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Rapid Responses: Rapid Responses published:
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Does this prove that nurses are not a safe substitute for anaesthetists?
- Richard G Fiddian-Green (30 July 2004)
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Flow monitored protocol for optimisation of circulatory status after cardiac surgery
- michael poullis (1 August 2004)
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Would like to see haemodynamic data
- Eugene B Campbell, Stephen Foley, and Anthony Shonde (3 August 2004)
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Surgeons contest the conclusions drawn from this study
- Fraser W.H. Sutherland, Geoffrey A. Berg (4 August 2004)
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Without strong biologically plausible explanation, dramatic impact on outcomes by single interventions is unlikely to be reproducible
- Ani C Anyanwu (9 August 2004)
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Senior author's reply
- Mervyn Singer, London, W1T 3AA (25 September 2004)
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Richard G Fiddian-Green, FRCS, FACS None
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This study (1)is very similar to that performed in the same institution by anaesthetists (2) but the nurses' results are not nearly as good as the anaesthetists. One reason for this apparent difference might be that anaesthetists in the institution have learned from the first study and are more attentive to volume resuscitation and that operative mortality in controls was lower in this study and the room for improvement less. The more likely reason would seem to be that current management is conceptually flawed and will continue to be associated with unexpected outcomes until thinking is changed. The nurses protocol did not improve outcome when measured in terms of complications and deaths. Twenty six controls, of the 174 patients having cardiac surgery studied by the nurses, had postoperative complications (two deaths) compared with 17 (four deaths) protocol patients (P = 0.08). In reality the mortality doubled with the nurses' interventions but the difference was not significant. If, however, a Fisher's exact test were done comparing the reslts of the two studies I suspect the difference in mortality might be highly significant. Every death and most complications in the present study as in the past study may be attributed to schaemia/reperfusion injury of gut mucosa but as gastric intramucosal pH was not measured that cannot be established as in the anaesthetists study. It is an important omission for in its absence management cannot be rational. Indeed even when anaesthetists were optimising stroke volume according to protocol an intramucosal acidosis persisted in some 12% of the patients. Deaths and complications will continue to occur unpredictably after all forms of surgery until this residual is eliminated by managing tissue energetics intelligently and effectively. And don't expect any miracles from "real-time feedback- controlled ultraprecise resuscitation", be it driven by intramucosal pCO2 or perfusion measured with a laser Doppler imager, or from nuclear magnetic resonance spectroscopy (3). The issues are complex (4) and even anaesthetists do not appear to appreciate just how complex they are. Anaesthetists are, however, far better qualified to appreciate, identify, address and resolve them than nurses. As good as some nurse anaesthetists undoubtedly are what medical professional would ever agree to be a subject in a prospective study comparing a anesthetist's performance with a nurse's? Having said that making anaesthesia more of a science than the art it is might make it possible for nurse anaethetists to compete much more favourably with anaesthetists. 1. Moira McKendry, Helen McGloin, Debbie Saberi, Libby Caudwell, Anthony R Brady, and Mervyn Singer Randomised controlled trial assessing the impact of a nurse delivered, flow monitored protocol for optimisation of circulatory status after cardiac surgery BMJ 2004; 329: 258-0 2. Mythen MG, Webb AR. Perioperative plasma volume expansion reduces the incidence of gut mucosal hypoperfusion during cardiac surgery. Arch Surg. 1995 Apr;130(4):423-9. 3. Real-time feedback-controlled ultraprecise resuscitation Richard G Fiddian-Green bmj.com, 27 Jul 2004 Rapid response to: Mark Ansermino and Carolyn Hemsley Intensive care management and control of infection BMJ 2004; 329: 220-223 4. Fiddian-Green RG. eLetters re: David Roy Dantzker Monitoring Tissue Oxygenation : The Quest Continues Chest 2001; 120: 701-702 Competing interests: None declared |
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michael poullis, Registrar Cardiac Surgery Liverpool L14
