Yugo Tagaito

Upper Airway Reflexes during a Combination of Propofol and Fentanyl Anesthesia

Background The effects of intravenous anesthetics on airway protective reflexes have not been fully explored. The purpose of the present study was to characterize respiratory and laryngeal responses to laryngeal irritation during increasing doses of fentanyl under propofol anesthesia. Methods Twenty‐two female patients anesthetized with propofol and breathing through the laryngeal mask airway were randomly allocated to three groups: (1) eight patients who received cumulative total doses of 200 [micro sign]g fentanyl given in the form of two doses of 50 [micro sign]g and one dose of 100 [micro sign]g spaced 6 min under mechanical controlled ventilation while end‐tidal carbon dioxide tension (PCO2) was maintained at 38 mmHg (fentanyl‐controlled ventilation group), (2) eight patients who received cumulative total doses of 200 [micro sign]g fentanyl while breathing spontaneously while end‐tidal PCO2 was allowed to increase spontaneously (fentanyl‐spontaneous ventilation group), and (3) six spontaneously breathing patients who were anesthetized with propofol alone (propofol group). The laryngeal mucosa of each patient was stimulated by spraying the cord with distilled water, and the evoked responses were assessed by analyzing the respiratory variables and endoscopic images. Results Before administration of fentanyl, laryngeal stimulation caused vigorous reflex responses, such as expiration reflex spasmodic panting, cough reflex, and apnea with laryngospasm. Increasing doses of fentanyl reduced the incidences of all these responses, except for apnea with laryngospasm, in a dose‐related manner in both the fentanyl‐controlled ventilation and the fentanyl‐spontaneous ventilation groups. Detailed analysis of endoscopic images revealed several characteristics of laryngeal behavior during the airway reflex responses. Conclusion Incremental doses of fentanyl depress airway reflex responses in a dose‐related manner, except for apnea with laryngospasm.

Pharyngeal Patency in Response to Advancement of the Mandible in Obese Anesthetized Persons

Background: During anesthesia in humans, anterior displacement of the mandible is often helpful to relieve airway obstruction. However, it appears to be less useful in obese patients. The authors tested the possibility that obesity limits the effectiveness of the maneuver. Methods: Total muscle paralysis was induced under general anesthesia in a group of obese persons (n = 9; body mass index, 32 +/‐ 3 kg sup ‐2) and in a group of nonobese persons (n = 9; body mas index, 21 +/‐ 2 kg sup ‐2). Nocturnal oximetry confirmed that none of them had sleep‐disordered breathing. The cross‐sectional area of the pharynx was measured endoscopically at different static airway pressures. A static pressure‐area plot allowed assessment of the mechanical properties of the pharynx. The influence of mandibular advancement on airway patency was assessed by comparing the static pressure‐area relation with and without the maneuver in obese and nonobese persons. Results: Mandibular advancement increased the retroglossal area at a given pharyngeal pressure, and mandibular advancement increased the retropalatal area in nonobese but not in obese persons at a given pharyngeal pressure. Conclusion: Mandibular advancement did not improve the retropalatal airway in obese persons.

Sniffing Position Improves Pharyngeal Airway Patency in Anesthetized Patients with Obstructive Sleep Apnea

Background:Appropriate bag-and-mask ventilation with patent airway is mandatory during induction of general anesthesia. Although the sniffing neck position is a traditionally recommended head and neck position during this critical period, knowledge of the influences of this position on the pharyngeal airway patency is still inadequate. Methods:Total muscle paralysis was induced with general anesthesia in 12 patients with obstructive sleep apnea, eliminating neuromuscular factors contributing to pharyngeal patency. The cross-sectional area of the pharynx was measured endoscopically at different static airway pressures. Comparison of static pressure–area plot between the neutral and sniffing neck positions allowed assessment of the influence of the neck position change on the mechanical properties of the pharynx. Results:The static pressure–area curves of the sniffing position were above those of neutral neck position, with increasing maximum cross-sectional area and decreasing the closing pressure at both retropalatal and retroglossal airways. The beneficial effects of the sniffing position were greater in obstructive sleep apnea patients with higher closing pressure and smaller body mass index. Conclusions:Sniffing position structurally improves maintenance of the passive pharyngeal airway in patients with obstructive sleep apnea and may be beneficial for both mask ventilation and tracheal intubation during anesthesia induction.

