Year : 2007  |  Volume : 10  |  Issue : 1  |  Page : 27--33

Efficacy of combined modified and conventional ultrafiltration during cardiac surgery in children


Naresh Kumar Aggarwal, Sambhu Nath Das, Gautam Sharma, Usha Kiran 
 Departments of Cardiac Anaesthesia and Cardiology, Cardiothoracic Sciences Centre, All India Institute of Medical Sciences, New Delhi., India

Correspondence Address:
Naresh Kumar Aggarwal
Department of Cardiac Anaesthesia, 7th floor, CN Centre, All India Institute of Medical Sciences, New Delhi.
India

Abstract

Thirty children undergoing cardiac surgery under cardiopulmonary bypass (CPB) were prospectively studied to assess beneficial effects of modified ultrafiltration (MUF) over and above conventional ultrafiltration (CUF). Transoesophaegeal echocardiography determined ejection fraction (EF), fractional area change (FAC) and posterior wall thickness in end-diastole and end-systole were measured and compared in two groups undergoing CUF (group I) and CUF plus MUF (group II). Haemodynamic data, haematocrit, temperature drift, postoperative chest tube drainage in first 48 hours, ventilation and intensive care unit (ICU) stay were also recorded. Within group data were analysed by general linear trend and intergroup comparisons were made with t-test. EF and FAC decreased at 0 min after CPB in both groups, but both recovered at 10 and 30 min after CPB in group II. Increase in EF and FAC in group II was about 12-15 % and 3-5 % from 0 min respectively. There was also significant improvement in posterior wall thickness and haematocrit (P<0.05) in group II. Patients in group II maintained better systolic blood pressure and heamoglobin after CPB. Chest tube drainage in first 48 hours was significantly less in group II (100 ±18 verses 85 ± 20 ml, P<0.05), but ventilation and ICU stay were not different between the two groups. Combined ultrafiltration has beneficial effect an haemodynamics with improvement in EF and FAC. It improves haematocrit and decreases chest pulse drainage.



How to cite this article:
Aggarwal NK, Das SN, Sharma G, Kiran U. Efficacy of combined modified and conventional ultrafiltration during cardiac surgery in children.Ann Card Anaesth 2007;10:27-33


How to cite this URL:
Aggarwal NK, Das SN, Sharma G, Kiran U. Efficacy of combined modified and conventional ultrafiltration during cardiac surgery in children. Ann Card Anaesth [serial online] 2007 [cited 2022 Jan 20 ];10:27-33
Available from: https://www.annals.in/text.asp?2007/10/1/27/37921


Full Text

The use of hypothermic cardiopulmonary bypass (CPB) in children may result in an increase in tissue water content leading to an increase in total body water after operation. This effect is most marked in small babies with low body weight, long CPB periods and haemodilution. [1] CPB induced inflammatory response contributes to capillary leak, which can result in pulmonary and myocardial oedema after cardiac operations leading to increased morbidity and mortality. [2],[3],[4] CPB associated haemodilution of platelets and coagulation factors also promote the haemostatic impairment. [5],[6]

Ultrafiltration introduced during 1970's, has become an important strategy for mitigating the adverse effects of haemodilution associated with the use of CPB. In paediatric cardiac surgical practice, there are two basic approaches to ultrafiltration. Conventional ultrafiltration (CUF) involves ultrafiltration during rewarming phase of CPB, whereas modified ultrafiltration (MUF) is performed after discontinuation of CPB. MUF was introduced by Naik and colleages in 1991 and is independent of CPB circuit volume. [7] With MUF, more fluid can be removed than with CUF and this difference may translate into greater efficacy in attenuating the deleterious effects of haemodilution. [6] CUF reduces fluid accumulation associated with CPB, congestive heart failure and diuretic resistant heart failure, induces haemoconcentration, decreases inflammatory mediators [8] as well as reduces blood loss and duration of mechanical ventilation. [8],[9] MUF also improves the immediate post-bypass haemodynamics, decreases myocardial oedema, reduces pulmonary vascular resistance, induces haemoconcentration, reduces bleeding and thus, the need for blood transfusion. [5],[10],[11],[12] This prospective randomized study was performed in paediatric patients undergoing corrective cardiac surgery to compare the effects of combined ultrafiltration (CUF+MUF) over conventional ultrafiltration (CUF) with emphasis on myocardial function using transoesophageal echocardiography (TOE).

 Methods



After obtaining approval from the Hospital Ethics Committee, this prospective clinical study enrolled 30 children between 1 to 5 years of age undergoing corrective cardiac surgery on CPB. Informed parental consent was obtained from each patient. The patients were divided into two groups of 15 each by randomization using sealed envelope technique. Exclusion criteria were, patients with transposition of great arteries, single ventricle, requiring redo and emergency surgeries and those on preoperative ventilatory support.

