Ann Thorac Surg 1995;60:630-634
© 1995 The Society of Thoracic Surgeons
Original Articles: General Thoracic
Pressure Gradient Across the Pulmonary Artery Anastomosis During Lung Transplantation
George J. Despotis, MD,
Menelaos Karanikolas, MD,
Anastasios N. Triantafillou, MD,
Charles G. Pond, MD,
George V. Kirvassilis, MD,
G. Alexander Patterson, MD,
Joel D. Cooper, MD,
Demetrios G. Lappas, MD
Departments of Anesthesiology and Surgery, Washington University School of Medicine, St. Louis, Missouri
Accepted for publication April 12, 1995.
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Abstract
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Background. Perioperative monitoring of pulmonary artery (PA) pressures in lung transplant recipients is critical. This report characterizes an intraoperative gradient across the PA anastomosis in a series of patients undergoing bilateral sequential lung transplantation.
Methods. Hemodynamic measurements were obtained in a series of 10 patients before anesthetic induction, during one-lung ventilation/perfusion of the newly transplanted first lung with the PA catheter proximal and distal to the anastomosis and after arrival in the intensive care unit. The following measurements were recorded: central venous pressure, cardiac output, PA occlusion pressure, and systemic and pulmonary arterial pressures (systolic, diastolic, mean).
Results. Although a systolic pressure gradient of more than 10 mm Hg across the anastomosis was observed in all patients, there was a significant variation in systolic (13 to 59 mm Hg), diastolic (2 to 10 mm Hg), and mean (5 to 27 mm Hg) PA gradients. Mean proximal systolic PA pressure measurements (56.2 ± 20.6 mm Hg) were greater when compared to measurements obtained distal to the anastomosis (28.6 ± 10.1 mm Hg, p = 0.001) and to those obtained in the postoperative period (32.1 ± 9.7 mm Hg, p = 0.004).
Conclusions. The present study demonstrates that during single-lung ventilation and perfusion, the PA pressure measured proximally may not reflect accurately the pressure distal to the vascular anastomosis.
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Introduction
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P ulmonary artery (PA) catheters allow clinicians to monitor continuously right atrial, PA, and pulmonary capillary wedge pressures [1] and to measure cardiac output (CO) [2] in patients undergoing major cardiac surgical procedures [3]. Furthermore, pulmonary (PVR) and systemic vascular resistance (SVR) can also be calculated. During lung transplantation, PA pressure measurements and PVR calculations can be used to provide an index of the resistive component of right ventricular afterload and determine the need for cardiopulmonary bypass to protect the heart and lungs. Similarly, SVR calculations can be used to provide an indirect assessment of left ventricular afterload. Because PA pressures are used to calculate PVR, accurate PA catheter readings are important in decision making and direction of therapeutic interventions.
It is well recognized that a gradient often exists across vascular anastomosis [4] including obstruction of right ventricular outflow, which has been described after single-lung transplantation [5]. Although in most instances the magnitude of the gradient is small and not clinically significant, an increased gradient can be seen during conditions of increased flow through the pulmonary artery. Such a circumstance exists after the first lung implantation during bilateral single-lung transplantation when the entire CO goes through that newly trans-planted graft. We have observed a pressure gradient across the first PA anastomosis in patients undergoing lung transplantation. Although the magnitude of the pressure gradient across the PA anastomosis can vary from a few to several millimeters of mercury, inaccurate pressure measurements, if not recognized promptly, can potentially influence intraoperative decision making. In this report we characterize an intraoperative gradient across the PA anastomosis in a series of lung transplant patients during single-lung ventilation and perfusion.