Efficacy of endoscopic static pressure/area assessment of the passive pharynx in predicting uvulopalatopharyngoplasty outcomes†

Objectives/Hypothesis: Although uvulopalatopharyngoplasty (UPPP) is an attractive surgical treatment for obstructive sleep apnea (OSA), the unpredictable outcome limits application of the procedure. Since UPPP corrects only retropalatal airway (RP) patency, we hypothesized that response to UPPP is determined by collapsibility of the retroglossal airway (RG), where UPPP does not correct. Methods: We estimated closing pressure (Pclose) for each pharyngeal segment by endoscopically obtaining the static pressure/area relationship of the passive pharynx in completely paralyzed and anesthetized patients with sleep‐disordered breathing (n = 41) before UPPP. Preferable response to UPPP was defined as the number of oxygen dips (ODI), obtained by nocturnal oximetry, less than 10 h−1 after UPPP. Results: Patients with negative Pclose at RG responded to UPPP significantly better than those with positive Pclose at RG (22/30 [73%] vs. 3/11 [27%], P < .05). ODI after UPPP was significantly correlated with age, Pclose at RP, and Pclose at RG. Conclusions: Endoscopic assessment of anatomic abnormality of the pharynx in paralyzed patients with sleep‐disordered breathing under general anesthesia has clinical value for the improvement of UPPP outcome.

Sitting Posture Decreases Collapsibility of the Passive Pharynx in Anesthetized Paralyzed Patients with Obstructive Sleep Apnea

Background:Obstructive sleep apnea (OSA) is an independent risk factor for difficult and/or impossible mask ventilation during anesthesia induction. Postural change from supine to sitting improves nocturnal breathing in patients with OSA. The purpose of this study was to evaluate the effect of patient position on collapsibility of the pharyngeal airway in anesthetized and paralyzed patients with OSA. The authors tested the hypothesis that the passive pharynx is structurally less collapsible during sitting than during supine posture. Method:Total muscle paralysis was induced with general anesthesia in nine patients with OSA, eliminating neuromuscular factors contributing to pharyngeal patency. The cross-sectional area of the pharynx was measured endoscopically at different static airway pressures. Comparison of static pressure-area plots between the supine and sitting (62° head-up) allowed assessment of the postural differences of the mechanical properties of the pharynx. Results:Maximum cross-sectional area was greater during sitting than during supine posture at both retropalatal (median (10th-90th percentile): 1.91 (1.52-3.40) versus 1.25 (0.65-1.97) cm2) and retroglossal (2.42 (1.72-3.84) versus 1.75 (0.47-2.35) cm2) airways. Closing pressure of the passive pharynx was significantly lower during sitting than supine posture. Differences of the closing pressures between the postures are 5.89 (3.73-11.6) and 6.74 (4.16-9.87) cm H2O, at retropalatal and retroglossal airways, respectively, and did not differ between the pharyngeal segments. Conclusions:Postural change from supine to sitting significantly improves collapsibility of pharyngeal airway in anesthetized and paralyzed patients with OSA.

Airway protective reflexes evoked by laryngeal instillation of distilled water under sevoflurane general anesthesia in children.

To investigate how sevoflurane modifies airway protective reflexes in anesthetized children, we recruited patients younger than 12-yr-old for our study. Anesthesia was induced with inhaled sevoflurane in oxygen. The airway was managed with a laryngeal mask airway and the patient breathing spontaneously. Depending on the depth of anesthesia, the subjects were divided into two groups: Group 1 and Group 2 (1% and 2% of end-tidal sevoflurane concentration, respectively). Behaviors of the larynx were assessed mainly by the fiberscopic images of the larynx as well as respiratory flow and esophageal pressure. A small dose, 0.02 mL/kg of distilled water (minimum 0.2 mL) was instilled to the larynx through a channel of the scope to evoke an airway protective reflex from the larynx. The responses were categorized into passive (laryngeal closure, laryngospasm, and apnea) and active (cough, expiration reflex, and swallowing reflex) responses. Ten subjects were included in each group. In both groups, the primary responses were passive; however, in Group 1, active reflexes were also observed in 8 of 10 subjects; no subjects in Group 2 had active reflexes (P < 0.01). We concluded that, in children, the depth of general anesthesia with sevoflurane modified airway protective reflexes.

