Thermodilution Cardiac Output Measurement in Infants and Small Children Following Intracardiac Surgery By 0. Alfieri, J. Agosti, and S. Subramanian
OST COMMONLY USED parameters for the assessment of the cardiac function after open heart surgery, i.e., heart rate, central venous and left atria1 pressures, systemic pressures, urine flow, mixed venous oxygen tension, etc., allow only indirect deduction about the available reserves of the circulatory system. Direct measurements of cardiac output represent the only objective information concerning cardiac performance. We have found that postoperative management of infants and small children who have undergone open intracardiac repair is greatly facilitated by serial determinations of cardiac output. As already pointed out by others,’ clinical evaluation may fail to reveal low output states at their initiation, and these situations are badly tolerated by sick infants. The purpose of this communication is to describe the application of the thermodilution technique for cardiac output determination in small children and infants after open heart surgery.
M
MATERIALS
AND METHODS
The model 9500 thermodilution cardiac output computer (Edwards Laboratories, Santa Ana, Calif.) in combination with a special infant thermodilution catheter (Fig. IA) designed by us is employed at our institution for routme measurements of cardiac output in infants who have undergone open heart surgery.
CATHETER
DESCRIPTION
The catheter is a size 4F polyvinyl chloride catheter, 75 cm long, and constructed so that divided into two lumina along the long axis. One lumen, extending its total length, contains fine insulated wires ending in a thermistor at the end of the device. The second lumen extends side orifice IO cm proximal to the tip in such a way that when the end of the catheter bearing thermistor is located in the pulmonary artery, the side orifice opens into the right atrium. lumen is employed for injection of the cold solution and for recording right atrial pressures.
Placement
ofthe
it is two to a the This
Catheter
Since the device is not flow directed, site. If the surgical procedure requires the tricuspid valve into the pulmonary catheter can be inserted coaxially into through a purse string and can be easily lation. Once in place, the purse string
it must be positioned at the end of the intracardiac repair a right atriotomy, the catheter is easily placed through artery with the aid of a curved clamp. Otherwise, the a plastic feeding tube that is placed into the right atrium positioned into the pulmonary artery by external manipuis tied around the device to prevent hemorrhage and hold
From the Department of Cardiovascular Surgery. Children’s Hospital. Buffalo, N. Y. Presented before the 6th Annual Meeting of the American Pediatric Surgical Association, San Juan, Puerto Rico. April 10-12, 1975. Address for reprint requests: 0. AlJieri, M.D., Department of Cardiovascular Surgery. Children’s Hospital. 219 Bryant St., Buflalo. 1%‘. Y. 14222. ‘Ed1975 by Grune & Stratton, Inc.
Jomd
of Pediatric Surgery, Vol. 10, No. 5 (October), 1975
649
ALFIERI,
Fig. 1. (A) The infant cardiac output checked by x-ray in the Intensive Care Unit.
thermodilution
catheter.
AGOSTI,
(8)
AND SUBRAMANIAN
Position
of catheter
is
its position. A second suture with Teflon pledgets is placed for further safety. The catheter is then brought out of the chest through the inferior end of the sternotomy incision. The position of the catheter is checked by x-ray in the Intensive Care Unit (Fig. 1B). Atrial location of the side orifice is accomplished by connecting the injection lumen to a pressure monitor. If a ventricular tracing is recorded, the catheter is withdrawn until atrial pressures are obtained. The distance of 10 cm between the side orifice and the thermistor provides adequate length for location of the tip of the catheter in the pulmonary artery, while the injection lumen remains in the right atrium in a large variety of patients varying from newborns to children up to 8 yr.
Thermodilution Cardiac Output Measurements For each determination, only 2 or 3 cc of 5% cold dextrose are required. Computation factors are also available for other volumes of injectate. The difference between the patient’s rectal temperature and that of the solution for injection is entered in the computer, computation lime is set for 20 set, an isoelectric base line is obtained by proper adjustment, the injectate is rapidly infused into the patient, and computed cardiac output appears on the digital display at the end of the computation cycle. The curve can also be recorded on paper.
