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PubMed1998

Surgical face masks and downward dispersal of bacteria.

The ability of face masks to prevent forward dispersal of bacteria is offset by the possibility that they may increase vertical shedding of bacteria from the face during facial movement. To investigate this, a blood agar plate was placed 30 cm directly below the lips of 20 volunteers who were encouraged to talk for 20 min while moving their heads from side to side, without a face mask for the first 5 min and then with a standard, soft pleated face mask for the subsequent 15 min. The agar plates were changed at 5-min intervals. Analysis of the number of bacterial colonies grown on each agar plate showed a statistically significant reduction in the median number of colonies cultured per plate when the mask was worn. Our results suggest that for procedures lasting less than 15 min, the operator should wear a face mask, particularly when the face is in close proximity to the operative field and the need for speaking is anticipated.

Anesthesiology↗

PubMed2000

An investigation into the quantity of secretions removed by inflated and deflated laryngeal mask airways.

It has been suggested that removal of a laryngeal mask airway with the cuff inflated may remove more secretions than with the cuff deflated. We performed a study to determine whether this suggestion is correct. Patients were randomly allocated to removal of the laryngeal mask airway with the cuff deflated (n = 75) or inflated (n = 74). The laryngeal mask airways were weighed before insertion and after removal, the difference in these two weights being taken to be the mass of secretions adherent to the airways on removal. The mean (SD) increase in laryngeal mask airway weight was 2.45 (1.47) g with the cuff deflated and 3.03 (1.76) g with the cuff inflated (p = 0.03). We conclude that removal of the laryngeal mask airway with the cuff inflated removes approximately 0.5 g more secretions than with the cuff deflated.

Adolescent↗

PubMed2001

Tracheal intubation and cervical spine excursion: direct laryngoscopy vs. intubating laryngeal mask.

Until recently, the most appropriate technique of intubating a patient with a cervical spine injury has been the subject of debate. Tracheal intubation by means of the intubating laryngeal mask (Fastrach), a modified conventional laryngeal mask airway, seems to require less neck manipulation. The aim of this study was to compare the excursion of the upper cervical spine during tracheal intubation using direct laryngoscopy with that during intubation via the laryngeal mask (Fastrach), by examination of lateral cervical spine radiographs in healthy young patients. The intubating laryngeal mask (Fastrach) caused less extension (at C1-2 and C2-3) than intubation by direct laryngoscopy. Direct laryngoscopy is still the fastest method to secure an airway provided no intubating difficulties are present. However, in trauma patients requiring rapid sequence induction and in whom cervical spine movement is limited or undesirable, the intubating laryngeal mask (Fastrach) is a safe and fast method by which to secure the airway.

Adult↗

PubMed2002

The cardiovascular response to insertion of the intubating laryngeal mask airway.

Sixty-one patients received a standardised anaesthetic and were randomly assigned to three groups: tracheal intubation via direct laryngoscopy, tracheal intubation via an intubating laryngeal mask airway with immediate removal of the device, and tracheal intubation via an intubating laryngeal mask airway with delayed removal. The cardiovascular response to intubation was of a similar magnitude in all groups, although delayed removal of the intubating laryngeal mask airway was associated with a second pressor response. Norepinephrine changed significantly over time following direct laryngoscopy and following immediate removal of the intubating laryngeal mask airway, but not after delayed removal. The findings of this study do not support using the intubating laryngeal mask instead of direct laryngoscopy purely to decrease the response to intubation.

Adult↗

PubMedDate not supplied

Skills retention for insertion of the Combitube and laryngeal mask airway.

