Vital capacity and tidal volume preoxygenation with a mouthpiece.
We have measured oxygen wash-in in 20 volunteers undergoing preoxygenation with a face mask, mouthpiece alone and a mouthpiece with a noseclip, in a crossover study. Tidal volume breathing and maximal deep breath techniques were studied with each type of equipment. When tidal volume breathing was used, the face mask and mouthpiece with noseclip were comparable, but the mouthpiece alone achieved a lower end-expiratory oxygen concentration than the two other methods after 3 min (P < 0.001 and P < 0.01), and after 5 min (P < 0.05 in each case). Conversely, during preoxygenation with vital capacity breaths, the mouthpiece and mouthpiece with noseclip were comparable, and both were more effective than the face mask (P < 0.001). In a second study, 20 patients who had undergone preoxygenation before induction of anaesthesia were asked later if they would have preferred the face mask or mouthpiece for this procedure. Significantly more patients (14 of 18 who expressed a preference) favoured the mouthpiece (P < 0.05; confidence limits 0.56-0.92). (+info)
Reading with central field loss: number of letters masked is more important than the size of the mask in degrees.
When the center of a readers, visual field is blocked from view, reading rates decline and eye movement patterns change. This is true whether the central visual field is blocked artificially (i.e. a mask) or through disease (e.g. a retinal scotoma due to macular degeneration). In past studies, when mask size was defined in terms of the number of letters masked from view, reading rates declined sharply as number of letters masked increased. Patients with larger central scotomas (in degrees of visual angle) also read slower. We sought to determine whether number of letters masked or size of the mask in degrees is the predominant factor affecting reading rates and eye movement behavior. By matching number of letters masked across several mask sizes (and compensating for reduced acuity in the periphery), we found that number of letters masked is the more important factor until mask size is quite large (> or = -7.5 degrees) and number of letters masked from view is more than seven. (+info)
Variability of aerosol delivery via spacer devices in young asthmatic children in daily life.
Pressurized metered dose inhalers (pMDI) are widely used together with spacers for the treatment of asthma in children. However, the variability of daily medication dose for pMDI/spacer combinations is not known. Electrostatic charge is a potential source of dose variability. Metal spacers have no static charge. This study assessed and compared within-subject variability of aerosol delivery of metal and plastic spacers. This was a randomized, crossover study in children with stable asthma aged 1-4 (group I, n=17) and 5-8 (group II, n=16) yrs. In both groups the amount of drug delivered to the mouth by a metal spacer (Nebuchamber) and one of two plastic (polycarbonate) spacers, i.e. Babyhaler in group I and Volumatic in group II was measured. The metal and plastic spacers were tested at home in a randomized order for 7 days each, using budesonide (200 microg b.i.d.). Aerosol was collected on a filter positioned between spacer and facemask or mouth. Budesonide on the filter was assessed by high performance liquid chromatography. The mean filter dose for each child (mean+/-SD) during the 7 days was expressed as a percentage of the nominal dose. Within-subject variability was expressed as coefficient of variation (CV). Mean filter dose in group I was 41.7+/-10.1% for Nebuchamber and 26.0+/-4.0% for Babyhaler (p<0.001). Mean filter dose in group II was 50.2+/-9.2% for Nebuchamber and 19.4+/-7.2% for Volumatic (p<0.001). Mean CV in group I was 34% for Nebuchamber and 37% for Babyhaler (p=0.44). Mean CV in group II was 23% for Nebuchamber and 34% for Volumatic (p=0.003). There was substantial within-subject dose variability in aerosol delivery in children using a pMDI/spacer at home. This variability was lower for the metal than for the plastic spacer in children 5-8 yrs of age. The dose delivered to the mouth was about two-fold higher for the metal than the plastic spacer independent of age. (+info)
Effect of the laryngeal mask airway on oesophageal pH: influence of the volume and pressure inside the cuff.
We studied gastro-oesophageal reflux (GOR) with a face mask and laryngeal mask airway (LMA), and the effects of inflation pressure and volume of the LMA cuff on oesophageal pH, in 60 patients. Patients were managed with either a face mask (group I) or LMA inflated to obtain a seal in the anaesthesia circuit at 7 cm H2O (group II) or 15 cm H2O (group III). A pH-sensitive probe with two electrodes, 10 cm apart, was placed in the oesophagus during anaesthesia and recordings were made continuously until patients awakened. There was a significant difference in the incidence of GOR between the face mask (group I) and the LMA (groups II-III) (P < 0.05) in the lower oesophagus but there was no difference in the mid-oesophagus. No correlation was found between pressure and volume inside the cuff and variations in oesophageal pH. We conclude that LMA use was associated with increased reflux in the low oesophagus but oesophageal pH was not influenced by variations in pressure or volume inside the LMA cuff. (+info)
Measurement for breath concentration of hydrogen and methane in horses.
