Cold-stress syndrome (CSS) is a significant cause of mortality in the Florida manatee (Trichechus manatus latirostris) and a frequently presented condition to rehabilitation facilities in winter months. An objective evaluation of clinical outcomes for current manatee CSS rehabilitation protocols has not been performed and could provide guidance for advancements in patient care. Additionally, clinical assessments of CSS manatees have been limited by the current standard methods for temperature acquisition such as oral or rectal measurements, which are considered unreliable indicators of core body temperature in manatees.1-3 The objectives of this study were to 1) evaluate manatee CSS rehabilitation data in context of case outcomes as a starting point for considerations on protocol optimization and to 2) establish a clinically reliable measurement of core body temperature in manatees to advance clinical assessments.
A retrospective review of case outcomes of CSS manatees admitted to one rehabilitation facility from 2007–2017 was conducted. The overall mortality rate was 21% (13/62). Two temporally distinct mortality groups were identified, with most manatees dying in the initial hours of rehabilitation (77%, 10/13, average 5 hours post rescue), compared to several weeks later (23%, 3/13, average 5 weeks). Manatees that died early in rehabilitation were significantly smaller in weight than those that died later (average 156 kg vs. 369 kg). This is consistent with previous metabolism studies that reported that manatees under 300 kg are most susceptible to hypothermia.4 Review of CSS rehabilitation protocols suggests current rewarming methods differ from methods utilized in other species with regards to water temperature and rewarming speed.5-8 Taken together, we hypothesize that the subset of manatees that died early in rehabilitation may have been susceptible to pathophysiological complications associated with this sensitive rewarming period, which is well described in other species.7-10 These findings highlight the importance of further study to strengthen interpretations and to validate best practices.
Currently, core body temperature data in CSS manatees is unknown and impractical to measure in clinical settings, therefore, the data of objective 1 demonstrate the need for improved measurement capabilities to clarify outcomes. A new clinically feasible non-invasive temperature methodology was established in manatees, namely esophageal measurements collected via the Digi-Sense thermometer (Cole-Parmer, Vernon Hills, IL, USA) placed with an orogastric tube, and was compared to current oral and nasal methods in twenty clinically healthy manatees. Statistical analysis indicated the esophageal as the most accurate and precise methodology (p>0.01, mean 35.4, SD 0.24, range 35.1–35.9°C), compared with nasal (p=0.33, mean 32.5, SD 1.80, range 29.1–34.7°C) and oral (mean 33.0, SD 1.61, range 29.8–34.8°C). The esophageal measurements were consistent with manatee core body temperature1, facilitating generation of the first reference interval for core body temperature in healthy manatees (34.97–35.84°C). Three CSS manatee medical cases were evaluated with the newly validated esophageal temperature methodology demonstrating the first confirmed hypothermic CSS manatees. The application of this newly established and logistically practical temperature measurement to CSS manatees will improve clinical assessments and further the understanding of CSS, thereby supporting optimization of rehabilitation protocols.
The authors wish to thank SeaWorld Orlando and the Florida Fish and Wildlife Conservation Commission for their contributions to this study and their efforts in cold-stressed manatee rehabilitation and conservation. Rescue and rehabilitation activities were conducted under the USFW permit #MA770191.
* Presenting author, + Student presenter
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