Effect of passive pneumoperitoneum on oesophageal pressure, cardiovascular parameters and blood gas analysis in horses P. A. CANOLA*, J. H. PEROTTA, L. M. LASKOSKI, A. ESCOBAR, C. A. MELO E SILVA † , J. C. CANOLA § , P. J. JOHNSON ‡ and C. A. A. VALADÃO § São Paulo State University, School of Agrarian Sciences and Veterinary Medicine, Veterinary Surgery Graduate Program, and § Department of Veterinary Clinics and Surgery, Jaboticabal, São Paulo, Brazil; † University of Brasília, Department of Phisioteraphy, Laboratory of Respiratory Physiology, Brasília, Distrito Federal, Brazil; and ‡ Department of Veterinary Medicine and Surgery, College of Veterinary Medicine, University of Missouri, USA. Keywords: horse; pleural pressure; pneumoperitoneum; oesophagus; blood gas analysis Summary Reasons for performing study: Standing surgical procedures are being employed to an ever-greater extent in horses. Pneumoperitoneum during abdominal surgery might adversely affect the work of breathing. Objectives: To determine whether development of pneumoperitoneum during abdominal surgery adversely influences the work of breathing. Methods: Eight healthy mature horses were equipped with carotid artery and thoracic vena cava catheters and an intraluminal manometry system. The following measurements were obtained before and at +5, +10, +15 and +30 min following establishment of pneumoperitoneum by paralumbar puncture using an 8 gauge needle: vital signs, oesophageal pressure, gastric pressure, arterial and central venous blood pressures, and arterial and mixed venous blood gas analyses. Results: Significant changes in oesophageal pressure, central venous pressure and results of arterial and mixed venous blood gas analysis were not detected. Arterial diastolic and mean pressures and rectal temperature increased slightly (P0.05). Conclusions: Passive pneumoperitoneum did not adversely affect breathing mechanics or haemodynamic variables under experimental conditions. Changes in arterial pressure could have occurred as a response to the passive pneumoperitoneum or be related to handling stress. Subtle variations in rectal temperature were not clinically relevant and likely resulted from stress associated with restraint. Potential relevance: It is unlikely that mature horses will develop signs of respiratory difficulty as a result of the development of passive pneumoperitoneum during standing laparoscopy. Introduction Laparoscopic approaches in standing horses have gained popularity in the past decade because they greatly minimise the risk of complications associated with general anaesthesia (Smith et al. 2005). Institution of pneumoperitoneum represents a first step during any standing abdominal procedure. During equine laparoscopy the peritoneal cavity is routinely distended using insufflated CO2 (capnoperitoneum), generating an intra-abdominal pressure (IAP) ranging from 12–15 mmHg (Latimer et al. 2003; Caron and Mehler 2009). Numerous complications have been reported to occur in the context of surgical pneumoperitoneum including harmful effects to both abdominal and thoracic viscera (Rauh et al. 2001; Gudmundsson and Heltne 2004; Silva et al. 2006). For example, diaphragmatic dislocation might directly compress both the heart and lungs leading to reduced ventricular and pulmonary compliance and cardiopulmonary failure (Benditt 2005). In order to evaluate the mechanics of breathing, it is necessary to measure both pleural pressure (Ppl) and IAP (Silva et al. 2006). The use of an intraluminal oesophageal catheter with a balloon manometer is commonly employed for purposes of estimating Ppl in order to preclude the (invasive) placement of an intrapleural canula (Fernandes 2006; Behazin et al. 2010). The use of oesophageal manometry has been well documented for evaluation of both static and dynamic Ppl in human and veterinary medicine (Lanteri et al. 1994; Fernandes 2006). As a first step to better understanding the influence of either passive or pressure-induced pneumoperitoneum during standing laparoscopy in horses, we investigated the effect of induced passive pneumoperitoneum on various indicators of cardiopulmonary function in mature, awake horses. Materials and methods In vitro studies In order to simultaneously and independently measure both oesophageal (Pes) and gastric (Pga) pressures, a catheter equipped with 2 latex balloon 1 manometers was constructed using polyethylene tubing (Fig 1). *Corresponding author email: pacanola@yahoo.com.br [Paper received for publication 24.05.10; Accepted 08.07.10] © 2010 EVJ Ltd 446 EQUINE VETERINARY JOURNAL Equine vet. J. (2011) 43 (4) 446-450 doi: 10.1111/j.2042-3306.2010.00304.x