Assessment of the Accuracy of the Method To establish the accuracy of the method, the results obtained with the thermodilution technique were compared in the dog lab with those obtained with the cardiogreen indicator technique. The infant thermodilution catheter was also placed under fluoroscopy control in the cardiac catheterization laboratory and the data obtained with thermodilution were compared with output data by the Fick method and dye dilution technique. An accuracy of &IO04 was documented in outputs ranging within normal limits. Only very low or very voked were differences in methods more significant. CLINICAL
high
output
states
experimentally
pro-
EXPERIENCE
Since January 1974, routine postoperative cardiac output been done in 61 small children and infants with various heart diseases, i.e., ventricular septal defect, atria1 septal Fallot, etc.
measurements have types of congenital defect, tetralogy of
THERMODlllJTlON
CARDIAC
OUTPUT
MEASUREMENT
651
Insertion of the catheter was easily performed at the end of the operation and no complications could be attributed to its use. Although the catheter was usually removed before the chest tubes, significant bleeding did not occur in any patient at the time the catheter was withdrawn. Figure 2 illustrates some of the clinical applications and usefulness of this method. Serial cardiac output measurements show the postoperative course of a 4-moold baby operated for severe aortic stenosis. Good correlation can be seen between thermodilution cardiac output data and mixed venous oxygen content (Fig. 2A). A normal postoperative follow-up in a 3-yr-old child operated for tetralogy of Fallot is shown in Fig. 2B. Cardiac output tends to remain in the low ranges for about 48 hr when it starts to increase. Similar patterns can be seen in most patients in whom a ventriculotomy has been performed. Another postoperative course of a 2-yr-old child with tetralogy of Fallot shows progressive decrease of cardiac output despite treatment until death occurred (Fig. 2C). Figure 2D shows variation of cardiac output in relationship to rate. As may be expected, atria1 pacing is more effective at the same rate than ventricular pacing. Between certain limits, the increase in cardiac output is solely related to frequency while the stroke volume remains constant. At the same heart rate, inotropic drugs increase cardiac output to a greater extent than atria1 pacing alone (Fig. 3). Atrial pacing can be combined with inotropic agent infusion to obtain a better cardiac performance with avoidance of some of the negative effects of the inotropic drugs such as an increased incidence of supraventricular arrhythmia. In this last instance, we have found it very useful to use an atria1 pacemaker able to generate up to 800 beats/min (Medtronic 1379 atria1 pacemaker) for obtaining the desired control by means of producing various degrees of atrioventricular block, 2: I, 3: I. COMMENT
Postoperative care of infants and children undergoing open heart surgery requires careful assessment of numerous parameters. Of these, cardiac output represents the only estimation that provides objective information about cardiac performance. The principles on which thermodilution cardiac output measurements are based are well documented and the practical application of this method has been already reported in adults.2-4 In infants and small children, assessment of the cardiac function by thermodilution, as described here, offers theoretical and practical advantages over the other available techniques, namely: (1) recirculation is usually absent because the distance between the injection site and the thermistor is very short, allowing accurate measurements even in low flow states; (2) blood withdrawal for calibration and sampling is not required; (3) the amount of fluid needed for each determination is minimal, permitting serial measurements without burden to the patient; and (4) the technique of measurement is very simple. We are aware that all presently available techniques of cardiac output determination bear certain errors’ but we think that, for a given patient, the error is constant between a wide range of cardiac outputs, and only in extremely low
ALFIERI,
652
AGOSTI,
AND SUBRAMANIAN
. hr KMI ap 101) wp 10
._ . .
I 1
hr 142
-. I.
.
ap 138
l*.,
VP
7
-35 .
%. . %.
2.2-
l*..
l.
l*., .
hrlso apuo VP 7
VENOUS PO’ . ..m. . . . .
.
* . -30 .
. . .
. * r
.
