Pressure Volume Index....small numbers are not small

Cerebral Blood volume (CBV)–PaCO2 curve is flatter than CBF-PaCO2.. (0.014 mL/100g/mm Hg) See the foto

Hence decreasing PaCO2 from 40 to 20 mm Hg will will decrease CBV to 2.8 mL/100g (a 28% change).

This translates into a 10–14 mL fall in whole-brain volume.

This look as small number ....
but in the light of Pressure Volume index it will not be considered as small??

Shapiro et al. showed that the amount of fluid that must be rapidly injected into or withdrawn from the intracranial space to change ICP tenfold (e.g., from 10 to 100 mm Hg) is normally ≈26 mL.

This is called the pressure-volume index (PVI). However, PVI values in patients with mass lesions
or closed head injuries may be as low as 5 mL.

In such situations, a change in CBV of 10–15 mL would be enormous, and it is not surprising that hyperventilation has come to occupy such an important position in acute ICP/brain-volume control.

PVI reflects the importance of hyperventilation in the acute management of brain edema...Keep in mind the overuse of Hyperventilation holds another risks...The risks of hyperventilation will be discussed later

1-Stroke 1974;5:630.
2-Kosteljanetz M. Acute head injury: Pressure- volume relations and cerebrospinal fluid dynamics.
Neurosurgery 1986;18:17–24.

Comments

Driving Pressure in ARDS: A new concept!

Driving Pressure and Survival in the Acute Respiratory Distress Syndrome Marcelo B.P. Amato, M.D., Maureen O. Meade, M.D., Arthur S. Slutsky, M.D., Laurent Brochard, M.D., Eduardo L.V. Costa, M.D., David A. Schoenfeld, Ph.D., Thomas E. Stewart, M.D., Matthias Briel, M.D., Daniel Talmor, M.D., M.P.H., Alain Mercat, M.D., Jean-Christophe M. Richard, M.D., Carlos R.R. Carvalho, M.D., and Roy G. Brower, M.D. N Engl J Med 2015; 372:747-755 February 19, 2015 DOI: 10.1056/NEJMsa1410639 BACKGROUND Mechanical-ventilation strategies that use lower end-inspiratory (plateau) airway pressures, lower tidal volumes (V T ), and higher positive end-expiratory pressures (PEEPs) can improve survival in patients with the acute respiratory distress syndrome (ARDS), but the relative importance of each of these components is uncertain. Because respiratory-system compliance (C RS ) is strongly related to the volume of aerated remaining functional lung during disease (termed functional lung size)...

Epidural catheter tests...not only the test dose

Siphon test The catheter is held upright and a fluid level sought. If the catheter is then elevated, the fluid level should fall (see inset) as the fluid siphons in to the epidural space, which is usually under negative pressure compared with atmospheric. If the fluid column continues to rise, this may suggest subarachnoid placement. The siphon test can be reassuring, but is not mandatory. Aspiration This should be considered mandatory. The Luer connector is attached to the catheter and a syringe is used to apply negative pressure. Free and continued aspiration of clear fluid can indicate subarachnoid placement of the catheter. However, if saline has been used for loss of resistance, it is not unusual for a small amount of this to be aspirated. If there is doubt, the aspirated fluid can be tested for glucose (cerebrospinal fluid will generally test positive) or mixed with thiopentone (cerebrospinal fluid forms a precipitate). If blood is freely and continuously aspirated, this sug...

Anaphylaxis updates part 2- Empty Ventricle Syndrome

Patients with anaphylaxis should not suddenly sit, stand, or be placed in the upright position. Instead, they should be placed on the back with their lower extremities elevated or, if they are experiencing respiratory distress or vomiting, they should be placed in a position of comfort with their lower extremities elevated. This accomplishes 2 therapeutic goals: 1) preservation of fluid in the circulation (the central vascular compartment), an important step in managing distributive shock; and 2) prevention of the empty vena cava/empty ventricle syndrome, which can occur within seconds when patients with anaphylaxis suddenly assume or are placed in an upright position. Patients with this syndrome are at high risk for sudden death. They are unlikely to respond to epinephrine regardless of route of administration, because it does not reach the heart and therefore cannot be circulated throughout the body

sedationstation

Search This Blog