Effect of fixed value positive end expiratory pressure valves on canine thoracic volume and atelectasis

The objective of this study was to investigate whether a fixed 10 cm H₂ O positive end-expiratory pressure valve would increase the aeration of, and reduce atelectasis formation in, the lungs after induction of anaesthesia in dogs undergoing thoracic CT.

28 dogs were paired based on breed, bodyweight and body condition score and then randomly allocated to either Group Z (0 cm H₂ O) or Group P (10 cm H₂ O positive end-expiratory pressure valve) immediately after the induction of anaesthesia. All patients received a standardised anaesthetic protocol, and their lungs were manually hyperventilated before image acquisition. Cardiorespiratory parameters were recorded every 5 minutes. Total lung volume, lung density and degree of atelectasis were determined for each dog from the acquired images.

The 10 cm H₂ O positive end-expiratory pressure valve significantly increased lung volume (mL/kg) (Group Z: 52 ±14; Group P: 83 ±17; P<0·001) whilst significantly reducing lung density (Hounsfield units) (Group Z: -775 ±30; Group P: -856 ±22; P<0·001) and the amount of atelectasis (P=0·004). Dogs in Group P had significantly higher end-tidal carbon dioxide (P<0·05), but there was no difference between the groups for respiratory rate or any cardiovascular variable.

A fixed-value positive end-expiratory pressure valve provides a simple, cost-effective technique for improving expiratory thoracic CT studies by increasing lung volume and decreasing atelectasis formation.