Article

Precise minute ventilation delivery using a bag-valve mask and audible feedback

Unlabelled imageminute ventilation delivery usin”>American Journal of Emergency Medicine (2012) 30, 1068-1071

Original Contribution

Precise minute ventilation delivery using a bag-valve mask and audible feedback?

Jung Soo Lim MD a, Yong Chul Cho MD a, O Yu Kwon PhD b, Sung Pil Chung MD c,

Kwoen Yu PhD d, Seung Whan Kim MD a,?

aDepartment of Emergency Medicine, Chungnam National University Hospital, Daejeon 301-721, Republic of Korea bDepartment of Anatomy, Medical College of Chungnam National University, Daejeon 301-747, Republic of Korea cDepartment of Emergency Medicine, Gangnam Severance Hospital, Seoul 135-720, Republic of Korea

dAging Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon 305-806, Republic of Korea

Received 29 June 2011; accepted 8 July 2011

Abstract

Objectives: The efficacy of a modified bag-valve mask (BVM) with a ventilation rate alarm system was compared with conventional BVM to maximize adequate minute Ventilation volume delivery in a manikin model.

Methods: After a 30-minute instructional session on how to use the 2 types of BVM, volunteers were randomly assigned to ventilate a manikin in a 2-minute arrest simulation using 2 different types of BVM. The manikin cardiopulmonary resuscitation was performed with a Mechanical chest compression device, to which we added a rate alarm, which makes a ticking sound to indicate each second and buzzes every sixth second, to ensure a regular ventilation rate (10 breaths per minute). Fifty-two volunteers attempted to squeeze the classic BVM at a rate of 8 to 10 times per minute during 2-minute trial (volume marked BVM [VBVM] ). After a 1-hour break, Artificial ventilation was performed at a rate of 9 times per minute with the guidance of the rate alarm (rate and volume adjusted BVM [RVBVM]).

Results: There were no correlations between the data and the participants’ physical characteristics or levels of training. In this study, the accuracy of minute ventilation between the 2 groups showed a significant difference (P b .001). The minute ventilation rate was constant in the RVBVM group, whereas in the VBVM group, the minute ventilation rate was irregular.

Conclusion: In a manikin arrest model, the use of RVBVM results in a more constant and regular minute tidal ventilation rate than the use of VBVM and is, therefore, expected to produce more favorable outcomes in practical resuscitative situations.

(C) 2012

Introduction

? This work was supported by a National Research Foundation of Korea Grant funded by the Korean Government (MEST) (2010-0009806).

* Corresponding author.

E-mail address: [email protected] (S.W. Kim).

Major factors associated with outcomes of cardiopulmo- nary resuscitation (CPR) include ventilation volume and rate. Hyperventilation is a very common problem in both inhospital and out-of-hospital settings, even when profes- sional rescuers perform artificial ventilation using bag-valve

0735-6757/$ – see front matter (C) 2012 doi:10.1016/j.ajem.2011.07.003

masks (BVMs) [1-3]. Although several new ventilation supporting devices have been developed, BVM ventilation is a critical resuscitative method in the emergency department, ambulance, and operating room. Bag-valve mask devices were first introduced in 1955 [4], and over subsequent decades, only minimal changes have been made to their shapes and basic mechanisms. It has been suggested that excessive positive pressure ventilation during resuscitation may be harmful [3]. Some investigators have used audio feedback during CPR to improve ventilation timing and rate [5,6], and use of a metronome for CPR guidance was reported to improve compression and ventilation rates during CPR on manikins in a randomized trial [7]. Therefore, we suggest that providing accessory ventilation rate alarm equipment may improve guidelines for CPR maneuvers.

Artificial ventilation with conventional BVM is widely performed in emergency situations but sometimes results in inadequate minute ventilation volume. In addition, emer- gency care providers may find it difficult to maintain correct ventilation rates due to distracting noises such as high-toned voices, ambulance sirens, and the sounds of medical equipment. In real CPR situations, maintaining an adequate constant ventilation rate is as important as maintaining the correct tidal ventilation volume to prevent complications such as gastric distension, Aspiration pneumonia, and high intrathoracic pressure.

The aim of our study was to compare the efficacy of a conventional BVM with that of a modified BVM with a ventilation rate alarm system to deliver adequate minute ventilation volume in a manikin model. We hypothesized that the use of a unique audible alarm signal alongside a BVM would help operators to maintain constant, adequate ventilation rates throughout the resuscitative interval.

