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HEMODYNAMICS
Hemodynamics can be both monitored by noninvasive and invasive techniques. The use of a blood pressure cuff to obtain a patients blood pressure is a simple but very important noninvasive technique in which to get important hemodynamic information about a patient. This part of the web site though is going to focus on invasive monitoring of hemodynamics as this can be one of the most challenging things to learn as a new Coronary Care Unit nurse. Invasive hemodynamic monitoring can actually measure pressures within the heart. Invasive hemodynamic monitoring can be used for early detection, identification, and treatment of life-threatening conditions such as heart failure and cardiac tampanade. Then it can be used to monitor the therapy that is used to treat these conditions, including the use of different medications/ and or mechanical support. It is important for the nurse using hemodynamic monitoring to be able to effectively and accurately use this modality. Inaccurate data obtained from the use of hemodynamic monitoring can have serious consequences in the treatment of the patient.
One of the most widely used methods of hemodynamic monitoring is the use of the Swan-Ganz Catheter. Through the use of the Swan-ganz catheter one can measure central venous pressure (CVP) and obtain the patients Cardiac Output via the Thermodilution Method. Another method for obtaining the cardiac output is using the Fick Method ( one can find information regarding this method elsewhere on this website ). Another port sits in the pulmonary artery and measures pulmonary artery pressures. This port also has a balloon that when inflated measures the pulmonary artery wedge pressure (PCWP). No more than 1.5ml of air should be used to inflate this balloon. Important to note also that if the wave form on the monitor shows the Swan to be in the permanent wedge position (without having blown the balloon up) a physician must be immediately contacted and the Swan needs to be repositioned. If left in the permanent wedge position the pulmonary artery can rupture which is a life-threatening condition. Below you will see the wave forms that occur with the insertion of the Swan-ganz Catheter: There are transducers that are part of the Swan-ganz system. These are attached to the ports that monitor the CVP and the pulmonary artery (PA) pressures. It is of the utmost importance that these transducers be at the correct level. They should be level with the phlebostatic axis (mid-axillary and fourth intercostal space). Generally these transducers are leveled and zeroed at least every four to eight hours. Incorrect leveling of the transducers can significantly alter the hemodynamic results that you get and thus possibly adversely effect the treatment of the patient. There are various aspects of the patients hemodynamics that can be measured with the Swan-ganz catheter. Preload is the degree of muscle fiber stretching present in the ventricles right before systole (the amount of blood available to be ejected at systole). CVP affects right ventricular preload. The normal values are 2-8mm Hg. This also measures right ventricular end diastolic pressure. Left ventricular preload is reflected by the PCWP which measures left ventricular end diastolic pressure. PCWP measures the additional fluid, which stretches the left ventricle just prior to systole. This is determined by the volume of blood in the right ventricle at the end of filling. The normal PCWP values are 4-12mm Hg. Afterload is the resistance against which the ventricles must pump in order to eject blood. Cardiac output and afterload have an inverse relationship. The lower the cardiac output the greater the afterload. Measurements that can be obtained using different hemodynamc findings: *Systemic vascular resistance (SVR): SVR=MAP-CVP/CO*80. This reflects left *Pulmonary vascular resistance (PVR) is a reflection of right ventricular afterload. *Cardiac Output (CO): CO=HR*SV dynes/\cm2.
*Heart Rate is one of the most overlooked hemodynamic parameters. *Stroke Volume (SV) is the amount of blood ejected with each beat of the heart. Hemodynamic Parameters *Mean Arterial Pressure (MAP): 70-90mm Hg Complications that can be associated with the use of the Swan-ganz catheter are increased risk of infection, thrombosis, and emboli. As mentioned earlier the wave form must be monitored closely to monitor for the possibility of the catheter winding up in the permanent wedge position which can rupture the pulmonary artery, Another possible complication can be caused by ventricular irritation from the catheter. Again the wave form must be closely monitored to watch for the possibility of the catheter slipping back into the right ventricle. Irritation of the right ventricle when this occurs can throw the patient into ventricular tachycardia. Again this is a situation where the physician must be immediately notified so that the catheter can be reposition. The Swan-ganz catheter should never be left in the right ventricle. Sometimes the balloon will not wedge. Sometimes this is simply because the patients pulmonary artery is too large for the balloon to occlude it. When this occurs the RN should use the PAD pressure to represent the PCWP. At other times when the balloon will not wedge the catheter has simply migrated and needs to be repositioned. Hemodynamics is a very important topic for the Coronary Care Unit nurse to understand. The above information is meant only as an introduction to the topic and further study is suggested. *The information on this web page was in part taken from Nurse Bob’s Hemodynamic Overview |
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