Fellow: Victoria Albano

Mentor: Joaquin Araos

DESCRIPTION (provided by applicant): 

Central respiratory regulation and respiratory muscle function after anesthesia in dogs are usually impaired, contributing to impaired respiratory function in the immediate postoperative period. Continuous positive airway pressure (CPAP) is a non-invasive ventilatory support technique that increases airway diameter and functional residual capacity (FRC), the volume of the lung at exhalation, both in humans and veterinary species, leading to improved oxygenation, larger tidal volumes, and normalized respiratory rates. The most commonly used method to deliver CPAP is with a dedicated helmet. Despite its increased use, there is much that remains unknown about optimizing CPAP settings. The flow of oxygen delivered into the helmet is responsible for “washing out” carbon dioxide (CO2). The level of pressure used for CPAP is responsible for opening the airway and improving FRC. Both variables are empirically selected in the clinical setting, even though inappropriate settings could lead to hypoventilation, hemodynamic impairment, and suboptimal FRC maximization. Therefore, this proposal aims to evaluate: 1) The impact of three rates of fresh gas flow on reinhalation leading to hypercapnia; 2) The impact of three levels of CPAP on hemodynamic stability; and 3) The effect of three levels of CPAP on FRC. Eight healthy research beagles will be sedated with a propofol controlled rate infusion to ensure comparable sedation levels. After instrumentation, a CPAP-helmet will be placed. For Aim 1, 30 minutes after helmet placement with an oxygen flow rate of 15 Lpm and achieving a CPAP level of 5 cmH2O (considered baseline for Aim 1), dogs will be administered oxygen flow rates of 10, 15, and 20 liters per minute (Lpm), in random order, each flow for 30 minutes each. The main outcomes will be the partial pressure of arterial CO2 (PaCO2) and the inspired pressure of CO2 (PiCO2) measured by arterial blood gases and side-stream capnography, respectively. For aims 2 and 3 (to be completed on a separate research week than Aim 1), three levels of CPAP will be administered: 5, 8 and 12 cmH2O, in random order, at a fixed oxygen flow rate of 15 Lpm. 30 minutes will be allowed to pass at a CPAP of 0 cmH2O (considered baseline for Aims 2 and 3). Thereafter, each randomized CPAP level will be maintained for 30 minutes, and then switched to the next CPAP level based on randomization. For aim 2, the main outcomes will be cardiac output, measured by pulmonary thermodilution, and mean arterial blood pressure (MAP). For aim 3, the main outcomes will be the end-expiratory lung impedance (EELI), a surrogate of FRC, and the change in regional distribution of ventilation associated with each CPAP level (both measured by electrical impedance tomography, EIT). For the three aims, respective measurements will be obtained at the end of the baseline period and at the end of each 30-minute randomized intervention. Our group has extensive expertise with the use of CPAP-helmet in dogs, both in clinical and research settings. Further, we have been using EIT to study changes in FRC and regional ventilation for over 3 years in different animal species. Finally, we have ample experience with hemodynamic monitoring techniques, including pulmonary thermodilution. We expect to generate relevant knowledge that will inform clinicians on how to optimize and individualize the rapidly expanding therapy with CPAP.