CASE REPORTS

Continuous Cardiac Output Measurements

Peter R. Lichtenthal, MD, and Leonard D. Wade, MS

C ONTINUOUS cardiac output (CCO) measurement first became clinically available in 1991.’ Now known

as the VigilanceiIntellicath Continuous Cardiac Output System (Baxter Edwards Critical Care, Irvine, CA), it uses a specialized pulmonary artery catheter that is capable of safely measuring a continuous time-averaged cardiac out- put.2 This system has overcome the problems associated with earlier designs and its performance has been summa- rized in several publications.3-h Whereas the most recent information confirms the accuracy of CC0,‘m9 these authors have often been asked if this technology was really useful, and could its use in light of its higher cost be justified. A case is described here where the use of the CC0 system had a direct impact on the postoperative care of a cardiac surgery patient.

CASE REPORT

A 67-year-old 79-kg man with a IO-year history of coronary artery disease was scheduled for repeat coronary artery bypass surgery. Nine years before this surgery, the patient had sustained a myocardial infarction and subsequently underwent coronary artery bypass surgery with an aneurysm repair. For 8 years he was controlled on medication until 1 year ago when he underwent laser percutaneous transluminal coronary angioplasty. After these proce- dures, the patient developed episodes of ventricular tachycardia that were treated by electrical ablation. Recent catheterization revealed severe coronary artery disease and a dyskinetic, hypoki- netic heart. Before surgery, the patient had been in congestive heart failure, which was successfully treated with diuretics. His medications included Nitropaste (E. Fougera and Company, Mel- ville, NY), 1 inch every 4 hours, diltiazem, 30 mg every 8 hours, Lasix (furosemide; Hoechst UK Ltd, Middlesex, England) 60 mg twice daily, Zaroxolyn (metolazone; Sandoz, Base], Switzerland) 5 mg every morning, digoxin, 0.125 mg every day, insulin NPH, 45 U, every morning, and regular, 20 U, every morning, and cimetidine,

From Northwestern University Medical School, Department of Anesthesia, Chicago, IL.

Dr Lichtenthal suppotied by Baxter Edwards Critical Care, Irvine, CA.

Address reprint requests to Peter R. Lichtenthal, MD, Northwestern University, Department of Anesthesia, Pas-360, 303 E Superior St, Chicago, IL 6061 I.

Copyright o 1994 by W B. Saunders Company 1053-0770194/0806-0012$03.0010 Key words: continuous cardiac output, pulmonary artery, monitor-

ing, cardiac sutgety

400 mg twice daily. After routine placement of two IVs and a radial artery catheter, a CC0 pulmonary artery catheter was placed via an internal jugular vein approach as part of an approved study that was being conducted to evaluate the accuracy of these new catheters. Anesthesia was induced using a fentanyl technique with pancuronium as a relaxant. The four-graft procedure proceeded routinely through a 3% hour cardiopulmonary bypass (CPB) run with a 2% hour cross-clamp time. There was difficulty weaning the patient from CPB and an intra-aortic balloon pump (IABP) was inserted via the left femoral artery. With the aid of IABP and infusions of epinephrine, norepinephrine, amrinone, and dopa- mine, the patient was successfully weaned from CPB, his chest was closed, and he was transferred, ventilated, to the intensive care unit (ICU). During the procedure, and in the ICU, the CC0 was continuously displayed both digitally and as a trend. Thermodilu- tion cardiac output (TDCO) was obtained at various time intervals. according to the study protocol. As can be seen in Fig 1, the CC0 system indicated that a somewhat precipitous drop in cardiac output had occurred the following morning in the ICU. Through- out the night the TDCO values had been stable, ranging from 4.3 to 4.6 Limin, which correlated well with the CCO. The last TDCO had been performed at 4:00 AM and was 4.6 Limin (Table I). After

Continuous Cardiac Output and Systolic Blood Pressure

7 04:oo

6 lo

_1

140 SEP -~~--

TD CO=4.6 E

cc0 -

I 5 ~---------~--~--~----.