Usefulness of continuous oxygen insufflation into trachea for management of upper airway obstruction during anesthesia.

Background Severe complications associated with upper airway obstruction often occur during the perioperative period. Development of a simple and reliable technique for reversing the impaired airway patency may improve airway management. The purpose of the current study is to evaluate the usefulness of transtracheal oxygen insufflation (TTI) for management of upper airway obstruction during anesthesia and to explore the mechanisms of TTI in detail. Methods During propofol anesthesia in eight spontaneously breathing patients, the upper airway cross-sectional area and pressure–flow measurements during neck flexion with TTI were compared with those during triple airway maneuvers (TAM) without TTI. Blood gas analyses assessed efficacy of CO2 elimination during TTI in an additional nine patients. Results TTI achieved adequate PaCO2 and PaO2 levels equivalent to those during TAM. In addition to a significantly smaller cross-sectional area during TTI, the location and slope of the pressure–flow relation during TTI completely differed from those during TAM, indicating that upper airway resistance was much higher during TTI. Notably, minute ventilation during TTI was significantly smaller than that during TAM, suggesting reduced dead space or other mechanisms for CO2 elimination. Conclusions TTI is capable of maintaining adequate blood gases through mechanisms different from those of conventional airway support in anesthetized subjects with upper airway obstruction.

Nonpeptide Orexin-2 Receptor Agonist Attenuates Morphine-induced Sedative Effects in Rats

Background: Sleepiness and decrease in attention are dose-limiting side effects of opioids. The orexin/hypocretin system plays an important role in maintaining wakefulness. This study aimed to explore the potential of a nonpeptide orexin receptor agonist to alleviate morphine-induced sedative effects. Methods: Morphine sedative effects were evaluated as changes in electroencephalogram (EEG), locomotor activity, and acoustic startle response in rats (n = 5 to 9 per group). Effects of intracerebroventricular orexin-A and systemic orexin type-2 receptor agonist, YNT-185, on EEG changes induced by morphine were examined. Furthermore, the authors examined effects of morphine administered with or without YNT-185 on locomotor activity and on acoustic startle response. Results: Morphine-induced, frequent, short epochs of increased power (total epoch duration: 0.5 [0.0 to 8.0] s/10 min during baseline vs. 74.0 [49.0 to 115.0] s/10 min during the post–morphine administration period; P = 0.012). EEG analyses revealed that morphine-induced, high-amplitude, slow activity (increase in spectral power of frequencies less than 15 Hz, baseline vs. postmorphine; P < 0.001). Orexin-A and YNT-185 attenuated these changes. Locomotor activity decreased after morphine (268 [103 to 889] ambulatory movement counts during baseline period [20 min] vs. 138 [7 to 434] counts during 40 to 59 min postadministration; P = 0.012), but did not change after morphine with YNT-185 (363 [121 to 636] vs. 864 [381 to 1092] counts, difference within morphine + YNT-185 group; P = 0.071). Startle response latency was longer after morphine (26 [20 to 28] ms) than after morphine with YNT-185 (17 [16 to 18] ms; P = 0.012). Conclusions: Orexin-A and/or YNT-185 attenuated morphine-induced sedative effects assessed by EEG changes and behavioral measures in rats. The authors’ results suggest that orexin-2 receptor activation alleviates morphine-induced sedative effects.

Ventilatory load compensation response to long-term chest compression in rat model

Short-term chest compression has been shown to decrease tidal volume and increase respiratory frequency. The present study was designed to assess and characterize the effect of long-term chest compression on breathing pattern and blood gases in awake rats. Chest compression was carried out by inflating a pneumatic cuff placed around the chest to a pressure of 25 mmHg and the pressure was maintained for 28 days. Respiratory frequency increased progressively until 14 days after chest compression whereas a decrease in tidal volume was stabilized within 3 days after chest compression. Although the changes in minute ventilation were small and no substantial change in Pa(CO2) was observed, an impairment of weight gain and a decrease in body temperature with a concomitant hypoxemia were evident during sustained chest compression. These observations suggest that the ventilatory response to chest compression may involve not only neural reflex mechanisms but also other non-reflex mechanisms. Sustained chest compression possibly impairs growth and metabolism.