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Early management of the severely injured major trauma patient

2014; Elsevier BV; Volume: 113; Issue: 2 Linguagem: Inglês

10.1093/bja/aeu235

1471-6771

Amy McCullough, Jo Haycock, Daren P. Forward, C.G. Moran,

Emergency and Acute Care Studies

The major trauma team relies on an efficient, communicative team to ensure patients receive the best quality care. This requires a comprehensive handover, rapid systematic review, and early management of life- and limb-threatening injuries. These multiple injured patients often present with complex conditions in a dynamic situation. The importance of team work, communication, senior decision-making, and documentation cannot be underestimated. The major trauma team relies on an efficient, communicative team to ensure patients receive the best quality care. This requires a comprehensive handover, rapid systematic review, and early management of life- and limb-threatening injuries. These multiple injured patients often present with complex conditions in a dynamic situation. The importance of team work, communication, senior decision-making, and documentation cannot be underestimated. Editors's key points•The trauma team must function as a unit with effective leadership and a clear understanding by team members of their roles.•Repeated briefing and review maintains clinical through the numerous transitions involved in the care of trauma patients.•A higher rate of failed intubation is seen in trauma patients than in other groups.•During intra-operative care, the patient's status should be reviewed every 10–30 minutes and the surgical plan modified if necessary. •The trauma team must function as a unit with effective leadership and a clear understanding by team members of their roles.•Repeated briefing and review maintains clinical through the numerous transitions involved in the care of trauma patients.•A higher rate of failed intubation is seen in trauma patients than in other groups.•During intra-operative care, the patient's status should be reviewed every 10–30 minutes and the surgical plan modified if necessary. Major trauma networks have recently been developed in England to provide optimal management of the severely injured patient. Numerous reports have highlighted the past problems in trauma care in the UK and the recent reorganization seeks to address these deficiencies.1Royal College of Surgeons of England and British Orthopaedic AssociationBetter Care for the Severely Injured. 2000http://www.rcseng.ac.uk/publications/docs/severely_injured.htmlGoogle Scholar, 2National Confidential Enquiry into Patient Outcome and Death (2007), Trauma: Who Cares? National Audit Office (2010). Major Trauma Care in England, Available from http://www.nao.org.uk/wp-content/uploads/2010/02/0910213.pdf (accessed 10 February 2014).Google Scholar, 3Intercollegiate Group of Trauma StandardsRegional Trauma Systems: Interim Guidance for Commissioners. Royal College of Surgeons of England, London2009http://www.rcseng.ac.uk/publications/docs/regional-trauma-systems-interim-guidance-for-commissionersGoogle Scholar This reorganization is based on the improved survival and outcomes observed when severely injured patients present to specialized (major trauma) centres (MTCs) that treat sufficient numbers and have a coordinated, multidisciplinary team to receive, resuscitate, and provide definitive care.4Demetriades D Martin M Salim A et al.The effect of trauma center designation and trauma volume on outcome in specific severe injuries.Ann Surg. 2005; 242: 512-517Crossref PubMed Scopus (296) Google Scholar 5Nathens AB Jurkovich GJ Maier RV et al.Relationship between trauma center volume and outcomes.J Am Med Assoc. 2001; 285: 1164-1171Crossref PubMed Scopus (442) Google Scholar This restructuring of major trauma care is the first nationally coordinated change trauma services since the inception of the National Health Service 60 yr ago and the first attempt at developing a national system to provide high-quality trauma care for the population in England. Twenty-six regional trauma networks have been established; each network has been designed to best serve the local geography, population and infrastructure. The East Midlands Major Trauma Network covers a population of 4.3 million and consists of one MTC with five supporting trauma units (TU). Severely injured patients are identified using a triage tool and are taken directly to the MTC if the journey time is 45 min from the MTC are taken to the nearest TU for resuscitation, evaluation, and detailed triage. Secondary transfer then will take place to the MTC if required. Other hospitals with A&E departments, designated as Local Emergency Hospitals, which do not have the facilities to receive major trauma patients are always by-passed by the pre-hospital system. At the receiving hospital, there should be agreed predefined activation criteria for a trauma call.6Cherry RA King TS Carney DE Bryant P Cooney RN Trauma team activation and the impact on mortality.J Trauma. 