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PubMed2006

Detecting dead regions using psychophysical tuning curves: a comparison of simultaneous and forward masking.

A dead region (DR) is a region of the cochlea where there are no functioning inner hair cells and/or neurones. We compared the edge frequencies, fe, of DRs estimated using four methods: the TEN(HL) test; psychophysical tuning curves (PTCs) measured in simultaneous masking (320-Hz wide noise masker) using a 'fast' method (sweeping masker) and a 'classical' method; and PTCs measured in forward masking (sinusoidal masker) using a 'classical' method. Fourteen subjects with high-frequency DRs were tested. For measurement of PTCs, the signal frequency was chosen to fall inside the DR; the tip frequencies of the PTCs were taken as indicating the values of fe. The values of fe obtained from the PTCs in forward and simultaneous masking (both fast and classical methods) were similar and were usually close to, but somewhat above, the values of fe estimated from the TEN(HL) test. Fast PTCs measured in simultaneous masking are recommended for use in clinical practice, as they give a precise estimate of fe and are quick to administer.

Acoustic Impedance Tests↗
PubMed2004

Development of prototypes of half-mask facepieces for Koreans using the 3D digitizing design method: a pilot study.

In the Korean market there are several respirators for industrial purposes. Some of them are imported from global manufacturers such as 3M, and the others are developed by domestic companies. However, some of the locally made respirators have a face-seal leakage problem because they were not designed taking into account Korean facial characteristics. This pilot study was conducted to develop three face models for a half-mask based on the Korean fit-test panel and also to design three well-fitting silicon prototypes (large, medium and small) for Korean faces. For a test panel, 50 subjects were selected on the basis of lip length and face length. Shapes of faces from the test panel were scanned by a 3D scanner (Vivid 900, Minolta). The facial dimension scales for three size groups were established through statistical analysis. To ensure that the shapes fit the mean facial dimensions of each size group, similarly shaped sample faces were selected from the test panel. Mean faces with representative facial dimensions as well as face models (mannequins) were made by the Rapid Prototyper (RP; Z400, Z Corps, USA). These were reshaped to fit the mean faces by clay-modeling. The face models were digitized to recheck the fit of the facial dimensions. On the basis of the face models, three types of masks were developed through digital modeling, and tangible models were prototyped by RP. Three differently sized prototype masks were made with silicon and examined by simple naked eye test. This procedure established the mask design process based on digital technology; it can be applied for similar design projects in the future. Further study is needed to verify whether these prototypes would be a good fit for Korean faces.

Computer Graphics↗
PubMed1992

Surgical face masks are effective in reducing bacterial contamination caused by dispersal from the upper airway.

We have studied the effectiveness of surgical face masks in reducing bacterial contamination of a surface, produced by dispersal of organisms from the upper airway. Twenty-five volunteers were asked to speak at blood agar plates positioned in close proximity to the mouth, initially whilst not wearing a face mask and then wearing a surgical face mask over the mouth and nose. A fresh face mask almost completely abolished bacterial contamination of agar plates 30 cm from the mouth. After 15 min there was an increase in the level of contamination which was statistically insignificant.

Adult↗
PubMed1994

Effect of education on oxygen mask placement.

We have investigated the effect of nurse and patient education on oxygen mask placement after surgery. In 15 patients, each studied for 8 h, masks remained positioned correctly in two and were removed a total of 37 times in the others. Median total removal time per patient (4 min 3 s) was less than in previous studies and maximum total time of mask removal was 1 h 33 min 57 s. Masks were removed for longer than 10 min on four occasions in two patients. None of these removals was for nursing care. This is an improvement compared with previous studies.

Adult↗
PubMed1998

Gastro-oesophageal reflux with the laryngeal mask during day-case gynaecological laparoscopy.

We have evaluated if breathing spontaneously via a laryngeal mask airway is associated with a higher risk of gastro-oesophageal reflux compared with positive pressure ventilation via a laryngeal mask airway in 40 patients undergoing day-case gynaecological laparoscopy. Patients were allocated randomly to receive either positive pressure ventilation or breathe spontaneously via a laryngeal mask airway. Using continuous oesophageal pH monitoring, three patients in the ventilated group and one in the spontaneous breathing group had gastrooesophageal reflux (P = 0.29). We found no evidence to suggest that breathing spontaneously via a laryngeal mask airway increased the risk of gastro-oesophageal reflux compared with positive pressure ventilation in this group of patients.

