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Template bleeding time for preoperative screening in patients having orthognathic surgery
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British Journal of Oral and Maxillofacial Surgery 46 (2008) 645–648
Template bleeding time for preoperative screening in patients having orthognathic surgery M. Modig ∗ , A. Ros´en, A. Heimdahl Department of Oral and Maxillofacial Surgery, Karolinska Institutet, Box 4064, SE-141 04 Huddinge, Sweden Accepted 31 March 2008 Available online 3 June 2008
Abstract Excessive blood loss is a serious but rare complication of orthognathic surgery. The aim of this study was to find out whether template bleeding time (TBT) could detect primary bleeding disorders in patients having orthognathic operations and how many false positive tests there were. We also examined the correlation between the perioperative bleeding rate and the result of preoperative TBT. Patients who had orthognathic operations at Karolinska University Hospital, Huddinge, from August 2001 to December 2006, were screened preoperatively by measuring TBT and the records of their operations were reviewed retrospectively. Prolonged TBT was recorded in 20 patients (13%), 19 female and 1 male (P = 0.02). After further examination, 10 of these patients were found to have a primary disorder of haemostasis. No detectable reason for the prolonged TBT could be found in the others. There was no significant difference in perioperative bleeding rate between patients with prolonged and normal TBT or between TBT and perioperative bleeding rate. In conclusion, the routine use of preoperative TBT for haemostatic screening in orthognathic surgery cannot be recommended because of the large number of false positive results. There was no significant correlation between prolonged TBT and bleeding during orthognathic surgery. © 2008 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved. Keywords: Orthognathic surgery; Haemorrhagic depressants; Template bleeding time; Bleeding rate; Blood loss
Introduction Orthognathic surgery is used to correct dentofacial abnormalities, and excessive blood loss is a serious but rare complication. Different preventive strategies such as preoperative screening for bleeding disorders, giving drugs during operation that improve blood clotting, and hypotensive anaesthetic techniques are generally used to minimise blood loss. Consequently, today, the need for blood transfusion is low.1,2 Blood loss during orthognathic surgery is reported to range between 0 and 4500 ml (mean 889 ml in bimaxillary surgery).3 Duke, and Ivy et al. have developed methods for estimating bleeding time,4,5 and modifications have been made to mea∗
Corresponding author. Tel.: +46858583950; fax: +4687743875. E-mail address: [email protected] (M. Modig).
sure template bleeding time (TBT), using a semiautomatic template device and later a disposable automatic device.6,7 TBT was originally used as a test for assessing functional platelet disorders, including von Willebrand disease (vWD), as it is consistently prolonged in patients with severe platelet diseases and serves as an indicator of prolonged primary haemostasis.8 However, the sensitivity of TBT is reduced in patients with mild bleeding disorders such as vWD-1 and platelet secretion defects. There are four clinical reasons to support the use of TBT: to screen patients before invasive procedures, to find out the cause of continuous bleeding, to explain previous episodes of bleeding, and to diagnose hereditary bleeding disorders.9 The routine use of TBT for the screening of surgical patients to assess the risk of perioperative and postoperative bleeding has been questioned by Lind because there are insufficient data for the calculation of the specificity, sensitivity, and pre-
0266-4356/$ – see front matter © 2008 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.bjoms.2008.03.017
646
M. Modig et al. / British Journal of Oral and Maxillofacial Surgery 46 (2008) 645–648
dictive value of TBT.9 The aim of this study was to find out whether TBT could detect primary bleeding disorders in orthognathic surgical patients and the number of false positive tests. We also examined the correlation between the perioperative bleeding rate and the result of preoperative TBT. To date, we know of no study that has been published on this topic in orthognathic surgery.
Statistics Differences between groups were assessed using the chisquare test. Probabilities of less than 0.05 were accepted as significant.
Results Patients and methods
Preoperative tests
Patients who had orthognathic operations at the Karolinska University Hospital, Huddinge, from August 2001 to December 2006, were screened preoperatively by TBT, and their records reviewed retrospectively.