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Material and Methods
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Patient Series and Intraoperative Anesthetic Management
From July 1993 to June 1994, a total of 32 consecutive bilateral single-lung transplantations were performed at Barnes Hospital, Washington University School of Medicine. After our initial intraoperative observation of a gradient across the PA anastomosis during lung transplantation, we measured and recorded hemodynamic data in 10 of these 32 lung transplant recipients. Presenting pulmonary diagnosis of the 10 patients included 1 patient with a preoperative history of interstitial pneumonitis, 2 with a history of cystic fibrosis, 2 with a history of pulmonary fibrosis, and 5 patients with a history of emphysema of which 2 had 
-1 deficiency. There were four women and five men in our series with a mean age of 48 years (47 ± 12 years). Our patients had a mean weight of 74 kg (74 ± 12 kg) and a mean height of 172.72 cm (172.72 ± 6.1 cm). Preoperative cardiac function data included right (0.39 ± 0.08) and left (0.59 ± 0.09) ventricular ejection fraction. Data were used in this study after approval from our Institutional Human Studies Committee. Before anesthetic induction, insertion of routine intravenous and intraarterial lines included peripheral venous cannulation with a 14-gauge intravenous catheter, radial arterial cannulation with a 20-gauge intraarterial catheter, and percutaneous cannulation of the right internal jugular vein with a 8.5F cordis sheath. Subsequently, an Opticath (Abbott Laboratories, North Chicago, IL) oximetric PA catheter was floated into the wedge position and secured. All patients were anesthetized with an opioid-based technique, and the anesthetic was supplemented with inhalational anesthetic agents, muscle relaxants, and benzodiazepines. A transesophageal echocardiography probe was inserted into the patient's esophagus to approximately 40 cm.
Operative Technique
All procedures described in this report were performed by one of the three experienced lung transplant surgeons in our center. As previously described, the surgical approach used in our patients for bilateral, sequential single-lung transplant procedures involved a bilateral anterolateral fourth interspace thoracosternotomy, explantation, and implantation [6]. Before surgical division of the PA, the PA catheter was routinely withdrawn to approximately 40 cm. Anastomotic sequence for each side was as follows: main bronchus, main pulmonary artery, and left atrium. Donor and recipient PAs were trimmed to avoid excessive length. The arterial anastomosis were performed with two running 5-0 polypropylene sutures knotted at two points in the anastomotic circumference. Minimal spacing between sutures was used to avoid anastomotic narrowing. The left atrial anastomosis was constructed between donor and recipient common left atrial cuffs using two running 4-0 polypropylene sutures knotted at two points in the anastomotic circumference. All anastomoses of interest in this report were judged by the operating surgeon to be technically satisfactory during their construction.
Technique for Measurement of Pulmonary Arterial Pressure Gradient
After transplantation of the first lung, the clamps were removed, the transplanted organ was reperfused, and the patients were monitored for hemodynamic or oxygenation derangements. Subsequently, the opposite lung was deflated and its PA clamped. At this point, PA catheter-derived measurements were obtained. Pulmonary arterial pressures were measured initially proximal to the PA anastomosis, with a corresponding PA catheter distance of 40 to 45 cm from the site of insertion into the introducer. To obtain measurement of PA pressures distal to the anastomosis, the balloon of the PA catheter was inflated and gently advanced into a ``wedge position.'' The catheter was then advanced 2 to 4 cm further, followed by balloon deflation. After advancement of the catheter (50 to 62 cm), the distal port of the PA catheter was invariably beyond the first PA anastomosis and this position was confirmed by direct palpation by the surgeon. Figure 1
schematically illustrates advancement of the PA catheter and corresponding strip recordings of heart rate, systemic, PA, and central venous pressure (CVP) measurements. In each of the patients of this report, the PA anastomosis was palpated and visually inspected by the operating surgeon and deemed of satisfactory caliber after the PA gradient was identified.
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Fig 1. . Schematic illustration of advancement of the pulmonary artery (PA) catheter through the left-sided PA anastomosis from the proximal (top) to distal positions (bottom) and corresponding strip recordings of heart rate, systemic arterial pressure (AP), PA, and central venous pressure (CVP) measurements. Systemic and PA pressure expressed as systolic/diastolic and mean (in parentheses) pressures. (A = anastomosis; LPA = left pulmonary artery; MPA = main pulmonary artery trunk.)
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Hemodynamic Measurements
Preoperative demographic and clinical data were obtained for each patient. Hemodynamic measurements included: systolic, diastolic, and mean (MAP) systemic arterial pressures; systolic, diastolic, and mean pulmonary arterial (MPAP) pressures; CVP; pulmonary artery occlusion pressure (PAOP); and CO measurements. Systemic vascular resistance and PVR were calculated using the formulas SVR = (MAP - CVP)/CO x 80; PVR = (MPAP - PAOP)/CO x 80, respectively. Hemodynamic data were collected at three distinct periods: (1) before the beginning of the operation (preinduction); (2) during one-lung ventilation of the transplanted first lung with the PA catheter in the proximal (intraoperative: proximal) and distal (intraoperative: distal) positions; and (3) after conclusion of the operation in the intensive care unit distal to the anastomosis (postoperative).
