|Photo courtesy Kimberly Clark Healthcare|
Mechanical ventilators are on the forefront of a revolution. They have evolved from small, pneumatically powered and pneumatically controlled devices to marvels of microprocessor technology capable of closed-loop control.1 This is especially important due to the rising need for mechanical ventilation across all patient populations. Pediatric mechanical ventilation is an area that requires a great deal of specialized care. Unfortunately, there is not yet a great amount of research in the field of pediatric mechanical ventilation. It is difficult to perform a randomized controlled study due to the low number of participants, wide disease variation, and age. For the most part, adult research is applied to teens, and neonatal research is adapted for children. The following procedures and concepts are ways to establish high-quality pediatric mechanical ventilation.
One of the most common reasons for ICU admission is the need for mechanical ventilation,2 often a result of patients being unable to maintain adequate work of breathing and going into respiratory failure, which can occur because of lung disease, congenital cardiac defects, neurological abnormalities, or multisystem organ failure/dysfunction, or secondary to the effects of surgery or cardiopulmonary bypass.2 Once the need for mechanical ventilation has been established, proper initiation and clinical management is imperative to achieve a good outcome.
Choosing the appropriate mode of ventilation is a major step toward successful ventilation. There is no data that clearly states which mode of ventilation provides the greatest benefit with the least risk to an individual pediatric patient.2 Some older ventilators were not equipped with mixed modes of ventilation. They had either pressure control or pressure support ventilation but not a combination of both. Pressure control is the mode of choice simply because that is what we as practitioners have always used, dating back to the time-cycled, pressure-limited ventilation of neonates. Pressure control with pressure support adapts well to the changes in pediatric breathing patterns. Having pressure as the control mode allows for safer ventilation, because there is direct control of the peak inspiratory pressures, and decelerating flow patterns can be utilized. Using synchronized intermittent mandatory ventilation (SIMV) will allow the patient to receive the inspiratory support needed on spontaneous breaths to overcome the resistance of the endotracheal tube, which can lead to an increase in overall patient comfort and possibly reduce the need for sedatives.
Pressure control allows the clinician to set a peak inspiratory pressure (PIP). Having direct control over the PIP is important to reduce the risk of barotraumas but may deliver inconsistent tidal volumes based on airway resistance and lung compliance. By using a lung protective strategy, if a tidal volume of 5 to 7 ml/kg is obtained, then adequate ventilation of the pediatric patient should occur. Tidal volumes can be measured on the ventilator, either at the expiratory valve, or at an external tidal volume analyzer that connects the ventilator circuit and the endotracheal tube. Compressible volume of the ventilator circuit should be taken into account when measuring tidal volumes.
|Figure. Decelerating flow waveform. Available at [removed]www.pedsanesthesia.org/newsletters/2000summer/images/Tidal.jpg.3[/removed]. Reprinted with permission.|
In pressure control, the use of a set inspiratory time allows for a decelerating flow pattern to be used (Figure).3 This will allow the patient to receive maximum flow at the initiation of inspiration. Inspiratory flow will decrease throughout the rest of the inspiratory phase. The rapid increase in inspiratory flow that occurs with decelerating flow leads to early filling of alveoli, sustaining alveolar pressure, thus potentially providing better alveolar recruitment and improving gas exchange throughout the lung.2 By improving gas distribution, lung compliance will improve and the risk for barotrauma will be reduced. The simple technique of using a decelerating flow pattern can vastly improve the comfort of pediatric patients.
Capnography is essential to proper pediatric ventilatory management, and is an easy way to assess ventilation based on trends, rises, and falls in the reading. If the end tidal CO2 is climbing or falling, then the patient’s lung compliance has changed and an intervention is needed. It is also helpful to note the reading on the capnograph just prior to any blood gas draws, to see how closely the capnograph is to the measured PaCO2. If the two values are extremely close, then it may reduce the need for frequent blood gas sampling.4 Capnographs are capable of monitoring more than just end-tidal CO2. Dead space is another key factor in managing pediatric patients. Dead space, or Vd/Vt, is the relationship between how much of the delivered tidal volume is participating in gas exchange at the alveolar level and how much is being trapped or not used in the rest of the airways.2 If the dead space increases, it can be due to atelectasis, pleural effusions, alveolar overdistension, increase in airway secretions, or airway obstructions. The Vd/Vt can become an easy way to forecast the progression of lung disease, and also the regression of lung disease.2
Alternative Modes of Ventilation
High-frequency oscillatory ventilation (HFOV) encompasses the use of high frequency, low tidal volume, and laminar flow to protect the lung and reduce the risk of barotraumas caused by conventional mechanical ventilation.5 Tidal volumes less the dead space volume of the patient are delivered during HFOV.2 The settings that need to be established for effective ventilation and oxygenation on HFOV are mean airway pressure, amplitude, inspiratory time, FiO2, and frequency. The ventilator will deliver 60 breaths per minute for every 1 Hz up to 900 breaths per minute. The Hz should be set to the highest level possible while still achieving adequate ventilation from a range of 3 to 15 Hz. HFOV has proven beneficial for patients requiring excessive PIPs on conventional mechanical ventilation and is used frequently in patients with acute lung injury and acute respiratory distress syndrome.2,5
Airway pressure release ventilation (APRV) is also an alternative mode. This mode may be beneficial to patients with chest trauma or ARDS, but there is limited data to support its use in the pediatric population.
