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PubMed1998

[Mask induction and one-lung ventilation with sevoflurane].

The low blood/gas solubility, the rapid uptake and nonpungent odor permits mask induction with sevoflurane in adults. Depending on the induction techniques (tidal breathing, deep breaths or single-breath induction), the use of nitrous oxide and the concentration of inspired sevoflurane anesthesia can rapidly be induced within 41-178 s. Adverse effects like coughing, breath-holding or increased secretions occur with a low incidence of 2%-20%. Some 88 to 100% of the volunteers or patients would accept a mask induction again. Clinical experience shows that sevoflurane is well indicated for mask induction in adults. Acute severe bronchospasm is a feared complication of anesthesia with an incidence of 1.7%. Although halothane is often recommended as the agent of choice in patients with reactive airways, there is little evidence in humans that it is more effective than other volatile agents. The bronchodilating effects of sevoflurane are comparable to those of other volatile anesthetics, it produces minimal airway irritation and allows rapid adjustment of anesthetic depth. These properties and our clinical experience suggest that sevoflurane is a useful choice for patients with reactive airways. Hypoxemia during one-lung ventilation (OLV) occurs in 9-27% of patients and remains a clinical problem. Although hypoxic pulmonary vasoconstriction is directly inhibited by volatile anesthetics in in vitro studies, this effect is usually of minor clinical consequence. The use of volatile anesthetics may be advocated because of their salutory effects on bronchomotor tone, high potency (allowing high inspired concentration of oxygen while avoiding awareness) and rapid adjustment of anesthetic depth. Sevoflurane possesses these attributes and may be useful for OLV.

Anesthesia, Inhalation↗
PubMed2000

Evaluation of half-mask respirator protection in styrene-exposed workers.

OBJECTIVE: The protection afforded by respirators to styrene (St)-exposed workers varies considerably. Our objective was to study the effective 'in the field' reduction in St exposure obtained by negative-pressure half-mask respirators worn by a group of fiberglass-reinforced plastics (FRP) workers. Protection was evaluated by measuring the reduction in urinary St (StU) excretion. METHODS: Seven FRP workers not using respiratory protection devices were studied for a week. External exposure to St was evaluated by personal passive sampling, and the internal dose by StU measurement. Then workers were asked to use a half-mask respirator for a week for the entire morning half-shift, and St exposure and internal dose were re-assessed. RESULTS: Mean environmental levels of St during the morning half-shift were 230-280 mg/m3, i.e., about three times the current limit proposed by ACGIH; the difference among days was not significant. Using respirators was accompanied by a large inter-individual and also intra-individual variability: the estimated reduction of StU values ranged from 30% to 90% (mean 60%). Mean StU values increased by 50% from Monday to Friday, while environmental St concentrations remained steady. Furthermore, the proportion of workers exceeding the biological equivalent exposure limit (BEEL) was 14% on Monday, double (33%) on Thursday, and triple (43%) on Friday. These data suggest a decrease of protection during the week. CONCLUSIONS: The protection afforded by negative-pressure half-mask respirators varies widely, which stresses the need to assess the effective reduction of exposure whenever these devices are introduced for St-exposed workers. If respirators are to be re-used for several days, their performance must be evaluated during the last shift of use. Measurement of urinary excretion of unmodified St proved a useful tool for the evaluation of respirator effectiveness in exposed workers.

Air Pollutants, Occupational↗
PubMed2003

[Improved patient repositioning accuracy by integrating an additional jaw fixation into a high precision face mask system in stereotactic radiotherapy of the head].

