Mac 3 vs Mac 4: My Final Rant!

I feel the sands keep shifting in this Mac 3/4 debate, so here’s my final rant on the topic…

Firstly, obviously I’m not disputing that airway management is primarily about alveolar oxygen delivery (Vortex Approach anyone?) but this discussion is about how to have an optimal attempt at laryngoscopy in as few tries as possible. When talking about best attempts at intubation, it is all about “getting the tube in”.

Secondly I’m not dismissing the importance of technique – but I’m assuming the operator is going to be equivalently trained and use the appropriate technique with either the 3 or the 4 blade – so technique shouldn’t be a factor in this discussion. There’s no technique I’m aware of that can be used with the 4 but not the 3 (lifting the epiglottis directly with the laryngoscope blade if desired is usually equally possible with the 3 blade and is part of choosing a blade that’s “long enough” – see below).

Thirdly it’s fine to talk about “the right tool for the right job” but you have to be able to specify how you’re going to make this choice in a particular patient. My whole point is that if you make the judgement that the 3 is long enough (which in my experience it is 95% of the time) it is the better blade – because as well as sufficient length it will provide added strength to lift (as demonstrated in the video). Clearly I’m not disputing that the 4 is better if the 3 is too short, no competition there. We are only discussing the situation in which the Mac 3 is considered long enough (which is pretty easy to judge prospectively by measuring the distance from the lips to the thyroid cartilage). So again, inadequate length of the Mac 3 shouldn’t be a factor in this discussion.

Fourthly the point has been made that force isn’t the major factor in optimal laryngoscopy. This may be true but there’s no doubt that sometimes in a difficult intubation, an extra bit of lift may be what gets you the glimpse of the arytenoids that makes the difference. This is particularly true when there may have been more than one previous attempt at laryngsocopy. The decrement in arm strength with multiple laryngoscopies is pretty marked and is one reason that getting another operator to have a try in a difficult intubation is so useful – as once other factors have been optimised between attempts, a return to “full power” using the “new arm” can be the difference between yielding the benefit of these optimisations and getting a view or not (otherwise these optimisations may be counterbalanced by a decrease in laryngoscopy strength with successive tries and the view may not improve). Clearly force of laryngoscopy can be an issue, and for many clinicians (esp. in a pre-hospital setting) having another clinician attempt laryngoscopy when they fatigue may not be an option, so why not maximise your own ability to lift the tissues at the tip of the blade by choosing the shorter blade (where that is going to be long enough!!). I’m not talking about unnecessarily using brute force – you don’t HAVE to pull as hard as you can, of course be gentle, but the ability to invoke use of that strength if required is there with the Mac 3. You might not need that extra strength on your first attempt (but then again you might!) but making optimal use of your residual strength may be critical on your second attempt. The suggestion has been made that this strength could be provided by alternative mechanisms (2 hands or an assistant). If you want to talk about losing the nuances of good technique, surely this would be when that would happen!

Finally I agree that it’s ultimately about personal preference and what “works for you” – but I get the impression that many staff I teach have chosen the Mac 4 from the outset on the logic of having been told by their seniors that a Mac 4 blade “is a 3 & a 4 combined”, without appreciating the mechanical disadvantage the Mac 4 brings with it. You can’t talk about personal preference if you haven’t given the alternative a decent try. You can’t say the Mac 3 doesn’t work for you if you’ve only used it once or twice as clearly it will feel awkward if it’s not your usual blade. Equally many clinicians have told me they’ve always felt they’ve been able to get a better view with the Mac 3 but couldn’t explain why. Hence the challenge to do 20 intubations using the Mac 3 before deciding.

In summary: when the Mac 3 is long enough and used with the appropriate technique and the minimum force required to get a view – why wouldn’t you want that added mechanical advantage up your sleeve in case you need it?  You’re losing nothing. At the end of the day it doesn’t matter which blade you choose, provided you choose it for the right reasons – because if you don’t you will be less successful at intubating. If you have used the Mac 3 repeatedly over many months/years,  and found you consistently get a better view with the Mac 4, even when the Mac 3 was long enough, then absolutely you should use the Mac 4 as your primary “go to” blade. Do what works.  #MakeYourFirstTryYourBestTry

ESA Status

CriCon meets the Vortex: by Nicholas Chrimes

Last week I had the opportunity to meet with Scott Weingart (@emcrit) in New York. One of the topics we discussed was my enthusiasm for his CriCon concept and the benefits of a staged escalation in emergency status to help overcome the psychological & practical hurdles of deciding to “cut the neck”.

CricCon

We also had a related discussion about the benefit of having “hard triggers” that give clinicians “permission” to initiate these escalations and help overcome the barriers to escalating care early enough.

