METHODS OF ASSESSMENT OF BLOOD LOSS IN THE SHOCKED AND INJURED PATIENT

Transcription

1 Brit. J. Anaesth. (1966), 38, 250 METHODS OF ASSESSMENT OF BLOOD LOSS IN THE SHOCKED AND INJURED PATIENT BY J. W. L. DAVIES MJ?.C. Industrial Injuries and Bums Research Unit, Accident Hospital, Birmingham 15, England The volume of blood lost by injured patients has been the subject of many studies since the direct measurements of plasma volume in battle casualties by Keith (1919). Less precise indices of blood loss have been described in terms of the amount of tissue damage (Grant and Reeve, 1951) and the degree of swelling of closed injuries of the extremities (Clarke, Topley and Flear, 1955). The standard methods of measuring blood volume depend on estimating the dilution of carefully measured amounts of either dyes or radioactive labels. These methods are much more accurate than those described by Grant and Reeve, but are also more laborious. The recently introduced semi-automatic instruments for measuring blood volume using radioactive methods (Williams and Fine, 1961; Hobbs, 1965) now give rapid estimations which are reliable and probably as accurate as careful estimations by the earlier radioactive methods. The advantages and disadvantages of these methods of assessing blood loss are summarized in table I. ASSESSMENT FROM THE AMOUNT OF TISSUE DAMAGE Grant and Reeve (1951) devised this method during their study of battle casualties in the War. The unit of volume is taken as the patient's hand the closed fist for deep wounds and the open hand for surface wounds. The following four categories of severity help the initial assessment of blood lost. (1) Small wounds (less than 1 hand of tissue damage) show a blood loss of rarely more than 20 per cent of blood volume. (2) Moderate wounds (between 1 and 3 hands of tissue damage), a blood loss of between 20 and 40 per cent of blood volume. (3) Large wounds (between 3 and 5 hands of tissue damage), a blood loss of about 40 per cent of blood volume. (4) Very large wounds (more than 5 hands of ( tissue damage), a blood loss of 50 per cent or more of blood volume. Although this assessment can be made with speed and ease its usefulness is limited in injuries such as closed fractures and stab wounds. The open hand also aids the assessment of the extent of tissue damage due to burning, since the area it covers is about 1 per cent of the body surface. MEASUREMENT OF LIMB VOLUME (a) Comparison of normal and injured limbs by fluid displacement. In normal individuals the volume of one limb does not usually differ in volume by more than about 5 per cent from that of its fellow, and below knee volumes do not differ by more than 50 to 75 ml. In closed fractures of the lower limb, therefore, volume differences of more than 100 ml are probably due to swelling (Clarke, Topley and Flear, 1955). (b) Comparison of circumferential measurements of normal and injured limbs (CotterilL 1951). The circumferential measurements are made with a tape measure at 2 cm intervals and the sum of the volume of the 2 cm high cylinders calculated. A per cent error is introduced by assuming that limbs have a circular cross-section. In practice increased limb volume due to swelling may be measured to within ±250 ml for a swollen thigh or ± 150 ml for the lower part of the leg (Clarke, Topley and Flear, 1955). Within 12 hours of acute injury the volume of blood contained in the tissues around a closed fracture agrees well with the measured decrease in blood volume (Clarke, Topley and Flear, 1955).

