Introduction
The volume of air that does not engage in alveolar gas exchange during ventilation is called dead space. 1 Physiological quiet space exists during normal breathing in the resting state. Anatomical and functional/alveolar dead space is included in physiological dead space. The physiological and anatomical dead space is nearly equal in a typical individual.
Alveoli with little or no blood flow have a minimal functional dead space. Therefore, the quiet room is impacted during anesthetic administration. 2 It is critical to minimize dead space to avoid re-breathing, resulting in hypercarbia, particularly in newborns and toddlers. The most typical effect of an increase in quiet physiological area is an increase in the partial pressure of carbon dioxide (PaCO2), which increases blood acidity and a reduction in pH. The minute volume must be raised to maintain an average PaCO2 level to compensate for the risen dead space.
3 With significant anatomical dead space, neither increased gas flow nor minute volume increase may be sufficient to avoid re-breathing.
The volume provided by a mask, an artificial airway, and the posture of the head all contribute to the rise in dead space during anesthetic administration. Age also plays a role since babies and children have smaller alveoli, and chest wall collapse may diminish quiet physical area when negative intrathoracic pressures are decreased. 4 Dead space may be calculated as 1 milliliter per pound (2.2 milliliters per kilogram) of body weight in a typical healthy individual, although this has been found to be erroneous. 5 In healthy lungs, the ratio of dead space to tidal volume is around 0.3. Increased total dead space is more significant in newborns than in adults, since children’s tidal volumes are lower. 2 Thus, any contribution to dead space is critical and should be minimized, since it may result in catastrophic repercussions such as hypercapnia, dysrhythmias, and even cardiac arrest.
At the Bloemfontein Academic Hospital Complex, formed masks with an inflatable polyvinylchloride (PVC) cuff are used in conjunction with circular, domed masks with a non-inflatable PVC cuff. Domed masks may be simpler to produce and do not need an inflated cuff, which makes them more affordable. Inflating or deflating the cuff has the effect of increasing or decreasing the mask’s dead space. According to Smith’s Anesthesia for Infants and Children, two paediatric face masks should be manufactured of translucent plastic to enable for cyanosis examination and to fit the child’s face securely. There are several varieties of face masks available, but the most often used is a plastic disposable mask with an inflated cuff. A mask of the proper size should sit on the bridge of the nose and reach all the way to the jaw. 2 For the reasons stated before, dead space should be reduced during anaesthesia.
Aim
The purpose of this research was to quantify and compare the volume contributed to anatomical dead space by formed and rounded masks of comparable size (Supplementary figure 1) to discover which style of mask contributes the least volume. Additionally, the influence of cuff inflation pressure on the volume of created masks was determined.
Methods
This was a laboratory experiment. The research used baby, child, and adult part-task trainers located in the Clinical Simulation Unit at the University of the Free State’s School of Medicine (UFS).
The trial enrolled no patients. We employed two different kinds of masks: shaped masks with inflated PVC cuffs and rounded masks with non-inflatable PVC cuffs.
The Department of Health provides these masks for usage at the Academic Hospital Complex in Bloemfontein.
Six sizes of formed masks were available (00, 02, 04, 06, 08, and 10) and three sizes of rounded masks (00, 02 and 04). The three adult-sized spherical masks were no longer manufactured at the time of the investigation.
Different situations were generated to determine the volume of the six produced masks of varying sizes. The created masks’ cuffs were inflated to a depth of 5 cm water (creating a soft air-filled cushion) and 70 cm water (creating a rigid stiff cushion). Pressure was determined using an aneroid cuff inflate. The mask volumes were determined by pressing the manufactured masks against the faces of part-task trainers and then on a flat surface. Due to the stiff cuff on the conventional spherical masks, an acceptable fit could not be achieved. Even with tremendous effort, mask leakage was unavoidable. As a result, the volume of the rounded masks was calculated just using a flat surface. The molded masks fit snugly against the parttask trainers without requiring excessive effort.
Measurements
To increase the measurement’s precision, the nose and mouth holes of the three part-task trainers were sealed with a temporary putty-like glue. The volume was calculated while the mask was on the face of the part-task trainer to account for characteristics such as nose and lip volume. For the measurements on a flat surface, external pressure was applied to the masks.
