The incidence of bronchopulmonary dysplasia (BPD) continues to compromise long-term health in neonatal patients despite mechanical ventilation’s success in reducing infant mortality.
Mechanical ventilation for neonates with respiratory failure, introduced in the 1960s and implemented widely in the 1970s, has resulted in a reduction in infant mortality. However, while this therapy has reduced the neonatal death rate from respiratory causes, the incidence of chronic lung disease, or bronchopulmonary dysplasia (BPD), continues to compromise long-term health.
Edwin Coombs, MA, RRT-NPS, ACCS, FAARC, director of marketing, Intensive Care & Neonatal Care North America, Dräger Medical Inc, indicated that mechanical ventilation has become so advanced that few newborns nowadays die because of acute respiratory failure. “Mortality now is predominantly from other complications of extreme prematurity, such as infection, necrotizing enterocolitis and intracranial hemorrhage or congenital anomalies,” he said. “As a result, much focus has shifted from reducing mortality to reducing the incidence of chronic lung disease.”
Oversight, Treatment and Challenges
At Rainbow Babies and Children’s Hospital in Shaker Heights, Ohio, approximately 40 respiratory therapists attend high-risk deliveries as primary airway clinicians and also administer specialized care in the neonatal intensive care unit (NICU). The facility practices “tiering,” ie taking a step up or down as the patient’s condition improves or declines, according to John Gallagher, MPH, RRT-NPS.
He explained that when a neonate presents with surfactant deficiency, therapists begin non-invasive ventilation with facial CPAP using a Neotech RAM cannula to support respiratory function. “When they are intubated, we start a surfactant. When we deem [infants weighing less than 1500 grams] need ventilatory support, we start non-invasive ventilation following the basic respiratory distress syndrome criteria,” he added.
Gallagher pointed out that treating this population requires close monitoring. For instance, strict oxygen management is critical, with a goal of maintaining saturation between 90 and 95%. “Determining the appropriate vent setting for a 550 gram infant is challenging. You have to be precise. You can’t throw out a random number for a set of lungs that small,” he said.
Also, it’s essential to create optimal synchrony between the ventilator and the patient. “The vent wants to respond to what the patient is asking for. But a small patient has minute requests and their signals are less obvious,” Gallagher said, citing a narrow margin of error when treating neonates. “You’re dealing with lung tissue that is continuing to develop.” As the infant develops, settings need to be modified accordingly.
Carbon dioxide (CO2) levels, among other indices, also require careful oversight. “Swings in CO2 levels put the patient at risk for cerebral vascular damage,” Gallagher noted. “Modern ventilator platforms have a number of components that give real-time feedback on patient data.”
Rainbow Babies and Children’s Hospital uses transcutaneous CO2 monitoring, endotracheal CO2 monitoring and cerebral oximeters to obtain information the ventilator cannot provide. Therapists also monitor progress through a combination of chest radiography, arterial blood gas measurements and the baby’s own efforts. “We pull the pieces of information together,” Gallagher said.
To further reduce the chance of ventilator-associated injury, therapists at Rainbow Babies and Children’s Hospital follow aggressive weaning practices. Once patients are stable, they are liberated from mechanical ventilation and offered post-extubation support, noted Gallagher. “We are more willing to give kids a fighting chance, let them have the opportunity to breath on their own. If they fail, we replace the therapy,” he said. “Every day on the vent leads to more severe morbidity. We make every effort to wean early.”
Tidal Volume Accuracy/Loss a Concern
Tidal volume accuracy and understanding of compressible volume loss in the circuit rank as other important concerns when ventilating neonates. Today’s medical device market has a number of different ventilator models that address the issues of both volume control/pressure and endotracheal tube leaks.
For one, the Dräger Babylog VN500 utilizes a proximal airway sensor that measures both inspiratory delivery and expiratory return, which allows for the accurate measurement of tidal volume delivery as well as leakage percentage. Coombs said, “Babylog VN500 takes this information into account and compensates automatically when ventilating neonates with set tidal volumes as low as 2 cm3. Additionally, to support a clinician’s workflow and adapt to the infant’s changing ventilatory support requirements, the VN500 can provide invasive, non-invasive and oxygen therapy all within the one device.”