Records of 166 consecutive orthognathic operations from August 2001 to December 2006 were evaluated, of which 15 were excluded because of incomplete data, such as lack of recorded volume of blood loss during operation, so a total of 151 consecutive operations were included in the study. Of the patients, 97 were female (14–62 years, mean 23.4) and 54 were male (15–40 years, mean 23.7). The TBT was done routinely 1–2 weeks preoperatively in all patients. Prolonged TBT was noted in 20 patients, 19 female, and 1 male (P = 0.02) (Table 1). After further examination, 10 of these patients were found to have a primary disorder of haemostasis, but no reasons for the prolonged TBT could be found in the rest. The TBT therefore gave an unacceptable number of false positives. During operation the mean blood loss was 266 ml (range 25–1560) and the mean operating time was 212 min (range 55–495). Mean bleeding rate was 1.25 ml/min.
Preoperative tests The patients were examined preoperatively by TBT. Before the test they were asked if they had taken any medication during the previous 7–10 days. An inflated cuff (pressure 40 mm Hg) was applied to the patient’s upper arm, and a 5 mm long, 1 mm deep, incision was made with a Surgicutt® or Surgicutt Junior® (International Technidyne Corporation, Edison, NJ, USA) on the inside of the underarm. The bleeding time was measured in seconds from the time at which the incision was made until the cessation of bleeding. The blood was regularly wiped away. A range of 120–540 s was considered normal for patients aged 15 years or over, and 80–540 s for patients less than 15 years old). Patients with prolonged TBT (>540 s) were referred for further investigation. Anaesthesia Preoperatively the patients were premedicated with paracetamol (Alvedon® 2 g) and morphine (Oxycontin® 7.5–10 mg). Anaesthesia was induced by remifentanil 0.8 g/kg, propofol 2 mg/kg, and rokuronbromide 0.6 mg/kg given intravenously, and was maintained by sevoflurane in oxygen/air and an intravenous infusion of remifentanil 0.05–0.4 g/kg. Local anaesthesia was given to all patients before (Xylocaine® adrenaline 10 mg/ml + 5 g/ml) and after (Marcain® adrenaline 2.5 mg/ml + 5 g/ml). The patient’s head was positioned above the heart during operation. Surgery Blood loss during operation was calculated by measuring suctioned blood after adjusting for the volume of saline used for irrigation and from compresses. The mean bleeding rate (ml/min) was then calculated. Before or during operation, or both, some patients were given tranexamic acid (Cyklokapron® ) 100 mg/ml or desmopressin (Octostim® ) 15 g/ml, or both, to reduce bleeding based on the surgeon’s clinical judgement. No drains were used.
Clinical observations Of the patients with a prolonged TBT, 12 had had haemorrhagic depressants given preoperatively because of prolonged TBT and subsequent investigations. Of the 131 patients with normal TBT, 23 were given haemorrhagic depressants during operation for intraoperative bleeding, based on the clinical judgement of the surgeon. There was no significant difference between the perioperative bleeding rate in patients with prolonged and normal TBT. Neither was there a significant relation between TBT and the perioperative bleeding rate (Fig. 1). Bleeding rate did not differ between men and women. None of the patients required a blood transfusion and none of the patients had
Table 1 Result of preoperative screening of bleeding in 151 consecutive orthognathic operations Sex
Total
Template Bleeding time Normal
Female Male Total
Impaired
97 (64) 54 (36)
78 (52) 53 (35)
19 (13)* 1*
151 (100)
131 (87)
20 (13)
Data are number (%) of patients. ∗ P = 0.02.
M. Modig et al. / British Journal of Oral and Maxillofacial Surgery 46 (2008) 645–648
647
Fig. 1. Preoperative template bleeding time in relation to perioperative bleeding ml/min.
excessive postoperative bleeding. There were no other appreciable complications such as haematomas.
