When I think back to my early days as a medical student, one of the first lessons on the physical exam involves checking central and peripheral perfusion as part of the cardiac exam. In the newborn to assess the hemodynamic status I have often taught that while the blood pressure is a nice number to have it is important to remember that it is a number that is the product of two important factors; resistance and flow. It is possible then that a newborn with a low blood pressure could have good flow but poor vascular tone (warm shock) or poor flow and increased vascular tone (cardiogenic shock or hypovolemia). Similarly, the baby with good perfusion could be in septic shock and be vasodilated with good flow. In other words the use of capillary and blood pressure may not tell you what you really want to know.
Is there a better way?
As I have written about previously, point of care ultrasound is on the rise in Neonatology. As more trainees are being taught the skill and equipment more readily available opportunities abound for testing various hypotheses about the benefit of such technology. In addition to my role as a clinical Neonatologist I am also the Medical Director of the Child Health Transport Team and have pondered about a future where ultrasound is taken on retrievals to enhance patient assessment. I was delighted therefore to see a small but interesting study published on this very topic this past month. Browning Carmo KB and colleagues shared their experience in retrieving 44 infants in their paper Feasibility and utility of portable ultrasound during retrieval of sick preterm infants. The study amounted to a proof of concept and took 7 years to complete in large part due to the rare availability of staff who were trained in ultrasound to retrieve patients. These were mostly small higher risk patients (median birthweight, 1130 g (680–1960 g) and median gestation, 27 weeks (23–30)). Availability of a laptop based ultrasound device made this study possible now that there are nearly palm sized and tablet based ultrasound units this study would be even more feasible now (sometimes they were unable to send a three person team due to weight reasons when factoring in the ultrasound equipment). Without going into great detail the measurements included cardiac (structural and hemodynamic) & head ultrasounds. Bringing things full circle it is the hemodynamic assessment that I found the most interesting.
Can we rely on capillary refill?
From previous work normal values for SVC flow are >50 ml/kg/min and for Right ventricular output > 150 ml/kg/min. These thresholds if not met have been correlated with adverse long term outcomes and in the short term need for inotropic support. In the absence of these ultrasound measurements one would use capillary refill and blood pressure to determine the clinical status but how accurate is it?
First of all out of the 44 patients retrieved, assessment in the field demonstrated 27 (61%) had evidence using these parameters of low systemic blood flow. After admission to the NICU 8 had persistent low systemic blood flow with the patients shown below in the table. The striking finding (at least to me) is that 6 out of 8 had capillary refill times < 2 seconds. With respect to blood pressure 5/8 had mean blood pressures that would be considered normal or even elevated despite clearly compromised systemic blood flow. To answer the question I have posed in this section I think the answer is that capillary refill and I would also add blood pressure are not telling you the whole story. I suspect in these patients the numbers were masking the true status of the patient.
How safe is transport?
One other aspect of the study which I hope would provide some relief to those of us who transport patients long distance is that the head ultrasound findings before and after transport were unchanged. Transport with all of it’s movement to and fro and vibrations would not seem to put babies at risk of intracranial bleeding.
Where do we go from here?
Before we all jump on the bandwagon and spend a great deal of money buying such equipment it needs to be said “larger studies are needed” looking at such things as IVH. Although it is reassuring that patients with IVH did not have extension of such bleeding after transport, it needs to be recognized that with such a small study I am not comfortable saying that the case is closed. What I am concerned about though is the lack of correlation between SVC and RVO measurements and the findings we have used for ages to estimate hemodynamic status in patients.
There will be those who resist such change as it does require effort to acquire a new set of skills. I do see this happening though as we move forward if we want to have the most accurate assessment of clinical status in our patients. As equipment with high resolution becomes increasingly available at lower price points, how long can we afford not to adapt?
It has been some time since I wrote on the topic of point of care ultrasound (POC). The first post spoke to the benefits of reducing radiation exposure in the NICU but was truly theoretical and also was really at the start of our experience in the evolving area. Here we are a year later and much has transpired.
We purchased an ultrasound for the NICU in one of our level III units and now have two more on the way; one for our other level III and one for our level II unit. The thrust of these acquisitions have been to reduce radiation exposure for one but also to shorten the time to diagnosis for a number of conditions. No matter how efficient x-ray technologists are, from the time a requisition is placed to the arrival of the tech, placement of the baby and then processing of the film, it is much longer than using a POC at the bedside. Having said that though is it accurate? There are many examples to choose from but when thinking about times when one would like an answer quickly I can’t think of anything much better than a pneumothorax.
