Choice Of Drug In Shock

On present knowledge the best drug would be one that both stimulates the myocardium and selectively modifies peripheral resistance to increase flow to vital organs.

• Dobutamine is used when cardiac inotropic effect is the primary requirement.

• Adrenaline is used when a more potent inotrope than dobutamine is required, e.g. when the vasodilating action of dobutamine compromises mean arterial pressure.

• Noradrenaline is used when vasoconstriction is the first priority, plus some slight cardiac inotropic effect, e.g. septic shock.

Monitoring drug use

Modern monitoring by both invasive and noninvasive techniques is complex and is undertaken in units dedicated to and, equipped for, this activity. The present comment is an overview. Monitoring will normally require close attention to heart rate and rhythm, blood pressure, fluid balance and urine flow, pulmonary gas exchange and central venous pressure. The use of drugs in shock is secondary to accurate assessment of cardiovascular state (especially of peripheral flow) and to other essential management, treatment of infection and maintenance of intravascular volume.

Restoration of intravascular volume7

In an emergency, speed of replacement is more important than its nature. Crystalloid solutions, e.g.

isotonic saline, Hartmann's, Plasma-Lyte, are immediately effective, but they leave the circulation quickly. (Note that dextrose solutions are completely ineffective because they distribute across both the extracellular and intracellular compartments.) Macro-molecules (colloids) remain in the circulation longer. The two classes (crystalloids and colloids) may be used together.

The choice of crystalloid or colloid for fluid resuscitation remains controversial. There have been no prospective, randomised trials of sufficient power in either sepsis or trauma, to detect a significant difference in mortality. Albumin is relatively expensive and offers no advantage over cheaper, synthetic colloids such as etherified starch.

Colloidal isotonic solutions of macromolecules include: dextrans (glucose polymer), gelatin (hydro-lysed collagen) and hydroxyethyl starch.

Dextran 70 (mol. wt. 70 000) has a plasma restoring effect lasting 5-6 h. Dextran 40 is used to decrease blood sludging and so to improve peripheral blood flow.

Gelatin products (Haemaccel, Gelofusine) have a plasma restoring effect of 2-3 h (at best).

Etherified starch. Several hydroxyethyl starch solutions are available, with widely differing effects on plasma volume. The high molecular weight (450 000) solutions have a volume restoring effect for 6-12 h, while that of medium molecular weight (200 000) starches last 4-6 h.

Adverse effects include anaphylactoid reactions; dextran and hetastarch can impair haemostatic mechanisms.

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