Effects of PEEP on Hemodynamic Variables of Pigs Submitted to Volume-controlled Ventilation under Pneumoperitoneum associated to Cephalodeclive

Background: Videolaparoscopic procedures have gained prominence due to their low invasiveness, causing less surgical trauma and better post-surgical recovery. However, the increase in intra-abdominal pressure due to the institution of pneumoperitoneum can alter the patient's homeostasis. Therefore, volume-controlled ventilation, associated with positive end-expiratory pressure (PEEP), improves arterial oxygenation and prevents pulmonary collapse, but it can lead to important hemodynamic changes. The aim of this study was to evaluate, comparatively, the effects of positive end expiratory-pressure (PEEP) on hemodynamic variables of pigs submitted to volume-controlled ventilation, during pneumoperitoneum and maintained in head-down tilt and determine which PEEP value promotes greater stability on hemodynamic variables. Materials, Methods & Results: Twenty-four pigs were used, between 55 and 65-day-old, weighing between 15 and 25 kg, randomly divided into 3 distinct groups differentiated by positive end-expiratory pressure: PEEP 0 (volume-controlled ventilation and PEEP of 0 cmH2O), PEEP 5 (volume-controlled ventilation and PEEP of 5 cmH2O) and PEEP 10 (volume-controlled ventilation and PEEP of 10 cmH2O). Volume-controlled ventilation was adjusted to 8 mL/kg of tidal volume and a respiratory rate of 25 movements per min. Anesthesia was maintained with continuous infusion of propofol (0.2 mg/kg/min) and midazolam (1 mg/kg/h). Pneumoperitoneum was performed with carbon dioxide (CO2), keeping the intra-abdominal pressure at 15 mmHg and the animals were positioned on a 30° head-down tilt. The evaluations of hemodynamic variables started 30 min after induction of anesthesia (M0), followed by measurements at 15-min intervals (from M15 to M90), completing a total of 7 evaluations. The variables of interest were collected over 90 min and submitted to analysis of variance followed by Tukey´s post-hoc test, with P < 0.05. The PEEP 10 group had higher values of CVP and mCPP, while the PEEP 5 group, mPAP and PVR were higher. The PEEP 0 group, on the other hand, had higher means of CI. Regarding the moments, there were differences in HR, SAP, DAP, MAP, CO, IC and TPR.Discussion: According to the literature, important hemodynamic effects due to pneumoperitoneum are reported, which can be caused by the pressure used in abdominal insufflation, CO2 accumulation, duration of the surgical procedure, hydration status and patient positioning. Mechanical ventilation associated with PEEP can also cause an increase in intrathoracic pressure and, therefore, reduce cardiac output. Cardiovascular changes are proportional to the PEEP used. Central venous pressure (PVC) measure the patient's preload, and intrathoracic pressure can interfere with this parameter. The peak pressure values in the PEEP 10 group were higher than the other groups, demonstrating that the increase in intrathoracic pressure results in higher PVC values. Regarding PAPm and PCPm, these variables can be influenced according to the PEEP values and the patient's position. In relation to CI, the increase in PEEP may reflect on intrathoracic pressure, resulting in greater compression of the heart, with a consequent reduction in cardiac output and cardiac index. Therefore, it is concluded that the PEEP effects of 0 cmH2O and 5 cmH2O on hemodynamics are discrete, under the proposed conditions. Keywords: mechanical ventilation, PEEP, head-down tilt, VCV, swine. Descritores: ventilação mecânica, PEEP, posição de Trendelenburg, suínos.

Effects of PEEP on Hemodynamic Variables of Pigs Submitted to Volume-controlled Ventilation under Pneumoperitoneum associated to Cephalodeclive

