Traumatic Cardiac Tamponade - MUN
Transcript of Traumatic Cardiac Tamponade - MUN
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Traumatic Cardiac Tamponade
Shane KF Seal19 November 2003
POS
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Objectives
• Definition• Pathophysiology• Diagnosis• Treatment
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Cardiac Tamponade
• The decompensated phase of cardiac compression resulting from increased intrapericardial pressure
• Physiologically, tamponade is a continuum
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• To tamponade the heart, the contents must:
1. Fill the pericardial reserve volume2. Increase at a rate exceeding pericardial
stretch3. Exceed the rate at which venous blood
volume expands to support the small normal pressure gradient for filling the heart
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Incidence
• In trauma, tamponade is most commonly associated with penetrating injuries
• Can occur with blunt chest trauma causing the pericardium to fill with blood from the heart, great vessels, or pericardial vessels
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Acute Tamponade
• May be referred to as ‘surgical’ tamponade
• In the acute setting, tamponade can quickly overwhelm compensatory mechanisms
• As little as 150cc of blood and clots can be rapidly lethal
• Chronic: as much as 1L
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Pathophysiology
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Transmural Pressure
• Filling pressure of the heart is the transmural pressure (cavity pressure minus intrapericardial pressure)
• Negative transmural pressures can cause atrial and ventricular collapse
• Chamber collapse coincides with a drop of 15-25% of CO
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Pressure-Volume Relations
• Pericardium has a J- shaped pressure volume curve
• Increasing fluid forces the heart to function on the steep portion of the curve
• At this point, small increases have large effects (***Tx***)
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Tamponade – Early Stages
• Initially, fluid fills up the pericardial reserve volume (flat portion of curve)
• Eventually this exceeds the limit of pericardial stretch
• The increasing pressure ultimately can exceed the atrial and ventricular filling pressures (phasically negative transmural pressure)
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Tamponade – Late Stages
• Right heart chambers are affected before the left
• Once the pressure from tamponade is great enough to overcome LV pressure, CO decreases dramatically
• ‘pure’ tamponade is when diastolic pressures in the LV & RV equilibrate with mean pressures in the LA & RA
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Coronary Blood Flow
• With normal coronary arteries, coronary blood flow is adequate to support aerobic metabolism
• This is due to a proportionate reduction in cardiac work: the ventricles are underloaded and operate at the lower end of the Frank-Starling Curve
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Frank-Starling Curve
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Compensatory Mechanisms
• Elevated CVP: improves diastolic filling against the increased intrapericardial pressure
• Tachycardia: to maintain CO• Vasoconstriction: peripheral vascular
resistance to maintain BP
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Other Organ Flow
• Renal and cerebral blood flow are partly supported by compensatory mechanisms
• Significant hepatic and mesenteric ischemia occurs secondary to increased peripheral vascular resistance
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Diagnosis
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Clinical Findings
• Beck’s Triad1. Hypotension2. Muffled Heart Sounds (with a relative
accentuation of S2)3. Elevated Central Venous Pressure
• High index of suspicion must be used with pre-existing HTN, noisy ERs, and hypovolemia
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Clinical Findings
• Kussmaul’s Sign (Inspiratory increase or lack of fall of JVP)
• Oliguria• Tachycardia• Tachypnea• Pulsus Paradoxus• Low-voltage EKG complexes• EKG Electrical Alternans
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Pulsus Paradoxus
• Systolic drop in arterial pressure of 10mmHg or more during normal breathing
• The difference between the pressures when systolic sounds are first heard and then are continuously heard gives the magnitude
• Usually signals large reductions in LV/RV volumes with equilibration of mean pericardial and all cardiac diastolic pressures
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Pulsus Paradoxus
• Deep x descent and blunted y descent can be seen on RAP tracing
• Diastolic pressure equalization causes a relative RV filling at the expense of the LV
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Electrical Alternans
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Chest X-Ray
• Enlarged heart shadow on radiography with clear lungs
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Echocardiography
• Short Axis/Cross-Section View of the Heart• PE = pericardial effusion
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Echocardiography
• 5% False -ve• Echo-Doppler
signs are less accurate
• Fluid in pericardium can be detected as part of a focused abdominal U/S exam
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EKG
• Can be normal• Often nonspecifically altered – ST-T
wave abnormalities• End-stage tamponade will show vagally
mediated bradycardia and PEA (electromechanical dissociation)
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Treatment
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Medical Treatment
• Experimental evidence is conflicting• Ultimately ineffective• Aimed to support compensatory
mechanisms, expand intravascular volumes, support inotropy and blood pressures
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Surgical Intervention
• Echocardiographically monitored pericardiocentesis or surgical drainage are treatments of choice
• In cases with extreme urgency, percutaneous needle paracentesis is indicated, particularly when the patient has not responded to resuscitative efforts
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Percutaneous Needle Paracentesis
• Subxiphoid approach safer than parasternal (decreased PTX, coronary artery laceration)
• 45º Head Tilt• 18-23 gauge spinal needle, inserted just
below and to the left of the xiphoid towards the Midclavicular point
• Continuous aspiration
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Percutaneous Needle Paracentesis
• EKG guidance with an alligator clip on the needle can identify cardiac penetration (ST elevation or ectopic beats with myometrium contact; deep Q waves once in the ventricle; PR elevation with atrial contact)
• Removal of only 20cc of blood can be life saving due to the position on the pressure- volume curve
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Surgical Drainage
• Subxiphoid pericardial windows and thoracoscopic drainage are effective treatments that have little morbidity and can be performed with local anesthesia
• However, it is preferable to have the patient in the OR for these procedures
• Blunt trauma patients with PEA are not candidates for resuscitative thoracotomy
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Final Notes
• The volume drained can not predict cardiac compression that still may exist
• Clots add a confounding issue with percutaneous pericardiocentesis
• All trauma patients with positive pericardiocentesis will require open thoracotomy or median sternotomy for further inspection of the heart