The 3 rd batch of Mansoura Manchester programme..

The 3 rd batch of Mansoura Manchester programme..

The 2 nd batch of Mansoura Manchester programme...

The 2 nd batch of Mansoura Manchester programme...

Thursday, December 27, 2007

Role of Caudal, Pudendal and Paracervical blocks : DR. Alaa Mosbah M.D OBS&GYN ,Egypt ,Mansoura

CAUDAL BLOCK Caudal epidurals in labour have become less popular because better perineal analgesia can be achieved by the use of epidural infusions and primigravidae are more likely to receive an epidural block. Also, there have been recent concerns about the risks of inadvertent intravenous and fetal injection. A modified caudal epidural technique can provide rapid onset perineal anaesthesia without cardiovascular disturbance and with relatively little loss of expulsive power. If used for perineal anaesthesia only, caudal block is a useful, safe technique for experienced anaesthetists provided that the volume of local anaesthetic is limited to a maximum of 10 mls, injected slowly (with multiple aspirations). It should be noted that this dose is less than half that which is required to achieve full labour analgesia. The block should be inserted before the head is on the perineum . Since it has been shown that pencil point spinal needles have a low incidence of headache (0 to 0.66% with 27G and 25G Whitacre needles) spinal anaesthesia is often more appropriate than lumbar or caudal epidural anaesthesia for rotational forceps, manual removal of placenta and, at times, low forceps delivery. INDICATIONS1. Unrelieved perineal pain.2. Premature urge to push.3. Low forceps delivery.4. When lumbar epidural analgesia is contraindicated. INCIDENCEIn most Australian hospitals, caudal blocks are being used less frequently in labour as the number of spinals has increased. The major indications for caudals are perineal pain, labour pain, forceps delivery, and manual removal of placenta. Less commonly, caudals can provide anaesthesia for artificial rupture of the membranes, suturing of episiotomies and repair of vaginal lacerations. CAUDAL ANALGESIA IN COMBINATION WITH OTHER MAJOR REGIONAL BLOCKS At the Royal Women's Hospital, of those women who had a caudal, at least 62% also had a lumbar epidural. The lumbar epidural was either already in situ or was inserted at the same time as the caudal. It has been shown that for the lumbar epidural route, increasing the volume of anaesthetic is more likely to secure good sacral blockade than injection in the sitting position. However, in our experience sacral blockade can occasionally only be achieved with a caudal or spinal block. COMPLICATIONSl. Vascular tap and intravascular injection of local anaesthetic .2. Failed block (8%) - the sacral hiatus is absent in 5% of adults. 3. Subarachnoid injection - the dural sac reaches S2 .4. Infection.5. Fetal injection . Modified caudal block is a safe technique with a limited specific place in modern obstetric anaesthesia. PARACERVICAL BLOCK The risk of complications, particularly fetal bradycardia, generally make this technique an unsuitable form of anaesthesia for obstetric patients. However, if used, it should be avoided in the presence of fetal distress or uteroplacental insufficiency and the fetal heart rate should be monitored continuously during and after insertion of the paracervical block . COMPLICATIONS1. Vaginal trauma.2. Systemic local anaesthetic toxicity due to excessive dosage or intravenous injection .3. Parametrial haematoma.4. Sacral plexus trauma.5. Infection and deep abscess formation.6. Fetal scalp injection of local anaesthetic.7. Fetal bradycardia probably caused by decreased uteroplacental perfusion.8. Needle stick injury. PUDENDAL NERVE BLOCK Pudendal nerve block provides anaesthesia for spontaneous vaginal delivery or low forceps delivery. The pudendal nerve (S2 - S4) is the major sensory innervation of the lower vagina, vulva and perineum and provides motor fibres to the external anal sphincter and the perineal muscles. Pudendal nerve block was first reported for vaginal delivery in 1916 . It is inadequate for rotational forceps delivery and manual removal of the placenta. Either a transvaginal or transperineal approach can be used. The bilateral success rate has been reported as 50% after the transvaginal approach and 25% after the transperineal approach. INDICATIONS.1. Low forceps delivery.2. Vaginal and perineal pain when lumbar or caudal epidural or spinal analgesia is unavailable, contraindicated or declined. COMPLICATIONS 1. Vaginal trauma.2. Systemic local anaesthetic toxicity due to excessive dosage or intravenous injection.3. Vaginal or ischio-rectal haematoma. 