This study concerns the establishment of a simple testing method for breath concentration of hydrogen and methane in horses. Twenty-eight healthy thoroughbreds and 24 Arabians were used. Breath samples were collected using one-minute closed circulatory respiration through an aluminum bag filled with 10 liters of pure oxygen, which was mounted on the subjects by means of a face mask. Breath samples obtained, were analyzed by gas chromatography. A significant correlation in both hydrogen and methane levels was observed for samples collected at separate times. These findings confirmed the usefulness of our approach for testing breath concentrations of hydrogen and methane in horses. (+info)
Oxygen therapy during exacerbations of chronic obstructive pulmonary disease.
Venturi masks (VMs) and nasal prongs (NPs) are widely used to treat acute respiratory failure (ARF) in chronic obstructive pulmonary disease (COPD). In this study, these devices were compared in terms of their potentiality to worsen respiratory acidosis and their capacity to maintain adequate (> 90%) arterial oxygenation (Sa,O2) through time (approximately 24 h). In a randomized cross-over study, 18 consecutive COPD patients who required hospitalization because of ARF were studied. After determining baseline arterial blood gas levels (on room air), patients were randomized to receive oxygen therapy through a VM or NPs at the lowest possible inspiratory oxygen fraction that resulted in an initial Sa,O2 of > or = 90%. Arterial blood gas levels were measured again 30 min later (on O2), and Sa,O2 recorded using a computer during the subsequent approximately 24 h. Patients were then crossed-over to receive O2 therapy by means of the alternative device (NPs or VM), and the same measurements obtained again in the same order. It was observed that both the VM and NPs improved arterial oxygen tension (p<0.0001) to the same extent (p=NS), without any significant effect upon arterial carbon dioxide tension or pH. However, despite this adequate initial oxygenation, Sa,O2 was < 90% for 3.7+/-3.8 h using the VM and for 5.4+/-5.9 h using NPs (p<0.05). Regression analysis showed that the degree of arterial hypoxaemia (p<0.05) and arterial hypercapnia (p<0.05) present before starting O2 therapy and, particularly, the initial Sa,O2 achieved after initiation of O2 therapy (p<0.0001) enabled the time (in h) that patients would be poorly oxygenated (Sa,O2 < 90%) on follow-up to be predicted. These findings suggest that, in order to maintain an adequate (> 90%) level of arterial oxygenation in patients with chronic obstructive pulmonary disease and moderate acute respiratory failure: 1) the initial arterial oxygen saturation on oxygen should be maximized whenever possible by increasing the inspiratory oxygen fraction; 2) this strategy seems feasible because neither the VM nor NPs worsen respiratory acidosis significantly; and 3) the Venturi mask (better than nasal prongs) should be recommended. (+info)
A simple new technique to measure the effective dead space of the face mask with a water volumeter in infants.
Measuring the effective dead space (EDS) of a face mask has been difficult in infants and the appropriate volume being deducted from lung volume measurements has varied between laboratories. This study measured EDS in 16 infants (age range, 5-36 months) who have cystic fibrosis, undergoing lung volume measurement by N2 washout. A thin plastic bladder, whose neck resided in the mask port, was shaped to fill a size 1 clear face mask. A water volumeter was made by inserting the body of a 20 mL plastic syringe into the neck of the bladder forming a tight seal with a snug fit against the inner surface of the mask port. The mask was placed on a horizontal surface and water was added until a level appeared in the syringe body (V1). At end-inspiration, the mask was briefly placed on the mouth and nose of the sleeping infant, causing the water level to rise in the syringe body (V2). The actual total dead space (V) of the mask when connected to the mouth port of the slide valve was 23 mL. EDS = V- (V2 - V1). Mean (95% confidence interval (95%CI)) EDS was 12.4 (95% CI 11.2, 13.6) mL. The smallest EDS was 8 mL since the connected ports (dead space, 8 mL) were unlikely to be penetrated by the infant's nose or lips. EDS decreased with increasing body weight and height, but seemed to be influenced by individual facial features too. In conclusion, a reliable noninvasive volumetric technique for the routine measurement of the effective dead space in infants has been developed. (+info)
The intubating laryngeal mask airway compared with direct laryngoscopy.
We have compared the ability of naive intubators to intubate the trachea using a laryngoscope and an intubating laryngeal mask airway (ILMA) after receiving basic training, in a randomized, prospective, crossover study in 60 patients. Ventilation of the lungs via the ILMA was also compared with ventilation with a face mask. There was no significant difference in successful intubation between the techniques (38 of 89 with the ILMA and 33 of 93 with direct laryngoscopy; ns). In patients in whom participants failed in their intubation attempts with the ILMA, investigators achieved success in 89% (16 of 18). Satisfactory ventilation was more common with the ILMA (50 of 51) than with the face mask (43 of 60) (P = 0.0001). A total of 98% (89 of 91) of ILMA were inserted successfully, with a mean insertion time of 19.6 s, and 78% (69/89) of these insertions were achieved in less than 26 s. The ILMA may be useful for emergency oxygenation and ventilation, but these results do not support its use for intubation by those not trained in advanced airway management and ILMA use. (+info)