Novokuznetsk State Institute of Postgraduate Medicine,

City Clinical Hospital #1, 

Novokuznetsk, Russia

 

It is not secret that polytrauma is the multi-component pathologic process. Regardless of injured regions it is accompanied by hypovolemia, hypoperfusion and non-adequate tissue oxygenation [1]. In its turn, injuries and hypoxia initiate the range of pathologic responses (release of oxygen radicals, proteolytic enzymes, excessive production of histamine, kinins, products of degradation of arachidonic acid, microclots etc.) which worsen preexisting disaster and favor development of multiple organ insufficiency [2]. Therefore, the primary task for any physician is discontinuation of the cascade by means of correction of hypovolemia and providing adequate tissue perfusion. The main method for this situation is infusion-transfusion therapy. The difficulty is associated with estimation of adequacy of infusion [3] considering the fact that precise volume of blood loss is practically impossible for estimation. Besides blood loss, other causes of non-adequate perfusion are heart contusion, disseminated intravascular coagulation and other states [1, 2]. Sometimes for estimation of therapy the physician uses the common and easy estimated values such as arterial pressure, heart beat, central venous pressure, diuresis rate. But pressure is not the analogue of volumetric rate of blood flow, because the parameter of resistance is not considered, and measurement is realized on the big vessels (buffer vessels) – the most passive region of blood flow [3]. Central venous pressure is able to predict susceptibility to volumetric load only in 47 % of cases, although this value is included into multiple protocols of infusion therapy [4]. But the main thing is that in pursuit of appropriate values of central hemodynamics we forget the final aim – providing adequate tissue perfusion. Microcirculatory bed is the place of final realization of transport function of cardiovascular system and provision of transcapillary exchange, which creates tissue homeostasis necessary for life [3, 5, 6, 7]. Therefore, it is necessary to realize capillary flow monitoring in any critical state including polytrauma.

Objective - to evaluate the changes of capillary blood flow and central hemodynamics at the background of infusion-transfusion therapy in polytrauma.

                

MATERIALS AND METHODS

The study was conducted in the trauma resuscitation department of Novokuznetsk Clinical Hospital #1 in 2013-2014. The study included 19 patients with polytrauma, the mean age of 39.73 ± 4.03, ISS = 29.61 ± 1.38, APACHE II = 10.3 ± 1.27. The patients were admitted to the hospital within 1 hour after injury. Blood loss was 20-40 % of circulating blood volume. Diagnosis was made on the basis of clinical picture, laboratory and instrumental examinations.    

The inclusion criteria were polytrauma (the combination of two and more injuries one of which or their combination creates immediate threat for patient’s life and is an immediate cause of traumatic disease) [1], age of 18-50. The exclusion criteria were chronical concurrent pathology in decompensation phase, severe traumatic brain injury, injuries to abdominal hollow organs with contamination of abdominal cavity at the moment of the injury, administration of sympathomimetics (their use causes changes in skin capillary blood flow) [8].    

The patients were distributed into two groups for estimation of efficiency of red blood cells transfusion. The indications to transfusion were made in concordance with the orders of Russian Ministry of Health #183n from 2.04.2013 and #363 from 25.11.2002. The volume of single transfusion of red blood cells was 500-800 ml.    

The first group included 9 patients with transfusion on the first day after trauma. The mean age was 39.71 ± 3.81, ISS = 30.12 ± 2.71, APACHE II = 11.85 ± 2.13. The level of hemoglobin was 68.5 ± 6.76 g/L and hematocrit – 21.08 ± 1.6 % in the first day. In this group the patients had the following combinations of traumatic injuries: 7 patients with fractures of pelvic bones, 6 patients with fractures of femoral bone, 4 patients with fractures of the lower leg, 5 patients with fractures of the humerus. Closed abdominal injury was in 8 patients. Laparoscopy found splenic injuries (6 patients), liver rupture (6 patients), rupture of mesentery (1 patient). 5 patients had severe chest injuries with multiple fractures of ribs, hemo- and pneumothorax, lung contusion.      

The second group included 10 patients who received transfusion of red blood cells on the second day. The mean age was 35.14 ± 3.28, ISS = 28.61 ± 4.18, APACHE II = 8.5 ± 0.92. In the patients of the second group the levels of hemoglobin and hematocrit were 85.75 ± 2.04 g/L and 25.87 ± 1.01 % in the first day. These levels were significantly higher than in the first group. The patients had the following combinations of traumatic injuries: fractures of pelvic bones in 5 patients, fractures of the femoral bone in 10 patients, fractures of the leg in 4 patients, fractures of the humerus in 3 patients. 6 patients had closed abdominal injury with splenic injury in 5 cases, liver rupture in 7 cases. 6 patients had severe chest injuries with multiple costal fractures, hemo- and pneumothorax and lung contusion.

