Anatomic accuracy, physiologic characteristics, and fidelity of very low birth weight infant airway simulators

Abstract

Background: Medical simulation training requires realistic simulators with high fidelity. This prospective multi-center study investigated anatomic precision, physiologic characteristics, and fidelity of four commercially available very low birth weight infant simulators.

Methods: We measured airway angles and distances in the simulators Premature AirwayPaul (SIMCharacters), Premature Anne (Laerdal Medical), Premie HAL S2209 (Gaumard), and Preterm Baby (Lifecast Body Simulation) using computer tomography and compared these to human cadavers of premature stillbirths. The simulators' physiologic characteristics were tested, and highly experienced experts rated their physical and functional fidelity.

Results: The airway angles corresponded to those of the reference cadavers in three simulators. The nasal inlet to glottis distance and the mouth aperture to glottis distance were only accurate in one simulator. All simulators had airway resistances up to 20 times higher and compliances up to 19 times lower than published reference values. Fifty-six highly experienced experts gave three simulators (Premature AirwayPaul: 5.1 ± 1.0, Premature Anne 4.9 ± 1.1, Preterm Baby 5.0 ± 1.0) good overall ratings and one simulator (Premie HAL S2209: 2.8 ± 1.0) an unfavorable rating.

Conclusion: The simulator physiology deviated significantly from preterm infants' reference values concerning resistance and compliance, potentially promoting a wrong ventilation technique.

Impact: Very low birth weight infant simulators showed physiological properties far deviating from corresponding patient reference values. Only ventilation with very high peak pressure achieved tidal volumes in the simulators, as aimed at in very low birth weight infants, potentially promoting a wrong ventilation technique. Compared to very low birth weight infant cadavers, most tested simulators accurately reproduced the anatomic angular relationships, but their airway dimensions were relatively too large for the represented body. The more professional experience the experts had, the lower they rated the very low birth weight infant simulators.

Fig. 1. Anatomic precision of the tested simulator airways dimensions compared with human cadavers:

a–d Computed tomography sagittal plane of the very low birth weight infant airway simulators. e–h Sagittal sections of anatomical specimens of premature stillborn infants with corresponding birth weight and gestational age. We measured the angles between the bony palate and (alpha) the nasal inlet, (beta) the mouth inlet, (gamma) the trachea, and (delta) the esophagus (b, f), the distance from the oral inlet to the glottis (c, g) for the oral tube position, and the distances from the nasal inlet to the glottis (d, h) for the nasal tube position. The baseline was placed as a tangent across the hard and soft palate. The line through the nasal inlet was placed centrally in the nasal ostium and then along the inferior conchae. The mouth opening was centered in the mouth inlet in the junction with the mouth outlet below the uvula. The lines through the trachea and esophagus were placed in their respective averaged long axes. In each case, a simulator and an anatomical specimen are shown as examples. In order to standardize the orientation in the figure, some images and the metric scale have been flipped horizontally.

Fig. 2. Airway dimensions of the tested simulators compared with reference values of human cadavers.

a Airway angle deviation and b airway distance deviation in very low birth weight airway simulators compared to anatomical specimen of stillborn preterm infants in corresponding weight categories. The dotted red line shows the mean, the red ribbons the minimal and maximal airway angles and distances in the corresponding reference cadavers.

Fig. 3. Airway and lung physiology of four very low birth weight airway simulators.

The figures show the a resistance, b static compliance, and c tidal volume of the simulators at three ventilation intensities (low, moderate, high) together with the 95% confidence interval of reference values for very low birth weight infants (red area). The ventilator settings were chosen using a constant inspiratory time of 0.3 s, oxygen fraction of 0.21, frequency of 50/min, and a gas flow of 8 l/min. Pressure was chosen as follows: low intensity: peak inspiratory pressure (Pip) low (brown boxplots): 15 cm H₂O, positive end-expiratory pressure (PEEP) 5 cm H₂O, moderate intensity: Pip 20 cm H₂O, PEEP 6 cm H₂O (green boxplots), and high intensity: Pip 25 cm H₂O, PEEP 7 cm H₂O (purple boxplots). We performed each physiologic measurement three times. The bottom figure illustrates the d air leak for tubes of different diameters (2.0, 2.5, 3.0 mm) for each simulator at moderate intensity. Each parameter was measured three times.

Fig. 4. Subcategories of expert rating for each very low birth weight airway simulator.

From left to right: anatomical fidelity, functional fidelity, visual and haptic fidelity, and recommendation level. Orange colors indicate poor rating values and poor recommendation levels.

Fig. 5. Linear multivariate regression model to analyze the impact of the experts’ and hospital characteristics and the simulator type on the total expert rating.

The simulator type impact estimated by the model refers to Premature Anne (Laerdal, Stavanger, Norway), taken as the reference simulator.