Dynamic behaviour of the soft palate during nasal positive pressure ventilation under anaesthesia and paralysis: comparison between patients with and without obstructive sleep-disordered breathing.

BACKGROUND: Difficult mask ventilation is common and is known to be associated with sleep-disordered breathing (SDB). It is our hypothesis that the incidence of expiratory retropalatal (RP) airway closure (primary outcome) during nasal positive pressure ventilation (PPV) is more frequent in patients with SDB (apnea hypopnea index ≥5 h-1) than non-SDB subjects. METHODS: The severity of SDB was assessed before surgery using a portable sleep monitor. In anaesthetized and paralysed patients with (n=11) and without SDB (n=9), we observed the behaviour of the RP airway endoscopically during nasal PPV with the mouth closed and determined the dynamic RP closing pressure, which was defined as the highest airway pressure above which the RP airway closure was reversed. The static RP closing pressure was obtained during cessation of mechanical ventilation in patients with dynamic RP closure during nasal PPV. RESULTS: The expiratory RP airway closure accompanied by expiratory flow limitation occurred more frequently in SDB patients (9/11, 82%) than in non-SDB subjects (2/9, 22%; exact logistic regression analysis: P=0.022, odds ratio 3.6, 95% confidence interval 1.1-15.4). Receiver operating characteristic curve analyses indicated AHI >10h-1 and presence of habitual snoring as clinically useful predictors for the occurrence of RP closure during PPV. Dynamic RP closing pressure was greater than the static RP closing pressure by approximately 4-5 cm H2O. CONCLUSIONS: Valve-like dynamic RP closure that limits expiratory flow during nasal PPV occurs more frequently in SDB patients.

Perioperative respiratory complications: current evidence and strategy discussed in 2017 JA symposium.

Respiratory management during general anesthesia aims to safely secure the airway and maintain adequate ventilation to deliver oxygen to the vital organs, maintaining homeostasis even during surgery. Despite its clinical importance, anesthesiologists often encounter difficulties in properly managing respiration during the perioperative period, leading to severe respiratory complications. In this year's JA symposium, 5 editorial board members of Journal of Anesthesia (JA) who are experts in the field of respiratory management in anesthesia discussed the following topics: quitting smoking before surgery: exposure to passive smoke is damaging to children, ventilator-associated pneumonia, high inspiratory oxygen concentration and lung injury, aspiration pneumonia, and postoperative respiratory management strategy in patients with obstructive sleep apnea. We hope that this special article regarding this year's JA symposium may be useful for JA readers to manage clinical anesthesia on a daily basis.

Difference in dental arch size between obese and non-obese patients with obstructive sleep apnoea.

A large tongue is recognised as a factor that increases the collapsibility of the upper airway in obstructive sleep apnoea (OSA) patients. We hypothesised that the propensity to develop severe OSA could be minimised if the dental arches were enlarged in obese OSA people who are thought to have a large tongue. We therefore compared the size of the dental arches in obese and non-obese OSA patients. Using a lateral cephalogram and study models, we compared the sizes of the tongue and dental arches in 23 obese and 23 non-obese Japanese male OSA patients, who were matched for age, apnoea hypopnea index (AHI) and maxillomandibular size. The median age (years) and AHI (events per hour) for the obese and non-obese groups were 36·5 and 39·0, and 13·4 and 14·3, respectively. The maxillomandibular size was matched with regard to SNA, SNB and lower face cage obtained from cephalometric measurements. The parameters that were measured for the study model included dental arch width, dental arch length, overjet and overbite. Tongue size (P < 0·05) and both upper (P < 0·01) and lower (P < 0·05) dental arch widths were significantly larger in obese than in non-obese OSA patients, and there was no difference in the severity of OSA between the two groups. These findings suggest that the tongue was larger and dental arches were enlarged in obese patients compared with non-obese patients under the same disease severity. Wider dental arches in obese OSA patients may help to offset the impact of the enlarged tongue on upper airway patency.

Airway research: the current status and future directions.

We highlight the areas we think important for future development of the subspeciality. The ultimate goal is to improve patient care and safety and to do this, we need to identify how and where episodes of harm arise. Simply continuing with current practice does not represent the best path towards our ultimate goal; objective evidence is needed to inform changes in practice.

Laryngeal inputs in defensive airway reflexes in humans.

