Aneasthesia Pearls July 2015

ANAESTHESIA PEARLS

OBSTETRIC ANAESTHESIA

AN UPDATE IN OBSTETRIC ANAESTHESIA
Prof Nolan McDonnell
Maternal Mortality
Maternal Mortality
There is generally good news on the subject of maternal mortality. Worldwide there has been a 34% decrease in the number of women dying in pregnancy and childbirth since 1990, with haemorrhage remaining the leading cause of death worldwide. In developed countries, key reports have emerged from both the UK and NZ. The 2006-2008 UK CMACE report documents a decreased number of maternal deaths, mainly due to a fall in deaths related to thromboembolism after vaginal birth and from haemorrhage.
Of note is that sepsis became the leading direct cause of maternal death and the report highlighted the need for modified early warning charts and prompt recognition with aggressive, skilled management of these women in a multidisciplinary environment.
Also, the CMACE report highlighted the important position of anaesthetists in the management of unwell women, with close to 50% of deaths receiving care from anaesthetists. The most recent MMR in Australia is better than New Zealand (8) and the UK (8), at 6 per 100,000 maternities. The current Indian Maternal Mortality is 200 per 100,000 for 2010-2014.
Analgesia for Labour and Delivery
Neuraxial Analgesia
Delivery Method – Infusions, bolus and mandatory bolus techniques Patient controlled or midwife administered bolus techniques appear to be superior to continuous infusion techniques, most likely due to the better spread of the solution in the epidural space. Patient controlled techniques (PCEA) have a number of advantages over midwife-administered top ups, particularly in regards to the decreased staff workload and improved maternal satisfaction. A background infusion is often used in conjunction with a patient administered bolus, the optimal combination of background and bolus dose volume and concentration is open to debate. To further improve on the PCEA technique, device manufacturers have been adding “mandatory intermittent bolus” or “programmed intermittent bolus” modes to their infusion pumps. These deliver a bolus of a set volume at a set interval, generally in addition to the patient’s own demands. These new modes have been associated with less overall local anaesthetic use and less motor block.
Ultrasound Assisted Placement
Ultrasound assisted neuraxial techniques have now been well described. ultrasound is useful in the morbidly obese parturient who does not have clearly defined anatomical landmarks, as well as in women with difficult insertions. In these situations the ultrasound can identify not only space but also the angle and potential depth of insertion. Routine use is difficult to recommend at present and like most techniques a learning curve is present and practice on less complicated cases is recommended.
Addition of Clonidine and Neostigmine
A number of options have been investigated to enhance neuraxial labour analgesia. These options may seek to prolong the initial duration of analgesia (and hence decrease supplementation needs), decrease motor blockade and decrease the incidence of hypotension. A number of additives to traditional neuraxial opioids and local anaesthetic have been examined with clonidine and neostigmine receiving recent attention. Clonidine has been extensively investigated and is a commonly used neuraxial adjunct. Neostigmine has undergone less investigation but appears safe. Interestingly, neostigmine causes severe nausea and vomiting if administered intrathecally but this does not appear to be an issue with epidural administration. In labour analgesia, Van de Velde et al administered neostigmine (500 mcg) and clonidine (75 mcg) epidurally after performing combined spinal-epidural analgesia in labour. The duration of initial analgesia was extended from 95 to 144 minutes and overall local anaesthetic consumption was less. Interestingly, nearly a quarter of the women in the neostigmine /clonidine group delivered before additional analgesia was required. This may serve to be a useful technique in the future.
Remifentanil
Not all women in labour will be able to have an epidural or will want an epidural. Remifentanil provides a viable option and has been shown to be better than pethidine. However it requires very close monitoring with 1:1 midwifery care and continuous SpO2 monitoring and significant respiratory complications have been reported. Neonatal metabolism is rapid, even in premature neonates.16 Bolus and infusion regimens vary, although a 40 mcg bolus with no background infusion has been recommended.
Caesarean Delivery
General Anaesthesia
Mortality – Regional versus General Anaesthesia
General anaesthesia has traditionally been associated with an increased maternal mortality and the most recent CMACE report highlights continued deaths associated with the management of general anaesthesia.
