Giving surfactant through an LMA. Time to ditch the endotracheal tube?

Giving surfactant through an LMA. Time to ditch the endotracheal tube?

 

In the spirit of full disclosure I have to admit I have never placed a laryngeal mask airway (LMA) in a newborn of any gestational age.  I have played with them in simulated environments and on many occasion mentioned that they are a great alternative to an ETT especially in those situations where intubation may not be possible due to the skill of the provider or the difficulty of the airway in the setting of micrognathia for example.

In recent years though we have heard of examples of surfactant delivery via these same devices although typically these were only case reports. More recently a small randomized study of 26 infants by Attridge et al demonstrated in the group randomized to surfactant administration through an LMA that oxygen requirements were reduced after dosing.  This small pilot provides sufficient evidence to show that it is possible to provide surfactant and that at least some gets into the airway of the newborn.  This proof of concept though while interesting, did not answer the question of whether such delivery of surfactant would be the same or better than through an ETT.  As readers of my blog posts know, my usual stance on things is that the less invasive the better and as I look through the literature, I am drawn to concepts such as this to see if they can be added to our toolbox of non or less invasive strategies in the newborn.

A Minimally Invasive Technique For The Masses?

This past month, a small study by Pinheiro et al sought to answer this question by using 61 newborns between 29 0/7 – 36 6/7 weeks and greater than 1000g and randomizing them to either surfactant via the INSURE technique or LMA.  I cannot stress enough so will get it out of the way at the start that this strategy is not for those <1000g as the LMA is not designed to fit them properly and the results (to be shown) should not be generalized to this population. Furthermore then study included only those infants who needed surfactant between 4 – 48 hours of age, were on CPAP of at least 5 cm H2O and were receiving FiO2 between 30 – 60%.  All infants given surfactant via the insure technique were premedicated with atropine and morphine while those having an LMA received atropine only.  The primary outcome of the study was need for subsequent intubation or naloxone within 1 hour of surfactant administration.  The study was stopped early after an interim analysis (done as the fellow involved was finishing their fellowship – on a side note I find this an odd reason to stop) demonstrated better outcomes in the group randomized to the LMA.

Before we get into the results let’s address the possible shortcomings of the study as they might already be bouncing around your heads.  This study could not be blinded and therefore there could be a significant bias to the results.  The authors did have predetermined criteria for reintubation and although not presented, indicate that those participating stuck to these criteria so we may have to acknowledge they did the best they could here.  Secondly the study did not reach their numbers for enrolment based on their power calculation.  This may be ok though as they found a difference which is significant.  If they had found no difference I don’t think I would be even writing this entry!  Lastly this study used a dose of surfactant at 3 mL/kg.  How well would this work with the formulation that we use BLES that requires 5 mL/kg?

What were the results?

Intervention Failure LMA Group ETT group p
Any failure 9 (30%) 23(77%) <0.001
Early failure 1 (3%) 20 (67%) <0.001
Late failure 8 (27%) 3 (10%) 0.181

What do these results tell us?  The majority of failures occurred within an hour of delivery of surfactant in the ETT group?  How does this make any sense?  Gastric aspirates for those in the LMA group but not the INSURE group suggest some surfactant missed the lung in the former so one would think the intubation group should have received more surfactant overall however it would appear to be the premedication.  The rate of needing surfactant afterwards is no different and in fact there is a trend to needing reintubation more often in the LMA group but the study was likely underpowered to detect this difference.  Only two patients were given naloxone to reverse the respiratory depressive effects of morphine in those given the INSURE technique so I can’t help but speculate that if this practice was more frequent many of the reintubations might have been avoided.  This group was quite aggressive in sticking to the concept of INSURE as they aimed to extubate following surfactant after 5 – 15 minutes.  I am a strong advocate of providing RSI to those being electively intubated but if the goal is to extubate quickly then I believe one must be ready to administer naloxone soon after extubation if signs of respiratory depression are present and this did not happen effectively in this study.  Some may argue those getting the INSURE technique should not be given any premedication at all but that is a debate that will go on for years I am sure but they may have a valid point given this data.

Importantly complications following either procedure were minimal and no different in either group.

Where do we go from here?

Despite some of the points above I think this study could prove to be important for several reasons.  I think it demonstrates that in larger preterm infants it is possible to avoid any mechanical ventilation and still administer surfactant.  Many studies using the minimally invasive surfactant treatment (MIST) approach have been done but these still require the skill of laryngoscopy which takes a fair bit of skill to master.  The LMA on the other hand is quite easy to place and is a skill that can be taught widely.  Secondly, we know that even a brief period of over distension from PPV can be harmful to the lung therefore a strategy which avoids intubation and direct pressure to the lung may offer some longer term benefit although again this was not the study to demonstrate that.

Lastly, I see this as a strategy to look at in more rural locations where access to highly skilled level III care may not be readily available.  We routinely field calls from rural sites with preterm infants born with RDS and the health care provider either is unable to intubate or is reluctant to try in favour of using high flow oxygen via mask.  Many do not have CPAP either to support such infants so by the time our Neonatal Transport team arrives the RDS is quite significant.  Why not try surfactant through the LMA?  If it is poorly seated over the airway and the dose goes into the stomach I don’t see them being in any worse shape than if they waited for the team to arrive.  If some or all of the dose gets in though there could be real benefit.

Might this be right for your centre?  As we think about outreach education and NRP I think this may well become a strong reason to spend a little more time on LMA training.  We may be on to something!

