Anaesthesia Pearls June 2017

ANAESTHESIA PEARLS

How Safe is to Give Neuraxial Blocks in Patients with Thrombocytopenia

Introduction :
People with a low platelet count (thrombocytopenia) often require lumbar punctures or an epidural anaesthetic. Lumbar punctures can be diagnostic (haematological malignancies, epidural haematoma, meningitis) or therapeutic (spinal anaesthetic, administration of chemotherapy). Epidural catheters are placed for administration of epidural anaesthetic. Current practice in many countries is to correct thrombocytopenia with platelet transfusions prior to lumbar punctures and epidural anaesthesia, in order to mitigate the risk of serious procedure-related bleeding. However, the platelet count threshold recommended prior to these procedures varies significantly from country to country. This indicates significant uncertainty among clinicians of the correct management of these patients. The risk of bleeding appears to be low but if bleeding occurs it can be very serious (spinal haematoma). Therefore, people may be exposed to the risks of a platelet transfusion without any obvious clinical benefit.

In a recently published systemic review[1] in The Cochrane Library on “Use of platelet transfusions prior to lumbar punctures or epidural anaesthesia for the prevention of complications in people with thrombocytopenia” extensively analysed the effects of different platelet transfusion thresholds prior to a lumbar puncture or epidural anaesthesia in people with thrombocytopenia.

Thrombocytopenia
Thrombocytopenia is defined as a platelet count less than 150 x 109/L (BCSH 2003), and severe thrombocytopenia as a platelet count less than 50 x 109/L. A platelet count less than 150 x 109/L occurs commonly in pregnancy (7% to 12% of pregnancies), but severe thrombocytopenia (platelet count less than 50 x 109/L) is much more uncommon (0.05% to 1% of pregnancies). A platelet count less than 150 x 109/L is very common in people with chronic liver disease (up to 76%).

In the general population, the risk of a spinal haematoma is very low (1 in 200,000 epidural anaesthetic procedures during labour to 1 in 3600 epidural anaesthetic procedures in older women having knee surgery). Risk factors for major bleeding are multifactorial and include: increasing age (the procedure is more difficult in older people due to changes to the spine that occur with age), low platelet count, abnormal coagulation (including anticoagulant medication) and traumatic needle or catheter insertion. Performing an LP or administration of epidural anaesthesia is a relative contraindication in people with thrombocytopenia due to this perceived higher risk of complications. However, overall, there are no current reliable estimates of the risks of adverse effects such as spinal haematomas in people with thrombocytopenia.