Hawkins published one of the most widely quoted papers highlighting the discrepancy in deaths between general versus regional anaesthesia. This data led to the common quote of a mortality difference 16-17 times higher for general anaesthesia over regional anaesthesia. However, this data is now relatively dated and looked at cases prior to 1990. In the intervening period there have been a number of advances in monitoring and equipment as well as education and protocols for the management of the difficult airway. It is perhaps not that surprising that when Hawkins looked at more recent data (1997-2002), there was no significant difference in mortality between general and regional anaesthesia. Of note, deaths secondary to regional anaesthesia had increased whilst those secondary to general anaesthesia had decreased.
Head-up Position
Placing the pregnant women in a 30-degree head-up tilt has been shown to increase the FRC. Although the mean increase is only approximately 190 ml this may be of benefit in a difficult airway. Unfortunately an increasing BMI seems to decrease the benefits from the head-up position. Despite this, it seems difficult not to recommend the adoption of a 30-degree head-up position prior to general anaesthesia in pregnancy.
Neonatal Outcomes
Traditionally it has been suggested that the effects of general anaesthesia on the neonate would be transient and of little concern when skilled resuscitation staff are present. Data from Brisbane has suggested, when controlled for confounders, that general anaesthesia for fetal distress is associated with lower Apgar scores at 5 min and with at least twice the risk of a NICU admission. This data is in keeping with data from Sydney published in 2009 which showed markedly increased early neonatal morbidity with general anaesthesia, with the greatest impact being on already compromised babies. Whilst failure to provide general anaesthesia may lead to poorer outcomes, it does highlight the need for close communication between all team members in the setting of fetal distress.
Prevention of Hypotension
Research into the prevention of hypotension under spinal anaesthesia has been focused on three main directions – vasopressors, fluid pre- or co-load and the use of lower concentrations of local anaesthetics (“low dose” spinals).
Vasopressors
Phenylephrine is now firmly established in obstetric anaesthesia with well documented benefits for neonatal acid base status and maternal blood pressure control. Metaraminol has not received as much attention and comparative studies with phenylephrine are lacking. Metaraminol has some potential advantages, particularly with respect to some effect at beta receptors, which may maintain cardiac output better. Of importance is that the majority of studies to date are in the elective caesarean situation with an uncompromised utero-placental unit. It is unclear whether the stress fetus may respond differently to these medications.
Fluids
The take home message is that fluids alone have an unpredictable efficacy and there is a high likelihood that vasopressors will be required. Preload is partly effective when a colloid is used but not when a crystalloid is used. Co-loading with either solution can be effective but again is unreliable.
Low Dose Spinals
A significant amount of research has been directed at lowering the dose of intrathecal local anaesthetic. Whilst it is clear that this decreases maternal hypotension and nausea, the incidence of intraoperative pain is unacceptable. The ED95 of hyperbaric bupivacaine is approximately 11 mg, but many studies define “low” dose as < 8mg. When used in this fashion, hypotension is reduced by approximately 20% but there is nearly a 4-fold increase in the requirement for intraoperative analgesic supplementation. Hypotension can readily be managed with vasopressors but intraoperative pain will often require conversion to general anaesthesia. In the future it is difficult to see the place of low dose spinals except in selected situations.
Post-Caesarean Pain Relief
Recent research has been concentrated around the TAP block and the incidence of chronic post-caesarean pain. The place of the TAP block has now been relatively well defined and appears to be useful when long acting neuraxial opioids are not used (eg GA caesarean).
A recent study has shown that gabapentin 600 mg pre-caesarean, when combined with intrathecal morphine 100 mcg, decreased pain post operatively. It is too early to make widespread recommendations in regards to gabapentin as the neonatal effects when administered pre-delivery have not been well assessed, but it may be a useful adjunct post-delivery in high risk women, with sedation the major side effect.
Complications
Haemorrhage
rVIIa, Tranexamic Acid and Fibrinogen Concentrate
The use of rVIIa has anecdotally appeared to decrease in obstetric haemorrhage. The World Health Organization (WHO) also suggests that there is not enough evidence to currently recommend its use. Antifibrinolytics such as tranexamic acid have a robust evidence base for the reduction of transfusion requirements outside of the obstetric setting. Interestingly, the WHO do recommend tranexamic acid as a potential therapeutic agent in post partum haemorrhage. Commonly used doses are 1 g intravenously, followed by another 1 g if additional bleeding issues are present from between 30 minutes to 24 hours after administration. Fibrinogen concentrate, presented as a powder for reconstitution, is a very attractive option in obstetric haemorrhage, especially in resource limited areas and given the correlation between fibrinogen levels and the degree of haemorrhage.