2007; 63: 326-330Crossref PubMed Scopus (46) Google Scholar These are most usually based on mechanism of injury, acute physiology, and anatomical factors. However, there is currently no agreed national consensus on the criteria used, and within units some discretion is exercised on a case-by-case basis. Activation of a Major Trauma Call before patient arrival (pre-alert) depends upon the accuracy of pre-hospital information. In most institutions, the trauma team will have predetermined members. It usually comprises emergency department (ED) physicians, anaesthetists, general and orthopaedic surgeons, with some units providing a radiologist, neurosurgeon, and intensive care physician.2National Confidential Enquiry into Patient Outcome and Death (2007), Trauma: Who Cares? National Audit Office (2010). Major Trauma Care in England, Available from http://www.nao.org.uk/wp-content/uploads/2010/02/0910213.pdf (accessed 10 February 2014).Google Scholar Exact membership and seniority will vary according to time of day, shift changes, other hospital activity, and so forth. The trauma team leader can come from any of the specialities, most usually from ED in England. The quality of leadership is paramount to the safe and efficient running of trauma calls.7Hjortdahl M Ringen AH Naess AC Wisborg T Leadership is the essential non-technical skill in the trauma team—results of a qualitative study.Scand J Trauma Resusc Emerg Med. 2009; 17: 48-49Crossref PubMed Scopus (47) Google Scholar Ideally the trauma team should be (pre)-alerted and attend the ED before the arrival of the patient. This provides time for introductions and briefing with respect to roles and expertise of team members, to check equipment, to share available patient information, to plan and prepare for anticipated therapeutic and diagnostic interventions. Whilst trauma team leadership is pivotal in these high stakes, complex, and dynamic clinical situations, so too is team followership, and training should focus on both roles. Providing the desirable high-quality, consistent, trauma team training, and experience for trainees and consultants across all TU and MTCs is a significant national challenge. Historically, medical training has focused on knowledge and skills, that is, technical factors. However, in recent years, there has been increased understanding and focus on human factors and, in particular, non-technical skills. These have been described for anaesthetists by the Anaesthetic Non-Technical Skills (ANTS) system.8Flin R Patey R Glavin R Maran N Anaesthetists' non-technical skills.Br J Anaesth. 2010; 105: 38-44Abstract Full Text Full Text PDF PubMed Scopus (286) Google Scholar The four skill categories described (task management, team working, situation awareness, and decision-making) are all critical determinants of successful trauma resuscitation. The anaesthetist often contributes to the trauma team in a non-leadership role, which is entirely appropriate given the very task-orientated role of airway and breathing assessment and management. However, the position at the head of the patient presents a unique overview of both the patient and situation as a whole. In addition to specialist airways skills, anaesthetists bring to the major trauma situation their skills in the recognition and management of acute physiological derangement, including haemorrhage and shock. Findings and concerns should be clearly communicated to the team leader. The anaesthetist is often the primary clinician providing direct continuity of care through the early part of the patient's pathway in the hospital. Multiple team and place transitions can be particularly difficult, but the use of repeated briefing and review can ensure agreed clinical understanding, shared goals, and planning to optimize team resource management. Checklists can be very helpful for equipment preparation, and can also be used to enhance safety at critical interventions and at key transitions, such as transfer to computerised tomography (CT) scan, theatre, or critical care. Transfer to these different environments necessitates safe handover of care at a time when information loss and corruption is a potential hazard. Emergency checklists can also be helpful in unusual or stressful situations such as the 'non-responder'. The factors most commonly causing clinical problems are decision-making and effective communication within and between teams. Particular attention needs to be paid to documentation of decisions and interventions. The objectives in ED are to undertake a rapid and systematic clinical assessment; to institute immediately life-saving treatment; to use information gleaned clinically and from imaging (focused assessment with sonography in trauma and CT) to decide the most appropriate patient pathway; and safe and timely patient transfer with clear forward communication. In the ED, the trauma team receives the patient after a comprehensive, clear handover is delivered