Discussion TBT was used as a screening method to detect impaired primary haemostasis. Of 151 patients, 20 had prolonged TBT and after further examination 10 had impaired function. No other patients had impaired haemostasis. In our study, 19/20 of the positive TBT that showed an abnormality were obtained in women. Bain and Forster found that the TBT was significantly longer in women than men (p < .001), because of a difference in blood vessels or supporting tissue.10 Gudmundsdottir et al. reported longer TBT in girls than boys, possibly because of increased skin fragility, as the platelet function analyser-100 closure time (PFA-100 CTs) was identical in both sexes.11 As this was a retrospective study, the girls’ individual menstrual cycles were not recorded. According to Harker and Slichter, the reproducibility of the TBT is low because of differences in the size and depth of puncture, skin temperature, and vascularity.12 The skin TBT does not necessarily correlate with bleeding in other anatomical sites.9 In patients with vWD, the TBT performs poorly, both diagnostically and prognostically. It is not a sensitive test for vWD, and may vary in the same patient over time.13,14 It may even be within normal limits in patients with type I vWD, and in patients with a history of bleeding problems.15 It alone is not diagnostic of primary bleeding disorders, and a positive TBT requires additional investigation. Consequently, it is in many ways an imperfect screening method, which we also found in the present study in orthognathic patients. Subsequently, most patients with a prolonged TBT were submitted to further examination, not just retested with TBT.
Most of the orthognathic operations were done as planned, and haemorrhagic depressants (tranexamic acid and desmopressin) were used occasionally. The decision to use them was taken in advance in patients with impaired haemostasis. Zellin et al. showed that blood loss during orthognathic procedures under hypotensive anaesthesia can be reduced significantly by the addition of a combination of tranexamic acid and desmopressin.16 We know of no scientific evidence about the exact use of desmopressin in orthognathic surgery. In the group of patients with impaired haemostasis for which the reason could not be detected, the decision to use haemorrhagic depressants was therefore based on clinical judgement during operation. There was no significant difference in bleeding rate during operation between the group with prolonged TBT who were given haemorrhagic drugs and those with prolonged TBT who were not. We were also unable to find any correlation between TBT and bleeding rate during operation. None of the patients required blood transfusion, and none of the patients bled postoperatively enough to require treatment. Koscielny et al. concluded that screening with a standard questionnaire, combined with additional specific tests when necessary, ensured the detection of impaired haemostasis in almost every case.17 Burns and Lawrence recommended that preoperative haemostatic screening should start with a history directed toward the uncovering of mild congenital bleeding disorders supplemented by prothrombin time and activated partial thromboplastin time.8 We know of no previous study that has been published about the correlation between TBT and blood loss during orthognathic surgery. The present results are based on retrospective data, so a prospective study of TBT and a standard questionnaire supplemented by prothrombin time and activated partial thromboplastin time for screening, would be of interest to find a good clinical screening method for the detection of patients at risk of bleeding.
648
M. Modig et al. / British Journal of Oral and Maxillofacial Surgery 46 (2008) 645–648
In conclusion, the routine use of preoperative TBT for haemostatic screening in orthognathic surgery cannot be recommended because of the large number of false positive results. There was no significant correlation between prolonged TBT and bleeding during orthognathic surgery.
Acknowledgements We thank Ms Ene Leipalu, Mrs Maria Lundgren, Mrs Anna Januszkiewicz, and Mr Peter Svensson for their help.
References 1. Ueki K, Marukawa K, Shimada M, Nakagawa K, Yamamoto E. The assessment of blood loss in orthognathic surgery for prognathia. J Oral Maxillofac Surg 2005;63:350–4. 2. Moenning JE, Bussard DA, Lapp TH, Garrison BT. Average blood loss and the risk of requiring perioperative blood transfusion in 506 orthognathic surgical procedures. J Oral Maxillofac Surg 1995;53:880–3. 3. Panula K, Finne K, Oikarinen K. Incidence of complications and problems related to orthognathic surgery, a review of 655 patients. J Oral Maxillofac Surg 2001;59:1128–37. 4. Duke WW. The relation of blood platelets to hemorrhagic disease. JAMA 1910;60:1185–92. 5. Ivy AC, Nelson D, Buchet G. The standardization of certain factors in the cutaneous venostasis bleeding time technique. J Lab Clin Med 1941;26:1812–22.
