Apnoeic oxygenation by nasal cannulae during RSI
October 22, 2015Apnoeic oxygenation has been around for a while and the NODESAT (Nasal Oxygen During Efforts Securing A Tube) application has become a fixture on many ED, ICU and Prehospital RSI checklists since the publication of Weingart and Levitan's 2011 article in the Annals of Emergency Medicine,
Preoxygenation and prevention of desaturation during emergency airway management.
Weingart SD1, Levitan RM. Ann Emerg Med. 2012 Mar;59(3):165-75.e1. doi: 10.1016/j.annemergmed.2011.10.002.
Epub 2011 Nov 3.
Weingart SD1, Levitan RM. Ann Emerg Med. 2012 Mar;59(3):165-75.e1. doi: 10.1016/j.annemergmed.2011.10.002.
Epub 2011 Nov 3.
Despite building it into my clinical practice and teaching it, I haven't written anything about on this site. So let me address that deficit now.
One of the difficulties with intubating sick, less than optimally prepared patients is their distressing tendency to rapidly desaturate, with the operator's heart rate rising at an inversely proportional rate to the patient's monitored oxygenation. And in a prehospital environment, where back up resources are not rapidly available, anything which buys time cheaply and without adding heavy, space consuming gear is likely to be looked on fairly favourably.
So when NODESAT apnoeic oxygenation was promoted on the F.O.A.M.ed outlets (well in advance of the actual article being published) and needed nothing more than a standard nasal canula set, a reliable oxygen source and a strong pair of hands, it seemed that a little bit more time had just been cheaply bought.
Thankfully, rather than having to wade through a long section of text explaining the ins and outs of NODESAT, I can point you all in the direction of good explanations on other critical care sites.
One of the difficulties with intubating sick, less than optimally prepared patients is their distressing tendency to rapidly desaturate, with the operator's heart rate rising at an inversely proportional rate to the patient's monitored oxygenation. And in a prehospital environment, where back up resources are not rapidly available, anything which buys time cheaply and without adding heavy, space consuming gear is likely to be looked on fairly favourably.
So when NODESAT apnoeic oxygenation was promoted on the F.O.A.M.ed outlets (well in advance of the actual article being published) and needed nothing more than a standard nasal canula set, a reliable oxygen source and a strong pair of hands, it seemed that a little bit more time had just been cheaply bought.
Thankfully, rather than having to wade through a long section of text explaining the ins and outs of NODESAT, I can point you all in the direction of good explanations on other critical care sites.
- Apnoeic Oxygenation by Nicholas Chrimes (Anaesthesia department, Monash Hospital)
- No Desat! by Rich Levitan (Emergency Physicians Monthly)
- Preoxygenation and prevention of desaturation during emergency airway management. Weingart SD1, Levitan RM. (Ann Emerg Med. 2012 Mar;59(3):165-75.)
- Apnoeic Oxygenation: Essential in Prehospital RSI. (Greater Sydney Area HEMS)
Essentially what the NODESAT approach does is fill the apnoeic window during RSI between taking off whatever facemask oxygen source (NRBM, BVM, NIPPV) you are using, getting a laryngoscopic view of the glottic aperature, placing the endotracheal tube and connecting that tube to the oxygen source via a BVM or portable ventilator.
The patients that we manage trackside, while mostly fit, are metabolically active, may have compromised lung function if there are thoracic injuries and may have full stomachs. So rapid desaturation can occur in the time between between removing the O2 supply and placing the ETT. Given the propensity for blunt head injury, hypoxia is a major enemy to avoid.
There are a couple of advantages to placing a set of nasal canulae on the patient and running the O2 at 15L/min prior to starting the RSI process:
The patients that we manage trackside, while mostly fit, are metabolically active, may have compromised lung function if there are thoracic injuries and may have full stomachs. So rapid desaturation can occur in the time between between removing the O2 supply and placing the ETT. Given the propensity for blunt head injury, hypoxia is a major enemy to avoid.
There are a couple of advantages to placing a set of nasal canulae on the patient and running the O2 at 15L/min prior to starting the RSI process:
- A resevoir of high FiO2 is built up on the naso and oropharyngeal spaces
- During apnoea, mass action and a bit of diffusion provides a continuous supply of O2 to the alveoli. The FiO2 may even increase at this time due to the lack of entrainment of surrounding air and dilution by the reduced exhalation of CO2.
- The low profile canulae do not get in the way of laryngoscopy and intubation
- The time to clinically significant desaturation is extended by anything from 3 to 50 minutes, depending on the patient context. This can be particularly important in the setting of cerebral trauma.
- The need to provide positive pressure ventilation while waiting for the neuromuscular blockade to kick in is reduced which in turn lessens the risk of insufflating a loaded stomach.
What's not to love?
Well there are some plausible disadvantages
Well there are some plausible disadvantages
- 15L/min of gas flow up the nasal passages may not be great where a compound base of skull fracture is suspected, though I don't know that this has ever been documented.
- The canula may cause a leak when trying to bag a hypoxic patient, though in practice I don't think this has been shown to be a major problem and I'd have more concerns about a great big bushy beard.
- The biggest problem trackside would probably be the need for a second O2 source; one for the BVM and one for the nasal cannulae.
- At 15L/min a full C-cylinder would last about 25 minutes and a D-cylinder a little over 2 hours.