 

A Strategy to Minimize Blood Sampling in ventilated premature and term infants

A Strategy to Minimize Blood Sampling in ventilated premature and term infants

As those of you who have been following this blog are aware, I am always on the lookout for strategies that can help minimize blood work without sacrificing care in the NICU.  At particular risk our the very premature infants in our units who for example at 1 kg have about 80-90 mL of blood.  It does not take very many 0.5 – 1 mL “small” draws to create anemia.  In a recent study (free article in link) of infants less than 1500g entitled A mathematical modeling approach to quantify the role of phlebotomy losses and need for transfusions in neonatal anemia, the authors studied 26 infants over a one month period.  The results were staggering in that these infants experienced 138 +/- 21 blood draws with an average of nearly four transfusions per patient.  While the authors do not specify what type of testing was done they did find a shocking statistic that 59% of the blood collected by weight of sample was discarded.  This certainly stresses the point that we should aim to minimize the volume of sample collected in each case to that which is only necessary for the equipment to run.  Furthermore, strategies to minimize sample draws should be utilized where possible and if accuracy permits point of care technology may further reduce volumes required and provide immediate results at the bedside.  Lastly where possible, utilizing non-invasive technology to avoid blood draws needs to be explored when possible and was the subject of another post on Masimo non-invasive HgB measurement (http://wp.me/p5NWfD-1t).

Certainly in sick neonates whether they be term or preterm the drawing of blood gases to monitor ventilation contributes to the anemia of prematurity which often culminates in a transfusion.  Sicker infants with greater lability due to respiratory compromise are deserving of optimal ventilation and this is achieved by monitoring pCO2 levels in arterial or venous samples.  There have been different strategies employed to replace the sampling of CO2 by blood gas analysis which have not been very successful but there is one that I believe has promise that I will discuss at the end.

Transcutaneous pCO2 measurement was introduced in the 1980s.  While this technology does allow measurement of pCO2 the variation between true arterial pCO2 and tcPCO2 can be wide making the technology difficult to implement on a consistent basis.  In particular the accuracy in infants <28 weeks has been quite poor leading to increased numbers of arterial and venous samples to “check” ow closely the results correlate.  As was described in 2005 by Aliwalas LL et al the technology in this group who actually have the highest number of blood draws does not meet the required standard to replace arterial pCO2 measurements (http://www.ncbi.nlm.nih.gov/pubmed/15496874)

Another method is of directly sampling exhaled CO2 in ventilated patients.  Traditionally such measurements were taken with proximal gas sampling and in neonates in particular the results were discouraging.  Problems encountered with proximal end tidal sampling were related to the lack of cuffed endotracheal tubes in part as the measured gas would be diluted with air in the presence of any leak around the tube leading to underestimation of true CO2 levels.  Furthermore, in the presence of significant pulmonary disease the clearance of CO2 may be impaired such that the arterial pCO2 – ETCO2 difference may be quite large.  For a review see the free article by Malloy and Deakins Are carbon dioxide detectors useful in neonates? The agreement between arterial and proximal sampling measured in this way has been quite variable and as such the technology has not really caught on to any great degree for monitoring ventilated infants.  That being said it can be quite useful at determining if the endotracheal tube is in the trachea or esophagus.  The presence of the waveform even if not yielding an accurate level confirms proper placement although where the tube sits in the trachea still needs confirmation.

The final method for sampling CO2 is the one which I believe holds the most promise for actually reducing blood draws and by extension risk of anemia and pain in the neonate.  Kugelman and colleagues in Haifa, Israel published the following paper (free article in the link) A novel method of distal end-tidal CO2 capnography in intubated infants- comparison with arterial CO2 and with proximal mainstream end-tidal CO2. This creative study utilized a double lumen endotracheal tube which had been designed for surfactant installation and distal pressure measurement to instead sample pCO2 near the carina. This strategy was postulated to eliminate the issue with dilution of gas from proximal sampling and provide a closer measurement of true pCO2 when compared to arterial CO2 and proximal sampling. They studied 27 infants with varying degrees of pulmonary condition severity although most had RDS.  When comparing the three methods of pCO2 measurement the following was found.

correlation CO2This demonstrates that while proximal measurement was quite poorly correlated with true arterial pCO2 the distal measurement was much more accurate.  In fact the mean differences between arterial pCO2 and distal measurement was -1.5 mm Hg while that of proximal measurement -10.2 mm Hg albeit with wide confidence intervals.  As found in other studies of proximal end tidal CO2 measurement, worse pulmonary disease correlated with worse accuracy as shown in table 2.

effect of severity

As the pCO2 rises above 60 the accuracy is less but remains much better than proximal measurements.  Interestingly the same group has published an additional trial using high frequency ventilation and confirmed the measurements remain accurate.  (http://www.ncbi.nlm.nih.gov/pubmed/22328495)

So what does the future hold?  in VLBW infants one concern may be the internal diameter of the smallest double lumen tubes and the effect of upsizing to a larger tube and risk of subglottic stenosis.  After a personal communication with Dr. Kugelman I understand that this has not been an issue in their unit as they tend to use these double lumen tubes in most if not all of the their infants.  The accuracy is sufficient enough from my point of view that units should be able to implement this strategy at least in larger infants at first (those who would need a 3.0 ETT and larger) to see the effect on blood sampling.  I suspect that one blood gas a day to determine accuracy in a given patient would be sufficient most of the time if the numbers were found to correlate well.

I would welcome feedback from people who work in units where this strategy has been utilized.  How effective is it?  Did it reduce your blood gas draws or increase them due to unreliability?  Have you seen a rise in subglottic stenosis?  Please send your feedback to either this site or at my Facebook page at www.facebook.com/AllThingsNeonatal.