Symposium on a Physiologic Approach to Critical Care

Use of Balloon Flotation Catheters in Critically III Patients H. J. C. Swan, MD., PhD.,* and William Ganz, MD., C.sc.**

In the late 1960's it became evident that management of the complex series of phenomena collectively identified under the title "acute myocardial infarction" could be greatly facilitated by an understanding of the hemodynamic changes associated with the different subsets of this common disease condition. 26 The inclusion of a wide variety of cardiac syndromes with differing prognoses and therapeutic needs within this single taxonomic designation did not facilitate clear conceptual thinking on the part of physicians nor a clear understanding of the relative significances of these syndromes to the patient and his family. Initial attempts to apply the techniques of conventional cardiac catheterization in the hemodynamic evaluation of such patients were associated with a relatively high incidence of serious complications including ventricular tachycardia and fibrillation. Hence, application of such techniques was essentially limited to investigative research or to the evaluation of a clearcut complication of acute myocardial infarction, for example, perforated ventricular septum. Use of the fine "microcatheters"3,20 obviated some, but not all, of these complications. This procedure using the "microcatheter" had the disadvantage of a relative nonreliability with a significant incidence of failure to catheterize the heart and, not infrequently, an extremely long period of manipulation before successful entry occurred. This was a particular problem in the more severely ill patients in whom the velocity of blood flow through the right atrium was depressed. From such studies it became clear that dependency upon measurement of central venous pressure as an index of "heart failure" in acute myocardial infarction was at best imprecise and in individual patients highly misleading. The combination of these two factors, the poor reliability of catheterization of the pulmonary artery by means of the microcatheter together with the known errors or potential errors accompanying the use of central venous pressure monitoring, underlay the development of ':'Director, Department of Cardiology, Cedars-Sinai Medical Center; Professor of Medicine, University of California, Los Angeles ':":'Senior Research Scientist, Department of Cardiology, Cedars-Sinai Medical Center; Professor of Medicine, University of California, Los Angeles

Surgical Clinics of North America- VoL 55, No.3, June 1975

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a reliable and relatively safe approach to catheterization of the pulmonary artery based on the flotation principle. The first option considered was a catheter planned to carry a small "sail" which could be extended into the blood stream for forward propulsion. Because of problems of construction and reliability of such device, the idea was abandoned in favor of a small inflatable balloon mounted at the tip of a highly flexible cardiac catheter. 27 The device did prove to be effective and allowed for the catheterization of pulmonary artery in a high proportion of applications, and usually in a short time. The advantages of balloon-tipped, flow-directed catheters were noted earlier by Lategola and Rahn 17 in an experimental investigation of the pulmonary circulation. In addition, the incidence of cardiac arrhythmias-frequent in conventional right '".iheart catheterization- was sufficiently small as to present a minimal risk. Other potentially serious complications have now proven to be uncommon or even rare, and usually resulting from failure to apply the device correctly in all details. The balloon flotation catheter principle has now been accepted widely, and numerous additional applications have been implemented. It does appear to be able to provide important and relevant data in clinical practice with a relatively high degree of safety. These data reflect fundamental parameters of cardiovascular function. The relevance of that data in patient management and therapeutic decision-making is high, and its significance is readily understandable to physicians, nurses, and critical care personnel. The purpose of this article is to outline the techniques of balloon flotation catheterization, the measurement of important variables utilizing these methods, the applications of such methods and data to certain disease states, and a discussion of the complications known to be associated with balloon flotation catheterization.

PRINCIPLES OF APPLICATION AND CONSTRUCTION OF CATHETER In its basic version, the device consists of a soft, flexible, polyvinylchloride double lumen catheter of outside diameter approximately 1.5 mm (equivalent #5 French). The smaller lumen is approximately 0.4 mm in diameter and is used to inflate a small latex balloon positioned at the catheter tip (Fig. 1). In practical application (see below), after the catheter has been introduced into the circulation and the tip is positioned in the superior or inferior vena cava or high right atrium, inflation of this balloon provides a relatively solid (nonliquid) element which is directed by the flowing stream of blood into the chambers of the right heart and pulmonary artery. The inflated balloon has a diameter of approximately 13 mm, and this appears sufficient to readily flow-guide the soft catheter through the right atrium and tricuspid valve into the right ventricle and from there into the main pulmonary artery and into a branch of the pulmonary artery, where its further progression is stopped by its impaction in a pulmonary vessel slightly smaller in diameter than the inflated balloon, much in the manner of a pulmonary embolus.

USE OF BALLOON FLOTATION CATHETERS IN CRITICALLY ILL PATIENTS

c~--- ~

503

/."

"-"--/ "T

Figure 1. A, Picture of the standard 5F balloon"tipped flow"directed catheter. The balloon is inflated and the stopcock of the inflation lumen closed. A pressure transducer is attached to the larger lumen. B, Close"up view of the inflated balloon protruding above the tip of the catheter. C, Close"up view of the proximal ends of the pressure lumen and of the inflation lumen in the stopcock.

When the balloon is deflated, the catheter shaft will recoil slightly into a larger pulmonary artery since the flowing blood carrying it into the distal pulmonary artery is now without a relatively sizable element (the inflated balloon) on which to act. The degree of "recoil" will depend upon the amount of catheter which has been advanced into the circulation during initial placement. If this is excessive, then the tip of the catheter will lie in a distal pulmonary artery, while if it is insufficient, the catheter may tend to recoil to the outflow tract of the right ventricle. Optimally, following deflation, the catheter should return to the main pulmonary artery. If, at a later time during the course of monitoring, the balloon is once again inflated, it serves to again flow-guide the catheter distally to impact in a somewhat smaller pulmonary artery. Failure to observe the principle that the balloon is intended to flow-guide the catheter into different locations has given rise to the few fatal complications heretofore reported with extensive utilization of the balloon flotation catheter systems. The physical properties of such catheters affect their successful utilization and the incidence of complications. A principal requirement is to avoid the development of substantive forces at the catheter tip or in shaft loops in the atrium or ventricle. Subendocardial irritation, noted even with the fine microcatheter systems,2 appears to have been largely avoided by particular attention to the location of the balloon at the catheter tip.27 When inflated for passage through the right ventricle, the balloon actually protrudes over the catheter tip which comes to lie below its surface in, as it were, "the hole in the doughnut." Forces which

