https://doi.org/10.30702/ujcvs/19.35/03(016-020)

Haemodynamic Changes in Coronary artery Bypass grafting using Colloidal and Crystalloid Solutions

Mazur A., Gurin P., Babich M.

Shalimov National Institute of Surgery and Transplantology, Kyiv, Ukraine

Abstract. Changes in haemodynamics during off-pump coronary artery bypass grafting have been studied. The comparative analysis of the application of colloidal and crystalloid solutions at the stages of distal anastomosis formation during off-pump coronary artery bypass grafting is given. The study included 80 patients operated at Shalimov National Institute of Surgery and Transplantology for ischemic heart disease, who underwent off-pump coronary artery bypass grafting.

The study group included 40 patients who used hydroxyethylstarch (HES) 130/0.4 solution or 4% gelatine solution in the intraoperative infusion therapy program. The comparison group consisted of 40 patients, which were exclusively crystalloid solutions in the intraoperative period. The changes in the cardiac index (CI), blood pressure (BP), pressure in the pulmonary artery (PAP), central venous pressure (CVP), the results of complete and biochemical blood tests, electrolyte, acid-base and gas composition of the blood were analysed. The statistical analysis of the material was carried out by standard methods using the application package MS Excel 2007 and Stat Plus 2007 Professional. Estimated mean, standard errors, statistical significance, Student’s t-test were used to assess the intergroup difference, while the relationship between the indicators was determined by the Pearson correlation analysis. Changes in intracardiac haemodynamics occurring at the stages of off-pump coronary artery bypass grafting were studied. The obtained results showed that when using colloidal solutions, the values of central haemodynamics at the stage of distal anastomosis formation (CI, BP, PAP and CVP) were significantly higher than in patients treated with crystalloid solutions. However, the decline in central haemodynamics in patients treated with crystalloid solutions was not critical and allowed off-pump coronary artery bypass grafting to be performed in all patients without involvement of cardio-pulmonary bypass (CPB).

Keywords: off-pump coronary artery bypass grafting, cardiac index, colloidal solutions, crystalloid solutions, haemodynamic changes.

In spite of the perfect modern technical support, cardio-pulmonary bypass (CPB) remains an antiphysiological procedure that has a number of specific complications associated with the heart and other organs and systems. Neurological disorders, coagulopathic bleeding, pulmonary complications are among the most common complications [1, 2]. In a number of cases, pathological changes that occurred at the anoxic stage of the operation are irreversible and result in damage to the myocardium [3].

The technique of off-pump coronary artery bypass grafting (CABG) has developed considerably in recent years. However, placing distal anastomosis on the posterior and lateral vessels of the heart may be characterized by unstable haemodynamics, which is accompanied with a decrease in the cardiac index (CI) and blood pressure (BP) [4]. Although an abnormal volume status is one of the most common causes of instable haemodynamics when performing any cardiosurgical interventions, most often they occur precisely during off-pump CABG. A decrease in CI due to hypovolemia leads to tissue hypoperfusion, disturbed tissue metabolism, increased frequency of perioperative complications and increased postoperative mortality [5, 6]. At the same time, hypervolemia increases the tension of the ventricular myocardium, increases the work of the heart and consumption of oxygen by the myocardium, leads to hemodilution, coagulopathy and fluid accumulation in the interstitial space.

During surgery, circulating blood volume (CBV) is supported with crystalloid solutions and, ultimately, with the colloid remaining in the vascular bed, while 30 to 60% of crystalloid solutions can be “lost” in the interstitial space [7]. On the one hand it is considered that the use of colloidal solutions to support CBV during surgery is appropriate for significant blood loss, on the other hand, the use of synthetic colloids affects coagulation haemostasis, and to some extent leads to an increase in blood loss. Therefore, the problem of choosing the optimal infusion therapy tactic in the perioperative period is still an unresolved issue [8].

The purpose of the study is to investigate changes in haemodynamics during off-pump CABG using different infusion solutions.

Materials and methods

The study was based on a prospective analysis of the surgical interventions in patients who underwent an isolated off-pump CABG from January 2015 to August 2016. The exclusion criteria for patients were left ventricular ejection fraction less than 50%, baseline blood creatinine > 140 µmol/l, haemoglobin level <120 g/l, platelet count <180x10⁹/l, pre-operative coagulopathy, hepatic dysfunction (ALT > 40 U/l, AST > 40 U/l), repeated CABG, urgent surgery. Antiplatelet agents (clopidogrel, ticagrelor) and aspirin were discontinued in all patients more than 5 days prior to surgery. 80 patients met these criteria and were included in the study.

