Tuesday, 13 September 2016

Lipid rescue for treatment of delayed systemic ropivacaine toxicity from a continuous thoracic paravertebral block. BMJ Jun 2016.

This case report describes a 66-year-old man who underwent a left minithoracotomy for pleural biopsies and thoracentesis of a left-sided lesion involving the T3 and T4 vertebral bodies and pedicles. He developed local anaesthetic systemic toxicity (LAST) 37 hours after placement and initiation of a left T3 paravertebral catheter. Patient had symptoms of convulsions without loss of consciousness, a burning sensation in his legs and penis and agitation. Ropivacaine infusion was ceased and bolus of intralipid 20% was administered, followed by an infusion. His symptoms resolved within an hour of cessation of local anaesthetic infusion. The total serum concentration of ropivaciane during the event was 2.1mg/L compared with a published toxic level of 2.2 mg/L in healthy human volunteers. As the infusion rate of ropivacaine was reasonable based on pharmacokinetics, it is postulated that systemic local anaesthetic uptake may have been increased by the proximity of the block to areas with more vascularity such as tumour and pleural biopsy sites. Another possible cause could be intravascular migration of the paravertebral catheter.

Anaesthesia on the Western Front – perspectives a century later. AAIC Jul 2016.

This interesting article by Dr McDonald takes us back in time to the battles of World War I and the significant effects on the development of anaesthesia that occurred as a result. In particular, the challenges of the Western Front, with its massive numbers of injured, saw progress in the understanding and management of trauma and shock, and significant improvement in the provision of anaesthesia and the training of anaesthesia providers. The result was increased anaesthetic safety for the civilian population after the war and further development of anaesthesia and resuscitation as a specialised area of medicine.

Gas: the greatest terror of the Great War. AAIC Jul 2016.

“To an anaesthetist the word ‘gas’ refers to our ‘everyday tools of the trade’. Just over 100 years ago, the world ‘gas’ has an entirely different and sinister meaning. Gas was to become synonymous with an almost inescapable form of agonising death of painful injury on a scale never before seen in human history.” In this illustrative article, Dr Padley outlines the development of the gas warfare – the first weapon of mass terror – during World War I. From the development of chlorine, phosgene and then mustard gas, to trench warfare and management of gas casualties, this article takes us through a journey and shows us the destructive effects innovations can bring when applied as a weapon.

Advances in the diagnosis of shock, its assessment and resuscitation during the Great War. AAIC Jul 2016.

On a different note, the Great War did bring about an accelerated understanding of physiology and medical treatment of shock and trauma patients. In this intriguing article Dr Bullingham discusses the history of management of haemorrhagic shock, multi-trauma, sepsis, oxygen therapy and blood transfusion during the Great War. It is fascinating to learn that much of the knowledge gained during this period is integral in our anaesthetic practice today.

The effect of intrathecal morphine dose on outcomes after elective caesarean delivery: a meta-analysis. AA Apr 2016.

This meta-analysis compared low dose (LD 50-100microg) spinal morphine to high dose (HD >100-250microg) as part of spinal anaesthesia for elective Caesarean section. 11 Articles found including 480 patients. Primary outcome found HD (>100-250) spinal morphine prolonged mean time to first request for supplemental morphine equivalent by 4.5 hrs (CI 1.85–7.13 hours; P = 0.0008, Moderate heterogeneity) compared to LD (50-100). Secondary outcomes - incidence of pruritis and PONV was significantly lower in LD group (OR 0.34 p =0.0001, OR 0.44 p = 0.002 respectively) but pain scores at 12 hours, morphine equivalent consumption at 24 hours and APGAR scores <7 at 1 min was not significantly different. This meta-analysis shows that higher dosage (>100-250) of spinal morphine compared with lower dose (50-100) will prolong time to first analgesic request by 4.5hrs but at the cost of increased chance of side effects (pruritis and PONV).
Summarised by: Brenton Sanderson

Early administration of epinephrine (adrenaline) in patients with cardiac arrest with initial shockable rhythm in hospital: propensity score matched analysis. BMJ Feb 2016.

Adrenaline has been used for resuscitation after cardiac arrest for decades in both shockable and non-shockable rhythm. It has been previously shown that delay in the first administration of adrenaline is associated with a decreased chance of good outcomes in both adults and children in hospital who experience cardiac arrest with an initial non-shockable rhythm. There is however a lack of published studies in such patients presenting with a shockable rhythm (pulseless ventricular tachycardia or ventricular fibrillation). This is a prospective observational cohort study which attempts to address this. This study included 2978 patients who experienced cardiac arrest with an initial shockable rhythm. 51% of patients received adrenaline within 2 minutes after the first defibrillation, which is contrary to current American Heart Association (and also Australian Resuscitation Council) guidelines. Adrenaline given within the first 2 minutes after the first defibrillation was associated with decreased odds of survival (OR 0.70, 95% CI 0.59 to 0.82; P<0.001). Early adrenaline administration was also associated with decreased odds of return of spontaneous circulation (OR 0.71, 0.60 to 0.83; P<0.001) and good functional outcome (0.69, 0.58 to 0.83: P<0.001). The biggest limitation is that being an observational study, no strong causal effect of early adrenaline administration can be made. These findings may still be of relevance to future guidelines and studies.

