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E-letters: Electronic letters published:
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Evaluation of the Whisperflow CPAP generator
- Stephen J Fletcher, Guy Glover (14 October 2009)
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Response to: Continuous flow positive airway pressure generator in critical ill patients: a moratorium
- Guy W Glover, Steve J Fletcher (12 October 2009)
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Continuous flow positive airway pressure generator in critical ill patients: a moratorium
- Pedro Caruso, Carolina FU, Carlos Roberto Ribeiro de Carvalho (21 September 2009)
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Stephen J Fletcher Bradford Teaching Hospitals NHSFT, Guy Glover
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BJA electronic letters Response to: Caruso P et al. Continuous flow positive airway pressure generator in critically ill patients: a moratorium (BJA e letter 21st Sept 2009) Editor, We are grateful to Caruso and colleagues for their interest in our paper. [1] They present persuasive arguments against the use of continuous high flow CPAP generators (HFCPAP) in the critically ill, specifically the Whisperflow (Philips Respironics). As demonstrated by both our and Caruso’s study the in vitro performance of this device is sub-optimal. [1,2] Furthermore there are clinical data indicating that CPAP in general may increase work of breathing and worsen outcome in hypoxaemic respiratory failure. [3,4] Whilst we are inclined to agree with Caruso’s proposal for a moratorium on the use of the Whisperflow and similar devices we must carefully consider the possible consequences. In the UK, the use of HFCPAP systems is widespread and indeed the Whisperflow is now being promoted for pre-hospital use. Use is often by non-intensivist physicians and therapists in patients with a wide range of causes of respiratory failure. The Whisperflow is used on the basis of low cost, simplicity and in the belief that it is effective and suitable for use by those without advanced critical care training and sometimes without close monitoring. If we prohibit this kind of use then demand for ‘formal’ critical care support will increase in an unsustainable fashion. Conversely, it could be argued that usage of non-invasive ventilatory support outside the critical care unit has always been inappropriate and has arisen because of resource limitations. Non-invasive respiratory support has been one of the great advances in critical care, and yet it must be used with care. As with any device it is vital that the user is fully aware of the limitations of the technology. Currently this is not the case. This is largely because formal evaluation of these devices prior to marketing is not mandatory. It is only now through the work of Caruso, ourselves and others that we are beginning to understand the performance of HFCPAP generators. The next generation of work must look at the patient’s requirements also. This is a largely neglected area of study. The ultimate question is whether HFCPAP devices like the Whisperflow are better than nothing at all. We do not know the answer to this question. Therefore we advocate extreme caution in the use of the Whisperflow and other HFCPAP devices rather than, at this stage, an outright hospital-wide ban. However, in our intensive care unit, with the availability of more sophisticated ventilators that provide non-invasive ventilation, along with appropriate monitoring, the Whisperflow is to be phased out. It is now incumbent on manufacturers to adequately assess existing and new products to ensure that they are fit for purpose. It is also incumbent on specialist societies and regulatory bodies such as the UK National Institute for Clinical Excellence to take a view on the use of these devices. Stephen J Fletcher Guy W Glover References: 1. Glover GW, Fletcher SJ. Assessing the performance of the Whisperflow continuous positive airway pressure generator: a bench study. Br J Anaesth 2009; 102: 875-81 2. Fu C, Caruso P, Janaina J et al. Comparison of two flow generators with a non-invasive ventilator to deliver continuous positive airway pressure: a test lung study. Intensive Care Med 2005; 31: 1587-91 3. L’Her E, Deye N, Lellouche F et al. Physiologic effects of non-invasive ventilation during acute lung injury. Am J Resp Crit Care Med 2005; 172: 1112-8 4. Declaux C, L’Her E, Alberti C et al. Treatment of acute hypoxaemic nonhypercapnic respiratory insufficiency with continuous positive airway pressure delivered by a face mask: a randomised controlled trial. J Am Med Assoc 2000; 284: 2352-60 Conflict of Interest:None declared |
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Guy W Glover , Steve J Fletcher
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Dear Editor, We are grateful to Dr Caruso for his interest and for presenting the persuasive arguments against the use of continuous high flow CPAP generators (HFCPAP) in the critically ill. As demonstrated by both our [1] and Dr Caruso and colleague’s study [2], the performance is indeed significantly sub-optimal. Furthermore, physiological in-vivo data and clinical outcome studies indicate that CPAP (however delivered) may be deleterious to the patient’s work of breathing [3] and may worsen outcome in hypoxaemic respiratory failure [4]. Whilst we do agree with Dr Caruso’s proposal of a moratorium on HFCPAP we must carefully consider the possible consequences and address the barriers to change. Furthermore we would like to develop the debate to consider the role of CPAP at all as a mode of respiratory support for acute hypoxaemic respiratory failure. In the UK, a significant number of HFCPAP systems are used in medical and surgical high dependency units, respiratory care units and emergency departments and indeed the Whisperflow is being promoted for pre-hospital use; they are used by non-intensivist physicians and therapists to provide CPAP to a variety of patients in respiratory failure of different aetiology. This system may be used on the basis of low cost and in the belief that it is a simple and safe form of respiratory support, suitable for use by those without advanced critical care training and sometimes without close monitoring. If we become unable to provide CPAP in these areas, or decide it is undesirable, then it is probable that the demands on ICU facilities will escalate significantly requiring additional expansion or at very least, greater use of 'outreach' arrangements. These