Developing a neonatal unit ventilation protocol for the preterm baby
Introduction
Neonatal intensive care involves life-threatening illness with high morbidity, cost and resource use. Mechanical ventilation is one of the most common therapies in the newborn intensive care unit (NICU), and is associated with increased morbidity and mortality. The management of infants receiving mechanical ventilation remains largely dependent on individual preferences. Mechanical ventilation is a complex and highly specialized area of neonatology, made more complicated by the availability of many different modes, techniques and devices. Ventilator manufacturers add to the confusion by using proprietary terminology to describe the various modalities. A physician who has trained in a NICU that uses a different device may find it difficult to transition to a new device and terminology. There are at least six kinds of high-frequency and twelve conventional ventilation devices in fairly widespread use throughout the world. In most NICUs staffing is provided on a rotating basis by attending physicians with varying research and clinical foci and a large number of house-staff with diverse background and training. No wonder that mechanical ventilation has been identified as one of the major risk factors for iatrogenic errors in the NICU [1]. Excessive practice style variation may not only lead to suboptimal clinical outcomes, but appears to also increase parental stress caused by multiple changes in care and have adverse consequences for the educational experience of house staff.
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Evidence in favor of ventilation protocols
Clinical trials evaluating various forms of mechanical ventilation have suffered from limitations related to the population studied, the specific device under study and the strategies employed. The inconsistent findings are open to interpretation and controversy continues to surround this important area. Experience has shown that there is a very long lag time between the time convincing scientific evidence becomes available and the time that a new practice becomes widely adopted. Clinical
Development of a ventilation protocol
For the development and implementation of a ventilation protocol a few general principles outlined below should be followed [8].
Proposed ventilation protocol
Ideally a unit protocol for respiratory support of newborn infants should be comprehensive and address all pertinent issues that impact on the eventual pulmonary outcome. This includes respiratory support in the delivery room (DR), the use of non-invasive support, criteria for intubation, surfactant administration, specific ventilation modes and usual range of settings, criteria for escalating therapy to high-frequency ventilation, weaning protocols, extubation criteria, and post-extubation
Delivery room care
There is strong evidence base in support of DR strategies aimed at facilitating lung fluid clearance and helping the preterm infant with insufficient chest wall rigidity to establish functional residual capacity (FRC). Positive pressure ventilation with high pressure and excessively large tidal volumes must be avoided. The use of a T-piece resuscitator is highly recommended, because of its ability to provide consistent, controlled inspiratory pressure and consistent positive end-expiratory
Non-invasive support
Nasal CPAP should be provided with bi-nasal prongs and a minimal pressure of 5 cm H2O. CPAP can be delivered with a bubble system, a constant flow ventilator, or a variable flow system. Bubble CPAP may have unique benefits, but the ease of use of ventilator CPAP and the ease of conversion to invasive or non-invasive positive pressure ventilation (NIPPV) make it an attractive pragmatic option. NICU's should develop local protocols for CPAP administration and focus on optimal application of the
Intubation criteria
The need of endotracheal intubation is often based on “clinical judgment”, which is highly subjective and requires considerable experience to apply well. In general, less experienced trainees are more aggressive in invading the airway, an intervention that is not without adverse effects. While latitude will always be necessary in clinical circumstances, reasonably specific criteria are needed to bring practice to a reasonable level of uniformity for all the reasons outlined previously. In the
General principles of mechanical ventilation
Optimal use of mechanical ventilation seeks to improve lung compliance, reduce oxygen requirement, prevent surfactant inactivation and ensure even tidal volume distribution by recruiting optimal lung volume and preventing atelectasis. The second key element of lung protective ventilation strategies is to minimize volutrauma and hypocapnia, the preventable elements of lung and brain injury by avoiding excessively large VT. Mild permissive hypercapnia and minimal FiO2 to achieve adequate oxygen