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McKendry et al raise a number of important points in their study, which need expanding or clarifying. They mention that base excess, urine output central and arterial pressures are the corner stones of ITU management in cardiac surgery, and this is true. However they fail to mention arterial line swing, the importance of a negative fluid balance, and the central and peripheral temperature profile of the patient. These are all important pieces of clinical information that are evaluated by the on call cardiac surgical registrar in ITU, differentiating them from someone who is just “chart or guideline trained”. The study purely demonstrated that more fluid is required than the usual ITU nurse care provides. This is evident on a daily basis to anyone who works in the ITU post cardiac surgery. It is common to find someone who has a CVP of +2cm, no base excess and adequate urine output with a negative balance of –500mL, NOT being given fluid by the nursing staff “because they are alright on the chart”. Practical experience shows they need more fluid. Cardiac tamponade is an easily missed complication of cardiac surgery. It does not always present in a classical way, and a normal CVP and adequate blood pressure on inotropes is not an uncommon finding. The flow chart presented will result in a delayed or a missed diagnosis. Excessive bleeding, and high dose inotrope usage is relatively common post cardiac surgery, so any trial that eliminates these patients has to be treated with caution as the results are unlikely to be applicable to the real clinical situation. Despite all patients being done on bypass, the lumping together of valves and / or coronarys, redo surgery and “other” reduces the power of the study considerably as they involve completely different risk profiles, hence the changing study groups in the cardiothoracic publications the Annals of Thoracic Surgery and The Journal of Cardiothoracic Surgery. With regard to risk profiles the use of Parsonnet scoring has been proven on numerous occasions, including the Society of Cardiothoracic Surgeons of England and Ireland, to be an inadequate way of risk assessing and comparing patients pre cardiac surgery, hence the evolution of the Euroscore additive and logistic. The duration of the study was 3 years, meaning about one case per week for the study at maximum. Did this mean only one surgeon was involved? This may have important implications as different surgeons use different bypass temperatures and methods of cardioplegia, which can all affect postoperative care. Liverpool is one of the largest cardiac surgical units in the UK. Our average ITU stay and hospital stay are significantly shorter than those in the study. The vast majority of our patients leave the ITU on day 2 and go home by day 8, so it is difficult to understand how their average stay was so high, nearly 1.5 times as much. In summary any competent cardiac surgical registrar, who are cognisant with oesophageal doppler, who have daily exposure to ITU post cardiac surgery will already knows that clinical examination of the patient and assessment of arterial line swing, fluid balance, and the central and peripheral temperature profile of the patient are far more helpful than blind flow chart driven oesophageal doppler probe use. The importance of an intelligent, clinically alert ITU nurse with previous experience should also not be underestimated. 1. Moira McKendry, Helen McGloin, Debbie Saberi, Libby Caudwell, Anthony R Brady, Mervyn Singer. Randomised controlled trial assessing the impact of a nurse delivered, flow monitored protocol for optimisation of circulatory status after cardiac surgery. BMJ 2004;329:258 Competing interests: None declared |
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Eugene B Campbell, Research Fellow University of Nottingham, Stephen Foley, and Anthony Shonde
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McKendry et al have made a valuable attempt to tackle the difficult problem of post-operative circulatory status. (1) They claim that outcomes after cardiac surgery may be improved by a nurse-delivered protocol optimising stroke volume index in the immediate post-operative period. However, we have some queries regarding the study. The study was powered to detect a reduction of 3 days in mean hospital stay. Even by the standards of April 2000 when the study began recruitment, their mean stay of 13 days seems long. Other UK centres had reported average hospital stays of 8 days back in 1995. (2) Even in this study which excluded any unstable patients the mean length of stay was over 11 days. Why is the average length of stay so long in UCL? Despite the input of the study nurses, nearly 40% of protocol patients failed to meet the stroke volume index target of 35ml/m2, and none of them received inotropes as per protocol. This latter was due to time-constraints and reticence of nurses. What hope then for the control patients if even the protocol patients failed to receive prescribed treatment, despite the extra input of 4 research sisters. The main finding of this study was the difficulty ensuring adequate resuscitation post-operatively. The authors state that standard monitoring consists of arterial and central venous pressures, urine output and arterial base deficit. None of these data are presented. Could the control patients have been underfilled by these usual criteria yet not acted on, again due to time-constraints and reticence? It would be interesting to know if blood lactate concentrations were available for all control and protocol patients. Most blood gas analysers now routinely measure lactate. Blood lactate concentration was a target of Polonen’s study of goal directed therapy (3), and hyperlactataemia can identify those at higher risk of complications and mortality. (4) Perhaps this measure allied to the standard monitoring could help guide and optimise circulatory status as effectively as a doppler probe. Finally a criticism aimed squarely at the BMJ. For a journal that trumpets ethical research so loudly, it publishes a print version of this study with not a single mention of informed consent from the study participants. Surely this is an important aspect of any study and should be included even in abridged versions. 