a different interspace—usually one interspace higher – If the reason for the dural puncture was difficult anatomy, a senior colleague should take over – Run the epidural as normal, but beware of intrathecal spread of LA – Be particularly cautious if the epidural catheter is topped up with a large dose of anesthetic for a Caesarean section – All top-ups should be given by an anesthetist – With either technique, the patient should be informed, at the earliest opportunity, that a dural puncture has occurred and of the likely sequelae – Labour itself may be allowed to continue normally. Arrange daily postnatal follow-up. Management of dural puncture: Late management Following a dural puncture with a 16G Tuohy needle, the incidence of PDPH is ~90% In only 40% of dural punctures CSF is recognized flowing from the Tuohy needle In >30% of individuals who develop PDPH, a dural puncture was not recognized in labour Headaches in the post-natal period are common The key differentiating factor between a ‘normal’ post-natal headache and PDPH is the positional nature of the latter Management of dural puncture Common features of PDPH include: – Typically, the onset is 24–48hr post-dural puncture, if untreated, they are said to last 7–10d, but the evidence is poor – Characteristically, PDPH is worse on standing. Headache is often absent after overnight bed rest but returns after mobilizing – The headache is usually fronto-occipital and may be associated with neck stiffness – The headache may be relieved by tight abdominal compression— while abdominal binders are no longer used as a treatment, this can be a useful diagnostic tool Management of dural puncture – Photophobia and difficulty in accommodation are common – Hearing loss, tinnitus, and 6th nerve palsy with diplopia are possible – If these signs develop, women should be encouraged to have a blood patch sooner rather than later, as these signs are an indication of a more severe headache, and the risk of more serious complications—seizures, subdural hematoma, and cerebral herniation—may be increased – Nausea in up to 60% of women Treatment is either to alleviate symptoms, while waiting for the dural tear to heal itself, or to seal the puncture Epidural blood patching is the only commonly used method of sealing dural tears, although neurosurgical closure has been reported Management of dural puncture: Prophylactic treatment There is a high incidence of bacteremia shortly after delivery This, combined with the poor efficacy of prophylactic blood patching, means that the use of prophylactic blood patching has fallen out of favour Although bed rest alleviates symptoms, the incidence of PDPH after 48hr is the same for those cases that mobilized throughout. Because of the risk of thromboembolism, bed rest should not be routinely encouraged in asymptomatic women Management of dural puncture: Symptomatic treatment Although there is no well-established mechanism for preventing PDPH, once a dural puncture has occurred, various treatments have been proposed to alleviate symptoms, while waiting for the dural puncture to seal itself Simple analgesics (paracetamol and NSAIDs) are the mainstays of symptomatic treatment. They should always be offered, even though they are unlikely to completely relieve severe PDPH Adequate fluid intake should be encouraged, although there is no evidence that hydration reduces the incidence of PDPH Caffeine/ theophyllines act by reducing intracranial vasodilatation, which is partially responsible for the headache. IV aminophylline has been shown to reduce the incidence of headache. However, concern has been expressed that the incidence of seizures following dural puncture may be increased in the presence of caffeine Management of dural puncture: Symptomatic treatment Epidural infusion of saline is no longer recommended. Although compression of the dural sac with epidural saline can alleviate symptoms, after 24hr of continuous infusion, the incidence of PDPH is only marginally reduced. However, radicular pain in the lower limbs may occur, and patients are immobilized In relatively small RCT studies, ACTH analogues reduced the incidence of headache after a known dural puncture, while IV dexamethasone increased the incidence. However, the studies are small, and the results need to be treated with caution.12,13 A number of case series have also supported the use of gabapentin or pregabalin. However, again the numbers are small, and the results need to be treated with caution Definitive treatment is with epidural blood patching Management of dural puncture: Epidural blood patch Epidural blood patch performed around 48hr post-partum has a 60– 90% cure