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Shock

A part of the presentation;

Outline
1- Definition of Shock
2- Signs and Symptoms of Shock
3- Categorization of Shock
4- The PA Catheter
5- Replacement Fluids
6- Vasopressors and Inotropes
7- Example Cases

What is Shock?
Shock is a physiologic state characterized by a systemic impairment in oxygen delivery as a result of reduced tissue perfusion, almost universally mediated by low blood pressure.

What is Shock?
The general physiologic mechanisms of how shock leads to irreversible cell damage and death include:

- Cell membrane ion pump dysfunction
- Intracellular edema
- Leakage of intracellular contents into the extracellular space
- Inadequate regulation of intracellular pH

Signs/Symptoms of Shock
* Cardiovascular – Hypotension
* Nervous – Agitation  Delirium  Coma
* Pulmonary – Tachypnea; hypoxia
* Epidermal – Cool, clammy skin; peripheral cyanosis
* Kidneys – Oliguria; increased BUN/Cr ratio
* GI – Ileus, hemorrhage; hepatic dysfunction
* Hematologic – Coagulopathy  DIC
* Diffuse Cellular Injury – Lactic acidosis

Physiologic Description of Shock
Pressure Gradient = Flow x Resistance (i.e. Ohm’s Law –> V=IR)

Perfusion Pressure = MAP – CVP
Perfusion Pressure = CO x SVR
Perfusion Pressure = HR x SV x SVR

SV is dependent upon preload, afterload, and myocardial contractility

Categories of Shock

Hypovolemic: Decreased Preload (from an extracardiopulmonary process)
Distributive: Decreased SVR
Cardiogenic: Decreased Contractility
Obstructive: Decreased Preload (from an intracardiopulmonary process)

Etiologies of Shock
Hypovolemic
- Loss of blood volume
- Loss of plasma volume

Distributive
- SIRS / Sepsis
- Anaphylaxis
- Myxedema Coma
- Neurogenic Shock

Cardiogenic
– MI
– Heart failure
– Myocarditis
– Arrhythmias
– Paplillary muscle rupture
– Acute AI

Obstructive
– Massive PE
– Tension pneumothorax
– Cardiac tamponade

The Pulmonary Artery (PA) Catheter
The PA Catheter:
The PA catheter allows measurement of 3 types of data:
1. Central venous, pulmonary artery, and pulmonary capillary occlusion (or “wedge”) pressures
2. Cardiac output and vascular resistence
3. Sampling of mixed venous blood

Situations in which PA catheters are most helpful:
1. Guiding the management of severe CHF
2. Estimating fluid status in non-cardiogenic pulmonary edema
3. Diagnosing pulmonary hypertension
4. Diagnosing right heart infarction

As the catheter is “floated” from either the internal jugular or subclavian veins, and advanced from the RA to the RV, and from the RV to the PA, a number of specific pressure waveforms should be observed.

Replacement Fluids
IV replacement fluids can be divided into two categories based on whether they do or do not have a tendency to stay intravascular:

Crystalloid – Normal saline, lactated Ringer’s, D5W

Colloid – Fresh frozen plasma, albumin

Although there are theoretical reasons to favor colloids over crystalloids for volume resuscitation in patients with shock, no data to date has shown any significant outcome difference.

Therefore, crystalloid is almost always the preferred choice, given its decreased cost and decreased risk.

Vasopressors and Inotropes
* Vasopressors – Act to increase SVR, and subsequently increase BP.
* Inotropes – Act to increase CO. BP may either be increased or decreased.

Together, vasopressors and inotropes are colloquially known as “pressors”.

* A given drug may have an effect on multiple receptors, and which receptors it interacts with may be dose dependent.
* Hypovolemia must be corrected prior to the institution of vasopressor therapy. Therefore, pressors are generally not helpful in hypovolemic shock.
* A given agent may affect systemic blood pressure through both direct actions, as well as indirect reflex actions.

Vasopressors and Inotropes (Generalized Summary)
Phenylepherine
Norepinepherine
Epinepherine
Dopamine
Dobutamine
Milrinone

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