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Acute cardiac tamponade: anticipate the complication.

Background

Cardiovascular disease is the leading cause of death for Canadians (Statistics Canada, 2007). At a cost of more than 18 billion dollars a year, caring for patients afflicted with cardiovascular disease far outweighs the cost of most other illnesses (Health Canada, 1998; Heart & Stroke Foundation of Canada, 2002). Coronary artery disease, the most common cardiovascular illness, results from a progressive blocking of the coronary arteries by atherosclerotic plaque. Although recent pharmacologic and technological advances have reduced the need for cardiac surgery, the number of coronary artery bypass graft (CABG) surgeries continues to increase each year (Heart & Stroke Foundation of Canada, 2003).

There are many potential surgical complications in the postoperative period including infection and arrhythmias. However, one of the most immediately life-threatening complications following cardiac surgery is the development of acute cardiac tamponade (ACT) as a result of bleeding. Cardiac tamponade is defined as "the progressive accumulation of blood in the pericardial sac" (Urden, Stacy, & Lough, 2006, p. 994). Acute cardiac tamponade is more specifically defined as occurring in the first five to seven days following cardiac surgery (Russo, O'Connor, & Waxman, 1993). Although the rates of ACT vary among the cardiac surgery population, several studies have reported that patients who undergo valve replacements are more likely than CABG patients to develop ACT (Kuvin, Harati, Pandian, Bojar, & Khabbaz, 2002; Unsworth-White et al., 1995). While the overall incidence of ACT is low, ranging from 0.5% to 5.8%, it is a life-threatening emergency (Russo et al., 1993).

Patient recovery and time to discharge following cardiac surgery can be improved by identifying the patients at risk for developing ACT. This is accomplished by recognizing early assessment findings, understanding the diagnostic criteria and anticipating the management of cardiac surgery patients who develop ACT. Therefore, CCNs play an important role in decreasing the incidence and severity of ACT.

Pathophysiology

The heart sits within a double-walled sac called the pericardium. The pericardium is a fibrous membrane structure comprising the visceral and parietal layers. This membrane acts as a physical barrier to infection and prevents displacement of the heart during movement. The pericardial sac contains pain and mechano-receptors that, when stimulated, cause changes in heart rate and blood pressure. Normally, the pericardial sac contains approximately 30 ml to 50 ml of serous fluid (McCance & Huether, 2006). A pericardial effusion is defined as the accumulation of fluid in the pericardial sac. Effusions tend to develop slowly and are not necessarily clinically significant. However, if the effusion develops quickly and causes cardiac compression, the condition known as cardiac tamponade can become immediately life-threatening (McCance & Huether, 2006).

While ACT can occur as a result of other medical conditions such as trauma, in the cardiac surgery population ACT is a consequence of post-operative bleeding. Because of limited room for expansion in the pericardial sac, rapid accumulation of blood will result in increased pressure. As the pressure in the pericardial sac increases, there is a decrease in right atrial and right ventricular diastolic filling capacity. The right side of the heart is initially affected because of lower diastolic pressures, resulting in decreased resiliency to pressure changes (McCance & Huether, 2006). As the bleeding continues, the patient is not able to accommodate for the rapid increase in pressure. The resulting cardiogenic shock is caused by the myocardial tissue's inability to propel blood forward due to the increase in pressure from the rapidly accumulating fluid in the pericardial sac (Urden et al., 2006). As the pressure surrounding the heart continues to rise tamponade ensues.

Preventing ACT

The prevention of ACT is central to improving outcomes in the cardiac surgery population. CCNs have a pivotal role in preventing the development of ACT in these patients. Prevention includes understanding the risk factors that affect the development of ACT and the management of post-operative bleeding in the cardiac surgery population. Risks for developing ACT. Post-operative bleeding is the major risk for the development of ACT in the cardiac surgery population. During post-operative assessment, the risk of ACT should be considered based on the surgical procedure. This risk is due to a number of factors including the location and complexity of the surgical procedure, and the skill of the surgical team (Bojar, 2005).

The pre-operative clinical history can affect the risk of bleeding and developing ACT following cardiac surgery. For example, patients who have taken Aspirin, warfarin, clopidogrel, heparin, or IIb/IIIa glycoprotein inhibitors pre-operatively, and are then placed on cardiopulmonary bypass (CPB) for the surgical procedure are at higher risk for developing post-operative bleeding (Bojar, 2005; Karthik, Grayson, McCarron, Pullan, & Desmond, 2004).

Peri-operatively, hemodilution can influence post-operative bleeding. Hemodilution can occur as a consequence of aggressive intravenous (IV) fluid administration. It can also result from the use of CPB, especially if bypass is sustained for longer than three hours (Bojar, 2005). Aggressive IV fluid administration and CBP dilute clotting factors, resulting in coagulopathy. The result is a decrease in the platelet count by up to 30% to 50%, thus increasing the potential for bleeding and development of ACT (Bojar, 2005).