considerations may become even more pertinent at a time of global pandemic planning. A moratorium on the use of HFCPAP may lead us to pose a broader question; do we believe it is reasonable to provide any advanced respiratory interventions in facilities, sometimes in remote locations, with non-specialist trained staff where there may be limited access to immediate level 3 care if the patient deteriorates? Whilst non-invasive respiratory support has been one of the great advances in critical care it has the potential to worsen outcome if used indiscriminately. With any device it is vital that the user is fully aware of the workings and limitations of the technology. Additionally it is vital that those caring for the critically ill understand the pathological basis of the perturbations in front of them and how to appropriately select different modes of mechanical support to address them. Notwithstanding the limitations of the Whisperflow, even complex ICU ventilators delivering CPAP do not perform well and do not adequately address increased work of breathing [2, 3]; we believe that CPAP itself as a mode of respiratory support, however delivered, may be inappropriate for many hypoxaemic patients, even when there is not gross hypoventilation and hypercapnia. Intensivists need effective tools to improve outcomes in respiratory failure; there is a danger that if all one has is a hammer, everything may become a nail. References: 1. Glover GW, Fletcher SJ. Assessing the performance of the Whisperflow continuous positive airway pressure generator: a bench study. British Journal of Anaesthesia 2009; 102: 875-81 2. Fu C, Caruso P, Janaina J et al. Comparison of two flow generators with a non-invasive ventilator to deliver continuous positive airway pressure: a test lung study. Intensive Care Med 2005; 31: 1587-91 3. L’Her E, Deye N, Lellouche F et al. Physiologic effects of non- invasive ventilation during acute lung injury. Am J Resp Crit Care Med 2005; 172: 1112-8 4. Declaux C, L’Her E, Alberti C et al. Treatment of acute hypoxaemic nonhypercapnic respiratory insufficiency with continuous positive airway pressure delivered by a face mask: a randomised controlled trial. J Am Med Assoc 2000; 284: 2352-60 Conflict of Interest:None declared |
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Pedro Caruso, MD Pulmonary Division-Heart Institute (Incor) - University of Sao Paulo Medical School, Carolina FU, Carlos Roberto Ribeiro de Carvalho
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In a recent article Glover and Fletcher assessed the performance of a continuous flow positive airway pressure generator (Whisperflow – Philips Respironics)1. It was tested in a bench study under dynamic conditions that simulated many clinical circumstances. We had also assessed the performance of two continuous flow positive airway pressure generators (Adjustable Downs Flow Generator-Vital Signs and the same Whisperflow) 2. As Glover and Fletcher, we found a poor performance of the Whisperflow generator under dynamic conditions, especially when those conditions were more demanding. On the other hand, the Adjustable Downs Flow Generator performed equally or better than a micro processed noninvasive mechanical ventilator (BiPAP Vision– Philips Respironics), even with a low pipeline supply pressure (1 bar). In view of the above studies and the considerations below, we believe that the use of the Whisperflow generator should be suspended in critical ill patients and even the use of the Adjustable Downs Flow Generator is unjustifiable. Besides the underperformance of the Whisperflow generator, there are some other reasons that should preclude the use of continuous flow positive airway pressure generators in critical ill patients: A- At least in Brazil, the simple turbine-driven CPAP machines that have obvious advantages on monitoring, alarms and noise, have similar acquisition cost to flow generators. Even that is not true worldwide, the elevated economical cost of a preventable adverse event would be enough to wreck the economical argument 3; B- In our personal experience the noise of generators is high enough to bother patients and intensive care unit staff, with probable negative impact in patients’ sleep 4 and delirium. In a recent study Cavaliere measured the noise of two CPAP systems with the Venturi effect (including Whisperflow) and it reached more than 90 decibels depending on the interface 5, (similar to a food blender at one meter distance); C- Continuous flow generators do not offer indispensable monitoring, as tidal volume and inspiratory/expiratory time and pressures that cannot be offered by the bedside monitor; D- Alarms are not available; and E- As our 2 and Glover and Fletcher study 1 demonstrated, the multiple possible adjustments in a continuous flow generator (fraction of O2, pipeline supply, valve load and flow adjustment) make the performance of a continuous flow positive pressure generator excessively variable and unpredictable. Besides that, the ubiquitous mask/circuit leak, a condition not tested in the Glover and our previous study 1-2 would make the performance of the flow generators even more unpredictable and certainly more unsuitable. We fully agree with Glover and Fletcher that further in vivo data are required, but due to the low efficacy and serious concerns about safety, we believe that local healthcare authorities or professional societies should consider a moratorium on the use of continuous positive airway pressure flow generators in critical ill patients. References 1 Glover GW and Fletcher SJ. Assessing the performance of the Whisperflow continuous positive airway pressure generator: a bench study. Br J Anaesth 2009; 102: 875-881 2 Fu C, Caruso P, Lucatto JJ, et al. Comparison of two flow generators with a noninvasive ventilator to deliver continuous positive airway pressure: a test lung study. Intensive Care Med 2005; 31: 1587-1592 3 Kaushal R, Bates DW, Franz C, Soukup JR and Rothschild JM. Costs of adverse events in intensive care units. Crit Care Med 2007; 35: 2479-2483 4 Gabor JY, Cooper AB, Crombach SA, et al. Contribution of the intensive care unit environment to sleep disruption in mechanically ventilated patients and healthy subjects. Am J Respir Crit Care Med 2003; 167: 708-715 5 Cavaliere F, Conti G, Costa R, et al. Exposure to noise during continuous positive airway pressure: influence of interfaces and delivery systems. Acta Anaesthesiol Scand 2008; 52: 52-56 Conflict of Interest:None declared |
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