Methods

The study protocol was reviewed and approved by the institutional review board of the study institution. This randomized, nonblinded prospective crossover trial was conducted in the emergency department of a 1200-bed academic urban tertiary care hospital with an annual visiting census of 40 000 patients.

We used CPR manikins such as Little Anne (Laerdal, Stavanger, Norway) for the arrest model. We used a Mechanical chest compression device (automatic simulta- neous sternothoracic CPR system), X-CPR (Humed, Seoul, South Korea), to which we added time alarm equipment that makes a ticking sound every second for 5 seconds and then buzzes every sixth second, to maintain a regular ventilation rate (10 breaths per minute). The maximal noise level of the X-CPR was measured by a sound level meter SDA (Kimo, Monpton, France) at 89 dB in an isolated room. Our improved ventilation volume delivery device is based on a conventional BVM, modified from a 1.6-L adult silicone resuscitator from Laerdal.

After a 30-minute instructional session, the 52 volunteers were each randomly assigned to ventilate a manikin with X- CPR using 1 of the 2 different types of BVM for a 2-minute trial, following the 2010 American Heart Association (AHA) guidelines of 500 to 600 milliliters per breath. The volunteers then switched groups and performed ventilation trials using the other type of BVM.

Each volunteer was instructed to conduct single-rescuer ventilation trials. We used a volume-marked BVM (VBVM) to eliminate bias introduced by inconsistent squeezing vol- umes. We also secured the manikin’s airway by orotracheal intubation and connected these to 2 types of manual resus- citators (Airway Management Trainer; Laerdal Medical, Wappingers Falls, NY). In a previous report, we investigated the effectiveness of a VBVM for achieving adequate tidal volume [8]. In the present study, we tested the hypothesis that the use of a modified BVM with a rate alarm system would facilitate a constant minute tidal ventilation rate.

Volunteers performed artificial ventilation with a standard VBVM (silicone resuscitator; Laerdal, Stavanger, Norway) at a rate of 8 to 10 times per minute for each 2-minute trial, and ventilation frequency per minute was recorded. After a 1-hour break, the volunteers performed artificial ventilation with the modified rate- and volume-adjusted BVM (RVBVM) at a speed of 9 times per minute following a metronome, and ventilation frequency per minute was recorded. Appropriate ventilation was defined as delivery of 8 to 10 times the tidal volume, whereas less than 8 times or greater than 10 times the tidal volume per minute was defined as inappropriate.

Statistical analysis

Categorical variables were expressed as counts and per- centages. The ?2 test or Fisher exact test was used to evaluate clinical factors for their impacts on the rate of ventilation. These data were statistically analyzed by the McNemar test. All analyses were performed using SPSS (version 15.0), and statistical significance was confirmed when P values were less than .05.

Results

We detected no correlations between the data and par- ticipants’ physical characteristics or training levels. Sex, age, job, and skill level did not influence the success rates of VBVM and RVBVM (Table 1). The success rates differed significantly between the 2 groups (Table 2). In the VBVM group, the minute ventilation volume showed an even dis- tribution, but only the RVBVM group delivered constant minute ventilation volumes and rates. According to the 2010 AHA guidelines, the recommended ventilation rate for an adult is 8 to 10 times per minute. All of the volunteers in the RVBVM group were instructed to follow the audible guidance of the modified device. The correct minute

Sex (n = 52)

Male 11 17

.895

28

0

Female 9 15

24

0

Occupation (n = 52)

Physician 7 10

17

0

Nurse 2 3

1.0

5

0

EMT 5 8

13

0

Student 6 11

17

0

Skill level, certificated (n = 52)

None 15 26

41

0

BLS provider 2 6

.122

8

0

ACLS provider 3 0

3

0

EMT indicates emergency medical technician; BLS, basic life support; ACLS, advanced cardiac life support.

ventilation rate was consistently achieved by the RVBVM group, whereas the rate was irregular in the VBVM group (Fig. 1).

Table 1 Comparisons of success rates between VBVM and RVBVM

Variables VBVM P RVBVM Success Failure Success Failure

Discussion

Excessive positive pressure ventilation during resuscita- tion can lead to unstable hemodynamics and negatively influence outcomes [3]. Some studies have reported that hyperventilation is common in both inhospital and out-of- hospital resuscitation, even for highly experienced rescuers [1-3]. Investigations combining laboratory with clinical observations have revealed that overinflation of artificial ventilation devices lowers coronary perfusion pressure during CPR and decreases 1-hour survival rates [3]. Several studies have reported that the introduction of audio feedback during resuscitation leads to improved ventilation times and rates [5,6].