and heard by the whole team. The importance of a handover by paramedics transferring the patient cannot be underestimated. They have knowledge of the scene, mechanism of injury, patient condition, and pre-hospital management that will affect assessment and further care. The MIST structure (M—Mechanism of injury: I—Injuries sustained or suspected: S—vital Signs at the scene and on transport: T—Treatment and response)9D'Amours S Sugrue M Russell R Nocera N Clinical Guidelines: Pre-Hospital Information and Hand-Over. Handbook of Trauma Care. 6th Edn. University of New South Wales, Sydney2002http://www.sswahs.nsw.gov.au/liverpool/trauma/handbook1.htmlGoogle Scholar is a useful tool for handover and forward communication. Initial assessment is managed according to Advanced Trauma Life Support (ATLS) principles with airway and cervical spine control taking priority but with management of ABC's in parallel rather than sequence.10American College of Surgeons: Advanced Trauma Life Support (ATLS), 2004, Available from http://www.facs.org/trauma/atls/information.html (accessed 10 February 2014).Google Scholar Primary survey findings are clearly communicated to the team leader and documented. The one exception to the 'ABCDE' approach of ATLS is uncommon in civilian practice but can occur, particularly in the context of penetrating wounds, when exsanguinating external haemorrhage poses the most immediate threat to life and must be controlled as a priority. This can be achieved in the limbs by direct pressure to the wound and immediate application of a pneumatic tourniquet with the tourniquet time clearly documented in indelible ink on the patient.11Moran CG Forward DP The early management of patients with multiple injuries an evidence based, practical guide for the orthopaedic surgeon.J Bone Joint Surg Br. 2012; 94-B: 446-453Crossref Scopus (17) Google Scholar In injuries of the junction of the thigh-groin and arm-axilla it is not possible to apply a tourniquet and haemorrhage control relies on direct pressure and packing. Control of haemorrhage from this 'junctional trauma' can be very difficult as large vessels are involved and often retract from the wound site. These patients may require emergent surgical haemorrhage control in theatre. Decision-making with respect to the need, timing, and method to achieve a definitive airway can be very challenging. Clear indications for intubation include actual and impending airway compromise. However, intubation and ventilation may also facilitate safe imaging, transfer, and required interventions in the shocked patient or the very agitated patient. In the presence of multiple painful or distressing injuries, when the inevitable destination of the patient is theatre or the intensive care unit, early anaesthesia, intubation, and ventilation is humane and offers best analgesia. NICE offers guidelines in the context of brain injury.12National Institute for Health and Clinical ExcellenceClinical guideline 56 (partial update) head injury: triage, assessment, investigation and early management of head injury in infants, children and adults. 2013http://www.nice.org.uk/nicemedia/live/11836/36259/36259.pdfGoogle Scholar Experienced clinical assessment will help to determine the need for a definitive airway and its urgency; the risks of securing a definitive airway vs not doing so; and the best intubation strategy. The decision-making, planning, and preparation should be shared with the rest of the trauma team. There is clear evidence from NAP4 that trauma intubations are more difficult: there is a higher rate of failed intubation, surgical airway, and serious complications from emergency airway management.134th National Audit Project (NAP4) of The Royal College of Anaesthetists and The Difficult Airway Society 'Major Complications of Airway Management in The United Kingdom' Report and findings, 2011, Available from http://www.rcoa.ac.uk/node/4211 (accessed 10 February 2014).Google Scholar In addition to the requirement for cervical spine neutrality and premorbid or injury related patient factors, there are the additional factors of a high pressure, time-critical situation, a noisy environment, ongoing resuscitation, potentially unrehearsed team, equipment preparation, and checking. Penetrating injuries to the neck pose considerable challenges to the anaesthetist. Both intubation and surgical access to the trachea may be difficult when bleeding into the cervical tissues causes swelling, oedema, and soft tissue distortion. An anaesthetic trainee in the trauma call setting must always be aware of the complexity of these cases, and should feel comfortable in requesting senior anaesthetic assistance and advice. The anaesthetist must clarify the skills and experience of any team member assisting them. Rapid sequence induction (RSI) is the most commonly used technique to establish a definitive airway in the context of trauma. Drug choices should balance known risks. Rather than attempting best possible visualization of