Stimulation of laryngeal receptors is the natural starting point of defensive airway reflexes including the cough reflex, expiration reflex, spasmodic panting, and apnoea with laryngospasm. Although several different types of laryngeal receptors have been reported, the laryngeal irritant receptors are considered to play the most essential role in elicitation of defensive airway reflexes. Based on the knowledge that the laryngeal irritant receptors are stimulated by water solutions lacking chloride anions, we have developed an experimental method to elicit defensive airway reflexes with a direct instillation of distilled water onto the laryngeal mucosa in humans. Using this experimental method, we studied the characteristics of defensive airway reflexes in lightly anaesthetized patients with multiple system atrophy (MSA). The reflex responses to water stimulation observed in these patients were characterized by apnoea with laryngospasm while the cough reflex was never elicited. Endoscopic images of the larynx in these patients were also characterized by laryngeal oedema. Considering the pathological changes occurring in the central nervous system and the laryngeal mucosa, it is possible that the defensive airway reflexes may be modified by central and/or peripheral mechanisms in patients with MSA.

Pathogenesis of laryngeal narrowing in patients with multiple system atrophy.

1. We do not fully understand the pathogenesis of nocturnal laryngeal stridor in patients with multiple system atrophy (MSA). Recent studies suggest that inspiratory thyroarytenoid (TA) muscle activation has a role in the development of the stridor. 2. The breathing pattern and firing timing of TA muscle activation were determined in ten MSA patients, anaesthetized with propofol and breathing through the laryngeal mask airway, while the behaviour of the laryngeal aperture was being observed endoscopically. 3. Two distinct breathing patterns, i.e. no inspiratory flow limitation (no-IFL) and IFL, were identified during the measurements. During IFL, significant laryngeal narrowing was observed leading to an increase in laryngeal resistance and end-tidal carbon dioxide concentration. Development of IFL was significantly associated with the presence of phasic inspiratory activation of TA muscle. Application of continuous positive airway pressure suppressed the TA muscle activation. 4. The results indicate that contraction of laryngeal adductors during inspiration narrows the larynx leading to development of inspiratory flow limitation accompanied by stridor in patients with MSA under general anaesthesia.

Effects of minor surgery and endotracheal intubation on postoperative breathing patterns in patients anaesthetized with isoflurane or sevoflurane.

We studied the effects of minor surgery and endotracheal intubation on postoperative breathing patterns. We measured breathing patterns and laryngeal resistance during the periods immediately before intubation (preoperative) and immediately after extubation following minor surgery (postoperative) in eight patients anaesthetized with sevoflurane and eight patients anaesthetized with isoflurane, breathing spontaneously through a laryngeal mask airway at a constant end-tidal anaesthetic concentration (1.0 MAC). In both sevoflurane-anaesthetized and isoflurane-anaesthetized patients, expiratory time was reduced and inspiratory and expiratory laryngeal resistance increased after surgery. In sevoflurane-anaesthetized patients, occlusion pressure (P0.1) increased without changes in inspiratory time (T(I)). Occlusion pressure did not change and T(I) was greater in isoflurane-anaesthetized patients after surgery. Minor surgery may have a small but significant influence on breathing and increased laryngeal resistance following endotracheal intubation may modulate these changes. The difference in breathing pattern between sevoflurane and isoflurane may be a result of different responses of the central nervous system to different anaesthetics in the presence of increased laryngeal resistance.

Modulation of swallowing reflex by lung volume changes.

We investigated the effects of changes in lung volume on coordination of respiration and swallowing in 11 healthy subjects. Swallowing reflexes were elicited by bolus injections of a small amount of distilled water (1 ml) and by continuous infusion of distilled water (3 ml/min) into the pharynx at three different levels of lung volume. The lung volume was changed by application of negative extrathoracic pressure (0, -20, and -40 cm H(2)O). We found that increases in lung volume prolonged the latency of swallows elicited by bolus injection of water and decreased the number of swallows during continuous infusion of water. In addition, the preponderant coupling of swallows with the expiratory phase observed before application of negative extrathoracic pressure was lost during application of negative extrathoracic pressure. These results may indicate that lung inflation has an inhibitory influence on the swallowing reflex, and modulates the timing of swallowing in reference to the respiratory cycle.

Developmental changes in collapsibility of the passive pharynx during infancy.

The upper airway configuration significantly changes during the first year of life in humans, possibly leading to alteration of collapsibility of the pharyngeal airway. The present study evaluated developmental changes of passive pharyngeal mechanics in nine normal infants ranging in age from 2 to 12 mo. The static pressure-area relationship of the passive pharynx was quantified under general anesthesia with complete paralysis. We found a direct association between age and maximal velopharyngeal area (r = 0.840, p = 0.005). Velopharyngeal closing pressure progressively decreased with increasing age (r = -0.809, p = 0.008) and the closing pressures were below atmospheric pressure in all infants (range: -0.7 to -9.8 cm H(2)O; mean +/- SD: -3.6 +/- 2.7 cm H(2)O). Shape of the pressure-area curves became steeper in slope with maturation, indicating increased pharyngeal wall stiffness during development. Accordingly, we conclude that anatomic properties of the pharynx gain stability in favor of maintaining patent airway during development in normal infants.