6. Mielke Jr CH, Kaneshiro MM, Maher IA, Weiner JM, Rapaport SI. The standardized normal Ivy bleeding time and its prolongation by aspirin. Blood 1969;34:204–15. 7. Smith C. Surgicutt: a device for modified template bleeding times. J Med Technol 1986;3:29–31. 8. Burns ER, Lawrence C. Bleeding time. A guide to its diagnostic and clinical utility. Arch Pathol Lab Med 1989;113:1219–24. 9. Lind SE. The bleeding time does not predict surgical bleeding. Blood 1991;77:2547–52. 10. Bain B, Forster T. A sex difference in bleeding time. Thromb Haemost 1980;43:131–2. 11. Gudmundsdottir BR, Marder VJ, Onundarson PT. Risk of excessive bleeding associated with marginally low von Willebrand factor and mild platelet dysfunction. J Thromb Haemost 2007;5:274–81. 12. Harker LA, Slichter SJ. The bleeding time as a screening test for evalutation of platelet function. N Engl J Med 1972;287:155–9. 13. Coller BS. von Willebrand disease. In: Coleman RW, Hirsh J, Marder VJ, Salman EW, editors. Hemostasis and thrombosis. Basic principles and clinical practice. 2nd ed. Philadelphia: Lippincott; 1987. p. 72. 14. Abildgaard CF, Suzuki Z, Harrison J, Jefcoat K, Zimmerman TS. Serial studies in von Willebrand’s disease: variability versus “variants”. Blood 1980;56:712–6. 15. Gralnick HR, Rick ME, McKeown LP, et al. Platelet von Willebrand factor: an important determinant of the bleeding time in type I von Willebrand’s disease. Blood 1986;68:58–61. 16. Zellin G, Rasmussen L, P˚alsson J, Kahnberg KE. Evaluation of hemorrhage depressors on blood loss during orthognathic surgery: a retrospective study. J Oral Maxillofac Surg 2004;62:662–6. 17. Koscielny J, Ziemer S, Radtke H, et al. A practical concept for preoperative identification of patients with impaired primary hemostasis. Clin Appl Thromb Hemost 2004;10:195–204.
British Journal of Oral and Maxillofacial Surgery 46 (2008) 645–648
Template bleeding time for preoperative screening in patients having orthognathic surgery M. Modig ∗ , A. Ros´en, A. Heimdahl Department of Oral and Maxillofacial Surgery, Karolinska Institutet, Box 4064, SE-141 04 Huddinge, Sweden Accepted 31 March 2008 Available online 3 June 2008
Abstract Excessive blood loss is a serious but rare complication of orthognathic surgery. The aim of this study was to find out whether template bleeding time (TBT) could detect primary bleeding disorders in patients having orthognathic operations and how many false positive tests there were. We also examined the correlation between the perioperative bleeding rate and the result of preoperative TBT. Patients who had orthognathic operations at Karolinska University Hospital, Huddinge, from August 2001 to December 2006, were screened preoperatively by measuring TBT and the records of their operations were reviewed retrospectively. Prolonged TBT was recorded in 20 patients (13%), 19 female and 1 male (P = 0.02). After further examination, 10 of these patients were found to have a primary disorder of haemostasis. No detectable reason for the prolonged TBT could be found in the others. There was no significant difference in perioperative bleeding rate between patients with prolonged and normal TBT or between TBT and perioperative bleeding rate. In conclusion, the routine use of preoperative TBT for haemostatic screening in orthognathic surgery cannot be recommended because of the large number of false positive results. There was no significant correlation between prolonged TBT and bleeding during orthognathic surgery. © 2008 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved. Keywords: Orthognathic surgery; Haemorrhagic depressants; Template bleeding time; Bleeding rate; Blood loss
Introduction Orthognathic surgery is used to correct dentofacial abnormalities, and excessive blood loss is a serious but rare complication. Different preventive strategies such as preoperative screening for bleeding disorders, giving drugs during operation that improve blood clotting, and hypotensive anaesthetic techniques are generally used to minimise blood loss. Consequently, today, the need for blood transfusion is low.1,2 Blood loss during orthognathic surgery is reported to range between 0 and 4500 ml (mean 889 ml in bimaxillary surgery).3 Duke, and Ivy et al. have developed methods for estimating bleeding time,4,5 and modifications have been made to mea∗
Corresponding author. Tel.: +46858583950; fax: +4687743875. E-mail address: [email protected] (M. Modig).
