Intraoperative Assessment of Fluid Responsiveness in Normotensive Dogs under Isoflurane Anaesthesia.

The aim of this study was to evaluate the incidence of fluid responsiveness (FR) to a fluid challenge (FC) in normotensive dogs under anaesthesia. The accuracy of pulse pressure variation (PPV), systolic pressure variation (SPV), stroke volume variation (SVV), and plethysmographic variability index (PVI) for predicting FR was also evaluated. Dogs were anaesthetised with methadone, propofol, and inhaled isoflurane in oxygen, under volume-controlled mechanical ventilation. FC was performed by the administration of 5 mL/kg of Ringer's lactate within 5 min. Cardiac index (CI; L/min/m2), PPV, (%), SVV (%), SPV (%), and PVI (%) were registered before and after FC. Data were analysed with ANOVA and ROC tests (p < 0.05). Fluid responsiveness was defined as 15% increase in CI. Eighty dogs completed the study. Fifty (62.5%) were responders and 30 (37.5%) were nonresponders. The PPV, PVI, SPV, and SVV cut-off values (AUC, p) for discriminating responders from nonresponders were PPV >13.8% (0.979, <0.001), PVI >14% (0.956, <0.001), SPV >4.1% (0.793, <0.001), and SVV >14.7% (0.729, <0.001), respectively. Up to 62.5% of normotensive dogs under inhalant anaesthesia may be fluid responders. PPV and PVI have better diagnostic accuracy to predict FR, compared to SPV and SVV.

Respiratory and hemodynamic effects of 2 protocols of low-dose infusion of dexmedetomidine in dogs under isoflurane anesthesia.

The aim of this study was to evaluate the respiratory and hemodynamic effects of a low-dose dexmedetomidine infusion [1 µg/kg body weight (BW) per hour], with or without a loading dose (1 µg/kg BW), in dogs under isoflurane anesthesia. Thirty dogs were premedicated with methadone [0.3 mg/kg BW intramuscular (IM)], induced with propofol intravenous (IV) and maintained with isoflurane (1.3% to 1.4%) under mechanical ventilation. Animals were randomly assigned to 3 intravenous (IV) treatments (n = 10): 1 µg/kg BW dexmedetomidine, followed by 1 µg/kg BW per hour (group BI); or saline solution bolus, followed by either an infusion of 1 µg/kg BW per hour dexmedetomidine (group I) or saline solution (group C). The infusions were interrupted after 30 minutes. Respiratory system static compliance (Cstat) and respiratory system resistance (Rrs), partial pressure of oxygen/fractional inspired oxygen ratio (PaO2/FIO2), intrapulmonary shunt (Fshunt), and cardiac output (CO) were determined 5 minutes before the bolus (BASELINE), at the end of the bolus (BOLUS), and at 15 (T15), 30 (T30), and 45 minutes (T45) intervals. In group BI, Cstat and PaO2/FiO2 were higher at T15 and T30 than at BASELINE in the same group and than group C at the same times. In group I, the same parameters at T30 were higher than at BASELINE and than group C at the same time. In group BI, Rrs and Fshunt were lower than at BASELINE and than group C at the same time. In group I, the same parameters at T30 were lower than at BASELINE and those of group C at the same time. Cardiac output (CO) at T30 was higher in groups BI and I than in group C. The results of this study showed that low-dose dexmedetomidine infusion improves oxygenation and respiratory system mechanics and has a stabilizing hemodynamic effect in dogs anesthetized with isoflurane and mechanically ventilated.

L'objectif de la présente étude était d'évaluer les effets respiratoires et hémodynamiques de l'infusion d'une faible dose de dexmedetomidine [1 µg/kg de poids corporel (BW) par h], avec ou sans une dose de charge (1 µg/kg de BW), chez des chiens sous anesthésie à l'isoflurane. Trente chiens ont été pré-médicamentés avec de la méthadone [0,3 mg/kg BW intra-musculaire (IM)], induit avec du propofol intra-veineux (IV) et maintenu avec de l'isoflurane (1,3 % à 1,4 %) sous ventilation mécanique. Les animaux étaient attribués au hasard à trois traitements IV (n = 10) : 1 µg/kg BW dexmedetomidine, suivi de 1 µg/kg BW par heure (groupe BI); ou un bolus de solution saline, suivi par soit une infusion de 1 µg/kg BW par heure de dexmedetomidine (groupe I) ou une solution saline (groupe C). Les infusions étaient arrêtées après 30 min. La compliance statique du système respiratoire (Cstat) et la résistance du système respiratoire (Rrs), le ratio pression partielle d'oxygène/fraction d'oxygène dans l'inspiré (PaO2/FIO2), le shunt intrapulmonaire (Fshunt) et le débit cardiaque (CO) furent déterminés 5 min avant le bolus (BASELINE), à la fin du bolus (BOLUS), et à des intervalles de 15 (T15), 30 (T30) et 45 min (T45). Dans le groupe BI, Cstat et PaO2/FIO2 étaient plus élevés à T15 et T30 qu'à BASELINE dans le même groupe et similaire au groupe C aux mêmes temps. Dans le groupe I, les mêmes paramètres à T30 étaient plus élevés qu'à BASELINE et plus élevés que ceux du groupe C aux mêmes temps. Dans le groupe BI, Rrs et Fshunt étaient plus bas qu'à BASELINE et similaire au groupe C aux mêmes temps. Dans le groupe I, les mêmes paramètres à T30 étaient plus bas qu'à BASELINE et ceux du groupe C aux mêmes temps. Le CO à T30 était plus élevé dans les groupes BI et I que dans le groupe C. Les résultats de cette étude ont démontré qu'une infusion d'une faible dose de dexmedetomidine améliore l'oxygénation et la mécanique du système respiratoire et a un effet hémodynamique stabilisant chez les chiens anesthésiés avec de l'isoflurane et ventilé mécaniquement.(Traduit par Docteur Serge Messier).