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would ordinarily be concentrated at the catheter tip are now dispersed over the wider surface of the flotation balloon. Complete absence of ventricular arrhythmias during catheterization is quite common, whereas the occurrence of significant or serious ventricular arrhythmias is uniquely low using the flexible balloon-tipped flotation catheter. For additional purposes, larger catheters have been developed with increasing degrees of wall stiffness, due to the construction of the catheter itself. In addition, certain catheters actually incorporate the principle of differential stiffenIng to allow for stable placement of catheters, particularly when cardiac pacing is required. A triple-lumen catheter is now available by means of which pressures in the right atrium and in the pulmonary circulation may be recorded simultaneously. A similar catheter incorporating a thermistor set back approximately 4 em from the catheter tip allows for the measurement of cardiac output by the thermodilution technique consequent upon the injection of liquid of known temperature in the right atriumP A further catheter incorporates electrodes which, when the catheter is properly positioned, lie near the apex of the right ventricle and high in the right atrium for the measurement of cavity potentials from each of these cardiac 10cations. 5 A catheter incorporating thermodilution, pressure measurement, as well as the multiple electrodes, has also been developed. Specific catheters for cardiac pacing have gone through a series of design and are either preshaped19 or incorporate differential stiffening so as to maintain an optimal location for their pacing function. The shafts of all catheters are marked to indicate 10 em distances from the catheter tip. This is to facilitate initial placement of the catheter and also to alert the user of loop redundancy. Appropriate connectors are provided for the various functions with due recognition of the need to adhere to principles of electrical safety and hazard associated with the presence of a low impedance pathway directly to the heart. To date, balloon flotation catheters have found use in such wide and diverse areas of medical practice as the coronary care unit, the medical intensive care unit, the postsurgical recovery unit, the intraoperative cardiovascular surgical suite, the neurosurgical and obstetric areas, anesthesiology, as well as in the diagnostic cardiac catheterization laboratory, the pulmonary intensive care unit, and the pulmonary function laboratory. Extension to outpatient facilities, including exercise laboratories and "noninvasive" laboratories, has also been accomplished.

TECHNIQUES OF BALLOON FLOTATION CATHETERIZATION Balloon flotation catheterization of the pulmonary arteries can be undertaken at the patient's bedside and without fluoroscopy. It may be carried out in any hospital location, but the effective observation and recording of the data to be derived demand appropriate support devices such as manometers and effective display units. During balloon flota-

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tion catheterization, all patients should be subjected to electrocardiographic monitoring so as to promptly detect any disturbance of cardiac rhythm which might be associated with initial passage of the catheters. The availability of a fluoroscopic facility or of a portable fluoroscopic unit may facilitate the effective placement of flotation catheters in some cases. Whenever possible, percutaneous insertion of balloon flotation catheters should be undertaken. The site of insertion will vary according to the practices and skills of the individual physician. It is possible to insert #5 or #6 flotation catheters from the antecubital fossa by percutaneous insertion or, more frequently, a venotomy may have to be made for catheter placement, particularly with catheters of larger size. Appropriately skilled physicians prefer the use of the subclavian or internal jugular approach and other physicians will utilize the femoral vein approach. The latter three insertion sites necessitate percutaneous venous puncture using various modifications of Seldinger's technique. They have the particular advantage that the arms of the patient are not encumbered by a catheter insertion and that patient movements are unlikely to alter the position of the catheter tip. However, higher skill levels are required for safe insertion of the catheter in the more central locations while antecubital fossa insertion is widely used by cardiologists and internal medicine physicians. For the average subject, advancement of 35 to 40 cm from the right and 45 to 50 cm from the left antecubital fossa, 10 to 15 cm from the internal jugular vein, 10 cm from the subclavian vein, and 35 to 45 cm from the femoral vein should place the catheter tip in or close to the right atrium. An increase in the pressure variations associated with the respiratory cycle will give an indication that the tip lies within the thorax. This is particularly evident in patients with increased respiratory effort. When the balloon is believed to be in the th_orax, it is inflated to the recommended level and advanced (Fig. 2). A record is made or a value recorded of the level of the pressure in the atrium together with its maximal and minimal values. As the catheter enters the tricuspid valve and passes into the right ventricle, a similar recording or a value report of right ventricular maximum and minimum pressure should be

lItO

_____ . .. _. . __ . _______ .! __.

. . _.

__

ttllllll+lotl+lot~tt IIHIIIIIIIII.IIU I,. ~lIm4+.ttll"IIIII.11I1 ••UUI~ Hit tlimH....... Figure 2. Pressure tracing recorded from the tip of a flow-directed balloon catheter during advancement from the right atrium into wedged position. eRA = right atrium; RV = right ventricle; PA = pulmonary artery; pew = pulmonary capillary wedge pressure.)

