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.

Time to shut down the acute care conveyor belt? MJA Dec 2015.

End of life care has recently been an active issue raised within our department as well as in healthcare across Australia. The author, distinguished anaesthetist/intensivist Ken Hillman, compared the current medicalisation of dying with medicalisaion of birthing in 1950s. End of life care is not being well managed in the hospital setting. Most admitting teams do not have the level of training to carry out a lengthy and complex discussion with patients and their carers, and they are often busy caring for the more conventional aspects of medical care. He suggests a strategy to manage this would be an end-of-life care team similar to the rapid response team, where patients in the at-risk group are identified and a clinician with appropriate skills, knowledge and experience to carry out end of life discussions. This is likely to be a palliative care nurse until more training is provided in the undergraduate and postgraduate levels for nurses and doctors.

Is ketamine ready to be used clinically for the treatment of depression? MJA Dec 2015.

To date, 8 randomised placebo-controlled trials involving almost 200 participants with depression showed antidepressant effects after a single dose of ketamine of 0.5mg/kg over 40 minutes IV.  A major drawback is that the antidepressant effects typically last for only several days after a single treatment. Recently Australian health authorities have curtailed medical practitioners offering a course of ketamine treatments to patients with depression. http://www.abc.net.au/news/2015-05-30/ketamine-offered-to-patients-with-depression-in-take-home-packs/6508232 A new trial is underway to assess the effects of a four week course of ketamine on patients with depression who have not responded to existing medications. http://www.abc.net.au/news/2015-11-09/grant-of-$2m-awarded-for-ketamine-depression-treatment-trial/6923788

Let’s watch this space.

The paternalism preference – choosing unshared decision making. NEJM August 2015.

This article discusses the medical informed consent process and how much information is adequate to give patients.  The last paragraph of the articlesummarises the points well… ”The doctors I admire most are characterized not by how much they know but by a sophisticated intuition about how best to share it. Sometimes they tell their patients what to do; sometimes they give them a choice. Sometimes, when discussing treatment options, they cover all seven tenets of informed consent. Sometimes, instead, seeing the terror of uncertainty in a patient’s face, they make their best recommendation and say, “I don’t know how things are going to turn out, but I promise I’ll be there with you the whole way.””

Teaching and learning in undergraduate anaesthesia: a quantitative and qualitative analysis of practice at the University of Auckland. Anaesthe Intensive Care Nov 2015

This is a survey article, covering multiple sources, examining anaesthetic teaching of medical students in a New Zealand University. It highlights some of the significant discrepancies between medical student expectations and actual learning experiences in anaesthesia. One of the key findings was the surprisingly limited exposure to IV cannulation, which has subsequently been de-emphasised in the University of Auckland learning objectives for the Anaesthesia rotation. Definitely worth a read.

AE

Neurodevelopmental outcome at 2 years of age after general anaestehsia and awake-regional anaesthesia in infancy (GAS): an international multicenter, randomised controlled trial. Lancet October 2015.

This is the first randomised controlled trial assessing the effect of general anaestheisa in infancy on neurodevelopmental outcome. This study randomised 363 infants (younger than 60 weeks) to receive awake-regional anaesthesia and 359 to general anaesthesia for inguinal herniorrphaphy. The primary outcome will be WPPSI-III Full Scale Intelligence Quotient score at 5 years (data is yet to be collected). The secondary outcome is reported here a composite cognitive score of Bayley Scales of Infant and Toddler Development III assess at 2 years. There is no difference in the cognitive composite score between the 2 groups at 2 years. The median duration of anaesthsia was 54 minutes. It should be noted that this is an analysis of secondary outcome, and reassessment at 5 years is necessary before definitive conclusions can be drawn.

An overview of the American College of Cardiology / American Heart Association 2014 Valve Heart Disease Practice Guidelines: What is its relevance for the anaesthesiologist and perioperative medicine physician? AA November 2015.

This is an excellent summary article by 3 of the most influential US cardiac anaesthetists. It covers the 2014 ACC/AHA guidelines on the management of valvular heart disease. The original article is very lengthy, but this summarises the pertinent points for anaesthetic practice in non-cardiac and cardiac surgery. 

