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Meeting the special needs of the open heart surgery patient.

Reliable and efficient point-of-care testing is advantageous in many clinical settings.|1~ For the open heart surgery patient, it is essential.

Candidates for open heart surgery have unique pathophysiologic needs. Because of the increasingly serious nature of patients' medical conditions, the clinical staff faces complex therapeutic decisions. Open heart patients are older than the average hospital patient; a growing percentage are older than 70 years. They are very ill, often critically so; they may have multi-organ failure, including liver and kidney dysfunction and cardiogenic shock.|2~ Their hemodynamic parameters are frequently unstable. Treatment typically includes multiple drugs. Mechanical devices are sometimes needed to provide circulatory support.

During heart-lung bypass, venous blood is taken from the circulation by means of cannulae placed in the superior and inferior venae cavae. The blood bypasses the heart and lungs and enters the circuit of the heart-lung machine. At this point, circulation becomes extracorporeal: The blood literally travels outside the body. Oxygenation takes place in the machine's oxygenator or artificial lung much as it does in the human lung.

The term "artificial lung" may be more accurate since the device not only oxygenates the blood but also removes carbon dioxide from it. The C|O.sub.2~ must be removed in the correct proportions to avoid excessive accumulation, which can lead to respiratory acidosis, and excessive elimination, a precursor of respiratory alkalosis.

Once the blood has been oxygenated and filtered and its temperature regulated, it is returned to the arterial circulation through a cannula. Proper oxygenation throughout surgery is crucial for the patient's well-being. Several professional medical organizations have urged that the total turnaround time for blood gases during open heart surgery be less than five minutes.|3,4~

* CPB. Cardiopulmonary bypass (CPB) involves distinctive pathophysiologic changes. Hemodilution and hypothermia with loss of pulsatile flow cause hemodynamics and organ perfusion to change markedly and constantly. Metabolic responses are further affected by anesthesia, heparin, protamine, the cardioplegic solution, and activation of complement.

Critical events occur during performance of the open heart procedure at defined time intervals. These include the events described in Figure I.

The first 12 hours after surgery represent a critical interval for the patient in the surgical heart unit. Hemodynamic instability with low cardiac output, arrhythmias, bleeding dyscrasia, low urine output, and arterial blood gas disorders may occur singly or in combination during this phase.

The unique needs of the cardiac surgery patient compound the anticipated needs of any sick patient undergoing a surgical procedure. In all patients undergoing surgery, laboratory testing used for monitoring and intervention must meet these criteria:

1. High reliability and reproducibility

2. Rapid determination

3. Frequent determination

4. Ease of performance

5. Low cost

6. Minimal use of labor, such as medical and respiratory technologists

Timely results on the following analytes are critical to manage the patient properly before, during, and after surgery: blood gases (pH, p|O.sub.2~, pC|O.sub,2~, electrolytes (K+, iCa++), hemoglobin or hematocrit, and coagulation studies in managing heparin use.

* Retrospective study. The experience of a community-based high-volume cardiac surgery service at the authors' hospital (Christ Hospital and Medical Center, Oak Lawn, Ill.) was reviewed retrospectively. Use of a portable analyzer was compared with traditional testing in the laboratory. The device was also considered in relation to the cardiac surgery service at another community hospital in the area (Edward Hospital, Naperville, Ill.) versus its integration into a preexisting program (Christ Hospital and Medical Center, Oak Lawn, Ill.).

Open heart surgery was performed on 564 patients at Christ Hospital and Medical Center in 1989 and on 618 patients in 1990. In 1989, all lab tests were performed in the traditional fashion. ABGs were sent to the respiratory lab for analysis, while electrolytes and H/H were performed by a medical technologist using an analyzer in a satellite lab adjacent to the operating room. In 1990, all ABGs, electrolytes, and H/Hs were performed with point-of-care devices in the adult and pediatric open heart suites.

Use of the device decreased the turnaround time-measured from the time at which the specimen was obtained to receipt of the test result--from an average of 25 minutes to less than three minutes. The device made it easy to obtain and rapidly analyze multiple specimens, which are needed more frequently in the hemodynamically unstable patient than in most other patients.

Having the point-of-care device available in the operating room made it possible for laboratory personnel to return to the central laboratory. As a result, it was not necessary to hire additional laboratorians or to allocate additional FTEs for lab support when the new cardiac surgery service was being established. The overall operating budget to provide these services for the open heart program was substantially reduced because of the reduction in labor. Current fixed or decreasing Medicare reimbursement makes such a saving especially welcome to the hospital.

* Resistance. Even technology that saves time, money, and personnel may be easier to introduce in a new cardiac surgery service than in an existing facility that already possesses satellite testing capabilities. The prospect of phasing in a point-of-care testing device while phasing out on-call lab facilities or staff may not be well received. Factors that bolster objections include anticipated budgets and revenue for individual cost centers, personnel problems, and, not uncommonly, issues of control and ego. Resistance may take the form of a battle over "turf".

The situation falls within the responsibility of the hospital's quality assurance program. Recognizing the needs of all disciplines involved and working together from the outset to integrate such innovations help effect a smoother transition and a more willing acceptance of evolving technology. Cooperation and communication with the lab are key.

