This clinical review feature article is presented in conjunction with the Department of Emergency Medicine Education at the University of Texas Southwestern Medical Center, Dallas.
Functional residual capacity (FRC):The volume of air present in the lungs at the end of a normal, quiet (passive) respiration.
Gastric insufflation:When air inadvertently enters the stomach with the use of a bag-valve mask.
Hypercapnia:Increased amounts of carbon dioxide in the blood.
Positive end-expiratory pressure (PEEP):A form of positive airway pressure therapy applied during exhalation.
Pulmonary barotrauma:Lung damage that occurs from rapid or excessive pressure changes; for this article, it_s used in reference to ventilator patients who are exposed to high airway pressure, but it can also occur in scuba and other forms of diving.
Tidal volume (Vt):The volume of air moved into or out of the lungs during a normal breath, assessed by observing the rise and fall of the chest.
You respond to a private residence for a child reported as having "difficulty breathing." You arrive to find an eight-year-old girl who_s on a ventilator and appears to be in obvious respiratory distress. The mother reports that her child has been ventilator dependent for three years, secondary to an anoxic brain injury. She says her daughter has been acting anxious for several hours and seems to be struggling to breathe. She_s concerned because the same thing happened last year, and her daughter was admitted to the ICU for four days. She says she has suctioned copious amounts of thick green sputum from her daughter_s tracheotomy (trach) during the past six hours.
On exam, you observe substernal and intercostal retractions. The patient is not interactive with the environment, and the mom reports that this is very unusual. On auscultation of the patient_s lungs, diffuse coarse breath sounds are heard bilaterally. The patient_s skin color is pink. She is tachypneic at 34 breaths perminute and has an SpO of 86%. The monitor reveals sinus tachycardia at a rate of 118 and a BP of 110/66. You package the patient, deciding to bring along her ventilator, and transport her to the nearest facility about 20 minutes away.
Four minutes into transport, the patient begins to rapidly deteriorate. Her respiratory rate drops to the ventilator-driven rate of 16, her SpO drops to 80%, and she now opens her eyes only to painful stimuli.
You know you need to intervene. You wonder if you should try adjusting the ventilator to increase her respiratory rate ortidal volume (Vt)or attempt to suction her trach like her mom had done earlier. Maybe it would be a better idea to use a bag-valve mask (BVM) to create a tight seal over her mouth and nose and manually ventilate her. You realize it_s going to be a long 16 minutes to the emergency department.
In the U.S., approximately 470,000 children are admitted to hospitals for respiratory conditions every year. Of these children, nearly 11,000 are intubated and receive mechanical ventilation at some course in their hospital stay. And with advances in technology, more children with chronic respiratory failure are being discharged on home ventilators.
The field assessment and treatment of pediatric patients with respiratory dysfunction is a complicated task, especially when the child is dependent on technology to breathe. The EMS provider_s understanding of the differences between the adult and pediatric respiratory systems, the thoroughness of their patient assessment, the patient_s chronic underlying conditions, whether the protocols concerning ventilation methods were followed properly, and the provider_s ability to interface with the technology that supports
the child_s life, all contribute to the outcome of the call.
Additionally, the majority of cardiopulmonary arrests in children are the result of progressive respiratory decline, making the EMS provider_s ability to assess and treat respiratory dysfunction even more important.
Pediatric Airway Anatomy
Every provider must understand the anatomic and physiologic features unique to the pediatric population. Many of these features change as a child grows, affecting the child_s presentation. Here, we_ll focus on the anatomy of the upper airway structures that affect the success of endotracheal intubation, as well as other areas influencing patient presentations and treatment decisions.
The upper airway consists of all airway structures superior tothe larynx. From a practical standpoint, the structures of the upper airway, or structures that influence it, are largely responsible for airway management difficulties. These structures also influence patient presentations. Infants and younger children have larger occiputs that put the airway out of alignment when the child is lying supine on a flat surface. They also have sucking pads (dense fibrous tissuein the cheeks) that make the oral passage highly resistant. Theirnecks are shorter, and the large, floppy epiglottis is higher in theneck. In fact, at birth, the larynx is situated at C1ÏC4, changing positions to C4ÏC7 in adulthood. The larynx is cone-shaped, with the narrowest region at the level of the cricoid ring, as opposed to the vocal cords, which is the narrowest region of the adult upper airway. The pediatric airway is smaller; vocal cords have anterior angulations (vocal cords are slanted), and arytenoid cartilages are prominent.
Airway sizes may vary unpredictably among pediatric patients of the same age and weight. For this reason alone, EMS personnel should always carry at least three different-sized endotracheal tubes (ETTs). Along with airway size differences, congenital syndromes (e.g., Pierre Robin, Down syndrome, Kenny-Caffey, Cri du chat) can further confound the scenario, creating major difficulties in airway management.
Pediatric patients between the ages of six and 12 years are more likely than other age groups to survive an illness or injury that requires the use of mechanical ventilation during transport. In comparison to the adult brain, the pediatric brain has a higher percentage of white matter than gray matter, thus explaining a greater resilience to severe blunt force trauma.
