title: Effect of retrobulbar nerve block on heart rate variability during enucleation in horses under general anesthesia.
abstract: OBJECTIVE
  Analysis of any effect of retrobulbar block during ocular surgery on heart rate variability and oculocardiac reflex.
  
  
  METHODS
  Prospective study.
  
  
  METHODS
  Horses (n = 16) undergoing eye enucleation due to chronic ophthalmologic diseases.
  
  
  METHODS
  Eye enucleation was performed under general anesthesia. The horses were randomly assigned to the first (inhalation anesthesia only, n = 10) or second group (inhalation and local retrobulbar anesthesia, n = 6). The retrobulbar block was performed using 12 mL of mepivacaine hydrochloride 2%. ECG data were taken by a Telemetric ECG before, during, and after surgery. Heart rate variability was analyzed in the time domain as mean heart rate, mean beat-to-beat interval duration, and standard deviation of continuous beat-to-beat intervals. The frequency domain analysis included the low- and high-frequency components of heart rate variability and the sympathovagal balance (low/high frequency). The low frequency represents mainly sympathetic influences on the heart, whereas high frequency is mediated by the parasympathetic tone.
  
  
  RESULTS
  All horses without a retrobulbar block showed a significant decrease in the heart rate during traction on the globe and pressure on the orbital fat pad for homoestasis (P = 0.04). Simultaneously, high-frequency power, as an indicator of vagal stimulation, increased significantly. High-frequency and low-frequency power in the retrobulbar block group increased in five horses, and heart rate decreased in only one horse. Both were not significant within the group, but there was a significant difference between both groups relating to the incidence of heart rate decrease occurring at globe traction.
  
  
  CONCLUSIONS
  Heart rate variability is a sensitive, non-invasive parameter to obtain sympathovagal stimulations during general anesthesia. The retrobulbar block can prevent heart rate decrease associated with initiation of the oculocardiac reflex.
authors.affiliation: Equine Clinic, Free University of Berlin, Oertzenweg 19b, 14163, Berlin, Germany.
authors.forename: Carolin
authors.initials: C
authors.lastname: Oel
authors.forename: Hartmut
authors.initials: H
authors.lastname: Gerhards
authors.forename: Heidrun
authors.initials: H
authors.lastname: Gehlen
mesh_terms: D000768:Anesthesia, General / Q000662:veterinary*; D000779:Anesthetics, Local / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D005128:Eye Diseases / Q000601:surgery / Q000662:veterinary*; D015353:Eye Enucleation / Q000662:veterinary*; D006339:Heart Rate / Q000187:drug effects*; D006734:Horse Diseases / Q000601:surgery*; D006736:Horses; D008619:Mepivacaine / Q000008:administration & dosage / Q000494:pharmacology; D009407:Nerve Block / Q000662:veterinary*
chemical_list: D000779:Anesthetics, Local; D008619:Mepivacaine
keywords: equine; eye enucleation; heart rate variability; oculocardiac reflex; retrobulbar block