Chest X-ray vs POC for Diagnosis of Pneumothorax
The diagnosis of a pneumothorax is easily diagnosed by ultrasound when there is an absence of lung sliding as seen in this video. In the majority of cases employing POC we are looking at ultrasound artifacts. In the case of pleural sliding which is best described as ants marching, it’s absence indicates the presence of a pneumothorax. The “lung point” sign as shown in this video marks the transition from pleural sliding to none and in a mode called “M” appears as a bar code when the pneumothorax is present.
Using such signs Raimondi F et al as part of the LUCI (Lung Ultrasound in the Crashing Infant) group compared traditional x-ray diagnosis as the gold standard to POC for diagnosis of pneumothorax. This study is important as it demonstrated two very important things in the 42 infants who were enrolled in the study. The first was the accuracy of POC. In this study each patient had both an ultrasound and an x-ray and the results compared to determine how accurate the POC was. Additionally in cases where there was no time for an x-ray to confirm the clinical suspicion the accuracy of the study was determined based on the finding of air with decompression along with abrupt clinical improvement. In case people are wondering infants as small as 24 weeks were included in the study with an average weight of 1531 +/-832 g for included infants.
The accuracy was stunning with a sensitivity and specificity of 100% each. Comparing this with clinical evaluation (transillumination, assessment of breath sounds) was far less accurate with a sensitivity of 84% (65-96) and specificity 56% (30-80).
Adding to the accuracy of the test is the efficiency of the procedure. “After clinical decompensation, lung ultrasound scans were completed in a mean time of 5.3 +/- 5.6 minutes vs a mean time of 19 +/- 11.7 minutes required for a chest radiograph (P < .001).” In short, it is very accurate and can be done quickly. In an emergency, can you think of a better test?
If efficiency weren’t enough what about the reduction in radiation exposure?
This was the focus of a recent paper by Escourrou G & Deluca D entitled Lung ultrasound decreased radiation exposure in preterm infants in a neonatal intensive care unit. The authors in this study chose to examine retrospecitively the period from 2012 – 2014 as in 2013 they rolled out a program of teaching POC ultrasound to clinicians. The purpose of this paper was to see if practitioners educated in interpretation of ultrasound would actually change their practice and use less ionizing radiation.
Their main findings are indicated in the table
|Min 1 x-ray during admission
|Mean x-rays per patient
|Mean radiation dose (microGy)
As they predicted use of ionizing radiation dropped dramatically. I should also mention that they tracked outcomes such as IVH, mortality and BPD to name a few and found no change over time. In conclusion the use of ultrasound did not affect major outcomes but did spare each neonate ionizing radiation.
Now before anyone hits the panic button I still think the amounts of radiation here are safe for the most part. In Canada the maximum allowed dose for the public per year is 1 mSv which is the equivalent of 1000 microGy. This was obtained from the Nuclear Safety agency in Canada in case you are interested in finding out more about radiation safety limits.
Back in 2012 at least in this study, 2 standard deviations from the mean would have put the level received at a little over a third of what the annual limit is but it is the outliers we need to think of. What about kids getting near daily x-rays while on high frequency ventilation or for monitoring pleural fluid collections? There certainly are many who could receive much higher dosages and it is for those kids that I believe this technology is so imperative to embrace.
It will take time to adopt and much patience. With any new roll out there is a learning curve. Yes there will be learners who will need to handle patients and yes there will be studies done at times to obtain the skills necessary to perform studies in an efficient and correct manner but I assure you it will be worth it. If we have a way of obtaining faster and accurate diagnoses and avoiding ionizing radiation don’t we owe it to our patients and families to obtain such skill? I look forward to achieving a centre of excellence utilizing such strategies and much like this last study it will be interesting to look back in a year an see how things have changed.
This post is meant to supplement an earlier post on the same topic.
Since introducing POC U/S in our unit there has been great enthusiasm and we will begin shortly introducing our nursing group to it’s use in order to enhance usage. Now that we have had some exposure we took the time to capture some our thoughts on this technology in this accompanying video graciously supported by the Children’s Hospital Foundation in Winnipeg. To watch this wonderful video by Dr. Ganesh Srinivasan a Neonatologist and technology aficionado in our institution click on the link below.
To quote Malcolm Gladwell, I think I witnessed a “Tipping Point” yesterday. The standard of practice for determining the presence or absence of pneumonia and pneumothorax has always been a chest radiograph. Determination of fluid collections by ultrasonography in the chest or abdomen, the domain of the Pediatric Radiologist.
