Evaluation of the Effects of Detomidine on Equine Myoelectrical Activity Using Electrointestinography

Abstract

Objective: To evaluate the effects of detomidine on equine intestinal slow-wave activity and frequency distribution measured by electrointestinography (EIG).

Design: Prospective, experimental study.

Setting: University teaching hospital.

Animals: A convenience sample of twelve 7- to 21-year-old clinically normal horses.

Interventions: Horses were randomly assigned to saline control (four horses) or detomidine treatment (eight). After obtaining a 30-min baseline EIG, a saline or detomidine bolus was administered, followed by a constant rate infusion, and another EIG was recorded. Ultrasonographic examinations monitored cecal and left ventral colon contractions. Spectral analysis was performed to evaluate changes in dominant frequency, dominant power, total power, percent frequency distribution, and changes in slow-wave rhythmic activity.

Measurements and main results: Median (interquartile range [IQR]) dominant frequency in cycles per minute (cpm) was similar for the cecum (2.4 cpm; IQR: 0.51 cpm) and left ventral colon (2.13 cpm; IQR: 0.16 cpm) and unchanged by either treatment (P > 0.074). Compared with saline, which was unchanged, detomidine reduced dominant power ratios for both cecum (0.45; IQR: 0.18) and left ventral colon (0.63; IQR: 0.35; P = 0.002). Detomidine decreased total power for the cecum in the 2-4 cpm frequency range from 55.0% (IQR: 4.4%) to 43.1% (IQR: 6.7%) and for the left ventral colon from 54.4% (IQR: 5.5%) to 27.3% (IQR: 9.3%; P < 0.087). Total power for the cecum was increased in the 8-12 cpm frequency range from 9.6% (IQR: 1.9%) to 18.5% (IQR: 6.6%; P = 0.0044) with detomidine. No change in frequency distribution was noted in controls (P > 0.08). Dominant power correlated with the rate of contractions measured ultrasonographically (P < 0.001).

Conclusions: Detomidine decreased dominant power ratios for both the cecum and left ventral colon and produced tachyarrhythmias in cecal slow-wave activity. The correlation of dominant power with intestinal contractions supports the clinical development of EIG to diagnose equine motility disorders.

Keywords: cecum; horse; intestine; motility; tachyarrhythmia.

FIGURE 1

Placement of electrodes and unipolar leads on the skin over (A) the cecum and (B) the left ventral colon after the identification of the organs with ultrasonography in a horse. The leads are placed in two staggered rows along the long axis of the organs, with the ground (black lead) placed cranial to the active leads (red and white) in the right flank.

FIGURE 2

Raw electrointestinography waveforms obtained from the left ventral colon of horse 6 (channel 10). (A) The waveform amplitude (in mV) before data cleaning with the “filloutliers” command shows sharp deviations (*) due to motion artifacts compared with (B) the waveform after the application of the algorithm.

FIGURE 3

Boxplot of the percentage of power distribution for frequency ranges in cycles per minute (cpm). The box represents the interquartile range, with the median represented by the line and the mean represented by an “x.” The whiskers extend to the minimum and maximum values, with outliers defined by points above or below this range. The saline controls show no difference in the percentage of total power compared with the baseline for (A) the cecum and (B) the left ventral colon (p > 0.08). The normal frequency range (2–4 cpm) shows a decrease in power for (C) the cecum and (D) the colon after treatment with detomidine (P < 0.01), with an increase in power noted in the higher frequencies (8–12 cpm) for the cecum (P = 0.004). Significant differences are indicated with an asterisk (*).

FIGURE 4

Boxplots of the ultrasonographic observations of cecal and left ventral colon motility in contractions per minute for (A) the saline control and (B) the detomidine treatment groups. The box represents the interquartile range, with median represented by the line and mean represented by an “x.” The whiskers extend to the minimum and maximum values, with outliers defined by points above or below this range. Observed contractions were unchanged for the saline‐treated horses compared with baseline measurements at all timepoints (P > 0.95). Cecal motility was decreased after the administration of detomidine for all timepoints compared with baseline observations (P < 0.045), whereas left ventral colon motility differed only when comparing baseline time 0 to time 30 after treatment (P = 0.032). Letters denote significant differences between groups.

FIGURE 5

Spearman's correlation between ultrasonographic contractions per minute for the cecum and left ventral colon and electrointestinography dominant power (µV). The 95% confidence interval is represented by the shaded area. The relationship between dominant power and rate of contractions was significant (rho = 0.478, P < 0.001).