OBJECTIVE: To determine if the skills to successfully ventilate using the laryngeal mask (The Laryngeal Mask Company Limited, Henley on Thames, United Kingdom) and Combitube (The Kendall Company, Mansfield, USA) can be retained after seven months. METHODS: Nursing, medical and theatre staff from Dunedin Hospital were recruited in a prospective study. Subjects were taught to insert and ventilate an Ambuman manikin using both devices. Subjects were tested on their ability to ventilate the manikin with both devices within one month then following a six-month period. RESULTS: A total of 101 subjects were recruited with 86 subjects retested at least six months later. Initial testing resulted in subjects successfully ventilating the manikin in 90% (laryngeal mask) and 92% (Combitube) of attempts. At retesting, successful ventilation was achieved in 85% (laryngeal mask) and 77% (Combitube) of attempts. The decline in skills level was significant for the Combitube only (95% CI 4% to 26%). CONCLUSION: The ability to successfully ventilate is better maintained with the laryngeal mask than the Combitube after seven months.

Clinical Competence↗

PubMed1999

Laryngeal mask for difficult intubation in children.

We present a new intubation technique using an oral preformed tracheal tube passed through a laryngeal mask. Six patients (neonate to six months old) with craniofacial malformations of head and neck and scheduled for reconstructive plastic surgery are the basis of this report. An inhalation induction with increasing doses of halothane in oxygen while maintaining spontaneous ventilation was performed. Once an adequate anaesthetic depth was achieved, a direct laryngoscopy was performed. The epiglottis could not be seen in any of the patients. Anaesthesia was deepened in order to insert the laryngeal mask, size 1 or 2, with an oral preformed 3.5 or 4.0 tracheal tube inside it. Correct position of the mask was confirmed by capnography. The preformed tracheal tube was then advanced 1-2 cm. and its position in the trachea verified. The 15 mm connector was then removed, and an adult intubating stylet was attached to the end of the tracheal tube. The laryngeal mask was removed, holding the stylet and tube in place. Once the mask was removed, the stylet was disconnected, and the 15 mm connector reattached. Our experience was that this takes about 20 to 30 s. We recommended this technique in paediatric patients in which a difficult intubation is foreseen.

Anesthesia, Inhalation↗

PubMed2003

[Comparison of different laryngeal mask airways in a resuscitation model].

OBJECTIVE: The standard laryngeal mask airway LMA-Classic is recommended in the ILCOR guidelines as alternative to facemask and tracheal tube during cardiopulmonary resuscitation. LMA-Unique, LMA-Fastrach and LMA-ProSeal are additional variants that are compared with the standard LMA in a resuscitation model. METHODS: Tidal volumes, chest compressions and signs of gastric inflation are measured in a standardized resuscitation model (Ambu Cardiac Care Trainer with notebook and thumper). Ten 3-minute resuscitation cycles were performed with facemask and all LMAs (Classic, Unique, Fastrach, ProSeal, all size 4) with a ventilation : compression ratio of 2:15. To allow comparison with tracheal tube and to judge safety margins, another ten resuscitation cycles were performed with tracheal tube and all laryngeal masks with continuous chest compressions after two initial ventilations. The bag-valve device used for ventilation was replaced by an automatic transport ventilator in a third series with continuous chest compressions. Cuff pressures were set at 80 cm H2O. RESULTS: During interrupted chest compressions, adequate ventilation was possible with all devices. Tidal volumes for facemask, LMA-Fastrach and LMA-ProSeal were significantly (p < 0.001) higher than with LMA- Classic and LMA-Unique. During continuous chest compressions, significant differences (p < 0.001) occurred when comparing tracheal tube, Fastrach and ProSeal with the other two laryngeal mask airways, which did not reach recommended tidal volumes. During ventilation with the automatic transport ventilator, values for all devices except LMA-ProSeal dropped significantly, adequate ventilation was possible with tracheal tube, Fastrach and ProSeal. Signs of gastric inflation were found during ventilation with facemask and - to a lesser extent - with LMA-Classic. CONCLUSION: In the resuscitation model chosen, all laryngeal mask airways are possible alternatives for ventilation during cardiopulmonary resuscitation. The new LMA-ProSeal and also the LMA-Fastrach allow higher tidal volumes even during elevated intrathoracic pressures caused by continuous chest compressions, performing superior to the standard laryngeal mask airway. For inclusion of these devices in the ILCOR guidelines, further research in patients is warranted.

