VMD 411: Veterinary Clinical Medicine-I (General and Systemic) (2+1)

MONITORING OF SHOCK

• Shock resuscitation is aimed at improving tissue oxygen delivery such that homeostasis can be maintained. Therapy should always be titrated to effect and halted once the endpoints of resuscitation are achieved.
• Over-zealous fluid administration can cause more harm than good, and complete shock volumes should not be given unless necessary. Therefore, it is important to constantly monitor endpoints of resuscitation during shock therapy. These include:

Heart rate

• This is the easiest modality to measure. For the patient in compensated shock, the heart rate should decrease during resuscitation. In cats, heart rate should increase to normal if presented with bradycardia. Unfortunately, ongoing pain or stress can obscure the response to therapy.

Pulse quality

• This should improve with shock therapy. However, pulse quality is a relatively imprecise indicator of blood pressure since pulse pressure is merely the difference between the systolic and diastolic pressures. A normal pulse quality does not mean that the animal is fine, but a poor pulse quality usually indicates ongoing issues.

Mucous membrane color

• MM color reflects the degree of tissue perfusion. If there is on-going vasoconstriction, MM color will remain poor. However, vasodilatory conditions such as sepsis may cause normal color even in the face of severe shock. Additionally, ongoing pain can contribute to peripheral vasoconstriction even without shock.

Mental status

• Improvements in mentation often lag behind normalization of other parameters, so it should not be used as the sole measure of shock resuscitation. However, improvements in mentation are expected as shock is resolved. Mental status can be difficult to asses in patients with CNS disease or head trauma.

Arterial blood pressure

• This modality is one of the most frequently used to assess shock states, but the astute clinician also should realize the limitations of blood pressure measurement.
• A normal blood pressure does not mean that the patient is fine, and an abnormal blood pressure definitely means that something is not right. Out of all parameters, blood pressure is the most protected by compensation for shock.
• Normalization of blood in conjunction with normalization of heart rate, mucous membrane color and mentation indicate the shock resuscitation has been successful.

PCV/TS

• These are insensitive indicators of shock resuscitation. Even with severe blood loss, redistribution of fluid from the interstitial to intravascular compartments takes time.
• Further changes in PCV will occur with fluid administration, or PCV can be falsely elevated due to splenic contraction. PCV can be useful for determining the need for blood transfusions.

Urine output and specific gravity

• Urine output is an excellent indicator of renal blood flow, provided that the patient does not have pre-existing renal disease. The normal urine output for a patient on IV fluids is 1-2 ml/kg/hr.
• The well-hydrated patient should have a urine SG of 1.012-1.020. Unfortunately, shock states can cause acute renal failure or impaired concentrated ability, which limit the usefulness of this as a monitoring tool.
• Additionally, evidence of good renal perfusion does not necessarily equal normal perfusion in other tissues.

Acid-base balance

• Shock states are usually associated with metabolic acidosis. Successful treatment of shock should cause an improvement in pH and base excess back towards normal. Failure of base excess to return to normal is associated with a worse prognosis.

Lactate

• This is a good marker of tissue perfusion, especially in the GI tract. Lactate is produced by tissues undergoing anaerobic metabolism. Remember that the measured value is the balanced between lactate production and clearance.
• Decreased clearance (i.e., liver disease) can cause elevations in lactate. Additionally, severely underperfused tissue can have lactate trapped, resulting in falsely low blood concentrations. Lactate has been shown to be an important prognostic marker. Failure to reduce lactate concentrations have been strongly correlated with a worse prognosis for multiple diseases.
  The important point is that multiple parameters should be assessed to judge response to shock resuscitation. No single marker has been shown to be strongly correlated with successful treatment, therefore, the entire patient should be reassessed frequently (every 10-15 minutes) during the resuscitation period.