Yesterday however, I was introduced to the use of bedside Point of Care Ultrasound (POC U/S) for the diagnosis of all of these aforementioned conditions. I spent the morning at a course on POC U/S for the Neonatologist and with that became comfortable much sooner than I expected with making such diagnoses based on some very straightforward criteria. Now before you think I am getting ahead of myself, I do not believe for a second that I am now competent to use U/S to replace radiographs as the “gold standard” in my practice. It has led me to consider though how one might go about reaching this level of confidence but I will share more on that later.
An example of how one can use ultrasound to exclude a pneumothorax is shown here https://www.youtube.com/watch?v=ws7DI4ZGQCo. The presence of bilateral “lung sliding” of the parietal and visceral pleura accompanied by “comet trails” excludes a pneumothorax. The absence of these findings is suggestive of a pneumothorax although other pathological findings can be present necessitating a chest x-ray. Think of how many times a patient develops a sudden increase in FiO2 and you do a chest x-ray to exclude a pneumothorax before increasing PEEP. This could change with acquisition of such technology.
The first question to really ask before taking the leap to replace or augment the classic chest radiograph is to look at the literature. With respect to the Neonate, the body of literature is not large but there are a couple of recent papers that are worth mentioning. The first is by Pereda MA et al. Lung Ultrasound for the Diagnosis of Pneumonia in Children: A Meta-analysis. (http://1.usa.gov/1CM24Sv) The review examined 9 studies of which 2 were in the neonatal population. The findings were intriguing. The sensitivity was 96% and specificity 93% when compared to the “Gold Standard” of either CXR or CXR with clinical diagnosis. To put this into context, there were 765 children who would have had thousands of x-rays during their hospital stay. This technology could reduce the number to ionizing radiation exposure by an extraordinary amount given the accuracy of the test compared to standard x-rays. The benefit of such reduction can be immediately appreciated when one considers that children are at an increased risk of malignancy compared to adults from ionizing radiation. Free supporting publication here.
The second paper to highlight is by Lovrenski J. Lung Ultrasonography of pulmonary complications in preterm infants with respiratory distress syndrome. Free supporting publication here
In this paper 120 patients with respiratory distress syndrome had U/S performed in the first 24 hours of life and then follow-up as indicated. Of this sample, 47 had complications including hemorrhage, pneumothorax, pneumonia, atelectasis and bronchopulmonary dysplasia. Of this group 45 were detected by ultrasound with the only two failures being small pneumothoraces. There were 512 ultrasounds performed compared to 612 clinically indicated chest x-rays during the same period. Again the potential reduction in ionizing radiation is astounding!
To be clear I am not suggesting that we do away with the chest x-ray but rather there is a great potential for reducing the need for the urgent chest x-ray when patient status changes. Depending on the situation in the unit you work in, an x-ray from the time it is ordered till the time it is performed and processed can be 15-30 minutes or more. The time it takes to perform a bedside ultrasound exam is 2-3 minutes at most making this modality at least in my mind a great first line option.
As I mentioned earlier though I am not an expert but merely an enthusiastic Neonatologist. This is not meant to replace the Pediatric Radiologist and in fact I would like to stress that I believe it is best suited to questions in which a binary yes/no answer is being asked. Does the patient have a pneumothorax, atelectasis, fluid in the abdomen or chest; all yes/no. Does the patient have a tumour in the liver and if so what type? That is a different kettle of fish and deserving of a Pediatric Radiologist’s opinion.
How do we go from “good to great” and utilize this technology accurately and safely. Clearly we are in need of practice, which can only come through training by qualified people who have demonstrated proficiency in the field. Thankfully in our situation we have access to individuals who have taught courses internationally and are willing to provide the training locally to us. Our strategy will include monthly U/S rounds supervised by these two experts who will provide a small group of us “superusers” with the training and ultimately confidence to put this into routine clinical practice. As confidence rises, the use of POC U/S to obtain vascular access will develop as will performance of such procedures as a bladder tap under direct visualization to improve our success rate. I suspect new uses will develop over time as we are at the forefront of this technology. There are courses offered abroad but like the paucity of Neonatal research in the area there are very few if any such programs for the Neonate specifically.
What I can say for sure is that the benefits of POC U/S are vast and I believe our patients will benefit both during their hospital stay and into adulthood due to the reduction in ionizing radiation that I see coming for these fragile infants. I for one am excited and energized by the future of this field and look forward to an expanding body of literature on the topic.