Ventilating difficult airways in the field
Automatic transport ventilators may improve ventilation rate, tidal volume and oxygenation for patients needing airway management and ventilator support
EMS providers perform a myriad of functions while attending to patients in the field. Perhaps the most critical and intensive set of tasks are identifying and managing the airway of a patient who is unable to spontaneously maintain patency. There are a wide range of airway tools and equipment available in the EMS marketplace to accomplish these tasks. This article will focus on tools and procedures that support the patient's ventilatory capacity.
Crash airway is a given in EMS
Out of hospital airway management should be approached with a "crash airway" mindset. Though no formal definition exists, most physicians consider a crash airway as one where one or more definitive interventions must be performed rapidly in order to preserve patency.
This definition encompasses all airway interventions outside the confines of a controlled operating suite. The more rapid the airway management intervention is required means a greater the likelihood of procedural failure. Therefore it is essential that EMS providers of all levels be proficient airway managers.
Identifying the difficult airway
Given the infinite range of airway conditions that can present during a medical emergency, it is critical to follow a process that can consistently and rapidly identify an airway that requires intervention. There are several airway algorithms in emergency medicine and anesthesia that have been published, including those by Levitan, Walls, Strayer and others .
During the patient assessment field care providers should ask and answer the following key questions:
1. What is the likelihood of airway failure?
It is a given that a patient who is unconscious and unresponsive has lost his ability to maintain his airway and will require one or more interventions. However, a heightened awareness of airway patency is needed for any patient who is not fully awake. A patient with altered mental status may abruptly block his airway with his tongue, secretions, or emesis.
Several medical conditions may result in the loss of upper airway patency, such as epiglottitis and anaphylaxis. The inhalation of hot gasses may result in the rapid onset of laryngeal edema. Other trauma mechanisms include a high cervical spinal cord injury, as well as penetrating or blunt trauma to the face or neck. In each of these cases, at least one provider should be tasked as the airway manager and continuously evaluate airway patency.
2. What are impediments to adequate airway control?
There are several anatomical findings that reduce the rate of airway management success. Creating an airtight seal with a mask is difficult in patients with large numbers of missing teeth, recessed chins, or full beards. A mask may need to be placed upside down in order to create a seal in such cases of unusual or difficult anatomic presentation. If a mask seal is not possible, the decision to place an advanced airway, such as an endotracheal tube or supraglottic airway, must be made quickly.
It may be difficult to position the head and neck for patients with a history of arthritis in the cervical region, patients who have an abnormal curvature of the upper thoracic spine, or patients who are obese. These patients may require support and elevation of the upper back using numerous blankets, sheets and or pillows to properly position the upper airway.
3. What airway resources are available?
While there may be dozens of different airway devices on the market, EMS providers can only use what is available to them at the time of the intervention. The resources available for airway management can also be limited by the number, training and scope of the personnel who are on the scene. The capability of a two person team is likely to be different, and more limited, than a crew of four, five or more available to help with procedures and equipment. The level of certification and licensure will also define what can and cannot be utilized during an airway procedure.
In addition, the availability of advanced airway management at a nearby emergency medical facility may provide an additional resource for EMS providers who are unable to establish or maintain a patient's airway.
Ventilating a patient
Manually ventilating a patient with a bag mask is an airway procedure that is commonly performed by all levels of EMS providers. A self-inflating vinyl bag is squeezed by hand to deliver a volume of air to the patient via positive pressure. Supplemental oxygen can be delivered through the bag, raising the oxygen concentration in each ventilation from 21 to nearly 100 percent.
The bag is attached to a soft mask that is placed over the patient's mouth and nose. An airtight seal is created between the patient's face and the mask by placing the thumb and one or more fingers of one or two hands over the mask, and pulling the patient's jaw upward into the mask.
Initially thought to be a simple technique, operating a bag mask it is anything but. Since bag masks have no controls in place for volume and rate, it is entirely dependent upon the provider to be accurate in providing ventilations to the patient at both and adequate volume to cause chest rise and at an appropriate rate. Several studies have shown that even experienced EMS and hospital providers have difficulty providing consistent and reliable ventilations with a bag mask [2, 3, 4, 5]. Excessive rates, hyperventilation, and depths of ventilation are common errors and can cause harm by eliminating excessive carbon dioxide from the body, which in turn reduces brain and coronary perfusion secondary to vasoconstriction. Excess air from over ventilating the patient can also increase the risk of gastric insufflation and vomiting.
