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Background: During mask ventilation, the mask volume can vary as it is pressurized or when it is squeezed. The change in volume of the mask may affect tidal volumes delivered and difference in inspired (V_ti) and expired tidal volumes (V_te). Objectives: To investigate whether hand squeeze and distensibility of the mask during ventilation influences tidal volume measurements. Methods: For both experiments, we ventilated a leak-free mask ventilation model using pressures of 25/5 cm H₂O through a t-piece. V_ti and V_te were measured. (A) Two consultants performed mask ventilation with (1) consistent hand squeeze, (2) release during inflation and squeeze during expiration, (3) squeeze during inflation, release during expiration, and (4) gentle squeeze. Results: (B) Thirty caregivers performed mask ventilation. Experiment A: V_ti was different during consistent hold (1) 8.1 ml (0.4) and loose grip (4) 8.2 ml (0.3), compared to squeezing during inflation (2) 18.9 ml (1.9), or expiration (3) 6.4 ml (3.5). Variance in difference between V_ti and V_te occurred only when the mask was squeezed during inflation (-47.4% (101.5)). Experiment B: volumes measured were consistent (intraindividual CV 3-5%, interindividual CV 9-10%). When comparing gas flow rate of 6-10 l/min, volumes increased by approximately 8%, differences in V_ti and V_te were small with both flow settings (-0.9% (-3.9-1.4) and -0.6% (-3.3-1.8); n.s.). Conclusion: Variation in mask hold during mask ventilation can influence volume measurement, but this hardly occurs when testing caregivers.

Abstractsof pressurization and variation in hand hold, influencing measurements. Aim To investigate whether mask volume varies during mask ventilation and influences measured tidal volumes and calculated mask leak. Methods Thirty caregivers of the neonatal unit were asked to mask-ventilate a leak free manikin with pressures 25/5 cm H 2 O and a gas flow rate of 6 and 10 L/min. A Laerdal 0/1 mask (40 mL) was glued leak free on the face in the right position but the participant was unaware why the mask position was fixed. The participant was told that mask hold, not positioning, was tested and that it was still possible to have leak. Tidal volumes were measured using a RFM. Results Inspired tidal volume (V Ti ) increased from 8.05 mL (0.76) at 6 L/min to 8.76 mL (0.75) at 10 L/min (p<0.01) and expired tidal volume (V Te ) from 8.15 mL (0.81)) at 6 L/min to 8.85 mL (0.75) at 10 L/min (p<0.001). Median (IQR) leak was -0.90 (-3.90-1.40) % with 6 L/min and did not increase with 10 L/min (-0.62 (-3.43-1.80