Adult↗
PubMed1998

Large goitre causing difficult intubation and failure to intubate using the intubating laryngeal mask airway: lessons for next time.

A 63-yr-old woman was anaesthetized for sub-total thyroidectomy. The thyroid gland was large, deviating the trachea to the right and causing 30% tracheal narrowing at the level of the suprasternal notch. Mask ventilation was easy but laryngoscopy was Cormack and Lehane grade 3. Despite being able to see the tip of the epiglottis, tracheal intubation was impossible. An intubating laryngeal mask was inserted and although the airway was clear and ventilation easy, it was not possible to intubate the trachea either blindly or with the fibreoptic bronchoscope. Tracheal intubation was eventually achieved using a 6.5-mm cuffed oral tracheal tube via a size 4 laryngeal mask under fibreoptic control. We describe the case in detail and discuss the use of the intubating laryngeal mask, its potential limitations and how to optimize its use in similar circumstances.

Contraindications↗
PubMed2000

The LMA 'ProSeal'--a laryngeal mask with an oesophageal vent.

We describe a new laryngeal mask airway (LMA) that incorporates a second tube placed lateral to the airway tube and ending at the tip of the mask. The second tube is intended to separate the alimentary and respiratory tracts. It should permit access to or escape of fluids from the stomach and reduce the risks of gastric insufflation and pulmonary aspiration. It can also determine the correct positioning of the mask. A second posterior cuff is fitted to improve the seal. A preliminary crossover comparison with the standard mask in 30 adult female patients showed no differences in insertion, trauma or quality of airway. At 60 cm H2O intracuff pressure, the new LMA gave twice the seal pressure of the standard device (P < 0.0001) and permitted blind insertion of a gastric tube in all cases. It is concluded that the new device merits further study.

Adult↗
PubMed1984

Visual processing deficits as assessed by spatial frequency contrast sensitivity and backward masking in normal ageing and Alzheimer's disease.

Visual functions of patients with senile dementia of the Alzheimer type were compared with those of young people and age-matched controls. Visual acuity and spatial frequency contrast sensitivity did not differ significantly between Alzheimer patients and normal elderly subjects, although both were impaired in comparison with young subjects. Alzheimer patients required more time than ageing controls to identify letters and were susceptible to the interfering effects of a backward pattern mask on letter recognition over a longer interval. The spatial extent over which the pattern mask was effective, as well as the time interval over which a homogeneous mask interfered with letter recognition, were equivalent in normal old people and Alzheimer patients. In all the masking tasks, young people performed better than the old. It is suggested that Alzheimer's disease affects later central visual functions more than early relatively peripheral ones.

Adult↗
PubMed1981

Age differences and practice in forward visual masking.

Three groups of subjects of mean age 24-, 65, and 74-years were contrasted with respect to performance on a forward visual masking task. Twenty-five-year-olds required 24.5 msec to escape masking, 65-year-olds required 52.2 msec, and 74-year-olds, 69.5 msec. These findings suggested that increased age yields a rise in susceptibility to forward masking by visual noise. The effects of practice on age reduction in the interstimulus interval required to escape masking for each age group. There was, however, no significant interaction between age and practice.

Adult↗
PubMed1989

Backward masking, information processing, and schizophrenia.

Many researchers have used backward masking to examine information-processing speed in schizophrenic subjects. The validity of this approach rests upon two main assumptions. One is that the mask effectively limits the time a previously presented stimulus is available for processing. The other is that the components of the masking mechanism in schizophrenic subjects are comparable to those in control groups. It is argued that the masking procedures used in these studies fail to meet either assumption. Alternative interpretations of these investigations, however, suggest important hypotheses for further research in our quest to understand information-processing deficits associated with schizophrenia.

Humans↗
PubMed1993

Use of a face mask in the measurement of resting ventilatory parameters and mouth occlusion pressures.

A recent study has suggested that mouth occlusion pressure (MOP) could be measured during sleep by using a face mask. The purpose of the present study was to examine the effects of a face mask on MOP and resting ventilatory parameters (RVP). Measurements of MOP and RVP were made by three different methods; while breathing through a mouthpiece with nose-clip (MP+NC), through a face mask breathing through the mouth only (FM/mouth), and through a face mask breathing through the nose only (FM/nose). There was a significant difference in several RVP parameters between MP+NC and FM, but no significant difference in MOP between different methods. Use of FM for the measurement of MOP appears to be warranted, and with regard to RVP consideration needs to be given to the differences found between MP+NC and FM.

