Anaestricks
Sevoflurane is (almost) all you need

We are spolied for choice here in Australia: Sevoflurane, desflurane and isoflurane. But do we really need all three? My opinion is: No!

There are many pharmacokinetic differences between these three volatiles, but when you actually look for clinically significant differences, there is little. In my view the important differences between the volatiles are suitability for gas induction, time to MAC awake, environmental impact, and cost.

When compared to sevoflurane:

  1. Isoflurane: Poor for gas induction, longer to MAC awake, and higher life cycle greenhouse effect. Isoflurane is a lot cheaper, but the cost of sevoflurane could be driven down if institutions buy more of it at the expense of isoflurane and desflurane. I worked in Sweden were we only had access to Sevoflurane. By standardising the available drug and buying tonnes of it, you can drive the price down.
  2. Desflurane: Poor for gas induction, slightly shorter time to MAC awake, much higher (2000%!) life cycle greenhouse gas effect, and more expensive. In my practice, the only time I use desflurane is for the last hour of an all day long (> 8 hours) case. This gives enough time for the sevoflurane to wash out, but minimises the use of the evil desflurane.

Some centres have recently stopped stocking desflurane citing environmental concerns. Other ways to avoid the volatiles include using regional techniques and propofol infusions. 

Simple Scavenging for T-Piece

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Anaesthetists often use a t-piece for paediatric anaesthesia as they are light-weight, have rapid wash in and wash out times, and give the best feel for lung compliance.

However, they are very polluting because they are open circuits, and wasteful as they require at least 6L/minute of gas flow to prevent rebreathing of CO2.

Swedish anaesthetists are very conscious of the potential risks to staff from exposure to volatile, and they do their utmost to reduce pollution. T-pieces are seldom used for this reason. In fact, they don’t exist at the Karolinska University Children’s Hospital. 

Unfortunately, pollution by volatile agents in anaesthetic rooms and operating theatres in Australia is not really perceived as a problem. The high turnover of cases and the frequent use t-pieces results in significant spillage of volatile in these areas. T-pieces allowing scavenging are often not available, are expensive and many are clumsy to use.

A very simple alternative scavenging system can be made using a 50ml leur lock syringe attached to the regular suction. The leur lock plugs nicely into the end of the suction tubing. 

Although not ideal, as this system does not allow easy scavenging when positive pressure ventilation is used, it noticeably reduces volatile pollution during the majority of a spontaneously ventilating case. 

Not Always Top 5 - Malignant Hyperthermia
  1. Get help
  2. Stop trigger (volatile/suxamethonium)
  3. Dantrolene (2.5mg/kg)
  4. Dantrolene
  5. Dantrolene

NB - Malignant hyperthermia (MH) is, by definition, a disease of the ryanodine receptor. Abnormal ryanodine receptors allow uncontrolled calcium release from the sacroplasmic reticulum causing all the clinical problems you see with MH. The only diseases actually associated with MH are:

  1. Central Core Disease
  2. Minicore Disease
  3. Evans Myopathy
  4. King Denborough Syndrome
  5. Nemaline Rod Myopathy

Similar clinical syndromes are seen with Anaesthesia Induced Rhabdomyolysis (AIR) and Propofol Infusion Syndrome, the major difference being that dantrolene may not help in the treatment.

Dantrolene is the priority in MH, however there are many other things that need to be done, so enlisting a team to help is essential. Many hospitals will have an MH trolly with all the equipment and medications needed, plus MH job cards that describe the tasks for each team member.

If you think about what the uncontrolled release of calcium would do, this   will help you remember what needs to be done to manage the patient.

  • Muscle contraction causing increased metabolic demand, production of heat, and release of potassium -> Deliver 100% oxygen, cool, and treat hyperkalaemia 
  • Inflammation and heat causing vasodilation -> pressor support
  • Stimulation of the clotting clotting cascade -> Treat disseminated intravascular coagulation
  • Increased cardiac activity causing arrhythmias -> Antiarrhythmic treatment
  • Muscle cell death causing myoglobin release -> Treat renal failure

Sub Tenons Eye Block

Fantastic video by David Olive, from The Royal Victorian Eye and Ear Hospital, with tips and tricks in performing sub tenons eye blocks for eye surgery. 

