Respiratory failure is the inability of the lungs to perform the vital function of gas exchange, and may be caused by an inability to either obtain sufficient oxygen or eliminate carbon dioxide. Numerically, respiratory failure may be defined on arterial blood gas measurement as hypoxemia, with a PaO2 <60 mmHg, or as hypercarbia, with a PaCO2 >45 mm Hg.1 Acute respiratory failure may be divided into four types. Type 1 respiratory failure is caused by acute hypoxia, and may be seen in patients with pulmonary edema, pneumonia, pulmonary hemorrhage, or acute respiratory distress syndrome. Type 2 respiratory failure may be seen with hypoventilation and an inability to rid the body of carbon dioxide. Examples of disease processes where this may be seen include central nervous system disorders where the respiratory drive is diminished, neuromuscular disorders where the muscles of respiration are not sufficiently able to produce ventilation, as well as in pulmonary conditions such as pneumothorax, airway obstruction, or pleural effusions. Significant atelectasis is the cause for Type 3 respiratory failure, and is most commonly seen after mechanical ventilation. Type 4 respiratory failure is seen in patients who have hypoperfusion of the muscles of respiration caused by another process, such as shock.2 Identifying the incidence of acute respiratory failure in the United States is extremely difficult but has been estimated near 140 cases per 100,000 individuals over the age of 5. Of the patients with acute respiratory failure, approximately 36% will not survive to hospital discharge. There seems to be a correlation with increased mortality seen in patients with increase in age, presence of multisystem organ failure, cancer, underlying liver disease, and HIV infection.3
Describe the causes of respiratory failure and anaphylaxis.
Describe interventions used in the prehospital environment to treat respiratory failure and anaphylaxis.
Delineate equipment useful in the prehospital management.
Outline some easy-to-use mnemonics for airway assessment in the field.
Describe unique challenges encountered in the prehospital environment.
Delineate medications that are appropriate for use in airway interventions in the prehospital environment.
There are many causes of acute respiratory failure, and oftentimes more than one in any given patient. Understanding the underlying disease process may better direct treatment and management of the patient in both the prehospital and hospital environments. Appropriate early interventions may have a significant effect on patient outcome and subsequent management.
Communication from the medullary respiratory center to the muscles of respiration is crucial in the mechanics of respiration. Disruption of neurotransmission may occur by several mechanisms. Severe intoxication or overdoses may decrease the intrinsic capability of the medullary respiratory center to function. Environmental clues may allow for the detection of organophosphate induced respiratory failure, which occurs within the first 4 days of exposure. It is believed that the central nervous action of the organophosphate has a larger role inducing respiratory failure compared to the peripheral effect.4 Myasthenia gravis, an autoimmune disease with an incidence of approximately 18 individuals out of 1 million,5 may also present as respiratory distress. Other diseases, such as Guillain-Barre or Eaton-Lambert syndrome may also present with weakness of the respiratory muscles. Trauma may result in damage to the brain or the cervical spinal cord that may also disrupt neurotransmission. A vital capacity less than 20 mL/kg or peak inspiratory pressures greater than −30 cm H2O combined with bulbar dysfunction are strong predictors of which patients may require mechanical ventilation for neuromuscular dysfunction.6
Gas exchange in the pulmonary vasculature depends on diffusion of both oxygen and carbon dioxide across the alveolar membrane and may be affected by several conditions. Interstitial lung disease, such as pulmonary fibrosis or sarcoidosis in addition to others, may destroy and cause a reduction in capillary-alveolar units. Pulmonary embolism is another vascular process that can lead to respiratory distress and failure, depending on the thrombus location and size. Pulmonary embolism creates a ventilation/perfusion mismatch and can lead to hypoxia, with massive pulmonary embolism creating significant cardiac dysfunction. Additional vascular causes of acute respiratory failure can be related to pulmonary hypertension or iatrogenic interventions secondary to pulmonary artery dissection. This can be seen following catheterization as well as cardiac valve replacement. Other disease processes affecting blood flow through the pulmonary vasculature include right-to-left mechanical shunts and may be found during a workup for another pathological finding, such as an ischemic stroke.
