Anestesia paravertebral torácica em cães
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Data
2016-03-18
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Universidade Federal de Goiás
Resumo
Thoracic paravertebral block (TPB) is a regional anesthesia technique which provides anesthesia and analgesia with hemodynamic stability, low incidence of complications and few contraindications. However, some techniques are still poorly studied in veterinary medicine due to difficulty in accessing specific nerves. The present study aimed at reviewing the thoracic anatomy, where TPB was conducted, determining values between reference points in order to implement this technique, assessing blockade’s quality and hemodynamic effects resulting from 2.5 mg/kg of bupivacaine 0.5% administration in dogs’ paravertebral space. Initially, structures involved when performing TPB were identified during an anatomical study in cadavers. In the second stage, eight healthy male or female dogs, mixed-breed, weighing 16.33 ± 4.04 kg, were submitted to TPB under general anesthesia with isoflurane. The blockage of thoracic T5, T6 and T7 nerves was performed with 2.5 mg/kg of bupivacaine 0.5%, guided by a neuro stimulator. Subsequently, the animals were anesthetized following the same protocol used in the previous stage for pulmonary-artery catheterization via the femoral vein, in order to assess hemodynamic effects of TPB. During TPB performance, the distances between the skin and the transverse process of thoracic vertebrae (STD) as well as the skin and paravertebral space (SPD) were obtained. Isoflurane supply was discontinued and analgesia evaluation was performed by pinprick test and hemostat pressure in conscious animals, after anesthesia recover. During hemodynamic evaluations the animals were kept anesthetized under spontaneous ventilation, while central venous pressure (CVP), cardiac output (CO), pulmonary artery pressure (PAP), pulmonary artery occlusion pressure (PAOP) and other cardiovascular variables were measured. Arterial and mixed venous blood were collected for blood gas analysis such as pH, oxygen partial pressure (PO2), carbon dioxide partial pressure (PCO2), bicarbonate (HCO3-), base excess (BE), anion gap (AG) and electrolytes such as sodium (Na+), potassium (K+), calcium (Ca2+) and chloride (Cl-), tissue oxygenation variables such as oxygen delivery (DO2), consumption (VO2) and oxygen extraction (OEF) were also calculated. Evaluations were made just before TPB (T0) and every 20 minutes in the next 80 minutes (T20, T40, T60, T80). Anatomical study revealed that some thoracic muscles’ innervation come from the brachial plexus. The average obtained for STD was 3.81 ± 1.07 cm and for SPD was 6.25 ± 0.93 cm. The anesthetic block was observed in 3.63±2.77 dermatomes during 250.25 ± 44.02 minutes. The variables CVP, CO, PAP, PAOP, DO2, OEF and PO2 in mixed-venous blood, increased significantly after bupivacaine administration. Similarly, PO2 from mixed venous blood as well as DO2 and OEF increased significantly during hemodynamic evaluations. TPB provided anesthesia in a limited region of the chest wall with clinically irrelevant hemodynamic effects, however this technique did not satisfactorily anesthetized all thoracic muscles’ layers so it should be used in combination with general anesthesia.
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Citação
VILLELA, A. C. V. Anestesia paravertebral torácica em cães. 2016. 98 f. Tese (Doutorado em Ciência Animal) - Universidade Federal de Goiás, Goiânia, 2016.