Video Laryngoscope Tip 3 - Pull Back

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A common complaint about using video laryngoscopes is that you can easily get a Grade I view of the cords, but then passing the tube through the cords can be tricky. To reduce the chance of this happening you can try the following:

  • Come back out slightly with the laryngoscope. If you are too close to the vocal cords, it can be very difficult to get the angle right for insertion of the tube. Plus the tip of the blade may get in the way of the tube, making it difficult to manouvre. You should be able to see the epiglottis at the top of the screen. If not then you are too close to the glottis. In some cases it may be beneficial to have a grade II view as it probably means you are a good distance from the cords.
  • Use a bougie instead of an intubating stilette, as the bougie is thinner and more flexible, and designed specifically to get into tight spaces.
Not Always Top 5 - Free Flap

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There are a few things that the anaesthetist can do that may increase the survival rate of a flap.

  • Keep perfusion pressure up to perfuse the flap
  • BUT, avoid high doses of vasopressors, which may mean accepting mild levels of hypotension
  • Delay anticoagulation for 6 hours after induction - avoids haematoma formation
  • Keep the patient warm but not hyperthermic - hyperthermia is bad for the brain
  • Good analgesia and PONV prophylaxis - avoids agitation and retching, which is especially important for abdominal flaps
  • Do not push fluids for a high urine output. 0.2mg/kg/hour is OK
  • Keep the haemoglobin around 80 to 90g/L

NB - Delaying DVT prophylaxis reduces the rate of haematoma formation, which can compromise blood flow to the flap. Delaying prophylaxis until haemostasis is achieved and the wound is closed would be ideal, but these procedures are often long, and so you have to balance this with the risk of DVT formation on the operating table. Use calf compressors and optimise pressure care.

Some surgeons are quite opposed to the use of vasopressors in free flap surgery, however the data to support this is flakey (animal studies). Flap perfusion is definitely known to be important so judicious use of vasopressors is probably OK. 

Some surgeons also believe that the haemoglobin should be above 100g/L to optimise oxygen delivery to the flap. Evidence for this is also scant, and since there is no other surgical group (except neonates) that benefit from such levels of haemoglobin, this is probably over-kill. However it is important not to let the haemoglobin to slip down to 60-70g/L. 

[Source D Scott]

Neuromuscular Monitoring - You Actually Need the Fancy Machine

A really great article recently published on GasExchange has changed my practice!

I used to think that quantitative neuromuscular monitoring with an accelerometer was a bit over the top. I was good enough to detect fade using a peripheral nerve stimulator with tactile or visual clues. However I now know that my fingers are only sensitive enough to detect fade up to a Train Of Four (TOF) ratio of 0.5. So patients with fade between 0.6 and 0.8 can be missed, and remain weak without reversal.

As I already new that the spontaneous recovery from neuromuscular blockade was unpredictable (especially with Rocuronium), I tended to reverse almost all patients regardless of time since the last dose. However, I now know that reversing a patient who has almost fully recovered from neuromuscular blockade (TOF > 0.8) can create weakness via the depolarising effect you get with large amounts of acetylcholine in the neuromuscular cleft.  

So now I use an accelerometer based neuromuscular monitor to decide whether the patient is ready to be reversed, and if so how much neostigmine they should be given. Or whether they should be given none. See the table attached to this post, which has been adapted from the Anesthesia Resident Blog.

[D Jolly http://www.gasexchange.com/articles/neuromuscular-myths-post-op-residual-curarisation/]

[http://anesthesia-resident.blogspot.com.au/2012/09/the-algorithm-for-nmj-monitoring-and.html]

Putty for MRI Earplugs

MRI scans are very noisy, and children anaesthetised for a scan often wake up quite agitated and upset. It’s thought that the noise of the scan is the culprit. 

Adult sized earmuffs and foam earplugs are often used to dampen the noise, but they hardly ever fit properly, and I don’t think they work very well.

While working in Stockholm earlier this year I discovered that they use dental impression putty to make perfectly fitting earplugs for children undergoing MRI. The putty comes in separate base and catalyst forms, which when mixed start to solidify. 

My impression was that the kids in Stockholm woke up much better than they do here in Melbourne, despite an otherwise identical anaesthetic technique. I reckon it’s the bespoke earplugs!

[Astrid Lindgren Children’s Hospital]

Case Report: Motor Neurone Disease for Lithotripsy

A 60 year old with advanced motor neurone disease comes to the anaesthetic clinic for assessment. He has renal stones, which are currently painful, and he is booked for lithotripsy. He has been bed bound for about three months, is unable to swallow, and feels short of breath when he lies flat. 