Patients were divided into two levels of a group of 40 persons: group 1 (study group) – patients who were treated with hydroxyethyl starch 130/0.4 (HES) solution during the intraoperative period or 4% gelatine solution (the maximum dose did not exceed 15 ml/kg); group 2 (comparison group) – patients who did not administer colloidal solutions intraoperatively and only crystalloid solutions were included in the infusion therapy program.

After induction of anaesthesia and tracheal intubation, an echocardiographic sensor was placed in the forestomach in each patient under the control of a laryngoscope so as to obtain optimal visualization of the left ventricular myocardial cross-section at the level of the papillary muscles. The depth and enhancement were individually selected for each patient and did not change until the end of surgery.

Pulmonary artery catheterization with a 20 g intravenous cannula was performed after sternotomy. This method of measurement of pulmonary arterial pressure (PAP) was chosen because the classical method of PAP measuring using the Swan-Ganz catheter, first, has many complications (carotid puncture, hematoma formation, pneumothorax, rhythm and conduction disturbances, pulmonary artery rupture), and secondly, this catheter is not approved for use in Ukraine. It allowed PAP monitoring and blood sampling to determine the acid-base status (ABS), lactate and calculation of arteriovenous oxygen difference.

CI was calculated as follows. At the beginning of the operation, at the stage of shunting of the left anterior descending artery (LAD) and after the end of the operation, CI was determined using transoesophageal echocardiography (TOE) by the formula:

CI = ((EDV – ESV) x HR / body surface area (BSA),

where

EDV is the end-diastolic volume, ml;

ESV is the end systolic volume, ml;

HR is the heart rate per 1 min.

During the shunting of the right coronary artery (RCA) and the left circumflex coronary artery (LCX), when the calculation by TOE was complicated, CI was calculated using the Fick’s formula:

CI = (VO₂ / (1.34 x Hb x (SaO₂–SvO₂) + (0.003 x PaO₂)) / BSA,

where VO₂ is oxygen consumption, ml/min.;

1.34 is Hüfner’s constant (reflects the ability of haemoglobin to bind oxygen);

Hb is blood haemoglobin concentration, g/l;

SaO₂ is saturation of haemoglobin of arterial blood, %;

SvO₂ is saturation of haemoglobin of venous blood, %;

PaO₂ is partial pressure of oxygen in arterial blood, mmHg.

VO₂ was calculated by the difference in oxygen content in the gas analyser circuit of the artificial lung ventilation apparatus. The result was multiplied by the value of respiratory minute volume.

Results and Discussion

Patients in the study groups did not differ in clinical and laboratory parameters before surgery. The mean age of the patients in the 1st group was 60.2 ± 10 years, in the 2nd – 59.9 ± 8.8 years (p = 0.88). All patients had angina pectoris of different functional classes, and the perioperative risk score according to the EUROScore scale was 1.12 ± 0.33% and 1.1 ± 0.3%, respectively, in the patients of the 1st and 2nd groups. There were also no significant differences in preoperative haemoglobin, coagulograms, etc.

Central haemodynamics was compared at the stage of distal anastomosis formation between the left internal thoracic artery (LITA) or the autoveneous and coronary arteries.

Anastomosis between LAD and LITA was performed in 39 patients (97.5%) of the study group and 40 patients (100%) of the comparison group.

To install an epicardial stabilizer on the area of the coronary artery for its shunting, the heart is displaced in advance by lining the drapes under it or pulling up the traction sutures. In all cases, placing an epicardial stabilizer results in moderate pressure on the left ventricle. There is a slight decrease in end-systolic and end-diastolic volume of the left ventricle. Compression of the left ventricle is more pronounced in the anterior-posterior direction and on the apex due to the direct pressure of the epicardial stabilizer on the anterior wall and on the apex of the left ventricle. Because the end-diastolic and end-systolic volumes decrease simultaneously after placing the stabilizer, the left ventricular ejection fraction changes slightly.

The wall of the right ventricle is thinner than the wall of the left ventricle, so the right ventricle is more sensitive to compression. Compression of the epicardial stabilizer leads to an increase in end-diastolic pressure of both ventricles, a decrease in blood pressure, a slight increase in central venous pressure (CVP).

Central haemodynamic parameters upon forming distal anastomosis between LITA and LAD when using HES solutions and crystalloid solutions are given in table 1.

Table 1

Haemodynamic parameters upon forming distal anastomosis between LITA and LAD

As can be seen from the table, when using colloidal solutions CI was higher by 12.5% and mean BP – by 10%. However, in the group where crystalloid solutions were used, the CI did not decrease below 2 l/min./m² during the shunting phase of LAD, and the mean blood pressure was below 70 mm Hg. CVP and PAP did not differ significantly between the patient groups. Parameters of adequate tissue perfusion include SvO₂, and plasma lactate concentration. SvO₂ did not decrease below 70% in both groups and lactate concentration did not increase more than 2 mmol/l.

