Scimitar syndrome

In an acute trauma patient with unrecognized scimitar syndrome, physiologic measurements used in patient management decisions were misleading due to the anatomic and physiologic anomalies of the syndrome. Pulmonary artery catheter measurements believed to reflect left atrial pressures were actually measuring central venues pressures because the catheter was terminating in the scimitar vein. These erroneous measurements led to early aggressive fluid erroneous measurements led to overly aggressive fluid resuscitation and iatrogenic pulmonary edema. The pathologic features of scimitar syndrome are reviewed, and the mechansism for potential mismanagement of patient volumne status created by aberrant pulmonary hemodynamics is discussed.

The scimitar syndrome, also referred to as hypogenetic lung syndrome or congenital venolobar syndorme, represents a rare, variable, and complex congenital anomaly classically consisting of a hypoplastic right lung with partial or complete systemic arterial supply and anomalous pulmonary return to the inferior vena cava (IVC). The syndrome may alos include anomalies of the tracheobronchial architecture, cardiovascular abnormalities, and diaphragmatic abnormalities.[1] The abnormal pulmonary venous pattern drainage typically produces a curvilinear shadow seen at the right lung base on chest radiography that resembles a sickleshaped sword or scimitar.

Herein we describe a patient with acute blunt trauma with initially unrecognized scimitar syndrome in whom a pulmonary artery (PA) catheter terminating in the abnormally draining vein indicated central venous pressure (CVP) rather than left atrial end-diastolic pressure. Management of the patient utilizing this misleading information resulted in development of iatrogenic pulmonary edema during fluid resuscitation.

CASE REPORT

A 49-year-old unrestrained driver involved in a motor vehicel accident was admitted to the Shock-Trauma Center of the University of Maryland Medical Center for evaluation and treatment of multiple thoracic, pelvic, facial, and extremity injuries. An early chest radiograph (Fig 1) revealed multiple right-sided rib fractures, opacification of a significant of a significant portion of the right hemithorax, and apparent shift of the mediastinum to the right. The overall appearance of the hemithorax initially suggested a combination of pleural fluid (most likely hemothorax and right lower lobe consolidation (most likely contusion and/or atelectasis). A "scimitar" draining vein shadow was visible at the right lung base (arrows), but was recognized as such only retorspectively after identification by thoracic computed tomography (CT). Due to the patient's multiplde injuries and need for intravenous fluid resuscitation, a PA catheter was introduced to monitor central and pulmonary artery pressures. Despite pulmonary edema by both clinical and radiologic criteria consistently in the normal range (6 to 12 mm Hg), the patient developed pulmonary edema by both clinical and radiologic criteria (Fig 2). Retrospective analysis of physiologic data revealed that CVP measurements were essentially equivalent to concurrent PCWP measurements (Fig 3). Since the PA catheter always terminated in the right pulmonary artery (note position in Fig 2), pressure measurements with the ballon inflated (wedged) reflected CVP rather than left atrial pressure end-diastolic pressure due to the anomalous systemic venous return Fig 4, diagram). These anomalous hemodynamic measurements contributed to overly aggressive fluid resuscitation resulting in iatrogenic pulmonary edema.

DISCUSSION

Scimitar syndrome is a rare congenital anomaly characterized by a hypoplastic, alomst invariably right-sided lung, anomalous venous return, and abnormal arterial supply. Additional features that may coexist include accessory or eventrated diaphragm, hemivertebrae, and scoliosis. Cardiovascular abnormalities, most commonly atrial septal defect, coarctation of the aorta, patent ductus arteriosus, and tetralogh of Fallot, may be present as well.[1,2]

Patients with scimitar syndrome are typically asymptomatic.[3] Because of this, the actual prevalence of this rare syndrome is difficult to determine. The diagnosis is usually suspected as a result of incidental discovery of the scimitar vein on chest radiograph. Symptoms when present, most often include the following: (1) recurrent pulmonary infection secondary to alteration of the tracheobronchial architecture; (2) congestive heart failure due to left to right shunt from the anomalous draining vein; or (3) associated cardiac malformations.

The PA catheter measurements very effectively monitor left atrial filling pressures allowing safe and adequate fluid resuscitation. The pulmonary artery catheter's value in determining the hemodynamic status of a patient is predicated upon the ability to obtain pressure measurements that can be extrapolated to reflect the volume status of the various heart chambers. Of paramount importance in most cases, and in this patient in particular, is a determination of the left ventricular end-diastolic volume. With the ballon inflated within a segment of the pulmonary artery, the pressure transmitted to the transducer is a reflection of the left atrial pressure. At end-diastole, with the mitral valve open, the transmitted pressure reflects the pressure at end-diastole in the left ventricle. These pressures are converted to volumes and cardiac function based upon the Starling relationship.[4]

The CVP is theoretically linked to the filling pressures of the ventricles but is removed from it by a significant series of "baffles" such as the right cardiac chambers which interfere with the ability to determine the left ventricular volume and pressure status. In a young lealthy adult with a normal cardiopulmonary circuit, the CVP may be an accurate reflection of all central filling pressures. However, with any pathologic or stress state, the baffle effect, as well as the varying compliance of the different conduits between the left ventricle and the central vein (pulmonary artery, right ventricle, right atrium, and vena cava) decrease the ability to determine left-sided cardiac function.

The PA catheter measurments are made with the premise that the catheter is wedged in a branch of the pulmonary artery and reflects left atrial pressures. Due to the unique pathophysiology of the scimitar syndrome, however, there is partial or complete drainage of the right lung into the systemic venous circulation, usually, as in the case, into the IVC, or less commonly into the right atrium or a hepatic vein. If, as in the case, the catheter is wedged in a branch of the right lung, the pressure readings erroneously reflect CVP rather than left atrial pressure. Fluid management will then be tailored to the CVP pressures and could result in iatrogenic pulmonary edema. Pressure readings reflecting low or normal "pseudo-left atrial pressures" would lead to a maintained or increased rate of fluid replacement since actual left atrial pressure are not being measured. In the current case, the pressure readings were a reflection of a very compliant right heart and veins and contributed to overly aggressive volume therapy with consequent pulmonary edema.

In patients in whom the presence of scimitar syndrome is known or is ascertained from the chest radiograph, placement of the pulmonary artery catheter into a branch of the left pulmonary artery would obviate these problems because of its normal venous drainage to the left atrium.

This case illustrates that when the pathophysiologic consequences of the abnormal pulmonary venous drainage pattern associated with the scimitar syndrome are not recognized, and pulmonary artery catheter measurements are obtained from the side with anomalous venous drainage, iatrogenic pulmonary edema may result.

REFERENCES

[1] Folger GM. The scimitar syndrome: anatomic, physiologic, developmental, and therapeutic considerations. AQngiology 1976; 27:373-407

[2] Heitzman RE. The lung: radiologic-pathologic correlations. 2nd ed. St. Louis: CV Mosby Co, 1984; 27-34

[3] Sweeney WB. Scimitar syndrome. Military Med 1988; 153:209-12

[4] Guyton AC. Textbook of medical physiology. 8th ed. Philadephia: WB Saunders Co, 1991; 106

COPYRIGHT 1993 American College of Chest Physicians
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