Background Little is known regarding the variations in effective ventilation during bag and mask resuscitation with standard methods compared with that delivered by ventilator-delivered mask ventilation (VDMV).
Aim To measure the variations in delivered airway pressure, tidal volume (TV), minute ventilation (MV) and inspiratory time during a 3-min period of mask ventilation comparing VDMV with three commonly used hand-delivered methods of bag and mask ventilation: Laerdal self-inflating bag (SIB); anaesthetic bag and T-piece Neopuff.
Methods A modified resuscitation manikin was used to measure variation in mechanical ventilation during 3-min periods of mask ventilation. Thirty-six experienced practitioners gave positive pressure mask ventilation targeting acceptable chest wall movement with a rate of 60 inflations/min and when pressures could be targeted or set, a peak inspiratory pressure (PIP) of 18 cm water, positive end-expiratory pressure (PEEP) of 5 cm water, for 3 min with each of the four mask ventilation methods. Each mode was randomly sequenced.
Results A total of 21 136 inflations were recorded and analysed. VDMV achieved PIP and PEEP closest to that targeted and significantly lower variation in all measured parameters (p<0.001) other than with PIP. SIB delivered TV and MV over twice that delivered by VDMV and Neopuff.
Conclusion During 3-min periods of mask ventilation on a manikin, VDMV produced the least variation in delivered ventilation. SIB produced wide variation and unacceptably high TV and MV in experienced hands.
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Of the 140 million babies born annually, an estimated 7–22.4 million (between 5% and 16 %) of all newborn babies require resuscitation, making this one of the most common medical emergency procedures.1 2 Most respond to effective positive pressure ventilation delivered by manual devices.3 Many babies who do not receive adequate ventilation may unnecessarily receive cardiac compression or epinephrine.4 Over-ventilation of the lungs is a potentially serious side-effect of positive pressure ventilation. In animal models of resuscitation, hyperventilation has been shown to affect haemodynamics adversely, increase pulmonary vascular resistance and increase mortality.5,–,8 Björklund et al9 demonstrated that as few as six excessive tidal breaths delivered to preterm newborn lambs caused severe lung injury. A recent study of extremely premature infants in the state of New South Wales, Australia, has determined that at least 24.6% are born in non-tertiary units.10 Staff in special care units and smaller hospitals have most likely been trained using term baby manikins yet would be called upon to resuscitate preterm infants delivered emergently in their units. Studies of human adult resuscitation have demonstrated that significant hyperventilation is common.8 Excessive ventilation with hypocarbia in preterm babies has been linked to the development of bronchopulmonary dysplasia,11 12 periventricular leucomalacia13,–,15 and intraventricular haemorrhage.16 17 In term babies, hypocarbia following intrapartum asphyxia has been associated with increased odds of death or serious neurodisability.18 A recent large survey of neonatal resuscitation education experience in New South Wales and Australian Capital Territory, Australia, has shown three-quarters of births occurring in rural or urban non-tertiary hospitals where one-third of health personnel are inadequately trained.19 We have previously reported unintended hyperventilation with resultant severe hypocarbia in 26% of a cohort of extremely preterm babies ventilated and monitored in a blinded fashion from delivery suite to arrival in the neonatal intensive care unit (NICU).20 Common devices used in resuscitation are self-inflating bags (SIB), flow-inflating bags (anaesthetic bags) and T-piece resuscitator systems using round masks or moulded anatomical masks. Laerdal manikins (Laerdal Medical, Oakleigh, Australia) are used most frequently to train resuscitators.21 We use the Laerdal manikin advanced life support trainer (ALST) baby model to teach mask ventilation and intubation. This device has dual lung ‘bags’ connected to the ‘trachea’ and an additional bag connected to an ‘oesophagus’ to simulate the leak into the stomach if there is incorrect head positioning. The Laerdal ALST manikin has a closed system with lung and stomach bags with no intended leak. The Laerdal ALST manikin has a hinged mandible allowing a realistic jaw thrust.21 This model differs from the Laerdal ‘Resusci baby’, which is simpler and has an intentional internal leak. Studies of effective ventilation of a neonatal manikin in training are few and have focused on delivered pressures22 23 and mask leak.24,–,29 Manikins have been variously and substantially modified to allow these assessments. Studies have not been conducted to examine the differences in delivered minute ventilation (MV) or the level of variance in tidal volumes (TV) and inspiratory times.