Cardiopulmonary Resuscitation↗

PubMed1997

[Fiber optic intubation using a modified laryngeal mask. Report of experiences with use in 105 patients].

PURPOSE: This study was made to investigate the suitability of a modified laryngeal mask airway as an aid for fibreoptic endotracheal intubation in patients with a difficult airway. We used a laryngeal mask airway split lengthwise on its convex site, the incision going from a point corresponding to the teeth down to the base of the cuff. The cuff remains uncut. By this modification it is possible to ventilate an anaesthetised patient and to pass down a fibreoptic bronchoscope via splitting of the laryngeal mask airway into the trachea at the same time. An endotracheal tube of any diameter already mounted over the bronchoscope is then guided into the trachea. The feasibility of this technique was tested and haemodynamic reactions and changes of the parameters of respiration were recorded. METHODS: This technique was used in 105 patients, 68 male and 37 female, mean age 34 years, when difficult intubation was expected or occurred. Blood pressure, pulse rate and peripheral oxygen saturation was recorded on arrival in the anaesthetic room, after induction of anaesthesia, during and after fibreoptic endotracheal intubation. The respiratory minute volume was measured after insertion of the laryngeal mask airway and during the course of fibreoptic intubation. The time needed was recorded. RESULTS: In all cases endotracheal intubation was successful using this technique. The time needed was between 4 and 16 minutes. There was a statistically significant increase in peripheral oxygen saturation and decrease of the pulse rate after induction of anaesthesia. There were no further significant changes of the recorded haemodynamic parameters and the oxygen saturation during and after fibreoptic intubation compared to the results after induction of anaesthesia. CONCLUSION: It could be demonstrated that a fibreoptic intubation is possible in cases of a difficult airway using the technique described here. There is no haemodynamic strain on the patient. This method can be carried out without pressure of time and without to endanger the patient by hypoxia as the patient can be ventilated during the fibreoptic intubation. In cases of impossible intubation and insufficient mask ventilation it can be tried to establish ventilation and to avoid a emergency surgical airway or transtracheal jet ventilation by using this technique.

Adult↗

PubMed1993

[The laryngeal mask with > 1900 general anesthesias--report of experiences].

Since November 1990 until January 1993, the laryngeal mask airway was employed for 1925 general anaesthesias, i.e. 19.6% of all general anaesthesias in our hospital. On the basis of the protocols the age distribution of the patients, the practice of anaesthesia (premedication with oral benzodiazepines, induction with thiopental, anaesthesia sustained with enflurane/nitrous oxide/oxygen) and the complications are reported. The complications not directly related to the laryngeal mask were: hypotension (5.92%), dysrhythmias (3.17%) and hypertensive states (1.71%). Other complications directly related to the laryngeal mask (bronchospasm, laryngospasm, difficult insertion of the mask, intraoperative vomiting) were less than 1.3% each. One aspiration was recorded, but could not be attributed to the laryngeal mask. Complications with major influence on the postoperative course and hospital stay were not seen.

Adolescent↗

PubMed1976

Intergration and interruption in the masking of form by form.

Paris of geometric forms of equal area were presented, one form after another, with interstimulus intervals t ranging from 0 to 250 ms. The subject's task in experiment 1 was to recognise both stimuli. Identification of the form presented first (backward masking) across all values of t was of a nonmonotonic nature, with greatest impairment at values of t from 30 to 60 ms. Identification of the second form presented (forward masking) increased monotonically with increasing t. Different forms were recognised with different effectiveness across all values of t where masking took place. The results are interpreted on the basis of a multiple-stage processing model which assumes interaction between stimuli at different levels at different values of t. In experiment 2 the subject's task was to detect the presence or absence of a predesignated form. This condition yielded monotonic functions for both backward and forward masking. An explanation in terms of attention-dependent masking is given.

Attention↗

PubMed1976

Word length and visual-noise texture in backward masking.