Preoperatively, all children received pro­methazine, 0.5 mg/Kg and morphine, 0.2mg/Kg intramuscularly as premedication. Anaesthesia was induced with ketamine 2 mg/Kg, rocuronium 0.9 mg/Kg and fentanyl 5 µg/Kg. Anaesthesia was maintained with fentanyl (15-20 µg/Kg), midazolam (0.1-0.15 mg/Kg), pancuronium (0.1-0.2 mg/Kg) and isoflurane-in-oxygen (end­tidal isoflurane concentration range of 0.5%-1.5%). A paediatric biplane TOE probe (Hewlett Packard T 6210) was inserted after induction of anaesthesia. All patients received methylprednisolone 30 mg/ Kg intravenously during prebypass period with the intention of decreasing the inflammatory response. Monitoring included 5 lead ECG, femoral arterial pressure, central venous pressure, pulse oximetry, end-tidal carbon dioxide (CO 2 ) and temperature.

Standard paediatric perfusion protocol was used in all patients with aortic and bicaval cannulation. Before CPB, all patients received systemic anticoagulation using unfractionated heparin (400 IU/Kg) to achieve an activated coagulation time more than 480 seconds. The pump was primed with 500 ml of crystalloid (ringer lactate) and 300 ml of packed red blood cells (PRBC). In addition, 1 meq/Kg of sodium bicarbonate, heparin 3 IU/ ml of prime and 5 ml/Kg of 20% mannitol were added. PRBC were also added whenever the haematocrit decreased to less than 25% during CPB. A nonpulsatile flow (125-150 ml/Kg/min) was achieved during CPB using a twin roller pump (Sarns 9000, Ann Arbor, Michigan, USA) and a hollow fibre membrane oxygenator (Capiox SX 10, Terumo Corporation, Tokyo, Japan) with a 40 arterial line filter (Afinity, Medtronic, Minneapolis, USA). Myocardial preservation protocol included moderate systemic hypothermia (nasopharyngeal temperature 28-32°C), cold (4°C) antegrade hyperkalaemic cardioplegia solution (Plegiocard, Samarth Pharma, India) with blood (1:4 propor­tions) and topical cooling of the myocardium with ice slush placed in the pericardial sac. The initial dose of cardioplegia was 20 ml/Kg, followed by half the initial dose every 20 minutes. Arterial blood gas measurements were performed every 15 to 30 minutes to maintain arterial CO 2 partial pressure at 35-40 mm Hg, unadjusted for temperature (α-stat) and oxygen partial pressure at 150 to 250 mm Hg. Once surgery was complete, patients were rewarmed to 36-37°C and weaned from CPB. After completion of modified ultrafiltration and removal of venous cannulae, 1.3 mg of protamine sulfate was administered for every 100 IU of total heparin dose to reverse the anticoagulant effect of heparin. All patients were weaned off CPB with infusions of nitroglycerin (0.5 µg/Kg/min) and dopamine (5.0 µg/Kg/min) as per institute protocol.

In group I, CUF was performed during CPB. Recirculation line from arterial filter was connected to inlet of polysulfone haemofilter (Capiox CX, Terumo Corporation, Tokyo, Japan). Outlet of haemofilter was drained into venous reservoir. Conventional ultrafiltrate volume of 20-30 ml/Kg was removed during CPB. CUF was stopped if venous reservoir level fell low. In group II, CUF was performed during CPB as in group I and arteriovenous MUF was performed after termination of CPB. For MUF, blood was drained from purge line of aorta at the rate of 10-25 ml/ min into the venous reservoir through a male to male venous line and then into oxygenator and heat exchanger. Blood was then passed through luerlock connector from the outlet of oxygenator to the inlet of haemofilter. The outlet of haemofilter was connected via another male to male venous line to right atrium as shown in [Figure 1]. Care was taken during MUF to avoid any air embolism and colour of urine was monitored for haemolysis. Systolic and diastolic arterial pressures were monitored during MUF and a decrease in systolic arterial pressure of 20% from start of MUF was treated by infusing blood through aortic cannula to maintain CVP of 5-6 mm Hg. The volume of modified ultrafiltrate removed was 20-30 ml/Kg. MUF was performed using a simple indigenous circuit involving additional male to male venous lines, made from intravenous (iv) transfusion sets. Filter portion of a sterile iv set was cut and male connection of another sterile iv set was attached to the cut end. This tubing thus has male connections at both ends.

Systolic function was assessed using ejection fraction (EF) and fractional area change (FAC). EF was calculated using Simpson method and FAC was calculated in transgastric short axis midpapillary view by subtracting left ventricular end-systolic area from left ventricular end-diastolic area and dividing by left ventricular end-diastolic area. Readings were taken before sternotomy, immediately after termination of CPB (0 min), 10 min and 30 min after termination of CPB. Posterior wall thickness was measured at end-diastole and end-systole in transgastric short axis view at papillary muscle level at similar time intervals to assess myocardial oedema. All the TOE data were obtained by an echocardiographer (cardiologist) blinded to the study. Heart rate, systolic and diastolic arterial pressures, haematocrit and temperature were recorded at corresponding time intervals. CPB time, aortic cross clamp time, inotropic support required during weaning, volume of conventional and modified ultrafiltrate removed, time to extubate and the length of intensive care unit (ICU) stay were also recorded. Patients were extubated when they were fully rewarmed, conscious, haemodynamically stable with low-dose or no inotropes/ vasodilator, without significant dysrhythmias and no significant mediastinal bleeding and maintaining saturation with adequate respiratory efforts.

