Skip to main content

Pheochromocytoma...In Search for ideal agent




A common initial approach has been to use phenoxybenzamine for long-term alpha  blockade.



Preoperative preparation should include 1–2 weeks of alpha -adrenergic–blocker.
Volume replacement is important when starting alpha blockers
and patients often have a decreased Hematocrit after beginning therapy
Preoperative treatment with phenoxybenzamine results in a significantly smoother course than in untreated patients.
This drug has a long half-life (approximately 12 hours) and is highly lipid soluble.
The starting dosage is 10– 20 mg daily in 2 doses. Every 3–4 days the dose is increased until either no marked symptoms of catecholamine excess are evident or the patient complains  of side effects from postural hypotension and/or a stuffy nose, with a final dosage range of 40–100 mg/d.

There are several disadvantages to the use of phenoxybenzamine
Adequate volume expansion after institution of the drug may take as long as 2–3 weeks. Thus, patients presenting for surgery who have been on phenoxybenzamine for a shorter time period should have their hypovolemia corrected preoperatively.
Alpha Blockade with phenoxybenzamine is irreversible and depends  on synthesis of alpha receptors
Thus, there may be continued alpha blockade following tumor removal, which can contribute to postoperative hypotension.

Prazosin and Doxazosin (selective alpha receptors blockers) have   been used with success for PREOP PREPARATION
The rationale behind their selection is a shorter duration of action providing easier dose adjustment and potentially decreasing the postoperative hypotension period. Reflex tachycardia is decreased because the presynaptic alpha receptors not blocked ...

Calcium channel blockers also have been advocated for preoperative and intraoperative blood pressure control in patients with pheochromocytomas.

In Comaprison to alpha blockers  calcium channel blockers do not produce orthostatic or overshoot hypotension.
In addition, therapy may be started as late as 24 hours prior to surgery and optimal cardiovascular effects are still obtained.
Several reports suggest that calcium channel blockers may be the drug of choice for antihypertensive therapy during preoperative preparation of the pheochromocytoma patient.

Bravo EL. Pheochromocytoma: an approach to antihypertensive management. Ann NY Acad Sci 2002;970:1–10.

Sparks WJ, Seefelder C, Shamberger R, et al. The perioperative management of a patient with complex single ventricle physiology and pheochromocytoma. Anesth Analg 2005;100:972–975.

Janetschek G, Neumann HP. Laparoscopic surgery for pheochromocytoma. Urol Clin North Am 2001;28:97–105




-
Labels:

Comments

Post a Comment

Popular posts from this blog

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)...
5 comments
Read more

The pressure volume loop...

In the pressure-volume loop below, cardiac work is best represented by:   the area of the curve  the slope of the line from points C to D  the distance of the line from points C to D  the slope of a line from points A to D .. .. ... .... ... .... .... .... In the pressure-volume loop below, cardiac work is best represented by:  the area of the curve Cardiac work is the product of pressure and volume and is linearly related to myocardial oxygen consumption. Cardiac work is best represented by the area of the curve of a pressure-volume loop.
Post a Comment
Read more

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
Post a Comment
Read more