Preoperative platelet transfusions
Current practice in many countries is to correct thrombocytopenia with platelet transfusions prior to an LP or epidural anaesthesia, in order to mitigate the risk of serious peri- or post-procedural bleeding. Up to 4% of all platelet components issued in the UK prior to a procedure are given to people with thrombocytopenia who need an LP.
The safe platelet count threshold recommended prior to an LP or epidural anaesthesia varies significantly from country to country.
For example, the platelet count threshold for LP in the US is 50 x 109/L; in the UK it is 50 x 109/L in adults (BCSH 2003), but 20 to 40 x 109/L in children (BCSH 2004); and in Germany it is 20 x 109/L unless it is an urgent procedure (e.g. diagnosing bacterial meningitis) when an LP should be performed irrespective of the platelet count.
The platelet count threshold for epidural anaesthesia also varies. In Italy and the UK, a platelet count of at least 50 x 109/L is recommended (BCSH 2003), while in France a platelet count of at least 80 x 109/L is recommended.
As there is currently no consensus on the standard platelet count threshold prior to an LP or epidural anaesthesia, the above systemic review compared the most commonly recommended platelet count threshold in national guidelines (50 x 109/L) against other recommended thresholds (10 x 109/L, 20 x 109/L, 30 x 109/L, 40 x 109/L, 80 x 109/L).
Authors’ conclusions
This review fails to provide any evidence to guide practice.
There is no evidence from RCTs to determine what is the correct platelet transfusion threshold prior to insertion of a lumbar puncture needle or epidural catheter. There are no ongoing registered RCTs assessing the effects of different platelet transfusion thresholds prior to the insertion of a lumbar puncture or epidural anaesthesia in people with thrombocytopenia. Any future RCT would need to be very large to detect a difference in the risk of bleeding. We would need to design a study with at least 47,030 participants to be able to detect an increase in the number of people who had major procedure-related bleeding from 1 in 1000 to 2 in 1000.
Another retrospective cohort study
A retrospective cohort study[2] using the Multicenter Perioperative Outcomes Group database to identify thrombocytopenic parturients who received a neuraxial technique and to estimate the risk of epidural hematoma. Patients were stratified by platelet count, and those requiring surgical decompression were identified.
A total of 573 parturients with a platelet count less than 100,000 mm–3 who received a neuraxial technique across 14 institutions were identified in the Multicenter Perioperative Outcomes Group database, and a total of 1,524 parturients were identified after combining the data from the systematic review. No cases of epidural hematoma requiring surgical decompression were observed. The upper bound of the 95% CI for the risk of epidural hematoma for a platelet count of 0 to 49,000 mm–3 is 11%, for 50,000 to 69,000 mm–3 is 3%, and for 70,000 to 100,000 mm–3 is 0.2%.
Relative risks related to neuraxial blocks in obstetric patients with Thrombocyopenia – Regional Anaesthesia UK Recommendations:
Idiopathic thrombo cytopenia
Normal Risk Platelets > 75 × 109.l−1 within 24 h of block
Increased Risk Platelets 50–75 × 109.l−1
High Risk Platelets 20–50 × 109.l−1
Increased High Risk Platelets < 20 × 109.l−1
Conclusions
The number of thrombocytopenic parturients in the literature who received neuraxial techniques without complication has been significantly increased.
Dr Joost van Veen et al[3] after analysing 17 national and international guidelines from blood transfusion and anaesthetic societies suggested that 80 × 109/l is a safe count for placing/removing an epidural or spinal anaesthetic and 40 × 109/l is a safe count for LP for general population. This, however, is provided that:
1 The platelet count is stable.
2 There is no other acquired or congenital coagulopathy.
3 The platelet function is normal and the patient is not on an antiplatelet drug.
4 The patient is not on an anticoagulant. If the patient is on a low molecular weight heparin, 12 h should have elapsed from the last dose of a prophylactic dose or 24 h after a therapeutic dose before an epidural or spinal anaesthetic is placed.
It is possible that lower platelet counts may also be safe but there is insufficient published evidence to make recommendations for lower levels at this stage. For patients with platelet counts of 50–80 × 109/l requiring epidural or spinal anaesthesia and patients with a platelet count 20–40 × 109/l requiring a LP, an individual decision based on risks and benefits should be made.
References :
1.  Estcourt LJ, Ingram C, Doree C, Trivella M, Stanworth SJ. Use of platelet transfusions prior to lumbar punctures or epidural anaesthesia for the prevention of complications in people with thrombocytopenia. Cochrane Database of Systematic Reviews 2016, Issue 5. Art. No.: CD011980. DOI: 10.1002/14651858.CD011980.pub2.
2. Risk of Epidural Hematoma after Neuraxial Techniques in Thrombocytopenic Parturients: A Report from the Multicenter Perioperative Outcomes Group. Anesthesiology 6 2017, Vol.126, 1053-1063.
3. Van Veen, J. J., Nokes, T. J. and Makris, M. (2010), The risk of spinal haematoma following neuraxial anaesthesia or lumbar puncture in thrombocytopenic individuals. British Journal of Haematology, 148: 15–25. doi:10.1111/j.1365-2141.2009.07899.x

