Imagine this clinical scenario: a five-year-old Labrador undergoing elective arthroscopy under general anaesthesia developed regurgitation and nausea following recovery from anaesthesia. The dog was otherwise healthy with no history of vomiting or regurgitation but developed oesophagitis as a complication of this. You want to explore the evidence behind the administration of preanaesthetic gastroprotectants in reducing the risk of gastro-oesophageal reflux (GOR, also known as GER or GERD).
Five papers were critically appraised, all of which were randomised prospective studies. Two studies were blinded, and a further study was double-blinded, which provides a high degree of confidence. Across all studies, GOR was defined by pH values lower than 4 (acid reflux episode), with Johnston (2014) additionally measuring GOR when pH values were above 7.5 (bile reflux).
Favarato et al. (2012) evaluated the number of acid and non-acid reflux events during anaesthesia in bitches undergoing ovariosalpingohysterectomy. Thirty dogs received 1mg/kg metoclopramide before induction and continuous infusion (1mg/kg/hr) immediately after anaesthetic induction, 30 received 2mg/kg ranitidine before induction and 30 were the control group. Non-acid reflux events were confirmed by oesophagoscopy after surgery. Preanaesthetic metoclopramide and ranitidine were not found to reduce GOR, with no difference in reflux episodes between groups. A study limitation is that metoclopramide doses were higher than normally used in practice.
Johnson (2014) evaluated maropitant treatment in 13 dogs undergoing elective soft tissue or orthopaedic surgery, with a further 13 dogs receiving saline as a placebo. While vomiting and retching were prevented in the maropitant group, GOR was not prevented with no difference in frequency between the groups. The small sample size limits the strength of the evidence as 4/13 treatment dogs had a reflux event versus 6/13 control dogs – a larger sample size may have shown a difference.
Omeprazole treatment was evaluated in a study by Panti et al. (2009); 22 dogs received omeprazole before anaesthesia for elective orthopaedic surgery, while the remaining 25 dogs only received premedication. GOR was decreased in dogs treated with omeprazole, with GOR occurrence 4.7 times more likely in the control group than the treatment group.
One study (Wilson et al., 2006) investigated different doses of metoclopramide against a saline infusion placebo in dogs undergoing elective orthopaedic surgery. Eighteen dogs received saline, 16 received a low dose of 0.4mg/kg of metoclopramide followed by 0.3mg/kg/hr continuous rate infusion before and during anaesthesia, and 18 received a high dose of 1mg/kg of metoclopramide, followed by 1mg/kg/hr continuous infusion. The high dose metoclopramide group was associated with a 54 percent reduction in relative risk of developing GOR. Limitations include that the high dose group received higher doses of metoclopramide than normally used, and the study was not blinded.
A double-blinded placebo-controlled study (Zacuto et al., 2012) compared esomeprazole treatment (22 dogs), esomeprazole and cisapride treatment (18 dogs) and saline as a placebo (21 dogs), in dogs undergoing elective orthopaedic surgery. All were given 12 to 18 hours and 1 to 1.5 hours before anaesthetic induction, which differs from the other studies appraised. The findings showed that preanaesthetic administration of cisapride and esomeprazole decreased the number of reflux events per dog, compared to the placebo, but esomeprazole alone did not. However, the proportion of dogs having a GOR episode did not differ significantly among groups.
There is moderate evidence that omeprazole or cisapride with esomeprazole decreases the incidence of GOR in the anaesthetised dog. The effectiveness of metoclopramide shows conflicting evidence, but a high dose of metoclopramide may decrease the incidence of GOR. Maropitant administration was shown to prevent vomiting but not the occurrence of GOR.
The patients in all the studies were fasted for at least 12 hours, which is compatible with a normal clinical setting. However, the anaesthetic drugs used in each study varied, as did patient sex, breed and position during surgery, which limits comparability across the studies.
While all the studies contained dogs undergoing elective soft tissue or orthopaedic surgery, this could be considered a limitation, as patients undergoing abdominal and orthopaedic surgeries are thought to be at higher risk of developing GOR (Rodríguez-Alarcón et al., 2015). Brachycephalic breeds are more susceptible to GOR due to the increase in negative intrathoracic pressure required to overcome upper respiratory tract obstruction associated with brachycephalic obstructive airway syndrome (Downing and Gibson, 2018). Therefore, the inclusion of brachycephalic breeds, which is unknown in these studies, may bias the results.
Overall, there is evidence that supports the use of preanaesthetic gastroprotectants in the prevention of GOR. Further research would also benefit from the consideration of potentially confounding factors, such as surgery type and dog breed, and should include larger sample sizes.