1. McKendry M, McGloin H, Saberi D, et al. Randomised controlled trial assessing the impact of a nurse delivered, flow monitored protocol for optimisation of circulatory status after cardiac surgery. BMJ 2004;329:258-61. 2. Birdi I, Izzat MB, Angelini GD, Bryan AJ. In-hospital audit underestimates early postoperative morbidity after cardiac surgery. Br Heart J 1995;74(5):556-8. 3. Polonen P, Ruokonen E, Hippelainem M, Poyhonen M, Takala J. A prospective randomised study of goal oriented hemodynamic therapy in cardiac surgical patients. Anaesth Analg 2000;90:1052-9. 4. Maillet JM, Le Besnerais P, Cantoni M, et al. Frequency, risk factors, and outcome of hyperlactatemia after cardiac surgery. Chest. 2003;123(5):1361-6. Competing interests: None declared |
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Fraser W.H. Sutherland, Specialist Registrar in Cardiothoracic Surgery Western Infirmary, Glasgow G11 6NT, Geoffrey A. Berg
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We express concern at the conclusions of this study. We contest, firstly, that this is an invasive intervention with little demonstrable impact on the primary outcomes cited in the study i.e. intensive care stay and hospital stay. In fact, both of these figures exceed the national averages. Average length of stay for all cardiac surgical patients admitted to the Western Infirmary, Glasgow for example was 7.2 days for 2004 and has varied little since 1994. A more pertinent question might be to ask why length of stay is so prolonged in this group’s experience. Secondly, important and irrefutable outcomes such as death were casually dismissed by the authors despite the fact that mortality was higher in the protocol group than the control group (4 vs. 2). Indeed, one is forced to go to the web to ascertain the precise circumstances of death. In that regard, we believe that the term ‘optimisation of circulatory status’ used throughout the study is presumptive especially given that multiorgan failure, low cardiac output and cardiac arrest were cited as causes of death in the protocol patients and that these patients all arrived in good condition in their intensive care unit (see exclusion criteria). In the cited morbidities, chest infection and wound infection were grouped together despite their separate aetiologies and the main reduction was in the incidence of AF which is not easily explained by the study and may be a spurious result. Finally, only 179 patients were recruited from this institution into the study over almost three years. We are, therefore, drawn to conclude that this study is representative of only a small and highly selected group of patients and that its results cannot be widely applicable. In conclusion, we purport that this study adds nothing to the scientific literature and that the technique has little to offer patients undergoing cardiac surgery. Competing interests: None declared |
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Ani C Anyanwu, Fellow in Cardiac Surgery Mount Sinai Hospital, New York, NY 10029, USA
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Sir I was most interested to read the article by McKendry and colleagues suggesting that optimizing stroke volume in the first four hours after cardiac surgery lead to an 18% saving in hospital bed days (1). It is unique that a single intervention lasting only four hours has such a dramatic effect on hospital bed occupation, which probably reflects why the BMJ gave their paper front page status. I however have some reservations about the study. The choice of hospital stay as the primary outcome is debatable. Length of stay as an outcome after cardiac surgery is at best a surrogate measure which does not necessarily bear relationship to success of surgery. Factors unrelated to outcome also influence hospital stay including physician preference and local practice. Indeed the hospital stay the authors report is longer than experienced in most UK cardiac units (the National registry reports 80% of patients were discharged within 10 days of surgery in 2000 and 2001 (2)). Although they list complications as a secondary outcome, some bear no conceivable association to their intervention (such as aortic regurgitation) and some relevant outcomes, such as low cardiac output, are not presented. The accuracy of their complication data is also questionable. The 6% incidence of atrial fibrillation in the protocol group is well below that experienced in cardiac surgical practice (where up to a third of operations are complicated by atrial fibrillation). No intervention introduced to reduce atrial fibrillation after cardiac surgery has achieved such low incidence of atrial fibrillation (3). The low incidence may represent under- reporting or biased reporting of complication data. Blanket application of any haemodynamic intervention to all cardiac surgical patients is not practical. The pathophysiology, and hence the approach to post-operative haemodynamic care, differs depending on pathology, cardiac function, and operative procedure (transplantation, coronary bypass, valvar stenosis, valvar regurgitation, congenital etc). Even with a recording of low stroke volume, fluid administration may not necessarily be the appropriate