Extubation Algorithm after Thyroidectomy Surgery

Extubation Algorithm after Thyroidectomy Surgery
Laura Cavallone, M.D.,
Most of the dreaded events related to thyroid surgery are manifested in the post-op period, which include, but are not limited to Hemorrhage, Laryngeal edema, RLN damage, Superior laryngeal nerve damage and Tracheomalacia.
The American Society of Anesthesiologists practice guidelines for management of the difficult airway recommend that, in addition to planning for intubation, the anesthesiologist should have a preformulated strategy for extubation of such patients.
Laura Cavallone, M.D., has designed the “Extubation Algorithm” major neck and upper airway surgery. In herrecent review article, she tried to summarize some of the practical recommendations; however, the evidence behind different extubation strategies and techniques remains sparse.
Extubation Algorithm for Major Neck and Upper Airway Surgery | Society for Head and Neck Anesthesia:
Ten Golden Rules of Extubation after Thyroidectomy:
1. Easy versus difficult intubation: the rationale for a differentiated strategy at extubation
When the airway is considered difficult [at intubation] there should be consideration for a staged extubation. The [Difficult Airway] Task Force regards the concept of an extubation strategy as a logical extension of the intubation strategy.
 2. Use of steroids in major neck upper airway surgery Controversial and scarce data from specific literature:
 Data from studies in ICU setting suggest that steroids administration prior to extubation decreases the odds ratio for laryngeal edema and subsequent need for reintubation;
 Dexamethasone 8 mg pre-operatively improves post-op nausea, vomiting, pain, subjective vocal function after thyroidectomy
3. Deep asleep versus fully awake extubation
Pros = patient still anesthetized avoids coughing and fighting ventilator which would lead to increased risk of re-bleeding at the site of surgery (due to increased venous pressure and straining on sutures.)
Cons = lack/decrease of protective airway reflexes may lead to increased risk for aspiration and airway obstruction;
 Caveats=easy intubation and mask ventilation are important prerequisites; increased risk of laryngospasm if performed during transition between deep anesthetized state and awake state
Fully awake
Pros = complete recovery of airway protective reflexes and effective spont. breathing are present and may increase safety in the presence of possible difficult re-intubation.
Cons = active protective airway reflexes may lead to increased risk of re-bleeding at the site of surgery (increased venous pressure and straining on wound).
Caveats= if pt. awake but NOT calm and cooperative, safe extubation procedures (e.g. flexible laryngoscopy, positioning of tube exchanger) may be extremely difficult
4. Use of airway exchange catheter for protected extubation
In the presence of a “difficult airway”, use of an Airway Exchange Catheter should be considered
5. Use of CPAP after upper airway surgery
Not always best choice/feasible:
Impaired access for suction
 Impaired possibility to monitor site of surgery
 Fit of mask may be changed after surgery (edema)
 Increased risks of post-op upper airway aspiration
6. Cuff leak test: validated methods
Measurements of expiratory tidal volumes after 4 complete respiratory cycles with the ETT cuff deflated;
 Measurements of expiratory tidal volumes with cuff deflated ONLY at the end of the end-  inspiratory pause
Proposed cut-off values:
 10-12% of the TV that was measured before cuff deflation (average-adult population);
 110-130 ml (average – adult population)
7. Direct laryngoscopy/video-assisted laryngoscopy/fibreoptic for pre-extubation airway exam
Scarce data from literature; considered marginally useful in ICU setting to predict post extubation laryngeal edema
 In the context of upper airway and neck surgery, where factors modifying airway anatomy and physiology and affecting post-extubation airway patency may have intervened intraopeartively, a thorough airway exam prior to extubation is advised.
8. Alternatives to early extubation (re-evaluation at 24-48 hrs versus temporary tracheostomy)
In selected groups of patients, early extubation after upper airway and neck surgery should be avoided and prolonged intubation or temporary tracheostomy should be considered as alternatives
9. Risk of vocal cord paralysis after major neck and upper airway surgery
A significant number of patients experience temporary or permanent vocal cord paralysis after thyroidectomy caused by RLN injury
Reported rates of RLN injury vary greatly in literature; rate reported also depends on the method of examining the larynx (e.g. temporary palsy: 1.4% to 38%)
 • Uncertain role of nerve monitoring during thyroid, PPV 40% and NPV 100%
 Thyroid surgery remains the most common cause of bilateral vocal fold immobility; non-thyroid surgeries (other neck, intracranial and intra-thoracic procedures) are the main cause of iatrogenic monolateral vocal cord paralysis
   Monolateral paralysis more than 50% of times is asymptomatic; bilateral presents with stridor/airway obstruction.
10. Flexible laryngoscopy for post-extubation airway exam
Recommend as “the gold standard method to examine the larynx after thyroidectomy”
Strategies to treat laryngospasm at extubation
Laryngospasm is most commonly seen in the post-extubation phase of anaesthesia, either in theatre or in the recovery area
1 Call for help.
2 Apply continuous positive airway pressure with 100% oxygen using a reservoir bag and facemask whilst ensuring the upper airway is patent. Avoid unnecessary upper airway stimulation
3 Larson’s manoeuvre: place the middle finger of each hand in the ‘laryngospasm notch’ between the posterior border of the mandible and the mastoid process whilst also displacing the mandible forward in a jaw thrust. Deep pressure at this point may help relieve laryngospasm
4 Low-dose propofol e.g. 0.25 mg.kg−1 intravenously may help

If laryngospasm persists and/or oxygen saturation is falling:

5 Propofol (1–2 mg.kg−1 intravenously) Whilst low doses of propofol may be effective in early laryngospasm, larger doses are needed in severe laryngospasm or total cord closure
6 Suxamethonium 1 mg.kg−1 intravenously. Worsening hypoxia in the face of continuing severe laryngospasm with total cord closure unresponsive to propofol requires immediate treatment with intravenous suxamethonium succinylcholine. The rationale for 1 mg.kg−1 is to provide cord relaxation, permitting ventilation, re-oxygenation and intubation should it be necessary
7 In the absence of intravenous access suxamethonium can be administered via the intramuscular (2–4 mg.kg−1), intralingual (2–4 mg.kg−1) or intra-osseous (1 mg.kg−1) routes
8 Atropine may be required to treat bradycardia
9 In extremis, consider a surgical airway.
Management of post-obstructive pulmonary oedema:
The negative intrathoracic pressure created by forceful inspiratory efforts against an obstructed airway can lead to post-obstructive (non-cardiogenic) pulmonary oedema. The commonest cause is laryngospasm (> 50%), but post-obstructive pulmonary oedema. Post-obstructive pulmonary oedema occurs after 0.1% of all general anaesthetics. It is more common in young muscular adults (male:female ratio 4:1)
Negative pleural pressures are generated by forceful inspiratory efforts, which increase the hydrostatic pressure gradient across the pulmonary capillary wall and cause fluid leak into the interstitial space. Efforts to exhale against airway obstruction are protective as they result in PEEP, which reduces the capillary wall pressure gradient and fluid leak into the interstitium; PEEP also counters alveolar collapse and de-recruitment.
Negative intrathoracic pressure results in increased venous return (preload) to the right ventricle and increase in the pulmonary capillary blood volume. Hypoxic pulmonary vasoconstriction facilitates fluid shifts into the interstitium. Right ventricular afterload also increases as hypoxia, acidosis and negative intrathoracic pressure increase pulmonary vascular tone. This may result in a shift of the interventricular septum into the left ventricular outflow tract, increasing left ventricular diastolic dysfunction and promoting pulmonary oedema.
Together with reactive catecholamine release, hypoxia, hypercarbia and acidosis cause systemic and pulmonary vasoconstriction, increasing left and right ventricular afterload. Increased hydrostatic pressure in the pulmonary capillaries causes disruption of the alveolar capillary membrane (stress failure), increasing permeability, and may contribute to the development of pulmonary oedema, or cause frank bronchial bleeding, although the generally benign nature and rapid resolution of post-obstructive pulmonary oedema suggest that this is not the predominant mechanism
Management of post-obstructive pulmonary oedema:
1 Treat the cause: relieve the airway obstruction
2 Administer 100% O2 with full facial CPAP mask. In addition to relieving upper airway obstruction, CPAP may reduce oedema formation by increasing mean intrathoracic pressure and minimise alveolar collapse by increasing functional residual capacity, improving gas exchange and reducing the work of breathing
3 Nurse the patient sitting upright
4 If there is fulminant pulmonary oedema with critical hypoxaemia, tracheal intubation and mechanical ventilation with PEEP are necessary. Less severe hypoxia responds to supplemental oxygen and/or non-invasive ventilation, or CPAP [200]
5 Intravenous opioids may help reduce subjective dyspnoea
6 Chest radiography may exclude other complications of difficult airway management and causes of hypoxia (gastric aspiration, pre-existing infection, pneumothorax, barotrauma, pulmonary collapse)
7 Frank haemoptysis may necessitate direct laryngoscopy and/or flexible bronchoscopy
8 Diuretics are often administered, but their efficacy is unproven.
References :
1. Extubation Algorithm for Major Neck and Upper Airway Surgery. Presented by Laura Cavallone, M.D., Washington University School of Medicine in St. Louis, Missouri. Society for Head and Neck Anesthesia.
2. Guidelines: Difficult Airway Society Guidelines for the management of tracheal extubation. Anaesthesia. Volume 67, Issue 3 March 2012 Pages 318–340.