Massive Transfusion Protocols and Monitoring of Coagulation
It has been recommended that massive transfusion protocols be in place in all obstetric hospitals. Protocols vary but most use a relatively aggressive ratio of red cells to coagulation factors. Fibrinogen levels appear to correlate well with increasing volumes / severity of haemorrhage. It is important to note that baseline levels of fibrinogen in pregnancy are higher than normal and hence using standard laboratory cut offs may not reflect the overall degree of fibrinogen deficiency. Experience is growing with the use of TEG and ROTEM in obstetric haemorrhage and normal values for pregnancy have been defined.
Interventional Radiology
Interventional radiology in the acute management of PPH has been shown to have excellent results. More controversial is the use of interventional radiology in the elective situation, despite it being recommended in some guidelines.
Post-dural Puncture Headache (PDPH) and its Management
Management options for PDPH that have been shown to be effective include ACTH, neuraxial opioids, epidural blood patch and the placement of intrathecal catheters. However, hydration, bed rest, caffeine and NSAIDs are not thought to have much of a role in management. Gabapentin may be a relatively novel agent in the management of PDPH. A blood patch performed within 24 hours is less likely to be effective. The optimal volume of blood for an epidural blood patch is still not clear. The most recent multi-centre study examined and 30 ml with partial relief being found in 61%, 73% and 67% respectively. Complete relief was surprisingly low at just 32% in the 20 ml group. Just under half of the patients in the 30 ml group did not receive the allocated volume secondary to back pain. The authors recommend aiming for 20 ml when performing an epidural blood patch. Another study examined the optic nerve sheath diameter as a measure of intra-cranial pressure with epidural blood patching and found that successful relief of PDPH was associated with evidence of a raised intracranial pressure, suggesting this as a possible mechanism of action of an epidural blood patch.
Stroke
Anaesthetists should be fully aware of the differential diagnosis of headache in pregnant or recently pregnant women, especially vascular causes and cerebral venous thrombosis. The incidence of stroke in pregnancy has increased by at least 50% in recent times with identified risk factors being hypertension, heart disease, obesity, diabetes and clotting disorders. Guidelines are now available for the management of cerebral venous thrombosis.
VTE Prophylaxis
Thromboembolism has traditionally been the leading cause of direct maternal mortality in the UK triennial reports but in the most recent report there was an over 50% decrease in the number of deaths. The decrease is generally put down to the adherence to risk assessment and management guidelines, with those of the RCOG being the most widely used throughout the UK. Interestingly, the reduction in deaths was primarily in antenatal women and those after a vaginal delivery, with little change in the number of women dying after caesarean delivery. Australasian consensus guidelines have now been published. The key take home messages are that pharmacological prophylaxis is recommended in most non elective caesareans and in elective caesareans with one additional risk factor. Important risk factors for the anaesthetist include post-partum haemorrhage, which dramatically increases the VTE risk. In addition, obesity appears to increase the risk with a higher risk with higher BMIs. Dosing guidelines for the obese obstetric patient are available but are based on expert opinion rather than evidence from clinical trials.
Source :
Annual Queenstown Update in Anaesthesia, 2012. Prof Nolan McDonnell.

AUTO DETECT SYRINGE

New Episure™ AutoDetect™ syringe (EAS)
New Episure™ AutoDetect™ syringe (EAS) for the identification of Epidural Space
INTRODUCTION
Epidural analgesia and anaesthesia are commonly used as a form of pain relief during childbirth, for the treatment of chronic back pain or as a means to provide anaesthesia or analgesia during specific operations. Epidural needle insertion is essentially a blind procedure. The failure of epidural analgesia usually results from failure to identify the epidural space correctly. During an epidural insertion, the operator tries to perceive which tissue layer the needle tip is passing through by feeling the resistances on the needle. This is a process known as ‘haptic’ feedback.