BACKGROUND: For high precision radiotherapy of the neurocranium a precise, reproducible positioning technique is the basic prerequisite. The aim of this study was to assess the influence of a modification of the commercially available stereotactical BrainLab-head mask system on accuracy in patient positioning during fractionated radiotherapy. MATERIAL AND METHODS: 29 patients were treated with stereotactic radiotherapy of the head. Immobilization was provided by a two layer thermoplastic mask system (BrainLab). 18 of these patients received an additional custom made fixation either of the upper jaw (OKF) or of the mandibula (UKF). The positioning accuracy was assessed by measurements of the shifting of anatomical landmarks in relation to the rigid mask system on biplanar simulator films using a digital imaging system. Before each measurement a fine adjustment of the simulator to an optical ring system was performed. The reference radiographs were done just before CT-planning. During a 2-7 weeks lasting course of radiotherapy displacement measurements in relation to the reference images for all three dimensions (z, y and x) were done once a week. In 29 patients 844 measurements were analyzed. RESULTS: An additional jaw fixation improves the reproducibility of patient positioning significantly in all three spatial dimensions. The standard deviation in lateral direction (x) was 0.6 mm with jaw fixation vs. 0.7 mm without jaw fixation (p < 0.001); in longitudinal direction (z) (measured in 0 degree radiographs) 0.5 mm vs. 1.3 mm (p < 0.001); in longitudinal direction (measured in 90 degrees radiographs) 0.5 mm vs. 1.5 mm (p < 0.001); in vertical direction (y) 0.6 mm vs. 0.9 mm (p = 0.001). No significant differences in standard deviations were found comparing OKF (n = 14) with UKF (n = 4). CONCLUSION: A significant improvement in reposition accuracy using an additional, individually formed jaw fixation can be acquired. The variability of positioning can be reduced especially in the z-direction. A further reduction of the safety margin around the target volume--especially in benign tumors--is possible by improved fixation technique.

Brain Neoplasms↗
PubMed2001

[Patient surgical masks during regional anesthesia. Hygenic necessity or dispensable ritual?].

OBJECTIVE: The use of surgical face masks (SFM) is believed to minimize the transmission of oro- and nasopharyngeal bacteria to wounds and surgical instruments. However, there are disadvantages for patients undergoing regional anaesthesia and wearing masks: deficient assessment of lip cyanosis, anxiety, retention of CO2, costs. Up to now no studies have been published investigating whether or not SFMs, worn by patients during regional anaesthesia, will reduce bacterial convection. METHODS: We investigated 72 patients during aseptic operations: 24 individuals with regional anaesthesia and SFMs, 22 individuals with regional anaesthesia without SFMs and 26 patients undergoing general anaesthesia. Using an air sampler (volumetric impaction method) 100 L air were collected on blood agar over 2 min. After incubation at 37 degrees C over 60 h the colony forming units (CFU) were counted and differentiated. Airborne culturable bacteria were sampled over the operation field, on the anaesthetic side of the surgical curtain, as well as 10 cm before and to the side of the patients mouth. RESULTS: At all 4 locations there were no significant differences in the number of CFUs between patients wearing a SFM or not (e.g. over the operation field: patient with SFM 5.5 +/- 1.1; no SFM 4.8 +/- 1.2; mean +/- SEM). Significantly more CFUs were detected in patients undergoing general anaesthesia (p < or = 0.05). The extent of the operation did not correlate with the number of CFUs; however, we observed a trend that more CFUs were detected with an increasing number of persons working in the operating room. CONCLUSION: Surgical face masks worn by patients during regional anaesthesia, did not reduce the concentration of airborne bacteria over the operation field in our study. Thus they are dispensable. A higher airborne germ concentration has been detected in patients during general anaesthesia. The reasons for this finding are unknown, but it may be discussed as being a result of a higher activity and number of staff involved during general anaesthesia causing more air turbulence.

Adult↗
PubMed2005

[Negative pressure pulmonary edema. Post-obstructive lung edema after use of a laryngeal mask].