What is already known on this topic
▶ There is significant variability in airway pressure delivery with different mask ventilation devices.
▶ Even a few excessive TV breaths delivered at birth in preterm animals have the potential to cause lung injury.
What this paper adds
▶ SIB and anaesthetic bag devices can deliver excessive, potentially harmful TV and MV with large variation compared with T-piece resuscitators and VDMV.
▶ VDMV in a manikin study achieved the closest PIP and PEEP to set values with the least variation compared with other methods.
The advances in the technology around manual ventilation from SIB, through to anaesthetic bags then to the T-piece resuscitator has allowed more consistent operator control in delivering a targeted positive end-expiratory pressure (PEEP) and peak inspiratory pressure (PIP).22 23 The T-piece resuscitators are similar to a ventilator with set PIP and set PEEP with the inspiratory time and rate variably determined by the finger occlusion time on the T-piece. Bennett et al30 have shown difficulty in rapidly increasing the PIP from 20 to 40 cm water using a T-piece resuscitator during a manikin study. The null hypothesis for this investigation was no difference in delivered ventilation (mean and variance) between the new mode of ventilator-delivered mask ventilation (VDMV) and the three standard methods of mask ventilation. We aimed to determine the delivered ventilation and its variability in a modified Laerdal neonatal manikin in periods of 3 min of mask ventilation comparing three ‘standard methods’ with that of VDMV using a Dräger Babylog 8000 plus ventilator (Dräger, Lubeck, Germany).
Materials and methods
Experienced staff working in the newborn intensive care nursery at a major teaching hospital (Nepean Hospital) in Western Sydney were invited to participate. A total of 36 volunteers from among medical and neonatal nursing staff performed 3-min episodes of mask ventilation on the modified Laerdal ALST baby manikin. The staff rotated through four test modes randomly allocated with 3-min rest periods between modes. All staff tested had previously had extensive training in neonatal resuscitation and demonstrated proficiency annually in the locally run NICU resuscitation course. This course uses the American Academy of Pediatrics Neonatal Resuscitation Program.31 The mask hold taught for SIB, Neopuff and anaesthetic bags is the two point top hold as described by Wood et al.25 Staff participating were grouped as: (1) senior staff specialists (n=4); (2) junior medical (registrars and fellows) (n=9); (3) senior nursing staff (unit managers and nurse educators) (n=5) and (4) neonatal nurses fully neonatal intensive care trained (n=18). The four modes of ventilation were: (1) anaesthetic bags; (2) Laerdal SIB; (3) Neopuff; (4) VDMV.
Description of the mask ventilation devices
The standard devices were: (1) an anaesthetic bag 500 ml (Vital Signs, Totowa, New Jersey, USA); (2) an SIB (Laerdal 240 ml resuscitation bag; Laerdal Medical); (3) a T-piece system delivering PEEP and PIP (Neopuff Fisher and Paykel Health Care, Auckland, New Zealand). The new method being compared was VDMV using a Dräger Babylog 8000 plus (Dräger) permanently mounted on a dedicated mobile intensive care resuscitation system with uninterrupted power supply (UPS) power, blended air/oxygen. The mask used was a Laerdal size 1/0 round silicone mask (Laerdal Medical). VDMV is taught using both hands to hold the mask to the face covering mouth, nose and tip of chin with the thumb and first finger holding the upper rim of the mask at four points equidistant applying balanced force down while the second to fifth fingers curl under the mandible to apply jaw thrust lift the face into the mask and correct head positioning (figures 1 and 2). The four-point grip applied in this manner does not distort the rim of the mask as may be the case with a single-handed mask application with only two fingers applied in a pincer grip.
