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Abstract
Objective: (1) To assess peak inspiratory pressure (PIP), positive end expiratory pressure (PEEP) and maximum pressure relief (Pmax) at different rates of gas flow, when the Neopuff had been set to function at 5 l/min. (2) To assess maximum PIP and PEEP at a flow rate of 10 l/min with a simulated air leak of 50%.
Design: 5 Neopuffs were set to a PIP of 20, PEEP of 5 and Pmax of 30 cm H2O at a gas flow of 5 l/min. PIP, PEEP and Pmax were recorded at flow rates of 10, 15 l/min and maximum flow. Maximum achievable pressures at 10 l/min gas flow, with a 50% air leak, were measured.
Results: At gas flow of 15 l/min, mean PEEP increased to 20 (95% CI 20 to 21), PIP to 28 (95% CI 28 to 29) and the Pmax to 40 cm H2O (95% CI 38 to 42). At maximum flow (85 l/min) a PEEP of 71 (95% CI 51 to 91) and PIP of 92 cm H2O (95% CI 69 to 115) were generated. At 10 l/min flow, with an air leak of 50%, the maximum PEEP and PIP were 21 (95% CI 19 to 23) and 69 cm H2O (95% CI 66 to 71).
Conclusions: The maximum pressure relief valve is overridden by increasing the rate of gas flow and potentially harmful PIP and PEEP can be generated. Even in the presence of a 50% gas leak, more than adequate pressures can be provided at 10 l/min gas flow. We recommend the limitation of gas flow to a rate of 10 l/min as an added safety mechanism for this device.
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The three main resuscitation devices in use to provide positive pressure ventilation are the self-inflating bag, flow inflating bag and more recently, the Neopuff T-piece resuscitator (Fisher & Paykel, Auckland, New Zealand). Each of these devices have potential benefits and disadvantages, and, currently, no one device is specifically recommended by the Neonatal Resuscitation Programme (NRP).1 2 Thus, equipment used varies from hospital to hospital,3 with 17 of 29 tertiary hospitals in Australia and New Zealand using the self inflating bag,4 and the T-piece resuscitator being the most popular in the UK.5
Hussey et al6 compared these three devices and found that the Neopuff and flow inflating bag can deliver a lower peak inspiratory pressure (PIP), and higher positive end expiratory pressure (PEEP) than the self inflating bag. Bennett et al7 subsequently showed that the Neopuff can deliver a more precise PIP and PEEP than the other two devices, but, using this device, it can take longer to adjust the PIP from 20 cm H2O to 40 cm H2O, if required.
In the absence of clinical trials comparing these three devices, the rationale for the use of the Neopuff is to provide better control over ventilatory pressures. This improved control, through a reduction in volutrauma and barotrauma, can reduce the incidence of pneumothoraces8 9 and bronchopulmonary dysplasia.10 11 12 We have equipped our entire tertiary neonatal unit, labour ward and postnatal wards with Neopuff T-piece resuscitators, following extensive staff training in the use of this device.
To set up the Neopuff according to the manufacturer’s recommendations, the gas flow is set to 5–15 l/min. The maximum pressure relief (Pmax) is then set by occluding both the PEEP cap and mask outlet, turning the PIP control to its maximum and adjusting the Pmax control. The next step is to set the PIP using the PIP control. The PEEP is then set by occluding only the mask side of the T-piece and twisting the PEEP valve clockwise to increase and anticlockwise to decrease PEEP13 (fig 1).
Diagram of the Neopuff T-piece resuscitator.
The operator manual of the Neopuff recommends that oxygen flow of 5–15 l/min should be used and states that “if the gas flow rate increases from five to 15 l/min, peak inspiratory pressure typically increases approximately 8 cmH2O”.13 The purpose of this study therefore was to validate the manufacturer’s reported observation of variations in pressures at different gas flow rates. In addition, we tested the PIP, PEEP and Pmax at maximum flow of the standard flow meter. Since air leak at mask level is a common feature of the clinical use of any flow device, we determined the maximum PIP and PEEP that can be achieved with an air leak of 50% at mask level, at a gas flow of 10 l/min.
Methods
For the purposes of this study, pressures were recorded using a digital manometer (Digitron model 2083P, Devon, England). This was found to correlate well with the manometer intrinsic to the Neopuffs, but allowed for accurate recording of pressures above 30 cm H2O. Gas flow meters used in our unit were the standard 0–15 l/min flow meters with a flush setting when 15 l/min was exceeded (Ohmeda medical/GE Healthcare, Diessenhofen, Switzerland). A rate of gas flow in excess of 15 l/min was measured, when necessary, using a digital flow meter (EKU model VP1, Leiningen, Germany).
Five Neopuffs were set to a gas flow of 5 l/min, and PIP of 20 cm H2O, PEEP of 5 cm H2O and Pmax was then set to 30 cm H2O. Without adjusting the pressure settings on the Neopuff, the gas flow was increased to 10 l/min, 15 l/min and to maximum flow, which was recorded as 85 l/min using the digital flow meter. The mask end of the circuit was closed with the manometer, which also recorded the pressure at mask level. PIP, PEEP and Pmax were recorded at each of these flows on each machine. Having set the Pmax to 30 cm H2O at a flow rate of 5 l/min, the maximum PIP that could subsequently be achieved at each gas flow rate, without further adjustment of the Pmax control, was recorded as the Pmax.
In order to determine if limiting the gas flow to 10 l/min would compromise the ability of the machine to provide adequate PIP and PEEP, we reduced the gas flow to 10 l/min on each machine and deactivated the Pmax valve by turning it to the maximum. We then recorded the maximum pressures achievable.