A 31-year-old male patient was scheduled for surgical treatment of a distal radius fracture under general anaesthesia using a laryngeal mask airway and spontaneous ventilation. The intraoperative course was uneventful. During recovery, the patient strongly bit the laryngeal mask, producing a complete obstruction of the artificial airway in combination with very forceful inspiratory efforts until the mask was removed. In the recovery room the patient developed dyspnea and desaturation. A portable chest radiograph demonstrated bilateral alveolar infiltration suggesting pulmonary edema. The patient was transferred to the intensive care unit where drug therapy (furosemide and hydrocortisone) and treatment with the continuous flow continuous positive airway pressure (CF-CPAP) system led to complete recovery within 24 h.

Adult↗
PubMed1995

[The laryngeal mask airway in the difficult intubation. The results of a prospective study].

OBJECTIVE: The laryngeal mask airway (LMA) was prospectively used in patients who were difficult to intubate to evaluate whether it improves ventilation compared to a face mask, facilitates fibreoptic intubation, and how often blind intubation would be possible. METHODS: In a university hospital, 30 patients who were difficult to intubate (35 operative procedures) and 50 normal subjects were investigated; 23 patients had had radical resection of a facial tumor with irradiation at a previous time and 7 could not be intubated conventionally (grade 3 and 4 visibility of the larynx according to Cormack [14]). Blind intubation was attempted with a bent bougie, a 6.0-mm uncuffed tube, or a straight bougie. RESULTS: Insertion of the LMA was possible in all except 1 patient with a mouth opening of 1 cm. Ventilation via the LMA was always excellent and, for tumor patients, superior to a face mask. In tumor patients, leak pressure was higher than in patients with normal cervical anatomy either with or without difficult intubation conditions (25.2 +/- 7.9, P < 0.05, vs. 20.8 +/- 4.4 vs. 20.6 +/- 4.9 cmH2O; n.s.; Fig. 2). Fibreoptic intubation through the LMA was successful in all cases and easier than via a nasal or oral route. Blind intubation was successful in 22% of difficult to intubate patients and 19% of normals, mainly using a 6.0 mm uncuffed endotracheal tube. Substitution of an uncuffed oral tube inserted via the LMA by a nasal endotrachel tube using a reinforced stomach tube is described (Fig. 4). CONCLUSION: The LMA improves ventilation, facilitates fibreoptic intubation, and offers the possibility for blind endotracheal intubation in difficult to intubate patients. Blind intubation though the LMA has to be practised extensively to have a high success rate. The LMA represents an additional aid for the anaesthetic management of patients who are difficult to intubate.

Anesthesia↗
PubMed2000

[The laryngeal mask in pediatric adenotonsillectomy. A meta-analysis of medical studies].

Anaesthesia both for adenotomy (AT) and for tonsillectomy (TE) frequently presents a challenge. On one hand, children scheduled for adenotomy often have upper airway infections and are thus at risk of laryngo- and bronchospasm; on the other hand the ENT surgeon and the anaesthetist have to share the "workspace" in the patient's mouth. Since the succinyl choline debate in the early 1990s, the question of the best muscle relaxant has gone hand in hand with that of the most appropriate means of securing the airway. The concept of the laryngeal mask as airway was initially greeted with scepticism. Following several years' use of the mask for this purpose in AT and TE in young children, we report our experience and summarise the literature on this topic. The laryngeal mask represents a safe alternative to intubation, provided there is close cooperation with the ENT surgeon.

Adenoidectomy↗
PubMed1998

[Frequency specificity of acoustic evoked potentials of early and intermediate latency with high-pass noise masking].

In contrast to auditory brainstem potentials (ABR), a more apically defined generation of middle latency evoked potentials (MLR) can be assumed due to the longer integration time present. To date, the effect of stimulus frequency spectra on MLR has not been completely known. By using masking with high-pass filtered white noise in 12 normal-hearing adults, we measured the dependence of amplitude and latency of ABR and MLR on filter frequency. No differences were found between the masking effects for ABR and MLR evoked by tone bursts of 0.5 and 2 kHz. The high-pass masking of click stimuli showed a greater influence on the amplitude and latency of the ABR than on MLR. These different qualities have to be considered clinically when evaluating the methods and results of hearing testing with acoustic evoked potentials. Our findings show that MLR evoked by tone bursts should be used for the frequency selective diagnosis of hearing thresholds, especially in low-frequency ranges.