While the Vortex clearly defines when performance of emergency surgical airway (ESA) is required, there is no objective point at which the it mandates initiating preparation for ESA. If optimal attempts at all three non-surgical airway (NSA) techniques have failed, the Vortex provides a clear “hard trigger” to initiate ESA but the need to begin preparing to perform an ESA in parallel with progressive failure of optimal NSA attempts is only implied (through descent into, and narrowing of, the funnel).

Fig6

If preparation for initiating ESA has not been made in advance of the decision to perform it, the delays can be surprisingly long in the context of a rapidly desaturating patient, and expose the patient to the risk of critical hypoxia in the interim. Scott suggested to me that ideally there should be a clear trigger to escalate the level of ESA preparedness.

In an attempt to achieve this I have modified the original Weingart CriCon model, condensing it down to 3 levels of preparedness. This has in part been achieved by removing CriCon 5 which is a default status and should therefore be part of the general preparation for all airway management. The remaining stages represent escalations from this during difficult airway management, with CriCon 1 & 2 (the “cutting” stages) being combined into the “GO” status. The colouring has also been reversed to provide a “traffic light” cue for performance of ESA.

ESA Status

These 3 levels of preparedness align with the 3 NSA techniques of the Vortex. A declared failure of an optimal attempt at any NSA technique mandates an escalation in ESA preparedness by the team. Sequential failure of optimal attempts at all three NSA techniques will therefore place airway management teams at “GO” status as they enter the ESA portion of the Vortex, having already prepared the necessary equipment during the “READY” and “SET” phases.

It is not the intention that this model will be included visually in the Vortex cognitive aid, for fear of cluttering it. In any case, as mentioned above, the impending need for ESA is already implied by spiralling deeper into the narrowing funnel. Instead Pete Fritz (@pzfritz) and I have agreed that as a standard part of Vortex training, when a declaration of a failed optimal attempt at any NSA technique is made, it should be accompanied by a request to escalate ESA preparedness. If this request is not made by the airway operator, then other members of the team will be empowered to make the suggestion and act upon it.

This modified CriCon model enables the escalation in ESA preparedness to be “hardwired” into the Vortex’s standardised template for difficult airway management. Using this model will hopefully better prepare clinicians, both practically & psychologically, to perform ESA in a timely manner when it is indicated. In addition, even in circumstances where ESA is ultimately not required, it should encourage this type of preparation to become routine as difficult airway scenarios deteriorate, removing some of the  self-consciousness which can form a significant barrier to even asking the team to “get out the cric kit”.

Nicholas Chrimes

(Thanks to Scott Weingart for his input into the modified CriCon model)

What is normal postop urine output? Define postop oliguria: By Nicholas Chrimes

Recent research indicates that a more restrictive approach to fluid administration in the post-operative period may improve patient outcomes (see refs below).

Current volumes of fluid administration are in part driven by the desire to achieve a urine output of ~0.5ml/kg/hr in catheterised patients. This value is widely accepted as “normal” for patients who are not post-surgery. In a postoperative patient we would expect a stress response, ADH secretion, fluid retention and thus a lower normal volume of urine output. So we may be overloading our patients in an effort to achieve unreasonable urine outputs in patients whose normal physiology favours fluid retention.

I can’t find a volume documented anywhere for normal post-operative urine output. What should we be aiming for? How do we define oliguira in the postoperative period?

 

Refs:

British Consensus Guidelines on IV Fluid Treatment for Adult Surgical Patients (GIFTASUP)

An Observational Study fluid balance and patient outcomes in the randomized evaluation of normal vs augmented level of replacement therapy trial. The RENAL Replacement Therapy Study Investigators. Critical Care Medicine 2012.

Joshi Intraoperative Fluid Restriction Improves Outcome After Major Elective Gastrointestinal Surgery. Anesthesia & Analgesia: August 2005 vol. 101 no. 2 601-605

Cocoran et al. Perioperative Fluid Management Strategies in Major Surgery: A Stratified Meta-Analysis. Anesthesia & Analgesia: March 2012 vol. 114 no. 3 640-651

Mac 3 vs Mac 4: The mechanical disadvantages of a longer laryngoscope blade: By Nicholas Chrimes

Video demonstrating the mechanical disadvantages of the Mac 4 http://youtu.be/gYxwhEmYb9w

The Mac 4 is often touted as the preferred size MacIntosh blade as it avoids the need to change blades and have an extra attempt at laryngoscopy if the Mac 3 is not long enough. This short video demonstrates why, when the Mac 3 is long enough, it will give you your optimal attempt at laryngoscopy on the first go.

