Peter W Dion

The Chinese University of Hong Kong, Hong Kong, Hong Kong

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Publications (23)76.14 Total impact

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    Hong Kong medical journal = Xianggang yi xue za zhi / Hong Kong Academy of Medicine 10/2013; 19(5):461-3.
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    Ho AM, Dion PW, Ng CS, Karmakar MK
    Anaesthesia 02/2013; 68(2):126-130. · 3.49 Impact Factor
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    Anaesthesia 02/2013; 68(2):126-30. · 3.49 Impact Factor
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    Anaesthesia 01/2013; 68(2):126-130. · 3.49 Impact Factor
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    ABSTRACT: Observational studies on transfusion in trauma comparing high versus low plasma:erythrocyte ratio were prone to survivor bias because plasma administration typically started later than erythrocytes. Therefore, early deaths were categorized in the low plasma:erythrocyte group, whereas early survivors had a higher chance of receiving a higher ratio. When early deaths were excluded, however, a bias against higher ratio can be created. Survivor bias could be reduced by performing before-and-after studies or treating the plasma:erythrocyte ratio as a time-dependent covariate.We reviewed 26 studies on blood ratios in trauma. Fifteen of the studies were survivor bias-unlikely or biased against higher ratio; among them, 10 showed an association between higher ratio and improved survival, and five did not. Eleven studies that were judged survivor bias-prone favoring higher ratio suggested that a higher ratio was superior.Without randomized controlled trials controlling for survivor bias, the current available evidence supporting higher plasma:erythrocyte resuscitation is inconclusive.
    Anesthesiology 03/2012; 116(3):716-28. · 5.16 Impact Factor
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    ABSTRACT: Observational studies on injured patients requiring massive transfusion have found a survival advantage associated with use of equivalent number of units of fresh frozen plasma (FFP) and packed red blood cells (RBCs) compared with use of FFP based on conventional guidelines. However, a survivorship bias might have favoured the higher use of FFP because patients who died early never had the chance to receive sufficient FFP to match the number of RBC units transfused. A Markov model using trauma data from local hospitals was constructed and various FFP transfusion scenarios were applied in Monte Carlo simulations in which the relative risk of death associated with exposure to high FFP transfusion was set at 1.00, so that the FFP : RBC ratio had no influence on mortality outcome. Simulation results showed that the relative risk associated with exposure to high FFP transfusion was less than 1.00 (0.33-0.56 based on programmed delays in achieving an FFP : RBC ratio of 1 : 1-2), thus demonstrating a survivorship bias in favour of FFP : RBC equal to or more than 1 : 1-2 in certain observational trauma studies. This bias was directly proportional to the delay in achieving a FFP : RBC ratio of 1 : 1-2 during resuscitation. Some observational studies comparing low and high FFP administration in injured patients requiring massive transfusion probably involve survivorship bias that inflates or creates a survival advantage in favour of a higher FFP : RBC ratio.
    British Journal of Surgery 01/2012; 99 Suppl 1:132-9. · 4.84 Impact Factor
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    Article: "1:1".