The masks were completely filled with water from a volumetric flask using various sized syringes each containing a specified amount of water. The volume contained inside the mask was calculated by subtracting the volume left in the volumetric flask from the initial volume.
Three student researchers worked under the direction of the study leader to determine the volume of each mask. The findings were documented on a data sheet.
Pilot study
To validate the methodologies and equipment, a pilot research was conducted utilizing the baby part-task trainer at the Clinical Simulation Unit of the School of Medicine, UFS. Three student researchers measured masks in sizes 02 and 04, which are suitable for newborn usage, in order to determine the volume of the formed and rounded masks in the various circumstances. While the masks were being filled with water, several techniques of closing the masks to avoid leaking were evaluated. No leakage occurred as a consequence of the putty-like glue and external pressure. The pilot research’s data were included into the larger study.
Data analysis
The data was put into an Excel® spreadsheet (Microsoft Corporation, Redmond, Washington, USA). To increase the accuracy, the mean of the three values from three distinct students was employed.
Means and standard deviations were used to summarize the data.
To compare mask kinds, paired t-tests were conducted with a significance threshold of 5%. Masks of the same size were compared in terms of volume; hence, for the three biggest sizes, only formed masks were compared, but for the three lesser sizes, both rounded and formed masks were compared.
Ethical considerations
The Health Sciences Research Ethics Committee (HSREC) of UFS authorized the project [HSREC-S 25/2016]. Permission to utilize the facility and its part-task trainers was secured by the Clinical Simulation Unit, School of Medicine, UFS.
Results
The volumes of various formed mask kinds and sizes on the faces of part-task trainers and on a flat surface are listed in Table 1. On a level surface, the volumes (ml) of the masks were considerably greater than those measured on the faces of the part-task trainers (5 cm p-value = 0.02; 70 cm p-value = 0.01). Masks with cuffs inflated to 70 cm water contained considerably more water than masks with cuffs inflated to 5 cm water (on part-task trainer, p-value = 0.07; flat surface, p-value = 0.16).
The volumes of the rounded masks for the three sizes for which these markings were accessible are listed in Table 2, along with the volumes of the matching formed masks.
The volume of rounded masks was greater than that of formed masks (Table 2), although not substantially (p-values ranging from 0.14 to 0.25).
Discussion
Comparing a mask worn on the face to a mask worn on a flat surface
As predicted, the nose, lips, and face features all have a substantial effect on the volumes by reducing them.
The created mask’s cuff was inflated to 5 centimeters of water, as opposed to 70 centimeters.
The volume difference between a constructed mask inflated to 5 cm water and one inflated to 70 cm water was not statistically significant.
Though the formed masks fit comfortably on the face (or part-task trainer), the somewhat increased pressure required for a snug fit combined with increased cuff inflation pressures may result in less dead space for that mask.
In comparison to shaped masks, rounded masks
The rounder masks had a larger volume than the shaped masks (but without statistical significance). This is to be anticipated, since shaped masks are meant to match the facial contour more closely and hence have a smaller volume, contributing less to dead space. The cuff of the circular masks cannot be inflated, which presumably simplifies and reduces manufacturing costs. As the unyielding cuff of the rounded mask makes achieving a snug fit more difficult, the pressure required to achieve a snug fit may result in less dead space. While a tight fit for the circular masks was not attainable on the part-task trainees, it may be conceivable on a child’s softer face tissue. In practice, however, one would avoid squeezing too firmly with a mask, since this may exacerbate claustrophobia and may cause tissue damage.
Limitations of the study
The sample size was less than anticipated due to the discontinuation of production of the three adult-sized spherical masks.
There were just three sizes available for the circular masks.
External force was required to create an effective seal between the mask and the surface of the part-task trainers’ faces. This reduced the volume of the mask, particularly in the rounded masks, to the point that readings on the part-task trainer’s face would be erroneous; hence, rounded mask measurements were conducted only on a flat surface.
Water was employed to determine dead space instead of air.
Due to the small sample size (one of each size), changes in production quality could not be determined. Additional research may be conducted to determine the quality and dependability of masks given to the hospital.
Conclusions
External force reduces the mask’s volume.
Masks that were formed supplied less dead space than masks that were rounded. The inflation pressure of plastic cuffs has a negligible influence on the amount of dead space.