B d E

interventlor TD co=25

Itlterventlon

A-Paced

050 07:oo 08:00 0900

2 Hours

Fig 1. Summary of a P-hour period in the intensive care unit that plots the patient’s systolic blood pressure (SBP), heart rate (HR)- recorded every 15 minutes-and continuous cardiac output @CO)- recorded every minute. The last previous thermodilution cardiac output (TDCO) was 4.6 L/min at 4:lNl AM. The CC0 plot indicates both the decline and eventual improvement in the patient’s hemodynamic status, whereas SBP and HR remained virtually unchanged.

668 Journal of Cardiothoracic and Vascular Anesthes/a, Vol8, No 6 (December), 1994: pp 668-670

CONTINUOUS CARDIAC OUTPUT 669

Table 1. Recorded Hemodynamic Parameters Throughout the Time Period of Interest During this Case

Time 0400 HR 87

BP 110159

MAP 75

PAD 17

CVP 8

TDCO 4.6

cc0 5.2

SVR 1078

Cl 2.3

0500 0600 0700 113 111 84

101/79 102/56 94144 88 69 74 17 16 15

8 9 7 -

4.2

(1524)

(2.2)

-

4.7

(1021)

(2.5)

-

3.9

(1374)

(2.0)

0749 0800 0840 0900

- 70 go* 90 - 103138 - 991’4.4

- 75 - 75 - 14 15 - 8 - 7

- 3.2 - 5.4

2.5 2.9 2.7 5.2

- 1748 - 1007

(1.3) 1.7 (1.4) 2.8

NOTE. Values in (parentheses) were derived from CCO. Dash denotes not done or not recorded.

“Atrial pacing.

morning surgical rounds, (approximately 7:00 AM), various changes were made in the patient’s drug therapy. The epinephrine was stopped, the amrinone was decreased, and the dopamine and nitroglycerin were left at the same rate (Table 2). Over the next hour, the CC0 decreased to 2.5 Limin with no significant change in the patient’s heart rate, systemic blood pressure, or pulmonary artery diastolic pressure. Normally, TDCOs are done at anywhere from l- to 4-hour intervals, depending on the patient’s hemody- namic status. In this case, the next set of TDCO determinations were to be done at 8:00 AM. Without any significant changes seen in his blood pressure and heart rate, there would have been no reason to perform TDCOs before the scheduled 8:00 AM time period for this patient. However, after watching the CC0 decrease from 3.0 to 2.4 Limin within 10 minutes, the house staff was notified and further adjustments were made to the drug therapy along with the eventual institution of atrial pacing. Once this was done, the CC0 began to increase. A TDCO of 3.2 Limin at 8:15 AM confirmed the accuracy of the CC0 reading. The CC0 gradually increased to 5.6 Limin by 9:00 AM (Fig 1) and the patient’s hemodynamics became stable. Eventually, the patient was successfully weaned off the infusions, the IMP was removed, and his overall postoperative status improved. The patient went on to leave the ICU in a satisfactory condition.

DISCUSSION

Integrated with other cardiovascular monitoring devices, TDCOs provide a useful clinical guide for fluid and drug therapy. Although TDCOs are relatively rapid and simple to perform, there does exist a certain amount of cost in both supplies and nurse/physician time. Therefore, unless a patient’s vital signs are so tenuous as to warrant immediate intervention, TDCO measurements in the ICU are usually performed only at regular time intervals. A continuous monitoring system for cardiac output is of considerable importance because the hemodynamic status of critically ill patients can decline both unexpectedly and rapidly without