-25
14-
. . . .
c I
‘.oc,
A4
1
pm
h
’
1
4 am
A*20 i
3.4 *
. 3.0 -
RIGHT ATRIAL PRESS ..... -15 * . f . -10
OST COMMONLY USED parameters for the assessment of the cardiac function after open heart surgery, i.e., heart rate, central venous and left atria1 pressures, systemic pressures, urine flow, mixed venous oxygen tension, etc., allow only indirect deduction about the available reserves of the circulatory system. Direct measurements of cardiac output represent the only objective information concerning cardiac performance. We have found that postoperative management of infants and small children who have undergone open intracardiac repair is greatly facilitated by serial determinations of cardiac output. As already pointed out by others,’ clinical evaluation may fail to reveal low output states at their initiation, and these situations are badly tolerated by sick infants. The purpose of this communication is to describe the application of the thermodilution technique for cardiac output determination in small children and infants after open heart surgery.
M
MATERIALS
AND METHODS
The model 9500 thermodilution cardiac output computer (Edwards Laboratories, Santa Ana, Calif.) in combination with a special infant thermodilution catheter (Fig. IA) designed by us is employed at our institution for routme measurements of cardiac output in infants who have undergone open heart surgery.
CATHETER
DESCRIPTION
The catheter is a size 4F polyvinyl chloride catheter, 75 cm long, and constructed so that divided into two lumina along the long axis. One lumen, extending its total length, contains fine insulated wires ending in a thermistor at the end of the device. The second lumen extends side orifice IO cm proximal to the tip in such a way that when the end of the catheter bearing thermistor is located in the pulmonary artery, the side orifice opens into the right atrium. lumen is employed for injection of the cold solution and for recording right atrial pressures.
Placement
ofthe
it is two to a the This
Catheter
Since the device is not flow directed, site. If the surgical procedure requires the tricuspid valve into the pulmonary catheter can be inserted coaxially into through a purse string and can be easily lation. Once in place, the purse string
it must be positioned at the end of the intracardiac repair a right atriotomy, the catheter is easily placed through artery with the aid of a curved clamp. Otherwise, the a plastic feeding tube that is placed into the right atrium positioned into the pulmonary artery by external manipuis tied around the device to prevent hemorrhage and hold
From the Department of Cardiovascular Surgery. Children’s Hospital. Buffalo, N. Y. Presented before the 6th Annual Meeting of the American Pediatric Surgical Association, San Juan, Puerto Rico. April 10-12, 1975. Address for reprint requests: 0. AlJieri, M.D., Department of Cardiovascular Surgery. Children’s Hospital. 219 Bryant St., Buflalo. 1%‘. Y. 14222. ‘Ed1975 by Grune & Stratton, Inc.
Jomd
of Pediatric Surgery, Vol. 10, No. 5 (October), 1975
649
ALFIERI,
Fig. 1. (A) The infant cardiac output checked by x-ray in the Intensive Care Unit.
thermodilution
catheter.
AGOSTI,
(8)
AND SUBRAMANIAN
Position
of catheter
is
its position. A second suture with Teflon pledgets is placed for further safety. The catheter is then brought out of the chest through the inferior end of the sternotomy incision. The position of the catheter is checked by x-ray in the Intensive Care Unit (Fig. 1B). Atrial location of the side orifice is accomplished by connecting the injection lumen to a pressure monitor. If a ventricular tracing is recorded, the catheter is withdrawn until atrial pressures are obtained. The distance of 10 cm between the side orifice and the thermistor provides adequate length for location of the tip of the catheter in the pulmonary artery, while the injection lumen remains in the right atrium in a large variety of patients varying from newborns to children up to 8 yr.
Thermodilution Cardiac Output Measurements For each determination, only 2 or 3 cc of 5% cold dextrose are required. Computation factors are also available for other volumes of injectate. The difference between the patient’s rectal temperature and that of the solution for injection is entered in the computer, computation lime is set for 20 set, an isoelectric base line is obtained by proper adjustment, the injectate is rapidly infused into the patient, and computed cardiac output appears on the digital display at the end of the computation cycle. The curve can also be recorded on paper.