Choice of basic synchronized ventilation mode
Assist/Control (AC) or Pressure Support Ventilation (PSV) is preferable to SIMV in preterm infants, because the small endotracheal tubes (ETT) impose a high resistance and work of breathing during the weaning process. AC results in more even tidal volume (VT), lower work of breathing and more rapid weaning from mechanical ventilation compared to SIMV. PSV provides more complete synchronization because it is flow-cycled, thus avoiding inspiratory hold, but may result in very short inspiratory
Choice of pressure vs. volume as primary control variable
Pressure limited ventilation became the standard of care early in the history of neonatal respiratory support because of its ease of use and ability to cope with large leaks around uncuffed ETTs. The main disadvantage of pressure limited ventilation is the risk of volutrauma and inadvertent over ventilation when lung compliance improves, as often happens soon after birth when lung fluid is cleared, surfactant is administered and optimal lung volume is achieved. Volume controlled (VC)
Suggested settings
Ventilation should be initiated with AC + VG or PSV + VG. The choice of appropriate VT is the key to success and depends on the infant's size, postnatal age and underlying disease process. One size does NOT fit all. Table 1 lists appropriate VT and initial inflation pressure limit for various conditions. The larger VT requirement in the smallest infants is due to the proportionally larger impact of instrumental dead space of the flow sensor. Infants with BPD or meconium aspiration need larger VT
Target blood gas values
Mild permissive hypercapnia is appropriate in most infants. The PCO2 should be maintained in the range of 45–50 mm Hg during the first 3 days of life with a pH above 7.25. PCO2 > 60 mm Hg during the first 3 days should be avoided due to the increased risk of intraventricular hemorrhage. Thereafter, a PCO2 target range of 45–55 mm Hg is appropriate, as long as pH is > 7.25. Minimal FiO2 needed to achieve adequate oxygen saturation (88–93%) should be used.
Weaning protocol
Weaning should be initiated as soon as the patient has begun to recover from respiratory problem that required the use of mechanical ventilation. Weaning is facilitated by permissive hypercapnia. The ideal weaning mode of ventilatory support remains the subject of debate, but recent systematic review and meta-analysis concluded that the use of volume targeted ventilation compared to traditional pressure-limited ventilation resulted in lower rate of death/BPD, shorter duration of ventilation,
Indications for high-frequency ventilation
When inflation pressures > 25–28 cm H2O are required consistently to achieve acceptable gas exchange in a preterm infant with RDS, a change to high-frequency ventilation (HFV) is recommended. For uncomplicated RDS, both jet and oscillatory ventilation may be used. When significant airleak is present high-frequency jet ventilation is preferred. HFV is also indicated in infants with congenital diaphragmatic hernia, pulmonary hypoplasia, severe abdominal distension and poor chest wall compliance [14].
Extubation
It is important to recognize that extubation is a critical transitional time and many patients can experience significant problems during this process. Therefore, for the extreme preterm infant, we recommend the presence of a staff with expertise in stabilization and reinstitution ventilatory support during the procedure. Mechanical ventilation protocols should incorporate extubation guidelines. In the absence of definitive trial data, these are by necessity somewhat arbitrary. In a preterm
Post-extubation support
The post-extubation respiratory support should be decided ahead of time and be available for immediate initiation after extubation. Preterm infants should always be extubated to some form of distending airway pressure. Standard CPAP is appropriate for most infants. NIPPV may be used in selected infants with questionable respiratory effort or history of extubation failure. HHFNC is less effective and should not be used as a substitute for CPAP in the immediate post-extubation period. The use of
Summary
Effective translation of evidence based strategies of respiratory support into practice is facilitated by the development of a unit ventilation protocol. This endeavor requires considerable commitment of time and expertise, but will reduce practice style variation, root out outmoded approaches and benefit patients, parents and trainees.
Conflict of interest statement
Dr. Sant'Anna has nothing to disclose. Dr. Keszler is a consultant to Draeger Medical and has received research grant support from the company.
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