[Intraoperative transesophageal versus preoperative transthoracic contrast echocardiography. A method for detection of patent foramen ovale in neurosurgical patients]. / Intraoperative transösophageale versus präoperative transthorakale Kontrast-Echokardiographie. Eine Methode zum Nachweis eines funktionell offenen Foramen ovale bei neurochirurgischen Patienten.

ABSTRACT

Preoperative detection of a patent foramen ovale (PFO) may be achieved employing either transthoracic echocardiography (TTE) with the Valsalva manoeuvre in the awake patient or trans-oesophageal echocardiography (TEE) in the anaesthesised patient. Our study was undertaken to validate these methods with regard to their efficacy in identifying patients at risk for paradoxical air embolism (PAE). METHODS. In 67 patients ranging from 28 to 70 years of age, TTE was performed utilising the Valsalva manoeuvre prior to surgery. The patients were informed about all procedures and agreed to take part in the study. After induction of anaesthesia the patients were evaluated with TEE in the supine and sitting positions. At end-inspiration 10 ml agitated gelatine solution (Gelafundin) was injected through a central venous catheter into the right atrium after airway pressure of 20 cm H2O had been maintained for 5 s. The injected bolus was observed throughout the ventilatory cycle, with special attention being given to early expiration and systole. A right-to-left shunt was assumed if five echo targets were observed in the left atrium. RESULTS. The prevalence of PFO detected by TTE/Valsalva was 9%. The diagnosis was confirmed by TEE in 2 patients in the supine and 1 in the sitting position. An echocardiogram in these patients showed bulging of the septum to the left, which was not seen in those patients in whom PFO was detected only by TTE. DISCUSSION. The reason for the lower incidence of PFO detected by TEE during airway pressure 20 cm H2O may have been an insufficient increase of pressure in the right atrium with a negative right-to-left atrial pressure gradient. A standardised ventilation manoeuvre with supra-atmospheric airway pressure of 20 cm H2O is not sufficient. Bulging of the intra-atrial septum from right to left during airway pressure is a possible indication of the efficacy of the manoeuvre, regardless of the influence of the breathing pattern.