Acoustic Stimulation↗
PubMedDate not supplied

Bilateral diaphragmatic paralysis after cardiac surgery: ventilatory assistance by nasal mask continuous positive airway pressure.

The case of an 8-month-old boy with bilateral diaphragmatic paralysis after surgical reoperation for congenital heart disease is presented. In order to avoid repeated intubation and long-term mechanical ventilation or tracheotomy, we used nasal mask continuous positive airway pressure (CPAP) as an alternative method for assisted ventilation. Within 24 hours the boy accepted the nasal mask and symptoms such as dyspnea and sweating disappeared. Respiratory movements became regular and oxygen saturation increased. Nasal mask CPAP may serve as an alternative treatment of bilateral diaphragmatic paralysis in infants, thereby avoiding tracheotomy or long-term mechanical ventilation.

Diaphragm↗
PubMed2002

[Drugs for supplementation in cataract surgery with a laryngeal mask].

BACKGROUND: We compared intraocular pressure (IOP), vitreous pressure and several anaesthesiological parameters for patients who underwent cataract surgery with propofol anaesthesia, laryngeal mask and different supplementations with reference to the effect of S-ketamin in particular. PATIENTS AND METHODS: In 4 groups with 15 patients cataract surgery (phacoemulsification) was carried out using anaesthesia with propofol, laryngeal masks and spontaneous breathing if possible, supplementation with propofol (0.6 mg/kg, group 1), S-ketamin (0.3 mg/kg, group 2), ketamin (0.6 mg/kg, group 3) or fentanyl (0.5 microgram/kg, group 4); IOP measurement with tonopen XL and scoring vitreous pressure at different times during anaesthesia (score 0-3). RESULTS: For IOP and vitreous pressure, none of the different supplementations showed a significant difference. Insertion of the laryngeal mask did not cause a rise in intraocular pressure. The number of patients with spontaneous breathing during the operation in group 4 was significantly lower than in groups 1-3. No significant differences were observed between the different anaesthesiological parameters. CONCLUSION: S-Ketamin had no significant effect on IOP and vitreous pressure during phacoemulsification. It offers a safe "handling" of patients because of a high spontaneous breathing rate and lower concentration compared to Ketamin.

Aged↗
PubMed2004

The circadian Clock mutant mouse: impaired masking response to light.

Synchronization of an internal clock (entrainment) and a direct response to light (masking) are complementary ways of restricting activity of an animal to day or night. The protein CLOCK has an important role in the oscillatory mechanism of mammalian pacemakers. Our data show that it is also involved in masking responses. Mice with the Clock/Clock mutation reduced their wheel running less than wildtypes when given 1-h light pulses of light (2-1,600 lx) in the night. With dimmer lights (<2 lx), there were no significant differences between mutant and wildtype mice. Impaired masking responses to light in Clock/Clock mice were confirmed in tests with ultradian light-dark cycles (3.5:3.5 h and 1:1 h). Tests with pulses of light longer than 1 h revealed that, although the mutants responded more slowly to light, they sustained the suppression of activity over the course of the 3-h tests better than wildtypes.

Activity Cycles↗
PubMed2005

The incidence and risk factors of difficult mask ventilation.