Assessment of the Accuracy of the Method To establish the accuracy of the method, the results obtained with the thermodilution technique were compared in the dog lab with those obtained with the cardiogreen indicator technique. The infant thermodilution catheter was also placed under fluoroscopy control in the cardiac catheterization laboratory and the data obtained with thermodilution were compared with output data by the Fick method and dye dilution technique. An accuracy of &IO04 was documented in outputs ranging within normal limits. Only very low or very voked were differences in methods more significant. CLINICAL
high
output
states
experimentally
pro-
EXPERIENCE
Since January 1974, routine postoperative cardiac output been done in 61 small children and infants with various heart diseases, i.e., ventricular septal defect, atria1 septal Fallot, etc.
measurements have types of congenital defect, tetralogy of
THERMODlllJTlON
CARDIAC
OUTPUT
MEASUREMENT
651
Insertion of the catheter was easily performed at the end of the operation and no complications could be attributed to its use. Although the catheter was usually removed before the chest tubes, significant bleeding did not occur in any patient at the time the catheter was withdrawn. Figure 2 illustrates some of the clinical applications and usefulness of this method. Serial cardiac output measurements show the postoperative course of a 4-moold baby operated for severe aortic stenosis. Good correlation can be seen between thermodilution cardiac output data and mixed venous oxygen content (Fig. 2A). A normal postoperative follow-up in a 3-yr-old child operated for tetralogy of Fallot is shown in Fig. 2B. Cardiac output tends to remain in the low ranges for about 48 hr when it starts to increase. Similar patterns can be seen in most patients in whom a ventriculotomy has been performed. Another postoperative course of a 2-yr-old child with tetralogy of Fallot shows progressive decrease of cardiac output despite treatment until death occurred (Fig. 2C). Figure 2D shows variation of cardiac output in relationship to rate. As may be expected, atria1 pacing is more effective at the same rate than ventricular pacing. Between certain limits, the increase in cardiac output is solely related to frequency while the stroke volume remains constant. At the same heart rate, inotropic drugs increase cardiac output to a greater extent than atria1 pacing alone (Fig. 3). Atrial pacing can be combined with inotropic agent infusion to obtain a better cardiac performance with avoidance of some of the negative effects of the inotropic drugs such as an increased incidence of supraventricular arrhythmia. In this last instance, we have found it very useful to use an atria1 pacemaker able to generate up to 800 beats/min (Medtronic 1379 atria1 pacemaker) for obtaining the desired control by means of producing various degrees of atrioventricular block, 2: I, 3: I. COMMENT
Postoperative care of infants and children undergoing open heart surgery requires careful assessment of numerous parameters. Of these, cardiac output represents the only estimation that provides objective information about cardiac performance. The principles on which thermodilution cardiac output measurements are based are well documented and the practical application of this method has been already reported in adults.2-4 In infants and small children, assessment of the cardiac function by thermodilution, as described here, offers theoretical and practical advantages over the other available techniques, namely: (1) recirculation is usually absent because the distance between the injection site and the thermistor is very short, allowing accurate measurements even in low flow states; (2) blood withdrawal for calibration and sampling is not required; (3) the amount of fluid needed for each determination is minimal, permitting serial measurements without burden to the patient; and (4) the technique of measurement is very simple. We are aware that all presently available techniques of cardiac output determination bear certain errors’ but we think that, for a given patient, the error is constant between a wide range of cardiac outputs, and only in extremely low
ALFIERI,
652
AGOSTI,
AND SUBRAMANIAN
. hr KMI ap 101) wp 10
._ . .
I 1
hr 142
-. I.
.
ap 138
l*.,
VP
7
-35 .
%. . %.
2.2-
l*..
l.
l*., .
hrlso apuo VP 7
VENOUS PO’ . ..m. . . . .
.
* . -30 .
. . .
. * r
.
-25
14-
. . . .
c I
‘.oc,
A4
1
pm
h
’
1
4 am
A*20 i
3.4 *
. 3.0 -
RIGHT ATRIAL PRESS ..... -15 * . f . -10