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obtained. Such records of both right atrial and right ventricular pressures may be valuable for diagnostic purposes. As advancement continues, the pressure tracing demonstrates the pulmonary artery pressure contour which is identified by a level of systolic pressure equal to right ventricular systolic pressure, but higher during diastole than right ventricular diastolic pressure. Advancement is continued until a pressure is identified which approximates pulmonary artery diastolic levels. The magnitude of this pressure is noted and, if possible, a recording of pressure on "hard copy" obtained. The balloon is then deflated and phasic pulmonary artery pressure should reappear. The pressure levels in the pulmonary artery are once again measured and reported or recorded. Particular attention is given at the time of initial insertion as to the possibility of "recoil" of the catheter tip into the right ventricle. The presence of intermittent right ventricular pressure complexes on the monitor or recorder will necessitate advancement of the catheter shaft by 1 to 2 cm. An anteroposterior x-ray picture of the chest may be obtained to confirm the optimal position of the catheter tip in the main pulmonary artery or one of its main branches. As the catheter material softens with time, the transcardiac catheter loop may shorten, resulting in migration of the catheter tip into smaller branches and into wedged postion. Particular attention should therefore be paid to the pressure contour. If at any time a pressure other than that characteristic of pulmonary artery pressure is observed and flushing the catheter lumen does not eliminate the distortion, the possibility of wedging should be considered and the catheter pulled back 1 to 2 cm. The possibility that the catheter tip is in a small pulmonary artery branch should be considered when the balloon is re-inflated for recording wedge pressure. Inflation of the balloon to the full recommended volume in a small branch may cause lateral tension sufficient to produce significant damage of the pulmonary vessels and parenchyma. Therefore, reinflation of the balloon should be performed slowly and with caution. While observing the contour of the pulmonary artery pressure, increments of 0.2 ml of air should be inserted into the balloon, until the change from pulmonary arterial to pulmonary wedge pressure is noted. If, at volumes substantively less than the recommended inflation value, a pulmonary wedge pressure is obtained, the catheter should also be withdrawn 1 to 2 cm. Fluid should never be used to inflate a flotation balloon since catheter flotation can be less satisfactory and it may be impossible to withdraw fluid from the balloon. Also the incompressible nature of liquid transmits extremely high forces to the containing walls which may be part of the lung structure. In the management of the critically ill, balloon flotation catheters have been left in place for 7 days and more. This practice is not now recommended with the ready availability of these devices. At the present time, the "life" of the latex used for flotation purposes is limited. In certain instances, immersion in flowing blood results in uptake of lipoproteins by the latex of the balloon with deterioration of its elastic qualities and a tendency to disintegrate. Hence, 48 hours of aggregate use in a single patient appears to be the upper limit of safe utilization. In like manner, when balloon flotation catheters are used for limited and short

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USE OF BALLOON FLOTATION CATHETERS IN CRITICALLY ILL PATIENTS

procedures, such as in the cardiac catheterization laboratory, a limitation on the number of uses is recommended. The processes of physical cleaning and sterilization may also serve to cause deterioration of the latex balloon, limiting the integrity of its structure.

MEASUREMENT OF PHYSIOLOGIC DATA Pressure Measurement Although the flotation catheters are flexible, their intrinsic distensibility and capacitance is small. Hence, they are suitable for the recording of intracardiac pressures as are other cardiac catheters. Dynamic response data has been determined for all catheters with conventional manometers and recorders. In general, it may be stated that they are adequate for most human cardiovascular hemodynamic recording (Table 1). However, the adequacy and fidelity of pressures recorded by balloon flotation catheters may be questioned for species with higher heart rates and more rapid pressure transients than occur in the normal adult human subject. As would be anticipated, fundamental agreement has been obtained in the levels of pressures recorded by balloon flotation catheters and more conventional catheters in regard to the right atrial pressure, the right ventricular pressure, and the pulmonary artery pressure. 27 The physical characterisitcs of the conventional No. 5 balloon flotation Table 1.

Physical Characteristics of Balloon Flotation Catheters" CATHETER FRENCH-

USABLE BALLOON LUMEN LENGTH CAPACITY

FREQUENCY

AREA

RESPONSE

SIZE

(cm)

(ml)

(mm')

(Hz)

5 6 7 7

110 110 110 110

0.8 0.8 1.5 1.5

0.8 1.2 1.8 0.75 eat

10 10 25 10.5, 14

4 5

60 60

0.5 0.8

0.5 0.8

15 10

ANGIOGRAPHY CATHETERS

7 8

90 100

1.5 1.5

1.8 2.3

15 15

THERMODILUTION

7

100

1.5

0.75 ea.t

10.5, 14

5

50

1.0

0.8

10

MONITORING

Double lumen

CATHETERS

Triple lumen PEDIATRIC DIAGNOSTIC CATHETERS PULMONARY

CATHETERS PEDIATRIC ANGIOGRAPHY CATHETERS

':'Data apply only to catheters manufactured by Edwards Laboratories, Santa Ana, California. The specifications of catheters offered by other manufacturers were not available to us. t Cross-section area of each of two monitoring lumens. The frequency response of the system involving the distal lumen is 10.5 Hz while that related to the proximal lumen is 14 Hz.

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catheter, when mated with conventional manometers (Statham P-23 series), appears, in fact, to be close to optimal, so that right atrial and right ventricular pressure contours are readily interpreted. As with all cardiac catheters, spurious recordings of pulmonary artery pressure may be obtained by reason of catheter movement associated with the beating heart. This spurious oscillation occurs at a frequency which is relatively higher (20 cycles per sec. or greater) than the more important biologic changes in intrapulmonary pressure (5 to 8 cycles per sec.) and catheter manometer recorder systems deserve therefore specific attention in regard to optimal damping to minimize this artefact. Pressures recorded by correctly fluid-filled and connected balloon flotation catheters are substantively identical to those obtained by other means. One of the most important applications of balloon flotation catheters is the recording of the so-called "pulmonary artery wedge" or pulmonary capillary pressure obtained when the catheter tip "impacts" into a smaller branch of the pulmonary vascular tree. Flow is interrupted by the impaction of the distended balloon into a vessel supplying a segment of the lung. Pressure is transmitted backwards through the static column of blood from the next active circulatory bed-the pulmonary veins. Such pressures recorded with the balloon flotation catheter may differ from those of the conventional wedge in that a larger number of pulmonary transmission segments are involved by reason of the impaction of the balloon in a larger parent vessel than would pertain to the conventional wedged catheter. 7 In theory, and probably in practice, this results in a pressure wave of magnitude and contour which more closely reflects the pressure in the pulmonary veins. Pulmonary venous pressure is of critical importance in clinical practice in that it provides information on two fundamental determinants of cardiopulmonary function. First, the level of pulmonary venous pressure is the prime determinant of pulmonary congestion and also the dominant factor in the transfer of fluid from the pulmonary venous bed into the interstitial spaces and the alveoli. In addition, pulmonary venous pressure relates closely to left atrial pressure and, in the absence of mitral valve disease, to left ventricular diastolic pressure. Mean pulmonary artery wedge pressure has been shown to be closely similar in contour to that recorded simultaneously in the left atrium. In addition, mean values for left atrial pressure obtained at the time of operation from catheters placed in the left atrium are identical to mean wedge pressures obtained simultaneously in the postoperative period by balloon flotation catheters. The relationship of mean pulmonary capillary pressure to left ventricular diastolic pressure is more complex. Mean pulmonary capillary pressure approximates left ventricular end diastolic pressure provided that the level is below approximately 15 mm Hg. Deviations occur in patients in normal sinus rhythm for middiastolic pressure levels above that magnitude. A study of the relationship of "a" wave magnitude obtained in pulmonary wedge pressure recordings indicates a much closer agreement to end diastolic ventricular pressure. Nevertheless, for clinical purposes the mean wedge pressure provides highly relevant data of practical significance.

