EDITOR: The foramen ovale between the two atria, which normally closes soon after delivery, retains some patency in 14.6% of people [1]. Some circumstances, such as pulmonary arterial hypertension, favour its reopening. Reopening could be triggered, for example, by a Valsalva manoeuvre, or during pulmonary surgery or hepatic transplantation [2,3], and would cause a right-to-left shunt. A 64-yr-old female, who had had surgery for carcinoma of the left breast in 1990, re-presented with a large hepatic metastasis. After chemotherapy, she was scheduled for right hepatectomy. Preoperatively, there were no clinical signs of cardiac or respiratory insufficiency. Her chest radiograph and electrocardiogram were normal. Her cardiac function had been normal at transthoracic echocardiography before chemotherapy. Respiratory function tests were normal, as were all other laboratory tests. Premedication was with hydroxyzine (100 mg) and alprazolam (0.5 mg). Anaesthesia was induced with midazolam (1 mg), propofol (2 mg kg−1), sufentanil (0.3 μg kg−1) and atracurium (0.4 mg kg−1) and maintained with desflurane and nitrous oxide (50%) in oxygen, with infusions of sufentanil (0.13 μg kg−1 h−1) and atracurium (0.3 mg kg−1 h−1). Haemoglobin saturation was monitored by pulse oximetry (SPO2/PLETH M1020A®; Hewlett Packard, Böbingen, Germany). A central venous catheter was placed via the right internal jugular vein (Nutricath S®; Vygon, Ecouen, France). A cannula was placed in the left radial artery (Seldicath 3F®; Plastimed, Saint-Leu-La-Forêt, France). A pulmonary flotation catheter was placed easily via the left subclavian vein (OptiQ SvO2/CCO®; Abbot, Rungis, France) by watching the intravascular pressures. Shortly after the right hepatic artery and vein were clamped, the patient became severely hypotensive and the pulse oximeter failed to read. The surgeons reported that the aorta was pulsatile, the inferior cava full, and the bowel a normal colour. She remained hypotensive, with systolic pressures between 40 and 70 mmHg, and pulse rate between 105 and 125 beats min−1, for about 100 min. Vasopressor drugs were infused (dopamine at up to 48 μg kg−1 min−1, epinephrine at up to 0.12 mg kg−1 h−1, dobutamine at 24 μg kg−1 min−1) and fluids were given (Table 1). Pulmonary artery occlusion pressure during this time reduced from 14 mmHg to 8 mmHg. Haemoglobin concentration was about 8.5 g dL−1 at the start of the episode, and at 50 min, but was 14.1 g dL−1 by the time the systolic pressure was back to 100 mmHg, and the saturation 99%, at 110 min.Table 1: Cumulative fluid loss and therapy during hypotensive episode.By the end of the operation, the patient was haemodynamically stable, although still on high doses of vasopressors, and pulse oximetry was back to normal. A chest radiograph was taken immediately postoperatively, and a knot was seen in the pulmonary artery catheter (Fig. 1). Transoesophageal echocardiography showed an empty, hyperkinetic left ventricle and an overfilled right ventricle. We suspected a patent foramen ovale, and confirmed it by contrast phase transoesophageal echocardiography, which showed microbubbles passing through the foramen ovale [4]. The catheter was unknotted by repeatedly rotating it back and forth during radiographic screening. Helped by replacing epinephrine with norepinephrine and by administering 10 ppm of inhaled nitric oxide, the right ventricle became less full, the pressures on the right side decreased, and the shunt ceased. This corrected the situation and from then on the patient's recovery was rapid. She was discharged from the intensive care unit 10 days postoperatively.Figure 1: Postoperative chest radiograph showing the knot of the pulmonary artery catheter.Two months later, transoesophageal echocardiography showed no right-to-left shunt when the patient was breathing normally, but it reappeared during a Valsalva manoeuvre. Six months later, she underwent surgery uneventfully for an incisional hernia. If the foramen ovale is potentially patent, it will open if the pressure in the right atrium exceeds that in the left. For our patient, a little more explanation is needed. There was probably hypovolaemia just before the hepatic artery was clamped. It is possible that the foramen then opened because the pulmonary artery catheter had impacted on it during insertion [5]. Opening did not occur simply because of the effects of mechanical ventilation: airway pressure was never high, and the patient had undergone two previous operations without any problem. Another possible cause is pulmonary arterial hypertension, but that usually occurs at declamping during hepatic transplantation. The explanation we favour is that the already relatively empty pulmonary artery was being obstructed by the knot in the pulmonary artery catheter, which we do not believe has been described before. This explanation is supported by the echocardiograph evidence of an overfull right ventricle but an empty left ventricle, without evidence of right heart failure. R. Tavan B. Coronel Anesthesiology and Intensive Care Department; Leon Berard Center S. Duperret Intensive Care Unit; Edouard Herriot Hospital P. Meeus R. Blondet Surgery Department; Leon Berard Center; Lyon; France