sure template bleeding time (TBT), using a semiautomatic template device and later a disposable automatic device.6,7 TBT was originally used as a test for assessing functional platelet disorders, including von Willebrand disease (vWD), as it is consistently prolonged in patients with severe platelet diseases and serves as an indicator of prolonged primary haemostasis.8 However, the sensitivity of TBT is reduced in patients with mild bleeding disorders such as vWD-1 and platelet secretion defects. There are four clinical reasons to support the use of TBT: to screen patients before invasive procedures, to find out the cause of continuous bleeding, to explain previous episodes of bleeding, and to diagnose hereditary bleeding disorders.9 The routine use of TBT for the screening of surgical patients to assess the risk of perioperative and postoperative bleeding has been questioned by Lind because there are insufficient data for the calculation of the specificity, sensitivity, and pre-
0266-4356/$ – see front matter © 2008 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.bjoms.2008.03.017
646
M. Modig et al. / British Journal of Oral and Maxillofacial Surgery 46 (2008) 645–648
dictive value of TBT.9 The aim of this study was to find out whether TBT could detect primary bleeding disorders in orthognathic surgical patients and the number of false positive tests. We also examined the correlation between the perioperative bleeding rate and the result of preoperative TBT. To date, we know of no study that has been published on this topic in orthognathic surgery.
Statistics Differences between groups were assessed using the chisquare test. Probabilities of less than 0.05 were accepted as significant.
Results Patients and methods
Preoperative tests
Patients who had orthognathic operations at the Karolinska University Hospital, Huddinge, from August 2001 to December 2006, were screened preoperatively by TBT, and their records reviewed retrospectively.
Records of 166 consecutive orthognathic operations from August 2001 to December 2006 were evaluated, of which 15 were excluded because of incomplete data, such as lack of recorded volume of blood loss during operation, so a total of 151 consecutive operations were included in the study. Of the patients, 97 were female (14–62 years, mean 23.4) and 54 were male (15–40 years, mean 23.7). The TBT was done routinely 1–2 weeks preoperatively in all patients. Prolonged TBT was noted in 20 patients, 19 female, and 1 male (P = 0.02) (Table 1). After further examination, 10 of these patients were found to have a primary disorder of haemostasis, but no reasons for the prolonged TBT could be found in the rest. The TBT therefore gave an unacceptable number of false positives. During operation the mean blood loss was 266 ml (range 25–1560) and the mean operating time was 212 min (range 55–495). Mean bleeding rate was 1.25 ml/min.
Preoperative tests The patients were examined preoperatively by TBT. Before the test they were asked if they had taken any medication during the previous 7–10 days. An inflated cuff (pressure 40 mm Hg) was applied to the patient’s upper arm, and a 5 mm long, 1 mm deep, incision was made with a Surgicutt® or Surgicutt Junior® (International Technidyne Corporation, Edison, NJ, USA) on the inside of the underarm. The bleeding time was measured in seconds from the time at which the incision was made until the cessation of bleeding. The blood was regularly wiped away. A range of 120–540 s was considered normal for patients aged 15 years or over, and 80–540 s for patients less than 15 years old). Patients with prolonged TBT (>540 s) were referred for further investigation. Anaesthesia Preoperatively the patients were premedicated with paracetamol (Alvedon® 2 g) and morphine (Oxycontin® 7.5–10 mg). Anaesthesia was induced by remifentanil 0.8 g/kg, propofol 2 mg/kg, and rokuronbromide 0.6 mg/kg given intravenously, and was maintained by sevoflurane in oxygen/air and an intravenous infusion of remifentanil 0.05–0.4 g/kg. Local anaesthesia was given to all patients before (Xylocaine® adrenaline 10 mg/ml + 5 g/ml) and after (Marcain® adrenaline 2.5 mg/ml + 5 g/ml). The patient’s head was positioned above the heart during operation. Surgery Blood loss during operation was calculated by measuring suctioned blood after adjusting for the volume of saline used for irrigation and from compresses. The mean bleeding rate (ml/min) was then calculated. Before or during operation, or both, some patients were given tranexamic acid (Cyklokapron® ) 100 mg/ml or desmopressin (Octostim® ) 15 g/ml, or both, to reduce bleeding based on the surgeon’s clinical judgement. No drains were used.
