Effect of endogenous progesterone and oestradiol-17beta on the incidence of gastro-oesophageal reflux and on the barrier pressure during general anaesthesia in the female dog.

Objective: To investigate the potential effect of increased blood progesterone (P(4)) and oestradiol-17beta (E(2)) concentrations on the barrier pressure (BrP) and the incidence of gastro-oesophageal reflux (GOR) in female dogs under general anaesthesia.

Study Design: Prospective, blinded experimental trial.

Animals: Seven female, adult, healthy dogs weighing 14-21 kg and aged 1-7 years.

Methods: Each of the animals was studied under the influence of high blood E(2) and basal P(4) (study O), basal E(2) and high P(4) (study P) and basal E(2) and P(4) (study C) concentrations. Animals were premedicated with acepromazine and anaesthesia was induced with thiopental and maintained with halothane. Lower oesophageal pH was monitored continuously for 1 hour after induction. GOR was defined as oesophageal pH >7.5 or <4. Manometry of the posterior oesophageal sphincter (POS) was then performed using the slow pull-through technique.

Results: Acid GOR was detected in only one animal of study O. The three studies did not differ significantly in GOR. Mean BrP was 11.2 (study O), 9.1 (study P) and 11.6 mmHg (study C). No significant differences were detected with respect to mean BrP, intra-gastric pressure and POS pressure.

Conclusions: It is unlikely that the increased concentrations of E(2) or P(4) during the normal ovarian cycle influence the functional efficiency of the POS as a major barrier to GOR in healthy, female dogs under general anaesthesia.

Clinical Relevance: The fact that female dogs undergoing obstetrical surgery represented a substantial sub-group of the animals which developed postoperative benign oesophageal stricture, should probably not be attributed to the effects of increased concentrations of female sex steroid hormones.