the larynx, a good enough view to pass a bougie is preferable. This minimizes the pressor response and risk of cervical spine movement. A well-fitting collar will make laryngoscopy difficult or impossible and so the neck should be protected with manual in-line immobilization during intubation. Airway strategy (NAP4) should be agreed and shared with the rest of the team, up to and including the plan for failure. A pre-RSI checklist is useful to check set-up and verbalize plans for failure. The Difficult Airway Society guidelines for failed intubation in RSI and 'can't intubate, can't ventilate' scenarios are familiar and widely accepted,14Henderson JJ Popat MT Latto IP Pearce AC Difficult Airway SocietyDifficult Airway Society guidelines for management of the unanticipated difficult intubation.Anaesthesia. 2004; 59: 675-694Crossref PubMed Scopus (841) Google Scholar but in the trauma patient, depending upon the urgency and indication for intubation, and the physiological status of the patient, the wake-up option is rarely appropriate or possible. Laryngeal mask airway placement may provide a useful temporizing measure for oxygenation, and conduit for fibreoptic and exchange catheter intubation, but the suitability of these options is again dependent on the same limiting factors. NAP4 highlighted the higher failure and complication rate associated with needle cricothyroidotomy as a rescue option. That fact and the need for definitive airway placement has changed our rescue option to surgical cricothyroidotomy with pre-RSI marking of the cricothyroid membrane, and identification of both the equipment and person to achieve the surgical airway using a standardized technique and equipment. Successful airway assessment and management depends upon a combination of expertise, equipment, and human factors. The airway strategy should be genuinely deliverable in the given situation. Assessment of breathing can be difficult in a noisy ED. The conscious patient may complain of respiratory difficulty, chest tightness, shortness of breath or pain. Careful clinical examination and serial arterial blood gas analysis will provide evidence of early or evolving respiratory compromise. Emergent chest decompression is required in the presence of tension pneumothorax (a clinical diagnosis). Needle thoracentesis should be performed in the non-ventilated patient. Thoracostomy can be performed in the ventilated, anaesthetized patient. Either should be followed by chest drain insertion, performed aseptically. Deterioration of clinical signs with a chest drain in situ should prompt an immediate check of the drain, for displacement or obstruction. Conventional practice has been to place a chest drain in the presence of pneumothorax, but also in the presence of rib fractures without pneumothorax if the patient is to receive intermittent positive pressure ventilation (IPPV). Chest drainage may be performed pre-anaesthesia and ventilation, but may also be achieved immediately post-induction of anaesthesia. However, chest drainage is not without both early and late complications (e.g. misplacement, displacement, lung injury, bleeding, and infection). Current intensive care practice is that patients with rib fractures alone or small pneumothorax will not necessarily need chest drainage. However, in the complex and dynamic context of polytrauma, damage control resuscitation (DCR) and surgery the decision against chest drain placement should only be made by a senior and experienced team: it depends entirely on confidence that early diagnosis and access to treat a developing pneumothorax would be possible.15Kirkpatrick AW Rizoli S Ouellet J-F et al.for the Canadian Trauma Trials Collaborative and the Research Committee of the Trauma Association of CanadaOccult pneumothoraces in critical care: a prospective multicenter randomized controlled trial of pleural drainage for mechanically ventilated trauma patients with occult pneumothoraces.J Trauma Acute Care Surg. 2013; 74: 747-753Crossref PubMed Scopus (44) Google Scholar Although chest is one of the two primary survey X-rays, a significant proportion of both rib fractures and pneumothoraces (particularly anterior) may be missed. The decision to CT scan earlier in resuscitation means that many trauma teams are foregoing the standard chest X-ray in favour of very early CT, which has a far higher diagnostic accuracy. Clinical factors (injuries and physiology) and arterial blood gas analysis will guide the decision to provide emergent ventilatory support. Lung protective strategies should be used in the presence of IPPV, aiming for VTe of 6–8 ml kg−1 and Pmax < 30. Normocapnia (4.5–5 kPa) is the ideal in all patients including the brain injured, with two exceptions: the first is the use of increased ventilation as a temporizing measure in the presence of impending brain stem herniation, the second is the use of permissive hypercapnia in the presence of lung injury. Both of these are senior decisions. Life threatening haemorrhage may be external or concealed within a body cavity. Evans and colleagues showed that 30% pre-hospital and in-hospital deaths after trauma were because of exsanguination.16Evans JA van Wessem KJ McDougall D et al.Epidemiology of traumatic deaths: comprehensive population-based assessment.World J Surg. 2010; 34: 158-163Crossref PubMed Scopus (328) Google Scholar The haemorrhage occurred from the aorta (23%), chest (23%), pelvic fracture (23%), abdomen (10%), and extremities (7%). Haemorrhage continues to be a cause of preventable death in trauma.17Tien HC Spencer F Tremblay LN Rizoli SB Brenneman FD Preventable deaths from hemorrhage at a level I Canadian trauma center.J Trauma. 