Clinical observations Of the patients with a prolonged TBT, 12 had had haemorrhagic depressants given preoperatively because of prolonged TBT and subsequent investigations. Of the 131 patients with normal TBT, 23 were given haemorrhagic depressants during operation for intraoperative bleeding, based on the clinical judgement of the surgeon. There was no significant difference between the perioperative bleeding rate in patients with prolonged and normal TBT. Neither was there a significant relation between TBT and the perioperative bleeding rate (Fig. 1). Bleeding rate did not differ between men and women. None of the patients required a blood transfusion and none of the patients had
Table 1 Result of preoperative screening of bleeding in 151 consecutive orthognathic operations Sex
Total
Template Bleeding time Normal
Female Male Total
Impaired
97 (64) 54 (36)
78 (52) 53 (35)
19 (13)* 1*
151 (100)
131 (87)
20 (13)
Data are number (%) of patients. ∗ P = 0.02.
M. Modig et al. / British Journal of Oral and Maxillofacial Surgery 46 (2008) 645–648
647
Fig. 1. Preoperative template bleeding time in relation to perioperative bleeding ml/min.
excessive postoperative bleeding. There were no other appreciable complications such as haematomas.
Discussion TBT was used as a screening method to detect impaired primary haemostasis. Of 151 patients, 20 had prolonged TBT and after further examination 10 had impaired function. No other patients had impaired haemostasis. In our study, 19/20 of the positive TBT that showed an abnormality were obtained in women. Bain and Forster found that the TBT was significantly longer in women than men (p < .001), because of a difference in blood vessels or supporting tissue.10 Gudmundsdottir et al. reported longer TBT in girls than boys, possibly because of increased skin fragility, as the platelet function analyser-100 closure time (PFA-100 CTs) was identical in both sexes.11 As this was a retrospective study, the girls’ individual menstrual cycles were not recorded. According to Harker and Slichter, the reproducibility of the TBT is low because of differences in the size and depth of puncture, skin temperature, and vascularity.12 The skin TBT does not necessarily correlate with bleeding in other anatomical sites.9 In patients with vWD, the TBT performs poorly, both diagnostically and prognostically. It is not a sensitive test for vWD, and may vary in the same patient over time.13,14 It may even be within normal limits in patients with type I vWD, and in patients with a history of bleeding problems.15 It alone is not diagnostic of primary bleeding disorders, and a positive TBT requires additional investigation. Consequently, it is in many ways an imperfect screening method, which we also found in the present study in orthognathic patients. Subsequently, most patients with a prolonged TBT were submitted to further examination, not just retested with TBT.
Most of the orthognathic operations were done as planned, and haemorrhagic depressants (tranexamic acid and desmopressin) were used occasionally. The decision to use them was taken in advance in patients with impaired haemostasis. Zellin et al. showed that blood loss during orthognathic procedures under hypotensive anaesthesia can be reduced significantly by the addition of a combination of tranexamic acid and desmopressin.16 We know of no scientific evidence about the exact use of desmopressin in orthognathic surgery. In the group of patients with impaired haemostasis for which the reason could not be detected, the decision to use haemorrhagic depressants was therefore based on clinical judgement during operation. There was no significant difference in bleeding rate during operation between the group with prolonged TBT who were given haemorrhagic drugs and those with prolonged TBT who were not. We were also unable to find any correlation between TBT and bleeding rate during operation. None of the patients required blood transfusion, and none of the patients bled postoperatively enough to require treatment. Koscielny et al. concluded that screening with a standard questionnaire, combined with additional specific tests when necessary, ensured the detection of impaired haemostasis in almost every case.17 Burns and Lawrence recommended that preoperative haemostatic screening should start with a history directed toward the uncovering of mild congenital bleeding disorders supplemented by prothrombin time and activated partial thromboplastin time.8 We know of no previous study that has been published about the correlation between TBT and blood loss during orthognathic surgery. The present results are based on retrospective data, so a prospective study of TBT and a standard questionnaire supplemented by prothrombin time and activated partial thromboplastin time for screening, would be of interest to find a good clinical screening method for the detection of patients at risk of bleeding.