Pulse Pressure Variation Can Predict the Hemodynamic Response to Pneumoperitoneum in Dogs: A Retrospective Study.

Pneumoperitoneum may induce important hemodynamic alterations in healthy subjects. Pulse pressure variation (PPV) is a hemodynamic parameter able to discriminate preload dependent subjects. Anesthesia records of dogs undergoing laparoscopy were retrospectively evaluated. The anesthetic protocol included acepromazine, methadone, propofol and isoflurane administered with oxygen under mechanical ventilation. The hemodynamic parameters were considered five minutes before (BASE) and ten minutes after (P10) the pneumoperitoneum. Based on the cardiac index (CI) variation, at P10, dogs were classified as sensitive (S group, CI ≤ 15%) and non-sensitive (NO-S group). Data were analyzed with the ANOVA test and the ROC curve (p < 0.05). Fifty-five percent of dogs (S) had a reduction of CI ≥ 15% at P10 (2.97 ± 1.4 L/min/m²) compared to BASE (4.32 ± 1.62 L/min/m²) and at P10 in the NO-S group (4.51 ± 1.41 L/min/m²). PPV at BASE was significantly higher in the S group (22.4% ± 6.1%) compared to the NO-S group (10.9% ± 3.3%). The ROC curve showed a threshold of PPV > 16% to distinguish the S and NO-S groups. PPV may be a valid predictor of the hemodynamic response to pneumoperitoneum in dogs. A PPV > 16% can identify patients that may require fluid administration before the creation of pneumoperitoneum.

Perioperative analgesic effects of an ultrasound-guided transversus abdominis plane block with a mixture of bupivacaine and lidocaine in cats undergoing ovariectomy.

OBJECTIVE: To evaluate the perioperative analgesic effects of a transversus abdominis plane (TAP) block with a mixture of lidocaine and bupivacaine administered to cats undergoing ovariectomy. STUDY DESIGN: Controlled, randomized, prospective, blinded clinical study. ANIMALS: A group of 20 healthy cats. METHODS: Robenacoxib (2 mg kg-1) was administered subcutaneously 0.5 hour before intramuscular (IM) administration of ketamine (5 mg kg-1), methadone (0.1 mg kg-1) and dexmedetomidine (0.01 mg kg-1). General anesthesia was induced with intravenous (IV) propofol and maintained with isoflurane. An ultrasound-guided TAP block was performed by injecting 0.5% bupivacaine (0.2 mL kg-1) diluted in a total volume of 1.5 mL 2% lidocaine bilaterally (TAP group, n = 10) or the same volume of saline solution bilaterally in controls (CTR group, n = 10). During surgery, a 20% increase in heart rate and respiratory frequency was treated with IV fentanyl (0.001 mg kg-1). Before premedication and at 1, 2, 3, 4, 6, 8, 12, 16, 20 and 24 hours after extubation, pain was assessed with a simple descriptive pain scale, that ranged from 0 (no pain) to 4 (intense pain). For pain scores ≥3, IM methadone (0.1 mg kg-1) was administered. Data were analyzed with the Friedman or the analysis of variance (anova) test, and p < 0.05 was considered statistically significant. RESULTS: Only two cats in the CTR group were administered one dose of fentanyl during surgery. At 2, 6, 8, 12, 16, 20 and 24 hours after surgery, the pain score was higher in the CTR group. A mean dose of 0.5 ± 0.2 mg kg-1 methadone was administered to all cats in the CTR groups within 24 hours. Methadone was not administered to the TAP group (pain score < 3). CONCLUSIONS AND CLINICAL RELEVANCE: Ultrasound-guided TAP block can be a reliable adjunctive technique, providing analgesia for up to 24 hours in cats undergoing ovariectomy.