Two levels of the inspired oxygen fraction in propofol-anesthetized dogs with high intracranial pressure: cardiopulmonary function

P.C Ferro Lopes,E.A Belmonte,G.B Pereira Neto,A.L.G Souza,N Nunes,R M Almeida,L.G.G.G Dias

doi:10.1590/1678-6519

P.C Ferro Lopes, E.A Belmonte + Show 5 more

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https://doi.org/10.1590/1678-6519

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Abstract

In the initial stage of traumatic brain injury, the use of 1.0 inspired oxygen fraction (FiO2) is indicated. However, high FiO2 has been correlated with atelectasis. Thus, the effects of FiO2= 1.0 and FiO2= 0.6 on the cardiopulmonary function in propofol-anesthetized dogs with high intracranial pressure (ICP) were evaluated. Eight dogs were anesthetized on two occasions, receiving, during controlled ventilation, an FiO2= 1 (G100) or an FiO2= 0.6 (G60). Propofol was used for induction (10mg.kg-1) followed by a continuous rate infusion (0.6mg.kg-1.minute-1). An increase in the ICP was induced by temporary obliteration of the right jugular vein (OJv) 50 minutes after induction of anesthesia. The measurement was taken twenty minutes after OJv (T0) and then at 15-minute intervals (T15 to T60). Alveolar oxygen partial pressure in G60 was lower than in G100 during the whole procedure. Alveolar-arterial oxygen gradient in G100 was greater than in G60 at T0 and at T60. No differences were observed for arterial oxygen partial pressure/inspired oxygen fraction ratio, arterial-to-alveolar oxygen pressure ratio, respiratory index, venous admixture, oxygen delivery, oxygen consumption, oxygen extraction, heart rate, mean pulmonary arterial pressure, pulmonary arterial occlusion pressure, cardiac index, stroke index and systemic vascular resistance index. In G100, mean arterial pressure at T0 was higher than at T45. In dogs with high ICP, the cardiopulmonary function was not influenced by the different FiO2 used.

Highlights

Normal intracranial pressure (ICP) in dogs is 5 to 12mmHg, similar to that of humans for whom 20mmHg is an arbitrary upper limit beyond which treatment for ICP may be instituted
Causes of intracranial hypertension can be nonvascular or vascular, which include cerebral vasodilatation caused by increased arterial partial pressure of carbon dioxide (PaCO2), distention of cerebral vessels or venous outflow obstruction (Sturges and Lecouteur, 2009)
Propofol was used in this study because it is known to maintain or decrease the ICP while it maintains the cerebral perfusion pressure (CPP) in patients with normovolemia and stable hemodynamics (McKeage and Perry, 2003), it may commonly be selected for patients with suspicious ICP increase (Armitage-Chan et al, 2007)

Summary

INTRODUCTION

Normal intracranial pressure (ICP) in dogs is 5 to 12mmHg, similar to that of humans for whom 20mmHg is an arbitrary upper limit beyond which treatment for ICP may be instituted. During anaesthesia, high FiO2 has been correlated with atelectasis (Hedenstierna et al, 1989), which can cause PaCO2 increase (Haskins, 2007) that can interfere with cerebral blood flow (Falcão et al, 2006) and promote the impairment of cerebral autoregulation (Häggendal and Johansson, 1965; McCulloch et al, 2000). Atelectasis formation with subsequent pulmonary shunting was shown to be related to impairment of gas exchange (Brismar et al, 1985). The hypothesis was that a FiO2 = 1.0 has a detrimental effect on pulmonary gas exchange and can aggravate intracranial hypertension. This study was designed to establish the effects of two different levels of FiO2 (1.0 and 0.6) on the cardiopulmonary function in propofol-anesthetized dogs with a high ICP

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DISCUSSION