any corresponding indications from their other vital signs, as this case demonstrated. The intermittent thermodilution regimen normally used in the authors’ ICU failed to warn of an impending hemodynamic collapse, whereas the CC0 system did. Although many anesthesiologists would argue that this deterioration in clinical status would have been detected with SVO, monitoring, that may not be the case. SO02 may not reliably reflect changes in cardiac output because multiple factors affecting oxygen extraction affect the SVO~.~O Patients can maintain a seemingly adequate S802 despite a decrease in cardiac output and still be in imminent danger of cardiovascular collapse.tr This is the case in patients with low cardiac output and an unchanging Sv02. CC0 avoids this problem by directly measuring the parameter of interest-cardiac output (rather than measur- ing something that is multifactorial, from which only infer- ences can be made, often incorrectly). With the actual cardiac output information, the patient’s cardiovascular status can be assessed much more accurately, as it certainly was in this case.

Therefore, a system providing continuous cardiac output information is very appealing. Although recent studies9 have verified the accuracy and response time of this system, one of the key questions repeatedly asked was whether or not a CC0 system would make a difference in actual clinical practice. It is believed that this case report answers that question with a resounding “yes.” CC0 can make a difference in a patient’s outcome. The Vigilance CC0 system (Baxter Critical Care, Irvine, CA) provided accurate continuous cardiac output information in the postoperative ICU setting, which was used to guide fluid and drug therapy when a potentially life-threatening decline in hemodynamic status had occurred and was undetected by routine monitor- ing procedures.

Table 2. Disposition of Various Therapeutic Interventions Throughout the Time Period of Interest During This Case

Time 6:OO AM 7:00 AM i’:49 AM 8:00 AM 8:40 AM 9:oo AM

Dopamine (kg/kg/min) 2.4 2.4 2.4 2.4 2.4 2.4 Nitroglycerin (mgihr) 4 4 4 4 4 4

Epinephrine (pg/min) 1.33 Off Off OR Off Off Amrinone (mg/min) 0.33 0.25 0.25 0.5 0.5 0.25

Dobutamine (pg/kg/min) Off Off Off OR Off 5.8

Atrial pacing (beats per minute) Off Off Off OR 90 90

670 LICHTENTHAL AND WADE

REFERENCES

1. Yelderman ML: Continuous measurement of cardiac output with the use of stochastic system identification techniques. J Clin Monit 6:322-332, 1991

2. Lichtenthal PR, Marchand G, Gordon D, et al: A safety comparison between a new continuous cardiac output monitoring system and a standard pulmonary artery catheter in sheep. Anesthe- siology ll:A473,1992

3. Khalil H: Determination of cardiac output in man by a new method based on thermodilution. Lancet 1:1352-1354, 1963

4. Barankay T, Jansco SN, Petri G: Cardiac output estimation by a thermodilution method involving intravascular heating and thermistor recording. Acta Physiol Hung Tomus 38:167-173, I970

5. Philip JH, Long MC, Quinn MD, Newbower RS: Continuous thermal measurement of cardiac output. IEEE Trans Biomed Eng 31:393-400, 1984

6. Norman RA, Johnson RW, Messinger JE, Sohrab B: A

continuous cardiac output computer based on thermodilution principles. Ann Biomed Eng 17:61-73. 19X9

7. Gilbert HC, Vendor JS. Myers P: Evaluation of continuous cardiac output in patients undergoing coronary artery bypass surgery. Anesthesiology 77:A472, I992

8. Davis RF. Sakuma G: Comparison of semi-continuous thermo- dilution to intermittant bolus thermodilution cardiac output deter- minations: Anesthesiology 77A477. 1992

9. Lichtenthal PR. Wade LD: Accuracy of the Vigilance. lntellicath continuous cardiac output system during and after cardiac surgery. Anesthesiology 79:A474. 1993

10. Nelson LD: Continuous venous oximetry in surgical pa- tients. Ann Surg 203329-333. 1986

I I. Vaughn S. Puri VK: Cardiac output changes and continuous mixed venous oxygen saturation measurement in the critically ill. Crit Care Med 16:49.5-498, 1988