Visual-noise masks composed of randomly scattered letter fragments disrupt the recognition of briefly viewed letter arrays when the masks are presented immediately after these arrays. According to the feature-similarity assumption, maximal disruption should occur when the target letters and the letter fragments comprising the mask share a common stroke width. This assumption was disconfirmed in the present experiment. Two-, four-, and six-letter arrays, whose stroke width subtended a visual angle of 3-8', were viewed tachistoscopically in conjunction with visual-noise masks whose letter fragments subtended visual angles of 1-2', 1-9', 3-8', 6-6', or 9-7'. The most effective mask for all three letter-array lengths was the one composed of letter fragments subtending 6-6'. The results, together with those of previous experiments, are accounted for in terms of a neural line-detecting mechansim.

Analysis of Variance↗

PubMed1983

An investigation into the representations involved in visual masking.

Two experiments are reported in which the nature of the representations involved in visual masking with spatially overlapping stimuli is investigated. Recent work is described which was consistent with the proposal of Breitmeyer and Ganz (1976) that masking phenomena can be understood in terms of interactions between spatial-frequency-tuned channels. In the first experiment targets which had been filtered to contain only high or low spatial frequencies were masked by high or low frequency masks. The results were more consistent with a model of masking in which higher-order representations, possibly derived from spatial-frequency information, were involved. A second experiment was carried out to test this conjecture which involved investigating the interaction between the effects of learning and the type of information used in target identification. The results provided further support for the model.

Discrimination Learning↗

PubMed1996

Gratings that induce perceptual distortions mask superimposed targets.

Masking is known to depend upon the relationship between the spatial-frequency content of target and mask. This relationship has been held constant in three experiments in order to investigate the separate contribution of the spatial parameters of the mask, in this case a grating with square-wave luminance profile. Thresholds for the detection of a probe target were highest when the background grating upon which the probe was superimposed had a spatial frequency of about 4 cycles deg-1 (experiment 1) and a duty cycle of 50% (experiment 3). In experiment 2, the thresholds were strongly affected by the size of the background grating even though the size of the target was small in proportion to the grating and remained constant. The increase in threshold was linearly related to the area of visual cortex to which the grating projected. The spatial parameters of gratings that maximise masking are therefore the same as those that have been shown to be optimal for the induction of perceptual distortions, suggesting a possible physiological mechanism for both the masking and the distortions.

Adult↗

PubMed2005

Visibility, visual awareness, and visual masking of simple unattended targets are confined to areas in the occipital cortex beyond human V1/V2.

In visual masking, visible targets are rendered invisible by modifying the context in which they are presented, but not by modifying the targets themselves. Here, we localize the neuronal correlates of visual awareness in the human brain by using visual masking illusions. We compare monoptic visual masking activation, which we find within all retinotopic visual areas, with dichoptic masking activation, which we find only in those retinotopic areas downstream of V2. Because monoptic and dichoptic masking are equivalent in magnitude perceptually, the present results establish a lower bound for maintenance of visual awareness of simple unattended targets. Moreover, we find that awareness-correlated circuits for simple targets are restricted to the occipital lobe. This finding provides evidence of an upper boundary in the visual hierarchy for visual awareness of simple unattended targets, thus constraining the location of circuits that maintain the visibility of simple targets to occipital areas beyond V1/V2.

Adolescent↗

PubMed2000

Apparent change of masking functions with compression-type digital hearing aid.

Signal perception ability under conditions of a narrow band masker in subjects with hearing aids was examined using a theoretical model of the auditory nerve fibre (ANF) with a deteriorated tuning curve in addition to measurements of actual masking function in subjects wearing hearing aids. The results obtained indicate that the apparent masking function could be affected by the frequency-gain character as well as by the degree of compression. Usually, the compression-type of amplification with flat and/or high-frequency weighted characteristics improves not only the apparent thresholds but also the apparent masked thresholds under conditions of lower frequency masking. On the other hand, a low-frequency masker amplified by a higher gain with low-frequency weighted amplification could cause larger upward-masking effects on the signal perception of the higher frequency signal in some conditions. The present study may contribute to our understanding of the underlying mechanisms of the effects of different amplification by the aid.