intervention. Indeed in certain post- operative conditions, such as cardiac tamponade, fluid administration is potentially harmful. Fluid administration to an already distended and failing ventricle (which will have a low stroke volume) can be catastrophic. The authors have not discussed problems that may arise from errors in stroke volume measurement or interpretation. Although the oesophageal doppler is well validated, it is subject to measurement and interpretation errors which, although minimal in the specialist and research setting, will be expected to increase as usage shifts from specialist and research users to the routine clinical setting. It would therefore be ill advised, as the paper seems to suggest, to direct clinical management based on stroke volume alone. Management decisions should depend on summation of pre-operative and operative history, clinical examination, various haemodynamic measures (including cardiac output), urine output and metabolic data. The authors have given no biologically plausible explanations as to how their intervention reduces hospital stay. The assumption that this is due to fewer complications is not borne by their data. The authors did not record any complication for majority (70%) of patients in the control group, yet half still spent 9 or more days in hospital; the occurrence of complications therefore did not correlate to hospital stay. It is unclear why they restricted the intervention to 4 hours as for most patients the period of critical haemodynamic management lasts for at least the first 12 hours; the protocol group would therefore have reverted to standard care for the rest of this critical period. The authors did not offer any explanation as to why the first 4 hours alone would have bearing on the rest of the post-operative period independent of the subsequent management. Two final issues deserve mention – acceptability by surgeons and safety. The authors recruited 5 patients a month in an institution that performed over 50 operations a month in the same period (2). Given their liberal inclusion criteria, only a minority of eligible patients was recruited. It is not stated what factors limited recruitment. There is no statement on the acceptance of their intervention by local surgeons and intensivists; indeed none of their surgeons have been acknowledged in the study. Additionally, despite a higher death rate in the intervention group, the authors do not discuss the possibility that their intervention could cause harm. They dismissed the four deaths in the intervention group as not directly attributable to the early post-operative care, yet all the patients sustained major haemodynamic complications, and in at least 3, the deaths were related to low-cardiac output states. Without further study, one cannot be certain that their intervention is indeed beneficial or that it can be extrapolated to the general cardiac surgical community. References 1) McKendry M, McGloin H, Saberi D, et al. Randomised controlled trial assessing the impact of a nurse delivered, flow monitored protocol for optimisation of circulatory status after cardiac surgery. BMJ 2004;329:258-61. 2) The Society of Cardiothoracic Surgeons of Great Britain and Ireland. National Adult Cardiac Database Report 2000-2001. Henley-on- Thames: Dendrite, 2003 3) Crystal E, Connolly SJ, Sleik K, Ginger TJ, Yusuf S. Interventions on prevention of postoperative atrial fibrillation in patients undergoing heart surgery: a meta-analysis. Circulation. 2002;106:75-80. Competing interests: None declared |
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Mervyn Singer, Professor of Intensive Care Medicine UCL, London, W1T 3AA
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Having just read the five rapid responses posted, I feel that some comment is needed to correct some of the misinterpretations stated. Fiddian-Green makes unnecessarily demeaning remarks about nurses when he should perhaps direct his ire elsewhere. The previous study he cited from our institution was performed INTRA- operatively and the approximate 40% reduction in hospital stay achieved in cardiac surgical patients through intravascular volume optimization was indeed impressive. Notwithstanding this result, any such protocolised haemodynamic optimisation has failed to become a standard of care and a significant morbidity persists. Thus the present study was designed to assess whether a belated POST-operative attempt to 'catch up' with the tissue oxygen debt incurred from inadequate intraoperative resuscitation could still have some impact in improving outcomes. The answer was yes, though was only half as effective as the similar fluid-loading protocol followed intraoperatively. The critical care nurses (not nurse anaesthetists as erroneously stated) were simply attempting to redress the damage induced by a synergistic combination of cytokine-generating trauma and tissue hypoxia. To draw comparison with 'skilled anaesthetists' is thus spurious in the extreme. However, we are in full agreement over the need to optimise tissue energetics - alas, the problem is that no appropriate monitoring device, including the one Fiddian-Green himself pioneered (gastric tonometry), has become a standard of care. The anaesthetic and surgical communities need to ask themselves why not. Poullis places the on-call cardiac surgical registrar on a lofty pedestal which is certainly not borne out in my experience. If only they were all so