Basic Fluid Administration and Anesthesia Flashcards
Why is lactated Ringer’s solution a good all-purpose crystalloid fluid to give to uncomplicated cases during anesthesia?
LRS is an isotonic crystalloid replacement solution that is cheap and expands both the vascular and interstitial compartments
Isotonic crystalloid fluids are commonly used to maintain plasma volume in uncomplicated anesthetized patients, to replace deficits in dehydrated patients, to restore third-space losses, and to maintain urine production at 1-2 ml/kg/hr
Is an IV fluid administration rate of 10 ml/kg/hr always necessary during anesthesia? Why or why not?
This rate was historically recommended for patients undergoing surgery to compensate for blood loss and third-spacing of fluids, but this rate is arbitrary and not based on medical evidence
Ideally, in’s should equal out’s
A rate of 2-4 ml/kg/hr is used for patient’s undergoing atraumatic or diagnostic procedures, while higher rates may be given for severe blood loss when combined with a colloid
What are the critical mean arterial pressures that describe the upper and lower limits of autoregulation of tissue blood flow?
Autoregulation is held constants as long as MAP is maintained between 60 and 160 mmHg
Why is mean arterial pressure not necessarily a good indicator of tissue perfusion?
It is difficult to directly measure local perfusion or total perfusion during clinical procedures
Describe your multiple-step action plan to improve blood pressure in an anesthetized patient.
Check anesthetic depth and lighten the patient if possible
- —Signs to evaluate for anesthetic depth include:
1. HR
2. Respiratory rate
3. Reflex activity (ocular, sphincter)
4. Muscle relaxation
5. Response to noxious stimuli
Evaluate the HR
- –CO = HR x stroke volume
- –Increasing the HR into a normal range should increase CO
Give an IV fluid bolus
- –Giving fluids will increase SV and result in improved CO because increasing SV results in an increase in the forcefulness of the cardiac contraction
- –We can give 25% of the total blood volume as a single LRS bolus
- —–To increase the duration of the LRS bolus add a colloid
- –Hypertonic saline is a crystalloid useful in treating acute hemorrhage
Start and inotrope/pressor infusion
Why do we need to administer 3-4 times more isotonic crystalloid than whole blood in the face of acute hemorrhage?
It is important to maintain circulating volume until the leak can be fixed
What physical properties of colloids tend to keep them in the plasma compartment?
Size (>35 kD, but the most useful are >60 kD)
Why is administration of IV crystalloid fluids necessary following hypertonic saline administration?
Hypertonic saline “robs” the interstitial compartment to pay the intravascular space and isotonic crystalloid fluids help repay the debt
Why is administration of colloid fluids necessary following hypertonic or isotonic crystalloid solutions?
A colloid should be added to increase plasma oncotic pressure
Both inotropes and pressors have the potential to raise blood pressure in hypotensive anesthetized patients, but inotropes are generally preferred. Why?
Inotropes improve perfusion by increasing contractility of the heart. Pressors are drugs that increase BP, generally by increasing vascular resistance. An increase in pressure and vascular resistance doesn’t necessarily improve perfusion
What are the effects of phenothiazines (acepromazine) on the CV system?
Dose dependent alpha-1 receptor antagonist
What are the effects of alpha-1 agonists (dexmedetomidine, xylaine) on the CV system?
Initial hypertension with bradycardia
Hypotension +/- bradycardia
Decreased cardiac index
What are the effects of dissociatives (ketamine) on the CV system?
Central sympathetic stimulation, direct myocardial depression
Sick patients are sympathetically depleted
What are the effects of propofol on the CV system?
Negative inotropic effect on myocardium
What are the effects of inhalant anesthetics (iso and sevo) on the CV system?
Peripheral vasodilation