Adult↗
PubMed1998

The placement of the cuffed oropharyngeal airway with sevoflurane in adults: a comparison with the laryngeal mask airway.

UNLABELLED: We sought to determine the anesthetic duration of sevoflurane required to achieve good conditions for placement of a cuffed oropharyngeal airway (COPA) or a laryngeal mask airway (LMA). Forty adult ASA physical status I or II patients presenting for elective surgery received single-breath vital capacity inhaled induction with 5% sevoflurane via face mask; thereafter, ventilation was manually assisted. The patients were randomized to receive either a COPA or LMA placement. The time of anesthetic exposure was varied for consecutive patients using the staircase method. The mean (95% confidence interval) anesthetic time required for acceptable COPA placement (100 [55-145] s) was significantly shorter than that for LMA (160 [101-219] s). The 50% and 95% effective doses (from logistic analyses) for acceptable conditions associated with COPA or LMA placement were 90 s and 145 s or 164 s and 261 s, respectively. These findings suggest that COPA insertion is less stimulating than the LMA. IMPLICATIONS: The cuffed oropharyngeal airway is a new airway device that is similar to a laryngeal mask airway in many ways. However, it requires shorter anesthetic duration for successful placement, which suggests that it can be placed with less stimulation. It may be an alternative to a laryngeal mask airway.

Adult↗
PubMed1999

Transient hyperdynamic response associated with controlled hypocapneic hyperventilation during sevoflurane-nitrous oxide mask induction in adults.

UNLABELLED: We assessed hemodynamic variables during sevoflurane face mask anesthetic induction in female ASA physical status I or II patients. Anesthesia was induced with a single-breath inhalation method with 8% sevoflurane in 50% nitrous oxide in oxygen. Thirty patients were randomized either to breathe spontaneously (SB group, n = 15) or to receive controlled ventilation (CV group, n = 15) for 6 min after the loss of consciousness. Noninvasive blood pressure and heart rate (HR) were recorded at 1-min intervals. Mean +/- SD HR increased from 83+/-18 to 112+/-24 bpm at 4 min in the CV group (P < 0.001 between groups and within group compared with baseline). Mean arterial pressure increased from 97+/-9 to 106+/-26 mm Hg at 4 min in the CV group, which was significantly higher than that in the SB group (P < 0.01). In the SB group, mean arterial pressure decreased significantly, from 96+/-8 to 78+/-13 mmHg, at 6 min (P < 0.001), and HR remained unchanged. Therefore, hyperventilation should be avoided during the induction of sevoflurane anesthesia via a mask. IMPLICATIONS: In this randomized, prospective study, we found that controlled hypocapneic hyperventilation delivered manually during sevoflurane/ N2O/O2 mask induction was associated with a significant transient hyperdynamic response. This kind of hemodynamic arousal can be detrimental to many patients and can be avoided by conducting sevoflurane mask induction with unassisted spontaneous breathing.

Adult↗
PubMed2001

The minimum alveolar concentration of enflurane for laryngeal mask airway extubation in deeply anesthetized children.

UNLABELLED: The end-tidal anesthetic gas concentration required to prevent the anesthetized patient from coughing or moving during or immediately after the laryngeal mask airway (LMA) extubation is not known. We sought to determine the minimum alveolar concentration of enflurane required for the removal of the LMA in children. We studied 21 nonpremedicated children between 4 and 11 yr of age, ASA physical status I, undergoing procedures below the umbilicus. General anesthesia was induced with a mask by using sevoflurane, nitrous oxide, and oxygen, and the LMA was inserted. Anesthesia was maintained with enflurane, nitrous oxide, and oxygen. At the end of surgery, a predetermined end-tidal enflurane concentration was achieved, and the LMA was removed. Each concentration at which the LMA extubation was attempted was predetermined by the up-and-down method (with 0.1% as a step size). When LMA removal was accomplished without coughing, clenching teeth, or gross purposeful muscular movements during or within 1 min after removal, it was considered a successful LMA removal. Removal was considered to be unsuccessful in patients who developed breath holding or laryngospasm during or immediately after LMA removal. The minimum alveolar concentration of enflurane at which 50% of children had a successful LMA removal was found to be 1.02% (95% CL, 0.95%-1.11%), and the 95% effective dose for successful extubation was 1.14% (95% CL, 1.07%-1.66%). In conclusion, the LMA removal may be accomplished without coughing or moving at 1.02% end-tidal enflurane concentration in 50% of anesthetized children aged 4-11 yr. IMPLICATIONS: There may be fewer problems associated with the laryngeal mask airway extubation when patients are deeply anesthetized. The purpose of this study was to determine the minimum concentration of enflurane for successful removal of the laryngeal mask in children.