PURPOSE: The ability to ventilate and oxygenate a patient using a bag-mask breathing system may be lifesaving in the case of failure of the initial intubation attempt. In this study, we aimed to determine the incidence of difficult mask ventilation (DMV) and to find preoperative risk factors for this procedure. METHODS: Based on methods used for overcoming some difficulties with bag-mask ventilation (MV), classification has been made into four categories: easy MV, awkward MV, difficult MV, and impossible MV. A univariate analysis was performed to identify potential risk factors predicting DMV, followed by a stepwise forward binary logistic regression, and the odds ratio and 95% confidence interval were calculated. RESULTS: A total of 576 patients were studied. Incidence of easy MV, awkward MV, and difficult MV were found to be 75.5% (n = 435), 16.7% (n = 96), and 7.8% (n = 45), respectively. Height, weight, age, male gender, increased Mallampati class, history of snoring, lack of teeth, and beard were found to be DMV risk factors (P < 0.05). Using a multivariate analysis, Mallampati class 4, male, history of snoring, age, and weight were found to be significantly associated with DMV. Although the incidence of DMV in general was 7.8% (n = 45), the incidence of DMV among patients with difficult intubation (n = 123) was found to be 15.5% (n = 19). CONCLUSIONS: Mallampati class 4, male patients, history of snoring, increasing age, and increasing weight were found to be risk factors for DMV in our study.

Adult↗
PubMed1992

Is rapid performance improvement across short precue-target delays due to masking from peripheral precues?

The role of lateral masking in more rapid performance improvement with peripheral than with central precuing was investigated. A peripheral precue to the inside of the target location provided less masking at zero precue-target delay than a precue to the outside (experiment 1) or a precue involving a partial target at the target location (experiment 2). There was no significant interaction between precue-target delay and precue type in a comparison of inside precues and precues involving a briefly-brightened box around the target location, although overall performance was significantly poorer with the latter (experiment 3). Performance was better at short precue-target delays with inside precues than with central precues (experiment 4), yet it did not improve significantly more rapidly. Minimizing lateral masking with peripheral precues thus eliminates the dramatic performance improvement sometimes observed across short precue-target delays, causing performance to be consistently better than with central precues across these delays.

Adult↗
PubMed1985

Continuous positive airway pressure by face mask in acute cardiogenic pulmonary edema.

The therapeutic efficacy of continuous positive airway pressure (CPAP) administered by face mask was studied in 40 patients with acute cardiogenic pulmonary edema and respiratory failure. Arterial blood gas values and pH, systemic arterial pressure, heart rate and respiratory rate were measured during administration of 30% oxygen with a high-flow face mask apparatus at ambient airway pressure. Twenty patients were then randomly chosen to continue ambient airway pressure breathing and 20 received 10 cm H2O of CPAP. The measurements were repeated 10, 60 and 180 minutes after therapy was initiated. During the first 10 minutes of CPAP treatment, arterial blood oxygen partial pressure increased 8 +/- 9 mm Hg (mean +/- 1 standard deviation), (p less than 0.01) and respiratory rate decreased 5 +/- 5 breaths/min (p less than 0.001). Systolic arterial pressure decreased 12 +/- 21 mm Hg (p less than 0.05), and heart rate by 10 +/- 11 beats/min (p less than 0.001). A decrease in respiratory rate by 2 +/- 5 breaths/min (p less than 0.05) was the only change that occurred in the control group. The improvement in arterial blood oxygenation persisted throughout the investigation period (p less than 0.05). Thirteen patients (65%) in the control group and 7 patients (35%) in the CPAP group met our criteria for treatment failure during the study (p = 0.068). Thus, CPAP administered by face mask improves gas exchange, decreases respiratory work, unloads circulatory stress, and may reduce the need for ventilator treatment in acute cardiogenic pulmonary edema.

Acute Disease↗
PubMed1975

Role of neocortex in binsural hearing in the cat. I. Contralateral masking.