rate at the 1st attempt (with a lower success rate if performed between 24 and 48hr post-partum, and lower still if performed at <24hr post-partum). The proposed mechanism of action is 2-fold: – Blood injected into the epidural space compresses the dural sac and raises the ICP. This produces an almost instantaneous improvement in pain – The injected blood forms a clot over the site of the dural tear, and this seals the CSF leak Management of dural puncture: Epidural blood patch Blood injected into the epidural space predominantly spreads cephalad, so blood patches should be performed at the same or lower interspace as the dural puncture Consent must be obtained. The patient should be apyrexial and not have a raised WCC Two operators are required. One should be an experienced ‘epiduralist’; the other is required to take blood in a sterile manner The patient should have a period of bed rest before performing the patch to reduce the CSF volume in the epidural space Aseptic technique must be meticulous both at the epidural site and the site of blood letting (usually the antecubital fossa) Management of dural puncture: Epidural blood patch An epidural should be performed at the same or a lower vertebral interspace as the dural puncture, with the woman in the lateral position to minimize CSF pressure in the lumbar dural sac Once the epidural space has been identified, 20mL of blood is obtained Inject the blood slowly through the epidural needle, until either a maximum of 20mL has been given or pain develops (commonly in the back or legs). If pain occurs, pause, and, if the pain resolves, try continuing with a slow injection. If the pain does not resolve or recurs, then stop To allow the clot to form, maintain bed rest for at least 2hr, and then allow slow mobilization Management of dural puncture: Epidural blood patch As far as possible, the patient should avoid straining, lifting, or excessive bending for 48hr, although there are obvious limitations when a woman has a newborn infant to care for Follow-up is still required. Every woman should have clear instructions to contact the anesthetists again if symptoms recur, even after discharge home Serious complications of blood patching are rare. However, backache is common, with 35% of women experiencing some discomfort 48hr post-epidural blood patch and 16% of women having prolonged backache (mean duration 27d) Other reported complications include repeated dural puncture, neurological deficits, epileptiform fits, and cranial nerve damage Suggestions that labour epidurals after blood patching may be less effective have not been confirmed Remifentanil for labour analgesia Remifentanil is an ultrashort-acting mu-agonist opioid, which is broken down by tissue and plasma esterases It has an analgesia half-life of about 6min and a rapid onset time of 30–60s. Although remifentanil readily crosses the placenta, it is also rapidly metabolized in the fetus These features make remifentanil a potentially useful analgesic agent in labour Like all opioids, it does not produce complete analgesia but appears to be more effective than IM pethidine. When compared with a fentanyl PCA, the analgesic effect may be little different, but, as might be expected, remifentanil is associated with less need for fetal resuscitation, which is good, and an increased incidence of maternal respiratory depression, which is potentially worrying Remifentanil for labour analgesia Up to 40% of women who use remifentanil PCA for pain relief in labour will develop respiratory depression. So remifentanil must only be used with direct (in the room) supervision and careful training of all the staff involved in its administration. There have been numerous case reports of maternal respiratory arrests with remifentanil The ideal PCA regimen has not been established. Many proposed techniques are based on body weight, but the technique below is based on a fixed dose which has the advantage of simplicity The addition of N2O may improve analgesia further but may increase the risk of hypoxemia Remifentanil for labour analgesia Technique: Of critical importance is establishing one-to-one care with a trained individual (midwife) who must be continuously present in the labour room No opioid should have been used in the previous 4hr Establish dedicated IV access PCA bolus dose of 20–40 micrograms and lockout of 2min Monitor with continuous pulse oximetry Give O2 if SpO2 <94% on air Thirty-minute observations of respiratory rate, sedation score, and pain scores Remifentanil for labour analgesia Always flush the cannula when PCA is discontinued Call the anesthetist if: – The patient is not rousable to voice – Respiratory rate <8 breaths/min – SpO2 <94% despite O2 supplementation Cesarean section (CS) With all Caesarean sections, it is vital that the obstetrician clearly communicates the degree of urgency to all staff. The four-point classification17 in Table is a modification of a system originally proposed by Lucas Cesarean section (CS) For all emergency Cesarean sections, the patient must be transferred to theatre as rapidly as possible. Fetal monitoring should be continued until abdominal skin preparation starts For category 1 (emergency) sections, the objective should be to deliver the fetus as quickly as possible, while not compromising maternal safety It is the obstetrician’s responsibility to call the urgency of the Cesarean section, but it is the anesthetist’s responsibility to choose a method of anesthesia that is safe While, in many centres, GA is commonly used for category 1 sections, do not be pressured into choosing a form of anesthetic that is inappropriate for the mother Regional anesthesia for Cesarean section Categories 2–4 Caesarean sections are usually performed under regional anesthesia Remember that the classification of urgency should be continuously reviewed. Category 1 sections can become category 2, and vice versa Regional anesthesia for Caesarean section was initially driven by maternal preference It was subsequently found that regional anesthesia is also safer than GA, although, with good-quality training, and modern anesthetic standards and equipment, the difference in maternal mortality appears to be less than it was in the past Regional anesthesia for Cesarean section: Advantages of regional anesthesia Minimal risk of aspiration and lower risk of anaphylaxis The neonate is more alert, which promotes early bonding and breastfeeding Fewer drugs are administered, with less ‘hangover’ than after GA Better post-operative analgesia and earlier mobilization Mothers who are nervous about having a Cesarean section under regional anesthesia should be given a clear explanation of the advantages and disadvantages of regional anesthesia and GA but should never be coerced into having a regional technique Regional anesthesia for Cesarean section There are three techniques for neuraxial anesthesia—epidural, spinal, and CSE Epidural anesthesia is most commonly used for women who already have labour epidural analgesia. Spinal anesthesia is the most popular technique for an elective Caesarean section, although, in some centres, CSEs are preferred The speed of onset of sympathectomy that occurs with spinal anesthesia (as opposed to epidural) results in a greater fall in maternal cardiac output and BP and may be associated with a more acidotic neonate at delivery This can be minimized by using a prophylactic phenylephrine infusion and careful positioning of the mother Regional anesthesia for Cesarean section When there is particular concern about the speed of onset of a block, a CSE approach can be used, injecting only a small dose of intrathecal LA and extending the block, if required, using the epidural catheter Spinal anesthesia generally provides a better quality of analgesia than epidural anesthesia Whatever technique is chosen, a careful history and an appropriate examination should be performed. This should include checking: – Blood group and antibody screen. Routine cross-matching of blood is not required, unless hemorrhage is expected or if antibodies that interfere with cross-matching are present. – Ultrasound reports to establish the position of the placenta. A low-lying anterior placenta puts a woman at risk of major hemorrhage, particularly if associated with a scar from a previous Caesarean section Regional anesthesia for Cesarean section An explanation of the technique must be offered. Although a Cesarean section under regional anesthesia becomes routine for the anesthetist, it can be an intimidating prospect for the mother. Reassurance and support are important. However, the possibility of complications must also be mentioned, including the possibility of intraoperative discomfort and its management Pain during regional anesthesia remains a leading obstetric anesthetic cause of maternal litigation Document all complications that are discussed Cesarean section: epidural Indications for a Caesarean section under epidural anesthesia include: – Women who already have epidural analgesia established for labour – Specific maternal disease (e.g. cardiac disease) where rapid changes in SVR might be problematic, although, more commonly, these individuals will have a careful CSE Cesarean section: epidural Table shows advantages and disadvantages of epidural for CS Cesarean section: epidural