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Cardiac Output Measurement The development of the triple-lumen balloon flotation catheter,9,13 incorporating the thermistor located 4 cm from the catheter tip, has greatly facilitated measurement of cardiac output by the thermodilution principle, The theory and practical steps of the determination of the cardiac output, by the dilution principle in general and by the thermal technique in particular, have been extensively reviewed elsewhere,I5 Suffice it to summarize the principles of the methodology as follows: If a known quantity of (negative) heat is introduced into the circulation, the resulting cooling curve at a position sufficiently downstream to have permitted mixing of the injected volume with the flowing blood stream allows for the calculation of the net blood flow over the time during which the change in temperature has been measured, Heat must not be lost from or gained by the system during the period of actual measurement, Passage of the blood-indicator mixture through two valves and a ventricular chamber is considered to produce adequate mixing. In practice, 10 ml of 5 per cent glucose or other appropriate solution of either room temperature or cooled to 0 to 5°C is injected into the superior vena cava. The change in temperature which occurs in the blood flowing through the pulmonary artery is measured, for a period after injection to accommodate the first "circulation" of the injected (negative) heat. (Fig. 3) A number of techniques have been developed to handle the resulting dilution curve, including simple planimetry. Electronic computational devices are now available (Edwards Laboratories, Instrumentation Laboratories, Waters Corporation etc.) which allow the online determination of cardiac output from a known quantity of injected

f\

co- 5.1

! \

f \ \

\

, - " - __ ~_~_"' ___ ~_~ ___ .A __

Y·"' ___ "'_"""''''-· _-'

PA

f~ r~~~~~Y~W~~1I~I~W'JI~~~'~~~~1~~~~~~M,f~~

_ 0 .

_

* Figure 3. Picture of an original tracing, showing two thermodilution curves, obtained within 30 seconds, with the values of cardiac output and records of the pulmonary artery and right atrial pressures obtained with the same flow-directed catheter.

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(negative) heat. Most computer devices depend upon the relatively constant relation between the earlier portions of the curve and its total area. Simply stated, the relationship between the curve integrated down to 30 per cent of peak amplitude deflection to the whole curve is highly consistent and allows for the automatic calculation of the whole curve with minimal error on a wide variety of curves in terms of temporal and amplitude magnitudes. A solution similar to that for dye dilution can be obtained by extrapolation of the curve as being defined by a single negative exponent, based on a sample of declining amplitude points on the downslope of the curve. This approach may increase the complexity of computational devices but adds little in terms of accuracy. The thermodilution cardiac output now appears to be the method of choice for the measurement of cardiac output in clinical practice. Although the method is invasive in that a catheter is passed to the main pulmonary artery, it has the intrinsic advantage of requiring injections of an inert indicator of minimal cost. More importantly, there is no requirement for the withdrawal of blood samples either from the arterial system or from other locations and removal of blood for calibration. Measurements can be performed in short intervals about twice per minute. For a triplicate cardiac output determinations carried out by the thermodilution technique, the reproducibility using 10 ml of cold indicator and a bedside computer was 2.5 per cent. 9 A slightly greater variability (3 per cent) has been observed when solutions at room temperature have been injected. However, practical considerations favor the use of room temperature solutions and their use is recommended in the absence of major variations in the temperature of pulmonary artery blood. This may occur in certain subjects including those who require the use of an automatic ventilator or in patients who exhibit Cheyne-Stokes breathing; also under circumstances associated with very high cardiac output the use of cold indicator may be preferable. The absolute levels of accuracy of blood flow determination by the thermodilution technique has been extensively investigated in animal and model systems where an accuracy of approximately ±2 per cent has been obtained. 15 Contractility Measurement

U sing the ratio of developed left ventricular pressure (aortic diastolic pressure minus mean capillary wedge pressure), divided by a correlate of left ventricular ejection time, i.e., the pre-ejection period, a ratio ~P/ ~T can be obtained. 6 It has been demonstrated that this is closely related in magnitude and in directional change to left ventricular dP/dt. This relationship is expressed by the formula: dP/dt = O.~P/~T, and can be used as a reasonable approximation to define left ventricular contractile state and changes therein. The ratio ~P/ ~T is as sensitive in terms of its prognostic significance as left ventricular dP/dt,1 Values of ~P/~T of less than 500 are indicative of depressed left ventricular contractile state, and values in excess of 1000 suggest a hyperdynamic state of left ventricular contractility.