Cats with earphones were trained with a shock avoidance procedure to detect the occurrence of 1 kHz tone pulses at one ear while continuous noise pulses were simultaneously presented to the opposite ear. For normal cats the presence of the noise produced a mean increase of 5.4 dB in the thresholds for detection of tones at the opposite ears. After large unilateral auditory cortex ablations the same cats exhibited an asymmetry between the ears in the size of the contralateral masking effect. There was a mean increase of 10.9 dB in the detection thresholds for tones at the ear contralateral to the damaged hemisphere when noise was presented to the ear opposite the intact hemisphere. Noise of the same physical intensity when presented to the ear contralateral to the damaged cortex produced no significant changes from the preoperative masking levels. Subsequent ablation of the auditory cortex of the opposite hemisphere resulted in a cancellation of the unilateral lesion effect; the cats exhibited interaurally symmetrical masking levels of the same magnitude as those observed prior to the first operation. Additional control tests indicate that the unilateral lesion effect is a central nervous system phenomenon and is specific to lesions of auditory cortex.

Animals↗
PubMed1980

Temporal response characteristics of cells in monkey striate cortex measured with metacontrast masking and brightness discrimination.

After measuring metacontrast masking psychophysically in two monkeys, recordings from parafoveal striate cortex of the monkeys were made while they performed a simultaneous brightness discrimination and while they judged the apparent brightness of a stimulus masked by metacontrast. The size and orientation of the stimuli were held constant regardless of receptive field parameters. In both tasks, the single-cell activity immediately following the presentation of flashed discrimination stimuli reflected only stimulus parameters, and was independent of the monkey's behavioral choice. Later activity (up to 400 msec post-stimulus) was significantly greater if the monkey was about to press the correct panel in the discrimination, or if he pressed the unmasked side (with greater apparent brightness but identical intensity) in the masking paradigm. One quarter of the cells showed a change in firing rate during the 250 msec preceding the behavioral response, though the difference in overall firing level between correct and incorrect brightness discrimination trials was diminished in this epoch, and the corresponding firing difference in metacontrast trials was not significant. The temporal pattern of firing also differed between correct and incorrect trials in the pre-response interval. The results suggest an iterative or recurrent coding of visual information, where the same cells participate in early, late, preresponse coding in different ways.

Animals↗
PubMed1986

Control of human optokinetic nystagmus by the central and peripheral retina: effects of partial visual field masking, scotopic vision and central retinal scotomata.

Optokinetic nystagmus (OKN) was elicited in humans by a horizontally moving grating covering the whole visual field. Selective stimulation of central or peripheral parts of the retina was achieved by partial masking or scotopic viewing conditions in normals; three patients with a unilateral central retinal scotoma were studied in addition. In all cases, the elimination of foveal stimulation was accompanied by a decrease in OKN slow phase velocity compared to whole field stimulation. Vertical masks with retinally stabilized edges were used to selectively occlude or stimulate central or peripheral sectors with a fixed retinal location. A central stimulus was always more effective than the complementary peripheral stimulus, until the central zone was narrowed down to a width of 5-10 degrees. This central dominance was found throughout the range of velocities (6-180 degrees/s) and spatial frequencies (0.05-0.5 cycles/deg) used. A horizontal central band of occlusion caused a smaller decrease of OKN than a vertical occlusion with the same width. Scotopic vision caused a uniform mild decrease in OKN gain throughout the velocity range, provided that the spatio-temporal frequency of the stimulus remained within the scotopic resolution range. The patients had a slightly lower OKN gain when viewing with the scotomatous eye than with the contralateral, normal eye. The normal slight preference for temporal-to-nasal motion was not accentuated by masking or scotopic vision in normal eyes, but was enhanced in the eyes with the pathological scotomata in two of the three patients. All responses were immediate; no slow build-up was seen under any condition.

Adult↗
PubMed1985

A semi-rigid transparent face mask in the treatment of postburn hypertrophic scars.

Scars, following burns to the face or subsequent skin grafts, can become hypertrophic. The concept of pressure in their treatment is not new. Elastic garments have been popularised and used successfully. However, they have certain limitations. To date, very little reference has been made in the literature to the use of masks. The use of a semi-rigid face mask in the treatment of hypertrophic scars is described. These masks are comfortable to wear, well tolerated and very effective. Case reports are presented and the technique of manufacture detailed.

Adult↗