At admission all patients received surgical stabilization for fragments of the long bones with external fixing devices (16 interventions) or skeletal traction (14 interventions), pleural cavity draining (11 interventions). 14 laparotomy procedures with suturing the liver ruptures (13 interventions), splenectomy (11 interventions) and bowel resection (1 intervention) were made. Surgical interventions were conducted in conditions of total intravenous anesthesia with artificial lung ventilation.             

All patients received the complex of intensive care including infusion-transfusion therapy with use of crystalloids, colloids and blood products, respiratory therapy according to the concept of safe artificial lung ventilation; if indicated, antibiotics of wide range; from the second day – nutritive support of enteral or mixed type; analgesia with narcotic or non-narcotic analgetics. The period of dynamic observation was 4 days of hospital stay.    

In the intensive care unit the patients received non-invasive monitoring of arterial pressure, pulse oximetry and ECG monitoring (Nihon Kohden, Japan). The level of systolic arterial pressure (SAP) and diastolic arterial pressure (DAP) was measured. Mean arterial pressure (MAP) was calculated automatically. Hourly urine output was measured. Central venous pressure (CVP) was measured with the venous catheter in the subclavian or jugular vein and Waldmann’s device. Manipulations were made with the patient in horizontal position. 0 point was installed at the level of the middle axillary line. Central venous blood saturation was estimated with the analyzer STAT PROFILE pHOx (Nova Biomedical, USA). The blood was collected through the central venous catheter with its distal end in the superior vena cava.         

The state of skin microcirculation was estimated with laser doppler flowmetry (LDF) by means of the laser analyzer for capillary blood flow (LAKK-OP, LASMA, Russia) with ability to make complex estimation of microcirculation [7, 9]. Skin microflow presents specific interest. Firstly, it is easy available, secondly, it responses to stimulation of sympathetic nervous system because of the features of capillary network and innervation [7, 8]. The examinations were made every day (not less than 3 times per day) on the skin of external lower one-third of the humerus on both hands or on the uninjured extremity. This region was chosen because it contains few arteriolovenular anastomoses, i.e. it provides most precise estimation of the state of blood flow in the capillary bed [7].       

The duration of a single examination was 3 minutes. The following values were registered during examination: mean value of microcirculation index (M) – it shows the degree of perfusion with fraction of red blood cells mainly, in units of volume of tissue per time unit, measured with perfusion units (p.u.). Standard deviation (SD, p.u.) of amplitude of blood flow variations from the mean arithmetic characterizes temporary changes of perfusion and reflects mean modulation of blood flow in all frequency bands. Dynamic estimation of the values identifies microcirculation disorders. So, increasing flow towards microcirculatory bed with increasing number of functioning capillaries characterizes hyperemic type of microcirculation changes. Rapid increase in M and decrease in SD happen. The spastic type of disorders is characterized with decreasing blood flow by means of spasms in arterioles; the common manifestations are decreasing M and SD. The congestive type is characterized with such changes as difficulties in outflow. The degree of changes in microcirculation depends on intensity of the process. So, M can be constant or increasing, because the number of red blood cells increases in the capillary bed, but SD decreases [9].        

The additional criterion for estimating microcirculation was estimation of dynamics of blood saturation (SO₂) by means of optical tissue oximetry (LAKK-OP). The technique is based on change of volume of hemoglobin fraction and mean relative level of blood oxygen saturation in microcirculatory bed in the examined tissue. Blood saturation estimation with the analyzer was based on the difference in optical properties of oxygenated (HbО₂) and desoxygenated (Hb) hemoglobin fractions during probing in green and red bands of radiation. Deepness of probing is 1-3 mm, i.e. commonly the examined region includes only small venules, arterioles, arteriovenous shunts and capillaries. Information is transferred from all mentioned links of microcirculatory bed. Therefore, blood saturation, which is examined with the device, shows (contrary to the devices for pulse oximetry) the mean relative blood contents of HbO₂, averaged along the whole microvascular bed. SO₂ is the mean arithmetic for venous and arterial blood in the examined region of tissue. As for arterial blood, SO₂ commonly presents the constant value. Moreover, the proportion of arterial blood with high contents of SO₂ is several times lower than in venous blood. As for microcirculation system, SO₂ characterizes venous level of oxygen, i.e. it allows indirect estimating oxygen consumed by tissues [10].

