A comparison of bag mask and mouth mask ventilation in anaesthetised patients

Device capable of reducing gastric inflation during artificial ventilation in a manikin model

Gastric inflation is a significant issue when ventilation is performed in cases of unprotected airway. The objective of this study was to compare the amounts of gastric insufflation and tidal volumes produced by a hose-extended bag-valve-mask (BVM) device supplemented by an interposed reservoir bag with a similar BVM without the reservoir in a simulated human model. Fourteen academic dental staff members performed 10 ventilations on a manikin using the reservoir-supplemented device in comparison to the control BVM in a randomized order. Lung compliance was adjusted to 45 (high) and 4.5 mL/mbar (low), and the lower esophageal sphincter pressure (LOSP) simulator to a pressure of 15 and 3 mbar, respectively, in different settings. Lower tidal volumes were observed with the new device than with the control BVM at high compliance with LOSP of 15 mbar (median 506 vs. 787 mL, respectively; p = 0.0002) and LOSP of 3 mbar (median 544 vs. 794 mL, respectively; p = 0.0006), as well as during ventilation at low lung compliance and LOSP of 3mbar (median 131 vs. 163 mL, respectively; p = 0.0342). No differences were detected at low lung compliance and LOSP of 15 mbar (median 175 vs. 194 mL; p = 0.3804). Gastric inflation almost exclusively occurred in case of low lung compliance, being markedly lower with the new device than with the control device at 15 mbar LOSP (300 vs. 2225 mL, respectively; p = 0.0006), and at 3 mbar LOSP (1138 vs. 3050 mL, respectively; p = 0.0001). Application of the hose-extended bag-valve-mask device supplemented with a reservoir bag reduces tidal volumes. Marked reduction of gastric inflation by use of this device becomes effective under conditions with low lung compliance.

Comparison of different flow-reducing bag-valve ventilation devices regarding respiratory mechanics and gastric inflation in an unprotected airway model

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.

The effect of neuromuscular blockade on the efficiency of mask ventilation of the lungs

We conducted a two-part study to assess the practice of withholding neuromuscular blockade until the ability to ventilate the lungs using a bag and face mask (mask ventilation) has been established following induction of anaesthesia. The first part of the study consisted of a postal survey (71% response rate) of 188 anaesthetists in the Oxford region to assess their current practice. Thirty per cent of respondents always checked mask ventilation before administering a neuromuscular blocking drug, whereas 39% of respondents (all them consultants) never did this. A further 31% only did so in the case of known or anticipated difficulty with the airway. In the second part of the study, we measured inspired (V(TI)) and expired (V(TE)) tidal volumes before and after neuromuscular blockade in 30 patients undergoing general anaesthesia. The ratio V(TE)/V(TI) was used as a measure of the efficiency of ventilation. There was no difference in V(TE)/V(TI) before [mean (SD) 0.47 (0.13)] and after [0.45 (0.13)] neuromuscular blockade. We conclude that neuromuscular blockade does not affect the efficiency of mask ventilation in patients with normal airways.

Advances in airway management

Emergency ventilation is an essential component of basic life support. Respiratory emergencies occur far more frequently than cardiac arrest and, if not treated promptly and effectively, may lead to cardiac arrest. Many respiratory emergencies require assisted ventilation to prevent the occurrence of hypoxemia, hypercarbia, and cardiac decompensation. Emergency assisted ventilation is often difficult to perform and is associated with several adverse complications, such as gastric inflation, regurgitation, and pulmonary aspiration. The American Heart Association sponsored conferences in 1999 and 2000 to review and revise guidelines for cardiopulmonary resuscitation. This article reviews the science behind guideline changes related to pulmonary resuscitation and discusses recent advances in emergency airway management, focusing on noninvasive techniques for ventilation (mouth-to-mouth ventilation, bag-mask ventilation) and alternative airway devices (laryngeal mask airway, the Combitube).

Towards early defibrillation--a nurse training programme in the use of automated external defibrillators

It is essential that all health care professionals are regularly trained in the practice of basic life support (BLS). In most cases of cardiac arrest, the chances of a favourable outcome depend not only on efficient BLS, but also on the early use of defibrillation. In a hospital environment, the first responders are most likely to be members of the nursing staff. The potential advantage of these personnel being able to perform early defibrillation, as well as BLS, is considerable. We describe an initiative in which instruction in the use of automated external defibrillators (AEDs) was introduced into routine BLS training sessions, with the aim of developing this capability. Using specifically-acquired training aids, 43 nurses and nine other members of the non-medical staff were trained in 12 teaching sessions over a period of 4 months. Refresher training was carried out after 6 months and 37 nurses were retrained during six sessions using a similar syllabus. The programme was well-received by all students, and a higher than expected level of motivation and competence was achieved. Throughout retraining all nurses appreciated the key importance of early defibrillation. We conclude that, although the initial workload is high, it is entirely feasible to augment BLS training for health care professionals with instruction in the use of AEDs. We recommend that this potentially life-saving tuition programme be widely adopted.