Entendendo melhor a insuficiência respiratória aguda / A better understanding of acute respiratory failure

A insuficiência respiratória aguda (IRpA) é uma síndrome potencialmente grave, constituindo uma das principais indicações de internação em unidades de terapia intensiva. Embora diferentes condições clínicas possam evoluir com IRpA, todas apresentarão comprometimento nas trocas gasosas que caracterizarão a síndrome.O conhecimento da fisiologia das trocas gasosas e os mecanismos pelos quais elas podem ser alteradas permite compreender a fisiopatologia da IRpA e as repercussões dos diferentes distúrbios sobre os gases arteriais. Este conhecimento permite a interpretação adequada da gasometria arterial e de indicadores derivados da mesma, facilitando a condução dos pacientes com IRpA, tanto em relação ao diagnóstico etiológico, quanto ao tratamento de suporte.Estes conceitos da fisiologia das troas gasosas e da fisiopatologia da IRpA e suas aplicações clínicas serão revisados neste artigo...

Acute respiratory failure (ARF) is a potentially severe syndrome, which is a common indication for admission to an intensive care unit. Although the ARF can be caused by different clinical conditions, all of them will present gas exchange impairments that will characterize the syndrome.By knowing the gas exchanges physiology and the mechanisms by which they can be impaired, one can understand the physiopathology of the ARF and how it can compromise the arterial gases. This knowledge allows the correct interpretation of arterial blood gases and other useful indicators, such as the alveolar-arterial oxygen gradient, which help us to manage patients with ARF, both in their diagnosis, and in their supportive treatment.These concepts about the gas exchange physiology and the ARF physiopathology, and their clinical relevance, will be discussed in this article...

Extrauterine Placental Support of Goat Fetuses Using Arteriovenous Bypass / 대한마취과학회지

BACKGROUND: The extrauterine fetal incubation system must meet stable blood gas exchange and sufficient oxygen supply to provide the physiologic oxygen consumption of the fetus. In the fetus, blood gas exchange is totally sustained by the placental circulation. The placenta can be regarded as an extracorporeal organ, and the basic structure of placental circulation comprises arteriovenous (AV) bypass. To mimic this mode of circulation, we used AV ECMO (extracorporeal membrane oxygenation) in the goat fetus, and attempted to achieve stable blood gas exchange and oxygen supply to the fetus. METHODS: Pregnant goats, weighting 30 - 35 kg, were anesthetized with N2O-O2-enflurane. We performed a cesarean section with a midline incision, and cannulated via the umbilical vessels after a hysterotomy, and connected the fetuses to an ECMO circuit. The fetus was transferred to an incubator containing normal saline mixed with antibiotics. Blood samples were obtained every 4 to 6 hours from the circuit for electrolytes, hemoglobin and blood gas analysis and arterial blood pressure and heart rate were monitored through the umbilical artery. Oxygen delivery and consumption were calculated from the measured parameters. Microscopic examinations of the liver, kidney and lung were performed 24 hours after ECMO to know the effect of AV ECMO on the circulation of the organ. RESULTS: AV ECMO was done for 24 hours in the six goat fetuses and the main cause of death was circulatory failure. Heart rates and blood pressure were stable during ECMO. Sodium bicarbonate was injected when mild acidosis occurred and blood gas exchange was maintained stable. Mean pump flow rate was 156 +/- 62 ml/min/kg and oxygen extraction ratio was 30.4%. The liver function tests were sustained within normal limits both before and 24 hours after ECMO, but BUN and creatininincreased beyond upper normal limits 24 hours after ECMO. Microscopic features of the liver and kidney showed congestion 24 hours after ECMO. The fetal lung after 24 hours of ECMO especially showed an increase of mature capillaries in the septum and wall of alveoli compared with the twin fetal lung. CONCLUSIONS: These results indicate that the extrauterine fetal incubation model used for this study was suitable to blood gas exchange and utility of oxygen for goat fetuses.