[Diagnosis of sites of upper airway obstruction in patients with obstructive sleep apnea].

Precise determination of the site of obstruction is mandatory for improvement of surgical outcome. The size of the upper airway depends on the balance between the upper airway(UA) muscle activity and intraluminal pressure. Structural property of the UA is considered to be a fulcrum of the balance model. Our final goal is to identify structural abnormalities within the UA. State-dependent and individual variability of the UA muscle activity and luminal pressure makes interpretation of UA size difficult. Measurements of UA size and evaluation of UA collapsibility may be less valuable during wakefulness and sleep without controlling the variability. Two unique approaches to identify the anatomic abnormalities while controlling the UA muscle activity and luminal pressure were reviewed.

[Long-term result after UPPP for OSAS by evaluation of nocturnal oxygenation].

The nocturnal oxygenation of 45 patients with OSAS who had UPPP at our hospital were evaluated by pulse oximetry before and after surgery and at the time more than one year after UPPP. "Successful case" is defined as the case that showed more than 50% reduced oxygen desaturation index(ODI) after UPPP. Twenty seven cases including 15 severe cases(ODI > or = 40) have showed continuously successful ODI for more than one year. We could not get good result in 8 cases, which kept high ODI. Four of them are now using dental appliance. We have recognized the recurrence of sleep apnea in 10 cases that once got successful results just after UPPP. Our report strongly suggests the importance of long-term follow-up after surgery.

Pre-and post-operative respiratory assessment of acromegalics with sleep apnea--bedside oximetric study for transsphenoidal approach.

PURPOSE: Although routine mechanical nasal packing after transsphenoidal surgery (TS) is thought to increase respiratory disorders during sleep, there has been little in the literature about the pre- and post-operative airway assessment of acromegalics with sleep apnea (SA). We describe 4 acromegalic patients with SA, who underwent transsphenoidal surgery. METHODS AND CASES: The patients were all men, aged from 47 to 59 years. The pre- and post-operative sleep study consisted with a computer calculated oximetry parameter of oxygen desaturation index (ODI), which was defined as the number/hour of oxygen desaturation episodes exceeding 4% from the base line (normal range < 15). The postoperative (postop.) sleep study was carried out from the 1st postop. day to the 8th day, for 1 to 8 days, varying for each patient. RESULTS: Only the worst postop. result is shown. Patient 1 had 2 operations, 2 years apart. ODI was 39.6 before the 1st operation and 45.9 postop.. In the second operation ODI was 21.8 preoperatively (preop.) and 57.9 postop.. Preop. and postop. ODI was 18.1 and 22.2 in patient 2, 21.6 and 22.5 in patient 3 and 45.5 and 18.9 in patient 4, respectively. ODI of patient 4 was 39.6, 3 weeks later. CONCLUSION: Our data showed that the postop. oxymetric study commonly showed worse results in acromegalics with nasal packing. The better result of patient 4 was probably due to a postop. sleepless state. REM sleep usually increases in the first several postop. days, when cardiopulmonary complications are more likely to occur. Since acromegalics with severe SA and postop. nasal packing may more readily suffer from cardiopulmonary complications, postoperative meticulous respiratory monitoring and care should be mandatory.

Bone CT evaluation of nasal cavity of acromegalics--its morphological and surgical implication in comparison to non-acromegalics.