The control values of microcirculation were obtained from 36 almost healthy individuals at the age of 25-46.

Considering the small size of the sample we used the non-parametric methods of statistical analysis. Statistical significance of intergroup differences was estimated with Mann-Whitney test. Intergroup differences were estimated with Wilcoxon test. Relationships between the values were estimated with Spearman's rank correlation coefficient. P < 0.05 was statistically significant difference [11].  

 

RESULTS

One should give attention to the differences in volume of infusion-transfusion therapy during the period of observation (table 1). Such therapy demonstrated higher statistical significance (58.84 ± 4.57 ml/kg). Such high volume of infusion was conditioned by correction of hypovolemia which was mainly caused by acute blood loss.   

Table 1
Dynamics of values of microcirculation and central hemodynamics  (M ± m)

Note: ® - statistical reliability of differences for 1st day in the group;
* - statistical reliability of differences between the groups.

Dynamic monitoring showed that SAP was higher than the critical level of 65 mm Hg within the whole study, and the statistically significant increase was noted only on 3rd day (table 1). There was no statistically significant change in HR within all days of observation. Increase in CVD was noted only by 3rd day from the moment of trauma. There were no changes in SvO₂ within the whole period of the study. Despite of differences in volume of infusion-transfusion therapy for the day 1, diuresis rate increased only by day 3 in the hospital.     

Dynamic monitoring of microcirculation showed that the mean level of perfusion was lower for day 1 in comparison with the controls. Its increase happened by day 2 and persisted within all days of observation. The similar pattern related to variability of capillary blood flow and tissue saturation which increased on the second day.    

Considering the fact that estimation with laser doppler flowmetry is based on indirect estimation of amount and velocity of red blood cells in the examined region, it would be interesting to estimate microcirculation before and after transfusion of packed red blood cells. The reliable increase in hemoglobin and hematocrit was noted on the following day after transfusion (table 2). There was statistically significant increase in low values of M, SD and SO₂. However considering the fact that transfusion of packed red cells was conducted in different days from the moment of trauma, the patients were distributed into 2 groups. 

Table 2
Dynamics of values of microcirculation, hemoglobin and hematocrit before and after transfusion of red blood cells  (M ± m)

Note: * -  statistical reliability of differences between the groups.

   

The table 3 shows the results with consideration of distribution of the patients into two groups. During the first day both groups demonstrated statistically significant low values of the middle level of perfusion, variability of capillary perfusion and saturation in the examined region in comparison with the controls; there were no statistically significant differences between the groups. The first group demonstrated reliable increase in M, SD and SO₂ next day after transfusion. The variability of capillary blood flow acquired higher statistical significance than in the control group. However reliable increase in these values was noted in the second group in comparison with day 1, although the level of mean perfusion was lower than in the control group. There were statistically significant intergroup differences in the values of microcirculation on the second day. There were no differences in SO₂. The differences between the groups disappeared on the third day.

Table 3
Dynamics of values of microcirculation depending on time of transfusion of red blood cells  (M ± m)

Note: ® - statistical reliability of differences for 1st day in the group;

* - statistical reliability of differences between the groups;

°- statistical reliability of differences with values of control group.

 

DISCUSSION

Isolated estimation of the common values of hemodynamics does not allow fully-featured estimation of peripheral blood flow. It was testified by absence of statistically significant changes in MAP on the second day of examination and HR within the whole period of observation considering reliable changes in microcirculation on the second day. Estimation of blood flow in critically ill patients should be based on the many-sided examination of volume and quality of blood flow. An individual value of hemodynamics does not give an idea about patterns of circulation [12]. This idea was supported by absence of correlation between the values of hemodynamics and peripheral perfusion. One should recall that MAP is the derivative from cardiac output (CO) and total peripheral vascular resistance (TPVR). Increasing MAP could be caused by two factors: increasing CO (it should be accompanied by improvement in perfusion) and increase in TPVR (resulting in decreasing perfusion and ischemia in tissues). Therefore, the analysis of MAP alone does not give information about presence or absence of spasm in arterioles that requires complex approach for estimation of circulation system [3, 6, 8, 12]. However we do not call for refusal from MAP and HR monitoring. These values are extremely important for fast identification of intense disorders of hemodynamics, which become irreversible if emergent correction is not conducted. Any physician knows about necessity of supporting MAP at the level above 65 mm Hg. It is the cut-off level of disarrangement of tissue perfusion. Other example includes patients with severe traumatic brain injury who need for MAP at the level of 100 mm Hg for provision of cerebral perfusion pressure. Estimation of HR is the essential part of monitoring for critical states. Tachycardia is one of the criterions of severity of patient’s state. Analysis of HR allows timely identification of rhythm disorders. Considering the fact of “easy” estimation of MAP and HR, the physician incorrectly replaces the term “perfusion” to the term “pressure”. It results in incorrect decisions during intensive care.                 