2 TABLE I The advantages and disadvantages of various methods of measuring blood loss. Method Disadvantages Advantages Estimate of volume of tissue damage. Relatively inaccurate, particularly in arterial injuries. A rapid and simple estimate suitable for massive soft tissue injuries. Measurement of limb volume. (a) Fluid displacement. (b) Circumferential measurement. Measurement of plasma volume. (1) T (2) Protein labelled with radioactive iodine ( 125 I or 13I I). Measurement of red cell volume. (1) Using "P. (2) Using <"Cr. Simultaneous estimates of red cell and plasma volume. Semi-automatic instruments. (a) Volemetron. (b) Hemolitrc. (c) Blood Volume Computer. Confined to closed injuries. Inaccurate when injuries cause shortening. Only used if single limb injured since uninjured limb acts as control. f Error of method = per cent. Assumption made that all of swelling consists of blood. Error of method often more than 10 per cent mainly due to presence of lipaemia or free haemoglobin. Multiple blood samples required. Estimation time = 1^-2 hours. Repeated estimations inconvenient. Estimations inaccurate in patients with burns. Radioactive materials. Multiple blood samples required. Estimation time=l hour. Calculation of RBCV from BV or PV is dependent on haematocrit. Radioactive counting equipment expensive. Estimations inaccurate in patients with burns. Estimation time=2i 3 hours. Label impermanent. Multiple blood samples required. Estimation time 1-li hours. Label almost permanent. Multiple blood samples required only from severely injured patients. Radioactive materials. Estimation time c. 2 hours. Radioactive materials. Calculation of BV from RBCV is dependent on haematocrit. Radioactive counting equipment expensive. Radioactive materials. Estimate of RBCV is dependent on haematocrit and equipment very expensive. Doses of radioactivity for instruments (a) and (b) fairly expensive and of short shelf life (3 weeks). Rapid measurement of the size of swelling and its rate of increase. No venepunctures or injection of radioactive materials. Freedom from hazards of radioactivity. Measuring equipment relatively cheap and found in most hospitals. No errors due to lipaemia or free haemoglobin. Either BV or PV measured. Error less than 10 per cent. Repeat estimations easy. Red cell volume measured with an error of less than 5 per cent in patients with burns and other injuries. No extra blood samples required. Estimate not dependent on haematocrit. Most accurate estimation of blood volume. Blood volume estimate within 20 min, using a 15-minute mixing time. RBCV and PV obtained 10 min later. Repeat estimations easy. Long shelf life (6 months) of 13S I albumin for instrument (c).

3 252 BRITISH JOURNAL OF ANAESTHESIA MEASUREMENT OF PLASMA VOLUME (a) Dye method. For a plasma volume estimation an accurately known volume (or weight) of a saline solution of T-1824 (c. 10 mg dye) is injected intravenously. Blood samples are taken from a remote vein 10, 20 and 30 minutes after the injection, the plasma separated and the concentration of dye in the plasma compared in a spectrophotometer with plasma standards containing known amounts of dye. In this measurement of plasma dye concentration a substantial error may arise from the presence of either free haemoglobin or lipaemia. Careful handling of blood samples can reduce haemolysis to neglible proportions and lipaemia is slight in persons who have been starved for about 12 hours. However, in emergency work blood samples taken soon after injury are often lipaemic, and this makes measurements of dye concentration inaccurate. The dye extraction processes remove lipaemia but are laborious and unsuitable for emergency work. Full details of the T-1824 plasma volume method have been described by Gregersen (1944). (b) Radioactive methods. Plasma volume estimations made with radioactively-labelled proteins do not suffer from these disadvantages, but the administration of radioactivity may sometimes be undesirable (e.g. in pregnancy). The technique of making a plasma volume estimation with either 115 I or 131 I labelled human albumin is essentially similar to that using T Since, however, plasma or whole blood may be assayed for radioactivity either the plasma or the blood volume respectively is determined. The red cell volume can be calculated from the plasma or blood volume using the venous haematocrit corrected for trapped plasma (Chaplin and Mollison, 1952) and the average body/venous haematocrit ratio (see below). Neither T-1824 nor radioactive iodine labelled albumin gives accurate plasma volume estimations in patients with burns (Davies, 1960). MEASUREMENT OF RED CELL VOLUME Prior to 1950 radioactive phosphorus ("P) was the label of choice for a red cell volume estimation. Although an estimation took approximately 3 hours mainly because of the time required to prepare the labelled red cells the result of a careful estimation had an error of less than ±5 per cent (Reeve and Veall, 1949). The modification introduced by Mollison et al. (1958), resulting in a more