4. Infection and deep abscess formation.5. Fetal trauma or direct local anaesthetic injection.6. Needle stick injury. Caudal Analgesia Although the caudal route was the first widely used approach to the epidural space for continuous block in labour (Hingson and Edwards, 1942), and remained in frequent use in a few centres until the late 1970's (McCaul), its present role is very limited. Apart from providing good analgesia for low instrumental deliveries and perineal repair, the use of caudal block is usually restricted to a very few enthusiasts and to those cases in which a lumbar epidural is anatomically impossible or contraindicated by local infection . (However, local sepsis may also preclude the use of caudal block) . The patient should be prepared according to the guidelines shown in . Following the provision of secure venous access and preloading with crystalloid, the patient is either turned into the left lateral position with both knees flexed and forward tilt of the upper hip, or (occasionally) the knee-elbow position according to patient or operator preference. The skin of the lumbosacral area is prepared with a bactericidal solution and sterile drapes are applied. A bleb of local anaesthetic is raised in the skin overlying the sacral hiatus, between the sacral cornua, at a site deep to the proximal extremity of the natal cleft. A 21- gauge needle may then used to infiltrate the deeper tissues, but this is not essential. A variety of needles and cannulae may be used for the block itself, including a:1. 7.6 cm 19-gauge caudal needle,2. disposable 3.8 cm 19-23g hypodermic needle,3. 20-24-g intravenous catheter for a "single-shot" technique, or4. Tuohy needle (17 or 18g) and catheter for a continuous technique. Whichever needle is used, it is gently inserted at an angle of 70-80degrees to the skin and slowly advanced until the bony resistance of the sacrum is detected . The needle is withdrawn slightly, the entry angle reduced by about half, and then reinserted until the resistance of the sacrococcygeal ligament is felt at a depth of 1.5-3.8 cm. The ligament is then penetrated and the needle or catheter inserted to a depth of 2-3 cm, bearing in mind that the dural sac terminates at the S2 level, and that dural puncture should be avoided . Test aspiration for blood or CSF is performed. If the test is negative, this is followed by the injection of a 3ml test dose of local anaesthetic, with a hand positioned over the sacrum to detect any tissue swelling, resulting from malposition of the needle or catheter either subperiosteally or along the dorsal surface of the sacrum. Following a negative test dose and in the absence of pain on injection, the definitive dose may be injected slowly in small, repeated increments . If CSF is aspirated or if blood continues to be aspirated after repositioning of the needle or catheter the block should be abandoned. Single-shot needles or cannulae are withdrawn following injection. Catheters are affixed to their connectors and filters and strapped in position. Lignocaine is preferred to bupivacaine in view of the potential for large doses of bupivacaine to produce cardiovascular collapse and intractable ventricular dysrhythmias . should intravascular injection occur into one of the abundant epidural veins . The dose and concentration of lignocaine depends on the indication for the block. A recommended dose for outlet forceps delivery would be 15 to 20mls of 1.5% lignocaine with adrenaline. For perineal analgesia, a dose of 10 to 15mls of 1.0% lignocaine with adrenaline would suffice . Pudendal Nerve Block During the second stage of labour, pain largely results from distension of the lower vagina, vulva and perineum. In addition, the musculature of the anterior compartment of the pelvis must be negotiated by the descending presenting part. These structures obtain most of their sensory and motor innervation from the second to fourth sacral nerve roots via the pudendal nerve. Pudendal nerve blocks are of value in providing analgesia for the second stage when contraindications to neuraxial blockade exist and for the provision of pelvic floor relaxation when forceps delivery is required. They may also be used to provide anaesthesia of the perineum in order to create or repair an episiotomy. Pudendal nerve blocks have been utilized in the past as an alternative to epidurals in assisted twin and breech deliveries . Increasing evidence supporting the safety of epidurals in these situations has contributed to a diminished use of pudendal nerve blocks . The anatomy of the pudendal nerve should be considered when performing the block. The block is performed with the patient in the lithotomy position. Two approaches have been described: transvaginal and transcutaneous or perineal. The basis of both approaches is to block the nerve before it gives off its terminal branches. Its most reliable landmarks are exploited - the ischial spine in the transvaginal, and the ischial tuberosity, in the perineal approach. Transvaginal approach:In the transvaginal approach, the ischial spine can be palpated either transvaginally or per rectum. It