Dexmedetomidine or fentanyl? Cardiovascular stability and analgesia during propofol-ketamine total intravenous anaesthesia in experimental pigs.

OBJECTIVE

To compare cardiovascular function and response to nociception during total intravenous anaesthesia in pigs with propofol, ketamine and either dexmedetomidine or fentanyl administered as a continuous infusion.

STUDY DESIGN

Blinded, randomized, balanced, crossover study ANIMALS: Eight immunocastrated male, mixed breed pigs with a mean ± standard deviation body weight of 26.4 ± 1.9 kg for dexmedetomidine and 27.5 ± 3.8 kg for fentanyl treatment.

METHODS

The animals were anaesthetized twice with either propofol-ketamine-dexmedetomidine (DEX) or fentanyl (FENT). DEX was infused at 2, 4 and 8 μg kg hour and FENT at 25, 50 and 100 μg kg hour. Each infusion rate was administered for 80 minutes prior to commencing the next. Heart rate (HR), 3-lead electrocardiogram, systolic, mean and diastolic arterial blood pressure (SAP, MAP, DAP) in addition to cardiac output measured by transpulmonary thermodilution was used to monitor cardiovascular function. Mechanical and electrical stimulation (nociceptive withdrawal reflex, NWR) was used to elicit nociceptive responses. Similar anaesthetic depth was determined based on the NWR response. Cardiovascular parameters were compared statistically at this time. Additionally, response to nociceptive stimulation and cardiovascular response over time were compared.

RESULTS

DEX-treated pigs had significantly higher HR, SAP, DAP, MAP, systemic vascular resistance, haemoglobin concentration, content of oxygen in arterial and venous blood and oxygen delivery index than FENT-treated pigs at similar anaesthetic depth, whereas stroke volume index was significantly higher in FENT. Motoric response to mechanical nociceptive stimulation was abolished prior to any decrease in NWR response in FENT, whereas the two responses decreased more in unison in DEX. The cardiovascular response to nociception was less pronounced in DEX than in FENT.

CONCLUSIONS AND CLINICAL RELEVANCE

Propofol combined with ketamine and either fentanyl or dexmedetomidine provides stable cardiovascular conditions in normovolaemic, healthy pigs. Based on cardiovascular response and depression of NWR, dexmedetomidine apparently provides superior analgesia to fentanyl.