PURPOSE: In order to numerically compare the morphological differences of the nasal cavity and nasal sinus between acromegalics and non-acromegalics, bone window CT scans sliced parallel to the transsphenoidal surgical route were performed. MATERIAL AND CASES: Acromegalic patients had small or large macroadenomas and were 13 (7 men and 6 women) in number, aged 53.2 +/- 16.1 years. Non-acromegalic patients had pituitary tumors and were 44 (21 men and 23 women) in number, aged 52.1 +/- 12.5 years. RESULTS: The results of acromegalics are described in comparison to non-acromegalics in parentheses. a) The width of the surgical corridor: piriform aperture, 27.6 +/- 2.7 (25.9 +/- 2.6) mm; origin of inferior nasal concha, 29.4 +/- 9.4 (26.6 +/- 4.0) mm; and origin of middle nasal concha, 29.8 +/- 3.2 (26.2 +/- 4.2) mm. b) The depth of the surgical corridor: the upper lip thickness, 18.1 +/- 2.7 (13.3 +/- 1.4) mm; the distances between piriform aperture and sphenoid wall, 52.9 +/- 4.6 (49 +/- 4.2) mm; sphenoid wall and sellar floor, 17.3 +/- 4.1 (18.7 +/- 4.1) mm; and sellar floor to dorsum sellae, 17.6 +/- 3.4 (15.6 +/- 4.0) mm. c) Marked carotid prominence: 7/13=53.4% (8/44=18.25%). d) Sinusitis: 8/13=61.5% (12/44=27.3%). DISCUSSION & CONCLUSION: The data presented above show that morphological differences in bony nasal cavity and soft tissue may be responsible for a deeper and narrower surgical field for acromegalics. Acromegalics had a marked carotid prominence more frequently, which needs special attention to avoid carotid injury, when enlarging the surgical field. Knowing these morphological differences will provide useful information for peri- and intra-operative care.

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.

Dose-dependent effects of mandibular advancement on pharyngeal mechanics and nocturnal oxygenation in patients with sleep-disordered breathing.

STUDY OBJECTIVES: To examine dose-dependent effects of mandibular advancement on collapsibility of the passive pharynx and sleep-disordered breathing (SDB). DESIGN: Prospective, randomized study. SETTING: University hospital. PATIENTS: Thirty-seven adult patients with SDB. INTERVENTIONS: Oral appliances with 2-, 4-, and 6-mm advancement of the mandible. MEASUREMENTS AND RESULTS: Overnight oximetry was performed with and without oral appliances. Each 2-mm mandibular advancement coincided with approximately 20% improvement in number and severity of nocturnal desaturations. Percentages of patients producing a > 50% improvement rate of the number of desaturations were 25%, 48%, and 65% with use of oral appliances with 2-, 4-, and 6-mm mandibular advancement, respectively. Static pharyngeal mechanics were evaluated in six completely paralyzed patients with SDB under general anesthesia with and without the oral appliances. Advancement of mandibular position was found to produce dose-dependent closing pressure reduction of all pharyngeal segments. Normalization of nocturnal oxygenation was associated with negative closing pressure, especially at the velopharynx. CONCLUSIONS: We conclude that improvement of both nocturnal oxygenation and pharyngeal collapsibility significantly depends on the mandibular position.

Experimental pain augments experimental dyspnea, but not vice versa in human volunteers.

BACKGROUND: Pain and dyspnea frequently coexist in many clinical situations. However, whether the two different symptoms interact with each other has not been elucidated. To elucidate the interaction between pain and dyspneic sensations, the authors investigated separately the effects of pain on dyspnea and the effects of dyspnea on pain in 15 healthy subjects. METHODS: Subjects were asked to rate their sensation of pain or dyspnea using a visual analog scale (VAS) during pain stimulation produced by tourniquet inflation (inflation cuff pressure: 350 mmHg) around the calf, and/or the respiratory loading consisted of a combination of resistive load (77 cm H2O x l(-1) x s(-1)) and hypercapnia induced by extra mechanical dead space (255 ml). In addition to changes in VAS scores, changes in ventilatory airflow and airway pressure were continuously measured. RESULTS: Pain stimulation and loaded breathing increased VAS scores, ventilation, and occlusion pressure (P0.1). The addition of a pain stimulus during loaded breathing increased the dyspneic VAS score (median 56 [interquartile range 50-62] vs. 64 [55-77]: before vs. after addition of pain stimulus, P < 0.05) with concomitant increases in minute ventilation (10.8 [10.1-13.3] vs. 12.4 [11.0-14.8] l/min, P < 0.05) and P0.1 (5.5 [4.9-7.2] vs. 6.8 [5.8-9.0] cm H2O, P < 0.05). The addition of respiratory loading during pain stimulation did not cause a significant change in pain VAS score (40 [33-55] vs. 31 [30-44]: before vs. after addition of respiratory loading), although both additional burdens increased further minute ventilation (10.0 [8.8-10.9] vs. 12.0 [10.6-13.2] l/min, P < 0.05) and P0.1 (2.5 [2.0-3.0] vs. 6.2 [4.9-7.0] cm H2O, P < 0.05). CONCLUSION: The authors' findings suggest that pain intensifies the dyspneic sensation, presumably by increasing the respiratory drive, whereas dyspnea may not intensify the pain sensation.

Sleep-disordered breathing in acromegalics--relation of hormonal levels and quantitative sleep study by means of bedside oximeter.