Background: Videolaparoscopic procedures have gained prominence due to their low invasiveness, causing less surgical trauma and better post-surgical recovery. However, the increase in intra-abdominal pressure due to the institution of pneumoperitoneum can alter the patient's homeostasis. Therefore, volume-controlled ventilation, associated with positive end-expiratory pressure (PEEP), improves arterial oxygenation and prevents pulmonary collapse, but it can lead to important hemodynamic changes. The aim of this study was to evaluate, comparatively, the effects of positive end expiratory-pressure (PEEP) on hemodynamic variables of pigs submitted to volume-controlled ventilation, during pneumoperitoneum and maintained in head-down tilt and determine which PEEP value promotes greater stability on hemodynamic variables. Materials, Methods & Results: Twenty-four pigs were used, between 55 and 65-day-old, weighing between 15 and 25 kg, randomly divided into 3 distinct groups differentiated by positive end-expiratory pressure: PEEP 0 (volume-controlled ventilation and PEEP of 0 cmH2O), PEEP 5 (volume-controlled ventilation and PEEP of 5 cmH2O) and PEEP 10 (volume-controlled ventilation and PEEP of 10 cmH2O). Volume-controlled ventilation was adjusted to 8 mL/kg of tidal volume and a respiratory rate of 25 movements per min. Anesthesia was maintained with continuous infusion of propofol (0.2 mg/kg/min) and midazolam (1 mg/kg/h). Pneumoperitoneum was performed with carbon dioxide (CO2), keeping the intra-abdominal pressure at 15 mmHg and the animals were positioned on a 30° head-down tilt. The evaluations of hemodynamic variables started 30 min after induction of anesthesia (M0), followed by measurements at 15-min intervals (from M15 to M90), completing a total of 7 evaluations. The variables of interest were collected over 90 min and submitted to analysis of variance followed by Tukey´s post-hoc test, with P < 0.05. The PEEP 10 group had higher values of CVP and mCPP, while the PEEP 5 group, mPAP and PVR were higher. The PEEP 0 group, on the other hand, had higher means of CI. Regarding the moments, there were differences in HR, SAP, DAP, MAP, CO, IC and TPR.Discussion: According to the literature, important hemodynamic effects due to pneumoperitoneum are reported, which can be caused by the pressure used in abdominal insufflation, CO2 accumulation, duration of the surgical procedure, hydration status and patient positioning. Mechanical ventilation associated with PEEP can also cause an increase in intrathoracic pressure and, therefore, reduce cardiac output. Cardiovascular changes are proportional to the PEEP used. Central venous pressure (PVC) measure the patient's preload, and intrathoracic pressure can interfere with this parameter. The peak pressure values in the PEEP 10 group were higher than the other groups, demonstrating that the increase in intrathoracic pressure results in higher PVC values. Regarding PAPm and PCPm, these variables can be influenced according to the PEEP values and the patient's position. In relation to CI, the increase in PEEP may reflect on intrathoracic pressure, resulting in greater compression of the heart, with a consequent reduction in cardiac output and cardiac index. Therefore, it is concluded that the PEEP effects of 0 cmH2O and 5 cmH2O on hemodynamics are discrete, under the proposed conditions. Keywords: mechanical ventilation, PEEP, head-down tilt, VCV, swine. Descritores: ventilação mecânica, PEEP, posição de Trendelenburg, suínos.

Postoperative Analgesia Time in Dogs Submitted to Mastectomy and Anesthetized with Tumescent Solutions of Lidocaine or Ropivacaine

Background: Mastectomy, a procedure with high pain stimulation, is the treatment of choice for bitches with breast cancer. Tumescent anaesthesia is widely used for transoperative and postoperative analgesia in bitches submitted to mastectomy, because facilitates tissue divulsion, also contributing significantly for the rapid recovery of patients. Although, there is no consensus as to which local anesthetic to use and at what concentration it should be used. Herein was investigated which local anesthetics, lidocaine or ropivacaine, when used in tumescent solutions, could provide a more lasting analgesic effect in the postoperative period in bitches submitted to radical unilateral mastectomy.Materials, Methods & Results: Sixteen bitches were sedated with chlorpromazine (0.3 mg/kg) and meperidine (3 mg/kg) followed by anesthesia with propofol and isofluorane. Then, bitches were randomly assigned to two groups (n= 8 each): LG group, infused with 15 mL/kg of tumescence solution containing 0.1% lidocaine; and RG group, infused with 15 mL/kg of tumescence solution with 0.1% ropivacaine. The study was conducted in a double-blind fashion. Control group did not include, because the patients would be submitted to severe or unbearable pain, according to the short-form of the Glasgow pain Scale (CMPS-SF). The heart (HR) and respiratory (ƒ) rates, and systolic blood pressure (SBP) were measured in the pre-operative period and immediately after extubation (Mextub) and at 0.5 h, 1 h, 2 h, 4 h, 8 h, and 12 h after the extubation. Analgesic efficacy was assessed using the CMPS-SF and von Frey filaments. Both groups showed higher means for HR at 0.5 h (167 ± 7 in LG; 170 ± 7 in RG) than at 4 h (117 ± 7 in LG; 120 ± 7 in RG). CMPS-SF revealed higher medians (P= 0.038) at the Mextub and 12 h time points for the LG [5 (3-6) and 1 (0-2)] than for the RG [5 (2-5) and 0 (0-1)].Discussion: Pain was excluded as a possible explanation for the difference presented for HR in both groups because, moderate pain is considered when more than two cardiorespiratory parameters show an increase of at least 20% in relation to baseline values, which did not occur in this study. Indeed, most animals were walking at 0.5 h after extubation and, in many cases, this occurred before the collection of data for the postoperative period. This may have influenced the results since exercise releases catecholamines and increases HR. Moreover at 4 h after extubation, most animals were asleep. As metabolism decreases during sleep, expected that HR would also decrease and that was indeed the case. Regarding CMPS-SF, the way the patients walks was the item that most contributed to the high score found for the Mextub time point because it's impossible to be performed seconds after extubation. As the reluctance to move occurred only immediately after extubation, the values obtained at the Mextub time point are more likely to be due to an anesthetic residual effect and not to the pain stimulus itself. When the groups were compared, the median values obtained at the LG were greater than RG at the Mextub and 12 h postoperative time points.  There was no need for analgesic rescue differing from those in literature that reported the need for analgesic rescue in 50% of the animals. Those study established a CMPS-SF score of 3.3 as indicative for analgesic rescue whereas our research established a score of 7. Tumescence solutions with lidocaine or ropivacaine provide equivalent postoperative analgesia for at least 12 h