2007; 62: 142-146Crossref PubMed Scopus (199) Google Scholar Recognition of haemorrhage can be very challenging in the polytrauma patient because of many factors including varied individual physiology and reserve, pre-hospital treatment, comorbidity, and medications. In some patients, exsanguinating haemorrhage (e.g. pelvic fractures or penetrating trauma) results in a Bezold Jarisch reflex with no tachycardia.18Kinsella SM Tuckey JP Perioperative bradycardia and asystole: relationship to vasovagal syncope and the Bezold–Jarisch reflex.Br J Anaesth. 2001; 86: 859-868Abstract Full Text Full Text PDF PubMed Scopus (221) Google Scholar 19Campagna JA Carter C Clinical relevance of the Bezold–Jarisch reflex.Anesthesiology. 2003; 98: 1250-1260Crossref PubMed Scopus (198) Google Scholar It is essential to use all available clinical information such as mechanism of injury and injury patterns, trends in physiological and metabolic parameters, changing levels of cerebration, peripheral perfusion, and urine output (once catheterized). Much of our understanding and management of haemorrhage in trauma has benefited significantly from conflict medicine. However, the UK trauma population is of varied age and comorbidity, and the mechanism of injury is predominantly blunt. There has, for some time, been a recognition that the shocked polytrauma patient with significant tissue damage and high injury severity score, is likely to be coagulopathic at presentation because of the acute coagulopathy of trauma (ACoT). This is associated with early systemic anticoagulation and hyperfibrinolysis.20Brohi K Cohen MJ Davenport RA Acute coagulopathy of trauma: mechanism, identification and effect.Curr Opin Crit Care. 2007; 13: 680-685Crossref PubMed Scopus (453) Google Scholar The effect of ACoT will only be compounded by failure to recognize and control haemorrhage, under-resuscitation, or overzealous use of crystalloid resuscitation contributing to the 'lethal triad' of acidaemia, coagulopathy, and hypothermia. Traditional coagulation testing has several limitations in the acutely bleeding trauma patient. The tests are poor predictors of the need for massive transfusion, and have limited ability to direct early blood product therapy, due in part to time delays and the application of arbitrarily chosen laboratory triggers. For example, the usual laboratory trigger for administration of fresh frozen plasma (FFP) is a PT>1.5 times normal, but in trauma it has been shown that a PT ratio of >1.2 is associated with both increased transfusion requirements and higher mortality.21Frith D Goslings JC Gaarder C et al.Definition and drivers of acute traumatic coagulopathy: clinical and experimental investigations.J Thrombosis Haemostasis. 2010; 8: 1919-1925Crossref PubMed Scopus (277) Google Scholar Point of care viscoelastic coagulation tests (thromboelastography and thromboelastometry) offer rapid information with respect to clot generation, strength and breakdown in whole blood, and may be useful for the early identification and focused management of coagulation abnormalities.22Davenport RA Khan S Management of major trauma haemorrhage: treatment priorities and controversies.Br J Haematol. 2011; 155: 537-548Crossref PubMed Scopus (70) Google Scholar All of these factors have led to the development of DCR strategies in patients with polytrauma and suspected major haemorrhage rather than the traditional high-volume resuscitation followed by definitive surgery. The key components of DCR are: time limited permissive hypotension, the use of massive haemorrhage protocols and tranexamic acid, and damage control surgery (DCS). Time to surgery (or angiography) and haemorrhage control is a key determinant of outcome (mortality) and the transfer to surgery should only be delayed for key, life-saving interventions. Time limited permissive hypotension aims to limit fluid resuscitation, thus reducing the risks of hydrostatically induced clot disruption and worsening dilutional coagulopathy, until haemorrhage control has been achieved (beyond which, definitive resuscitation is the aim). It is a balance of risks, and the chosen target pressures have been the subject of extensive discussion and some controversy, particularly in the context of the severely injured patient with both traumatic brain injury and active bleeding.23Wiles MD Blood pressure management in trauma: from feast to famine?.Anaesthesia. 