The incidence of accidental arterial cannulation and injection varies from 1 in 56,000 to 1 in 3,440. 1 Many cases of accidental arterial cannulation and injection have been reported in literature, but a seemingly simple peripheral venous cannulation landing in a preformed arteriovenous malformation (AVM) is of special interest and has not been reported earlier. After obtaining written informed consent from the patient, we report such a rare case of accidental AVM cannulation in which its

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... recognition prevented any further complication. A 22-year-old woman, known case of hydrocephalous, presented to the operating room for endoscopic third ventriculostomy. A 22-gauge cannula was already in situ, just above the wrist on the radial side of the forearm. As per the standard protocol, all monitors were attached and an infusion of normal saline was started through peripheral intravenous cannula. Immediately, we noticed a profuse backflow of blood in the intravenous line. We checked the force of backflow even by attaching an empty 2-mL syringe to it, which got rapidly filled by backpressure. On transducing the pressure, a distinct arterial waveform could be appreciated but with low mean pressure. The blood gas analysis report revealed partial pressure of oxygen: 77 mm Hg, partial pressure of carbon dioxide: 48 mm Hg, arterial oxygen saturation: 88% at fraction of inspired oxygen: 0.4, end-tidal carbon dioxide: 30 mm Hg, and pulse oximetry oxygen saturation: 100%. These values were indicative of mixed arteriovenous sample. We secured another intravenous access for carrying out surgery. After the tracheal intubation, standard anesthesia technique was followed for maintenance of anesthesia, and the surgery proceeded uneventfully. To seek the reason for these abnormal findings, we used an ultrasound to insonate the area where the cannula was placed. We could distinctly appreciate an aberrant connection between an artery and vein on long-axis view (►Fig 1A). The findings were confirmed by pulse wave Doppler study, which showed arterial and venous waveforms at respective sites (►Fig 1B). After scanning the area, we removed the cannula immediately. In the postoperative period, we observed the left hand for development of any complications. In the operating room, an accidental arterial cannulation is suspected by bright red color of the blood, pulsatile flow, and an arterial blood gas (ABG) analysis. In our case, there was a good backflow even from the small-caliber 22G cannula, but ABG report showed a mixed sample. Even pressure transduction could not confirm that it was an arterial placement. The possibility of an AVM could not be ruled out, though there was no palpable thrill/bruit or any such prior history. In an AVM, there is often a nidus interposed between the feeding arteries and draining veins. The nidus is a convoluted, densely packed, and poorly differentiated blood vessel with a very low resistance bed. 2 On scanning the arteriovenous anatomy with an ultrasound, we were able to discover a distinct communication between the arterial and venous channel. The cannula tip could be in the venous end of the nidus, which was probably the reason of a low-pressure flow of the vascular bed. The pulsed wave Doppler study showed attenuated but pulsatile flow at the abnormal communication channel. The incidence of AVM formation secondary to peripheral cannulation is less than 0.003%. 3 There was no history of trauma, past cannulation, or surgery of the left hand. As the patient was completely asymptomatic, it was decided not to carry out J Neuroanaesthesiol Crit Care Fig. 1 (A) Ultrasonographic long-axis image showing a communication between the artery and the vein. (B) Pulse wave Doppler showing arterial waveform.