Statistical Analysis
Mean and standard deviation values were calculated for each set of measurements. Measurements obtained from each period were compared to measurements obtained from the preinduction or intraoperative (proximal) periods for statistical significance using Student's t test for unpaired observations. A t test for unequal variances was used if variances between groups were statistically different as assessed using Bartlett's test. A p value less than 0.05 was considered statistically significant.
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Results
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Proximal and distal PA pressures obtained intraoperatively along with calculated gradients are listed for each individual patient in Table 1. In addition, Table 1 lists the corresponding perfusion results for the initially transplanted graft. As demonstrated by the wide ranges, there was a significant variation in systolic (13 to 59 mm Hg), diastolic (2 to 10 mm Hg), and mean (5 to 27 mm Hg) gradients. Mean systemic and intracardiac or extracardiac pressures for each of the perioperative periods are summarized in Table 2. In 1 patient we confirmed PA pressure measurements by comparing them to measurements obtained directly through a needle. Figure 2 illustrates the similarity between PA pressure measurements obtained using our technique for catheter advancement and PA pressure measurements obtained simultaneously with direct needle measurements in this patient.
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Fig 2. . Comparison of pulmonary artery (PA) pressure measurements obtained with a PA catheter (PA catheter) to measurements obtained simultaneously directly through a needle (Needle) in 1 patient. Measurements are compared in both proximal and distal positions in reference to the PA anastomosis using our technique for catheter advancement (see text for description). Pulmonary artery pressure measurements obtained with the PA catheter are displayed and expressed as systolic/diastolic and mean (in parentheses) pressures.
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Mean systemic arterial pressure values obtained intraoperatively were statistically less than those obtained before anesthetic induction. Proximal systolic PA pressure measurements were greater when compared to corresponding measurements obtained distal to the anastomosis (p = 0.001) and to those obtained in the postoperative period (p = 0.004). Diastolic PA pressure tended to be greater when proximal and distal measurements were compared, but this difference did not reach statistical significance (p = 0.1). Proximal mean PA pressure values were greater than corresponding measurements obtained distal (p = 0.009) to the anastomosis and those obtained in the postoperative period (p = 0.01). Mean SVR values were similar between measurement intervals. Mean PVR values calculated using proximal intraoperative PA pressure were greater than mean PVR values using distal intraoperative values (p = 0.03) and postoperative values (p = 0.02).
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Comment
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Perioperative monitoring of PA pressures in lung transplant recipients is critical. Increases in PA pressure are commonly encountered during lung transplantation and may be related to either elevation of PVR or stenosis at the site of PA anastomosis [4]. In this setting, PA pressure measurements and PVR calculations are frequently used to assess indirectly right ventricular afterload and determine the need for cardiopulmonary bypass. Cardiopulmonary bypass is sometimes used with lung transplantation to protect the heart, provide hemodynamic stability, and provide adequate oxygenation in the setting of donor pulmonary dysfunction. Although use of cardiopulmonary bypass with lung transplantation has been implicated in early graft dysfunction [7], another report [8] indicated that use of cardiopulmonary bypass did not seem to affect adversely outcome in bilateral sequential lung recipients. Use of cardiopulmonary bypass has been shown to be associated with increases in extravascular lung water even if it is not accompanied by severe pulmonary dysfunction [9]. It is important, therefore, to determine the accurate PA pressures and differentiate proximal versus distal PA pressure values as treatment will be decided accordingly. On this basis, this study was designed to characterize the degree of a gradient across the PA anastomosis and its potential impact on intraoperative monitoring and management of hemodynamics. The significance and implications of this gradient on residual anastomotic stenosis in the postoperative period was not assessed.