What are you going to do?

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Use a Warming Blanket to Hold the Ultrasound Probe!

Sometimes the best tricks are the simplest. In this case the anaesthetist used an inflated warming blanket to hold the ultrasound probe while doing a femoral catheter nerve block.

It makes perfect sense: You get the best picture with your probe and keep it in place. Then you move the needle into the image, rather than the other way around. If you start moving the probe to find the needle you might not get the best image of your target.

An added advantage of using something static to hold the probe, is that you can use your free hand to inject the local, and you can watch the catheter being inserted under vision.

[V NaRanong]

Save Your Fingers: Flexible LMA with MacGill’s

I try to avoid putting my fingers in a patients’ mouths. Although the risk is very small, there is always a chance they could bite down and damage your fingers. 

I use MaGill’s forceps to place flexible LMAs. Hold the MacGill’s as you normally would. Grab onto the laryngeal mask just behind the cuff (see closeup picture). With the tips of the MacGill’s nestled behind the cuff, if the forceps slip the cuff of the LMA will prevent the forceps coming into contact with the patient’s airway.

Usually you only need the forceps to help slip the LMA past the base of the tongue. A little downward pressure on the tube sticking out of the mouth is then usually enough to seat the LMA. Occasionally you will need to grab onto the tube more proximally with the MaGill’s and gently push the LMA into the hypo pharynx.

If you encounter real difficulties getting the LMA to sit you can use a laryngoscope to gently pull the tongue anteriorly and to the left, which will make more room in the hypo pharynx. 

Case Report: 150kg with Acute Quadriplegia

An otherwise-well 40 year old presents to a teaching hospital with acute incomplete quadriplegia, secondary to a disc prolapse at C5/6. He is 150kg and 6’8” (205cm). He is booked for an emergency decompression in the prone position, and then fixation ateriorly. He has a thick neck, smallish mouth with a Mallampatti of 3, and thyromental distance is borderline. The surgeon has specifically requested that you be careful with neck extension as it worsens the patient’s neurology.   

What are the issues?

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(Almost) All Drugs Should Be Given By Weight - Practice

Before my paediatric anaesthetic rotation, the last time I had done any significant amount of mental arithmetic was in primary school! Needless to say I was pretty rusty in the beginning.  

Whenever you do a paediatric case,  take a sheet of paper and write down the dose of emergency drugs for each patient before the case. Also write down the volume of the dilution you have, as during the confusion of an emergency, the last thing you will want to be doing is maths in your head. As an aside, in paediatrics I try not to dilute emergency drugs for boluses, so there is no confusion when I work with a trainee or another anaesthetist.

Of course, there are tonnes of smartphone apps that can do this for you now, but one day you might be out of battery, without reception, or even without your phone! Plus it’s good practice, especially for trainees.

PS - I am in the process of making a new drug card especially for paediatrics. To be released soon. 

Case Report: Single Lung with Obstructive Tumour

A 40 year old with a congenitally absent left lung presents with a tumour obstructing the bronchus intermedius on the right. Rigid bronchoscopy to relieve the obstruction in a smaller hospital was aborted due to persistent hypoxia. The patient is now in the ICU in your hospital, intubated, ventilated and still relatively hypoxic. The surgeons want to attempt the same procedure again, which would involve flexible bronchoscopy via a rigid bronchoscope.

How are you going to anaesthetise this patient?

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Systolic Pressure Variation Guides Intravascular Filling

Systolic pressure variation gives very useful information about the volume status of a patient.

You need an arterial line, and ideally the patient should be positive pressure ventilated, but it’s not essential. In fact if you can identify systolic pressure variation in a spontaneously ventilated patient, then you know that their venous return and cardiac filling is seriously imparired. 

It’s much easier to identify when you slow the arterial line down to 6.25mm/second, which is the same speed as the capnograph. A difference of 10mmHg or more between the lowest and highest SBP is significant, and indicates that the patient is under filled. 

The picture above shows significant systolic pressure variation in a young, awake, patient with a mediastinal mass just prior to induction. This patient was fluid resusitated and induced breathing spontensouly to avoid further depression of cardiac output by positive pressure ventilation. Despite a normal blood pressure, the patient is tachycardic, which is the common presentation of young and otherwise fit patients who are hypovolaemic. So always beware tachycardia in young patients who have reason to be haemodynamically compromised. 

Rapid induction of this patient would most likely result in a hypovolaemic arrest.