Noninvasive ventilation is a major aspect in pediatric mechanical ventilation. The use of continuous positive airway pressure (CPAP) and bilevel positive airway pressure can reduce work of breathing, open collapsed airways due to atelectasis or obstruction, and reduce the rate of reintubation.
|Table 1. Minimal pressure support required for ETT size.|
Many feel that a limiting factor to liberation from mechanical ventilation is the overuse of sedation and analgesia. There is limited evidence to guide us in providing safe sedation, analgesia, and neuromuscular blockade of the pediatric patient.6 Practices vary widely. Some adult ICU drugs, like propofol, used off-label, may have significant side effects in the pediatric population.7 Find a successful regimen, protocolize it, and utilize it as consistently as possible.8 Proper assessment of neurological status and spontaneous respiratory mechanics require that sedation be lightened or even interrupted daily (for a “sedation holiday”). The level of sedation and paralysis should be assessed on a standardized scale such as “COMFORT.”9 Assessment of static respiratory mechanics may require an increase in sedation. Capnography may provide valuable monitoring for ventilation changes related to sedation.10 Ventilator settings must be adjusted to meet patient needs for comfort. Reduce patients’ sedation needs, discomfort, and dyssynchrony by assuring that the ventilator provides a timely response to their breathing effort with adequate flow and pressure transitions.
|Table 2. Respiratory rates required for extubation.|
Assessing a patient for extubation readiness can be a tedious process, but, if done properly, it can greatly reduce the rate of reintubations or the need for noninvasive ventilation. An extubation readiness test can determine many things, including an assessment of the patient’s respiratory mechanics, ability to maintain adequate ventilation and oxygenation, and overall breathing comfort while trying to overcome the resistance of the endotracheal tube.11 To start, the patient must be set at the minimal pressure support level according to the size of the endotracheal tube (Table 1). At minimal pressure support, the patient needs to achieve adequate spontaneous tidal volumes, usually at least 5 ml/kg. If they do not reach this volume, then there will be an increased risk of atelectasis, and respiratory distress post extubation. Another aspect of extubation readiness is the patient’s PEEP setting. PEEP should be set to 5 cm H2O or less prior to extubation. On this level of PEEP, the patient should show no signs of respiratory distress, including oxygen desaturation. The patient’s FiO2 should be set to 50% or less, and the patient needs to be able to maintain a SpO2 of 95% or greater. Since the patient is breathing spontaneously, a stable respiratory rate is key (Table 2). Another major aspect of extubation readiness is the patient’s level of sedation. It is imperative that all members of the health care team (doctors, nurses, physician’s assistants, pharmacists, etc) collaborate in the effort to extubate the patient. If the patient is oversedated and cannot adequately breath independently, then a consultation with the staff nurse and covering physician may be necessary to make the proper adjustments. If all these elements are achieved, the patient can be reasonably classified as ready to extubate.
Pediatric mechanical ventilation can be safely achieved through quality clinical care, attention to detail, and further research.
Brendan Lillie, BS, RRT-NPS, is staff therapist, Department of Respiratory Care, Children’s Hospital, Boston. Michael Jackson, RRT-NPS, is clinical educator, Department of Respiratory Care, Brigham and Women’s Hospital, Boston. For further information, contact [email protected]
- Branson RD, Johannigman JA. Innovations in mechanical ventilation. Respir Care. 2009;54: 933-47.
- Cheifetz IM. Invasive and noninvasive pediatric mechanical ventilation. Respir Care. 2003;48:442-51.
- Society for Pediatric Anesthesia. Summer 2000 Newsletter. Available at: www.pedsanesthesia.org/newsletters/2000summer/images/Tidal.jpg. Accessed December 22, 2009.
- Bullock Kevin. Continuous capnography: emerging applications in critical care. ADVANCE for Respiratory Care & Sleep Medicine. March 17, 2009. Available at: respiratory-care-sleep-medicine.advanceweb.com/Article/Continuous-Capnography.aspx. Accessed December 22, 2009.
- Randolph AG. Management of acute lung injury and acute respiratory distress syndrome in children. Crit Care Med. 2009;37:2448-54.
- Jenkins IA. Current United Kingdom sedation practice in pediatric intensive care. Pediatr Anesthesia. 2007;17:675- 83.
- Pate MFD, Steelman R. Questions unanswered: propofol use in the pediatric intensive care unit. AACN Adv Crit Care. 2007;18:248–52.
- Hartman ME. Efficacy of sedation regimens to facilitate mechanical ventilation in the pediatric intensive care unit: a systematic review. Pediatr Crit Care Med. 2009;10:246-55.
- lsta E, van Dijk M, Tibboel D, de Hoog M. Assessment of sedation levels in pediatric intensive care patients can be improved by using the COMFORT “behavior” scale. Pediatr Crit Care Med. 2005;6:58–63.
- McQuillen KK. Capnography during sedation/analgesia in the pediatric emergency department. Pediatr Emerg Care. 2000;16:401-4.
- Soo Hoo GW. Blood gases, weaning and extubation. Respir Care. 2003;48:1019-21.