technique History/examination/explanation and consent. Ensure that antacid prophylaxis has been given Establish 16G or larger IV access. Start crystalloid co-load Insert epidural catheter at the L2/3 or L3/4 vertebral interspace. Position the patient in the supine position with a left lateral tilt or wedge Give supplemental O2 by face mask if SpO2 <95% on air. (This is very important in obese patients, who may become hypoxic when supine, and may also be beneficial for a compromised fetus) Test the dose, then incrementally top up the epidural with LA and opioid: Five to 8mL boluses of 2% lidocaine with 1:200 000 adrenaline every2–3min, up to a maximum of 7mg/kg (~20mL), or Five mL of 0.5% bupivacaine/levobupivacaine/ ropivacaine every 4–5min, up to a maximum of 2mg/kg in any 4hr period. (The single-enantiomer LAs may offer some safety advantage; however, lidocaine is still safer than either ropivacaine or levobupivacaine.) Opioid (e.g. 100 micrograms of fentanyl or 2.5mg of diamorphine) improves the quality of the analgesia, and a slightly lower dermatomal block height may be accepted before starting surgery (i.e. T6 to light touch) Establish an S4–T4 block (nipple level). Always check the sacral dermatomes, as epidural LA occasionally does not spread caudally Cesarean section: epidural technique Anesthesia to light touch is more reliable at predicting adequacy of block than loss of cold sensation Document the level of block obtained and the adequacy of perioperative analgesia Hypotension is much less common than with intrathecal techniques. However, if hypotension does occur, treat hypotension with: Boluses of 500 mL of crystalloid Fifty to 100 micrograms of phenylephrine IV bolus (expect a reflex bradycardia) or 6mg of ephedrine IV. α-agonists may be more effective and may be associated with less fetal acidosis than ephedrine Increasing the left uterine displacement At delivery, give 2–5IU of oxytocin as a slow IV bolus. If tachycardia must be avoided, then an IV infusion of 30– 50IU of oxytocin in 500mL of crystalloid, given over 4hr, is an acceptable alternative At the end of the procedure, give NSAID, unless contraindicated (100mg of diclofenac PR) Epidural diamorphine given at the time of surgery improves post-operative analgesia, while epidural fentanyl has little post-operative analgesic benefit Cesarean section: spinal Spinal anesthesia is the most commonly used technique for elective Cesarean sections It is rapid in onset, produces a dense block, and, with intrathecal opioids, can produce long-acting post-operative analgesia. However, hypotension is much commoner than with epidural anesthesia Cesarean section: spinal technique History/examination/explanation and consent Ensure that antacid prophylaxis has been given Establish 16G or larger IV access. Start crystalloid co-load Position the patient. A sitting position usually makes finding the midline easier, which may be helpful with obese patients, and may be associated with a faster onset, although the height of block is less predictable. A lateral position is associated with a slower onset of block, particularly if a full lateral position is maintained until the block has fully developed. The block height may be slightly more consistent, and the women may sometimes find it more comfortable than sitting if the fetal head is very low Perform spinal anesthetic at L3/4 interspace, using a 25G or smaller pencil-point needle. (The level of the iliac crests usually corresponds to the spinous process of L4 (Tuffier’s line), although there is variation between individuals) With the orifice pointing cephalad, inject the anesthetic solution, e.g. 2.5mL of 0.5% hyperbaric bupivacaine with 300 micrograms of diamorphine or 15 micrograms of fentanyl. Intrathecal diamorphine improves post-operative analgesia, while intrathecal fentanyl has little post-operative analgesic benefit. (A total of 100 micrograms of preservative-free morphine is also used and can produce prolonged postoperative analgesia. However, there is a high incidence of PONV and an increased risk of late respiratory depression) Cesarean section: spinal technique After injection of the solution, move the woman to a supine position with a left lateral tilt or wedge. When hyperbaric LA solutions are used, it is important that the cervical spine is kept elevated (pillow) to prevent LA from spreading to the cervical dermatomes. If supine hypotension occurs, increase the tilt, or, if severe, temporarily move the woman to a full lateral position Start pressor infusion. Hypotension is commoner with spinal anesthesia than epidural anesthesia. Try to prevent hypotension, rather than treat it after it has