    Resuscitation 02/2011; 82(5):627-8. · 4.10 Impact Factor
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    Article: "1:1"
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    ABSTRACT: “1:1” Sir, Wethank Professors Fries and Luger for their comments. Indeed, there is massive confusion on how to administer fresh frozen plasma (FFP) in trauma patients with massive and ongoing bleeding (MOB).1 Stanworth et al.’s systematic review of studies mostly done in the era of whole blood as opposed to packed red blood cells (PRBCs), showing that prophylactic administration of FFP in euvolemic patients, most of whom had no pre-existing haemostatic deficiencies, undergoing elective non-exsanguinating procedures did not lead to reduced blood loss/use2 is again used as a lightning rod by opponents of the so-called “1:1” strategy in the trauma and MOB setting. It is true that liberal administration of FFP, or any fluid for that matter, in a euvolemic patient risks overloading. The topic of our discussion is, however, on patients who are presenting with MOB, whose problems include hypovolemic shock and coagulopathy. The early use of sufficient quantities of FFP, or “1:1”, would hopefully reduce the likelihood of persistent coagulopathy after euvolemia is finally restored, and thus prevent the problem of having to administer large quantities of FFP at that stage. We agree that albumin is potentially harmful to patients with head injury, and it would be better to administer target therapy based on thrombelastography and the use of fibrinogen and prothrombin complex concentrates. Unfortunately, thrombelastography and factor concentrates are not available in emergency or operating rooms in many parts of the world. We do appreciate the acknowledgement that there is a need to replace coagulation factors, which, in many countries, still come mainly in the form of FFP. Citrate toxicity occurs with rapid transfusion of large quantities of blood products. It is easily recognized, monitored, treated, and is seldom a significant consideration in the decision making process for us when transfusing blood products. FFP is implicated in TRALI, although other blood products are not entirely innocent. There are two questions that need to be answered. First, does the aggressive use of FFP to achieve an FFP:PRBC ratio of almost 1:1 early on in trauma patients with MOB result in higher use of blood products? Second, does “1:1”, again in trauma patients with MOB, result in more TRALI, respiratory failure, sepsis, or most importantly, higher mortality rate? On the first question, we refer our readers to studies showing that “1:1” results in the same or reduced amount of exposure to blood products.3–5 On the second question, we refer to studies showing “1:1” improves survival.6–8 Not all studies show that “1:1” is superior in the trauma with MOB setting, but the vast majority of them do. On survivorship bias (SB), Snyder et al.’s study purportedly showed that when observational data were analyzed in a way to eliminate SB, the survival benefit of “1:1” did not reach statistical significance.9 We agree that a significant proportion of observational studies on “1:1” are susceptible to SB. Nonetheless, we wish to point out that Snyder et al.’s study was possibly underpowered, and their non-“1:1” and “1:1” groups were not independent. Patients were transitioning from the former to the latter group almost entirely unidirectionally during the course of resuscitation. That tells us that clinicians in the study were responding to ongoing bleeding and serious coagulopathy by giving FFP. In other words, as we argue the merits of “1:1”, our front line colleagues are already “doing it”. It is quite possible that when a patient transitions from a low FFP to “1:1”, he is also bringing the perils of excessive coagulopathy from the former cohort to the latter. In other words, if “1:1” is superior, we do not expect that it could immediately deliver that advantage as soon as that magic ratio is reached – it could already be too late. Which brings us to another bias, confounding by indication. In centres without an aggressive FFP transfusion protocol, it is those patients who have more severe bleeding and coagulopathy that tend to get more FFP in an observational study. Staying with SB, one way to reduce that bias is the use of two entirely different and independent cohorts. Numerous authors have compared outcomes between patients before and after the implemention of a “1:1” protocol and have found “1:1” to be clearly superior.4–6,10 Granted that resuscitation techniques must have progressed for the better to have explained the better outcomes enjoyed by the “after” group, we should at least acknowledge that perhaps that “1:1” is a component of that progression for the better. Riskin et al.’s study5 is particularly worth a close look. They found that the FFP:PRBC ratios were identical before and after implementaion of a “1:1” protocol. The