Transcranial Doppler ultrasonography as a screening technique for detection of a patent foramen ovale before surgery in the sitting position

Background: Venous air embolism has been reported to occur in 23-45% of pat ients undergoing neurosurgical procedures in the sitting position. If venou s air embolism occurs, a patent foramen ovale (PFO) is a risk factor for pa radoxical air embolism and its sequelae. Preoperative screening for a PFO i s therefore recommended by some investigators. The reference standard for i dentifying a PFO is contrast-enhanced transesophageal echocardiography (c-T EE), Contrast-enhanced transcranial Doppler ultrasonography (c-TCD) and con trast-enhanced transthoracic echocardiography (c-TTE) are noninvasive alter native methods, but so far there are no studies as to their diagnostic vali dity in neurosurgical patients. Methods: The sensitivity and specificity of c-TCD and c-TTE in detecting a PFO were determined in a prospective study using c-TEE as the reference sta ndard. Preoperative c-TCD, c-TTE, and c-TEE studies were performed during t he Valsalva maneuver after intravenous echo-contrast medium (D-Galactose, E chovist-300, Schering AG, Berlin, Germany) was administered in 92 consecuti ve candidates (47 men and 45 women; mean age, 51 yr, range, 25-72 yr) befor e neurosurgical procedures in the sitting position. Results: A PFO was detected in 24 of the 92 patients (26.0%) using c-TEE. c -TCD correctly identified 22 patients, whereas c-TTE only correctly identif ied 10. This corresponds to a sensitivity of 0.92 for c-TCD and 0.42 for c- TTE. The negative predictive value was 0.97 for c-TCD compared with 0.83 fo r c-TTE, The prevalence of a PFO in patients with a posterior fossa lesion was 27%, and in the group with cervical disc herniation was 24% as detected by c-TEE. The incidence of intraoperative venous air embolism was 35% In c ases of cervical foraminotomy and 75% in posterior fossa surgery as detecte d by c-TEE, Conclusions: c-TCD is a highly sensitive and highly specific method for det ecting a PFO, Because c-TCD is noninvasive, it may be more suitable than c- TEE for routine preoperative screening for a PFO. C-TIE is not reliable in detecting a PFO.