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APPLICATIONS IN CLINICAL PRACTICE Diagnostic Cardiac Catheterization Balloon flotation catheters are now finding general acceptance in the diagnostic cardiac catheterization laboratories. 23 This rapid increase in application is because of the decreased incidence of ventricular arrhythmias and shorter duration of right heart catheterization using the balloon device. In fluoroscopically controlled catheterization using the balloon guidance system, the time of passage from the right atrium to the pulmonary artery is usually around 10 to 20 seconds. It was our earlier impression27 that the presence of tricuspid valve incompetence and/or pulmonary valve incompetence prevented the manipulation of the catheter into the pulmonary artery in a significant number of instances. However, using the slightly stiffer #7 catheter with a larger balloon, consistent catheterization of the pulmonary artery has apparently been obtainable. 23 In addition, the application of the balloon flotation catheter in the diagnostic study of infants and children with congenital heart disease has been apparently beneficial. Since the catheter will follow the stream of blood flow, the inflated balloon will "find" its way into different chambers of the heart and the great vessels, irrespective of their actual position in the mediastinum and the inter-relationship of cardiac chambers and great vessels. It is usual for the balloon flotation catheter to enter the principal ventricle filled by the systemic venous return rapidly, even wben abnormallypositioned. 17 When the heart is catheterized from the saphenous or femoral vein approach via the inferior vena cava, it will frequently pass into the left atrium and from thence via the left-sided atrioventricular valve into the left ventricle and aorta. 21 By this means, successful catheterization of the pulmonary artery in cases of complete transposition has been accomplished in a majority of such patients. 16 Such catheters2I also permit the completion of diagnostic angiography with reduced hazard in regard to cardiac perforation or intramyocardial injection of contrast material. The incidence of dysrhythmias associated with prolonged manipulation, and presumably the degree of subendocardial damage in diagnostic cardiac catheterization, are apparently much reduced by use of balloon flotation catheters. Assessment of Cardiac Performance in Critically III Patients The initial application of balloon flotation catheters was in the management of acutely ill patients with acute myocardial infarction. The assessment of circulatory function in the preoperative, intraoperative, and postoperative period is of particular interest to the practicing surgeon and anesthesiologist. In addition, of course, the application of such techniques in the management of critically ill patients suffering from other diseases is self-evident, in particular in patients with pulmonary and renal diseases and in disturbances of intra- and extravascular volumes. The principal data obtained include the filling pressures of the right and left ventricles, taP/taT, and the cardiac output. Of these, left ventricular filling pressure appears to be one of the most valuable single

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parameters of cardiovascular function on which to base therapeutic decisions and on which to evaluate their effectiveness. In the critically ill, particular attention must be paid to performance of the left ventricle. While the level of central venous pressure (CVP) is, from time-to-time, valuable in the assessment of the blood volume, imbalances between the complex and interrelated functions of right and left ventricles in disease require a knowledge of left ventricular filling pressure reflected with reasonable accuracy by the pulmonary artery wedge pressure. 24 The mean pulmonary capillary wedge pressure is a direct determinant of the degree of pulmonary congestion and of fluid transfer at the pulmonary capillary level and relates closely with x-ray changes in the lungs. Is In patients with myocardial infarction the relation between CVP and the pulmonary artery wedge pressure is sufficiently imprecise as to preclude useful decisions on the basis of CVP alone.lO A knowledge of cardiac output as a basic component of cardiovascular function has always been accepted as important by the cardiovascular physiologist. However, many clinicians have doubted the value of precise data on cardiac output levels and changes. With an ability now to measure this variable without particular difficulty or increased hazard to the patient, the significance of such measurements in clinical practice is becoming recognized more widely. The value of knowledge of left ventricular contractile state as indicated by the absolute levels of and changes in .:lP/.:lT remains to be assessed. Several definable states of cardiovascular function can now be identified in pathophYsiologic terms and specific therapies can be indicated on hemodynamic basis. A. A normal cardiac output associated with a normal left ventricular filling pressure does not require specific cardiovascular therapy and indicates that abnormal symptoms or signs suggestive of cardiovascular dysfunction may have another basis. The observation of normal hemodynamic data in the early portion of an illness is valuable as changes may occur with the passage of time. Left ventricular filling pressures of between 8 and 12 mm Hg, right atrial pressures of 0 to 5 mm Hg, and a cardiac index of 2.5 L per min per M2 or greater characterize a normal cardiovascular state in a patient confined to bed in a hospital. B. A high cardiac output may be seen in conditions of anemia, hyperthyroidism, fever, and in approximately 10 per cent of patients with acute myocardial infarction (hyperreactive subset)}' The cardiac index exceeds 3 L per min per M2, there is frequently tachycardia, mild hypertension with a widened pressure pulse may be present, and the left ventricular filling pressure is usually 10 to 18 mm Hg. If heart rate is excessive, small doses of propranolol (Inderal) may relieve palpitation and anxiety. As little as I mg given slowly intravenously will cause a reduction in heart rate, a drop in cardiac output, and a reduction in blood pressure. ' . C. Pulmonary congestion with adequate cardiac output 4 (Fig. 4): Many .~atients with acute myocardial infarctions of small or moderate size have pulmo. nary congestion and dyspnea, yet the cardiac output is found to exceed 2.2 L per min per M2. However, pulmonary capillary wedge pressure may be elevated-exceeding 18 mm Hg and perhaps as high as 25 mm Hg. In this instance, cardiac performance is adequate to meet the ordinary metabolic needs of the body. Hence, therapy must be directed to reduction in filling pressure and not towards enhancement of cardiac output. Some diuretics will reduce filling pressures within minutes, with amelioration of cardiac symptoms, followed within a short time by normalization of previously abnormal physical signs and in a slightly

USE OF BALLOON FLOTATION CATHETERS IN CRITICALLY ILL PATIENTS

513

CARDIAC OUTPUT

L/min/Me

Figure 4. Tracing from a patient with acute myocardial infarction. The cardiac output and systemic arterial pressure are within normal limits; the pulmonary capillary wedge pressure indicates pulmonary congestion.

ARTERIAL PRESSURE mmHg PCW mmHg

ECG

Lead

n

CARDIAC OUTPUT

L/m;n 1M2

ARTERIAL PRESSURE mmHg PCW mmHg

ECG

A

CARDIAC OUTPUT

L/mln/M2

ARTERIAL PRESSURE mmHg PCW mmHg ECG

B

Figure 5. A, Tracing from a patient with acute myocardial infarction and clinical signs of shock. The cardiac output is low. The pulmonary capillary wedge pressure is high, indicating that myocardial depression is the main cause of the low cardiac output and shock. B, Tracing from a patient with acute myocardial infarction and clinical signs of shock. The cardiac index is low. The mean pulmonary capillary wedge pressure is not elevated, indicating that hypovolemia is the main cause of the low cardiac output.