Amount of CVP depends on multiple parameters in the body whether it be the basic state of the cardiac muscle or ALV. As result it is difficult to assess the degree of volemia only with this parameter. The study shows statistically significant increase in CVP on the third day after trauma, although the values did not exceed the references (40-120 mm Hg). Absence of increase in CVP above the normal values indicated better tolerability of infusion load rather than state of volemic status.  

Statistically significant increase in diuresis rate on the third day (despite of high level of infusion on day 1) was conditioned by initiation of mechanisms for correcting hypovolemia and stabilizing hemodynamics. Acute blood loss resulted in decreasing renal perfusion that initiated the cascade of rennin-angiotensin-aldosterone system (RAAS) with natrium and water retention resulting in decreasing urine output. This compensatory process relates to the mechanisms of delayed action, and the maximal potential is observed in the end of the first day after trauma. Thereafter, its inactivation also requires long term time interval [1, 2, 5, 13].    

Multiple studies showed that SvO₂ demonstrates more clear association with oxygen transport in comparison with MAP and HR [6, 8]. However in our study SvO₂ was higher than the critical level of 65 %. Absence of reliable changes within the whole period of observation could be explained by the fact that other studies with analysis of dynamics of SvO₂ were realized in the extremely severe patients with non-stable arterial pressure, but we had no such situations in our study. Moreover, we started examination from the moment of admission to the hospital, i.e. the patients received infusion therapy at the stage of emergent medical aid; therefore, we did not know the basic values of SvO₂.

The results of altering state of microcirculation in polytrauma are in agreement with other studies [14, 15]. So, on the first day after trauma the concurrent decrease in mean level of perfusion and variability of blood flow indirectly indicated development of spastic disorders of microcirculation which are characterized with deceleration of capillary blood flow, decreasing oscillation of vascular wall and decreasing amount of functioning capillaries [9]. Spastic disorders of skin perfusion developed as result of mechanisms of blood flow centralization with providing adequate perfusion in the vital organs [3, 5, 14]. The statistically low values of SO₂  on day 1 could be explained by spastic disorders of microcirculation. Such events were removed with the conducted therapy.

Primary substantiation of changes in microcirculation next day after transfusion of packed red cells is explained by the fact that LDF is based on estimation of amount and velocity of red blood cells in the examined region. With increasing amount of red blood cells we stimulate increase in mean level of perfusion and tissue saturation. However infrared spectroscopy for estimation of transfusion and its influence on microcirculation did not show any persistent improvement in capillary blood flow [16] that gave an impetus to analyze microcirculation values with the patients distributed into two groups in concordance with timing of transfusion therapy.               

Despite the absence of transfusion on day 1 in the group 2, on the following day we observed reliable increase in mean level of perfusion, variability of capillary blood flow and blood saturation. It is explained by sufficient volume of infusion. According to the literature the adequate compensation of circulating blood volume results in increasing preload and increase in CO. CO is the indirect index of volumetric blood flow. Consequently its increase favors increasing tissue perfusion [6, 8, 12].

Statistically significant increase in values of microcirculation in the first group after transfusion is explained by several mechanisms. Compensation of circulating blood volume improved microcirculation in the group 2. Other moments were: firstly, supply of donor red blood cells into the blood flow, secondly, specific properties of red blood cells. So, Fridlender et al. found that transfusion of red blood cells improved elasticity of red blood cells by means of possible replacement of injured rigid red blood cells by relatively intact red blood cells [16]. There were no intergroup differences in M, SD and SO₂ in the second group on the third day.           

 

CONCLUSION

The isolated analysis of such values as hemodynamics, MAP, CVP and HR does not provide full picture of peripheral perfusion. Monitoring of microcirculation with laser doppler flowmetry and tissue oximetry is the essential supplement to the common indices of central hemodynamic monitoring in polytrauma, because it allows finding disorders of microcirculation and estimating changes in peripheral perfusion at the background of infusion-transfusion therapy.