only difference was that “1:1” led to an earlier use of FFP. The lesson there is that you can give FFP earlier proactively, or you can give it later reactively. Either way, you will wind up giving a lot of FFP, except that playing “catch up” has a serious price to pay in terms of outcome. It is a good thing no one has done observational studies on whether surgery is useful in trauma patients with MOB, otherwise surgery would also have been found to have “benefitted” from SB, and, with all of its attending side-effects of infection, bleeding, immunologic suppression, pain, scarring, etc., dismissed altogether. On the issue of volume replacement with the newest types of synthetic colloids, hydroxyethyl starch 130/0.4-0.42/6 comes to mind. There is a dose limit of 50 mL/kg because of dose-dependent adverse haemostatic effects. Prof. Fries and Luger ask, was it the volume effect of FFP or was it the coagulation factors that bring increased survival? We gratefully acknowledge their tacit agreement that FFP given appropriately aggressively in trauma patients with MOB does seem to be useful. For now, to a frontline colleague, that is all he needs. “1:1” is balanced; any major deviation from this ratio represents an intrinsically anaemic or factor-deficient mixture. As mentioned earlier, frontline clinicians are already “doing it”. That does not necessarily mean that they are right, but disregarding the power of observations of somanyexperienced clinicians and studies because of statistical and methological imperfections, is not right either. Ultimately, perhaps a better question than asking if “1:1” is good is this: Next time an exsanguinating trauma patient presents, what mixture are you going to give? Conflict of interest statement None to declare. References 1. Ho AMH, Dion PW, Yeung JH, et al. Fresh-frozen plasma transfusion strategy in trauma with massive and ongoing bleeding Common (sense) and sensibility. Resuscitation 2010;81:1079–81. 2. Stanworth SJ, Brunskill SJ, Hyde CJ, et al. Is fresh frozen plasma clinically effective? A systematic review of randomized controlled trials. Br J Haematol 2004;126:139–52. 3. Dente CJ, Shaz BH, Nicholas JM, et al. Improvements in early mortality and coagulopathy are sustained better in patients with blunt trauma after institution of a massive transfusion protocol in a civilian level I trauma center. J Trauma 2009;66:1616–24. 4. Gunter Jr OL, Au BK, Isbell JM, et al. Optimizing outcomes in damage control resuscitation: identifying blood product ratios associated with improved survival. J Trauma 2008;65:527–34. 5. Riskin DJ, Tsai TC, Riskin L, et al. Massive transfusion protocols: the role of aggressive resuscitation versus product ratio in mortality reduction. J Am Coll Surg 2009;209:198–205. 6. Cotton BA, Au BK, Timothy C, et al. Predefined massive transfusion protocols are associated with a reduction in organ failure and postinjury complications. J Trauma 2009;66:41–9. 7. Sperry JL, Ochoa JB, Gunn SR, et al. An FFP:PRBC transfusion ratio ≥1:1.5 is associated with a lower risk of mortality after massive transfusion. J Trauma 2008;65:986–93. 8. Watson GA, Sperry JL, Rosengart MR, et al. Fresh frozen plasma is independently associated with a higher risk of multiple organ failure and acute respiratory distress syndrome. J Trauma 2009;67:221–30. 9. Snyder CW, Weinberg JA, McGwin Jr G, et al. The relationship of blood product ratio to mortality: survival benefit or survival bias? J Trauma 2009;66: 358–64. 10. Zaydfudim V, Dutton WD, Feurer ID, et al. Exsanguination protocol improves survival after major hepatic trauma. Injury 2010;41:30–4. Anthony M.-H. Hoa,∗ Peter W. Dionc Calvin S.H. Ngb Chi Wai Cheungd Janice H.H. Yeunge Lester A.H. Critchley a a Department of Anaesthesia and Intensive Care, The Chinese University of Hong Kong, Hong Kong b Department of Surgery, The Chinese University of Hong Kong, Hong Kong c Department of Anaesthesia, St. Catharines General Hospital, Hong Kong d Department of Anaesthesiology, The University of Hong Kong, Hong Kong e Accident and Emergency Department, Prince of Wales Hospital, Hong Kong ∗ Corresponding author at: Department of Anaesthesia and Intensive Care, Prince of Wales Hospital, Shatin, NT, Hong Kong. Tel.: +852 26321133; fax: +852 26372422. E-mail addresses: hoamh@hotmail.com, hoamh@yahoo.com (A.M.-H. Ho) 16 December 2010
    Resuscitation 01/2011; 82:627-628. · 4.10 Impact Factor
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    ABSTRACT: During trauma resuscitation involving massive transfusion, the best fresh-frozen plasma to packed red blood cells ratio is unknown. No randomised controlled trial (RCT) is available on this subject, although there are plenty of observational studies suggesting that the ratio should be about 1:1. This ratio also makes more physiological sense, and we suggest that in patients with massive and ongoing bleeding, it is a sensible strategy with which to start resuscitation.