Pressure-limited, time-cycled, continuous flow ventilation has been the standard of care in neonatal ventilation for more than 30 years. But exceedingly high inspiratory pressures have been thought of as a chief contributing factor of lung injury, although the issue is not well understood.1 “One of the advantages cited for the preference for pressure-limited over volume-controlled ventilation has been the ability to directly control the inspiratory pressure. Over the past eight to ten years, a wealth of accumulated evidence shows that volume, rather than pressure, is the critical determinant of ventilator-induced lung injury,” Coombs said.
As a result of overwhelming evidence that excessive tidal volume, rather than high inspiratory pressure, is the primary determinant of lung injury, most clinicians now monitor the delivered tidal volume when using pressure-limited ventilation, volume-targeted ventilation or volume guarantee (VG).2
The critical importance of distributing the tidal volume evenly into an optimally aerated lung has not been as widely appreciated and requires attention at the bedside. If extensive atelectasis is allowed to persist, the normal physiologic tidal volume entering the small proportion of open alveoli inevitably leads to over-expansion of the relatively healthy portion of the lung, with subsequent volutrauma and/or biotrauma, according to Coombs. The collapsed portion of the lung is also damaged, a condition known as atelectotrauma. So the benefits of volume-targeted ventilation cannot be realized without ensuring that the tidal volume is distributed evenly throughout the lungs.3
“By design, the Dräger algorithm is geared toward slower adjustment for low tidal volume and more rapid adjustment for low tidal volume and more rapid adjustment for excessive, potentially dangerous tidal volume,” he said.
In practical terms, optimization of lung inflation, referred to as the “open lung concept,” is achieved by applying adequate positive end-expiratory pressure (PEEP), Coombs continued. “It is important to understand that there is no single ‘safe’ PEEP level. Optimal end-expiratory pressure must be tailored to the degree of lung injury. For example, in infants who have no lung disease and, thus, normal lung compliance, a PEEP of 3 cm H2O is probably appropriate, and a PEEP of 5 cm H2O may result in overexpansion of the lungs, with impairment of venous return, elevated cerebral venous and systemic venous pressures, and decreased cardiac output,” he said. “Conversely, severely atelectatic, poorly compliant lungs may require PEEP levels as high as 8 to 10 cm H2O or more to achieve adequate lung volume and improve the ventilation/ perfusion ratio.”
In addition to monitoring tidal volume delivery to neonates, which should range between 2 and 5 mL, gas mixing needs to be supervised. “A teaspoon of gas gets delivered and ventilators need to know the delivery of that range of tidal volume. You have to monitor tidal volume as accurately as possible,” said Mark Rogers, RRT, RCP, senior product manager for CareFusion. “Some gas delivery systems deliver small tidal volume as well as accurate oxygen delivery. This is targeted to deliver consistent FIO2, but sometimes there are some fluctuations.”
Ventilation Challenges in Neonates
Rogers pointed out that babies’ lungs are stiff and non-compliant. CareFusion’s AVEA ventilator features volume guarantee in pressure control and in time cycled pressure limited for neonatal specific ventilation. With targeted ventilation, tidal volume might be lost to the patient circuit. “You need to monitor what gets into the lungs. If you have a flow sensor at the end of the trach tube, it helps to monitor this.” Proximal flow sensing allows for accurate monitoring in the neonatal intensive care unit (NICU), which facilitates reliable triggering to help improve patient synchrony for these patients.
Ventilators with on-board compressors assist with transport, but still require an oxygen source, Rogers pointed out. The AVEA ventilator contains a scroll compressor and is able to operate for up to two hours on battery. For babies who are able to tolerate non-invasive ventilation, CareFusion provides NIV positive pressure ventilation via Infant Flow SiPAP System, a combination of nasal CPAP and Biphasic modalities.
Much like the tiered system at Rainbow Babies and Children’s Hospital, the “arc of acuity” follows the patient’s respiratory needs and responds accordingly, said Rogers. “You start the patient off with the least invasive technology. As the patient’s acuity increases, you meet the acuity and it goes down rapidly on the other side. The timeframe varies for switching from non-invasive ventilation to invasive ventilation,” he said. “Some hospitals may institute within minutes with invasive ventilation. In labor and delivery, they may start non-invasive ventilation. It depends on the underlying pathology.”