Sleep-disordered breathing (SDB) is common in patients with growth hormone (GH) secreting pituitary adenomas. Since long-term untreated SDB aggravates systemic conditions (hypertension and arrhythmia etc.), the therapeutic outcome of SDB is important in reducing morbidity and mortality rates. But the results of a quantitative analysis of the lowered GH and IGF-1 levels in SDB in a relatively large number of patients are not detailed. Ten consecutive acromegalic patients were studied with a bedside oximeter. Preoperatively they were divided into two groups based on the presence (SDB group = 6 patients) or absence (non-SDB group = 4 patients) of clinical symptoms of SDB such as habitual snoring, excessive daytime somnolence and nocturnal apneic episodes. The serum IGF-1 averaged 931.7 ng/ml in SDB group and 898.3 ng/ml in non-SDB group. The oxygen desaturation index (ODI) (the number of oxygen desaturations exceeding 4% from the base line) was 29.1+/-15.4 in the SDB group and 2.5+/-1.8 in the non-SDB group (P=0.01). Other oximeter parameters such as the percent of the time spent at O2 saturation < 90% and the mean and the lowest O2 saturations closely correlated with the degree of the clinical symptoms. A postoperative sleep study was conducted in 5 patients in the preoperative SDB group, 4 months or more after the surgery. The serum GH and IGF-1 levels normalized in 3 patients but remained slightly high in 2. ODI became 9.1+/-5.6, which was significantly lower than the preoperative value (P=0.026). One patient had a complete clinical resolution. The other 4 obtained slight to moderate improvement clinically and oximetrically despite normalized or decreased hormonal levels. This study clarified that the response of SDB to lowering of the GH level varies from one patient to another and persisting SDB despite the normalization of the hormonal levels suggests the involvement of other factors in the production of SDB.

MRI of growth hormone-secreting pituitary adenomas: factors determining pretreatment hormone levels.

Preoperative serum growth hormone (GH) level is one of the most important determinants of outcome. Our aim was to assess MRI findings which may correlate with pretreatment GH levels in GH-secreting adenomas. We retrospectively studied 29 patients with acromegaly caused by a pituitary adenoma. Tumor size (height, width, thickness and volume), suprasellar extension, sphenoid or cavernous sinus invasion, signal intensity and contrast enhancement were studied. Linear regression analysis or Fisher's exact probability test was used for statistical analysis. Factors related to high GH levels were the maximum dimension of the tumour (r = 0.496, P < 0. 01), its volume (r = 0.439, P < 0.05), spenoid sinus invasion (P < 0. 01) and intracavernous carotid artery (encasement (P < 0.01). The other items were not related to serum GH levels. Since we believe surgery is the first choice of treatment and the cavernous sinus is difficult of access with a conventional surgical approach, preoperative assessment of invasion into the cavernous sinus is critical for predicting the surgical outcome. Low GH levels (5-50 ng/ml) were found with tumours medial to the intercarotid line and high levels (more than 101 ng/ml) with invasive tumours with carotid artery encasement. Variable GH levels were noted with tumours extending beyond the intercarotid line. Because functioning adenomas invading the cavernous sinus tend to have markedly high hormone levels, and only patients with carotid artery encasement showed markedly elevated GH levels, we believe carotid artery encasement a reliable MRI indicator of cavernous sinus invasion.

Collapsibility of passive pharynx in patients with acromegaly.

Sleep-disordered breathing (SDB), either central or obstructive in nature, is common in patients with acromegaly. However, no study has systematically examined the collapsibility of the pharynx in acromegaly to date. We evaluated intrinsic mechanical properties of passive pharynx in 10 anesthetized and paralyzed patients with active acromegaly before transsphenoidal adenomectomy for their pituitary adenoma. Static pressure-area relationships of the velopharynx and oropharynx were obtained by step changes in airway pressure during endoscopic cross-sectional area measurement of each segment. Moreover, curve fitting analysis by an exponential function estimated the closing pressure (P'close) of each segment. Preoperative nocturnal oximetry identified five acromegalic patients with an oxygen desaturation index (ODI) greater than 10 h-1 and clinical symptoms suggesting presence of SDB. The pharyngeal airway of all five acromegalic patients with SDB was highly collapsible at both velopharynx and oropharynx with positive P'close. Compared with age-, body mass index (BMI)-, and ODI-matched SDB patients without acromegaly, SDB patients with acromegaly had a higher P'close of the oropharynx, indicating that the etiology of SDB in acromegaly appears to differ from that of ordinary sleep apnea. Our results suggest that anatomic abnormality, especially at the base of the tongue, appears to play a significant role in development of SDB in acromegaly.