Obstetrics Anesthesia

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 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

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

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: Inhaled N2O (Entonox®) Opioids 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

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) 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 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 Information about labour analgesia should always be available antenatally Most UK anesthetists do not take written consent before inserting an epidural for labour analgesia, but ‘appropriate’ explanation must be given The explanation and, in particular, the possible hazards discussed must be documented, as many women do not accurately recall information given in labour Preferably an information leaflet for mothers including the incidence of a variety of potential complications, including neurological injury

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

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

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

Give an appropriate test dose Using 0.5% bupivacaine significantly increases motor block Using 1: 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’!

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: Intermittent top-ups of LA administered by a PCEA A continuous infusion of LA (5–12mL/hr of –0.1% bupivacaine with 2 micrograms/mL fentanyl) Intermittent top-ups of LA administered by midwives

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

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

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 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

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 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 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 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

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 local LA intravascularly 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 LA’s 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: to 1:15 000 Major neurological damage probably occurs in <1: neuraxial procedures in the obstetric 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 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
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

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 post-natal 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

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

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: Symptomatic treatment
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 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 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

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 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)

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

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

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 classification 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

Regional anesthesia for Cesarean section
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 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 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

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, CSE’s 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

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

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

Cesarean section: epidural
Table shows advantages and disadvantages of epidural for CS

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

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 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 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

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

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Obstetrics Anesthesia

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