Anesthesia, Inhalation↗
PubMed2002

Intubating laryngeal mask airway size selection: a randomized triple crossover study in paralyzed, anesthetized male and female adult patients.

UNLABELLED: We determined the optimal size of intubating laryngeal mask airway (ILM) for ventilation and blind tracheal intubation in men and women. We also determined the distance the tracheal tube needs to protrude beyond the distal aperture to ensure that the cuff is through the vocal cords. Fifty male and 50 female anesthetized, paralyzed patients (ASA physical status I or II, aged 18-80 yr) were studied. Three operators (A, B, and C) were involved for the purposes of blinding. The size 3, 4, or 5 ILM was inserted into each patient in random order by Operator A, and the quality of ventilation was scored (adequate, suboptimal, or failed) by Operator B. The fiberoptic position (correct, too shallow, or too deep) and the distance between the distal aperture and the vocal cords was determined by Operator B. A single attempt at blind intubation was made by Operator C. Operators B and C were blinded to the size of the ILM. Operator C was also blinded to the information recorded by Operator B. All ILMs were inserted into the laryngopharynx at the first attempt. For men and women, the ventilation score was smaller for the Size 3 than the Size 4 or 5 (all: P < 0.002). For men, correct positioning was less common with the Size 3 than the Size 4 or 5 (both: P < 0.02). For women, correct positioning was similar among sizes. For men, tracheal intubation was successful less frequently with the Size 3 (84%) than the Size 4 (100%) or 5 (98%) (both: P < or = 0.01). For women, tracheal intubation success was similar among sizes (Size 3, 4, and 5: 86%, 96%, and 92%, respectively). Intubation was always successful if the ILM was correctly positioned and always failed if it was too shallow or deep. In both male and female patients, the distance between the distal aperture and the vocal cords increased with increasing ILM size (all: P < 0.04) and patient height (P < 0.0001) and was always longer for men (all: P < 0.0001). The overall mean distance (95% confidence interval) that the tracheal tube needed to protrude was 10-12 cm (8-13 cm) in men and 8-11 cm (8-12 cm) in women. We conclude that for men, the Size 4 and 5 ILMs are better than the Size 3 for ventilation and blind intubation. For women, the Size 4 and 5 ILMs are better than the Size 3 for ventilation, but there is no difference among sizes for blind intubation. The length the tracheal tube must protrude from the distal aperture to ensure that the cuff is completely through the vocal cords is 8-13 cm, depending on ILM size, the tracheal tube size, and the sex and height of the patient. IMPLICATIONS: For men, the Size 4 and 5 intubating laryngeal mask airways are better than the Size 3 for ventilation and blind tracheal intubation. For women, the Size 4 and 5 are better than the Size 3 for ventilation, but there is no difference among sizes for blind intubation. The length the tracheal tube must protrude from the distal aperture of the intubating laryngeal mask airway to ensure that the cuff is completely through the vocal cords is 8-13 cm, depending on the size of the mask and tracheal tube and on the sex and height of the patient.

Adolescent↗
PubMed1995

A cost analysis of the laryngeal mask airway for elective surgery in adult outpatients.

BACKGROUND: Since the introduction of the laryngeal mask airway (LMA) into the United States in 1991, the device has become widely used in anesthesia practice. The purpose of this economic analysis was to use existing data to evaluate the costs of the LMA relative to three other common airway management techniques and to identify the variables that had the greatest effect on cost efficiency. METHODS: We evaluated four airway management techniques for healthy adults receiving an isoflurane-nitrous oxide-oxygen anesthetic for elective outpatient surgery: (1) LMA with spontaneous ventilation; (2) face mask with spontaneous ventilation; (3) tracheal intubation after succinylcholine with subsequent spontaneous ventilation; and (4) tracheal intubation after nondepolarizing neuromuscular blockade and controlled ventilation. We analyzed published clinical studies of the LMA and obtained cost data from Stanford University Medical Center. The best available estimates of the independent variables were incorporated into a baseline case. For each airway technique we derived cost equations that excluded costs common to all four techniques. RESULTS: Relative to airway management with an LMA, calculated values for the baseline analysis included additional isoflurane costs for use of a face mask ($ 0.12/min) and for tracheal intubation with ($ 0.043/min) and without neuromuscular blockade ($ 0.06/min). With a neuromuscular blocking drug cost of $ 0.21/min and an LMA cost per use of $ 20, the face mask with spontaneous ventilation was the cost-efficient airway choice for anesthetics lasting as long as 100 min. Increasing the LMA reuse rate from 10 to 25 made the LMA the least costly airway technique for cases lasting more than 70 min. CONCLUSIONS: If the LMA is reused 40 times, the LMA is the cost-efficient airway choice for outpatients receiving an isoflurane-nitrous oxide-oxygen anesthetic lasting longer than 40 min. This finding does not change if the cost of neuromuscular blockade or the incidence of airway-related complications is varied over a clinically relevant range.

