Early detection of dysphagia after stroke is an important part of acute stroke management.
Diagnosis of dysphagia begins with suspecting its presence. When dysphagia is suspected, patients with high risk should be screened by means of simplified bedside swallowing tests.
Videofluoroscopy (VF) and fiberoptic endoscopic evaluation of swallowing (FEES) are well- validated investigations of swallowing and they are considered as gold standards for assessment of swallowing.20, 99 However, the most frequently used swallow test is the bedside clinical swallowing assessments. Availability of VF and FEES is limited universally in many clinical settings in which stroke patients are managed. Therefore the bedside clinical swallowing assessments (BSA) have become widely used initial tests to screen for dysphagia.
The assessments are perceived as simple, quick to perform and can be repeated frequently.20 The bedside swallowing tests are gag reflex, water swallowing test and pulse oximetry.19, 100
2.12.1 Fiberoptic endoscopic evaluation of swallowing (FEES) is safe and effective for assisting in swallowing evaluation. The patient is seated comfortably. A flexible fiberoptic endoscope is introduced transnasally to the patient's hypopharynx where the clinician can clearly view laryngeal and pharyngeal structures. The patient is then led through various tasks to evaluate the sensory and motor status of the pharyngeal and laryngeal mechanism. Food and liquid boluses are given to the patient so that the integrity of the pharyngeal swallow can be determined. Information obtained from this examination includes ability to protect the airway, the ability to sustain airway protection for a period of several seconds, the ability to initiate a prompt swallow without spillage of material into the hypopharynx, timing and direction of
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movement of the bolus through the hypopharynx, ability to clear the bolus during the swallow, presence of pooling and residue of material in the hypopharynx, timing of bolus flow and airway protection, sensitivity of the pharyngeal/laryngeal structures and the effect of anatomy on the swallow.101-103
2.12.2 Videofluoroscopy (VF) is an X-ray that looks at the way swallowing works. The studies are captured using fluoroscopy in video or digitized format that allows detailed analysis of the oropharyngeal swallowing process. The patient is seated in front of an X-ray machine. Earrings, necklaces and zipped tops are removed from the patient before the test as they can interfere with the X-ray image. Food and drinks, mixed with contrast (Barium), of different consistencies are given to the patient to swallow. The x-ray machine is only turned on during swallowing so that the patient does not get too much radiation. All studies are started with the patient in the lateral view where aspiration is most efficiently detected, and then finished with an anterior-posterior view to assess swallow symmetry and vocal cord function. A video recording is also made during the test. The procedure takes about 30 minutes.104
2.12.3 The pharyngeal reflex or gag reflex is a reflex contraction of the back of the throat evoked by touching the soft palate or sometimes the back of the tongue. The afferent limb of the reflex is supplied by the glossopharyngeal nerve (cranial nerve IX), which inputs to the nucleus solitarius and the spinal trigeminal nucleus, and the efferent limb is supplied by the vagus nerve (cranial nerve X) from the nucleus ambiguus.105 Studies have suggested that an absent gag reflex is predictive of aspiration106-108 but refuted by others.109, 110
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2.12.4 Pulse oximetry is a noninvasive method of bedside swallow testing.20, 111 Desaturation during swallowing may help to identify aspiration in stroke patients. It has been suggested that aspiration causes reflex bronchoconstriction and therefore ventilation-perfusion imbalance, leading to hypoxia and desaturation.112 Others have suggested that abnormal swallowing leads to poor breathing and ventilation-perfusion mismatching because of reduced inspiratory volumes.113 Using pulse oximetry for the assessment of dysphagic patients is based on the principle that reduced and oxygenated hemoglobin exhibit different absorption characteristics to red and infrared light emitted from a finger (or earlobe) probe.111 Oxygen desaturation ≥2% was considered to be clinically significant.111, 114-116
2.12.5 Difficulty in drinking small volumes of water has been used to screen for dysphagia in stroke patient.59, 106, 110, 116-118 Presence of involuntary cough, choking, change in voice
quality, drooling, respiratory difficulty and delayed swallowing are considered to be abnormal and indicative of swallowing difficulty.20, 72, 100, 119, 120 Studies showed that sensitivity of water swallowing test in detecting swallowing difficulty ranged from 20.8% - 85.5% and specificity ranged from 50% -98.75%.114-116, 121, 122 A study showed that sensitivity and specificity of cough/ voice change in detecting dysphagia using water swallowing test were 72% and 67%
respectively.123 The sensitivity of swallowing speed in detecting the swallowing dysfunction was 85.5%, and the specificity was 50%.122 The sensitivity of using choking or wet-horse voice as the sole factor for predicting the presence of aspiration was 47.8%, while the specificity was
91.7%.122Some studies combined both water swallowing test and measurement of oxygen desaturation using pulse oximetry to screen for dysphagia. The sensitivity and specificity were found to range between 94.1% - 100% and 62.1% - 70.8% respectively.114-116
36 2.13 Effect of dysphagia on stroke outcome
Studies have shown that morbidity and mortality after acute stroke is increased if swallowing problems are present even in patients with no reduction in level of consciousness.27, 59, 124-127 A study showed that mortality in stroke patients with dysphagia was 37%.124 Another study reported this to be as high as 42%.127 Conditions that result from swallowing difficulties in stroke patient are aspiration pneumonia,19, 27, 59, 124 dehydration,59, 117 deterioration in nutritional status and increase in length of hospital stay.27, 126. Aspiration pneumonia was particularly associated with increased risk of both short-term and long-term mortality.53, 55, 56, 128 It was reported that approximately 1 of 3 early deaths among stroke patients are related to pneumonia.53, 55
Aspiration pneumonia, which develops as a result of entrance of foreign materials into the bronchial tree causing chemical pneumonitis with superimposed bacterial infection, is different from hypostatic pneumonia which is one of the complications of prolonged bed rest. It usually occurs in those with debilitated disease who remain recumbent in the same position for a long period. The pneumonia results from infection developing in the dependent portion of the lung due to decreased ventilation of these areas, with resulting failure to drain bronchial secretion.