is important to use a needle with a guide in order to limit the depth of submucosal penetration ("Huber" security point ). When a left sided block is performed, the ischial spine is palpated with the index finger of the left hand, the syringe is held in the right hand and the needle is guided between the index and middle fingers of the left hand towards the ischial spine. The sacrospinous ligament lies 1 cm medial and posterior to the spine. The needle is passed through the ligament for a distance of 1 cm until a loss of resistance is appreciated. The tip now lies in the area of the pudendal nerve. The pudendal vessels are closely associated. After aspiration, 10 mls of local anaesthetic solution are injected. The block is repeated on the other side. Perineal approach:The perineal approach is considered valuable when the engaged head makes vaginal palpation difficult. The ischial tuberosity is located by palpation . The needle is introduced slightly medial to this point, for a distance of 2.5 cm. The nerve is usually encountered without eliciting paraesthesia. Up to 8 mls of solution is infiltrated at this point. The needle is then withdrawn and directed into the deep and superficial tissue of the vulva along its anterior margin in order to block the the ilioinguinal and genitofemoral component . The block is repeated on the other side. The limitations of this block include:- Failure to provide adequate analgesia. It has been reported that up to half of all bilateral pudendal blocks are ineffective on one or both sides . A pudendal nerve block will not abolish sensation to the anterior part of the perineum because this region is supplied by branches of the ilioinguinal and genitofemoral nerves. Subcutaneous infiltration anteriorly along the vulva is therefore described as a component of this technique. Failure to wait sufficient time is a commonly cited reason for failure of a pudendal block. Pudendal nerve blocks do not abolish the pain of uterine contraction and cervical dilation which is transmitted via sympathetic nerve fibres derived from spinal levels T10 - L2 . It does not cause relaxation of the uterus. - Intravascular injection with subsequent local anaesthetic toxicity is a risk imposed by the close proximity of the pudendal vessels . - Fetal complications are uncommon. Exposure of the fetus to a high plasma level of local anaesthetic is a possibility that should be considered. Delivery usually occurs within a short period of time which may not allow for clearance of local anaesthetic from fetus via the placenta. 1% lignocaine is the most commonly used agent. Peak concentrations occur within 10 - 20 minutes. The maternal plasma concentrations which occur after this block are much lower than after either epidural or paracervical blocks. This block has been reported to prolong the second stage of labour as a result of loss of the bearing-down reflex. The addition of adrenaline may further prolong the second stage of labour . Paracervical Block Paracervical blockade may be used as a means of reducing pain during the first stage of labour. Pain associated with uterine contraction and cervical stretching and dilatation is transmitted from these structures on visceral afferents which accompany sympathetic fibres. These pass sequentially through the uterine, cervical, inferior hypogastric and superior hypogastric plexuses to the lumbar and lower thoracic sympathetic chains. During early labour, the bulk of these enter the spinal cord at the T11 - T12 segments. As pain becomes more severe, the two adjacent segments, T10 and L1 become involved . The block is performed bilaterally with the patient in the lithotomy position. The proximity of the broad ligaments just deep to the lateral fornices of the vagina is exploited with the aim of interrupting pain transmission at the level of the uterine and pelvic plexuses . An 18.5 cm needle with a security tip (Iowa trumpet, Kobak) is used to limit the injection to within 1.5 - 2 cm of the epithelium. The needle is connected to a 20 ml Luer-Lok syringe. Measures to avoid intravascular injection are vital. After careful aspiration non-adrenaline containing local anaesthetic solution is infiltrated. The specific injection sites have been variously described: 3 and 9 oclock; 4 and 8 oclock; or alternatively all sites . The distribution of radio-opaque dyes observed in X-ray studies is similar . An interval of 15 minutes should be observed between injections during which time signs of maternal and fetal toxicity should be excluded. Paracervical blockade can be used to provide analgesia during the first stage of labour when contraindications of epidural analgesia are present. The optimal time for institution of this block is the accelerated phase of the first stage when the severity of pain increases. The presenting part is typically engaged. The cervix is thin and effaced and has a