CVCI or CICO?: By Nicholas Chrimes

Before the advent of the laryngeal mask, the phrase “can’t intubate, can’t (face mask) ventilate” accurately described the trigger for requiring a surgical airway. More recently the term “can’t intubate, can’t oxygenate” has been popularised. Does it mean the same thing? Which term do you prefer?

My experience is that many clinicians are unclear by what is meant by the term “oxygenation”.

  • Alveolar oxygenation
  • Blood oxygenation
  • Tissue oxygenation

Whilst tissue oxygenation is clearly the ultimate goal, alveolar oxygenation is the only concept relevant to the decision to perform a surgical airway. Unfortunately alveolar oxygenation cannot be directly assessed in “real time” during an airway crisis, and indirect measures such as “ventilation” or “blood oxygenation” must be used to make a judgement about whether alveolar oxygenation is occurring. Blood oxygenation, on the other hand, can be assessed directly via pulse oximetry but factors other than airway patency (such as alveolar oxygen reserves achieved during preoxygenation and the efficiency of oxygen transfer from alveoli to pulmonary capillaries), impact on the reading seen – such that it often doesn’t correlate with airway patency and thus its relevance to decision making in a difficult airway is questionable.

Does CICO introduce a poorly defined and difficult to assess concept into time-critical decision making?

Given that the assessment of patency via any non-surgical airway technique is made by the ability to ventilate (ideally using ETCO2), was “can’t ventilate (via a facemask or laryngeal mask), can’t intubate” a better term? Ultimately isn’t the decision to proceed to surgical airway based simply on an assessment that we “can’t ventilate” – by any non-surgical airway device?

CVCI, CICO or just CV?

What are your thoughts?

Alfentanil for Procedural Analgesia: By Nicholas Chrimes

For surgical procedures done under local anaesthesia with sedation (LAWS), the sedation is provided predominantly to remove the pain of local anaesthetic infiltration. The drug most commonly chosen by anaesthetists for this task is propofol – a drug devoid of analgesic properties. Avoidance of pain using propofol sedation is therefore achieved by simply rendering the patient unconscious. This puts the patient at risk of airway obstruction and can make them uncooperative both during the painful stimulus (from which they often reflexly withdraw and need to be restrained) and for a variable time afterwards.

Ketamine, whilst better at preserving airway patency and patient cooperativity, is not usually an alternative for elective day surgery procedures, due to prolonged disorientation and emergence phenomena.

Over the last 12 months I have been using alfentanil 15mcg/kg for these type of procedures. This provides intense analgesia & effective anxiolysis with minimal sedation and preservation of the patient’s ability to maintain the patency of their own airway. Onset of effect occurs within 90secs of administration and the effects last around 10mins. Some points:

  • Respiratory depression can be profound but my experience is that patients ALWAYS remain awake and cooperative and will breathe on request. Thus voluntary control of respiration is retained, even in frail or elderly patients.
  • Airway patency is maintained. I have NEVER needed to intervene to support the airway, even when using these doses of alfentanil in patients as old as 90yrs.
  • The profound bradycardia frequently seen with alfentanil when used in conjunction with propfol for induction of general anaesthesia does not appear to occur provided no other sedative/anaesthetic agents are administered. Early on I was prophylactically co-administering small doses of glycopyrrolate but have since realised this is unnecessary. Even in elderly patients with a low baseline heart rate the impact of alfentanil on HR has been minimal.
  • There is little or no amnesia so the technique is not suitable for patients in whom this is desirable.
  • I have had one patient (from a denominator approaching 50) become very nauseated about 45mins after the procedure. There was no haemodynamic cause for the nausea. It significantly outlasted the expected duration of the alfentanil (which was the only drug received other than antibiotics and the local anaesthetic) and did not respond to either standard antiemetics or to naloxone. The patient had to remain an inpatient overnight. The significance of this is unclear.
  • The above statements about haemodynamic and airway safety are only true if alfentanil is the ONLY anaesthetic drug administered. I would be wary of using these sorts of doses in combination with other sedative/anaesthetic agents.
  • I have only used this technique in an elective setting. Whilst patients remain alert & cooperative I wouldn’t want to bet on them protecting their airways (given that awake patients on remifentanil will often tolerate an ETT without coughing). As such I wouldn’t advocate use of this technique in unfasted patients. Also, using potent opioids in an emergency patient whose haemodynamics are dependent on sympathetic outflow could have catastrophic consequences.

Though purely anecdotal, my impression is that in patients who are not concerned about being aware of their surroundings during a procedure, this techinque of “local anaesthesia with analgesia” (rather than with sedation using propofol) seems to be superior.

Please post your thoughts, experiences or references to any related literature.