HISTORY
A well-known technique referred to as LOR essentially involves identification of the epidural space by compression of either fluid or air as the epidural needle encounters the various ligaments of the lumbar vertebral column. This was first explained in early 20th century and is the most common method used by many anaesthesiologists. Sicard and Forestier used fluid as a medium for this technique in 1921. Dogliotti explained the principle behind it and popularised the technique. The advantages of this technique are that it is easy to learn, cost effective, and not cumbersome with high sensitivity and specificity. People who have experience in appreciating ‘give way’ feel can adopt this technique. It is not a very good technique for the beginners.
Both air and fluid can be used as a medium for this technique, but the debate is still on as to which medium is superior. Air becomes the popular medium with some reasons. First is historical, as until the 70’s, syringes were made from glass and were non‑disposable. Disadvantages of using air are possibility of causing pneumocephalus headache, cervical emphysema, patchy block, and air embolism.
With the availability of plastic syringes fluid gained popularity as a medium as it eliminated most of the problems of air as a medium. The main disadvantages with the use of saline are dilution of local anaesthetic agent affecting sensory blockade, and confusion with cerebrospinal fluid if accidental dural puncture occurs.
NEW EPISURETM AUTODETECT SYRINGE
The LOR is a subjective feeling, so most of the failure rates occur with inexperienced practitioners. Baraka A reported ‘saline infusion technique’ in which the saline from the infusion set enters the epidural space as there is negative pressure in the epidural space. The main advantage of this technique is that the needle can be gripped by both the hands and also directed according to the needs. It is easy to learn especially for beginners, has a high success rate.
Based on this principle, a new spring‑loaded AutoDetect syringe Episure™ was designed by Indigo Orb, Inc., Santa Clara, CA, USA. EAS, is a new LOR syringe with an internal compression spring that applies constant pressure on the plunger [Figure]. This obviates the need to apply pressure on plunger, allowing operator to use both hands while continuously advancing the epidural needle. The plunger automatically depresses when needle enters epidural space, providing an objective, visual confirmation of LOR, as opposed to subjective “feel” required with standard LOR syringes. These advantages may help the resident anaesthesiologist to achieve higher success rate in identifying the epidural space.
AUTODETECT-SYRINGE
In an observational pilot study, the use of the device was reported to confer increased success in epidural space identification, primarily with resident anaesthesiologists.
EpisureTM AutoDetect Trainer Video
Ref :
Joseph EJ, Pachaimuthu E, Arokyamuthu V, Muthukrishnan M, Kannan DK, Dhanalakshmi B. Comparative study of Episure™ AutoDetect™ syringe versus glass syringe for identification of epidural space in lower thoracic epidural. Indian J Anaesth [serial online] 2015 [cited 2015 Jul 23];59:406-10.
Available from: http://www.ijaweb.org/text.asp?2015/59/7/406/160933

PERINEURAL Vs INTRANENURAL INJECTIONS

Perineural Versus Intraneural Injections
Perineural Versus Intraneural Injections for Regional Anesthesia
Xavier Sala-Blanch, MD et al
Introduction
Before ultrasound-guided regional anesthesia (UGRA), little information was available on the location of the needle necessary to accomplish successful and safe nerve blockade. This lack of information is because localization techniques without ultrasound guidance depend on an indirect assessment of needle location, such as electrical current intensity or patient reports of paresthesias (needle-nerve contact). The introduction of UGRA has allowed for greater precision of needle placement and deposition of local anesthetics (LA), and has helped in our understanding of many aspects of peripheral nerve block (PNB).
For instance, although nerve stimulation was thought to decrease the risk of needle-nerve contact, an evoked motor response during low-intensity currents (eg, <0.5mA; 0.1msec) with nerve stimulator-guided nerve localization seems to commonly result only after the needle enters the epineurium of the nerve.
Several recently published clinical reports document the inadvertent intraneural placement of the needle and subsequent injection of LA without clinically apparent neurological injury.
Anatomy of the Peripheral Nerve
Axons are the essential conducting units of peripheral nerves. Axons are surrounded by supporting connective tissue called the endoneurium or endoneural network. With their adjacent endoneurium, axons are protected by a dense layer of cells organized into a surrounding membrane called the perineurium. The perineurium creates both a physical and chemical barrier, which translates into a degree of protection for the peripheral nerve fascicles.
When fascicles coalesce together into fascicular bundles, they are embedded in the interfascicular epineurium, and bound by joint perineurium. The fascicles, or groups of fascicles, are embedded in a varying degree of protective fibroadipose tissue called the epineurium.