tendency to be drawn up during uterine contractions . Paracervical blockade does not provide analgesia of the perineum during the second stage during which pain is transmitted primarily via the pudendal nerves to the S2 - 4 spinal cord segments . The technique has several limitations. The failure rate is reported to be as high as 18% . The proximity of uterine blood vessels in the vaginal fornices creates maternal and fetal risks. Fetal bradycardia occurs in 10-50% of cases . This is attributed to asphyxia which is believed to result from transient uterine artery vasospasm due to high concentrations of local anaesthetic in the paracervical region. The technique has a duration of action limited to 90 minutes with plain lignocaine. The use of adrenaline or bupivacaine in an attempt to increase the duration of the block should be avoided as both increase the incidence of fetal bradycardia . Preparation and Monitoring for Regional Blockade Adequate preparation of the obstetric patient is vital in order to minimise the complications of regional anaesthesia. This will be achieved by obtaining a history, performing a physical examination, and, if indicated, performing preliminary investigations. Of particular relevance in the history is the presence of cardiac disease, pre-eclampsia, coagulopathy, or any maternal condition which may present a relative contraindication to neuraxial blockade. The presence of any of these conditions may preclude the selection of the spinal and/or epidural route for analgesia or anaesthesia. Informed consent must be obtained. Fasting and acid-aspiration prophylaxis should be observed in patients undergoing caesarean section. The presence of a skilled assistant is essential. During the performance of the block and subsequently, careful attention to positioning will increase the likelihood of a succesful block. Large bore intravenous access and adequate prehydration will be required to minimise hypotension. Either reusable or disposable Tuohy needles and syringes may be used. Tuohy needles feature blunt cutting tips whose ends are curved. This assists in identification of the epidural space without dural puncture. The commonly used sizes for obstetric analgesia are 16g and 18g. These needles accept 18 and 20 gauge catheters respectively. Epidural catheters are typically made from PVC. The tip features either three helically-arranged lateral injection holes, or a single end hole . Three holed designs have been criticised for their potential to result in a malpositioned catheter such that individual holes may lie between different meningeal layers or in an epidural vein. This can result in a multi-compartment block or inadvertent intravascular injection of local anaesthetic . Single ended catheters have a higher incidence of false negative aspiration for blood and missed segments. Appropriate monitoring should be instituted. This should include monitoring of:1. The maternal circulation (pulse rate and blood pressure).Hypotension may complicate neuraxial blockade despite careful attention to prehydration and avoidance of aortocaval compression. A baseline pulse rate and blood pressure must be obtained before initiating the block. Blood pressure should be measured at intervals of not more than 5 minutes during establishment of the block and thereafter hourly whilst the block is being maintained. During caesarean section the blood pressure should be measured at 5 minute intervals. A qualified person should be responsible for hemodynamic monitoring. Appropriate management of hypotension should be instituted early. 2. The level of the block.The level of the block should be monitored 3. The fetus. Methods of monitoring fetal wellbeing include:a. Auscultation of heart rate with pinnards or doppler.b. Graphical display of the cardiotocograph .c. The use of scalp electrodes.d. Measurement of fetal scalp pH. The fetus should be monitored whenever an epidural is being utilised. In uncomplicated labours this is usually accomplished with a cardiotocograph. Scalp electrodes are used when the cardiotocograph fails to generate a reliable trace or when fetal distress is present. This requires a sufficiently dilated cervix. Scalp pH is used to gain more information on fetal wellbeing when other signs of fetal distress are present. 4. Bladder function.Painless bladder distension as the result of neural blockade may contribute to postpartum stress incontinence. This has been observed to occur in association with concentrations of bupivacaine of 0.5% .The bladder should be emptied intermittently. Prevention of local anaesthetic toxicity How do we Prevent the Development of Local Anaesthetic Toxicity? The use of local anesthetics (LA) may be accompanied by systemic and Iocalised adverse reactions, usually secondary to:1. accidental intravascular injection,2. inadvertent intrathecal injection, or3. administration of an excessive dose. Intravenous injection of 20-25 mg of bupivacaine has been reported to induce fatal cardiovascular collapse . Factors which can diminish the incidence of toxic reactions are:1. fractionation of the injected dose, 2. aspiration before injection, 3. selection of less toxic LAs . 