AE

PS60 Guidelines on the perioperative management of patients with suspected or proven hypersensitivity to chlorhexidine. ANZCA 2015.

Chlorhexidine is a broad spectrum antiseptic that is extensively used in healthcare environments. It is observed that incidence of anaphylaxis has been increasing in recent years. There is no centralized database in Australia for reporting chlorhexidine allergery. However in Royal North Shore Hospital Anaesthetic Allergy Clinic alone, there are 29 cases of confirmed chlorhexidine anaphylaxis between 2007 to 2015. This is the third most common allergen after neuromuscular blockers and antibiotics

Issues include:
  • Difficulty in identifying products containing chlorhexidine
    • Chlorhexidine is increasingly incorporated in antiseptic handrub solutions, gels, pastes, dressings and devices (including central venous catheters and drape).
    • There is inconsistent labeling of products that contain chlorhexidine
  • Difficulty avoiding contact with chlorhexidine products once identified
Suggested perioperative management of patients with chlorhexidine allergy include:
  • development of a chlorhexidine product register throughout each hospital
  • development of a “chlorhexidine free box” in operating theatres – containing chlorhexidine free laternative for common procedures such as skin antisepsis, lubrication jelly for IDC insertion, chlorhexidine free central venous access device

Intravascular complications of central venous catheterization by insertion site. NJEM September 2015.

In this multicenter trial, 3471 central venous catheters were assigned to ICU patients to the subclavian, jugular or femoral vein. The primary outcome was a composite of major catheter-related bloodstream infection and symptomatic DVT.

Key points for this article:

  1. Subclavian line is associated with less bacterial bioburden (longer subcutaneous course to the entry of vein); less likelihood of disruption of dressing) - i.e. less colonisation, which is also associated with less catheter related infection and LESS deep vein thrombosis. This is most important when the catheter is going to be used for longer term.
  2. Mechanical complications of pneumothorax was higher in subclavian approach. 
  3. Considering infectious, thrombotic and mechanical complications all together – there is little difference between the three approaches. Mechanical complications can be reduced by improved skills and ultrasound use for subclavian approach.
ML

Evaluation of perioperative medication errors and adverse drug events. Anesthesiology November 2015.

One in 20 perioperative medications given was an error. More than one third of the errors led to observed adverse events, and the remaining two thirds had the potential for harm. These rates are markedly higher than those reported by retrospective surveys. 

Specific solutions exist that have the potential to decrease the incidence of perioperative medication errors.

In summary: We give a lot of drugs and could do a better job of making sure we're doing it right.

MD

Difficult Airway Society 2015 guidelines for management of unanticipated difficult intubation in adults. BJA December 2015.

This is the revised version of the DAS guidelines for management of the unanticipated difficult airway, originally published in 2004.

The majority of the changes have come about from the findings of NAP4. Analysis of the adverse airway events in the UK from 2008-2009 showed that human factors were directly responsible for poor outcomes in 40% of the cases reported, and a contributing factor for all cases. The authors acknowledge that this was occurring despite the DAS guidelines being published and widely available.

One of the factors that they attribute this to is the confusing nature of the original DAS algorithm. They acknowledge that the original guidelines had too many choices or options at each level and this could lead to paralysis of indecision. In view of this the new guidelines are much simpler.

A brief over view of the new algorithm for the unanticipated difficult airway:
During assessment of the patient’s airway consider ease of BMV, LMA insertion, intubation and front of neck access for all patients. Have a plan that will give you the best likelihood of first attempt success for all possible interventions.