The epineurium is classified into 2 distinct anatomic structures:
the interfascicular epineurium.
the outer epineurium that both houses the peripheral nerve contents and connects the nerve to the neighboring structures
An injection that occurs outside the outer epineurium will be referred to as perineural (adjacent to the outer epineurium), whereas an injection within outer epineurium (under the epineural membrane) will be considered intraneural.
epineurium
Fig: Histologic anatomy of the peripheral nerve. Fascicles are grouped into fascicular bundles and protected by perineurium. A large amount of epineurium is seen within outer epineurium (gray arrows). Black arrows indicates perineurium; F, nerve fascicles; V, blood vessels.
outer-epineurium
An intraneural injection can occur in 2 functionally and distinctly different locations, under the outer epineurium and
Within the interfascicular epineurium (without breaching the fascicle’s perineurium) or
Within fascicles or fascicular bundles (indeed breaching the perineurium).
The interstitial fluid inside the endoneurium in the brachial plexus roots has been demonstrated to consist of cerebrospinal fluid with retrograde communication to the spinal cord. The roots are also surrounded by a dural sleeve (connected to the dura mater), whereas fascicles within the nerve roots are extensions of the spinal nerve.
Practical implications of the latter feature is that injection within a nerve root can result in a syrinx, epidural anesthesia, or spinal anesthesia.
Ultrasonografic Signs of an Intraneural Injection
The following findings, when seen during ultrasound-guided PNBs, are considered signs of an intraneural injection.
Visualization of the needle inside the nerve (within outer epineurium) at the time of injection.
Increase in nerve diameter and cross-sectional area of the nerve by ≥15%
Separation of the fascicles and/or fascicular bundles by the injectate.
Diffusion of the LA within epineurium in a proximal and distal direction.
High-resolution ultrasound can differentiate injection outside the outer epineurium from the injection into the epineurium, whereas very high-resolution ultrasound can differentiate the fascicle in superficial nerves.
An intraneural injection that occurs within fascicles (with consequent disruption of the perineum, its contents and/or feeding blood vessels) is obviously the least desired and most hazardous location. However, an intraneural injection inside the epineurium but outside of the fascicles seems to represent an acceptable risk/effectiveness ratio for rapid onset, successful sciatic popliteal block.
Ultrasound-image
Fig: Ultrasound image of intraneural needle placement. The needle is seen within the epineurium of the popliteal sciatic nerve. Fascicular bundles are being separated by the injection of the local anesthetic. NDL indicates needle; Tip, tip of the needle; F, nerve fascicles; Arrows, outer epineurium.
Reports of intraneural injections for the sciatic nerve block in the popliteal fossa to date have not led to neurological complications in the absence of motor response to lowcurrent nerve stimulation and abnormally high resistance to injection.
Practical Considerations and Current Recommendations
As no clinically applicable imaging technique has the ability to detect this delicate balance, an intentional intraneural injection with other peripheral nerve blocks cannot be recommended as safe or acceptable practice.
This is particularly important if intraneural injection is performed without risk-reduction modalities (avoidance of high resistance to injection, motor response at ≤ 0.2 to 0.3 mA) to reduce likelihood of intrafascicular injection or hydraulic disruption of any fascicle architecture.
On the basis of available information and collective clinical experience, injection within epineurium of the popliteal sciatic nerve or within tissue sheaths (space) that envelop major plexuses (eg, brachial plexus) are often done, and is considered a common and acceptable practice.
However, intraneural injection with other peripheral nerves may be associated with an unacceptable risk of complications, and cannot be recommended.
Summary
Intraneural but extrafascicular injection of LA is a common occurrence with low-current intensity nerve stimulator-guided popliteal sciatic nerve blocks. Such injections seem to be associated with high success rate and low risk of neurological injury when the motor response is not present at ≤ 0.2-0.3mA (0.1 msec), injection pressure is low (≤15 psi), and/or the patient is asymptomatic.
Therefore, based on available data, it may be suggested that the goal of ultrasound-guided blocks of the brachial plexus and popliteal sciatic nerve should be similar to that of nerve stimulation—injection within the outer epineurium or tissue space (sheath), but outside of the fascicles or fascicular bundles.
Posted in ANAESTHESIA PEARLS 2015

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