One of the challenges of prehospital patient care is some of the austere environments that may be encountered. Working in enclosed environments with limited air ventilation, some patients may have exposure to hypoxic environments or be exposed to chemicals which may alter the body’s ability to appropriately exchange carbon dioxide and oxygen. Poisoning by carbon monoxide, a byproduct of fossil fuel combustion, may result from intentional or unintentional means. Carbon monoxide with an increased affinity for both hemoglobin and myoglobin, effectively decreases the amount of oxygen available for tissue delivery and can interfere with mitochondrial cytochrome oxidase. Carbon monoxide exposures account for approximately 15,000 emergency department visits and up to 500 deaths annually in the United States.7 Caring for patients exposed to carbon monoxide should focus on removing the patient from the environment while taking care not to unnecessarily expose prehospital providers. High flow supplemental oxygen should be administered and hyperbaric oxygen therapy, although controversial, may be indicated. Pulse oximetry may not be accurate in patients with carbon monoxide poisoning but an arterial blood gas with cooximetry will give more accurate values. Cyanide poisoning, commonly seen in fire-related injuries, can also result from iatrogenic exposure from prolonged nitroprusside infusion.8 The primary toxic effect of cyanide is inhibition of mitochondrial cytochrome oxidase.9 Several antidotes to cyanide toxicity exist, each having a unique mechanism of action and with varying degrees of side-effects from the antidote.10
Chronic obstructive pulmonary disease (COPD) is increasing in prevalence and incidence throughout the United States and contributes to approximately 5% of deaths annually. Tobacco smoking has been attributed in up to 75% of COPD cases.11 Airflow obstruction seen in COPD is not completely reversible and is caused by small airway disease as well as parenchymal disease in varying degrees. The hallmark of outpatient management for COPD has remained β-agonist as well as steroid therapy with supplemental oxygen needed in the more severe cases.12 Approximately 10% of patients with COPD who experience an acute exacerbation will require hospitalization. Etiology of exacerbations may be related to bacterial or viral infections, with Moraxella catarrhalis, Haemophilus influenza, and Streptococcus pneumonia being the most common organisms. Cardiac dysfunction may be seen as a concomitant disease process and may be the underlying process worsening respiratory status. In patients without an explained cause for the acute exacerbation, pneumothorax and pulmonary embolism should be considered, noting that pulmonary embolism may have a prevalence as high as 25% in unexplained exacerbations.13 Treatment for the acute exacerbation may require an increase in oxygen, inhaled β-agonist and anticholinergic, as well as systemic glucocorticoids, and possibly noninvasive positive pressure ventilation. Reactive airway disease, such as asthma, may affect individuals of any age, but has a higher prevalence among children than adults. Overall, the prevalence in the United States is slightly higher than 8% and increasing.14 Asthma symptoms occur when the airway diameter is decreased due to smooth muscle contraction, development of bronchial secretions and bronchial wall edema, as well as with vascular congestion. Exacerbations are due to a variety of causes including environmental temperature, exercise, as well as allergens. Management depends on the degree of the disease process, but typically includes short-acting β-agonists, anticholinergics, steroids, noninvasive positive pressure ventilation, and severe acute exacerbations may also include magnesium and/or endotracheal intubation and mechanical ventilation.15,16
With some patients, an acute presentation of respiratory distress or failure may be caused by a potentially reversible structural cause. For example, a patient with a spontaneous or traumatic pneumothorax may present with chest pain or dyspnea, which may progress rapidly to a tension pneumothorax. Aeromedical transportation is not an absolute contraindication when considering the entire clinical picture. If tension physiology is encountered, emergent thoracostomy is indicated, with some prehospital providers performing both needle and/or tube thoracostomy17 (Figure 34-1). Successful placement of a needle thoracostomy depends on several factors including length and physical properties of the catheter. Thoracostomy appears to have more of a role in penetrating thoracic trauma, but can also successfully be employed in blunt trauma.18,19
FIGURE 34-1.
Needle thoracostomy. Tension pneumothorax with return of air bubbling through blood out of a large-bore IV catheter placed through the anterior chest wall at the second intercostal space, midclavicular line. (Reproduced with permission from Corbett SW, Stack LB, Knoop KJ. Chest and abdomen. In: Knoop KJ, Stack LB, Storrow AB, Thurman R, eds. The Atlas of Emergency Medicine. 3rd ed. New York, NY: McGraw-Hill; 2010:chap 7.)
Reduction of the thoracic cavity volume, by either compression from the abdominal cavity as in severe cirrhosis with ascites or extrapulmonary thoracic conditions such as pleural effusions, may result in reduced total lung capacity and cause respiratory distress. Many of these conditions do not develop suddenly, but are more insidious. Understanding the underlying disease process allows for targeted therapy, although procedures such as thoracentesis and paracentesis are not performed in the prehospital environment, knowledge that they may be indicated may direct destination determination. Supportive measures including supplemental oxygen, patient positioning, and noninvasive positive pressure ventilation20,21 may assist in improving symptoms until definitive care can be obtained.