    Resuscitation 09/2010; 81(9):1079-81. · 4.10 Impact Factor
  • Peter W. Dion, Anthony M. H. Ho
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    ABSTRACT: Problems in projectile motion are a time-honored staple of high school and even first-year university physics. They can become confusing for some students, yet boring for the stronger students. Herein we present two alternative approaches to such questions, one we call ``breaking down gravity,'' which makes these questions easier to solve, and the other we call ``getting rid of gravity,'' which converts such questions into a more interesting and challenging form.
    The Physics Teacher 01/2010; 48(4).
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    ABSTRACT: Airway, breathing, and circulation are top priorities in any resuscitation. However, in cardiac tamponade, the decision to intubate the trachea and initiate positive pressure ventilation (PPV) should only be taken after consideration of the deleterious haemodynamic effects of positive intrathoracic pressure. We suggest that the threshold for intubation and PPV should be raised in tamponade and that intubation and PPV should, if possible, be timed so that relief of tamponade can immediately follow. In the trauma setting, emergency thoracotomy is the best approach. When intubation is unavoidable because of very low oxygen saturation or cardiac arrest, high ventilatory pressures should be avoided.
    Resuscitation 01/2009; 80(2):272-4. · 4.10 Impact Factor
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    ABSTRACT: The laryngeal mask airway (LMA) is now standard airway management equipment in prehospital and Emergency Department (ED) care. Most providers may not be able to match the pediatric LMA sizes to the appropriate weights of pediatric patients. The exact inflation volumes are also difficult to memorize. To overcome this problem, we propose the following equations: Weight (kg) of patient = 2(2 x LMA), where LMA is the size; cuff inflation volume (mL) = 5 x LMA.
    Journal of Emergency Medicine 06/2008; 35(3):299-300. · 1.33 Impact Factor
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    ABSTRACT: Randomized controlled trials of how best to administer fresh frozen plasma (FFP) in the presence of ongoing severe traumatic hemorrhage are difficult to execute and have not been published. Meanwhile, coagulopathy remains a common occurrence during major trauma resuscitation and hemorrhage remains a major cause of traumatic deaths, suggesting that current coagulation factor replacement practices may be inadequate. We used a pharmacokinetic model to simulate the dilutional component of coagulopathy during hemorrhage and compared different FFP transfusion strategies for the prevention or correction, or both, of dilutional coagulopathy. Assuming the rates of volume replacement and loss are roughly equal, we derived the hematocrit and plasma coagulation factor concentration over time based on the rate of blood loss and replacement, the hematocrit and coagulation factor concentration of the transfusate, and the hematocrit and plasma factor concentration at the time when FFP transfusion begins. Once excessive deficiency of factors has developed and bleeding is unabated, 1-1.5 units of FFP must be given for every unit of packed red blood cells (PRBC) transfused. If FFP transfusion should start before plasma factor concentration drops below 50% of normal, an FFP:PRBC transfusion ratio of 1:1 would prevent further dilution. During resuscitation of a patient who has undergone major trauma, the equivalent of whole-blood transfusion is required to correct or prevent dilutional coagulopathy.
    Canadian journal of surgery. Journal canadien de chirurgie 01/2006; 48(6):470-8. · 1.63 Impact Factor
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    ABSTRACT: Hemorrhage is a major cause of trauma deaths. Coagulopathy exacerbates hemorrhage and is commonly seen during major trauma resuscitation, suggesting that current practice of coagulation factor transfusion is inadequate. Reversal of coagulopathy involves normalization of body temperature, elimination of the causes of disseminated intravascular coagulation (DIC), and transfusion with fresh-frozen plasma (FFP), platelets, and cryoprecipitate. Transfusion should be guided by clinical factors and laboratory results. However, in major trauma, clinical signs may be obscured and various factors conspire to make it difficult to provide the best transfusion therapy. Existing empiric transfusion strategies for, and prevailing teachings on, FFP transfusion appear to be based on old studies involving elective patients transfused with whole blood and may not be applicable to trauma patients in the era of transfusion with packed red blood cells (PRBCs). Perpetuation of such concepts is in part responsible for the common finding of refractory coagulopathy in major trauma patients today. In this review, we argue that coagulopathy can best be avoided or reversed when severe trauma victims are transfused with at least the equivalent of whole blood in a timely fashion.
