Anesthesia and Increased Hypercarbic Drive Impair the Coordination between Breathing and Swallowing

Abstract

Background Coordination between breathing and swallowing helps prevent aspiration of foreign material into the respiratory tract. We examined the effects of anesthesia, and hypercapnia on swallowing-breathing coordination. Methods In a randomized controlled cross-over study, general anesthesia with propofol or sevoflurane was titrated using an up-down method to identify the threshold for suppression of the motor response to electrical stimulation of the forearm. Additional measurements included bispectral index, genioglossus electromyogram, ventilation (pneumotachometer), and hypopharyngeal pressure. During wakefulness and at each level of anesthetic, carbon dioxide was added to increase its end tidal pressure by 4 and 8 mmHg. A swallow was defined as increased genioglossus activity with deglutition apnea and an increase in hypopharyngeal pressure. Spontaneous swallows were categorized as physiological (during expiration or followed by expiration), or pathological (during inspiration or followed by an inspiration). Results A total of 224 swallows were analyzed. Anesthesia increased the proportion of pathological swallows (25.9% versus 4.9%), and decreased the number of swallows per hour (1.7 ± 3.3 versus 28.0 ± 22.3) compared to wakefulness. During anesthesia, hypercapnia decreased hypopharyngeal pressure during inspiration (-14.1±3.7 versus -8.7±2 mmHg), and increased minute ventilation the proportion of pathological swallows (19.1% versus 12.3%), and the number of swallows per hour (5.5 ±17.0. versus 1.3 ± 5.5). Conclusions Anesthesia impaired the coordination between swallowing and respiration. Mild hypercapnia increased the frequency of swallowing during anesthesia and the likelihood of pathological swallowing. During anesthesia, the risk for aspiration may be further increased when ventilatory drive is stimulated.

Swallow-breathing coordination during incremental ascent to altitude

“…Hypoxia has also been studied in nonnutritive swallow in newborn lambs which showed a decrease in frequency during quiet sleep (Duvareille et al, 2007). Interestingly, hypercapnia shifts swallows towards In and Ex-In (D’Angelo et al, 2014) while we found that hypocapnia with hypoxia shifts swallow toward In-Ex. In light of the present data, further studies may need to investigate swallow-breathing coordination not only with variation of respiratory drive but swallow drive as well.…”

“…Specifically, alterations in respiratory mechanics due to chronic obstructive pulmonary disease (Nagami et al, 2017; Pinto et al, 2017) and/or upper abdominal laparotomy can shift swallow occurrences to inspiration, potentially increasing risk of aspiration (Pitts et al, 2015b). Additionally, there is also limited evidence that alterations in blood gasses (i.e., oxygen [O 2 ] and carbon dioxide [CO 2 ]) can also increase the likelihood that swallow will occur during inspiration (D’Angelo et al, 2014), (Ghannouchi et al, 2013).…”

Mandibular advancement impairs swallowing ability more than head extension but less than mouth opening in the supine position

“…In previous studies of swallowing ability, EMG 11,12 , manometry 13,14 , timing of swallowing 14 , radiography 13 , or fibreoptic endoscopic evaluation of swallowing 15 was used. Radiography or manometry may be superior to electromyography; however, the insertion of a catheter can influence salivary secretion 16 .…”

Recent advances in understanding and managing postoperative respiratory problems

“…during hypercapnic respiratory failure) can lead to high transpulmonary pressure during inspiration, which increases lung stress. Supplementation of inhaled carbon dioxide was shown to reverse upper airway collapsibility induced by propofol 13 , but excessive hypercapnia increases the likelihood of pathological swallowing 14 . Thus, perioperative physicians need to balance their interventions to keep ventilatory drive within normal limits.…”

“…Sedation commonly leads to upper airway dysfunction, resulting in insufficient respiration (hypopnea/apnea) but also affects the breathing–swallowing coordination and pharyngeal muscle strength, both of which contribute to pharyngeal dysfunction and increased risk of aspiration 12 . Supplementation of inhaled carbon dioxide was shown to reverse upper airway collapsibility induced by propofol 13 , but excessive hypercapnia increases the likelihood of pathological swallowing 14 . Thus, perioperative physicians need to balance their interventions to keep ventilator drive within normal limits.…”