rapid and efficient labelling of red cells, reduced the time required for an estimation of equal accuracy to about 2 hours. The introduction of radioactive chromium ( 51 Cr) by Sterling and Gray (1950) further reduced the time required for an estimation to less than 2 hours. It simplified the process of preparing the labelled red cells and also made possible the study of red cell survival since the 51 Cr label within the red cell is relatively permanent (Mollison and Veall, 1955). Red cells are labelled with "Cr by incubation with radioactive sodium chromate solution at room temperature. The labelled cells are washed twice with isotonic saline before intravenous injection of an accurately known volume (or weight) of the cell suspension. A blood sample is taken after a mixing time of 15 minutes unless disturbances of the circulatory system suggest an abnormal mixing time, when three or more blood samples should be taken at 10-minute intervals. The red cell volume is calculated from the observed dilution of radioactivity using the venous haematocrit corrected for trapped plasma. The whole blood volume is calculated from the red cell volume and the body haematocrit (i.e. venous haematocrit X 0.90). The use of the haematocrit in the calculation of blood volume from plasma or red cell volume may introduce an error due to the difference between the venous (or arterial) haematocrit and the body haematocrit. Because the haematocrit of blood in very small capillaries is much lower than that in large vessels, the body haematocrit is only about 90 per cent of the venous haematocrit. Whilst the body/venous haematocrit ratio averages 0.90, its range in a variety of clinical conditions lies between 0.70 and 1.00 Because of this possible variation the most accurate estimate of blood volume is the sum of the red cell and plasma volume separately and simultaneously measured. Immediately sequential estimations of red cell and plasma volume can be used, but the known and sometimes rapid fluctuations in plasma volume make this method potentially less accurate than simultaneous estimations.

4 BLOOD LOSS IN THE SHOCKED AND INJURED PATIENT 253 SIMULTANEOUS MEASUREMENTS OF RED CELL AND PLASMA VOLUME Most simultaneous estimations have so far been made with T-1824 and «P or 51 Cr labelled red cells. The accuracy is, however, limited by that of the plasma volume estimate. Recently more accurate and reliable estimates of blood volume have been obtained using lis l labelled albumin and 51 Cr labelled red cells. Although these two isotopes are injected simultaneously, their radiation characteristics are sufficiently different that 51 Cr may be accurately assayed in the mixture. Separation of plasma from whole blood allows assay of the 135 I alone. For further details of these red cell and plasma volume methods using radioactive labels, see Davies and Topley (1959), Davies (1960, 1966). SEMI-AUTOMATIC INSTRUMENTS FOR MEASURING BLOOD VOLUME The recently developed semi-automatic instruments for blood volume measurement (e.g., Volemetron, Hemolitre and Blood Volume Computer) have simplified these estimations by eliminating most of the manipulations required in the standard methods. The net amount of radioactivity (usually 13l I labelled albumin) injected into the patient is determined by assay of the contents of a disposable plastic syringe before and after intravenous injection. The dilution of the injected radioactivity is measured after a 15-minute mixing time by assay of a blood sample taken from a vein remote from that into which the radioactivity was injected. The dilution volume is calculated by the instrument and presented on a dial or register directly reading in litres of blood volume. A blood volume estimate is available about 5 minutes after taking the 15-minute blood sample and a red cell volume estimate 10 minutes later using the haematocrit measured in a high-speed centrifuge. Red cells labelled with 51 Cr may also be used to measure blood volume in some of these instruments. The advantages of a rapid estimation are, however, lost when the labelled red cells are prepared by the standard method. Substitution of l "I labelled albumin for 1S1 I labelled albumin as the injected dose of radioactivity has further improved the convenience of blood volume estimations. The long radioactive half-life of 125 Iodine (58 days) ensures a shelf life of about six months for doses of 1IS I labelled albumin (cf. three weeks for 131 I labelled albumin). The instrument specifically designed to use 115 I (the Blood Volume Computer) costs about half that of other iastruments and has only one-tenth of the weight (Hobbs, 1965). Whilst these instruments have improved the convenience and rapidity with which a blood volume estimation can be made, the calculated red cell or plasma volume is less accurate because of use of the haematocrit. Until a semi-automatic instrument becomes available which will separately assay a mixture of isotopes and thus give estimates of both red cell and plasma volume, standard methods must be used if the most