Amiodarone, lidocaine, or placebo in out-of-hospital cardiac arrest. NEJM May 2016.

This double-blind, randomised trial compared amiodarone, lidocaine and placebo in out-of-hospital cardiac arrest for shock-refractory ventricular fibrillation or pulseless ventricular tachycardia. Paramedics enrolled patients at 10 North American sites. 3026 patients were randomly assigned to amiodarone, lidocaine or placebo; of those 24.4%, 23.7% and 21.0% respectively survived to hospital discharge. There were no significant differences in the survival rate or neurological outcomes between the 3 groups. This study concluded that neither amiodarone nor lidocaine resulted in a significantly higher rate of survival or favourable neurological outcome than the rate with placebo among patients with out-of-hospital cardiac arrest due to initial shock-refractory VF or pulseless VT.

Stopping vs continuing aspirin before coronary artery surgery. NEJM May 2016.

This randomised controlled trial is a part of the ATACAS trial (Aspirin and Tranexamic Acid for Coronary Artery Surgery), to help answer whether aspirin should be stopped before coronary artery surgery. Only results regarding aspirin were presented in this paper. 1047 patients were randomly assigned to receive 100mg aspirin 1 to 2 hours before surgery and 1053 to receive placebo. The primary outcome was a composite of death and thrombotic complications (nonfatal myocardial infarction, stroke, pulmonary embolism, renal failure, or bowel infarction) within 30 days of surgery. There was no significant difference in the primary outcome events in aspirin (19.3%) vs placebo group (20.4%) (RR 0.94, 95% CI 0.80-1.12; P=0.55). There was also no difference in major haemorrhage events leading to reoperation (1.8% vs 2.1%, P=0.75) and cardiac tamponade rates (1.1% vs 0.4%, P=0.08) in the 2 groups.

Factors associated with vancomycin nephrotoxicity in the critically ill. Anaesth Intensive Care Sept 2015.

Vancomycin is commonly used to treat methicillin-resistant Staphylococcus aureus (MRSA). Recently there has been an increase in the prevalence of MRSA with reduced susceptibility to vancomycin. Serum concentrations of <10mg/l is associated with the emergence of vancomycin-resistant Staphylococcus aureus. Current consensus guidelines recommend a target serum vancomycin trough concentration between 15 and 20 mg/l, compared to a historical target of 5 to 10mg/l. Vancomycin related nephrotoxicity is common and has been reported in up to 40% of recipients. This single centre retrospective study of 159 patients who received vancomycin showed that 8.8% manifested new onset AKI. Multivariate logistic regression analysis showed mean trough concentration, APACHE II score and simultaneous aminoglycoside prescription as significant predictors of AKI. These data suggest high trough vancomycin serum concentrations are associated with greater odds of AKI in the critically ill.

Obstetric Anaesthetists’ Association/Difficult Airway Society difficult and failed tracheal intubation guidelines – the way forward for the obstetric airway. BJA Oct 2015.

Last year a joint working group from Obstetric Anaesthetists’ Association (OAA) and the Difficult Airway Society (DAS) published the first obstetric-specific difficult airway guideline in UK. This editorial discusses the major points in difficult obstetric airway management. I have also included the OAA/DAS guideline for your review.
Summary of important points:

  • ‘Worst case’ is category 1 Caesarean section.
  • Use airway assessment to predict global airway management difficulty, not just laryngoscopy and intubation problems.
  • Before induction, make provisional plan should intubation fail – either awaken or proceed with surgery – communicate this with the team.
  • Head up position and apnoeic oxygenation can prolong safe apnoea time.
  • Gentle mask ventilation with cricoid pressure after administering induction agents is recommended.
  • Cricoid pressure should be reduced or released if there is a poor view at laryngoscopy.
  • Supraglottic airway device or facemask ventilation are valid first options after failed tracheal intubation. A second-generation supraglottic airway device is recommended.
  • After failed intubation, the immediate situation will determine the decision to awakening or proceed with surgery.
  • Unless it is safe or essential to proceed, the patient should be awakened.
  • Safety – strong indications for waking the patient after failed intubation include one or more of: obstructed airway, inadequate capnogram, hypoxaemia secondary to hypoventilation; a relative indication is if the patient has eaten recently.
  • Essential to proceed – strong indications to proceed are maternal compromise or fetal indications with an identified sentinel event (review current status), difficulty with providing alternatives (regional anaesthesia, awake securement of the airway).
  • Awakening – during failed intubation at category 1 Caesarean section for fetal indications without an identified sentinel event, there is a high chance that fetal condition will remain the same or even improve.
  • Proceed with surgery – if there is adequate airway/ventilation, further intubation attempts are discouraged unless a new factor presents that significantly increases the chance of success, or there is an indication for prolonged airway control.
  • Can’t intubate can’t oxygenate – if this occurs, ensure muscle paralysis before performing front-of-neck access procedure.
  • After failed intubation at Caesarean section, there is increased risk of neonatal admission to the neonatal intensive care unit; the neonatologist should be informed about the problem.