Pneumonia has the highest overall mortality of any infectious disease in the United States. Annually, approximately 5.5 million cases of community-acquired pneumonia are diagnosed with around 20% requiring hospitalization. Streptococcus pneumoniae remains the primary causative organism of bacterial pneumonia. One of the challenges in treating patients with pneumonia is the coinfection with other organisms as well as bacterial drug resistance.22 Patients with pneumonia may present with cough, sputum production, chest pain, or shortness of breath, with elderly patients having fewer or nonspecific symptoms.23 Management in the prehospital setting should focus on general supportive measures addressing hemodynamic stability and oxygenation. If the patient shows evidence of shock, appropriate measures should be employed including fluid resuscitation and possibly airway management as indicated.
Anaphylaxis is a Type 1 hypersensitivity immune-mediated reaction based on IgE-mediated effects with multisystem involvement including urticaria, angioedema, hypotension, or bronchospasm. Identified etiologies include food, medications (specifically antibiotics), as well as envenomation.24 Diagnosis of anaphylaxis is based on clinical presentation and history, with laboratory values having no clinical importance in the immediate treatment phase. Epinephrine administered intramuscular is the emergent intervention of choice with no absolute contraindication. Intravenous resuscitation with isotonic fluids and other medications including antihistamines and corticosteroids may be administered, but definitive treatment still relies on administration of epinephrine. Respiratory failure may be seen in anaphylaxis as a result of bronchospasm, angioedema, or hypotension with a systemic lack of perfusion.25
Prompt recognition of patients requiring respiratory support is crucial. Oftentimes, the history obtained from the patient or others will provide the most clues as to how patient care should be approached and which interventions, if any, will help improve symptoms. Identifying the underlying etiology of the respiratory distress may prove more challenging but is of secondary importance. Reviewing a patient’s medical history and obtaining an accurate list of medications for review may prove helpful. A patient may have wheezing on examination and review of their medications may show treatments for chronic obstructive pulmonary disease, congestive heart failure, asthma, or other etiologies that could guide management. Sometimes, patients may be in extremis and not able to contribute, but family members present may be able to help significantly. Environmental exposures are also good clues as to the underlying disease process. If the patient is at a chemical plant or found near a pesticide, this could easily direct management and help the prehospital providers take extra precautions so as not to contaminate themselves or anyone else. Removing a patient from an environment may be the simplest intervention needed to improve a patient’s symptoms. Clothing may serve as a reservoir for chemical agents, and these should be removed quickly. Physical examination is helpful in evaluating all patients, but especially those who are not able to contribute verbally or answer questions appropriately. Physical examination is not reliable to exclude pneumothorax or hemothorax, as patients still may have breath sounds.26 Reduced air movement may also not allow for breath sounds to be adequately auscultated. Work of breathing may change in patients who are improving or deteriorating necessitating serial observation and continuous monitoring.
Management of respiratory distress, insufficiency, and failure in the prehospital setting may be affected by the uncontrolled environment but has the potential to greatly improve patient outcome. A patient may require anything from supplemental oxygen to aggressive invasive airway control during treatment and transport. Continuous monitoring will allow the provider to determine if an intervention is sufficient or if more support is necessary. Prehospital airway management is an ongoing challenge, which requires close attention from EMS physicians.27
The use of oxygen is widely accepted in a variety of patient conditions. The routine use of pulse oximetry in the prehospital setting allows for identification of patients who are hypoxic and can guide therapy. The use of oxygen in patients with chronic obstructive pulmonary disease is still debated regarding the target oxygenation level with concern related to eliminating the hypoxic respiratory drive and worsening hypercapnia.28 Waveform capnography is another tool available to the prehospital provider to identify hypercapnia and initiate other treatments such as noninvasive positive pressure ventilation.
Select populations of patients with hypoxemic respiratory failure may benefit by noninvasive positive pressure ventilation (NIPPV) with a reduced intubation rate and decreases in intensive care unit stay and mortality29 and has been used and advocated for in the prehospital setting.30,31 NIPPV has been shown to reduce the need for intubation in patients with pulmonary edema, chronic obstructive pulmonary disease, and asthma.32 Individuals with COPD as well as acute pulmonary edema may benefit from continuous positive airway pressure (CPAP), a form of NIPPV. Utilizing CPAP for patients with severe acute pulmonary edema improves oxygenation,33 decreases hospital mortality, and decreases need for intubation.34 Overall hospital length of stay did not significantly decrease, but duration of intensive care unit stay did.35
In the event that a patient has decreased mental status, or will not tolerate other forms of airway support, invasive devices may be indicated. The classic airway involves placement of an endotracheal tube by direct laryngoscopy, but multiple other devices are becoming available to the prehospital provider.
