The effect of the stage of the ovarian cycle (anoestrus or dioestrus) and of pregnancy on the incidence of gastro-oesophageal reflux in dogs undergoing ovariohysterectomy

ObjectiveTo investigate the potential association of increased blood progesterone (P-4) concentrations and/or late pregnancy with the incidence of gastro-oesophageal reflux (GOR), in healthy bitches undergoing ovariohysterectomy under general anaesthesia during anoestrus or dioestrus or during the second half of pregnancy. Study designProspective observational study. AnimalsNinety-four healthy, female, dogs, aged 1-8years presented for elective ovariohysterectomy. MethodsNon-pregnant animals were classified into group A (anoestrus) (n=35) if blood P-4 concentration was sufficiently low or group D (dioestrus) (n=26) if blood P-4 concentration was sufficiently high. All animals in the second half of pregnancy were classified into group P (n=33). Acepromazine (0.05mgkg(-1)) was administered intramuscularly as preanaesthetic medication, and sodium thiopental (10mgkg(-1), with additional doses if needed) was administered intravenously (IV) for induction of anaesthesia. After endotracheal intubation, halothane (1.1-1.3% end-tidal concentration) in oxygen was used for maintenance of anaesthesia. Lower oesophageal pH was monitored continuously throughout surgery using a pH-measuring probe. Reflux was considered to have occurred whenever pH values of >7.5 (alkaline reflux) or <4 (acid reflux) were recorded. On completion of surgery, carprofen (4mgkg(-1)) was administered IV. Further administration of analgesics post-operatively was dictated by visual analogue scale pain scoring. ResultAcid GOR was observed in five of 26 dogs in group D, six of 35 group A, and 12 of 33 group P (p=0.152). The incidence of GOR in group P approached statistical significance and was higher than the incidence in the combined group A+D (one sided p=0.044, two sided p=0.077). ConclusionsIn dogs undergoing ovariohysterectomy, GOR during anaesthesia occurs with a high incidence in dogs in the second half of pregnancy compared to non-pregnant animals during anoestrus or dioestrus. Clinical relevanceMeasures could be taken in such cases to avoid the consequences of potential reflux.