Monday, 14 March 2016

The changing face of malignant hyperthermia: less fulminant, more insidious. Anaesth Intensive Care Jul 2015.

Due to modern anaesthetic techniques, the clinical presentation of malignant hyperthermia is becoming increasingly insidious. The 4 case reports in this article highlight such presentations. Fulminant MH is characterised by a combination of rapidly evolving signs of hypermetabolism (hypercapnia, tachycardia, hypertension, hyperthermia), muscular symptoms (masseter spasm, rigidity) and rahdbdomyolysis. As anaeshtetists we should be aware of the more subtle signs of MH which include:

  1. Foremost: persistent, unexplained and difficult-to-correct hypercapnia
  2. Rapidly increasing and/or inappropriately elevated body temperature
  3. Masseter spasm following suxamethonium
  4. Clinical or biochemical evidence of rhabdomyolysis: increased postoperative CK level, voiding of cola-coloured urine (myoglobinuria), with or without hyperkaelamia

Cardiac complications in patients undergoing major noncardiac surgery. NEJM Dec 2015.

Perioperative deaths are common. If perioperative death were considered as a separate category, it would rank as the third leading cause of death in the US. Major perioperative cardiac complications are important because they account for at least one third of perioperative deaths. This detailed review article discusses the current evidence for preoperative coronary revascularization, noninvasive cardiac testing, preoperative use of aspirin and clonidine, and post operative monitoring of haemodynamics and troponin.  

A randomized trial comparing skin antiseptic agents at cesarean delivery. NJEM Feb 2016.

This single-centre, randomised controlled trial compared the use of chlorhexidine-alcohol and iodine-alochol for preoperative skin antisepsis for prevention of surgical-site infection after cesarean delivery. 572 patients were assigned to chlorhxidine-alcohol and 575 to iodine-alcohol. Surgical-site infection was diagnosed in 23 patients (4%) in the chlorhexidine-alcohol group and 42 (7.3%) in the iodine-alcohol group (RR 0.55, 95% CI 0.34–0.90; p=0.02). These results are consistent with those of prior studies that suggest the superiority of chlorhexidine-based antiseptics over iodine-based antiseptics for the prevention of surgical-site infection. Although these previous studies suggested the superiority of chlorhexidine-based antiseptics, it remained unclear whether the superiority was attributable to the chlorhexidine, the alcohol, or the combination and whether these results would apply to cesarean delivery.

Perioperative thermoregulation and heat balance. The Lancet Jan 2016.

This is a well-written review article which revisits the topic of thermoregulation under anaesthesia.
Important points to note include:

  • General anaethetic agents – volatiles, nitrous oxide and propofol – all reduces vasoconstriction and shivering threshold in a concentration-dependent manner, but has minimal effect on sweating threshold
  • Sedatives such a midazolam even combined with typical opioid doses do not appreciably impair thermoregulatory control
  • Neuraxial anaesthesia impairs thermoregulatory control such that patients are as hypothermic as those given a GA for similar operations. Effects of neuraxial and general anaesthesia on thermoregulatory control are additive
  • Peripheral nerve blocks do no have substantive thermoregulatory effects beyond preventing local thermoregulatory responses
  • Consequences of hypothermia include
    • coagulopathy – 1°C of hypothermia significantly increases blood loss by about 20%
    • delays wound healing
    • increases risk of wound infection
    • prolongs drug action – vecuronium, atracurium, propofol
    • prolongs recovery stay and hospital stay
  • Measures to maintain normothermia
    • Prewarming – prewarmed patients stay 0.4°C warmer
    • Most surgical patients will be hypothermic from passive insulation alone, forced air warmer is recommended
    • Fluid warming should be used if being given to patients in large volume (>1L/h). Each litre of room temperature fluid and each unit of blood reduces mean body temperature by 0.25°C in a 70kg patient
  • Temperature monitoring is recommended for general anaesthesia case over 30 minutes and substantial neuraxial cases
    • Best sites to monitor core temperature include the pulmonary artery, distal oesophagus, nasopharynx with the probe inserted 10-20cm and tympanic membrane,

Liberal transfusion strategy improves survival in perioperative but not in critically ill patients. A meta-analysis of randomised trials. BJA Oct 2015.

This meta-analysis of RCTs investigates the influence of liberal and restrictive blood transfusion strategies on mortality in perioperative (17 trials) and critically ill (10 trials) adult patients. Patients in the perioperative period receiving a liberal transfusion strategy had lower all-cause mortality when compared with a restrictive transfusion strategy. There was no difference in mortality in critically ill patients receiving liberal vs restrictive transfusion strategies. This is the first meta-analysis to focus on the perioperative setting.