Plan A:
  • BMV and direct laryngoscopy using optimum equipment and positioning, pre-oxygenation etc as dictated by your assessment of the patient.
  • No more than 3 attempts at direct laryngoscopy (one more allowed if more senior anesthetist available)
  • No repeat attempts at laryngoscopy without changing something in your approach learned by the experience gained in previous intubation attempts.
  • If fail to intubate move to Plan B

Plan B:
  • Plan B is always a supraglotic device
  • Supraglotic device should be chosen and available prior to induction
  • 2nd generation are preferred
  • If failed then no more than 3 attempts at insertion, consider changing size or type
  • If succeed STOP and THINK: Wake patient? Intubate via LMA? Proceed with procedure under LMA? Tracheostomy or cric?
  • If fail proceed to Plan C

Plan C:
  • One final attempt at rescuing situation by BMV
  • Be aware that this is highly unlikely to be successful after multiple airway interventions
  • Use knowledge of BMV gained during plans A and B to optimize attempt at BMV during Plan C
  • Prepare for Plan D
  • If fail proceed to plan D

Plan D:
  • Surgical airway
  • Position patient appropriately for surgical airway
  • Advocate either scalpel bougie or needle cric, operators choice
  • More emphasis on scalpel bougie due to support from literature including NAP4
  • STOP and Think – proceed with case or postpone surgery?

Other changes

Cricoid:
Still advocated in 10N/30N form but now advocates removal if difficulty intubating rather than waiting till failed ventilation via LMA to remove as per old guidelines

Choice of muscle relaxant for RSI:Rocuronium or sux supported for RSI
BMV should not be deemed to be impossible unless the patient is fully paralysed

Apneoic oxygenationApnoeic oxygenation using normal NP or HFNP is recommended for the expected difficult intubation

CICO
Regular practice is the best way to prepare for this, ANZCA’s efforts to ensure regular CICO training was acknowledged in the paper

There is a large emphasis on human factors in this publication. Particularly they note the importance in calling for help, ensuring someone maintains situational awareness and the importance of announcing when a particular intervention has failed so that the team is aware that we are proceeding to the next step.

Overall these guidelines are a massive improvement over the 2004 version. They also more accurately reflect current practice and provide a better framework with in which to operate.

I have included an editorial by Professor Keith Greenland that discuss the role of human factors in more detail. Several other editorials and articlesrelated to airway management are also published in this months BJA.

DD

Transplantation of the heart after circulatory death of the donor: time for a change in law? MJA September 2015.


The author suggests that heart procurement after circulatory death does not conform to present statute law. He states that for a transplanted heart to function and sustain life in a recipient, it must mean that the circulation of the donor is never ceased irreversibly and therefore that the donor of the heart is never dead until his or her heart is removed. The author concludes that medical personnel involve in heart procurement after DCD could face criminal charges if the definition of death in the law is not changed. As anaesthetists are often present at organ harvests this article provides us with some food for thought.


Perioperative bridging anticoagulation in patients with atrial fibrillation. NEJM August 2015.
This BRIDGE trial is a randomised, double-blind, placebo-controlled trial involving 1884 patients with atrial fibrillation requiring perioperative interruption of warfarin therapy. These patients were assigned to receive bridging and no bridging anticoagulation. The primary outcome were arterial thromboembolism (stroke, systemic embolism, or TIA) and major bleeding. The incidence of arterial thromboembolism was 0.4% in the no-bridging group and 0.3% in the bridging group (significant for noninferiority). The incidence of major bleeding was 1.3% in the no-bridging group and 3.2% in the briding group (significant for superiority). The paper concludes that in patients with AF who had warfarin treatment interrupted for an elective operation, forgoing briding anticoagulation was noninferior to perioperative bridging with LMW heparin for prevention of arterial thromboembolism and decreased the risk of major bleeding. Some limitations of the study include few patients had CHADS2 score of 5 or 6 (mean score 2.3), patient undergoing major surgical procedures associated with high rates or arterial thromboembolism and bleeding were excluded, and overall rates of arterial thromboembolism was lower than expected which potentially affected the power of the trial.

Septic shock – Advances in diagnosis and treatment. JAMA August 2015.

This is a systematic review of the literature with evidence based guidelines for management of septic shock. Interesting advances include focused ultrasonography to manage complicating physiology (eg hypovolaemia or cardiogenic shock), hydroxyethyl starch may cause harm and protocolised early goal-directed therapy is not superior to usual care in early septic shock.