Automatic transport ventilators – is it time?
Flow restricted, oxygen powered devices (FROPD) have been in existence for many decades. While early-generation devices were crude in design and use, current versions are more sophisticated and can be tailored to both the patient's needs and the provider's abilities.
Modern devices, called automatic transport ventilators (ATV), are small and lightweight. Precise ventilation rates and amounts of air, the tidal volume, can be delivered to the patient. Several models can also provide continuous or bi-level positive airway pressure (CPAP or BiPAP), useful adjuncts in managing pulmonary edema secondary to hypertension, or bronchoconstriction found in asthma or COPD.
ATVs have a variety of visual and audible warning devices to signal when airflow is blocked. Troubleshoot a ventilator alarm with the DOPE mnemonic:
Dislodged: Is the endotracheal tube or supraglottic airway dislodged?
Obstructed: Is the tube obstructed by blood, emesis or mucous?
Pneumothorax: Are bilateral breath sounds present, clear and equal?
Equipment: Is the ventilator correctly connected to the airway?
There are several potential advantages to ATV use over manual bag mask. In the intubated patient, the ATV takes over the function that formerly required a dedicated provider. When an ATV is used with a mask the rescuer can fully focus on maintaining an airtight mask seal.
Breath rate and volume are discretely controlled, providing consistent gas exchange and reducing the chance of lung overfilling, lung injury and gastric distension. Supplemental oxygen can be titrated to reduce the chance of hyperoxemia.
There are limitations to ATVs. ATVs are contraindicated when the patient's airway is obstructed or in patients with pneumothorax. Because they are oxygen powered, an adequate supply of oxygen must be immediately available. A bag mask should be kept nearby in case oxygen tanks need to be changes.
ATVs are also contraindicated in children. Check the manufacturer's guidelines and recommendations for an age or weight-based limitation for use.
Lung compliance cannot be felt by the rescuer when an ATV is in operation. Similarly, tube displacement cannot be detected by an ATV. Finally, the assembly that connects to the mask or endotracheal tube can be bulky and difficult to secure during transport.
ATVs have been used successfully in critical care and air medical transport environments for many years. EMS systems are increasingly using ATVs for scene calls.
Using an ATV requires training and practice to apply the equipment quickly and reliably. However, once in place, an ATV can free up a team member to perform other patient care tasks during transport.
Identifying and managing a crash airway can be stressful. EMS providers must be well-versed in the practice of airway management and capable of using every device in their airway toolboxes. The increasing use of automatic transport ventilators to better manage a patient's ventilatory needs may signal another evolution in the field management of out of hospital airway practice.
1. Life in the Fast Lane. Difficult Airway Algorithms. http://lifeinthefastlane.com/ccc/difficult-airway-algorithms/ retrieved 12/17/2015.
2. Aufderheide TP, Sigurdsson G, Pirrallo RG, Yannopoulos D, McKnite S, von Briesen C, Sparks CW, Conrad CJ, Provo TA, Lurie KG. Hyperventilation-induced hypotension during cardiopulmonary resuscitation. Circulation 2004: 109:1960-1965.
3. Lee HM, Cho KH, Choi YH, Yoon SY, Choi YH. Can you deliver accurate tidal volume by manual resuscitator. Emergency Medicine Journal 2008: 10:632-634.
4. Bassani MA, Filho FM, de Carvalho Coppo MR, Marba STM. An evaluation of peak inspiratory pressure, tidal volume, and ventilatory frequency during ventilation with a neonatal self-inflating bag resuscitator. Respiratory Care 2012:57:525-530.
5. Maharjan, R. K., R. P Aacharya, and P. N. Prasad. "Impact Of Duration Of Prolong Manual Bag Ventilated Patients In The Emergency Service." Journal Of Institute Of Medicine 36.2 (2014): 57-65.