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longer time of favorable changes in the chest roentgenogram. In this instance, cardiac performance has been adequate and therapy should not be directed to its alteration. D. In the presence of more severe degrees of heart failure, particularly that associated with extensive acute myocardial infarction or with cardiomyopathy, the cardiac index may be depressed to levels below 2.2 L per min per M2 (Fig. 5A). If the reduction in cardiac index is due to or associated with hypovolemia, then a filling pressure of 12 mm Hg or less may be seen (Fig. 5B). If the filling pressure is severely depressed (0 to 4 mm Hg), then such patients will respond promptly to fluid loading by an increase in cardiac index and an increase in the arterial blood pressure. If the filling pressure lies between 9 and 12 mm Hg, it is our practice to elevate filling pressures to approximately 18 mm Hg. Beneficial effects on cardiac index are not seen in patients in whom left ventricular filling pressures are already elevated above these levels. Pressure levels above 18 mm Hg are associated with increasing degrees of pulmonary congestion, dyspnea, and pulmonary edema, resulting in increases of both cardiac and respiratory work. In these instances, the effects of impedance reduction' to facilitate left ventricular emptying has proven to be of immense significance in management of severe power failure of the heart. E. Deficiencies due to depressed myocardial contractile state include the cardiomyopathies, certain patients with ischemic heart disease, disorders of valve function, hypertensive heart failure, and many forms of pulmonary heart disease. The effects of selected inotropic agents on cardiac performance can be assessed by observation of cardiac index and ~P/ ~T as well as the level of left ventricular filling pressure. Increases in left ventricular dP/dt unassociated with increases in cardiac index or decreases in left ventricular filling pressure are unlikely to be of overall benefit either to body metabolic economics as a whole or to the metabolic state of the myocardium. F. By use of the multipurpose catheter incorporating atrial and ventricular pacing electrodes, the changes in cardiac performance associated with heart rate may be accurately measured, and if needs be, optimal heart rate may be established by selective pacing (Fig. 6).

HEART RATE CARDIAC OUTPUT

75

97

CI-2.0

L/min/M 2

RV ELECTROGRAM

Figure 6. Patient hospitalized with an acute myocardial infarction and severe hypotension (systolic pressure in radial artery around 60 mm Hg). A multipurpose flow-directed catheter inserted into the pulmonary artery showed a low cardiac index (2.0 L per min per M') at a relatively low heart rate of 75 beats per min (left hand panel). It was therefore decided to gradually raise the heart rate by atrial pacing, using the multipurpose catheter. The right hand panel illustrates the dramatic effect of elevated heart rate (to 97 per min) on cardiac index from 2.0 to 2.8 L per min per M2 arterial pressure (systolic value from 60 to 95 mm Hg).

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01

:r E E

* Figure 7. Picture of an original tracing showing elevated pulmonary artery pressure and following inflation of the balloon pulmonary capillary wedge pressure. The large "V" waves in the pulmonary wedge tracing are indicative of mitral regurgitation (in this case due to papillary muscle dysfunction following acute myocardial infarction).

Differential Diagnosis of Circulatory Syndromes Balloon flotation catheterization has been used to establish a precise diagnosis in more complex situations in the acutely ill. These include identification of mitral regurgitation as evidenced by a tall peaked V wave in the wedge position, ventricular septal defect due to ruptured ventricular septum, demonstration of significant pulmonary hypertension, and an increase in the oxygen saturation of the blood in the pulmonary artery over and above that of blood in the right atrium or in the cavae (Figs. 7 and 8). Chronic pulmonary disease is associated with a differential between diastolic pulmonary artery pressure and a mean or average pulmonary capillary wedge pressure in excess of 10 mm Hg. Cardiac tamponade2B may be suspected by equivalency of pressures in the right atrium and in the pulmonary capillary wedge position. In cardiac tamponade, the difference between these pressures is small in contrast to a minimal difference of 7 mm Hg in normal subjects.

t

ART. 02 SATURATION - 99 %

PRESSURE 200 mmHg 100

o PRESSURE 100 mmHg 50

t

~

o LEAD n Figure 8. Pulmonary artery hypertension and higher hemoglobin O2 saturation in the pulmonary artery (P A = 93 per cent) than in the right atrium (RA = 71 per cent) in a patient with ruptured interventricular septum following acute myocardial infarction.

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RATE

RA

RV

LEAD

n

Figure 9. Diagnosis of ventricular tachycardia by means of a flow-directed multipurpose catheter. The surface electrocardiogram (Lead II) shows wide QRS complexes appearing at a rate of 143 per min with no clearly identifiable atrial complexes. In the right atrial (RA) intracavity electrocardiogram atrial complexes appear at a regular rate of 97 per min, lower than the rate of ventricular complexes in the right ventricular (Ry) intracavity electrocardiogram, indicating atrioventricular dissociation.

The Diagnosis of Cardiac Arrhythmias The multipurpose catheter incorporating sensing electrodes in the ventricle and atrium allows for a differentiation of a number of complex cardiac arrhythmias (Fig. 9). The clear identification of ventricular activation, atrial activation, and their interrelationship allows for the recognition of a large number of important and specific arrhythmias. The quality of these signals is such as to facilitate automatic data processing applied to the recognition of dysrhythmias, their categorization, and the frequency of their occurrence. In addition, the effectiveness of conventional antiarrhythmic agents may be assessed with great objectivity and hard data endpoints by use of such signals which may be categorized and tabulated by automated detecting equipment.

COMPLICATIONS As indicated in the introductory paragraph of this article, the construction specifications of balloon flotation catheters are such as to minimize the occurrence of complications. The flexibility of the catheter shafts and the protective characteristics of the inflated balloon when the catheter passes through the right ventricle have contributed to the extremely small incidence of complications. However, this very simplicity and low incidence of complications inevitably results in disregard

