Following cardiac surgery a few patients continue to bleed in the intensive care unit, and despite all the measures mentioned in the previous section being undertaken, around 3 to 5% of those need to be re-explored. The indications, timing, and methods of re-exploration vary from centre to centre, but there are some basic guidelines which govern this situation.
In a 75 kg person with a normal coagulation profile, more than a litre of bleeding in the first 2 to 3 hours or more than 150 ml in each hour for 5 to 6 hours may be an indication for re-exploration. Some patients show apparent stability for the first 8 to 12 hours with acceptable levels of bleeding and then they start bleeding. In this situation, more than 200 ml for a consecutive 3 to 4 hours with normal coagulation should warn the surgeon about the possibility of a surgical cause for the bleeding. After the first postoperative day, any bleeding that is more than 300 ml and associated with a drop in the haematocrit or a change in the haemodynamics, is of concern.
Clearly, in a 40 kg person 700 ml of bleeding is as significant as one litre in a 75 kg person. Similarly, in a 120 kg person the limit for indication of exploration may be extended to 1500 to 1800 ml. All decisions in these situations should be based on the overall condition of the patient. In the paediatric group, more than 5 ml/kg/hr for 2 to 3 hours consecutively or more than 3 ml/kg/hr for 5 to 6 hours should be considered as significant bleeding.
Rarely, bleeding can be concealed and the suspicion of bleeding can only be gauged by the haemodynamic instability or by the unexplained drop in the haematocrit with persistent need for transfusion. In this scenario, if time permits, a chest radiograph and an echocardiogram are of an immense value, as a large collection of blood in either mediastinum or in the pleural space would demand re-exploration. A sudden decrease in the recorded blood loss from the drains should alert the surgeon to the possibility of blocked drains rather than an actual decrease in the amount of bleeding. In these cases, the surgeon should rule out that possibility by thorough milking of the drains and by dislodging of the clots from the drains.
When surgery has been fraught, and it has been noted that the tissues are friable, the surgeon may choose to accept higher than normal blood losses. In this situation, extra-clinical vigilance is mandatory.
If the amount of bleeding exceeds the capacity of the drainage tubes, then it will accumulate in the pleural space and the mediastinum and may lead to cardiac tamponade. In this scenario, ever expanding blood clot can progressively compress the heart chambers, especially the atria. The surrounding bony cage being rigid, leads to a rapid decrease in the venous return and the cardiac filling, both causing a low cardiac output state. Keeping both pleurae open does not offer immunity against cardiac tamponade, as commonly thought, but putting more mediastinal drains may delay the onset of this situation.
Cardiac tamponade may manifest itself with hypotension, high jugular pressure, and poor end-organ perfusion resulting in oliguria. The patient may be peripherally cold and clammy, and the hypotension responds poorly or temporarily to inotropes like calcium chloride, given intravenously. In the paediatric setting, the first sign of tamponade may be failure to rewarm in a normal way. Many cardiac centres follow the doctrine "if in doubt, re-explore''.
As the surgical expertise and the management of haematological deficits have improved, the frequency of requirement for wound packing has decreased. Wound packing, however, remains a very useful method of salvaging a patient in a seemingly dire situation.
Topical haemostatic agents like Tisseel and floSeal can be applied to a specific raw area of the surgical site, followed by a light packing with Surgicel. The remaining area of the wound can be packed with swabs soaked in warm saline. The drains are inserted and, then, the wound can be closed with the temporary sutures. If stable haemody-namics can be achieved, the patient can be transferred to the ITU with a view to returning to the operating theatre in 24 to 48 hours.
During these 24 to 48 hours, the patient is kept in optimal haemo-dynamic state, with strict avoidance of hypertensive episodes. The patient's coagulation profile and other abnormal parameters like acidosis, hypothermia, and anaemia are corrected.
Haemostasis is often successful with this manoeuvre, but potential infection of the mediastinum remains a major concern. Mediastinitis and sternal infection following chest packing is as high as 14%34 and carries a high mortality.
Causes of infection in these cases are multi-factorial and as follows:
• Presence of foreign body.
• Immunocompromise due to CPB/multiple blood transfusions.
• Low cardiac output state.
Auto-transfusion, Cell-Savers, and Haemodilution in Cardiac Surgery
Despite the best efforts of the transfusion service, receiving homologous blood confers potential risks on the patient. This together with the rising cost of blood products has increased the practice of autotransfusion. This can be achieved by two methods. In the first method, the patient donates a unit of blood every week for 2 to 3 weeks before the elective operation, and the donated blood can be transfused back to the patient during the perioperative period. A major disadvantage of this method is that the stored blood is devoid of many clotting products and platelets. In the second method, the blood is collected during the operation, after anaesthesia, but before heparin has been administered. Up to two units of blood can be collected with this technique over a short period of time and replaced with a similar volume of colloid or crystalloid expanders. The collected blood can be transfused back to the patient at the end of the operation, when surgical haemostasis has been largely achieved. The blood is fresh in this method of auto-transfusion, and haemodilution is also achieved. There is, however, a possibility of haemodynamic instability in critically ill patients.
Cell-savers (as shown in Fig. 4) are being increasingly used in cardiac surgery, in many centres. With the cell-saver, blood that is shed during the surgery is collected with the addition of heparinised saline, to prevent clots in the circuit. The collected blood is washed and filtered, and the red cells are suspended in normal saline, ready for transfusion back to the patient. This red cell mass is free of heparin. Cell-savers can be connected directly to the chest drains that collect postoperatively shed blood. This shed blood can then be recovered, washed, and returned. This latter method can reduce the need for re-exploration of the patient, although it is rarely successful when the bleeding is brisk.
Haemodilution is another method of reducing blood loss. During CPB, the haematocrit is maintained at around 25 to 30 instead of the normal 45 to 50. This technique reduces the viscosity of blood and, therefore, improves the rheological function of the formed elements of the blood. With haemodilution there is also improved microcirculation of the tissues, which is a by-product of the decrease in viscosity. The third and the most important potential benefit of haemodilution is that it decreases the amount of injury to the blood and the level of inflammatory response.
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