4. reduction in the concentration of LA, and 5. test-dosing before injection of the main dose. The diagnosis of inadvertent intravascular placement of an epidural needle or catheter can be made by using either air or a sympathomimetic amine as the 'marker' agent. Unintended intrathecal placement can be diagnosed by the injection of an appropriately small dose of a rapid onset LA. Injection of 1 ml of air into an epidural catheter can be a highly specific and sensitive marker of intravascular catheter Iocalisation, but the safety of the doppler test has yet to be proven and, moreover, a precordial doppler and an extra person have to be available . Epinephrine, the catecholamine currently used in most test-doses, has several disadvantages. This mixed alpha- and beta-adrenergic agent does not consistently produce maternal tachycardia in laboring women. Cyclic maternal heart rate changes, due to painful uterine contractions, occur normally in unanesthetised parturients. The effect of epinephrine superimposed on these physiological changes in heart rate is not always discernible. Moreover, a major adverse effect of systemic epinephrine is its inhibition of uterine blood flow (UBF). This reduction of UBF has been demonstrated in gravid ewes and lasts for 2-5 minutes . Although the chronotropic response in term pregnant women is reduced, a test dose containing 5 mcg of isoproterenol (isoprenaline) might be a safer and more effective alternative .Isoproterenol produces a superior increase in maternal heart rate with minor effects on uterine blood flow in the chronic maternal fetal sheep preparation . In this animal model, incorporation of isoproterenol as a test dose does not produce neurotoxicty . These results suggest that isoproterenol may be safe for use as an epidural test dose in pregnant women. Some contradictory results exist concerning the increased sensitivity, during pregnancy, to the toxicity of local anesthetics. Santos et al. compared the systemic toxicity of ropivacaine and bupivacaine in non-pregnant and pregnant ewes and concluded that..."The systemic toxicity of ropivacaine or bupivacaine is not enhanced by gestation in sheep. This is in contrast to an earlier study in which cardiotoxicity of bupivacaine was enhanced during ovine pregnancy." A major concern in pregnancy is the trans-placental distribution of local anesthetics . Differences in the cord-to-maternal plasma drug concentration ratio essentially reflect trans-placental differences in the extent of plasma binding . When this ratio is high there should be a delay in the equilibration of drug in fetal tissues. Conversely, similar umbilical artery and umbilical vein concentration ratios observed for the various agents argue against large differences in their equilibration rates in the fetus. Thus, the impact, if any, of plasma binding on the risks of fetal toxicity is unclear . The prevention of toxicity of local anesthetics in the mother and the fetus is of utmost importance but, in this field, many questions remain to be answered. Regional techniques compared The use of subarachnoid local anaesthetic agents and narcotics for labour and delivery varies between institutions and individual anaesthetists. While practices may vary, the role of subarachnoid anaesthesia in comparison with other regional techniques can be defined in terms of the relative advantages and disadvantages of this method of anaesthesia. Efficacy and application of blockade:Local anaesthetics may be used intrathecally to accomplish sacral anaesthesia for instrumental vaginal deliveries and for other obstetric procedures. Subarachnoid blockade to a level above T7 may also be employed for cesarean section. Under these circumstances, subarachnoid blockade provides reliable, dense surgical anaesthesia. Epidural anaesthesia is also suitable for both labour and delivery but, sometimes, sacral segments may be difficult to block (with a lumbar epidural) and the blocks may occasionally be patchy or asymmetrical . In comparison to subarachnoid blockade, caudal blockade is only suitable for sacral anaesthesia . Opiates may also be administered by the subarachnoid route and provide good analgesia for labour but not for delivery . Furthermore, intrathecal opiates provide superior analgesia when compared to opiates administered via the epidural route . Side effects such as pruritus may be higher in patients receiving intrathecal opiates. Speed of onset:When compared to epidural or caudal anaesthesia, subarachnoid anaesthesia offers a rapid onset of action which is often of benefit to the patient, anaesthetist and