Respiratory mechanics and gas exchange in an ovine model of congenital heart disease with increased pulmonary blood flow and pressure.

In a model of congenital heart disease (CHD), we evaluated if chronically increased pulmonary blood flow and pressure were associated with altered respiratory mechanics and gas exchange. Respiratory mechanics and gas exchange were evaluated in 6 shunt, 7 SHAM, and 7 control age-matched lambs. Lambs were anesthetized and mechanically ventilated for 15 min with tidal volume of 10 mL/kg, positive end-expiratory pressure of 5 cmH2O, and inspired oxygen fraction of 0.21. Respiratory system, lung and chest wall compliances (Crs, CL and Ccw, respectively) and resistances (Rrs, RL and Rcw, respectively), and the profile of the elastic pressure-volume curve (%E2) were evaluated. Arterial blood gases and volumetric capnography variables were collected. Comparisons between groups were performed by one-way ANOVA followed by Tukey-Kramer test for normally distributed data and with Kruskal-Wallis test followed by Steel-Dwass test for non-normally distributed data. Average Crs and CL in shunt lambs were 30% and 58% lower than in control, and 56% and 68% lower than in SHAM lambs, respectively. Ccw was 52% and 47% higher and Rcw was 53% and 40% lower in shunt lambs compared to controls and SHAMs, respectively. No difference in %E2 was identified between groups. No difference in respiratory mechanics was observed between control and SHAM lambs. In shunt lambs, Rcw, Crs and CL were decreased and Ccw was increased when compared to control and SHAM lambs. Pulmonary gas exchange did not seem to be impaired in shunt lambs when compared to controls and SHAMs.

Ultrasound-guided catheterization of the femoral artery in a canine model of acute hemorrhagic shock.

OBJECTIVE: To describe a technique for gaining ultrasound-guided access to the femoral artery in an experimental model of acute hemorrhagic shock in anesthetized dogs. CASE SERIES SUMMARY: Five healthy, purpose-bred adult male intact Beagles were enrolled in a respiratory mechanics study under general anesthesia. Upon completion of the primary study a hypovolemic state was induced by blood removal to achieve a mean arterial pressure ≤ 55 mm Hg. Dogs were positioned in dorsal recumbency with the hind limb extended caudally. An ultrasound probe was applied to the medial aspect of the hind limb and positioned in the transverse orientation so that the femoral artery was visualized in its short axis. The artery was identified by lack of compression and presence of visible pulsation. The probe was rotated 90° into the longitudinal orientation such that the artery was visualized in its long axis. Under ultrasound guidance a 19-gauge introducer needle was advanced into the lumen of the femoral artery. Using a modified Seldinger technique the needle was removed and a catheter was placed in the femoral artery. Correct placement of the catheter was verified by observation of the characteristic arterial blood pressure waveform. Upon completion of the study dogs were humanely euthanized. The femoral artery was successfully catheterized in 4/5 dogs and a hematoma was reported in 1/5 dogs. NEW OR UNIQUE INFORMATION PROVIDED: Ultrasound-guided femoral artery catheterization is feasible on anesthetized dogs with concurrent acute hemorrhagic shock.

Dose-finding study comparing three treatments of remifentanil in cats anesthetized with isoflurane undergoing ovariohysterectomy.

Objectives Three infusion rates of remifentanil were used in isoflurane-anesthetized cats undergoing ovariohysterectomy. The aim of this study was to identify a dosage regimen that would provide optimal anesthetic and surgical conditions, as well as to compare cardiovascular response to surgical stimulation, postoperative analgesia, anesthetic duration and quality of recovery among the tested remifentanil infusion rates. Methods Twenty-seven client-owned, mixed-breed adult healthy female cats were randomized to receive remifentanil 0.1 µg/kg/min (REMI01), remifentanil 0.2 µg/kg/min (REMI02) or remifentanil 0.4 µg/kg/min (REMI04). After premedication with acepromazine and induction of anesthesia with propofol, cats were mechanically ventilated and anesthesia was maintained at approximately 1.0 minimum alveolar concentration (MAC) of isoflurane (1.63% end-tidal isoflurane [ETISO]). Remifentanil infusion rate was increased or decreased by 20% if blood pressure had increased or decreased by 20% from previous values. Pulse rate (PR), systolic arterial pressure (SAP), esophageal temperature, pulse oximetry, end-tidal partial pressure of CO2 and ETISO were recorded at different time points during surgery. Meloxicam was administered before the end of surgery. Data within each treatment group were analyzed using a mixed-model ANOVA and Friedman's test followed by the Wilcoxon signed rank test. Bonferroni or Dunnett's post-hoc tests were used. The Kruskal-Wallis test followed by Dunn's post-hoc test were used to compare data between groups; significance was set at P <0.05. Results Time to sternal recumbency and time to standing were significantly longer in REMI04 than in the other groups. SAP was higher when compared with baseline in REMI01 and REMI02 groups than in REMI04. No significant difference in PR among groups was observed. One cat in REMI01 and another in REMI02 required postoperative rescue analgesia. Conclusion and relevance The dosage regimen of 0.4 µg/kg/min seemed to be the most appropriate to be used in cats undergoing ovariohysterectomy and anesthetized with 1.0 MAC of isoflurane.

Isoflurane sparing action of epidurally administered xylazine hydrochloride in anesthetized dogs.

OBJECTIVE: To evaluate the influence of epidural administration of xylazine hydrochloride on the minimum alveolar concentration of isoflurane (MAC(ISAO)) and cardiopulmonary system in anesthetized dogs. ANIMALS: 6 clinically normal dogs. PROCEDURE: Dogs were anesthetized with isoflurane in oxygen after randomly being assigned to receive 1 of the following 4 treatments: epidural administration of saline (0.9% NaCl) solution or xylazine at a dose of 0.1, 0.2, or 0.4 mg x kg(-1). Experiments were performed on 5 occasions with at least a 1-week interval between experiments; each dog received all 4 treatments. Following instrumentation, the concentration of isoflurane was maintained constant for 15 minutes at the MAC(ISO) that had been determined for each dog, and data on heart rate, arterial blood pressure, respiratory rate, tidal volume, minute volume, arterial partial pressure of oxygen, arterial partial pressure of carbon dioxide, and arterial pH were collected. The epidural treatment was administered, and 30 minutes later, data were again collected. From this point on, determination of the MAC(ISO) following epidural treatment (ie, MAC(ISO+EPI)) was initiated. Cardiopulmonary data were collected before each electrical supramaximal stimulus during MAC(ISO+EPI) determinations. RESULTS: The mean (+/-SD) MAC(ISO) was 1.29 +/- 0.04%. The epidural administration of xylazine at doses of 0.1, 0.2, and 0.4 mg x kg(-1) decreased the MAC(ISO), respectively, by 8.4 +/- 2.4%, 21.7 +/- 4.9%, and 33.4 +/- 2.64%. Cardiopulmonary effects were limited. CONCLUSIONS AND CLINICAL RELEVANCE: Epidural administration of xylazine decreases the MAC(ISO) in a dose-dependent manner and is associated with few cardiopulmonary effects in anesthetized dogs.