The present study demonstrates that during lung transplantation, the PA pressure measured proximally may not reflect accurately the pressure distal to the vascular anastomosis. In our series of 10 lung transplant recipients, all patients had a systolic PA pressure gradient of more than 10 mm Hg across the anastomosis that was observed during the transplantation of the second lung when all pulmonary blood flow was diverted to the newly transplanted lung. Accordingly, elevated PA pressures and the pressure gradient observed across the PA anastomosis were reduced after unclamping of the contralateral graft. Although 10 bilateral lung transplant recipients had anastomotic gradients during one-lung ventilation and perfusion, the exact incidence of this phenomenon is not known. It is noteworthy that PA pressures distal to the anastomosis were similar to those obtained during the postoperative period. This indicates that when a significant anastomotic gradient is demonstrated intraoperatively, the distal pressures obtained intraoperatively may be used to approximate the distal PA pressure postoperatively.
During lung transplantation, elevated PA pressures attributable to elevated PVR are frequently treated with administration of pulmonary vasodilator drugs such as prostaglandin E1 or prostacyclin to minimize reperfusion injury to the transplanted lungs [10, 11] and to reduce right ventricular afterload [12]. Pharmacologic manipulation of PVR to reduce elevated PA pressures can only be beneficial if it is based on data reflecting accurately the pressure in the pulmonary vascular tree of the transplanted lung beyond the PA anastomosis. In certain patients the readings of the PA catheter may significantly overestimate the pressure in the PA and corresponding estimates of PVR in the vascular tree of the graft as demonstrated by our data. Because pulmonary endothelial dysfunction has been shown to correlate with PVR after reperfusion [13], an intervention initiated to reduce the PA pressure to attenuate reperfusion injury to the graft or reduce right ventricular afterload, may not be indicated and potentially could be deleterious.
The total load to the right ventricle comprises the static load presented by PVR but also the dynamic load dictated by vascular compliance and wave reflection [14]. In patients with elevated proximal PA pressures, the load imposed on the right ventricle is probably determined predominately by the dynamic vascular compliance that has been transformed into a fixed or reduced vascular compliance by the anastomosis. Although prostaglandin E1 can improve right [15] and left [16] heart function in patients with heart failure, large doses of pulmonary vasodilators such as prostaglandin E1 can also reduce preload and afterload [17], which may result in hypotension and unnecessarily compromise an already hemodynamically unstable patient. Accordingly, use of large doses of pulmonary vasodilators would not be indicated for proximal PA hypertension. Inotropic and vasopressor therapy is often combined with intravascular volume expansion to maintain systemic blood pressure in this setting. Preferential use of these agents would be indicated to optimize right ventricular function in the setting of isolated proximal PA hypertension as it has been demonstrated that vascular stiffening may limit ventricular reserve capacity under conditions of increased demand [18].
Pulmonary arterial stenoses were not evident postoperatively as demonstrated by perfusion scans that did not reveal significant discrepancies in blood flow between lungs in this series of patients (Table 2
). However, postoperative perfusion scans do not fully exclude the presence of an anastomotic stenosis that may have relevance in the postoperative period when patients initiate exercise. Under these higher CO conditions, right ventricular strain may occur if the afterload is elevated because of a significant anastomotic gradient. A confounding factor relates to whether or not both anastomoses have a gradient and to what degree. If only a unilateral anastomotic gradient exists, blood flow would be diverted preferentially to the contralateral lung and a gradient may not be demonstrated until a much higher CO is achieved. Therefore, the work load on the right ventricle may not be increased dramatically. Evaluation of a pressure gradient in the postoperative period would be difficult based on our inability to reproduce the intraoperative conditions involving one-lung perfusion during the postoperative period. Right ventricular function can be evaluated in this setting using intracardiac pressure measurements or transthoracic echocardiography, or both. Although not evaluated in this study, an anastomotic gradient may also have a protective effect on the first transplanted lung. Further studies, preferentially using animal models, are needed to completely address these issues.
Although misleading wedge pressure measurements have been cited after pneumonectomy [19], this report describes the presence of a significant pressure gradient across the PA anastomosis in lung transplant recipients. Physicians managing these patients should be aware of this discrepancy. Accordingly, therapeutic interventions based on misleading information may be unnecessary and potentially compromise hemodynamic stability. Further studies are needed to determine the incidence of low-grade anastomotic stenoses and whether or not they affect right ventricular performance in the postoperative period when patients initiate exercise.
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Acknowledgments
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We express our appreciation to Dr Paul M. Heerdt for his review of this study.
