Neurogenic Shock and Phenylephrine

Neurogenic shock occurs when loss of sympathetic tone from the brain or spinal cord causes the blood vessels to dilate. This in turn causes the vascular space to enlarge. If the patient doesn't loose a single drop of blood, this increase in the vascular space causes a hypovolemia that is relative to the newly enlarged vascular space. The initial treatment is the same as it is for all the other forms of shock. Fluids. Drug treatment for neurogenic shock is to increase the vascular tone of the blood vessels. This requires stimulation of the alpha adrenergic receptor. This is best done with the drug phenylephrine which is a pure alpha agonist. Other drugs that are sometimes used are dopamine or norepinephrine-- both of these drugs act on both alpha and beta-1 receptors.

Shock is a symptom not a disease

There are some very common errors when treating shock. The most common error is that shock is the presence of hypotension (low blood pressure). Not true. Shock occurs when there is inadequate oxygen delivery to vital organs such as the heart brain or kidney. Shock can occur with a normal blood pressure. In fact, the presence of a low blood pressure or rapid heart rate are considered LATE signs of shock. The other important consideration is that shock is only a symptom of a much bigger problem. A provider wants to treat the cause of shock not just the symptom of shock, eg. hypotension. If a patient has a low blood pressure from dehydration secondary to diabetic ketoacidosis, starting dopamine will increase the blood pressure, but it will actually DECREASE the blood flow and oxygen delivery to the vital organs. Said another way, the blood pressure will go up but the shock will be worse. In that case you need to treat the blood sugar and replace the fluids from the dehydration.

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Mannitol

Mannitol is a sugar that is used as an osmotic diuretic. Diuretics are drugs the cause people to increase their urine output. Mannitol is unique in that it initially causes volume expansion and the water follows the mannitol as the molecule is filtered through the kidney. Mannitol is commonly used for the treatment of cerebral hypertension or increased intracranial pressure following head trauma. When to actually give mannitol in victims of head trauma has been a source of great discussion and controversy. The dilemma in the prehospital environment is the inability to look at a CT scan and characterize the injury. If the patient has active intracranial bleeding say from an epidural hematoma, the argument has been that administration of mannitol wil increase the bleeding and increase the mass lesions (blood collection). This has led to the recommendation that without the presence of a CT scan, the patient should have lateralizing signs to be considered for the administration of mannitol.

Mannitol is contraindicated in patients who are in anuric renal failure (ie. not making urine) or in patients with severe dehydration or hypovolemia. Also mannitol administration can lead to pulmonary edema in patients with congestive heart failure.

In cold temperatures that are often encountered in a prehospital environment, Mannitol may crystalize.

(keywords: mannitol, EMS, emergency, EMT, paramedic, prehospital pharmacology, PHTLS)

Vasopressin in ACLS

Some quick notes for the use of vasopressin in the use of ACLS. Vasopressin is one of drugs that actually has a name that makes some sense in that it is a vasopressor. Vasopressin is unique from epinephrine. Epinephrine uses the adreneric receptor and vasopressin uses a different receptor. Vasopressin can be used in VF and pulseless VT as a one time only dose of 40 units IV. Vasopressin is a potent vasoconstrictor and it does not increase oxygen consumption by the heart. It cannot be used in repeated dose like epinephrine. Vasopressin is effective even when the patient is acidotic. Remember for VT/VF epinephrine should be repeated at a dose of 1 mg every 3 to 5 minutes.

(keywords: vasopressin, ACLS, EMS, emergency, EMT, paramedic, prehospital pharmacology, PHTLS)

Supraventricular Tachycardia (SVT)

For the treatment of stable supraventricular tachycardia (SVT) amiodarone is recommended in a dose of 150 mg IV. What differentiates stable from unstabel SVT? Blood pressure for one. If your patient has a systolic blood pressure of less than 80 mmHg that would be considered unstable. Also the presence of chest pain would be another unstable factor. If your patient has unstable SVT, remember the treatment is elctrocardioversion. A common pitfall is that once you have cardioverted your patient people often fail to bolus and start the patient on an anti-arrhythmic drug. What often will happen then is the heart rhythm will then degenerate back to the original arrhythmia.

Beta blockers and hypoglycemia

One of the warnings of beta blockers is something called hypoglycemic unawareness. When a person has a low blood sugar they will exhibit symptoms such as tachycardia, diaphoresis, and restlessness. These symptoms are adrenergic mediated. That means that they are due to increases in the adrenergic hormone epinephrine. Beta blockers block the adrenergic receptor. Therefore, if a patient with diabetes has a low blood sugar the symptoms of hypoglycemia may not appear due to the presence of beta blockers. The danger is that the patient will have a dangerously low blood sugar and will not be aware of the problem due to the absence of symptoms.

Intraosseous lines are just not for kids

It is is tremendous misperception that IO lines are only for kids. IO lines were developed by the military during World War II for use in ADULT combat victims. After the war, the application fell out of favor and was picked up for the use in the resuscitation of infants and children in PALS. If is a skill that easily learned, has good skill retention, and in the scope of practice of many EMTs. I have a full podcast on the topic on the ICU rounds podcast (www.icurounds.com)

Sodium bicarbonate after cardiac arrest?

It used to be taught in versions of ACLS long past, the sodium bicarbonate should be administered as part of ACLS for the treatment of cardiac arrest. This is no longer the practice, but why? The principle academic answer is that there has not been any demonstrable improvement in outcomes. The practical explantation is that in an arrest situation, if an acidosis is present it is most likely from a respiratory cause--- respiratory acidosis. Therefore, the appropriate treatment would be to support the airway and provide mechanical ventilation.

How does acidosis affect pharmacology

Drugs interact wit various tissues through receptors. The interaction of a drug and a receptor are a complex relationship like a lock and key. A lock and key have a complex three dimension structure, and if the structure of either the lock or key change, then they are not capable of interacting.

When a person is in shock they have may have a low blood pH or acidosis. Acidosis causes the structure of the receptors to change shape. When the shape of a lock changes, then a key will not work. This is the problem often with acidosis. When a person has a low plasma pH, some drugs will not be able to bind with receptors and produce the desired physiological response. This is a problem, because if you administer an adrenergic drug like norepinephrine (Levophed) to an acidotic patient you will not see the desired response of an increase in blood pressure.

Norepinephrine (Levophed) is an adreneric agent used to increase blood pressure. It binds with adrenergic receptors.

Negligence

Administration of medications can be dangerous and result in injury to a patient. You need to know the four elements of negligence and what are those definitions. Listen to the latest podcast at www.prehospitalpharmacology.com

Welcome.  This is a blog that will serve as a companion to one of my textbook, "Pharmacology for the Prehospital Professional."   This is a book that is published and will be scheduled for release in February 2009.   

I am of the opinion that pharmacology is a hard topic to learn.   So many names that are hard to remember and so many difficult thing to remember.   I doesn't need to be so hard for the student or experienced paramedic.   I spent a great deal of effort to try to make this topic understandable for everyone.  We have also set up a podcast that is available for download. With the podcast, I provide a 15 minute lecture that is free to download.  This way you can study your pharmacology while driving, exercising, or working in the yard.

With this blog, I hope to connect the students and the author.  This way we can have a really real time discussion regarding topics and questions that you might have regarding prehospital drug therapy.