occurred. When possible, a continuous infusion of the pressor agent should be started at the time of the injection of spinal LA Continue as for epidural anesthesia for Caesarean section Cesarean section: combined spinal/epidural To be completed in a later time Inadequate anesthesia To be completed in a later time Hypotension Preventing maternal hypotension, rather than treating BP after hypotension has occurred, is associated with better fetal outcome and less maternal nausea There are two principal methods of treating hypotension—pressor agents and fluid Hypotension: Pressor agents Using prophylactic pressor agents is beneficial for both mother and fetus. Ephedrine was used to treat hypotension in obstetric neuraxial anesthesia for many years. However, in the last decade, it has been established that treatment to normotension with phenylephrine is associated with better fetal umbilical pH than when ephedrine is used, although the difference is marginal. If phenylephrine is used, bolus doses of 50–100 micrograms can cause profound reflex bradycardias, so, if possible, use a phenylephrine infusion instead A simple regime is to use a syringe driver with a solution of 100 micrograms/mL of phenylephrine (i.e. make up 10mg in 100mL of saline, and decant 20mL into a syringe) Start infusing at 30mL/hr, as the spinal solution is injected Titrate to response, adjusting the rate of infusion up or down in increments of 10mL/hr During the infusion, expect the HR to gradually slow, so give anticholinergic agents, as required Reduce and stop the infusion post-delivery Be careful with this technique in hypertensive individuals. Start at a lower infusion rate. Metaraminol can be used as an alternative to phenylephrine. Hypotension: Fluid A fluid preload was a traditional part of the anesthetic technique for regional anesthesia. It had two functions: To maintain the intravascular volume in a patient who is likely to lose 500–1000mL of blood To reduce the incidence of hypotension associated with regional anesthesia However, crystalloid preloading is very ineffective at preventing hypotension In addition, in women with severe pre-eclampsia, large preloads are harmful, as the rise in filling pressures and the reduced colloid osmotic pressure will predispose to pulmonary edema Using colloids as a preload is more effective, but colloids may be associated with significant problems such as anaphylaxis There is evidence that co-loading with crystalloid (giving fluid as the block is establishing) is more effective than preloading. Hypotension: Fluid A co-load should be: – Timely (given immediately before or during the onset of the regional technique to minimize redistribution) – Limited to 10–15mL/kg of crystalloid. Larger volumes should be avoided, as they offer little advantage and may be harmful – More fluid should only be given as clinically indicated – Emergency Caesarean section should not be delayed to allow a fluid preload to be administered Cesarean section: general anesthesia Elective GA is now uncommon in the UK, limiting opportunities for training. The majority of complications relate to the airway. Failed intubation is much more frequent in obstetric than non-obstetric anesthesia. All obstetric theatres should have equipment to help with the difficult airway, and all obstetric anesthetists should be familiar with a failed intubation drill Indications for GA include: Maternal request Urgent surgery (in experienced hands and with a team that is familiar with rapid regional anesthesia, a spinal or epidural top-up can be performed almost as rapidly as a GA) Regional anesthesia contraindicated (e.g. coagulopathy, maternal hypovolemia) Failed regional anesthesia Additional surgery planned at the same time as a Caesarean section Cesarean section: GA technique History and examination. In particular, assess the maternal airway—mouth opening, Mallampati score, thyromental distance, neck mobility Antacid prophylaxis, including 30mL of 0.3M sodium citrate Start appropriate monitoring Position supine with a left lateral tilt or wedge Preoxygenate for 3–5min or, in an emergency, with 4–8 VC breaths with a high flow through the circuit. Ensure a seal with the face mask. At term, women have a reduced FRC and a higher respiratory rate and O2 consumption. This reduces the time required for denitrogenation, but also reduces the time from apnea to arterial O2 desaturation Perform RSI with an adequate dose of induction agent (e.g. 5–7mg/ kg of thiopental) A 7.0mm ETT is adequate for ventilation and may make intubation easier Propofol has also been used for Cesarean section, without any major reported complications, although, at