5.4 Aspiration Post ABI

Define aspiration.

1.    Entry of material into the airway below the level of the true vocal cords.

Aspiration is defined as “entry of material into the airway below the level of the true vocal cords”.  Since many patients with dysphagia do not aspirate, the two terms are not synonymous, although they are closely associated.

5.4.1 Incidence of Aspiration Post ABI

What is the incidence of aspiration post ABI?

The incidence of dysphagia in patients entering rehabilitation post-ABI ranges from 25-78%. This incidence has been shown to vary depending on the definition of dysphagia used and the acuity of the patient at admission. An incidence of 42-65% in patients admitted to an ABI rehabilitation unit has been observed in more recent studies.

Terre and Mearin7evaluated aspiration improvements in 26 patients at 1, 3, 6, and 12 months post ABI. Videofluoroscopic (VFS) results indicate that aspiration decreased for the majority of patients during the 12 month period following their injury.  For the majority of patients the most significant changes were seen at the 3 month evaluation period.

O’Neil-Pirozzi et al.8studied 12 patients all of whom were trached.  Patients successfully completed a modified barium swallow (VMBS). Only 3 patients aspirated on some of the various liquids introduced to the patients. These three patients were either in a minimally responsive state or a vegetative state at the time of testing. All patients were given various oral exercises, or taste and thermal stimulation to improve swallowing.

Mackay et al.9performed  a series of VMBS studies on 54 young severely brain injured patients, an average of 17.6 days post-injury and noted a 61% incidence of dysphagia. Of these patients 41% aspirated. Other swallowing abnormalities included loss of bolus control (79%), reduced lingual control (79%), and decreased tongue base retraction (61%) delayed trigger of swallowing reflex (48%), reduced laryngeal closure (45%), reduced laryngeal elevation (36%), unilateral pharyngeal paralysis (24%), absent swallow reflex (6%) and cricopharyngeal dysfunction (3%)9.

Schurr et al.10conducted beside evaluations in 47 patients. Of these, 31 were admitted to the VMBS study. VMBS results indicate that 22 of the 31 patients aspirated during feeding. Five patients had laryngeal penetration and aspiration was observed in another 8. All responded to a modified diet.

5.4.2 Silent Aspiration

Define silent aspiration.  How common is it following ABI?

  1. Penetration of food below the level of the true vocal cords, without cough or any outward sign of difficulty. 
  2. The incidence of silent aspiration in ABI patients has not been well documented. 
  3. Such cases may be missed in the absence of VMBS studies.

Aspiration cannot always be diagnosed by a bedside examination.  Patients may aspirate without outward signs. “Silent aspiration”, is defined as “penetration of food below the level of the true vocal cords, without cough or any outward sign of difficulty” 11. Detailed clinical swallowing assessments were shown to under diagnose or to miss cases of aspiration 12-14.  Silent aspirators were considered to be at increased risk of developing more serious complications such as pneumonia.  Silent aspiration should be suspected in the ABI patient with recurrent lower respiratory infections, chronic congestion, low-grade fever or leukocytosis 15. Clinical markers of silent aspiration may include a weak voice or cough or a wet-hoarse vocal quality after swallowing. Lazarus and Logemann 16identified aspiration in 38% of their TBI patient group, noting many of these patients, despite aspirating, did not produce a reflexive cough and they required prompting to clear aspirated material 6. In a more recent study by Terre and Mearin7, they found approximately 33% of their subjects were silent aspirators. Dietary changes were made to reduce the risk of aspirating. For many, issues with aspiration seemed to resolve within the 12 months of the study.