Airway management in the prehospital environment is messy business.
A recent study of prehospital intubation in trauma found that 44.3 percent of the patients had gross contamination of the airway at the time of intubation (most commonly blood, followed by vomit, teeth or brain).
While the literature is divided on whether prehospital intubation increases the risk of aspiration versus ER intubations, aspiration can have significant short and long-term sequellae that all providers must be aware of.
WHAT IS ASPIRATION?
Aspiration in the context of prehospital airway management can be divided into three categories: massive aspiration, pneumonitis and pneumonia.
Massive aspiration implies a partial or complete airway obstruction and involves the rapid onset of hypoxia and dyspnea.
Aspiration pneumonitis is an acute response to non-infectious aspirated materials and is also known as Mendelson syndrome. Classically, it is described as the inflammatory response to lung tissue exposed to acidic, but essentially sterile, gastric contents.
In contrast, aspiration pneumonia represents an inflammatory reaction to microbes in the aspirated material. A specific subset of aspiration pneumonia, ventilator associated pneumonia (VAP) is likely caused by the migration of oral flora into the lung parenchyma and is of greatest concern after 5 to 7 days of intubation.
Signs of massive aspiration are usually obvious, such as visible contamination of the airway, along with signs of diffuse alveolar infiltrates such as dyspnea, tachypnea, adventitious breath sounds and hypoxia.
Additionally, increasingly higher pressures are required for ventilation—a reflection of the aspirates effect on lung compliance. Aspiration pneumonitis can be much more insidious and symptom severity and onset is dictated by the volume and acidity of the aspirated substance.
Small volume aspiration can lead to vague symptoms such as recurrent cough, hoarseness and dysphagia that make ‘silent aspirators’ difficult to detect but common in high-risk patients like those who are tube fed or have GI obstructions. More significant aspirations can lead to signs of bronchospasm as well as dyspnea and bloody or frothy cough.
Aspiration pneumonia requires signs of infection such as fever or system signs of sepsis and is unlikely in the context of aspiration secondary to prehospital airway management, as the infection takes time to develop. The likelihood of developing aspiration pneumonia from aspiration pneumonitis is dependent on a number of variables, for example aspirated vomit is more likely to lead to pneumonia than aspirated blood.
Many of the mainstays of aspiration prevention, such as fasting and premedication, are not realistic in the 911 environment.
Minimizing gastric distention can prevent an increased risk of regurgitation. To accomplish this, all patients should have bag-valve mask ventilations performed at the minimum pressure required to provide adequate tidal volume and maintain oxygenation.
Optimizing airway positioning and the use of airway adjuncts such as oral or nasopharyngeal airways can decrease the pressures required during ventilation. Similarly, supraglottic airways (SGA) also can help reduce airway pressures as well as help seal the esophagus from unwanted air entry to the stomach and it is important to use a larger gastric opening for aspiration management.
If time allows, a nasogastric (NG) tube is effective at decreasing gastric contents. They do not impact direct laryngoscopy and new generation SGA permit the passage of NG tubes without affecting the seal.
Cricoid pressure (Sellick’s maneuver) has become a dogmatic part of airway management. This external pressure is applied to the cricoid with the intent to occlude the opening of the esophagus and decrease regurgitation.
Recently, much debate has revolved around the effectiveness of the intervention. Arguments against this suggest the procedure is ineffective at preventing aspiration and makes intubation more difficult
During laryngoscopy, inadequate sedation can lead to cough and gag, increasing the risk of aspiration. Rapid sequence induction (RSI), the administration of an induction agent and a neuromuscular blocking agent, is the gold standard for intubating a patient with a full stomach.
Absent the ability to RSI in the field, it falls to the clinical decision making of the provider. If there is a high risk of vomiting and adequate sedation cannot be achieved in the prehospital setting, then a less invasive method of airway management maybe a safer option for the patient.
Once the patient has been intubated, simple interventions such as elevating the head of the bed (30 o to 45o), maintaining appropriate ETT cuff pressures (21-29cmH20) as well as suctioning the oro-pharynx before deflating the ETT cuff can decrease the risk of ventilator associated pneumonia.
Massive aspirations in the prehospital environment are airway obstructions and should be treated as such. Suction can be performed orally, under direct laryngoscopy or endotracheally. Hypoxia, in the setting of aspiration, should be managed by increasing both the concentration of oxygen and positive end expiratory pressure (PEEP).
Antibiotic therapy is not typically indicated in the prehospital environment as it is generally reserved for those patients who go on to develop fever and leukocytosis.
Minimizing gastric distention can prevent an increased risk of regurgitation. Optimizing airway positioning and the use of airway adjuncts such as oral or nasopharyngeal airways can decrease the pressures required during ventilation, a nasogastric (NG) tube is effective at decreasing gastric contents.