Patient A
A 34-year-old male patient was scheduled for neurosurgical removal of a left-sided vestibular schwannoma in a semi-sitting position. Apart from a diagnosis of multiple sclerosis in 2018, there were no other preexisting conditions in the patient's history. The left-sided schwannoma was incidentally discovered during regular MRI follow-up examinations for multiple sclerosis. Although the patient was mostly asymptomatic, with only mild hypacusis, surgical removal was recommended due to the tumor's persistent growth, and the patient was referred to our hospital.
General anesthesia was administered without complications prior to surgery. Following our standardized approach, the patient was equipped with an endotracheal tube, an arterial cannula, a urinary catheter, and a central venous catheter. The catheterization of the left inferior jugular vein was performed under ultrasound guidance. The placement of the left central venous catheter was easy, without resistance or unusual complications. To detect a patent PFO as a potential right-to-left shunt, the interatrial septum was examined using contrast echocardiography (microbubbles) and color Doppler. This assessment was conducted during the release of a Valsalva maneuver, as this is when right-to-left flow is most likely to occur. This study revealed a significant number of bubbles solely in the left atrium, leaving the right atrium bubble-free (Fig. 1).
Manometry monitoring showed a venous pressure curve, but blood gas analysis from the left central line displayed typical arterial measurements, suggesting its possible localization in a pulmonary vein (Table 1). Consequently, the left central venous catheter was not used for administering medications, and another catheter was placed into the right internal jugular vein under ultrasound guidance. A CT scan of the thorax was initially interpreted to show an incorrect mediastinal position of the left central line with possible perforation of both the left brachiocephalic vein and the left upper pulmonary vein. However, further investigation of the CT images involved an interdisciplinary approach with radiologists, cardiac surgeons, neurosurgeons, and anesthesiologists. After careful analysis and discussion, the central line was identified to be inside a filiform persistent left superior vena cava (Fig. 2).
The microsurgical removal of the vestibular schwannoma was successfully completed. In the ICU, the left central line was removed without complications, followed by frequent echocardiographic exams to rule out cardiac tamponade and hemothorax (Fig. 3). The patient was extubated the following day and transferred to the general ward. He experienced a mild aggravation of his preexisting hypacusis, and initial postoperative vertigo was successfully treated with physical therapy. The patient was discharged after seven days.
Table 1
Patient A’s blood gas analysis with sample taken from the left sided central line expressing values typical for an arterial sample (bolded)
| time | 15:33 | 17:40 | | |
| pH | 7.41 | 7.40 | | (7.37–7.45) |
| pO₂ | 294 | 230 | mmHg | (35–45) |
| base excess | -1.2 | -1.0 | mmol/l | (-2 - +3) |
| K+ | 3.84 | 4.23 | mmol/l | (3.6–4.8) |
| Na+ | 137 | 139 | mmol/l | (135–145) |
| Ca2+ | 1.19 | 1.22 | mmol/l | (1.15–1.35) |
| Cl− | 106 | 108 | mmol/l | (95–105) |
| COHb | 0.2 | 0.1 | % | (< 2.0) |
| MetHb | 0.5 | 0.4 | % | (< 1.5) |
| Hb | 13.1 | 13.8 | g/dl | (12–15) |
| Hct | 39 | 41 | % | |
| Glc | 84 | 100 | mg/dl | (65–100) |
| SO₂ | 99.5 | 99.1 | % | |
| source | venous | arterial | | |
Patient B
Since the aforementioned neurosurgical procedure is frequently performed at our institution, a similar case occurred just a few weeks later. A 40-year-old female patient was found to have a previously unknown intracardiac right-to-left shunt during perioperative transesophageal echocardiography (TEE). She presented with mild numbness and paresthesia on the right side of her face, mild hypacusis with preserved useful hearing, and occasional unsteady gait. An MRI scan revealed a suspected neuroma of the vestibulocochlear and facial nerve, leading to the scheduling of neurosurgical removal of the mass in a semi-sitting position.
Standard anesthesiological management was conducted, including the induction of general anesthesia. The patient was equipped with an endotracheal tube, an arterial cannula for blood pressure monitoring, a urinary catheter, and a left-sided central venous line inserted under ultrasound guidance according to our standard operating procedure. Comprehensive transesophageal echocardiography was performed, and a bubble study with agitated saline was conducted to rule out possible right-to-left shunts. Air bubbles appeared immediately in the left atrium, followed by the left ventricle, and shortly thereafter in the right atrium. Further focused TEE views suggested an unroofed coronary sinus and the presence of a cor triatriatum dexter (CTD) (Fig. 4).
Similar to the investigative methods used for Patient A, blood gas analysis of the central line blood sample revealed typical arterial localization, leading the anesthesiological team to assume the sample was taken from a pulmonary vein or the left atrium (Table 2). The left-sided central line was immediately removed and replaced with one inserted into the right jugular vein. Due to the inability to fully diagnose the underlying congenital heart defect (CHD) and anatomical variants using TEE alone, a recommendation was made against the semi-sitting position in favour of lateral positioning to avoid the risk of intraoperative VAE and potential stroke.
The operation was successfully completed, and the patient was observed in the neurosurgical ICU for one night before being transferred to the general ward the following day. To further investigate the underlying CHD, a consultation was obtained from colleagues in the Department of Pediatric Cardiology and Congenital Heart Diseases. Transthoracic echocardiography and an additional repeated saline contrast study could not fully confirm the initially suspected unroofed coronary sinus or cor triatriatum dexter. However, the images indicated an anatomical variant of an approximately 8mm wide vessel entering the innominate vein (Fig. 5), suggesting a pre-existing anomalous pulmonary venous connection (APVC). The patient was discharged five days after the operation with mild residual hypacusis.
Table 2
Patient B’s blood gas analysis with sample taken from the left sided central line expressing values typical for an arterial sample (bolded)
| time | 11:05 | 14:28 | | |
| pH | 7.42 | 7.42 | | (7.37–7.45) |
| pCO₂ | 34.5 | 36.5 | mmHg | (35–45) |
| pO₂ | 300 | 192 | mmHg | |
| base excess | -2.1 | -0.8 | mmol/l | (-2 - +3) |
| K+ | 3.49 | 4.05 | mmol/l | (3.6–4.8) |
| Na+ | 139 | 144 | mmol/l | (135–145) |
| Ca2+ | 1.15 | 1.19 | mmol/l | (1.15–1.35) |
| Cl− | | 112 | mmol/l | (95–105) |
| COHb | 0.3 | 0.3 | % | (< 2.0) |
| MetHb | 0.3 | 0.2 | % | (< 1.5) |
| Hb | 11.4 | 11.8 | g/dl | (12–15) |
| Hct | 34 | 35 | % | |
| Glc | 94 | 104 | mg/dl | (65–100) |
| Lac | 7.6 | 5.5 | mg/dl | < 16 |
| HCO₃− | 21.9 | 23.3 | mmol/l | |
| SO₂ | 99.5 | 98.9 | % | |
| source | venous | arterial | | |