Experience with point-of-care testing devices in the OR and intensive care unit has shown the authors that the instruments improve patient care. The use of the equipment markedly improves the therapeutic turnaround time. As a result, appropriate changes in therapy can be made at critical times during the open heart procedure. The quality of care, especially for the hemodynamically unstable patient, is thereby enhanced at a lower overall cost.

1. Zaloga, G.P.; Hill, T.R.; Strickland, R.A.; et al. Bedside blood gas and electrolyte monitoring in critically ill patients. Crit. Care Med. 17(9): 920-925, September 1989.

2. Jones, E.L.; Weintraub, W.S.; Craver, J.S.; et al. Coronary bypass surgery: Is the operation different today? J. Thoracic Cardiovascular Surg. 101(1): 108-115, January 1991.

3. Scannell, G.J.; Brown, G.E.; Buckley, M.J.; et al. Report of the Inter-Society Commission for Heart Disease Resources. Optimal resources for cardiac surgery: Guidelines for program planning and evaluation. Circulation 52: A-23, 1975.

4. Emergency Care Research Institute. Risk analysis: Cardiopulmonary perfusion equipment. J. Extra-Corporeal Tech. 19: 238, 1987.

Figure I

Critical events during open heart procedures

1. Induction phase of anesthesia

Deepening levels of anesthesia affect circulatory dynamics and metabolic changes on a cellular level. Blood pressure may increase or decrease markedly. Myocardial and respiratory depression may occur, with resulting changes in arterial blood gases and electrolytes.

2. Initiation of cardiopulmonary bypass (CPB)

The heart is unloaded by partial or full removal of all venous return to the heart. The heart rhythm alters, frequently becoming bradycardic and often arresting rapidly. The need of the heart muscle cell for oxygen decreases considerably in the beating, empty (vented) state.

3. Cooling phase

The heart may arrest 2 |degrees~ to cold or as a result of various cardioplegic solutions instilled at this time to achieve electromechanical arrest, placing the heart in a flaccid state. Cardioplegic solution contains high concentrations of potassium along with other chemicals. When infused, potassium causes an immediate arrest of the heart, and the low temperature begins to reduce the heart's oxygen consumption. Cellular metabolic processes are gradually altered so that the situation reverts to anaerobic metabolism. The oxyhemoglobin curve shifts to the left, increasing the difficulty of oxygen release to the cells.

4. Maintenance of CPB

The effect of nonpulsatile flow remains unclear. The acceptable flow rates of 2-2.4 L/min./|m.sup.2~, achieved through the heart-lung machine, are adequate for tissue perfusion.

5. Rewarming and reperfusion

This stage, when ischemic damage may occur, is considered the critical time by many investigators. Too-rapid rewarming (less than three minutes for each incremental degree Celsius) may cause nitrogen to come out of solution. High-pressure reperfusion may enhance myocardial cellular edema, affect membrane permeability, and increase the ischemic changes, rarely resulting in a "no-reflow" phenomenon. Buckberg has advocated a warm cardioplegic dose at low pressure before release of the aortic cross-clamp to enhance recovery of the heart muscle. Arterial p|O.sub.2~, venous |O.sub.2~ sat, and pH must be managed very closely through this stage, along with electrolytes (K+ and iCa++).

6. Separation from CPB

In this phase, the heart must take over on its own. From time to time, especially in preoperatively impaired heart muscle, separation from CPB must be done gradually, with careful monitoring of optimal preload and afterload, as well as hematocrit, electrolytes (especially K+ and iCa++), and acid-base-balance.

7. Stabilization after CPB, and before and after chest closure

The heart must respond appropriately after repair such as coronary bypass or valve replacement, then return to adequate contractility and function. All these steps are strongly influenced by volume and metabolic parameters. Chest closure alters pulmonary dynamics and venous return and may transiently result in low cardiac output.

Figure II

Major impediments to acceptance of a point-of-care device into an existing open heart surgery service

* Turf battles

Laboratory for H/H and electrolytes

Respiratory therapy for ABGs

Nursing department


Private practitioner vs. hospital

* Cost center allocation

* Utilization of existing equipment

* Utilization of existing personnel

* Hospital responsibility for qualify assurance

Figure III

How point-of-care testing enhances patient care

* Portability; monitoring at bedside (OR, ICU)

* Real-time results

* Constant availability, especially useful in emergencies

* Makes "alpha stat" easy

* Ease of use

* Confidence of clinicians in the extent of quality control

* Multi-service use (cardiac, vascular, trauma)

Dr. Davis is medical director of the cardiovascular surgery program at Edward Hospital in Naperville, III., and in private practice with Cardiovascular Renal Consultants in Naperville and at Christ Hospital and Medical Center in Oak Lawn, III. Dr. Pappas is a cardiovascular surgeon in private practice with the same group, for which Foody is senior perfusionist.
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Title Annotation:MLO Special Issue: Point-of-Care Testing
Author:Davis, Zen; Pappas, Pat; Foody, Walter
Publication:Medical Laboratory Observer
Date:Sep 1, 1991
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