2013; 68: 445-452Crossref PubMed Scopus (8) Google Scholar, 24Harris T Rhys Thomas GO Brohi K Early fluid resuscitation in severe trauma.Br Med J. 2012; 345: e5752Crossref PubMed Scopus (68) Google Scholar, 25Wiles MD Evidence for damage control resuscitation is lacking.Br Med J. 2012; 345: e7205Crossref PubMed Scopus (2) Google Scholar Pre-hospital practice uses a strict fluid resuscitation protocol of 250 ml boluses of crystalloid titrated to achieve a palpable radial pulse, which estimates a systolic blood pressure of about 70 mm Hg.26Fisher JD Brown SN Cooke MW UK Ambulance Service Clinical Practice Guidelines. Ambulance Service Association, London2006Google Scholar In hospital resuscitation target pressures should acknowledge the nature of traumatic injury (which is predominantly blunt in the UK), and the complex comorbidity of our ageing trauma patient population. The key to permissive hypotension is that it must be time limited, with the earliest possible haemorrhage control, either by surgery or interventional radiology. This requires prompt recognition of the primary source of haemorrhage. Massive transfusion protocols have been developed in recognition of the fact that shocked, severely injured polytrauma patients are known to arrive coagulopathic. They facilitate the early administration of both blood and blood products to resuscitate not only volaemic status, but also oxygen carrying capacity and haemostatic capacity. Military experience in recent conflicts has shown that early administration of FFP and platelets reduces the requirement for packed red cells in those patients requiring massive transfusion and the military have moved the administration of massive transfusion protocols forward to the pre-hospital phase.27Callcut RA Johannigman JA Kadon KS Hanseman DJ Robinson BR All massive transfusion criteria are not created equal: defining the predictive value of individual transfusion triggers to better determine who benefits from blood.J Trauma. 2011; 70: 794-801Crossref PubMed Scopus (55) Google Scholar 28Nunez TC Young PP Holcomb JB Cotton BA Creation, implementation, and maturation of a massive transfusion protocol for the exsanguinating trauma patient.J Trauma. 2010; 68: 1498-1505Crossref PubMed Scopus (104) Google Scholar Activation of a massive transfusion protocol should be based on predetermined criteria and require a single phone call to the blood bank technician. With excellent communication from pre-hospital medical teams, some MTCs are able to activate the protocol before the patient arrives. The exact composition of the sequential packs will be determined locally, and should be reviewed regularly in light of continual audit of patient outcome balanced against product utilization and wastage. Hypocalcaemia is a real risk with the use of massive transfusion protocols, therefore calcium levels should be checked by regular arterial blood gas sampling and corrected as necessary. Blood products should be warmed and given rapidly. The optimal patient management requires close communication and cooperation with the haematology service, and, if available, the rapidity of point of care testing facilitates a much more individualized treatment of patient coagulation status from the early stages of management. The use of this antifibrinolytic drug has demonstrated few adverse events and no increase in thromboembolic complications. The CRASH-2 study found early treatment with tranexamic acid, within 1 h from injury significantly reduced the risk of death from bleeding.29The CRASH-2 CollaboratorsEffects of tranexamic acid on death, vascular occlusive events, and blood transfusion in trauma patients with significant haemorrhage (CRASH-2): a randomised placebo controlled trial.Lancet. 2010; 376: 23-32Abstract Full Text Full Text PDF PubMed Scopus (2112) Google Scholar It is more effective in penetrating than blunt trauma but because it has a high therapeutic index, tranexamic acid should be administered early (within 3 h of injury) to all trauma victims with a systolic blood pressure 110, or both with evidence of haemorrhage.30The CRASH-2 CollaboratorsThe importance of early treatment with tranexamic acid in the bleeding trauma patients: an exploratory analysis of CRASH-2 randomised controlled trial.Lancet. 2011; 377: 1096-1101Abstract Full Text Full Text PDF PubMed Scopus (797) Google Scholar Tranexamic acid is now administered as part of pre-hospital care in many regions. The CRASH 2 study results are based on a dose of 1 g over 10 min with a further 1 g over 8 h. Pelvic fracture can result in catastrophic haemorrhage with associated occult coagulopathy. Early splinting of pelvic fractures reduces movement and protects clot formation. The use of pelvic binders is now routine in the pre-hospital setting, with correct placement at the level of the greater trochanters decreasing the pelvic volume in open book fractures (clas