Statistical analysis was performed using SPSS software package (SPSS Inc, Chicago, IL). Perioperative data were calculated prospectively and were expressed as mean ± standard deviation. General linear trend analysis was performed for continuous serial values in same group, whereas inter-group comparison was done using t- test. A p-value [6] Blood exposure to artificial surfaces also activates the inflammatory cascade and complement system releasing a number of cytokines. [8]

Although CUF and MUF can be carried out by different methods, we used an indigenous and simple circuit for this purpose. This circuit was cheap and cost effective and uses only modified intravenous lines as described.

Many endpoints for termination of MUF have been suggested, such as target haematocrit value, complete salvage of circuit contents, duration of MUF and volume removed depending upon body weight. [6],[10] In our study, the volume of ultrafiltrate removed during CUF and MUF was based on body weight.

TOE determined EF and FAC were used in our study to assess systolic function of the heart, although these are load-sensitive indices, but filling pressures were kept constant. Significant decreases in EF and FAC in both groups immediately after CPB could be because of adverse effects of CPB. There was a significant improvement in both these parameters at 10 and 30 min post-CPB in group II suggestive of better systolic function. These findings are consistent with Davies et al who had shown improvement in left ventricular systolic function in 21 infants undergoing MUF compared with control group. [13] They assessed left ventricular systolic function by the slope of preload recruitable stroke work index, which increased significantly in MUF group but did not change in control group.

Adverse effects of CPB could have contributed to increase in posterior wall thickness in end­diastole and end-systole in both groups. The significant decrease in posterior wall thickness observed in group II after CPB is suggestive of beneficial effects of MUF in reducing myocardial water content or oedema. These findings are similar to Davies et al who had also observed reduction in left ventricular posterior wall thickness in MUF group as an evidence of decreased myocardial water content. [13] Gaynor and associates also found beneficial effects of MUF in reducing myocardial oedema but they used myocardial cross sectional area instead of posterior wall thickness to demonstrate reduction in myocardial oedema. [12]

In our study, combined ultrafiltration was effective in reducing posterior wall thickness and myocardial cross sectional area and thus myocardial oedema over and above CUF. This may be due to improvement in myocardial contractility associated with reduction in myocardial water content.

The systolic arterial pressure at 10 and 30 min in group II was significantly higher. In the Naik's study there was an increase in arterial pressure in all patients and heart became visibly smaller during MUF. [11] Hodges and associated also confirmed an increase in systemic arterial pressure and cardiac index after MUF. [14] Haemodynamic improvement seen after ultrafiltration may be related to modification of the inflammatory response to CPB and ischaemia.

Haematocrit improved by 10-11% in group II after modified ultrafiltration in our study. Elliott et al observed increase in haematocrit of 15-20 %, comparing MUF and control group. [5] Davies et al observed an increase in haematocrit of about 10 % in patients undergoing MUF [13] and Kiziltepe et al found an increase of about 5.7 % with MUF. [15] Thompson et al in their study had shown improvement of 1-2 % in CUF group and 3-4 % in zero balanced MUF group. [6] Our study demonstrates advantage of combined ultrafiltration in improving haematocrit over CUF alone. The relatively higher haematocrit seen in combined ultrafiltration group could be related to higher volume of ultrafiltrate removed.

There was no difference in duration of ventilation and ICU stay in the two groups. This is consistent with the results observed by Maluf et al. [16] Significant reduction in blood loss in first 48 hours observed in group II in our study is consistent with results observed in a few other studies. [9],[17],[18] This may be related to concentration of clotting factors and platelets by haemofiltration.

Most of the studies have compared the effects of CUF and MUF. Our study is different from others in comparing effects of CUF versus CUF + MUF with emphasis on myocardial function in children using TOE. The beneficial effects of MUF added upon the benefits observed with CUF alone. These benefits could be crucial in sicker and compromised children, such as those who are already in congestive cardiac failure. Further studies are necessary to assess beneficial effects of MUF over and above CUF in critically ill patients and patients undergoing surgery requiring longer bypass time.

Limitations of our study are the absence of control group (neither CUF nor MUF), indices to assess myocardial function were load sensitive, and critically sick patients in whom MUF could be more beneficial, were excluded.

To conclude, use of combined ultrafiltration has a beneficial effect on haemodynamics as well as improvement in EF, FAC and decrease in posterior wall thickness. Combined ultrafiltration also improves haematocrit and preserves haemostasis in children undergoing corrective cardiac surgery over and above conventional ultrafiltration.

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