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. 

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.

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]

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]

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]

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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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]

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. 

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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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. 

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 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.

• Have high suspicion for mediastinal mass.
• Beware tumour lysis syndrome.
• Be empathetic to both patient and parents.

PS -

• If mediastinal mass is present ask oncologists to consider treatment before anaesthesia for biopsy. Anaesthetising a patient with a mediastinal mass is risky.
• If pretreatment, then patients may be at risk of tumour lysis syndrome. In which case, don’t give steroids, as this may precipitate tumour lysis. If in treatment, then patients are often hyperhydrated to assist in maintaining electrolyte balance. Don’t stop the fluids when they come to theatre.
• Be nice to the child and their parents. They’re all scared. 

Rob McDougall, anaesthetist from the Royal Children’s Hospital Melbourne, discusses perioperative fluids in children.

• Why should we avoid hypotonic solutions?
• Why aren’t we using Hartmann’s with 1% glucose?
• Why should we change the 4,2,1 rule to 2,2,1.

Originally posted at www.anaesthesiacases.com

Click here to get a higher resolution PDF of the pain pathway.

I use this pathway to teach junior trainees about pain. When I think about acute pain, I think about the targets I can hit with the various drugs I have at the time. By no means is scheme all-inclusive, in fact there are many oversimplifications. But at least it gives you a framework to hang your ideas on. This is a work in progress, and I’d love to hear from others about what could be added or changed.

Break pain up into the following areas:

• Transduction - Conversion of physical energy, such as pressure or heat, to electrical an electrical signal via the action of a nociceptor.
• Transmission - Fast sodium channels in nerves allow the transmission of electrical signals from the periphery to the spinal cord.
• Modulation - The activity of interneurons within the spinal cord can either transmit or block the signal to the brain. 
• Perception - Interpretation of sensory signals reaching the brain as pain.

PS - Top down modulation is also an important aspect of the pain pathway, but I have omitted it to keep things simple. Signals from the midbrain descend to modulate the transmission of pain in the spinal cord. Noradrenaline and serotonin, as well as relaxation and stress reduction are involved. 

[Adapted from S Batistich]