Adult↗
PubMed1996

Laryngeal mask airway in pediatric practice: a prospective study of skill acquisition by anesthesia residents.

BACKGROUND: A prospective study was conducted to determine the rate of skill acquisition with the laryngeal mask airway in pediatric anesthesiology practice. The aim of the study was to provide information about the amount of supervised training required before satisfactory levels of skill were achieved. METHODS: Eight anesthesia residents in their third year of training with no prior experience using the laryngeal mask airway were observed using the device in 75 pediatric patients each (600 patients in total). Residents were given standardized guidelines for laryngeal mask airway usage in accordance with the manufacturer's recommendations and followed a predetermined protocol for anesthetic management. Induction was achieved with propofol followed by either a propofol infusion or isoflurane and either controlled or spontaneous ventilation as clinically indicated. Predefined major and minor problems were documented during the induction, maintenance, and recovery phases of anesthesia by a randomly selected supervising consultant trained in the study protocol and problem definitions. RESULTS: The total number of problems was 189 occurring in 121 children. Fifty-five children had one problem, sixty-four children had two problems, and two children had three problems. Of the problems, 77 were major and 112 were minor. The problem rate per patient for overall, major, and minor problems was 31.5%, 12.8%, and 18.7%, respectively. The problem rate comparing the first to last epochs of 15 uses decreased from 62% to 2% for overall problems, 23% to 2% for major problems, and 39 to 1% for minor problems. The residents with the most problems in the final epoch had problem rates of less than 10% after 60 uses. There was a significant decrease in the overall problem rate for induction, maintenance, and recovery (P < 0.05). The major problem rate decreased significantly for induction and maintenance (p < 0.05), but not for recovery. The minor problem rate decreased significantly for induction and recovery (P < 0.05). CONCLUSIONS: This study confirms that there is a rapid improvement in laryngeal mask airway skills when the standard recommended technique is employed and that a low problem rate can be achieved within 75 uses. Pediatric anesthesiologists with problem rates greater than 10% should determine if they are using the device suboptimally.

Adolescent↗
PubMed1999

Pulmonary airway resistance with the endotracheal tube versus laryngeal mask airway in paralyzed anesthetized adult patients.

BACKGROUND: The hypothesis that airway resistance is less with the laryngeal mask airway than with the endotracheal tube was tested. METHODS: Thirty-six paralyzed, anesthetized adult patients with no respiratory disease (American Society of Anesthesiologists physical status 1-3; age, 18-80 yr) were randomly allocated (9 men, 9 women in each group) to receive either a size-4 laryngeal mask airway or an endotracheal tube (men, 9-mm ID; women, 8-mm ID). A pulmonary monitor with flow transducer and esophageal balloon was used to measure peak airway pressure and mean airway resistance (device resistance plus pulmonary airway resistance) at three different tidal volumes (5, 10, and 15 ml/kg). Device resistance was measured in vitro with the distal end of the endotracheal tube or laryngeal mask airway open to the atmosphere and using the same ventilator settings. Pulmonary airway resistance was derived by subtracting the mean device resistance from the mean airway resistance. RESULTS: Peak airway pressure, mean airway resistance, device resistance, and pulmonary airway resistance were greater for the endotracheal tube (all P < 0.0001). CONCLUSIONS: The laryngeal mask airway triggers less bronchoconstriction than does the endotracheal tube in paralyzed anesthetized adult patients. This may have implications for maintaining intraoperative pulmonary function and reducing the risk for atelectasis and pulmonary infection.

Adolescent↗