    The American Journal of Surgery 10/2005; 190(3):479-84. · 2.52 Impact Factor
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    ABSTRACT: Continuous central pressure monitoring and simultaneous continuous infusion via the same central venous catheter are sometimes necessary. Based on theoretical calculations and experimental measurements, we have determined that pressure monitoring is essentially unaffected if the continuous infusion rate is 50 ml.h(-1) or less for an adult and a paediatric central catheter. At rates > 200 ml.h(-1), the central venous pressure is exaggerated by up to 4 mmHg and 8 mmHg for the adult and paediatric catheters, respectively.
    Anaesthesia 10/2005; 60(10):1027-30. · 3.49 Impact Factor
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    A M-H Ho, M K Karmakar, P W Dion
    Anaesthesia 05/2004; 59(4):404-5; author reply 405. · 3.49 Impact Factor
  • Anesthesiology 05/2003; 98(4):1025-6; author reply 1026-7. · 5.16 Impact Factor
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    ABSTRACT: To evaluate, by systematic review, the efficacy of heliox on respiratory mechanics and outcomes in patients with acute asthma. The search strategy included searching electronic databases (MEDLINE, EMBASE, and The Cochrane Library) and the references of relevant articles. Study quality was assessed based on allocation concealment. Randomized controlled trials (RCTs) comparing heliox to an air-oxygen mixture (airO(2)) as an adjunct treatment in patients with acute asthmatic attacks were analyzed. For the qualitative portion of the analysis, all reports of the use of heliox in patients with acute asthma were included. Four RCTs (n = 278) were found to have a common respiratory parameter (peak expiratory flow rate as a percentage of predicted) suitable for meta-analysis. Within the 92% confidence interval (CI), there was a small benefit with the use of heliox compared to airO(2) (weighted mean difference, + 3%; 95% CI, - 2 to + 8%). There was also a slight improvement in the dyspnea index (weighted mean difference, 0.60; 95% CI, 0.04 to 1.16) with the use of heliox over airO(2). Overall, five RCTs, one nonrandomized unblinded parallel trial, one retrospective case-matched control trial, three case series, and one case report had results in favor of heliox; one RCT and one case series showed no improvement with heliox; one RCT showed a possible detrimental effect with heliox; and 1 small RCT was inconclusive. Most investigators did not prevent entrainment of room air during heliox use or compensate for the lower nebulizing efficiency of heliox. Based on surrogate markers, heliox may offer mild-to-moderate benefits in patients with acute asthma within the first hour of use, but its advantages become less apparent beyond 1 h, as most conventionally treated patients improve to similar levels, with or without it. The effect of heliox may be more pronounced in more severe cases. There are insufficient data on whether heliox can avert tracheal intubation, or change intensive care and hospital admission rates and duration, or mortality.
    Chest 04/2003; 123(3):882-90. · 7.13 Impact Factor
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    ABSTRACT: Heliox has a lower density than oxygen and nitrogen, and can improve ventilation rapidly in patients with critical upper airway obstruction. The choice of the best helium:oxygen ratio depends on whether the predominant problem is hypercarbia or hypoxia. In the former situation, 80% helium should be used, and in the latter, 100% oxygen is appropriate.
    Resuscitation 04/2002; 52(3):297-300. · 4.10 Impact Factor
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    ABSTRACT: Omission of a confidence interval (CI) associated with the risk of a serious complication can lead to inaccurate interpretation of risk data. The calculation of a CI for a risk or a single proportion typically uses the familiar Gaussian (normal) approximation. However, when the risk is small, "exact" methods or other special techniques should be used to avoid overshooting (risks that include values outside of [0,1]) and zero width interval degeneration. Computer programs and simple equations are available to construct CIs reasonably accurately. In the special case in which the complication has not occurred, the risk estimated with 95% confidence is no worse than 3/n, where n is the number of trials.
    Regional Anesthesia and Pain Medicine 01/2002; 27(2):207-10. · 3.46 Impact Factor