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- Methods and materials
Objectives Following the results of the Confidential Enquiries into Maternal Deaths report, which claims two maternal deaths annually in the UK from postpartum haemorrhage, our aim was to assess the accuracy of ‘visual estimation of blood loss’ and produce suitable pictorial and written algorithms to aid in the recognition and management of massive obstetric haemorrhage.
Design Observational study to determine discrepancy between actual blood loss (ABL) and estimated blood loss (EBL).
Setting Teaching hospital.
Population Hundred and three obstetricians, anaesthetists, midwives, nurses and healthcare assistants.
Methods Clinical scenarios were reproduced in the form of 12 Objective Structured Clinical Examination (OSCE) style stations augmented with known volumes of whole blood. Individual staff estimated the blood loss visually and recorded their results. Digital photographs were used to produce a pictorial ‘algorithm’ suitable for use as a teaching tool in labour ward.
Main outcome measures Areas of greatest discrepancy between EBL and ABL.
Results Significant underestimation of the ABL occurred in 5 of the 12 OSCE stations: 500-ml (50-cm diameter) floor spill, 1000-ml (75-cm diameter) floor spill, 1500-ml (100-cm diameter) floor spill, 350-ml capacity of soaked 45- × 45-cm large swab and the 2-l vaginal postpartum haemorrhage on bed/floor.
Conclusions Accurate visual estimation of blood loss is known to facilitate timely resuscitation, minimising the risk of disseminated intravascular coagulation and reducing the severity of haemorrhagic shock. Participation in clinical reconstructions may encourage early diagnosis and prompt treatment of postpartum haemorrhage. Written and pictorial guidelines may help all staff working in labour wards.
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- Methods and materials
‘Why Mothers Die’ 2000–2002 revealed a striking increase in the number of maternal deaths resulting from postpartum haemorrhage (PPH), from one case in 1997–99 to ten cases in the latest triennium.1 Life-threatening obstetric haemorrhage occurs in approximately 1 per 1000 deliveries.2 The importance of accurate estimation of blood loss, prompt recognition and treatment of clotting disorders, early involvement of a consultant haematologist, involvement of a consultant anaesthetist in resuscitation, use of adequately sized intravenous cannulae and precise monitoring of central venous pressure have all been repeatedly advocated. Introduction of specialised obstetric anaesthetists, labour ward protocols, participation in regular ‘fire drills’ and improved obstetric training have gone part way to addressing these important issues; yet, visual estimation of blood loss at vaginal and abdominal delivery remains inaccurate.3
Physiological adaptation of the cardiovascular system in pregnancy results in a 48% increase in plasma volume from 2600 ml to 3850 ml, relatively exceeding that of the 17% increase in red cell mass from 1400 ml to 1640 ml.4 The protective haemodilution initiates a fall in haemoglobin, haematocrit and red cell count but maintains mean corpuscular volume and mean corpuscular haemoglobin concentration.5 Circulating blood volume rises by 37% from approximately 4000 ml to 5500 ml, providing not only adequate placental perfusion but also a compensatory reserve such that a healthy woman can usually tolerate acute losses at delivery of up to 1000 ml.
Shock is defined as a profound haemodynamic and metabolic disturbance characterised by failure to maintain tissue perfusion.4 Hypovolaemic shock in the nonpregnant individual presents with a deterioration in vital signs (tachycardia, hypotension and a falling urine output), but as a consequence of physiological adaptation, these vital signs become relatively insensitive during pregnancy. Tachycardia does not develop until blood loss exceeds 1000 ml6 and blood pressure is usually maintained in the normal range well beyond this level. The relative masking of signs during pregnancy hinders recognition of hypovolaemia and delays treatment, resulting in further blood loss and increased risk of haemorrhagic shock. Consequently, hypovolaemic women who begin to decompensate, as evidenced by hypotension, will deteriorate extremely rapidly.
Provided that intravascular volume remains adequate for perfusion, a haemoglobin concentration of 7 g/dl (equivalent to a haematocrit of 0.21) has been shown to provide sufficient oxygen carrying capacity to maintain cardiopulmonary function.7 Treatment of haemorrhagic shock requires initial restoration of intravascular volume and judicious transfusion of blood products. Concerns regarding infection, transfusion reactions and cost, however, have resulted in a recent fall in transfusion rates.8 Furthermore, recent governmental measures to minimise the risk of transmission of variant Creutzfeldt-Jakob Disease (vCJD) through blood transfusion has reduced the number of suitable blood donors and the Department of Health have therefore advocated a reduction in use of blood products.9
Accurate visual estimation of cumulative blood loss forewarns of impending haemorrhagic shock. Estimates of blood loss by paramedics10 and surgeons11 are inaccurate, and studies following vaginal12 and abdominal delivery13 show visual estimation to be of limited clinical use. Menstrual pictograms to facilitate the assessment of menorrhagia in the field of gynaecology14 have now been produced; however, little pictorial data yet exist to facilitate similar estimations of blood loss in obstetrics.
