The two common sites for venipuncture in snakes are the caudal ventral vein and the heart (reviewed in Hernandez-Divers 2006). Several authors (Brown 2010) and two studies (Isaza and others 2004, McFadden and others 2011) support the safety of cardiocentesis for blood sampling or intravenous drug administration. However, although some authors anecdotally suggest that there is a risk of cardiac tamponade as a consequence of cardiocentesis, this has not yet been described in snakes.
A seven-year-old Hog-island Boa (Boa constrictor imperator) was presented with a two-month history of anorexia. On physical examination the snake was in moderate body conditions, and no abnormalities were reported except for mild mucosal pallor. Diagnostic work-up included a complete blood count, serum chemistry profile and multiple radiographs. The snake was restrained in dorsal recumbency and the heart beat was observed at the caudal aspect of the cranial third of the body and an ultrasound probe was used to verify the presence of the heart. By use of digital pressure, the heart was gently pushed cranially and stabilised to prevent movement during sampling. Blood was withdrawn using a 23-gauge, 25 mm needle directed in a craniodorsal direction (McFadden and others 2011). Heterophilic leukocytosis and anaemia were present. Furthermore potassium concentration was increased.
The snake was treated with 2 mg/kg marbofloxacin (Marbocyl®; Vétoquinol) intramuscularly every 48 hours, whilst awaiting the results of blood culture. Four hours after discharge the owner reported that the snake's condition had substantially deteriorated. When re-admitted the boa was dead. At necropsy massive cardiac tamponade was evident. Examination of the heart revealed multifocal granulomatous lesions and both ventricles were dilated; histopathology showed a severe bacterial myocarditis.
Although cardiocentesis appears to be safe in healthy Ophidians, caudal and palatine vein should be the preferred venipuncture site in snakes in which cardiac status has not been previously established.