The manikin model
The Laerdal ALST baby manikin was modified minimally by inserting a calibrated COSMO Plus (Phillips Respironics, Amsterdam, The Netherlands; http://cosmomainstream.respironics.com) pressure differential pneumotach with dead space of less than 1 ml between the standard Laerdal lung bags and the manikin tracheal tube. The manikin was tested for internal leak by intubating and blocking the upper airway at the ‘larynx’, connecting the Babylog 8000 plus (Dräger) and determining a zero leak from the Dräger hot wire pneumotach during ventilation. The ‘oesophageal’ tube and ‘stomach’ bag were specifically left intact to allow findings of this study to be more easily applied to the commercially available Laerdal ALST baby manikin. The static compliance of the model was calculated by measuring the inspired volume of the system (with oesophageal tube blocked). When pressured to 25 cm water this was 3.9 ml/cm water. This is comparable with that of a term newborn with healthy lungs.32
The COSMO plus connected serially to a laptop running Analysis Plus V5 (Phillips Respironics). Respiratory wave forms for pressure, flow and volume were collected at 100 Hz generating data for breath by breath mechanics. Data for each breath were exported to a statistical program. The COSMO plus disposable pneumotach is pressure differential in type and was calibrated externally with a syringe of known volume and pressure/flow by means of a ventilator calibration analyser with pressure resolution of 0.1 cm water; with pressure accuracy of ±0.5% and flow calibration with resolution of 0.1 l/min with accuracy of ±1% (RT-200, Timeter Instrument; Allied Healthcare Products, St Louis, Missouri, USA). Analysis plus software produced breath by breath TV expired, MV, PIP and PEEP.
Instructions to participants
Each person was asked to provide adequate bag and mask ventilation for a 3-min period using each of the four methods, the sequence of which was randomly generated by computer card. The task was to ventilate the manikin with instructions to aim for consistent and adequate chest excursion or when pressures could be measured or set, a PIP of 18 cm water, PEEP of 5 cm water and a rate of 60 inflations/min. There was a 3-min rest period between each mode. The new mode of VDMV was explained, demonstrated and sufficient practice time given to each staff member for them to feel comfortable with the technique before starting the study.
Data were analysed using Stata version MP10. Data from each participant for each mode were averaged with 144 datasets grouped by the level of resuscitator and device mode. Means and coefficients of variations (CV) were determined. Differences between means were analysed with repeated-measures analysis of variance reporting p values for adjusted F test using Box's conservative epsilon. This allows for valid statistical comparison between different methods of mask ventilation delivered by the same individual when repeat measurements between individuals are not independent. Interaction terms were examined between the level of resuscitator and device mode. p Values less than 0.05 were considered significant. This study was approved by the Sydney West Area Health Service Human Research and Ethics Committee.
Thirty-six experienced staff members (four consultants, nine registrar/fellows, five senior nurses and 18 intensive care nurses) participated in this study. A total of 21 136 inflations was recorded and analysed from the 36 participants. There were no statistically significant differences between medical and nursing staff at all levels (data not presented). PIP were not significantly different between devices (table 1). Neopuff and VDMV had the least CV of PIP. PEEP was significantly different between modes and rate values closest to the desired settings compared with the other modes, with VDMV having the smallest CV (p<0.001) (figure 3 and table 1). MV was 2.3 times greater with SIB and 1.9 times greater with anaesthetic bags than VDMV (p<0.001) (figure 4). Compared with the mean expiratory TV from VDMV (14 ml), SIB was 2.1 times greater at 30.2 ml (p<0.001), with little difference between anaesthetic bags 17.8 ml and Neopuff 15.6 ml (figure 5 and table 1). As PEEP cannot be delivered by the SIB, analysis was conducted without data for PEEP in the SIB group. Average PEEP for anaesthetic bags was 4.1 cm water, for Neopuff 4.4 cm water and VDMV 4.8 cm water (p<0.001) (figure 3 and table 1).