Many different manufacturers have created various forms of blind insertion airway devices that are passed through the oropharynx and occlude the esophagus while allowing ventilation to occur. These devices are deployed quickly and can be used as a primary36 or backup airway device.37 In the case of cardiac arrest, these devices may be preferred, as placement does not require interruption of chest compressions.38
Endotracheal intubation is considered the gold standard for airway management. Prehospital intubation success has been reported with a rate as low as 50% and as high as 98%, with success increased by using rapid sequence algorithms.39 Video laryngoscopy is also becoming an option for increasing numbers of prehospital providers.40 There are several different video laryngoscopes available, and some have suggested this as a primary tool in patients with cervical spine injuries or expected difficult airway.41 Using a video laryngoscope during cardiopulmonary resuscitation with chest compressions may decrease the time needed for definitive airway control.42
Airway management in the prehospital environment is not always easily attainable. In some circumstances, multiple devices may be required to appropriately ventilate a patient. Surgical airway management has primarily been reserved as an option in the failed airway algorithm, and rarely is the primary method for obtaining an airway. A failed airway has been proposed as either the inability to ventilate and oxygenate a patient or three unsuccessful attempts at placement of an endotracheal tube by an experienced operator.43 It is important to note that in some circumstances proper bag-valve-mask ventilations may provide sufficient oxygenation and ventilation. A number of devices are commercially available to help perform a cricothyroidotomy from surgical kits to those using the Seldinger technique. Providers should be familiar with the technique and equipment available to them to obtain a surgical airway (Figure 34-2). Consider transtracheal jet ventilation in children under the age of 10 given anatomic differences between pediatric patients and adults.44
Many patients who utilize emergency medical services will do so because of respiratory distress and prehospital providers should be ready and capable to respond and care for them. Frequent reassessments should identify if further interventions are required in managing the patient with respiratory distress. Using equipment such as a pulse oximetry, electrocardiogram, end-tidal or waveform capnography may help direct therapy toward the underlying cause of respiratory distress. Evaluating the airway is crucial in managing patients in respiratory distress. If the patient can converse appropriately without distress, the airway is likely intact. If the patient has a muffled voice, one may suspect an obstruction. Stridor may be another physical examination finding that can signal a patient with potential airway compromise. Auscultation of the lungs may allow the provider to notice abnormal or diminished lung sounds. Medications such as bronchodilators may improve lung sounds as well as the patient’s symptoms. Absence of lung sounds, in addition to other physical examination findings, may signify a tension pneumothorax that may necessitate immediate intervention. Anaphylaxis and allergic reactions pose a challenge to prehospital providers. Provider safety is essential but the patient may need to be moved quickly from the environment in which they are found. Anaphylaxis is a true emergency, and when suspected, treatment should not be delayed.
Identification and preparation for airway management oftentimes will lead to a greater success rate. Understanding the limitations to airway management in the prehospital environment is crucial, as is evaluating the patient and circumstances surrounding the working environment. Several mnemonics45 have been developed for the rapid evaluation of potential difficulties in bag-valve-mask-assisted ventilations, intubation, blind insertion airway devices, and cricothyroidotomy.
All providers should maintain competence in the basic airway technique of bag-valve-mask (BVM) ventilation (Figure 34-3). The ability to effectively oxygenate and ventilate a patient using a BVM may be crucial and can be potentially lifesaving. Assist devices such as nasopharyngeal or oropharyngeal airway placement may improve the effectiveness of BVM ventilations. There are several rapid assessment areas that focus on setting up for success utilizing a BVM and can be easily remembered by the MOANS mnemonic.
Mask seal. Facial fractures or deformities, either congenital or from prior trauma, may impede the ability to form an airtight seal. Facial hair may also limit the quality of seal that can be obtained. Appropriate mask and bag size selection is also crucial, especially in the pediatric population.
Obesity or Obstruction may make ventilation more challenging and not provide for sufficient tidal volumes. Obese individuals have an increase in weight that must be displaced for adequate ventilation and may have redundant pharyngeal tissue that may lead to an airway obstruction. Other factors for consideration include the presence of foreign bodies or anatomical upper airway obstructions.
Age-related factors also need to be taken into account. Both the young and old may have a lack of supporting skeletal structures needed to create a good mask seal. Elderly patients may also lack muscle tone in the upper airway and tend to an obstruction.
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