Abstract

First demonstrated in a horse in 1714,¹ arterial blood pressure has proven the most reliable clinical indicator of the adequacy of circulation.² For nearly twenty years, arterial blood pressure monitoring has been officially recognized to be an important, if not mandatory, part of the management of anesthetized animals.^2,3 No indirect method of arterial blood pressure monitoring has been validated in pinnipeds. A simple, clinically applicable method of direct arterial blood pressure monitoring in pinnipeds was demonstrated at IAAAM 2012.⁴ To follow, the results of direct arterial blood pressure in 13 pinniped clinical cases are described.

Subjects were sedated with various combinations of drugs (Table 1). Ten California sea lions (Zalophus californianus), one South American fur seal (Arctocephalus australis), one South African fur seal (Arctocephalus pusillus), and one harbor seal (Phoca vitulina) were evaluated. The median artery of the pectoral flipper was cannulated in all but the harbor seal, where the pelvic flipper saphenous artery was cannulated. As cardiovascular compromise can begin upon injection of sedative agents and may easily remain through recovery, the anesthesia duration was documented as the time from preanesthetic medication injection to extubation. Anesthesia duration ranged from 140–296 minutes.

Hypotension may be defined as a mean arterial blood pressure of less than 60 mm Hg.² Eight of the subjects were hypotensive. The average time to first detection of hypotension was 85 minutes after preanesthetic deliver. Treatment included addressing the cause (e.g., inhalation anesthetic reduction where possible), intravenous fluid administration where appropriate, and application of inotropic drugs. Dobutamine 0.2–2.0 mcg/kg/min IV increased blood pressure (increases contractility and cardiac output). It should be noted, however, that this is well below rates of most veterinary patients² and often lead to tachycardia. Ephedrine 0.05 mg/kg IV was also useful as an inotrope in three subjects. The strongest association with hypotension in these cases was the use of minimal preanesthetic sedation (midazolam alone) thus likely necessitating a greater use of the direct dose-dependent cardiovascular depressive inhalation anesthetics isoflurane and sevoflurane (by causing vasodilation and some depression of contractility). Non-invasive arterial blood pressure by oscillometric method was also attempted simultaneously to direct arterial blood pressure monitoring in four of the subjects (cuff bladder width to limb circumference ratios 32%, 39%, 42% and 42%). Unfortunately, the agreement (precision and bias) appeared to be poor in this limited application.

It is a myth that a strong palpable pulse indicates good blood pressure and perfusion.⁵ The only way to accurately assess blood pressure is to measure it, and the consequence of failure to detect hypotension (or more specifically tissue perfusion and oxygen delivery) is organ injury. The brain and kidneys are certainly at risk in cases of hypotension, but so are the muscles of these potentially large subjects. There is a strong correlation between development of myopathy and hypotension (as well as positioning and padding).⁶ Rhabdomyolysis was previously described in a South African fur seal document to be hypotensive by direct arterial blood pressure measument.⁴ It is now reasonable and responsible to expect that direct arterial blood pressure monitoring become standard in the care of pinnipeds undergoing anesthetic events.

Table 1. The drugs used to sedate California sea lions

Table 1 (continued)

FeAgent = fraction expire inhalation anesthetic; Vap = vaporizer setting %; SAP = systolic arterial blood pressure; DAP = diastolic arterial blood pressure; MAP = mean arterial blood pressure; At = Atropine; Atp = Atipamezol; B = Butorphanol; Dex = Dexmedetomidine; Dob = Dobutamine; Eph = Ephedrine; Fen = Fentanyl infusion; Flu = Flumazenil; Nalox = Naloxone; Nalt = Naltrexone; Intraop = drug given intraoperatively; Iso = Isoflurane; M = Midazolam; Med = Medetomidine; Mep = Meperidine; Sevo = Sevoflurane
Anesthesia duration was documented as the time from injection of premed to extubation.
Time of detection of hypotension was time after preanesthetic delivery and generally coincided with the time of placement of the arterial catheter.

Acknowledgements

The authors would like to thank the many trainers, veterinary technicians, and veterinarians of involved in making this work possible. Special thanks go to Dr. Stephen Ferrara Chief of Interventional Radiology of the Naval Medical Center and especially to the primary clinicians on these cases, including Dr. Carolina Le-Bert and Dr. Jennifer Meegan of the National Marine Mammal Foundation, Dr. Lara Cotte of the Navy Marine Mammal Program, Dr. Tom Reidarson of the Reidarson Group Marine Mammal Specialists, Dr. Lydia Staggs of Gulf World Marine Park, Dr. Mike Selig of Cleveland Metroparks Zoo, Dr. Bob Stevens of Dolphins Plus, and Dr. Carla Flanagan of Mundo Aquático-Zoomarine Portugal. We also wish to acknowledge Dr. Sam Ridgway of the National Marine Mammal Foundation, Dr. Mike Walsh of the Aquatic Animal Health Program of the University of Florida and Dr. Bruce Heath of Seven Seven Anesthesia Consulting for their long standing support for improvement in marine mammal anesthetic patient monitoring.

* Presenting author

Literature Cited

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2.  Wagner AE, Brodbelt DC. 1997. Arterial blood pressure monitoring in anesthetized animals. J Am Vet Med Assoc. 1997 May 1;210(9):1279–85.

3.  American College of Veterinary Anesthesiologists. 1995 (updated 2009) Anesthesiology Guidelines Developed. JAVMA 206(7): 936–937.

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