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for the true potential hazards of any invasive technique. Further, the highly variable skill backgrounds, knowledge and expertise of the different categories of users of balloon flotation catheters are resulting in a significant number of avoidable, yet serious complications. 1. Probably the commonest single complication associated with balloon flotation catheterization are those associated with damage to the pulmonary parenchyma. In the first report of the complications of cardiac catheterization, Swan and Braunwald25 commented on the incidence of pulmonary infarction. Some balloon-tipped catheters tend to migrate peripherally. Persistent undetected wedging of the catheter tip is the most common mechanism of pulmonary infarction in long-term catheterization. The pulmonary infarction is usually small and· .•~ totally asymptomatic and only recognizable on careful comparison of chest _. roentgenograms before and after the catheter has been in position. 8 The incidence, extent, and seriousness of these infarcts may be increased if solutions are injected at relatively high pressure through the catheter lumen in order to restore an apparently damped pressure trace. Occasionally, pulmonary infarction is productive of symptoms and may result in evident consolidation in the lung fields. Pulmonary infarction can be avoided by monitoring catheter tip pressure continuously or at short intervals (15 to 30 min.). As a general rule, no attempt should be made to continuously monitor pulmonary capillary wedge pressure. It should be measured intermittently, particularly if there is substantive difference between diastolic pulmonary artery pressure and pulmonary capillary wedge pressure on first introduction of the catheter. It is our practice not to allow the catheter to remain in the wedge position for more than 1 or 2 minutes at anyone period of time. The balloon is then deflated, and the catheter allowed to record pulmonary artery pressure continuously. If the pressure is damped, the catheter is gently withdrawn 1 to 2 cm and a small injection of fluid is made to insure patency of the catheter lumen. To obtain subsequent wedge pressures, the balloon is again inflated slowly until the contour of the pulmonary arterial pressure alters to that of the pulmonary wedge pressure. If the volume of air required to inflate the balloon is substantively less than that recommended for initial flotation of the catheter, the catheter may lie in a distal pulmonary vessel close to the wedge position. An x-ray picture of the chest should be obtained, and if the catheter does lie peripherally, it should be withdrawn an appropriate distance so that it lies. in the main pulmonary artery or one of its primary branches. Rupture of the pulmonary artery has been recorded in association with balloon flotation catheterization. l • Rupture was associated with inflation of the balloon in a distal portion of the pulmonary vascular bed to provide a static obstruction. In one instance, saline was used to inflate the balloon. If the catheter tip lies distally in the pulmonary tree in a vessel which is not substantively larger than the dimensions of the catheter shaft, forces of great magnitude will be imposed upon the pulmonary arterial wall when the balloon is inflated. Normal pulmonary arteries are relatively thin structures of limited tensile strength and rupture of these vessels by an inflated balloon seems to be a ready possibility. As an alternate possibility, repeated flexion of a catheter tip in a distal vessel may account for nonfatal hemoptysis with disintegration of a more distal component of the pulmonary vascular bed. The hazard will be greater in patients receiving anticoagulants and in patients in whom serious pulmonary hypertension coexists. The primary prevention of pulmonary complications associated with balloon flotation catheterization is a continued awareness on the part of personnel as to the potential occurrence of these complications and their seriousness. This awareness and reasonable care in the placement of balloon catheter should IniniInize their occurrence. However, disregard for these potentially serious complications is an open invitation to disaster. 2. Although cardiac arrhythmias are extremely rare, several instances of relatively serious dysrhythInias have now been reported. These appeared to be ventricular fibrillation (readily resuscitated) and episodic ventricular tachycardia.

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Perhaps more commonly these complications are associated with a displacement of the catheter tip from the main pulmonary artery into the outflow tract of the right ventricle. When this occurs, the unprotected catheter tip may readily stimulate the sensitive endocardium of the right ventricular outflow tract. Inflation of the flotation balloon will allow the catheter to be propelled once again into the pulmonary artery. Otherwise, it should be withdrawn to the right atrium and if continued monitoring is necessary, recatheterization carried out in the routine fashion. 3. Thromboembolism: Whenever a foreign body exists in the cardiovascular system, it may serve as a focus for the buildup of thrombotic material. This is particularly important in the chronic seriously ill cardiac patient in whom hypercoagulability develops during the course of his acute illness. Under usual circumstances, anticoagulation is not necessary for a patient in whom flotation catheters are used for monitoring. However, if a hypercoagulable state exists or if prolonged monitoring becomes necessary, then serious consideration concerning anticoagulation is required. Numerous instances of thrombus formation on the balloon, on the shaft of the catheter, in the superior vena cava at the point at which the catheter enters the right atrium, and pulmonary infarctions which could·be due to pulmonary embolus originating from a thrombus on the catheter have been reported. 4. Balloon rupture is not uncommon, particularly in catheters which have been used on more than one occasion. Thin latex membranes possess the property of absorbing lipoproteins from the blood stream, thereby losing their elastance and favoring disintegration and rupture. Balloon rupture is more frequent if the recommended inflation volumes are seriously exceeded. This complication appears to be not uncommon (5 per cent) in catheters which have been subjected to multiple uses. In the normal circulation this does not appear to be a hazardous complication since the contained 0.8 to 1.5 ml of air is productive of neither symptoms nor adverse consequences. However, should air enter the left side of the heart, then the possibility of coronary or cerebral air embolus is a real one. For this reason, it is recommended that CO 2 be used as the inflation medium in diagnostic cardiac laboratories in which congenital heart disease with access to the left side of the circulation and the aorta is a possibility. However, CO 2 diffuses rapidly through thin latex membranes and is not readily available in most acute units. Possibly, the only serious complication of balloon rupture other than air embolus to the left side of the circulation is the fragmentation of a balloon so that a small segment embolizes in the distal pulmonary tree. Restriction of balloon flotation catheters to a single use or at the most a limited number of inflation-deflation cycles is indicated. 5. With the provision of a low impedance pathway to the central circulation by means of electrodes or a fluid column, attention must be given to the possibility of induction of serious cardiac dysrhythmias. Isolation of electrical and electronic devices are essential. 6. Infections have been reported, and localized thrombophlebitis associated with manipulation of the catheter or poor skin sterilization techniques. These necessitate removal of the catheter and are seldom of serious import. 7. Knotting in the catheter associated with continued manipulation was reported early in experience. Knotting is most frequent with the smallest catheters and the least frequent with the larger, in which the shaft's flexibility is limited. To date, catheter knotting, while certainly a cause of concern and embarrassment to physicians, has not proven to be of serious importance in that the catheter can usually be gently withdrawn to the site of insertion and, if need be, a venotomy carried out for removal of the tightened knot. Knotting is most readily avoided if on insertion care is taken not to continue to advance the catheter greatly beyond those distances at which entrance to the ventricle would be ordinarily anticipated, particularly when fluoroscopy is not available.