Table 2 Median values (25%-75% interquartile ranges) and accuracy of ventilation rates using each type of BVM

VBVM RVBVM P

Accuracy of optimal ventilation (n, %)

Success 20 (38.5%) 52 (100%) b.001

Failure 32 (61.5%) 0 (0%)

Success rate (%) 50 (25%-93%) 100 b.001

Ventilation rate (n/min) 8.1 (7.0-9.5) 9 b.001 Ventilation type (n, %)

Hypoventilation 22 (42.3%) 0 (0%)

Normoventilation 20 (38.5%) 52 (100%) b.001

Hyperventilation 10 (19.2%) 0 (0%)

Hypoventilation, ventilation rate 7 or less; normoventilation, 8 <=

ventilation rate <= 10; hyperventilation 11 or more; hyperventilation, ventilation rate 11 or more.

Fig. 1 Scatter plot showing differences in ventilation rates between trials using VBVMs and RVBVMs. Dashed lines show the range of optimal ventilation rates according to the 2010 Advanced Cardiac Life Support guidelines for adults.

The recommended ventilation volume for an adult is approximately 500 to 600 mL in each breath, according to the 2010 AHA guidelines. bag-valve mask ventilation with an adequate squeezing rate is likely to minimize or eliminate excessive ventilation volume, a common complication that is associated with high peak airway pressures, gastric inflation, and decreased Cardiac arrest survival. It is challenging to avoid hyperventilation with high or low volume in high- stress situations such as cardiac or respiratory arrest. The use of automatic rate alarm equipment with audio feedback allows the maintenance of adequate minute ventilation volume and provides a simple solution that effectively prevents complications.

In most Emergency care settings, BVM devices are readily available and frequently used. There are some reports that auditory warnings may cause problems in critical care contexts such as intensive care units and Operating rooms, but no studies have been conducted specifically in the emergency care setting. In emergent situations, there are many loud medical devices and personnel, which can be distracting. Moreover, in emergency care facilities, the distractions of noise are further complicated by crowding while performing delicate emergency procedures under demanding circumstances. At present, several types of BVM are commercially available worldwide and can be found in emergency care settings. The maximal tidal volume of an adult manual resuscitator in common use is within the range of 1 to 2 L. There is no definite consensus on how to educate emergency providers as to the most accurate use of BVM and how we can maintain this level. Because the 2 major differences between RVBVM and conventional BVM are

the addition of a regular volume and rate delivery function, education for 30 minutes before each investigation may be adequate to familiarize volunteers with the equipment due to its simplicity.

A previous study reported that metronome guidance was not associated with improved quality of adequate chest compression depth and decreased rescuer fatigue but was associated with correct chest compression rates [9]. The introduction of metronome guidance into a clinical care setting produced higher end-tidal carbon dioxide concentrations [1,10,11]. The simple use of audio prompts to guide chest compression rates, hands-off times, and intubation attempts using a specific-rated metronome and a siren was closely related to improved CPR quality in cardiac arrest patients [12]. Another previous experiment reported that a unique combination of ticking and voice prompting metronomes was effective for directing correct chest compression and ventilation rates before and after intubation [7].

Limitations

Some study limitations should be noted. First, there may be differences in the instructional learning periods required for the 2 devices, despite their relatively simple operations. Second, conventional BVM is more commonly used in emergency care settings, and although the learning period for RVBVM was short, participant performance may have been biased due to familiarity with the conventional BVM. Third, a limitation of rate-adjusted BVM is that it does not account for other factors affecting CPR quality, such as hand position, chest recoil time, compression depth, or personal ability. Finally, we only evaluated ventilation rates for 2 minutes and not throughout the total chest compres- sion procedure period. Because the lung compliance of cardiac arrest patients decreases steeply, it is difficult to investigate the relationship between actual tidal volume and changes in Respiratory physiology. Further investigations are required to more accurately compare RVBVM and conventional BVM equipment.

Conclusions

Raste- and volume-adjusted BVM, a type of adjusted manual resuscitator, allowed emergency care personnel to deliver more constant minute tidal ventilation than VBVM in a manikin model of cardiac arrest. The use of RVBVM is expected to produce more favorable outcomes in clinical resuscitative situations.

References

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