Hypothermia is responsible for bleeding complications in the immediate post-operative period and can be a contributing factor to ACT. Hypothermia occurs when core body temperature is below 35[degrees]C. The effects of hypothermia include vasoconstriction, hypoxic tissue damage, coagulation alterations, and changes in the microcirculation. Hypothermia inhibits the function of platelets, which are essential for control of bleeding and coagulation. Platelets are, thus, rendered less effective and result in clotting impairment and bleeding (McCance & Huether, 2006).

Post-operatively, key serum laboratory values should be assessed for the risk of ACT. These values include a significant drop in the hemoglobin level attributable to active bleeding, prerenal azotemia due to renal hypoperfusion during the early stages of decreased cardiac output (Russo et al., 1993), and a decrease in the number of platelets, which is indicative of a platelet dysfunction or defect. An example of thrombocytopenia is heparin-induced thrombocytopenia (HIT). This occurs after the patient has been exposed to heparin, which is commonly used during cardiac surgery. HIT results in a reduction in the number of circulating platelets and, as a consequence increases the risk of further bleeding and abnormal clotting.

Heparin rebound effect is another post-operative complication that leads to bleeding in the post-operative cardiac surgery patient. This occurs when heparin reappears in the blood stream a few hours following post-operative protamine administration. Signs of heparin rebound may include an increased volume of chest tube losses, sanguineous oozing at dressing sites, or an increase in the partial thrombplastin time (PTT) on coagulation tests. Increased PTT can be caused by incomplete heparin reversal due to an inadequate dose of protamine or by heparin being released from tissue stores after protamine has been metabolized and is no longer effective. Heparin rebound effect re-exposes the patient to heparin and increases the risk of bleeding and development of ACT (Bojar, 2005).

It is important for CCNs to realize that the risk for ACT in the cardiac surgery patient persists for several days post-operatively. For example, a significant event that may lead to the development of ACT is the removal of epicardial pacing wires. Epicardial pacing wires, which are generally removed on postoperative day five, have the potential to cause ACT by lacerating or disrupting fresh graft sites and causing bleeding into the pericardial sac (Abu-Omar, Guerrieri-Wolf, & Taggart, 2006; Reade, 2007). Thus, the CCN must be diligent in assessing the patient for signs of bleeding and ACT following the removal of the epicardial pacing wires.

Caring for the patient with ACT

Despite diligent efforts to prevent ACT, post-op cardiac surgery patients can and do develop this life-threatening complication. Hence, CCNs play a key role in the early detection of ACT. Recognizing the specific signs of ACT is of paramount importance in order to establish an accurate etiology of cardiogenic shock. This, in turn, will lead to appropriate diagnosis and optimal management of the patient with ACT.

Signs of ACT. As ACT develops, impairment of right ventricular diastolic filling and subsequent decrease in blood volume in all four cardiac chambers occurs. This results in decreased stroke volume and cardiac output with the initial presenting signs of tachycardia and peripheral vasoconstriction (Hawley & Dreher, 2002). These signs of compromise signal the early phase of cardiogenic shock with adrenergic compensation, and the release of systemic catecholamines to promote an improvement in cardiac function. Consequently, the heart rate increases and peripheral vasoconstriction develops to shunt blood away from less vital organs like the skin, kidneys, and splanchnic arteries toward the heart and brain (McCance & Huether, 2006). Hypotension occurs as the compensatory mechanisms fail. As well, a change in the patient's mental status, such as confusion or anxiety, may signal a decrease in cerebral perfusion (Hawley & Dreher, 2002).

Pulsus paradoxus is a key clinical sign of ACT. This phenomenon is defined as a decrease in the systolic blood pressure of greater than 10 mmHg between expiration and inspiration

(McCance & Huether, 2006). In the patient with ACT, pulsus paradoxus is the result of impairment of diastolic filling of the left ventricle, and the subsequent decreased blood volume in all four cardiac chambers. Pulsus paradoxus can also be observed by a decrease in the systolic upstroke on an arterial pressure monitor. If using invasive pulmonary hemodynamic monitoring, there may be an equalization of right atrial pressures and pulmonary capillary wedge pressures. This occurs as the pericardium becomes tauter on inspiration, as a result of diaphragmatic traction and is called the inspiratory traction sign (Yarlagadda & Hout, 2006).

Beck's triad, defined as muffled heart sounds, hypotension, and a narrowed pulse pressure is described in the literature as a distinctive sign of ACT. The patient may also present with distended neck veins as the pressure increases in the pericardial sac, impeding the forward flow of blood (Hawley & Dreher, 2002).