present, thiopental is still the most commonly used agent in the UK Use ‘overpressure’ of the inhalational agent to rapidly increase the end-tidal concentration of the anesthetic agent to at least 0.75 MAC (e.g. 2% isoflurane for 5min, then reduce to 1.5% for a further 5min) Cesarean section: GA technique At delivery: – Give 2–5IU of oxytocin IV bolus. If tachycardia must be avoided, then an IV infusion of 30–50IU of oxytocin in 500mL of crystalloid, infused over 4hr, is effective – Administer opioid (e.g. 10–15mg of morphine ± 100 micrograms of fentanyl), IV paracetamol, and IV diclofenac (unless contraindicated) – Ventilate with 35% inspired O2 concentration in N2O. The inhalational agent can be reduced to 0.75 MAC to reduce uterine relaxation At the end of the procedure, consider performing bilateral ilioinguinal nerve blocks, rectus sheath, or TAP blocks which can all improve post-operative analgesia If a woman has eaten shortly before surgery, consider passing a large-bore orogastric tube to empty the stomach before extubation Extubate awake. Be aware that extubation is a high-risk time. Give additional IV analgesia, as required Recovery: Be aware that recovery units are potentially dangerous places for mothers after GAs, particularly if the recovery is staffed by midwives who may be less familiar with airway care. The same standard of recovery staff should be available to women on labour wards as in a normal theatre recovery unit Effect of general anesthesia on the fetus Lower fetal 1min and 5min Apgar scores are commoner when GA is used for Cesarean section Most anesthetic agents, except for muscle relaxants, rapidly cross the placenta Opioids administered before delivery may cause fetal depression. Which can be rapidly reversed with naloxone (e.g. 200 micrograms IM or 10 micrograms/kg IV) If there is a specific indication for opioids before delivery, they should be given, and the neonatologist informed Hypotension, hypoxia, hypocapnia, and excessive maternal catecholamine secretion may all be harmful to the fetus Failed intubation Failed intubation is ten times commoner in the obstetric population (~1:300, compared to 1:3000) Causes of failed intubation include obesity, increased fatty tissue, pharyngeal/laryngeal edema, large tongue, large breasts, incorrect cricoid pressure, complete dentition, and the experience and training of anesthetic staff When intubation fails, but mask ventilation succeeds, a decision on whether to continue with the Caesarean section must be made. A suggested grading system is shown in Box Failed intubation For grade 1 cases, surgery should continue, and for grade 5 the mother should be woken. The action between these extremes must take account of additional factors, including the ease of maintaining the airway, the likely difficulty of performing a regional anesthetic, and the experience of the anesthetist Once a failed intubation has occurred and an airway has been established, while waiting for the muscle relaxant to wear off, reapply fetal monitoring as this may give useful additional information to guide management If the surgery continues, decisions will have to be made on whether to use 1st- or 2nd-generation laryngeal masks and whether to use muscle paralysis (if yes, then rocuronium with an availability of sugammadex may be useful) Ask the obstetricians to avoid fundal pressure at delivery, if possible, because fundal pressure can increase intragastric pressure to >70 mmHg Antacid prophylaxis Aspiration of particulate matter, blood, or bile is associated with worse outcome than aspiration of gastric fluid. Fluid aspiration is commonly associated with chemical pneumonitis, and the severity of this is, in turn, dependent on the volume and acidity of the aspirated fluid. Use of antacids and prokinetic agents can elevate the gastric pH and reduce the intragastric volume. A suggested regime is as follows Elective surgery • Ranitidine 150mg orally, 2hr and 12hr before surgery • Metoclopramide 10mg orally, 2hr before surgery • A total of 30mL of 0.3M sodium citrate immediately before induction of GA. (Gastric pH >2.5 is maintained for only 30min after 30mL of 0.3M sodium citrate. If a GA is required after this, a further dose of citrate is required) Emergency surgery (if prophylaxis has not already been given) • Ranitidine 50mg by slow IV injection immediately before surgery (PPIs are an alternative). Remember this will not alter the risk of aspiration during induction but may offer benefit by the time of extubation • Metoclopramide 10mg IV injection immediately before surgery • A total of 30mL of 0.3M sodium citrate orally immediately before induction of GA Thank you