C-Section Made Safer With Automated BP System

C-Section Made Safer With Automated BP System:
C-Section Made Safer With Automated BP System: DIVA (Double Intravenous Vasopressor Automated)
Doctors at KK Women’s and Children’s Hospital (KKH), Singapore  have developed the world’s first fully-automated system to enhance the management of blood pressure in women undergoing caesarean section under spinal anaesthesia.
The novel Double Intravenous Vasopressor Automated (DIVA) System detects and responds rapidly to low blood pressure and/or slow heart rate in real-time by autoadministering a precise amount of the recommended medication to manage reduced blood pressure (vasopressor). The system uses an advanced decision algorithm to ensure enhanced patient safety.
Enhanced management of low blood pressure during c-section under spinal anaesthesia
Peri-operative hypotension during spinal anaesthesia for caesarean section is common owing to the loss of sympathetic tone and the physiological predisposition of pregnant women to hypotension. The consequences of maternal hypotension are potentially severe, affecting both the mother and child. Maternal effects include nausea, vomiting and headache attributable to inadequate organ perfusion; fetal adverse effects may include fetal acidosis and poor neurological outcomes because of a lack of placental vascular autoregulation, which renders its perfusion pressure-dependent. While several strategies, both pharmacological and nonpharmacological, have been used to treat hypotension, the optimal treatment is still debatable. Non-pharmaco-logical methods alone are often not effective; hence, the use of vasopressors is often required. Recent data support the use of alpha-1 adrenergic agonists such as phenylephrine, although ephedrine (a mixed alpha- and beta-adrenergic agonist) may be useful in the event of concomitant hypotension with bradycardia.
Optimal timing and dosing of vasopressors is dependent on accurate and timely blood pressure monitoring. Conventional non-invasive blood pressure monitoring occurs at 60 second intervals – which could result in a potential delay in detecting rapid blood pressure changes within these 60 seconds.
Setting a new standard in speed and accuracy, the DIVA System is an automated dual-pump system which innovatively integrates continuous non-invasive blood pressure monitoring to ensure closed-loop vasopressor administration during the surgery. It continuously measures and records blood pressure and heart rate every second, allowing the extremely rapid detection of blood pressure changes and episodes of low blood pressure. When low blood pressure and/or slow heart rate are detected, the DIVA System automatically and promptly administers the precise amount of the appropriate vasopressor required to restore optimal blood pressure – making the process much more efficient than manual administration.
Study: DIVA System clinically effective in management of blood pressure
B. L. Sng et al conducted a randomised, controlled, double-blinded trial involving 213 healthy women who underwent elective caesarean delivery under spinal anaesthesia using 11 mg hyperbaric bupivacaine with 15 lg fentanyl and 100 lg morphine. The automated vasopressor group had better systolic pressure control, with 37/106 (34.9%) having any beat-to-beat systolic pressure reading < 80% of baseline compared with 63/107 (58.9%) in the control group (p < 0.001). There was no difference in the incidence of reactive hypertension, defined as systolic pressure > 120% of baseline, with 8/106 (7.5%) in the automated vasopressor group vs 14/107 (13.1%) in the control group, or total dose of vasopressors. The automated vasopressor group had lower median absolute performance error of 8.5% vs control of 9.8% (p = 0.013), and reduced incidence of nausea (1/106 (0.9%) vs 11/107 (10.3%), p = 0.005).
Results showed that the DIVA System is clinically more effective in maintaining blood pressure during caesarean section under spinal anaesthesia, as it is able to detect and normalise blood pressure fluctuations more quickly and effectively than traditional physician administered techniques using conventional blood pressure monitoring.
How the DIVA System works
The DIVA System calculates the amount of vasopressor to administer using a customised algorithm based on integrated blood pressure data from a continuous non-invasive arterial blood pressure (CNAPTM) monitoring system. A closedloop feedback system controls vasopressor administration, ensuring that the patient receives only the precise dosage required (Figure 1).
    1.Two alternating finger cuffs measure the patient’s arterial blood pressure and heart rate per second.
2. The data is exported to a laptop computer, and integrated every fifteen seconds using a customised programme to determine the dosage of vasopressor required.
3.If low blood pressure occurs, phenylephrine is administered automatically via a syringe pump. If low blood pressure occurs in conjunction with slow heart rate, ephedrine is administered instead via a different syringe pump.
4. The vasopressor is administered over 15 seconds, followed by a 30-second lockout period to permit the vasopressor to take effect.>
Benefits of the DIVA System
  • Non-invasive, rapid and automatic detection and response to low blood pressure and slow heart rate
  • Delivers individualised optimal vasopressor dosing regimen
  • Maintains systolic blood pressure near baseline blood pressure
  • Alleviates pre-delivery nausea and vomiting
Reference:
1. Sng BL, Wang H, Assam PN, Sia AT. Assessment of an updated double-vasopressor automated system using Nexfin for the maintenance of haemodynamic stability to improve peri-operative outcome during spinal anaesthesia for caesarean section. Anaesthesia. 2015 Jun;70(6):691-8.
2. Sing Health Medical News. www.singhealth.com.sg
Posted in ANAESTHESIA PEARLS 2017

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