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Footnotes
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Address reprint requests to Dr Despotis, Division of Cardiothoracic Anesthesia, Department of Anesthesiology, Washington University School of Medicine, Box 8054, 660 S Euclid Ave, St. Louis, MO 63110.
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References
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- Lappas D, Lell WA, Gabel JC, et al. Indirect measurement of left atrial pressure in surgical patients-pulmonary capillary wedge pressure and pulmonary artery diastolic pressure compared with left atrial pressure. Anesthesiology 1973;38:394–7.[Medline]
- Kohanna FH, Cunningham JN. Monitoring of cardiac output by thermodilution after open heart surgery. J Thorac Cardiovasc Surg 1977;73:451–7.[Abstract]
- Waller JL, Johnson SP, Kaplan JA. Usefulness of pulmonary artery catheters during aortocoronary bypass surgery. Anesth Analg 1982;61:221–2.
- Griffith BP, Magee MJ, Gonzalez IF, et al. Anastomotic pitfalls in lung transplantation. J Thorac Cardiovasc Surg 1994;107:743–54.[Abstract/Free Full Text]
- Ritchie ME, Davila-Romain VG, Barzilai B. Dynamic right ventricular outflow obstruction after single-lung transplantation. Chest 1994;105:61–611.
- Pasque MK, Cooper JD, Kaiser LR, Haydock DA, Triantafillou A, Trulock EP. Improved technique for bilateral lung transplantation: rational and initial clinical experience. Ann Thorac Surg 1990;49:785–91.[Abstract]
- Aeba R, Griffith BP, Kormos RL, et al. Effect of cardiopulmonary bypass on early graft dysfunction in clinical lung transplantation. Ann Thorac Surg 1994;57:715–22.[Abstract]
- Triantafillou AN, Pasque MK, Huddleston CB, et al. Predictors, frequency, and indications for cardiopulmonary bypass during lung transplantation in adults. Ann Thorac Surg 1994;57:1248–51.[Abstract]
- Boldt J, von Bormann B, Kling D, Scheld HH, Hemplemann G. The influence of extracorporeal circulation on extravascular lung water in coronary surgery patients. Thorac Cardiovasc Surg 1986;34:110–5.
- Christie NA, Waddell TK. Lung preservation. In: Patterson GA, Cooper JD, eds. Lung transplantation. Chest Surg Clin North Am 1993;3:29–48.[Medline]
- Sundaresan S, Trachiotis GD, Aoe M, Patterson GA, Cooper JD. Donor lung procurement assessment and operative technique. Ann Thorac Surg 1994;56:1409–13.
- Pacher R, Globits S, Wutte M, et al. Beneficial hemodynamic effects of prostaglandin E1 infusion in catecholamine-dependent heart failure; results of a prospective, randomized, controlled study. Crit Care Med 1994;22:1084–90.[Medline]
- Kimblad PO, Sjoberg T, Steen S. Pulmonary vascular resistance related to endothelial function after lung transplantation. Ann Thorac Surg 1994;58:416–20.[Abstract]
- Piene H. Matching between right ventricular and pulmonary bed. In: Yin FCP, ed. Ventricular/vascular coupling. New York: Springer-Verlag, 1986:192–9.
- Armitage JM, Hardesty RL, Griffith BP. Prostaglandin E1: an effective treatment of right heart failure after orthotopic heart transplantation. J Heart Transplant 1987;6:348–51.[Medline]
- Virgolini I, Kaliman J, Fitscha P, et al. Beneficial effect of long-term PGE1 treatment in left ventricular heart failure. Prostglandins Leukot Essent Fatty Acids 1989;38:177–80.[Medline]
- Moncada S, Flower RJ, Vane JR. Prostaglandins, prostacyclin, thromboxane A2, and leukotrienes. In: Goodman LS, Gilman EG, eds. The pharmacological basis of therapeutics. New York: MacMillan, 1985:660–73.
- Kelly RP, Tunin R, Kass DA. Effect of reduced aortic compliance on cardiac efficiency and contractile function of in situ canine left ventricle. Circ Res 1992;71:490–502.[Abstract/Free Full Text]
- Whittnich C, Trudel J, Zidulka A, Chiu RC-J. Misleading ``pulmonary wedge pressure'' after pneumonectomy: its importance in postoperative fluid therapy. Ann Thorac Surg 1986;42:192–6.[Abstract]
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Abstract
Introduction
