Emergency Medicine News:
Dr. Bruen is a fellow in critical care medicine and emergency cardiology at Hennepin County Medical Center in Minneapolis. He has special interest in stabilization, resuscitation, hemodynamic evaluation, and emergency cardiovascular care.
A 68-year-old woman with a history of schizophrenia, severe coronary artery disease, hypertension, and type 2 diabetes mellitus was found in her bed minimally responsive by staff at the group home where she lived. She had been discharged from the hospital two days earlier with a diagnosis of segmental pulmonary embolism and on Coumadin anticoagulation. Lower extremity Doppler ultrasounds were negative for deep vein thrombosis during that hospitalization.
EMS brought her to the emergency department, and had intubated for airway protection. She was febrile, tachycardic, and hypotensive, and had a hemoglobin of 4 g/dL. An abdomen/pelvis CT revealed a large retroperitoneal hematoma. She was admitted to the ICU in critical condition. She was fluid resuscitated, and started on norepinephrine. A central venous catheter was placed, and the EKG strip shown was obtained.
Central venous pressure (CVP) reflects the right atrial pressure and by inference the right ventricular filling pressure. Using the Frank-Starling relationship, higher filling pressures are required to generate larger right ventricular stroke volumes or to maintain the same stroke volume in the setting of right ventricular dysfunction. Unfortunately, there is a tendency to concentrate only on this average value. A tracing of the central venous pressure shows a series of waves. If we understand the origins of these waves, close observation of the waveform can provide invaluable additional hemodynamic information.
It is helpful to evaluate a CVP tracing in conjunction with an ECG. The mechanical events during the cardiac cycle are responsible for the sequence of waves seen in the CVP. Coinciding with the ECG p wave and atrial contraction is an increase in right atrium pressure seen as the a wave. Blood leaves the atrium through the tricuspid valve into the ventricle, and the pressure in the atrium then decreases. This is denoted as the x descent on the waveform. The ventricles contract at the beginning of systole, marked by the QRS complex, and the tricuspid valve closes, causing a temporary interruption in the x descent seen as the c wave. The atrium begins filling in late systole by passive return from the vena cavae. The pressure peak, v wave, is released when relaxation of the ventricle occurs to the point that the tricuspid valve opens and blood from the atrium fills the ventricle. This decrease in pressure is designated the y descent.
Find a complete case discussion and more information on interpreting the CVP waveform by reading Spontaneous Circulation in EMN's iPad App on Feb. 5 or in the Spontaneous Circulation blog at http://bit.ly/EMNblogPage on Feb. 12, where additional EKGs are also available.
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