648
M. Modig et al. / British Journal of Oral and Maxillofacial Surgery 46 (2008) 645–648
In conclusion, the routine use of preoperative TBT for haemostatic screening in orthognathic surgery cannot be recommended because of the large number of false positive results. There was no significant correlation between prolonged TBT and bleeding during orthognathic surgery.
Acknowledgements We thank Ms Ene Leipalu, Mrs Maria Lundgren, Mrs Anna Januszkiewicz, and Mr Peter Svensson for their help.
References 1. Ueki K, Marukawa K, Shimada M, Nakagawa K, Yamamoto E. The assessment of blood loss in orthognathic surgery for prognathia. J Oral Maxillofac Surg 2005;63:350–4. 2. Moenning JE, Bussard DA, Lapp TH, Garrison BT. Average blood loss and the risk of requiring perioperative blood transfusion in 506 orthognathic surgical procedures. J Oral Maxillofac Surg 1995;53:880–3. 3. Panula K, Finne K, Oikarinen K. Incidence of complications and problems related to orthognathic surgery, a review of 655 patients. J Oral Maxillofac Surg 2001;59:1128–37. 4. Duke WW. The relation of blood platelets to hemorrhagic disease. JAMA 1910;60:1185–92. 5. Ivy AC, Nelson D, Buchet G. The standardization of certain factors in the cutaneous venostasis bleeding time technique. J Lab Clin Med 1941;26:1812–22.
6. Mielke Jr CH, Kaneshiro MM, Maher IA, Weiner JM, Rapaport SI. The standardized normal Ivy bleeding time and its prolongation by aspirin. Blood 1969;34:204–15. 7. Smith C. Surgicutt: a device for modified template bleeding times. J Med Technol 1986;3:29–31. 8. Burns ER, Lawrence C. Bleeding time. A guide to its diagnostic and clinical utility. Arch Pathol Lab Med 1989;113:1219–24. 9. Lind SE. The bleeding time does not predict surgical bleeding. Blood 1991;77:2547–52. 10. Bain B, Forster T. A sex difference in bleeding time. Thromb Haemost 1980;43:131–2. 11. Gudmundsdottir BR, Marder VJ, Onundarson PT. Risk of excessive bleeding associated with marginally low von Willebrand factor and mild platelet dysfunction. J Thromb Haemost 2007;5:274–81. 12. Harker LA, Slichter SJ. The bleeding time as a screening test for evalutation of platelet function. N Engl J Med 1972;287:155–9. 13. Coller BS. von Willebrand disease. In: Coleman RW, Hirsh J, Marder VJ, Salman EW, editors. Hemostasis and thrombosis. Basic principles and clinical practice. 2nd ed. Philadelphia: Lippincott; 1987. p. 72. 14. Abildgaard CF, Suzuki Z, Harrison J, Jefcoat K, Zimmerman TS. Serial studies in von Willebrand’s disease: variability versus “variants”. Blood 1980;56:712–6. 15. Gralnick HR, Rick ME, McKeown LP, et al. Platelet von Willebrand factor: an important determinant of the bleeding time in type I von Willebrand’s disease. Blood 1986;68:58–61. 16. Zellin G, Rasmussen L, P˚alsson J, Kahnberg KE. Evaluation of hemorrhage depressors on blood loss during orthognathic surgery: a retrospective study. J Oral Maxillofac Surg 2004;62:662–6. 17. Koscielny J, Ziemer S, Radtke H, et al. A practical concept for preoperative identification of patients with impaired primary hemostasis. Clin Appl Thromb Hemost 2004;10:195–204.