In five Neopuffs, we also simulated a 50% air leak using a Y connector and connecting the free end to a flow meter. The rate of gas flow through the free end was adjusted using a mechanical device which provided variable compression. The Pmax valve was, again, deactivated and the PIP control was also turned to the max. The gas leak was adjusted until the flow at maximum PIP was equal to 5 l/min. This allowed us to determine the maximum PIP that the machine could provide in the setting of a 50% air leak. The other end of the Y connector was attached to the manometer to determine the pressure that would be provided to the neonate in the presence of this artificial leak.
Results were inputted to SPSS V.16. Means and 95% confidence intervals (CIs) of pressures at each flow were generated.
Results
On five Neopuffs, the gas flow was set to 5 l/min and PEEP, Pmax, and PIP were set to 5 cm H2O, 30 cm H2O and 20 cm H2O respectively. As the oxygen flow was increased from 5 to 15 l/min, the mean PEEP increased from 5 to 20 cm H2O (95% CI 20 to 21), the mean PIP increased from 20 to 28 cm H2O (95% CI 28 to 29) and the Pmax increased from 30 to 40 cm H2O (95% CI 38 to 42) (fig 2). At these pressure settings, increasing the oxygen flow to 85 l/min, resulted in a mean PEEP of 71 cm H2O (95% CI 51 to 91) and PIP of 92 cm H2O (95% CI 69 to 115).
Graph showing the effect of increasing gas flow rate without adjusting Neopuff settings. PIP, PEEP and Pmax had been set to 20, 5 and 30 cm H2O respectively at 5 l/min. PIP, peak inspiratory pressure; PEEP, positive end expiratory pressure; Pmax, maximum pressure relief.
When the gas flow was limited to 10 l/min, the maximum possible PIP with the Neopuff was 73 cm H2O (95% CI 69 to 78) and maximum PEEP was 36 cm H2O (95% CI 33 to 39). An artificial leak of 50% allowed a maximum PIP of 69 cm H20 (95% CI 66 to 71) and a PEEP of 21 cm H20 (95% CI 19 to 23) to be achieved at this gas flow of 10 l/min.
Discussion
In this study, we have confirmed that the PIP, PEEP and Pmax will change if flow is altered, and that the maximum flow achieved with the standard flow meter can be as high as 85 l/min. We have also shown that the maximum pressure relief valve on the Neopuff is a potentially misleading feature. The purpose of a pressure relief pressure valve is to prevent the accidental delivery of an excessively high PIP.14 However, the pressure relief valve on the Neopuff prevents the PIP from exceeding the pre-defined limit only at the rate of gas flow at which it was originally set. Increasing the gas flow overrides this pressure relief, and allows the provision of pressures in excess of the preset maximum. Some babies occasionally need high pressures to initially expand their lungs. We have also shown that limiting the rate of gas flow to 10 l/min will still allow the provision of far in excess of these pressures, even in the presence of a 50% air leak at mask level. This limitation, however, would reduce the likelihood of inadvertently providing excessive pressures through increasing the rate of gas flow and subsequently overriding the maximum pressure relief valve.
Our main clinical concern with the Neopuff is that personnel, in an emergency situation, may increase the gas flow during a resuscitation without resetting the pressures. In addition, PIP and PEEP as high as 92 cm H2O (95% CI 70 to 115) and 71 cm H2O (95% CI 51 to 91) can inadvertently be generated if maximum flow (85 l/min) is allowed. These are the pressures achieved if the Pmax has been set to 30 cm H2O at a gas flow of 5 l/min. Thus, we conclude that the maximum pressure relief valve is not a true pressure relieving (pop off) valve.
The flow inflating bag and Neopuff can both generate PIP and PEEP. However, the flow-inflating bag will distend like a balloon if excessive pressures are being provided, alerting the operator to these excessive pressures. Excessive pressures are recognised in the Neopuff only by checking the manometer.
We have shown that limiting the Neopuff gas flow to 10 l/min will still allow more than adequate maximum PIP and PEEP of 73 cm H2O and 36 cm H2O to be provided, respectively. O’Donnell et al15 16 showed that large leaks around the face mask can be a significant problem. Our concern, in limiting the rate of gas flow to 10 l/min, would be a subsequent reduction in the ability to ventilate the neonate. In this study, we have shown that more than adequate PIP and PEEP can be generated using the Neopuff at a gas flow of 10 l/min, even with a 50% air leak at mask level.
The Neopuff can be a safe device, if used by trained personnel according to the manufacturer’s instructions. We suggest that gas flows above 10 l/min are unnecessary, and in order to enhance the safety of the device, consideration should be given to limiting the rate of gas flow to 10 l/min. During neonatal resuscitation certification and recertification, operators must be made aware of the effect of adjusting gas flow on the PIP and PEEP generated by the Neopuff. Pressures must be rechecked and reset should gas flow be altered following initial set up for any reason during a resuscitation. Operators should also be aware that while the Pmax can limit pressures generated at specified flows, it is not a true pressure relieving pop-off valve, since increases in gas flow will override the initial Pmax.
What is already known about this topic
Use of the Neopuff T-piece resuscitator is becoming increasingly popular in neonatal departments.
The Neopuff allows greater control over the pressures provided during neonatal resuscitation than the self inflating and flow inflating bags.
What is this study adds
Increasing the rate of gas flow can substantially increase the pressures that are provided unless the settings on the Neopuff are reset.
This study highlights the potential for overriding the maximum pressure relief setting on the Neopuff through increasing the rate of gas flow.
Acknowledgments
We thank B O’Connell for his assistance with the use of biomedical devices. We also thank E Kinsella for drawing fig 1.
REFERENCES
Footnotes
Competing interests None.
Provenance and Peer review Not commissioned; externally peer reviewed.