Children have a higher basal metabolic rate, higher O consumption/CO production, and thus higher ventilatory requirements. Further, the lungs have a natural tendency to collapse, while the chest wall has a natural tendency to remain in its neutral anatomical position (as if no forces were acting on it). Because the healthy lung is more compliant than the chest wall, the lungs do not collapse and do retain a certain amount of air; this is thefunctional residual capacity (FRC).Therefore, less pressure is required to ventilate due to the compliance of both the lungs and the chest wall. The younger the child, the lower the FRC, which results inthe rapid deterioration often seen with young children suffering from respiratory dysfunction.
The diseased lung loses compliance and has the potential of becoming less compliant than the chest wall in the very young. This fights the outward excursion of the chest wall in normal breathing, accounting for the retractions often seen in children with diseased lungs and those in respiratory distress. Ventilation becomes much more difficult in children with decreased lung or chest wall compliance.
Ventilator-dependent children tend to have difficulty executing respiratory drive, respiratory effort or both. These patients are typically connected via a trach tube placed into an existing stoma. They may be completely ventilator dependent, or they may need only occasional support when the respiratory system is stressed, asoccurs with infections or during sleep periods. Regardless of the presenting condition, personnel must decide whether to support ventilation manually or transport the child with the home ventilator. In order to make that decision, it helps to understand the basics of how mechanical ventilators work.
There are two major settings on mechanical ventilators used in homes: ventilator mode and volume- or pressure-targeted delivery.Tables1and2 outline the differences between these settings. Two types of targeted delivery methods are preferred for pediatric emergency transport. The first, volume pressure ventilation, delivers a preset tidal volume (600 mL/per breath), withpulmonary barotraumabeing the most common complication if the volume is set too high. The second is pressure-driven ventilation, which continuously delivers gas when functioning in the preset pressure mode. However, it tends not to deliver enough tidal volume, which canbe dangerous to an already compromised pediatric patient.
Pressure ventilators are used to reduce the risk of pulmonary barotraumas in neonates and infants. In the older pediatric group,volume ventilators are preferred during transport. Its capabilitiesallow it to control and prevent alveolar collapse upon exhalation.
Some models are currently favored for use during transport because of their versatility for both invasive and non-invasive monitoring. Baseline pressure is stabilized by a back-up flow when thepositive end-expiratory pressure (PEEP)mode is on, making it highly efficient for pediatric transport use. The downside of using these models for transport is that oxygenation worsens due to air trapping that results from fast respiratory rates and increased airway resistance. Such models as the Bear Cub BP-2001 Infant Ventilator are mainly designed for use as pressure ventilators, whichis favorable for patients exhibiting signs of gastric distention.
During transport, oxygen or ventilator tubing might inadvertently get kinked. For this reason, a spring-loaded pressure-relief valve helps protect the patient from increasing pressures that might occur with tube blockage. Nearly all models have built-in safety mechanisms to minimize patient injury.
Volume-cycled ventilators and pressure-limited ventilators have advantages and disadvantages. The main advantage of volume-cycled ventilators is that they can consistently deliver a set volume to the patient. Their main disadvantage is that they can_t correct areas of atelectasis because collapsed alveoli need even greater pressure to open.
With pressure-limited ventilators, proper volumes are achieved by increasing the peak inspiratory pressure and lowering the flow rate. Unfortunately, pressure-limited ventilation is not tidal volume controlled. Tidal volume changes are triggered automatically as the patient_s airway resistance and lung compliance change. A decrease in lung compliance results in a corresponding and equal reduction in the tidal volume delivered. These ventilators tend to be a better choice for EMS, mainly due to their ease of use, fewer working parts, and the reduced likelihood that they_ll inflict pulmonarybarotraumas to the patient because of their limited pressure output.
The mechanical ventilators mentioned have the same indications for pediatric transport use as for use in the adult population. Acute respiratory acidosis, apnea or impending respiratory failure are the top three indications for mechanical ventilation. Patients in cardiopulmonary arrest with underlying etiologies, including chronic pulmonary infections, trauma, near drowning or drug overdose, should receive mechanical ventilation when possible.
A new method of mechanical ventilation, neural ventilatorassist, is in the clinical trial stage of research. It aims to retrain the brain_s respiratory center to activate and take control of the mechanical ventilator via complete neural control. It gives the patient freedom to breathe spontaneously while remaining ventilator dependent. This could lead EMS providers to prefer mechanical instead of manual ventilation during transport, especiallywhen transporting a long-term patient to an acute-care facility.
Many home ventilators are capable of being synchronized to a pediatric patient_s specific respiratory needs and breathing pattern. Ventilator settings allow for more consistent control of ventilation rate, tidal volume and PEEP. These settings reduce negative metabolic outcomes and increase patient comfort.
Efforts should be made to transport a pediatric patient on their ventilator as long as the home ventilator is functional, has an independent power source, and is capable of utilizing an alternative power source (e.g., an inverter), and the child is not demonstrating signs of respiratory compromise. When manual ventilation must be used, reasonable efforts should be made to transport theventilator with the patient.