The key bit to get right in all of this is to make sure that the entire airway is kept patent, from the nasal cavities all the way down to the alveoli. Nasal canula gas flow at 15L/min is not positive pressure ventilation and an obstructed airway will result in all of that oxygen simply venting out through the mouth and nose into the surrounding environment. So suction out that oropharynx, get a good jaw thrust going (even if that means getting a second pair of hands involved) and be aware of lower airway problems such as tension pneumothoraces, haemothoraces and lung contusions.
So everything is looking rosy for NODESAT nasal canula apnoeic oxygenation, right?
And then the FELLOW trial gets published. Ah!
At first glance, it looks like the honeymoon is suddenly over for nasal canula apnoeic oxygenation as the primary study outcome demonstrates that there is "no difference between apneic oxygenation and usual care in the lowest oxygen saturation experienced by critically ill adults undergoing emergent endotracheal intubation". Oh dear!
I'm still using NODESAT and will continue to do so and not just because the tubing is cheap, light and already in pretty much every airway pack I use both inside a hospital and trackside. Here's why.
I think they measured the wrong thing. All patients will eventually become hypoxic; that's not the big gain. What matters is the time that I've bought until the desaturation starts to become a problem. From previous studies of various forms of apnoeic oxygenation in anaesthetic and critical care populations the time to "significant" desaturation was moved from 2 - 6 minutes to 3 - 55 minutes (Remember, SpO2 probes are time machines and tell you what the calculated Hb-O2 levels were on average 2 minutes ago).
The FELLOW study primary outcome measured the lowest SpO2 recorded up to 2 minutes after successful ETT placement, the median time to which was 2 - 3 minutes. Perhaps data from the patients who took longer to intubate might have indicated a benefit for NODESAT. Additionally, perhaps those control patients who desaturated quicker might have benefited from NODESAT but were denied it due to their study group allocation (therapeutic misalignment).
There are some suggestions that this might be the case, along with some other possible flaws such as queries about maintenance of airway patency and effect dilution due to pre-oxygenation strategies, which are presented here:
Kudos to both Scott Weingart, one of the original NODESAT paper authors, who interviewed Matt Semler, one of the FELLOW study authors, in which they discuss these issues:
Finally, it is important to remember that whether you choose to use NODESAT or not (You really should - just sayin'), it should be part of a complete package tailored to the needs of the particular patient in front of you, which at a minimum should include proper positioning (ear-to-sternal notch level, face parrallel to the ceiling/sky, ramping where needed), a decent attempt at optimal preoxygenation and denitrogenation, removal of the c-spine collar and the use of end-tidal CO2 monitoring (NAP-4 people, NAP-4).
There is a fair bit of contention here, on both sides, so please get involved and leave your comments below
So everything is looking rosy for NODESAT nasal canula apnoeic oxygenation, right?
And then the FELLOW trial gets published. Ah!
At first glance, it looks like the honeymoon is suddenly over for nasal canula apnoeic oxygenation as the primary study outcome demonstrates that there is "no difference between apneic oxygenation and usual care in the lowest oxygen saturation experienced by critically ill adults undergoing emergent endotracheal intubation". Oh dear!
I'm still using NODESAT and will continue to do so and not just because the tubing is cheap, light and already in pretty much every airway pack I use both inside a hospital and trackside. Here's why.
I think they measured the wrong thing. All patients will eventually become hypoxic; that's not the big gain. What matters is the time that I've bought until the desaturation starts to become a problem. From previous studies of various forms of apnoeic oxygenation in anaesthetic and critical care populations the time to "significant" desaturation was moved from 2 - 6 minutes to 3 - 55 minutes (Remember, SpO2 probes are time machines and tell you what the calculated Hb-O2 levels were on average 2 minutes ago).
The FELLOW study primary outcome measured the lowest SpO2 recorded up to 2 minutes after successful ETT placement, the median time to which was 2 - 3 minutes. Perhaps data from the patients who took longer to intubate might have indicated a benefit for NODESAT. Additionally, perhaps those control patients who desaturated quicker might have benefited from NODESAT but were denied it due to their study group allocation (therapeutic misalignment).
There are some suggestions that this might be the case, along with some other possible flaws such as queries about maintenance of airway patency and effect dilution due to pre-oxygenation strategies, which are presented here:
- FELLOW trial: Randomized Trial of Apneic Oxygenation during Endotracheal Intubation of the Critically Ill - The Bottom Line review by Celia Bradford (Intensivist at RNSH)
- The FELLOW Trial: An End to Apneic Oxygenation? - R.E.B.E.L. E.M.
- Journal Club: The last breath for apnoeic oxygenation? - St Emlyn's
Kudos to both Scott Weingart, one of the original NODESAT paper authors, who interviewed Matt Semler, one of the FELLOW study authors, in which they discuss these issues:
Finally, it is important to remember that whether you choose to use NODESAT or not (You really should - just sayin'), it should be part of a complete package tailored to the needs of the particular patient in front of you, which at a minimum should include proper positioning (ear-to-sternal notch level, face parrallel to the ceiling/sky, ramping where needed), a decent attempt at optimal preoxygenation and denitrogenation, removal of the c-spine collar and the use of end-tidal CO2 monitoring (NAP-4 people, NAP-4).
There is a fair bit of contention here, on both sides, so please get involved and leave your comments below
Posted by Matthew Mac Partlin. Posted In : Clinical topics