surgeon. Unfortunately, an increased speed of onset of anaesthesia is only purchased at the price of a greater degree of hypotension . Postdural puncture headache:Postdural puncture headache may occur in up to 20% of patients when a 25-gauge spinal needle is used . This miserable complication occurs more frequently in young females and is responsible for the reluctance of many anaesthetists to use this technique in the parturient. Except in cases of inadvertent dural puncture with the needle, this problem is not seen with epidural or caudal anaesthesia. The use of 26-gauge spinal needles has been shown to lower the incidence of postdural puncture headache . The use of 29-gauge needles has been associated with little risk of postdural puncture headache, even in young patients . The low incidence of headache with these small needles increases the acceptability of subarachnoid blockade in obstetric anaesthesia . Titratable level of blockade and continuous infusions:The use of epidural catheters to provide a means by which the level of anaesthesia can titrated, topped up, or continuously infused for labour and delivery has been well established. The routine use of subarachnoid catheters for uncomplicated vaginal delivery has not gained wide acceptance in obstetric anaesthesia for several reasons. It has been stated that the large bore needles usually employed to introduce catheters would be associated with a high incidence of postdural puncture headache but this does not appear to occur in clinical practice . These catheters may increase the risk of infection, although again, there is very little supporting evidence for this concern. In an attempt to address these issues, microcatheters (32-gauge) which can be passed through a standard 25 or 26-gauge spinal needle have been used. Continuous spinal anaesthesia is obtained with negligible risk of local anaesthetic toxicity to the mother and fetus. Significant problems have been reported with these microcatheters and include cauda equina syndrome, kinking, difficulty in threading and catheter fracture. The more recent use of combined spinal epidural techniques allows for continuous and titratable anaesthesia with the advantage of a rapid and dense subarachnoid block. The potential disadvantages of an intrathecal catheter are avoided and, with a small spinal needle, the risk of postdural puncture is minimal . Overall, because of its advantages spinal anaesthesia (especially with the use of smaller spinal needles) continues to challenge the pre-eminent role of epidural anaesthesia in obstetrics. CHARACTERISTICS OF LOCAL ANESTHETIC TOXICITY (I) CNS toxicity:a) Excitation Phase: tinnitus, confusion, restlesness, perioral numbness or tingling, metallic taste, lightheadness, sense of dread and impending doom.b) Convulsive Phase: grand-mal clonic-tonic seizurec) Depression Phase: CNS depression with drowsiness and unconsciousness.d) Repiratory depression and apnea. (II) CVS Toxicity:a) Excitation Phase: - hypertension, tachycardia (with convulsions) b) Depression Phase:(i) Negative inotropic effect with decreased blood pressure, cardiac output and stroke volume.(ii) Peripheral vasodilation with further hypotension. c) Cardiovascular Collapse KEY FEATURES OF BUPIVACAINE TOXICITY (i) More likely to result in cardiovascular collapse (CV collapse dose / dose for convulsions = 3.7 for bupivacaine and 7.1 for lidocaine). (ii) Ventricular arrhythmias are more likely to accompany cardiac toxicity (use bretylium). (iii) Pregnant women are more sensitive to cardiac toxicity from bupivacaine. (iv) Resuscitation is usually legthy. (v) Toxicity is enhanced by acidosis and hypercarbia. PossibleEffects of Major Regional Blockade on Cardiotocographic Patterns. Uterine Contractions Mechanism Increased Frequency and intensity Analgesia decreases catechol amine leels Decreased Frequency and intensity Decreased blood supply to uterus. ?Inhibition of motor nerve supply to uterus?Direct effect of Local Anaesthetic on smooth muscle Fetal heart rate: beat to beat variability Increase Acute fetal hypoxia due to placental hypoperfusion Decrease Direct effect of local anaesthetic agents.Chronic hypoxia and acidosis from placental hypoperfusion Fetal heart rate:Long term deceleations Early Head compression from increased uterine tone. Late Placental insufficiency worsened by placental hypoperfusion Variable/td> Cord compression aggravated by maternal hypotension and increased intensityof uterine contractions. RECOMMENDED MAXIMUM DOSES OF LOCAL ANAESTHETICS -Illustrated in the case of a 60Kg woman Drug Dose Dose/Kg AMIDES Lidocaine with epi 420 (7mg/kg) Lidocaine plain 300 (5mg/kg) Bupivacaine with epi 180 (3mg/kg) Bupivacaine plain 120 (2mg/kg) Etidocaine 240 (4mg/kg) Mepivacaine 420 (7mg/kg) Prilocaine 720 (12mg/kg) ESTERS Cocaine 180 (3mg/kg) Procaine 840 (14mg/kg) Chloroprocaine 840 (14mg/kg) Tetracaine 180 (3mg/kg)