No evidence exists to suggest that either manual ventilation with a BVM or mechanical ventilation provides better respiratory support to the pediatric patient during prehospital transport. Before deciding to use the BVM over a home or transport mechanical ventilator, the provider must consider the benefits and drawbacks.
If a BVM is used, it should be a self-inflating bag or an anesthesia bag. EMS systems usually require use of self-inflating bags, which don_t require a constant gas source. Additionally, they regulate maximum inspiratory pressure through a built-in pop-off valve, thereby reducing the likelihood of pulmonary barotraumas. The pop-off valve helps reduce the likelihood of life-threatening complications associated with positive-pressure ventilation, such as pneumothorax.
Manual ventilation by BVM requires minimal set-up time, and its frequency of use offers the provider a level of familiarity and comfort with utilization techniques. It may also allow for early identification of conditions, such as tension pneumothorax or trach tube obstruction, through changes in bag compliance.
However, the drawbacks include increased likelihood ofgastric insufflation and vagal response, especially in pediatric patients. In addition, hyperventilation by the EMS provider can lead to respiratory alkalosis cardiac dysrhythmias, hypotension and abnormal arterial blood gases.
Manual ventilation ideally requires additional transport personnel and is labor intensive, making it impractical during extended transports. The BVM tends to deliver inconsistent ventilation rates and volume due to differing application procedures and fatigue among providers. Providers may also find it difficult to synchronize BVM application with patients who are breathing irregularly.
An additional concern with manual ventilation is the inherent difficulty of pediatric intubation. Provider inexperience, variability of anatomy, and underlying conditions that usually present when faced with a ventilator-dependent child serve to make the intubations even more difficult. Due to the short airway, slight movements of the head can easily result in extubation in patients who have been orally intubated. Intubating through an existing stoma is often an option with ventilator-dependent children.
Many EMS systems don_t allow for pediatric intubation, although their protocols often fail to address ventilator-dependent children. Research suggests that manual ventilation with the facemask is frequently sufficient, especially in EMS systems with short transport times.
Whether manually ventilating through an ETT or with a well-fitting facemask, the provider must maximize control of the airway. This usually requires the use of a backboard, even when spinal injury is not suspected, to prevent misalignment of the airway and extubation.
It_s also recommended that additional personnel be employed when manually ventilating a patient by a facemask. This procedure often requires one person to squeeze the BVM while another maintains the seal of the facemask. In infants and young children, a tidal volume of 4Ï8 mL/kg should be delivered at a rate of 30Ï35 breaths per minute. In children with respiratory distress syndrome, tidal volumes should be decreased and respiratory rate increased to maintain partial pressure of carbon dioxide between 45 and 55. Permissivehypercapniamay help to prevent some lung injuries.
When deciding whether to transport a patient on a home ventilator, consider set-up time, portability, secure mounting and crew accessibility. Some ventilators require large amounts of pressurized oxygen or liquid oxygen systems in order to function.
During transport, a ventilator-dependent patient_s respiratory status may begin to deteriorate. In this situation, the provider should first readjust the airway and head position. The provider should then inspect the trach tube for dislodgement and apply suctioning techniques to clear any possible obstruction. If these efforts fail to resolve the patient_s distress, mechanical ventilation should be discontinued and manual ventilation initiated.
If EMS personnel decide to forgo mechanical ventilation in favor of manual ventilation, they should reassess the patient prior to removal from the ventilator at the time of initiating manual ventilation and every five minutes throughout transport. If possible, the patient_s own ventilator should be transported along with them, even in cases where manual ventilation is selected.
Transporting a patient on a home ventilator and manually ventilating both require a great deal of knowledge, skill and judgment. Fortunately, because family and other caregivers are often very familiar with the use of the child_s home ventilator and underlying conditions, we can often recruit their help, thereby providing an additional resource for the emergency care of the child.JEMS
James F. Goss,MHA, MICP, is program director and lead paramedic instructor for NCTI in Riverside, Calif. He_s also assistant professor of emergency medical care at Loma Linda University in Loma Linda, Calif., and a frequent contributor to JEMS. Contact him email@example.com.
Allen Patee,BS, is a senior medical student at Loma Linda University School of Medicine. He_s a graduate of Loma Linda University_s emergency medical care (EMC) program and had worked as an EMT/FF for San Bernardino County Fire Department prior to medical school. Contact him firstname.lastname@example.org.
Sarah Green,BS, CRT, RCP, is a respiratory therapist working for QRS Registry Inc. in Long Beach, Calif., and a graduate of Loma Linda University EMC program.
Diane Schoendienst,BS, MICP, has worked as an EMT-P/FF for Cal Fire Riverside County and American Medical Response, and currently works at the Loma Linda University Medical Simulation Center. She_s a graduate of the Loma Linda University EMC program.
Cynthia Navis,MICP, is a Los Angeles-based paramedic and an EMS educator for the National College
of Technical Instruction.