Questions...need assistance!

[srknurse]

I am an RN that is tutoring a nursing student presently in advanced med-surg. I am not a practicing OR/ICU nurse, and so she had the following questions...that I had difficulty answering. Can someone help me? Thanks!

Why is hemodilution so important for heart bypass if the blood is

already being heparinized? Why is it important to dilute and bring the Hct

down so low?

In cardiopulmonary bypass, blood is still circulating to the body but

not the coronary arteries/heart? The machine moves the oxygenated blood

back into the aorta for circulation, but isn't the aorta clamped off to

keep blood out of the heart?

Why would a pacemaker have a 1st letter identification 0 for "no

chamber paced", or 2nd ) for "no chamber where intrinsic activity is sensed",

or 3rd ) for "no response after sensing intrinsic rate"?

How does nursing management differ between patients with temporary and

permanent pacemakers?[/i]

[Corey Narry, MSN, RN, NP]

Wow, are you sure this is a nursing student asking these questions (especially the first one)? They sound like questions asked of cardiothoracic surgery and anesthesia fellows. Definitely way too advanced for nursing students.

Here's what I found regarding the first question...

From an excerpt in DeFoe, G., et al. Lowest hematocrit on bypass and adverse outcomes associated with coronary artery bypass grafting. Ann Thorac Surg 2001;71:769-776.

"Hemodilutional anemia is a frequently used technique during cardiopulmonary bypass. Since the development of CPB, hemodilutional anemia has been used to reduce blood viscosity, allowing maintenance of baseline blood flow during hypothermic CPB without the need for elevated arterial pressures [1,2]. This technique is believed to reduce the risks of adverse outcomes due to arterial hypertension such as aortic dissection and collateral blood flow to the coronary arteries during cross-clamping of the aorta. In addition, intraoperative exposure to autologous blood transfusions is reduced with the crystalloid priming techniques developed to induce hemodilutional anemia [3]"

1. Guyton A., Richardson T. Effects of hematocrit on venous return. Circ Res 1961;9:157-164.
   
2. Kaplan J. Cardiac anesthesia. New York: WB Saunders Co, 1993.
   
3. Cooley D.A., Beal A.C., Grondin P. Open heart operations with disposable oxygenators, 5 per cent dextrose prime, and normothermia. Surgery 1962;52:13-19

Regarding the second question...

The bypass machine removes unoxygenated venous blood through cannulation of the superior and inferior vena cava that pulls blood away from the body into the machine then returns oxygenated blood back through cannulation of the ascending aorta distal to the aortic clamp.

Regarding the third question...

I found a good wesbite that explains the letters better than I can type a response here:

http://www.hrsonline.org/swPositionStatementFiles/ps101035678.asp

Regarding the fourth question...

In cardiac surgery temporary pacemakers are, well... temporary, so the control center is externally located and the nurse has full access to the pacemaker settings. The wires are placed after completion of bypass and are implanted in the epicardium. Usually there are 2 atrial and 2 ventricular wires but surgeons do not always put both atrial and venrticualr wires. Because they are used in cases when arrhythmias are felt to be temporary or self-limiting, the nurse needs to check the underlying ryhthm more frequently and examine if the pacemaker is appropriately sensing and/or pacing the underlying arrhythmia.

Internal or permamnent pacemakers are implanted for permanent rhythm irregularities and are programmed once placed. They are later interrogated by the device rep or any trained specialist using equipment brough to the bedside. The nurse can not change settings but can use a round magnet in cases where the internal pacemaker needs to be turned off.

Others are welcome to take a shot at this...

[srknurse]

THANK YOU, THANK YOU, THANK YOU!!!!

I thought I was CRAZY, but you are right, these questions are way too advanced for many nursing students! I am an RN and didn't touch on these questions while in nursing school....THANK YOU!!!! I thought I was losing my mind!!!!!

[Wile E Coyote, ASN, RN]

To add the the nursing mgmnt of the diff. pacers...

A temporary pacer takes several forms, be they dedicated transvenous pacing catherters, a Swan with pacing ability, epicardial wires passed through the chest wall, good ole transcutaneous (external pads) and a few others. They have many differences (obviously) however, they all have one important difference from permanent pacers, in regards to safety. Any temporary pacing method, by nature, is less predictable, and requires closer monitoring. A transvenous pacing electrode can float, from pt repositioning as one example, and lose capture. There are many more examples, but the 'brass tacks' explaination is just this.......temporary pacing requires closer monitoring of the pulse generator, the delivery method (cath, wires, pads), the pt, and the monitor.