Podcasts

The effect of lidocaine on gastrointestinal motility in dogs | VETgirl Veterinary Continuing Education Podcasts

Lidocaine is a sodium channel blocker that is widely used in both large and small animal medicine as a local anesthetic, analgesic, and as a class 1B antiarrhythmic. A perhaps less common application for this medication in small animal medicine is as a gastrointestinal promotility agent in cases of ileus. The effects of lidocaine on improving the clinical signs of ileus in post-operative horses (1) and humans (2) have already been documented. However, what about dogs? So, Johnson et al out of the University of Wisconsin School of Veterinary Medicine wanted to evaluate the effect of lidocaine on gastrointestinal motility in dogs. The authors aimed at measuring the effects of lidocaine CRI’s at two different doses on the gastrointestinal transit times of healthy adult canines as compared to saline CRI controls (3).

In this study, 6 healthy adult Beagles were used and all were subjected to each of the three treatments with a washout period between treatments. The control treatment involved receiving a 0.05 mL/kg bolus of 0.9% NaCl prior to a CRI of 10 mL/hr for 12 hours. The first lidocaine treatment involved receiving a bolus of lidocaine at 1 mg/kg (this equated to a volume of 0.05 mL/kg IV) followed by a CRI at a rate of 25 mcg/kg/min for 12 hours. The second lidocaine treatment group involved receiving the same 1 mg/kg bolus of lidocaine prior to a more concentrated CRI at 50 mcg/kg/min for 12 hours. This higher lidocaine dose range represents the known upper end of lidocaine’s analgesic effects before crossing over into the antiarrhythmic effect range. In both of the lidocaine treatment groups, the lidocaine CRI’s were diluted in such a fashion as to fit a fluid rate of 10 mL/hr. This dilution was necessary in order to keep the observers blinded to the treatment groups.

The beagles were fasted for 24 hours prior to their treatments, administered BIPS, and fed. Baseline radiographs of the abdomen were obtained after oral ingestion of the Barium impregnated polyethylene spheres (BIPS) in food, and then were repeated hourly during the 12-hour duration of their assigned treatment, and then once more 4 hours after their treatment ended. The radiographs were evaluated in regards to the quantifiable amount of BIPS present within the various regions of the gastrointestinal tract with most emphasis placed on how quickly the BIPS exited the stomach (gastric emptying time) and when they reached the large intestine (gastrointestinal transit time).

So, what’d they find in this study? The use of lidocaine CRI at either dose range did not appear to increase the gastric emptying times at any time point within the 12 hours treatment window. However, there did appear to be a favorable trend in decreasing gastrointestinal transit times, although statistical significance was not achieved. The 25 mcg/kg/min group had a very minimal increase in gastrointestinal transit time documented as 6 hours from onset of treatment. The higher dose of lidocaine appeared to nominally decrease the gastrointestinal transit time starting between 4 and 6 hours from the onset of treatment. Nausea scores for the 25 mcg/kg/min lidocaine group did not differ significantly from the control group, but in the 50 mcg/kg/min lidocaine group, all dogs vomited. Within the 50 mcg/kg/min lidocaine group, one dog developed such severe vomiting that it had to be withdrawn from that portion of the study. The onset of nausea after starting lidocaine administration occurred most notably at 4-5 hours after treatment onset and again at 11-12 hours after treatment onset. The sedative effects of the lidocaine were also more pronounced in the higher lidocaine CRI group, but both lidocaine groups exhibited sedation as compared to the saline group.

In conclusion, although the BIPS entered the colon quicker (between 4-7 hours) in the high dose lidocaine CRI group, the overall percentage amount of BIPS did not vary between treatment groups and the control group. Therefore, this study could not claim with statistical significance that lidocaine improved gastrointestinal motility, although they did notice at least a trend in decreased gastrointestinal transit time in the high dose lidocaine group only. That said, trends don’t mean anything unless they are statistically significant! Another limitation of this study is that there is some controversy on how well BIPS assess gastrointestinal motility.

So why do we clinically see a quicker resolution of post-operative ileus in horses and humans (and perhaps in canines) when we use lidocaine CRI’s in the postoperative period? The direct promotility effects of lidocaine should not be overemphasized, but authors have suggested theories as to why lidocaine use may still result in clinical improvement of ileus following GI surgeries. Lidocaine CRI’s have analgesic effects that can help to minimize the use of higher doses of opioids. Perhaps by lowering the need for opioids in the post-operative period, this will lessen the degree of opioid-induced ileus. Lidocaine also reduces proinflammatory cytokines and acts as a free radical scavenger, which may have a role in minimizing ileus as it relates to GI inflammation. Perhaps, and most importantly, lidocaine helps to decrease pain signals from the intestines and/or decrease the sympathetic tone caused by painful GI conditions, thereby lessening the intestinal response to pain, which would normally result in GI ileus.

So, what do we take from this VETgirl podcast?

What we have learned from this study is that lidocaine in high doses may exhibit a small promotility effect on intestinal transit, though not enough to be statistically significant over controls. Despite not having a significant effect on intestinal motility, lidocaine may exhibit strong indirect effects on intestinal motility by decreasing the triggers of GI ileus. In human medicine, clinicians suggest stopping lidocaine CRI’s within the first day after surgery to acquire the benefits of lidocaine’s analgesic and free radical scavenging properties without causing significant or prolonged nausea (1). If you are faced with a patient that is already exhibiting significant nausea and you do not want to risk exacerbating that nausea with lidocaine, alternative medications could be sought to mimic lidocaine’s indirect effects on ileus. Hypertonic saline has been mentioned to have free radical scavenging effects that perhaps could help mitigate reactive oxygen species in the post-operative period. Pain medications outside the opioid group such as gabapentin, ketamine, and dexmedetomidine could help to dampen the intestine’s paralytic response to painful stimuli. Maropitant has also been suggested to have visceral analgesic properties. The use of lidocaine in post-operative patients for the purpose of reducing ileus should be weighed with the significant nausea that this medication can cause. Luckily, the nausea produced by the lidocaine CRI’s quickly dissipated after cessation of the CRIs. Lidocaine remains an excellent analgesic when used as part of a multimodal anesthetic protocol, and may have global beneficial effects on the patient’s outcome in the post-operative period. However, know that the promotility effects are minimal.

Abbreviations:
BIPS = Barium impregnated polyethylene spheres

References:
1. Malone E, Ensink J, Turner T, et. al. Intravenous continuous infusion of lidocaine for treatment of equine ileus. Vet Surg 2006;35(1):60-66.

2. Rimback G, Cassuto J, Tollesson PO. Treatment of postoperative ileus by intravenous lidocaine infusion. Anes Analg 1990;70:414-419.

3. Johnson RA, Kierski KR, Jones BG. Evaluation of gastric emptying time, gastrointestinal transit time, sedation score, and nausea score associated with intravenous constant rate infusion of lidocaine hydrochloride in clinically normal dogs. A J Vet Research 2017;78(5):550-557.

  1. Hi there, just wondering if you could recommend any articles regarding use of hypertonic saline for free radical scavenging and gabapentin use in tx of GI pain. Thanks!

Only VETgirl members can leave comments. Sign In or Join VETgirl now!