Efeitos do óxido nitroso sobre parâmetros cardiovasculares em suínos anestesiados com propofol e mantidos em ventilação controlada à pressão

This paper evaluated the effects of the ratio of nitrous oxide to oxygen (50% of each) on cardiovascular parameters in pigs anesthetized with propofol and maintained in ventilation with intermittent positive pressure. Sixteen Large White pigs, weighing between 15 and 20 kg, were divided into two groups of eight animals, and designated as follows: GPN (propofol/nitrous oxide) and GPA (propofol/compressed air). In order to allow endotracheal intubation, the animals received azaperone (2 mg kg-1, IM) followed, after 20 minutes, by intravenous propofol. After successful intubation, continuous infusion of propofol was initiated at a dose of 0.4 mg kg-1minute-1. From this point, the GPN group received N2O (diluted in 50% oxygen), while the GPA group received compressed air (diluted in 50% oxygen). Rocuronium was then administered by continuous intravenous infusion at 0.6 mg kg-1h-1. Pressure-controlled ventilation (PCV) was started and adjusted to 15 cmH2O, and the respiratory rate was set to reach capnometry readings between 35-45 mmHg. The measurement of parameters (heart rate, mean arterial pressure, cardiac index, systemic vascular resistance index, stroke index) begun 15 minutes after the administration of rocuronium, and was repeated in 15-minute intervals for 60 minutes. Data were statistically analyzed by ANOVA followed by Bonferroni test. The results showed that the 1:1 ratio combination of nitrous oxide to oxygen (50% each) did not alter the mentioned parameters in pigs anesthetized with propofol and maintained at pressure-controlled ventilation, indicating that it is a safe protocol for the cardiovascular system.Objetivou-se com este trabalho avaliar os efeitos da associação de óxido nitroso (N2O) ao oxigênio, na proporção de 50% cada, sobre os parâmetros cardiovasculares em suínos anestesiados com propofol e mantidos em ventilação com pressão positiva intermitente. Para isso, foram utilizados 16 suínos da raça Large White com pesos entre 15 e 20 kg, distribuídos em dois grupos de oito animais cada, assim nomeados: GPN (GrupoPropofol/Óxidonitroso) e GPA (GrupoPropofol/Arcomprimido). Os animais receberam azaperona (2mgkg-1,IM) e após 20 minutos, administrou-se propofol por via intravenosa, em doses suficientes para permitir a intubação traqueal. Após intubação, iniciou-se a infusão contínua de propofol na dose de 0,4mgkg-1minuto-1. A partir deste momento, os animais do GPN receberam N2O diluído em 50% de oxigênio e os do GPA, ar comprimido diluído em 50% de oxigênio. Ato contínuo, administrou-se, por infusão intravenosa contínua, rocurônio a 0,6mgkg-1h-1. A ventilação controlada a pressão (VCP) foi iniciada e ajustada a 15cmH2O e a freqüência respiratória foi regulada para alcançar valores de capnometria entre 35-45mmHg. A medição dos parâmetros (freqüência cardíaca, pressão arterial média, índice cardíaco, índice da resistência periférica total, índice sistólico) iniciou-se após 15 minutos da administração de rocurônio, repetindo-se a cada 15 minutos, durante um intervalo de 60 minutos. Os dados foram submetidos à análise estatística pela ANOVA seguida pelo teste de Bonferroni. Os resultados mostraram que a associação do óxido nitroso ao oxigênio na proporção de 50% cada em suíno anestesiado com propofol e mantido em ventilação controlada à pressão não provoca alterações cardiovasculares clinicamente relevantes