accurate estimation of blood volume is required. DISCUSSION In the shocked and injured patient disturbances of the circulation may cause a prolonged mining time. In these circumstances serial blood samples should be taken at intervals of about 10 minutes until mixing appears complete. Blood samples taken immediately after complete mixing will give the most accurate estimations of red cell or plasma volume. In seriously injured patients with oligaemia, vasoconstriction may, however, make venous sampling difficult at a time when multiple blood samples are desirable. Although a carefully performed red cell or plasma volume estimation may have an error of not more than 5 per cent, a considerably greater error may be introduced when the result is compared with the patient's expected normal red cell or plasma volume to give an estimate of blood loss. Whilst the most accurate estimate of these normal values is derived from lean body mass (Muldowney, 1957) its estimation from total body water is time-consuming and unlikely to be reliable after serious injury. In emergency work only height and weight can usually be measured. From these two measurements the most accurate prediction of normal values is given by the following regression equations (Nadler et al., 1962): blood volume (adult males) =0.3669H R ; blood volume (adult females) =0.3561H VF ; where H=height kilograms. in metres and W=weight in

5 254 BRITISH JOURNAL OF ANAESTHESIA The normal male red cell volume is 44 per cent of the male blood volume and the normal female red cell volume 40 per cent of the female blood volume. If the nature of the injury prevents accurate measurement of weight the normal values may be predicted from height alone with an error of up to 15 per cent. This error is reduced to about 5 per cent when the patient's weight is near the ideal for height. The amount and timing of blood loss in both Service and civilian injuries (Prentice et al., 1954; Clarke et al., 1961) has been calculated from serial blood volume estimations usually made soon after injury, before and after reparative surgery and during the ensuing weeks. Similar studies have been made in patients with burns (Topley and Jackson, 1957; Davies, 1964). Although the estimations made soon after injury may be less accurate than those made postoperatively when the circulation is more stable, the trend of the results suggests that the initial estimation usefully indicates the amount of early blood loss. Blood lost during surgical procedures may also be directly measured by weighing soaked swabs, etc., and aspirate, or more accurately by estimation of the haemoglobin or electrolyte content of aspirate and the fluid in which all bloodstained items have been washed (Coller, Crook and lob, 1944; Gardiner and Dudley, 1962). A retrospective estimate of blood loss is obtained from haemoglobin or haematocrit values estimated during the second week after injury. By this time the presence of anaemia suggests that the early blood loss was inadequately replaced by blood transfusion (Topley and Clarke, 1956). By comparison of measured losses with the extent and severity of injury, these serial blood volume estimations have provided information for use as a guide to the management of future patients. With increasing clinical experience of the amount and timing of blood loss, however, the most valuable role of blood volume estimations is probably as a check on the adequacy of blood volume replacement rather than as a measure of the need prior to replacement. REFERENCES Chaplin, H., and Mollison, P. L. (1952). Correction for plasma trapped in the red cell column of haematocrit. Blood, 7, Clarke, R., Fisher, M. R., Topley, E., and Davies, J. W. L. (1961). Extent and time of blood loss after civilian injury. Lancet, 2, 381. Topley, E, and Flear, C. T. G. (1955). Assessment of blood loss in civilian trauma. Lancet, 1, 629. Coller, F. A., Crook, C E., and lob, V. (1944). Blood loss in surgical operations. J. Amer. med. Ass., m, I. Cotterill, M. S. (1951). Methods of measuring the swelling of limbs. Physiotherapy, 37, 49. Davies, J. W. L. (1960). A critical evaluation of red cell and plasma volume techniques in patients with burns. J. clin. Path., 13, 105. (1964). Blood volume changes in patients with burns treated with either colloid or saline solutions. Clin. Set., 26, 429. (1966). Blood Volume Studies; chapter on "Radioisotopes in medical diagnosis". London: Butterworth (in press). Topley, E. (1959). A critical evaluation of red cell and plasma volume techniques in patients with civilian injuries. 7. clin. Path., 12, 289. Gardiner, A. J. S., and Dudley, H. A. F. (1962). The measurement of blood loss at operation. Brit. J. Anaesth., 34, 653. Grant, R. T., and Reeve, E. B. (1951). Observations on the general effects of injury in man, with special reference to wound shock. Spec. Rip. Ser. Med. Res. Coun., No London: H.M.S.O. Gregersen, M. I. (1944). A practical method for the determination of blood volume with the dye T J. Lab. clin. 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