RCA shunting was performed in 35 (87.5%) patients in the study group and 31 (77.5%) patients in the comparison group. When placing a distal anastomosis of the branches of the RCA, the changes in haemodynamics are mainly associated with moderate compression of the heart right sections. Upon RCA shunting, the apex of the heart is pulled outwards, while the Trendelenburg’s position is preserved and the table is rotated to the left to improve the examination of the operating wound. The right ventricle is compressed with a stabilizer, and the heart left sections is displaced without contraction between the two surfaces. Due to this, there is no significant decrease in blood pressure.

Central hemodynamic parameters upon forming distal anastomosis between the aorta and RCA when using colloidal solutions and crystalloid solutions are presented in table 2.

Table 2

Haemodynamic parameters upon forming distal anastomosis between the aorta and RCA

As can be seen from the table, when using colloidal solutions, the CI value was higher by 10%, and the mean blood pressure – by 13%. However, in the comparison group the CI at the stage of forming distal anastomosis between the aorta and RCA decreased to a level that was not critically lower than 2 l/min./m², and the value of mean blood pressure – below 70 mm Hg. SvO₂ did not decrease below 65%, and plasma lactate concentration was recorded at a level corresponding to adequate tissue perfusion at this stage of surgery in both groups.

LCX shunting was performed in 33 (82.5%) patients in the study group and 30 (75%) patients in the comparison group. The branches of the circumflex artery are on the lateral wall of the left ventricle. To position them, the heart should be displaced to the right and up. The Trendelenburg’s position and rotation of the operating table to the right are used for convenience of exposure of the heart lateral surface. The heart displacement leads to a deterioration of the filling of the ventricles, insufficiency of atrioventricular valves. When examining the branches of the circumflex artery, the surgeon temporarily shifts the heart and creates compression on the left ventricle, which can lead to ventricular extrasystoles, which will affect the haemodynamics. Mean BP and CI decrease. Correction of haemodynamics is necessary already in the first phase of elevation and rotation of the heart, to avoid a sharp drop in blood pressure and rhythm disturbances when installing the stabilizer. When positioning LCX the cavity of the left ventricle significantly decreases, the left atrium increases, and the right ventricle and atria are subjected to considerable compression.

Upon TOE there is a displacement of the anterior-cardiac septum to the left, compression of the cavity of the right ventricle, reduction of the left ventricle size. The normalization of blood pressure provides support for coronary perfusion pressure and blood flow through the formed anastomosis of LITA and LAD.

Arteriotomy and formation of the distal anastomosis with the circumflex artery begin after BP and HR stabilization. Haemodynamics was stabilized by increasing mean BP with the help of vasoconstrictors, as well as the choice of the optimal position of the heart and installation of the epicardial stabilizer without compression of the ventricles.

Table 3 shows central haemodynamic parameters in forming distal anastomosis between the aorta and LCX using colloidal solutions and crystalloid solutions.

Table 3

Haemodynamic parameters upon forming distal anastomosis between the aorta and LCX

As can be seen from the table, changes in haemodynamics are most pronounced when shunting the LCX pool. In patients of group 1, CI was higher by 27% and mean blood pressure – by 20%. Although being higher, mean PAP was not significant. Dopamine infusion at a dose of 5-8 µg/kg/min was used in 6 (20%) patients of group 2.

Decrease in the cardiac index occurs due to left and right ventricular dysfunction and is most pronounced when the heart is displaced from the pericardium during LCX revascularization. A decrease in blood pressure during cardiac displacement may be reduced by an increase in pre-loading, as demonstrated in the patients of group 1. Systemic hypotension may be caused by impaired right ventricular ejection due to compression of the right atrium and right ventricle as the heart is displaced and rotated. If the CI normalization does not occur after additional infusion of solutions, infusion of vasopressors and/or inotropic agents is required.

Conclusions

1. Shunting the vessels of the anterior and lateral surfaces of the heart results in compression of the heart and a decrease in the EDV of the ventricles, which leads to a decrease in the stroke volume of the left ventricle, a decrease in CI and mean BP, an increase in CPB and systemic PAP and mean PAP.

2. When shunting the vessels of the posterior surface of the heart, hemodynamic disorders are caused by impaired filling of the ventricles due to enucleation (verticalization) of the heart, occurrence or aggravation of mitral insufficiency, obstruction of the excretory ducts, and are manifested in a decrease in mean BP up to 25%, CI up to 27%. In some cases, correction of haemodynamics is required.

3. Usage of crystalloid solutions results in pronounced changes in haemodynamics at the stages of LCX shunting compared with colloidal solutions, but even with a decrease in CI <2 l/min./m², SvO₂ and lactate values do not change below the reference values.

4. With planned surgical interventions it is recommended to use crystalloid solutions as basic in the program of perioperative infusion therapy.

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Published: March 2019