This study was designed to compare which of four different methods of mask ventilation delivered the least variation and best targeted the ventilation parameters requested. The study found VDMV delivered ventilation significantly closest to the targeted pressures with least variation. The SIB mode delivered at least twice the MV and TV of VDMV and Neopuff modes. Assuming a 3 kg model, Neopuff and VDMV both delivered approximately 5 ml/kg TV compared with 10 ml/kg with SIB. The MV of SIB (627 ml/min per kilogram) was 2.3 times greater than Neopuff (273 ml/min per kilogram) or VDMV (280 ml/min per kilogram). Wood et al24 25 and O’Donnell et al29 have shown manikin study mask leaks of approximately 50% in a group of neonatal expert resuscitators, which with intense training could only be reduced to approximately 30%. We speculate that mask leak may counter to some extent the excessive TV and MV delivered by the SIB method; however, this is likely to be intermittent within one operator and highly variable. The strengths of this study lay in the large number of inflations analysed in an expert group of users and the minimal alteration of the Laerdal ALST manikin. We proposed that this would allow better extrapolation of results to unaltered commercially available manikins. Other groups have removed the Laerdal Resusci manikin lung bags for ventilator test lungs,24 25 27,–,29 which may not perform mechanically similarly to an unaltered manikin. The majority of babies resuscitated are at term, may have some degree of perinatal depression and do not have poorly compliant lungs typical of acute respiratory distress syndrome. Therefore our model using the supplied Laerdal lung bags with compliance similar to that of healthy newborn lungs may better reflect a standard training environment for most resuscitators. Excessive mechanical ventilation can cause significant hypocarbia and may reduce cerebral blood flow in a potentially comprised infant. This study was designed to demonstrate which method of mask ventilation examined produced the least variation and targeted the desired ventilation more precisely. There is no mechanical reason for these results to be different if higher pressures were used. It was noted consistently that during VDMV using a two-handed four-fingered rim grasp the Dräger Babylog lung mechanics frequently displayed values less than 10% and often a zero leak. Large variation expressed as a percentage CV was found in delivered PIP, PEEP, TV and MV. VDMV delivered significantly less variation during a 3-min episode of mask ventilation. One small pilot study investigated ventilator-delivered resuscitation in comparison with an anaesthetic re-breathing circuit in preterm infants.33 The results of that study showing significantly higher PEEP with lower CV with the ventilator resuscitation mode are consistent with our findings.
In clinical practice, resuscitations and the need for mask ventilation may exceed 3 min and it is plausible to postulate worsening variation as a result of operator fatigue. Swings between inadequate inflations and excessive inflations may reflect as swings from lung atelectasis to overdistension—one of the processes associated with the development of bronchopulmonary dysplasia in very low birth weight infants.12
Limitations are shared with other manikin studies of the ability to generalise to actual human newborn resuscitations; however, practice simulation models are the best system of teaching to date and are strongly advocated.34 In particular, the rapidly changing newborn lung from fluid-filled to air-filled with the establishment of an effective functional residual capacity is not modelled by any manikin, and so studies on mask ventilation on manikins cannot provide guidance to starting or maintenance airways pressures required during resuscitation at birth. The airways pressures set in this study reflect our unit's starting point for resuscitation with rapid graded increase tailored to the infants' response to resuscitation.20 Others may advocate higher starting pressures with resuscitation of a newborn infant. The current International Liaison Committee on Resuscitation consensus statement on neonatal resuscitation comments that in term infants optimum pressure, inflation time and flow required to establish an effective functional residual capacity have not been determined and that peak pressures have varied widely in case studies from 18 to 60 cm water.35 VDMV would require further studies in newborns to confirm clinical superiority. An obvious limitation is the requirement for a mechanical ventilator at the point of delivery. This clearly limits this method to units with such technology in delivery suites and to newborn intensive care units. Another possible limitation is the potential confounding of the mask hold used with VDMV. The two-handed mask hold taught with VDMV may have produced less mask leak than with the other methods using a one-handed two-point top mask hold and so accounted for the differences found. As this study was not designed to explore mask leak it was not measured with the standard methods of mask ventilation and so potential confounding is not measured. We justify the two-handed mask hold as described as integral in the method of delivering VDMV with jaw thrust. VDMV is a potential new technique for large tertiary units with newborn intensive care units who have such systems at point of delivery. However, VDMV may be more widely useful as an alternative method of delivering mask ventilation within a NICU when a baby requires mask ventilation before intubation and placement on a ventilator.
This study has demonstrated significant differences in delivered ventilation between three common methods of bag and mask ventilation compared with VDMV. SIB has the potential to deliver excessive and potentially harmful pressures, TV and MV. SIB and anaesthetic bags both produced larger variations of PIP, TV and MV. VDMV provided the best targeting of ventilation with least variation. We used the Laerdal ALST baby manikin for our resuscitation studies as it is one of the most anatomically realistic manikins. Our modification of the manikin was intended to be minimal to allow our results to be easily generalised to the standard commercial Laerdal ALST baby manikins. Due to the complexity of VDMV, this method may only be useful in tertiary intensive care units for mask ventilation of premature infants. A randomised controlled trial of VDMV compared with current standard methods in premature infants is recommended.
The authors would like to thank the staff of the Nepean Newborn Intensive Care Unit, Nepean Hospital Sydney West Area Health service for their participation.
Competing interests None.
Ethics approval This study was conducted with the approval of the Human Research and Ethics Committee Sydney West Area Health Service, Nepean Campus.
Provenance and peer review Not commissioned; externally peer reviewed.
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