The aims of this study were to identify areas of greatest discrepancy between estimated blood loss (EBL) and actual blood loss (ABL) and thus identify those clinical scenarios where inaccurate estimation of blood loss is most likely to occur. From these observations, we planned to produce simple written and pictorial guidelines that would facilitate accurate visual estimation of blood loss at obstetric haemorrhage.
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- Methods and materials
Visual estimation of blood loss following both vaginal and abdominal delivery is notoriously inaccurate15 and has been shown to be of limited clinical use. The considerable range in EBL recorded by individuals within each professional group (Table 2) highlights the failings of untrained subjective assessment. Overestimates as well as underestimates can have significant clinical implications and both should be considered.
Significant underestimation in the volumes of large floor spillage, large surgical swab capacity and massive PPH was demonstrated by this study. Previous studies confirm that blood loss at vaginal delivery are underestimated by −35% (EBL = 260 ml versus ABL = 401 ml)3 and that mean ABL at a first caesarean section is in fact 1290 ± 240 ml,13 significantly more than the EBL recorded by most obstetricians. Losses in excess of 1500 ml predispose to increased risk of severe hypovolaemic shock. If prolonged by delayed or inadequate resuscitation, hypovolaemic shock will trigger disseminated intravascular coagulation and myocardial ischaemia.16 Consequently, accurate cumulative estimation of blood loss should constitute a vital element of postpartum care.
The maximum capacity of a saturated large 12 ply 45- × 45-cm surgical swab is 350 ml. All professional groups underestimated the capacity of a large swab, most noticeably the obstetricians who were the least accurate (median percentage error =−57%). As swab count is a universal method for estimating blood loss at caesarean section, accurate knowledge of swab capacities is essential. Capacities of various swab sizes are included for reference in Table 3.
Table 3. Guidelines for visual estimation of blood loss
|Small, 10- ×10-cm 32 ply swab (maximum saturated capacity)||60 ml|
|Medium, 30- × 30-cm 12 ply swab (maximum saturated capacity)||140 ml|
|Large, 45- × 45-cm 12 ply swab (maximum saturated capacity)||350 ml|
|1-kg soaked swabs||1000 ml|
|50-cm diameter floor spill||500 ml|
|75-cm diameter floor spill||1000 ml|
|100-cm diameter floor spill||1500 ml|
|Vaginal PPH limited to bed only||Unlikely to exceed 1000 ml|
|Vaginal PPH spilling over from bed to floor||Likely to exceed 1000 ml|
Percentage errors ranked by profession (Table 1, bottom row) substantiate the perception that, when specifically compared with other professional groups, such as orthopaedic surgeons,17 anaesthetists tend to overestimate blood volume (P= 0.0039). In this study, the anaesthetists were the most accurate estimators of blood loss, recording a median overestimate of just 4% and the smallest interquartile range. The EBL documented in surgical notes is often inconsistent with the clinical condition of the patient. The anaesthetic tendency to ‘overestimate’ blood volumes is almost certainly a compensatory response to surgical underestimation. Furthermore, planning of routine postoperative fluid management and fluid management of emergency resuscitations is often the responsibility of the anaesthetist and this may contribute to their ‘estimating’ skills.
Overestimation of blood volumes can also have significant implications. Unnecessary cross matching of blood wastes valuable time and resources. Blood is becoming an increasingly precious resource and over transfusion of patients, if marked, can result in morbidity as well as unnecessary exposure to the known risks of blood products.18
Participation in this simple study provided a valuable learning tool for a variety of healthcare professionals who routinely estimate peripartum blood loss. The equipment required to stage these scenarios was minimal and easily obtained in labour ward. The acquisition of blood products required the cooperation of our consultant haematologist and the local blood service centre based at Colindale. Regulations pertaining to the use of blood products may differ according to region, although replication of these scenarios as a teaching aid should not be problematic. The study took just a few hours to prepare and approximately 30 minutes for participants to complete the questionnaire, obtain appropriate feedback and review their own results. By virtue of the subject matter and realism/novelty of the scenarios, the experiment stimulated much interest among health professionals of all grades. Most claimed to have benefited from the experience and have welcomed a repeat of such an exercise.