Specific to CT losses, there are two warning signs for ACT. The first is the sudden slowing or cessation of CT bleeding when bleeding had previously been noted. This is indicative of clotting of chest tubes and the development of increased pressure within the pericardium. The second is the development of a sudden large volume of chest tube blood loss, which is a sign of acute bleeding and may rapidly lead to ACT (Unsworth-White et al., 1995).

Although electrocardiogram (ECG) tracing changes are not definitive, they may be a sign of the development of ACT. Significant ECG changes may include tachycardia, atrial arrhythmias, or low voltage QRS complexes, due to a decrease in cardiac output. ST segment changes or T wave abnormalities may occur and are suggestive of ischemia or infarction (Russo et al., 1993).

Managing risks for developing ACT. A comprehensive assessment of the risk factors for ACT provides the CCN with the insight required to manage these risks. Persistent postoperative bleeding must be treated aggressively to avoid the development of ACT. The recommendation is to begin with less-invasive strategies to rectify the bleeding. Therefore, maintaining chest tube (CT) patency is critically important to prevent the compartmentalization of fluid within the pericardial space. The CCN plays a central role in the management of CT drainage in the post-operative cardiac surgery patient. According to Unsworth-White et al. (1995), suspicious blood loss in the cardiac surgery patient population is defined as drainage exceeding 500 ml in the first hour, greater than 400 ml an hour in each of the first two hours, 300 ml an hour in each of the first three hours, more than 1,000 ml in the first four hours or greater than 1,200 ml in the first five hours. During ongoing post-operative bleeding, the risk of ACT increases when the drainage is blocked by an occluded chest tube (Bojar, 2005).

A variety of methods to restore patency to chest tubes are commonly practised, including stripping, tapping, and milking the tubes. According to a fairly recent Cochrane Review (Wallen, Morrison, Gillies, O'Riordan, Bridge, & Stoddart, 2002), there is insufficient evidence to support or refute the relative efficacy of any of these ACT prevention strategies. However, the stripping of chest tubes remains a controversial practice because the generation of negative pressure of up to 1,500 mmHg within the CT, can potentially result in damage to the surrounding tissue, including the bypass graft sites (Lancey, Gaca, & Vander Salm, 2001). Recommendations are that gentle milking or stripping of chest tubes should be employed to maintain CT patency, but aggressive stripping is not advised (Bojar, 2005).

Important strategies to prevent bleeding in the post-operative cardiac surgery patient include achieving normothermia and treating agitation and hypertension. Interventions to achieve normothermia include warming the ventilatory circuits in mechanically ventilated patients, using warming blankets, and administering warmed intravenous fluids. These actions reverse hypothermia and decrease the risk of coagulopathy (Bojar, 2005). The treatment of shivering and agitation are also important in the prevention of post-operative bleeding. Careful consideration should be given to administration of effective doses of medications to prevent shivering and agitation in the immediate post-operative period. Similarly, hypertension should also be addressed without delay during this period. Following effective pain and anxiety control, vasodilators or beta-blockers should be considered if hypertension is uncontrolled in the immediate post-operative period (Bojar, 2005).

Administration of specific blood products is an important strategy to consider when significant bleeding occurs in the early post-operative period. For example, patients who have been on warfarin pre-operatively or have hepatic dysfunction are prone to clotting factor deficiencies and, therefore, may benefit from a transfusion of fresh frozen plasma (FFP). An indication for the need for FFP is an elevated PTT, which signals either a disturbance in the intrinsic coagulation cascade or supports evidence of a persistent heparin effect on coagulation parameters. In the presence of anemia, the administration of packed red blood cells (PRBCs) should be given simultaneously with other blood products to prevent myocardial tissue damage related to insufficient tissue oxygen supply (Bojar, 2005). Because hemodilution is another indication for PRBCs, it is critically important to examine the hematocrit along with the hemoglobin concentrations. Finally, the CCN must be aware that PRBCs do not contain clotting factors. Therefore, this should not be used as the sole management strategy for the reversal of bleeding complications (Bojar, 2005).

Autotransfusion of shed blood, as a bleeding management strategy should be implemented with caution. If administered in amounts of greater than 1,000 ml, autotransfusion may worsen a coagulopathy by elevating the prothrombin time (PT), PTT and D-Dimer and reduce the fibrinogen levels leading to a potential increase in post-operative bleeding. However, if given in smaller amounts, ranging from 500 ml to 1,000 ml, autotransfused blood has been found to be effective in reducing transfusion requirements, while not worsening the coagulopathy (Bojar, 2005).

