Objective: Gastric inflation (GI) is a significant issue when ventilation is performed on unprotected airways.
Design: Experimental analysis on the respiratory effects of hose extended bag-valve ventilation devices designed to reduce inspiratory pressure and flow.
Setting: Laboratory with lung/oesophageal sphincter simulator and pressure-flow-volume analyser. Lung compliance: 300ml/kPa, airway resistance: 0.5kPa/l/s. Lower oesophageal sphincter pressure (LOSP): 0.5kPa.
Interventions: Bag-valve ventilation of lung simulator. Twelve academic dental staff members used four devices: Ambu Mark III attached to either a reservoir bag (R) or a pressure relief valve (SV), SMART BAG (SB), and Easy Grip (EG) as control.
Results: After Bonferroni correction (p-level of significance 0.0083) for multiple comparisons, no evidence of difference between inspiratory tidal volumes (TVIN) administered by use of R (median 137ml) and SB (149ml) was found. Differences in TVIN were only detected between R and SV (188ml) (p=0.002). Only a trend towards TVIN differences between SB and R in comparison to EG (195ml) was found (p=0.009). Distributions of peak pressures differed when R (median 0.7kPa) and SV (1.0kPa) (p=0.006) or SB (0.7kPa) and SV (p=0.002) were compared. Peak inspiratory flow rates differed between EG (median 59l/min) and R (32l/min) as well as SB (42l/min) and between SB and SV (50l/min) (all with p=0.001). GI was lowest by use of R (median 103ml) compared to all other devices (EG: 518ml, SV: 394ml, SB: 271ml) (p=0.001). The areas under the pressure/flow over time curves were larger during SB compared to R ventilation. Mean airway pressures were significantly lower by use of R (0.1kPa) compared to SB (0.3kPa) (p<0.008).
Conclusion: Lowering GI by pressure-flow reduction may result in lower TV depending on the device used. Lowest GI resulted from R ventilation. This may be explained by the specific pressure/time or flow/time patterns achieved by use of this device.