sábado, 21 de septiembre de 2013

Vasoconstricción pulmonar hipóxica/Hypoxic pulmonary vasoconstriction




Vasoconstricción pulmonar hipóxica: mecanismos y controversias


Hypoxic pulmonary vasoconstriction: mechanisms and controversies.
Aaronson PI, Robertson TP, Knock GA, Becker S, Lewis TH, Snetkov V, Ward JP.
Department of Asthma, Allergy and Respiratory Science, New Hunt's House, Guy's Hospital Campus, King's College London, London SE1 1UL, UK. philip.aaronson@kcl.ac.uk
J Physiol. 2006 Jan 1;570(Pt 1):53-8. Epub 2005 Oct 27.
Abstract
The pulmonary circulation differs from the systemic in several important aspects, the most important being that pulmonary arteries constrict to moderate physiological (20-60 mmHg PO2) hypoxia, whereas systemic arteries vasodilate. This phenomenon is called hypoxic pulmonaryvasoconstriction (HPV), and is responsible for maintaining the ventilation-perfusion ratio during localized alveolar hypoxia. In disease, however, global hypoxia results in a detrimental increase in total pulmonary vascular resistance, and increased load on the right heart. Despite many years of study, the precise mechanisms underlying HPV remain unresolved. However, as we argue below, there is now overwhelming evidence that hypoxia can stimulate several pathways leading to a rise in the intracellular Ca2+ concentration ([Ca2+]i) in pulmonary artery smooth muscle cells (PASMC). This rise in [Ca2+]i is consistently found to be relatively small, and HPV seems also to require rho kinase-mediated Ca2+ sensitization. There is good evidence that HPV also has an as yet unexplained endothelium dependency. In this brief review, we highlight selected recent findings and ongoingcontroversies which continue to animate the study of this remarkable and unique response of the pulmonary vasculature to hypoxia.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1464287/pdf/tjp0570-0053.pdf





Efectos de dexmedetomidina sobre la oxigenación durante ventilación de un solo pulmón en cirugía torácica de adultos

Effects of dexmedetomidine on oxygenation during one-lung ventilation for thoracic surgery in adults.
Kernan S, Rehman S, Meyer T, Bourbeau J, Caron N, Tobias JD.
Department of Anesthesiology, University of Missouri, Columbia, Missouri.
J Minim Access Surg. 2011 Oct;7(4):227-31. doi: 10.4103/0972-9941.85645.
Abstract
STUDY OBJECTIVE: To evaluate the effects of dexmedetomidine on hypoxic pulmonary vasoconstriction (HPV) and oxygenation during one-lungventilation (OLV) in adults undergoing thoracic surgery. DESIGN: Prospective, randomized, double-blinded trial. SETTING:Tertiary care, University-based hospital. PATIENTS: Nineteen adult patients undergoing thoracic surgery requiring OLV. INTERVENTIONS:During inhalational anesthesia with desflurane, patients were randomized to receive either dexmedetomidine (bolus dose of 0.3 μg/kg followed by an infusion of 0.3 μg/kg/hr) or saline placebo. MEASUREMENTS:Three arterial blood gas samples (ABG) were obtained to evaluate the effects of dexmedetomidine on oxygenation. Secondary outcomes included differences in hemodynamic parameters (heart rate and mean arterial pressure), end-tidal desflurane concentration required to maintain the bispectral index (BIS) at 40-60, supplemental fentanyl to maintain hemodynamic stability, and phenylephrine to keep the mean arterial pressure (MAP) within 10% of baseline values. MAIN RESULTS:Oxygenation during OLV did not change following the administration of dexmedetomidine (PaO2/FiO2 ratio of 188 ± 115 in dexmedetomidine patients versus 135 ± 70 mmHg in placebo patients). There were no differences in hemodynamic variables or depth of anaesthesiabetween the two groups. With the administration of dexmedetomidine, there was a decrease in the expired concentration of desflurane required to maintain the BIS at 40-60 when compared with the control group (4.5 ± 0.8% versus 5.1 ± 0.8%). In patients receiving dexmedetomidine, fentanyl requirements were decreased when compared to placebo (2.7 μg/kg/patient versus 3.1 μg/kg/patient). However, more patients receiving dexmedetomidine required phenylephrine to maintain hemodynamic stability (6 of 9 patients versus 3 of 10 patients) and the total dose of phenylephrine was greater in patients receiving dexmedetomidine when compared with placebo 10.3 μg/kg/patient versus 1.1 μg/kg/patient). CONCLUSION: Dexmedetomidine does not adversely affect oxygenation during OLV in adults undergoing thoracic surgical procedures. The improvement in oxygenation in the dexmedetomidine patients may be related to a decrease in the requirements for inhalational anaesthetic agents thereby limiting its effects on HPV.
KEYWORDS: Dexmedetomidine, hypoxic pulmonary vasoconstriction, one-lung ventilation, thoracoscopy, thoracotomy

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3193692/




Ventilación mecánica selectiva
Erwin S. Asprilla Pérez, Hans Fred García Araque
Rev Colomb Neumol 2010; 22(3): 108-118
RESUMEN
La ventilación pulmonar selectiva (VPS) es un procedimiento empleado en la cirugía torácica instaurado antes de la apertura de la pleura, que consiste en ventilar un solo pulmón (pulmón declive), mientras se colapsa el pulmón que va a ser intervenido quirúrgicamente (proclive), cuyos objetivos principales son la protección pulmonar, control de la ventilación pulmonar, y mejorar el acceso quirúrgico; facilitando así la técnica de las intervenciones y la reducción en el tiempo quirúrgico. Se realizó una revisión bibliográfica de la fisiología respiratoria durante la VPS en decúbito lateral, sus indicaciones absolutas y relativas, los cambios fisiológicos que se presentan en la mecánica ventilatoria del pulmón comprimido y con movilidad limitada, en especial la vasoconstricción pulmonar hipóxica (VPH) como proceso de autorregulación, los diferentes agentes e intervenciones anestésicas a emplear para modular la respuesta pulmonar de vasoconstricción ante la hipoxia, como el uso de anestésicos halogenados, medicamentos vasoactivos, los niveles de CO2 , la PEEP, la anestesia epidural y la hipotermia; y otros factores a tener en cuenta como la liberación de sustancias vasoactivas que también pueden causar la inhibición de la VPH, así como sus repercusiones gasométricas importantes como el aumento en el espacio muerto alveolar (PaETCO2). Se reviso los parámetros ventilatorios establecidos para la VPS en los diversos estudios, que deben seguirse dependiendo de las condiciones pulmonares previas del paciente para evitar complicaciones respiratorias intraoperatorias como la hipoxemia, el atrapamiento aéreo y el barotrauma. La decisión de emplear la técnica de la VPS debe basarse en los beneficios relativos que ofrece e sta técnica y en la tolerabilidad individual de cada paciente, siguiendo como recomendación general la identificación de los pacientes con factores de riesgo para desarrollar una posible lesión pulmonar aguda (LPA) o síndrome de dificultad respiratoria del adulto (SDRA), tras a ser sometidos a una VPS.
Palabras clave: ventilación pulmonar selectiva, pulmón declive, vasoconstricción pulmonar hipóxica, protección pulmonar, ventilación mecánica, ventilación con presión controlada


http://www.asoneumocito.org/wp-content/uploads/2012/02/Vol-22-3-7_g.pdf





Atentamente
Dr. Juan Carlos Flores-Carrillo
Anestesiología y Medicina del Dolor
www.anestesia-dolor.org
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