Pharmacological modalities are another important strategy in the prevention and management of bleeding in the post-operative cardiac surgery patient. For example, Tranexamic acid, an antifibrinolytic drug, has been found to be useful in decreasing the associated mediastinal chest tube losses following cardiac surgery. Tranexamic acid competitively inhibits the activation of fibrinolysis, which, if left untreated, may lead to significant bleeding (Schneeweiss, Seeger, Landon, & Walker, 2008; Shore-Lesserson, Reich, Vela-Cantos, Ammar, & Ergin, 1996).

Protamine sulfate, a heparin antagonist, is another pharmacological agent used to control post-operative coagulopathy and bleeding in the cardiac surgery patient. It is usually given in doses of 25 mg to 50 mg when the PTT is elevated or when increased bleeding is observed in relation to CT loss or sanguineous dressing sites post-operatively.

Aprotinin was a frequently used plasmin inhibitor in the past. However, it has recently been reported to increase the risks of allergic reactions, renal failure, stroke, myocardial infarction, and mortality rates (Ray, 2008; Schneeweiss et al., 2008). In fact, Health Canada (2007) released an advisory on the use of Aprotinin related to concerns of life-threatening allergic reactions and increased risk of renal failure in patients who received this drug. Therefore, the use of Aprotinin is no longer common practice.

Diagnosis of ACT. Factors to consider in the diagnosis of ACT are multifaceted. Hence, it is important to take a systematic approach when considering the differential diagnosis. The process of diagnosing ACT begins with the identification of the clinical signs and is confirmed through the use of key diagnostic tools.

Chest x-ray radiographic findings that show a widened mediastinum or displacement of the cardiac silhouette are indicative of fluid or a blood clot in the mediastinal space (Bojar, 2005). A characteristic "water-bottle" shaped configuration of the cardiac silhouette may also be observed (McCance & Huether, 2006; Yarlagadda & Hout, 2006). The most definitive tool for diagnosing ACT is a 2D echocardiogram (Chadwell, 2006). Echocardiograms are able to detect fluid collections in amounts as little as 20 ml (McCance & Huether). In the presence of ACT, the echocardiogram findings will reveal collapse or partial collapse of the atria or ventricles related to the development of the pericardial effusion (McCance & Huether). As well, there will be distention of the inferior vena cava and a fluctuation in flow of mitral and tricuspid filling velocities with respiratory variation (Kuvin et al., 2002).

There are two possible approaches when performing an echocardiogram. The first is the transthoracic method, a noninvasive procedure that uses an ultrasound probe placed on the patients' chest. The limitation of this view is the inability to see posterior compartmented effusions. The second method, a transesophageal approach, is used in more complex cases and is considered to be superior because this approach is more invasive, requiring pharyngeal intubation. This test is generally performed only when there is a suboptimal transthoracic view (Chadwell, 2006; Russo et al., 1993).

Management of ACT. ACT is one of the major reasons for cardiac re-operation. For the patient who is diagnosed with ACT, re-sternotomy is generally the only option to determine and alleviate the underlying cause of the bleeding. Ideally, the patient is returned to the operating theatre. However, if the patient has a cardiac arrest, emergent re-sternotomy in the intensive care unit (ICU) setting may be required (Fiser, Tribble, Kern, Long, Kaza, & Kron, 2001). Patients who require re-sternotomy are more likely to require inotropic agents. They will also have a longer ICU stay, and an overall prolonged hospital stay than those patients who do not require this additional procedure (Karthik et al., 2004). In addition, patients who develop ACT are at higher risk of mortality than those who do not develop this complication. Therefore, prevention and early detection of ACT is central to optimizing cardiac surgery patient outcomes.

Conclusion

ACT is a rare, but life-threatening complication following postoperative bleeding in the cardiac surgery patient population. Therefore, anticipating this complication is central to optimal patient care. Critical care nurses are instrumental in affecting the outcome of these patients. This article has provided a comprehensive overview of the pathophysiology, the assessment, and management of ACT risk, and the care of the patient with ACT. This knowledge will enable the CCN to anticipate and prevent this life-threatening complication and, thus, optimize outcomes for this complex surgical population.

References

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By Sandra L. Christie, RN, BN, and Jo-Ann V. Sawatzky, RN, PhD

About the authors

Sandra L. Christie, RN, BN, Graduate Student (Nurse Practitioner Stream), Faculty of Nursing, University of Manitoba.

Jo-Ann V. Sawatzky, RN, PhD, Associate Professor, Faculty of Nursing, University of Manitoba.

Address for correspondence: Sandra L. Christie, Cardiac Sciences Program, St. Boniface General Hospital, 409 Tache Ave., Winnipeg, MB R2H 2A5. Phone (204) 235-3511; e-mail: schristie@sbgh.mb.ca
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Author:Christie, Sandra L.; Sawatzky, Jo-Ann V.
Publication:Dynamics
Article Type:Clinical report
Geographic Code:1CANA
Date:Dec 22, 2008
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