SUMMARY In summary, balloon flotation catheterization of the central circulation provides data in patient management which are meaningful and im-

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portant. It has allowed the application of sound physiologic principles to the understanding of the circulatory abnormalities characterizing an illness in an individual patient, and provides a rational basis for selection of therapy with objective, quantitative assessment of patient response. The procedures are simple, the complication rate is low, and the information highly relevant to clinical care.

REFERENCES 1. Agress, C., Wegner, S., Forrester, J. S., Chatterjee, K., Parmley, W. W., and Swan, H. J. C.: An indirect method for evaluation of left ventricular function in acute myocardial infarction. Circulation, 46:291-297, 1972. 2. Bleifer, V. W.: Bettseitige Kathetertechniken. Intensivmedizin, 10:232-239, 1973. 3. Bradley, R. D.: Diagnostic right heart catheterization with miniature catheters in severely ill patients. Lancet, 2:941-942, 1964. 4. Chatterjee, K., and Swan, H. J. C.: Vasodilator therapy in acute myocardial infarction. Mod. Conc. Cardiovas. Dis., 43:119-124,1974. 5. Chatterjee, K., Swan, H. J. C., Ganz, W., Gray, R., Loebel, H., Forrester, J. S., and Chonette, D.: Use of a balloon-tipped flotation electrode catheter for cardiac monitoring. Submitted to Am. J. Cardioi. 6. Diamond, G., Forrester, J. S., Chatterjee, K., Wegner, S., and Swan, H. J. C.: Mean electromechanical ilP/ilT. Am. J. CardioI., 30:338-342,1972. 7. Fitzpatrick, G. F., Hampson, L. G., and Burgess, J. H.: Bedside determination of left atrial pressure. J. Can. Med. Assoc., 106:1293-1298, 1972. 8. Foote, G. A., Schabel, S. I., and Hodges, M.: Pulmonary complications of the flowdirected balloon-tipped catheter. N. Eng. J. Med., 290:927-931, 1974. 9. Forrester, J. S., Ganz, W., Diamond, G., McHugh, T., Chonette, D., and Swan, H. J. C.: Thermodilution cardiac output determination with a single flow-directed catheter. Am. Heart J., 83:306-311, 1972. 10. Forrester, J. S., Diamond, G., McHugh, T., and Swan, H. J. C.: Filling pressures in the right and left sides of the heart in acute myocardial infarction: A re-appraisal of central-venous-pressure monitoring. N. Eng. J. Med., 285:190-193,1971. 11. Forrester, J. F., Chatterjee, K., and Swan, J. J. C.: Subsets in acute myocardial infarction. (In press) 12. Ganz, W., and Swan, H. J. C.: Measurement of blood flow by thermodilution. Am. J. CardioI., 29:241-245, 1972. 13 Ganz, W., Donoso, R., Marcus, H. S., Forrester, J. S., and Swan, H. J. C.: A new technique for measurement of cardiac output by thermodilution in man. Am. J. CardioI., 27:392396, 1971. 14. Golden, M. S., Pinder, T., Anderson, W. T., and Cheitlin, M. D.: Fatal pulmonary hemorrhage complicating use of a flow-directed balloon-tipped catheter in a patient receiving anticoagulant therapy. Am. J. CardioI., 32:865-867, 1973. 15. Hosie, K. F.: Thermal dilution techniques. Circ. Res., 10:491-504, 1962. 16. Jones, S. M., and Miller, G. A. H.: Catheterization of the pulmonary artery in transposition of the great arteries using a Swan-Ganz flow-directed catheter. Br. Heart J., 35:298-300, 1973. 17. Lategola, M., and Rahn, H.: A self-guiding catheter for cardiac and pulmonary arterial catheterization and occlusion. Proc. Soc. Exp. BioI. Med., 84:667-668, 1953. 18. McHugh, T., Forrester, J. S., Adler, L, Zion, D., and Swan, H. J. C.: Pulmonary vascular congestion in acute myocardial infarction: Hemodynamic and radiologic correlations. Ann. Int. Med., 76:29-33, 1972. 19. Meister, S. G., et al.: Transfemoral pacing with balloon-tipped catheters. J.A.M.A., 225:712-714,1973. 20. Scheinman, M. M., Abbott, J. A., and Rapaport, E.: Clinical uses of a flow-directed right heart catheter. Arch. Int. Med., 124:19-24, 1969. 21. Schwartz, D. C., and Kaplan, S.: Cardiac catheterization and selective angiography in infants with a new flow-directed catheter. Am. J. CardioI., 33:181,1974. 22. Stanger, P., Heymann, M. A., Hoffman, J. E., and Rudolph, A. M.: Use of the Swan-Ganz catheter in cardiac catheterization of infants and children. Am. Heart J., 83:749-754, 1972. 23. Steele, P., and Davies, H.: The Swan-Ganz catheter in the cardiac laboratory. Br. Heart J., 35:647-650,1973. 24. Swan, H. J. C.,: Central venous pressure monitoring is an outmoded procedure of limited practical value. In Ingelfinger, F., et al. (eds.): Controversy in Internal Medicine. Philadelphia, W. B. Saunders Co., 1974,2:185-193.

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25. Swan, H. J. C., and Braunwald, E.: Angiocardiography. Cooperative study on cardiac catheterization. New York, Am. Heart Assoc., May, 1968. 26. Swan, H. J. C., Forrester, J. S., Diamond, G., Chatterjee, K., and Parmley, W. W.: The hemodynamic basis of shock and acute myocardial infarction: A conceptual model. Circulation, 45:1087-1110,1972. 27. Swan, H. J. C., Ganz, W., Forrester, J. S., Marcus, H., Diamond, G., and Chonette, D.: Catheterization of balloon-tipped catheter. N. Eng. J. Med., 283:447-451,1970. 28. Weeks, K., Chatterjee, K., Block, S., Matloff, J., and Swan, H. J. C.: Bedside hemodynamic monitoring-its value in the diagnosis of tamponade complicating cardiac surgery. Submitted to the N. Eng. J. Med.

Department of Cardiology Cedars-Sinai Medical Center 4833 Fountain Avenue Los Angeles, California 90029