Acoustic Stimulation↗

PubMed2002

Comparison of chamber and face-mask 6.6-hour exposures to ozone on pulmonary function and symptoms responses.

Because of increased interest in an 8-h ozone (O(3)) federal air quality standard, acute pulmonary function responses to prolonged square-wave O(3) exposure between 0.08 and 0.12 ppm have been examined in several U.S. Environmental Protection Agency (EPA) chamber studies. A low-cost face-mask O(3) exposure system was developed in this laboratory and found to produce closely similar pulmonary responses to those observed in prolonged exposures by U.S. EPA investigators. The primary purpose of the present study was to investigate the pulmonary function and subjective symptoms effects of 6.6-h square-wave exposure to 0.12 ppm O(3) by these two methods using the same group of subjects. In addition, further investigation of pulmonary function and symptoms responses upon 6.6-h exposures to lower levels of O(3) (0.04-0.08 ppm) were studied with the face-mask inhalation system. Thirty young adult subjects completed five 6.6-h exposures with six 50-min periods of exercise at an intensity requiring a minute ventilation rate (V(E)) of ~20 L/min/m2 of body surface area, each followed by 10 min of rest, except following 3 h when the rest period was lengthened for a lunch break. The total O(3) doses for the chamber and face-mask exposures to 0.12 ppm O(3) were not significantly different from each other, since the additional O(3) dose during the 35 min lunch break in the chamber exposure was offset by a slightly lower average exercise V(E) (i.e., 19.1 L/min/m2). The data convincingly demonstrated that the two methods of exposing young adults to nearly identical total inhaled O(3) doses at 0.12 ppm produce very similar pulmonary function, symptoms, and exercise ventilatory pattern responses. On the other hand, results of the 6.6-h face-mask exposures to 0.08 ppm O(3) in the present study, compared to similar U.S. EPA exposure study results, revealed several incongruities that may be due primarily to high individual subject variability in responses to a relatively low O(3) exposure. Thus, a comparison of chamber exposure responses to those elicited via face-mask exposure to 0.08 ppm O(3) in the same subject group seems warranted.

Adult↗

PubMed1987

Comparison of indirect calorimetric measurements of resting energy expenditure with a ventilated hood, face mask, and mouthpiece.

This study compared three techniques for indirect calorimetric measurement of resting energy expenditure: ventilated canopy, face mask, mouthpiece plus noseclips. A total of 18 healthy men and women underwent all three measurement techniques in three consecutive 20-min measurement periods in a Latin square design. No significant effects were found for either period or method with respect to oxygen consumption, respiratory exchange ratio, and caloric expenditure. Oxygen consumption was (mean +/- SD) 250 +/- 45, 251 +/- 47, and 254 +/- 49 mL/min for hood, mask, and mouthpiece, respectively (ns). The respiratory exchange ratio was lower for the hood (0.809 +/- 0.051) than mask (0.837 +/- 0.043) and mouthpiece (0.847 +/- 0.045) but this difference was not statistically significant (p = 0.07). Calculated caloric expenditure was 1.20 +/- 0.22, 1.21 +/- 0.22, and 1.23 +/- 0.23 kcal/min for hood, mask, and mouthpiece, respectively (ns). Thus, in healthy individuals similar results are obtained by the three methods and the face mask and mouthpiece are acceptable alternatives to the ventilated hood for estimation of resting energy expenditure.

Adult↗

PubMed1992

Regurgitation of gastric contents during general anaesthesia using the laryngeal mask airway.

We have investigated the incidence of regurgitation of gastric contents during general anaesthesia administered via a laryngeal mask airway (LMA) or face mask and Guedel airway in 56 patients with no risk factors for regurgitation. Patients swallowed a gelatin capsule containing methylene blue 10 min before induction of anaesthesia. Fibreoptic laryngoscopy in the LMA group or conventional laryngoscopy in the face mask group was performed at the end of surgery. Dye was observed within the laryngeal mask in seven of 28 patients (25%). No patients in the face mask-Guedel airway group regurgitated dye (P = 0.005). There was no evidence of aspiration of dye.

Adult↗