Magdalena M. Dougherty1, DVM; Gregory D. Bossart2, DVM, PhD; James D. Guest3, MD, PhD, FRCS(C); Eric Belanger3, MD, FRCS(C); Sentiel Rommel4, PhD
The Florida manatee (Trichechus manatus latirostris) is an endangered subspecies of the order Sirenia. In 1999 watercraft-related deaths accounted for thirty percent of the total number of deaths in Florida. This is the highest absolute number of deaths from watercraft in recorded history. Deaths are attributed both to the impact of the watercraft hulls and propeller wounds. The need to clinically deal with this increasing number of injuries continues to be a challenge for marine mammal veterinarians.
An adult male manatee presented in July of 1999 with a severe propeller wound to his dorsal lumbar area. Three other manatee carcasses with similar injuries were found in the same area. From the lesions, the estimated length of the propeller was six feet. The wound itself was a complete thoraco-lumbar fracture dislocation and spinal cord transection. Initial diagnostics showed that the manatee was also suffering from acute renal failure. He showed an interactive and social behavior when placed in the rehabilitation pool with other manatees.
From blood values and urinalysis it was concluded that the renal failure was both from the impact of the trauma itself and from myoglobinuria (3630 µg/L) that resulted from the severe muscle damage. While the prognosis was poor, his interactive behavior with the other manatees guided the direction of his treatment. He responded favorably to increased fresh water and a diuretic (furosemide 1 mg/kg IV). For the primary wound, we used fibrin glue to seal the open rostral spinal canal and locally deliver antibiotics (Amikacin 250 mg/ml Hemaseel™ Fibrin Glue[G]). Systemic antibiotics were started since the initial rescue and were later directed against a Pseudomonas aeruginosa that was cultured from the spinal canal. Neurologically his tail fluke was amotile but he had positive anal sphincter tone and penile sensation. Anatomically manatees, like other marine mammals, have a conus that is located mid-thoracically. In some other terrestrial mammals it is in the thoraco-lumbar area.
To reduce the fracture dislocation, the manatee was sedated using midazolam (0.045 mg/kg) IM and meperidine (0.5 mg/kg) IM. To provide epidural anesthesia, a central venous catheter was fed and left for a distance of 20 cm rostrally and xylocaine (1%) was infused. Since the first lumbar vertebra was displaced beneath the last thoracic vertebrae, a partial corpectomy of the first lumbar vertebrae was performed. TSRH Pedicle screws (6.5 mm diameter, 4.5 mm to 5.5 mm length) were bilaterally placed into T18, L2, and L3. Stainless steel rods (1/4-inch diameter and 14 cm in length) were sequentially tightened down to the pedicle screws for reduction. Increased activity was observed for 3 days postsurgically.
He deteriorated from sepsis on the twenty-sixth day after rescue, and acutely expired while swimming in his rehabilitation pool. Necropsy findings showed death involved an overwhelming bacterial infection, myocardial failure, and thromboembolic disease.
Watercraft propeller wounds and impact trauma will continue to have a major impact on the manatee population. Clinically dealing with these cases will continue to be a priority at manatee critical care facilities.
The authors wish to thank Sofamor Danek, Haemacure Corporation, the Public Health Trust of Miami, The University of Miami Departments of Neurosurgery and Comparative Pathology, and the Florida Marine Research Institute for their valuable contributions to this case.