Cutaneous sensory block area, muscle relaxing effect and block duration of the transversus abdominis plane block. RAPM August 2015.

The purpose of this randomised, blinded and placebo controlled study of the TAP block was to:
1. Characterise the cutaneous sensory area by sensory mapping
2. Using ultrasound investigate the abdominal wall muscle relaxing effect
3. Use self reporting to determine the duration of sensory and motor block

16 healthy volunteers were randomised to receive an ultrasound guided unilateral TAP block with 20mls 0.75% ropivicaine and placebo on the contralateral side. Exclusion criteria included: age < 18, ASA 3 or >, body weight < 50kg, BMI 35 or greater, analgesics 24 hrs prior to examination, prior surgery to the abdominal wall and allergy to study drugs. All study volunteers and investigators were blinded to treatment allocations.

Volunteers were assessed before the TAP blocks (baseline) and 90 minutes after the end of injection. Primary outcome measure was cutaneous sensory block area 90 min after the end of the injection. Secondary outcomes measures were differences between baseline and T90 in muscle thickness of the lateral abdominal wall, waist circumference, mechanical detection threshold and mechanical pain threshold and subjective reported duration of skin numbness and abdominal wall muscle relaxing effect.

As there was no cutaneous effect on the control side at T90, the cutaneous sensory block area did not cross the midline in any volunteers. Both the mechanical detection and pain threshold increased significantly on the blocked side. There was also a significant increase in abdominal circumference from baseline to T90 in the relaxed state. Lateral abdominal wall muscle thickness decreased significantly from baseline to T90 on the blocked side. In terms or reported sensory and motor blockade, the average sensory blockade was 570min and the motor was 609min.


The study found that TAP block resulted in a non dermatomal cutaneous sensory block area. In previous study regarding TAP block there has been a lack of precise description of the assessment of the cutaneous effect. All volunteers had a consistent and highly significant effect on all 3 muscle layers. The effect of this clinically, is unknown but may contribute to the analgesic effect. There was a large variation in the duration of the sensory and motor blockade, but on average was approximately 10hrs for both.

The limitations of the study included using only ultrasound for imagining. MRI or fluoroscopy would have given additional information about the spread of local anaesthetic.

MK

Lung injury after one-lung ventilation: a review of the pathophysiologic mechanisms affecting the ventilated and the collapsed lung. AA August 2015.

This article provides an overview of the mechanisms of lung injury after one-lung ventilation (OLV), and suggests strategies to prevent this from occurring. Postthoracoctomy acute lung injury (ALI) occurs in 4% to 15% of patients. ALI and ARDS are leading cause of death after thoracic surgery and significantly reduce 1-year survival (56% vs 92%). Mechanisms of lung injury in the ventilated lung include volutrauma, atelectrauma, hyperperfusion, biotrauma and oxidative injury. Mechanisms of lung injury in the collapsed lung include atelectasis, ischaemia-reperfusion injury, biotrauma and surgical trauma. This article recommends the following strategies to prevent lung injury after OLV:

Before OLV:

  • Ventilation with volatile agents may reduce risk of ALI
  • Avoid overhydration
  • Routine recruitment maneuvers after GA induction and endotracheal intubation – provides sustained oxygenation benefit for OLV and improves lung compliance and CO2 elimination
  • Lung isolation should only be established when necessary to minimise its duration
During OLV (collapsed lung):
  • CPAP to be considered to avoid dense atelectasis and minimise the shunt fraction
  • Minimise suctioning to avoid negative pressure trauma
  • Slow airway pressure increases and cycling maneuvers and using lower FiO2 during lung recruitment at the end of OLV
During OLV (ventilated lung):
  • Low Vt of 4 – 5 ml/kg predicted boy weight
  • PEEP of 5 – 10 cmH2O
  • Respiratory rate and minute ventilation targets to be relaxed to allow mild hypercapnia (PaCO2 40-60)
  • High FiO2 may be necessary at the onset of OLV but should be reduced after approximately 20 to 30 minutes of OLV
After OLV
  • Avoid hyperoxia
  • Protective 2-lung ventilation
  • Post extubation NIV may be considered