Whether clinicians use invasive or non-invasive ventilation, the procedures for newborns continue to pose some challenges. “In terms of ‘mechanical issues,’ there are inherent leaks due to the use of uncuffed endotracheal tubes during invasive ventilation,” said Coombs. “During noninvasive ventilation, the proper fit of a nasal or mask interface is paramount to minimize leaks and increase patient comfort. In either case, when leakage is excessive, this may lead to hypoventilation and hypercarbia.”
Learning Curve
Gallagher explained the facilities typically have only one or two ventilation platforms and with good reason. “Patient safety is number one. Limiting the number of platforms leads to a smoother learning curve for physicians, therapists, nurses and other staff. People have a better understanding and mastery of the device,” he said. “Also, you get a better deal if you buy in volume. If the facility purchases 25 machines, they get a better deal than they would if they bought two. Last, with different platforms you have reusable sensors, valves and disposable circuits. They are proprietary to each platform and need to be processed. Having control over the disposable and reusable parts is easier to do with a limited number of platforms. It reduces the chance of error and improves the workflow.”
Depending on the device, the timeframe needed to learn and understand how to use the machine varies. For instance, the Babylog VN500 employs a user-intuitive interface that incorporates easy-to-read data, prioritizes alarm management, and provides for on-screen user support.
Coombs explained, “The interface can be configured to a variety of ways to accommodate clinician preferences, as well as provide for trended data screens up to seven days. Additionally, to support clinicians when using Dräger ventilation and neonatal products, our customers have access to the Intensive Care Online Network (ICON), which provides support 24/7/365 to discuss equipment, therapeutic management, and provide educational support.”
CareFusion’s Rogers added that the learning curve might be a bit steeper for those who are moving from one platform to another. “For instance, you might be used to doing things one way and then have to change to do them another,” he said, “but when you’re trained for a few days, it’s usually easy to operate the device. A post-sale education team at CareFusion trains respiratory therapists on the devices. It’s a patient safety issue.” Rogers pointed out that CareFusion uses Simple Touch, which is a common user interface.
Hospital systems that purchased AVEA when it was first introduced in 2002 have the option of upgrading to the newest platform, which saves the facility money in the long run. “Those who bought the AVEA when it was initially released, don’t need to buy a new device. We make the new technology available to existing customers,” said Natasha Barany, product manager for AVEA ventilators. “The software system used with AVEA looks at greater practices surrounding the vent and increased measures and reporting. It saves time with paperwork and improves workflow.” The Alaris pump, a smart integrated system, is the backbone and gives AVEA the ability to communicate better.
In today’s health care environment, it is critical that medical devices “talk to each other.” Barany noted that CareFusion is currently devoting significant attention to communications as an area of development. She said that connectivity with the electronic medical record (EMR) allows for the transfer of important data through a portal, which serves as a repository of data.
“Software connects the device and makes the data meaningful for the hospital quality system,” Barany said, noting that CareFusion currently transfers medical data for its adult patients this way. “The respiratory therapist looks at the data to see where the clinical process varies. This leads to better care and less time on the ventilator. You can measure and report data. The knowledge portal shows the respiratory therapist which patient may have a reportable health event. With neonates we’re looking at tracking the delivery of oxygen. This is very important in the care of neonates.”
Coombs pointed out that the development of chronic lung disease in extremely preterm infants is multi-factorial, not always due to mechanical ventilation. “The degree of prematurity and presence of intrauterine inflammation have a very significant effect that may minimize the impact of a protective ventilation strategy,” he said. “Thus, it will be difficult to demonstrate substantial differences in various ventilation strategies specific to long-term outcomes.”
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Phyllis Hanlon is a contributing writer to RT.
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References
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Keszler M. “Volume targeted ventilation.” NeoReviews, Vol.7; No.5 May 2006.
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Wheeler K, Klingenberg C, McCallion N, Morley CJ, Davis PG. “Volume-targeted versus pressure-limited ventilation in the neonate (Review).” The Cochrane Collaboration. Published by John Wiley & Sons, Ltd. 2010.
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McCallion N, Lau R, Morley CJ, Dargaville PA. “Neonatal volume guarantee ventilation: effects of spontaneous breathing, triggered and untriggered inflations.” Arch. Dis. Child. Fetal Neonatal Ed. 2008;93;36-39; originally published online 8 Aug 2007;?doi:10.1136/adc.2007.126284