haemodynamically astute! It is easy to throw barbs at the ICU nurse but surely postoperative care mandates a multi- disciplinary team approach. If it is so apparent that "more fluid is required than the usual ITU nurse care provides. This is evident on a daily basis to anyone who works in the ITU post cardiac surgery" then why has he and his ilk not sought to improve this suboptimal care being provided to his patients, be it through education or positioning themselves at the bedside and providing hands-on care? Our study does indeed highlight the imperfections in current management and shows that "someone who is just chart or guideline trained” can indeed improve upon standard care being offered by surgeons, anaesthetists, intensivists .. and nurses. Incidentally, our need for high-dose inotropes either intra- or post- cardiac surgery is uncommon - thankfully, this is one injurious and misbegotten 'therapy' that is generally avoided in our institution. At the time the protocol was designed, Parsonnet was the 'in' score but we accept that it has been superceded by other scores. We recruited cases performed by four surgeons and the slow recruitment was due in part to other competing studies and in part to pregnancy 'affecting' three of the four study nurses who worked consecutively rather than together. With regard to bed stay, I would point out the disproportionately high proportion of valve procedures among our study group. In answer to Campbell et al, please see the above comment on length of stay. I would suggest they audit the performance in their own postoperative unit to see what amounts of fluid are given in the first four postoperative hours -it may be revealing! Word count restrictions prevented publication of all the haemodynamic data but these can be supplied on request. Standard triggers for fluid administration such as low blood pressure, low urine output, increasing base deficit etc.. were routinely observed and acted upon in the control patients. The use of blood lactate levels will be confounded by any concurrent use of lactate-containing solutions such as Hartmann's and the accelerated glycolytic effect seen with adrenaline. I am also unaware of studies showing clear superiority of lactate over base deficit in prognosticating outcomes. Sutherland also queries the length of stay and slow recruitment - again, please refer to above. We did not 'casually dismiss' the deaths - indeed, their management was carefully reviewed and they did not receive large amounts of fluid (or inotropes) in the first 4 hours to provide a cause attributable to the protocol for their subsequent demise. Chest and wound infection were grouped together - a strong argument could be made for their similar aetiology - namely, poor tissue perfusion leading to poor wound healing, increased lethargy, reduced mobilisation, weakened cough and chest infection. It is also a well known fact that one of the commonest causes of post-operative atrial fibrillation is hypovolaemia, particular when inotropes are being given - thus the improvement in the protocol group is expected rather than spurious. They conclude that our study adds nothing to the scientific literature and the technique has little to offer patients undergoing cardiac surgery. They are obviously entitled to their opinion. However, there are now two orthopaedic studies, two abdominal surgery studies and one other cardiac study all showing outcome improvements with similar protocols using the same oesophageal Doppler device. There's only so much sand one can stick one's head in! Dr Anyanwu should also refer to the host of peroperative studies using Doppler, PA catheters and the like whereby short-term protocolised intervention lasting hours made a huge difference to subsequent outcomes. With regard to hospital stay, we would argue that it is an irrefutable endpoint and the randomisation technique takes into account local practice, surgeon preference, etc.. The low rate of AF is fully commensurate with adequate fluid loading and avoidance of inotropes - I would commend this approach to him. He suggests that blanket application of any haemodynamic intervention to all cardiac surgical patients is impractical - I disagree entirely. The principles of post-op care are identical, namely pain relief, adequate gas exchange, adequate filling and maintenance of an oxygen delivery sufficent to maintain tissue perfusion. This obviously requires tailoring to the individual but the principles remain. The use of a Starling fluid challenge avoids excessive fluid loading and aids detection of conditions such as tamponade before catastrophes ensue. I fully agree that correct use of any device is mandatory - a good education program with regular refreshing is essential. The biologically plausible explanation for the improvement seen is the reduction in tissue hypoperfusion - this translates into less lethargy, less ileus, and a greater ability and will to mobilise. We did acknowledge the medical staff (this does include the surgeons!) though not by name. The technique has been in common use on the ICU for over 10 years thus general acceptance of its utility is not an issue. This study was, however, the first by which its use was protocolised for post-operative management. We too would encourage further study to confirm or refute the generalisability of our results. Competing interests: senior author of the study |
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