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Toronto Notes 2019 Intraoperative Management Blood Pressure
Causes of Intraoperative Hypotension/Shock
• shock:conditioncharacterizedbyinabilityofcardiovascularsystemtomaintainadequateend-organ perfusion and delivery of oxygen to tissues
a) hypovolemic/hemorrhagic shock
■ most common form of shock, due to decrease in intravascular volume
b) obstructive shock
■ obstruction of blood into or out of the heart
■ increased JVP, distended neck veins, increased systemic vascular resistance, insufficient cardiac
output (CO)
■ e.g.tensionpneumothorax,cardiactamponade,pulmonaryembolism(andotheremboli–i.e.fat,air)
c) cardiogenic shock
■ increased JVP, distended neck veins, increased systemic vascular resistance, decreased CO
■ e.g. myocardial dysfunction, dysrhythmias, ischemia/infarct, cardiomyopathy, acute valvular
dysfunction d) septic shock
■ see Infectious Diseases, ID21
e) spinal/neurogenic shock
■ decreased sympathetic tone
■ hypotension without tachycardia or peripheral vasoconstriction (warm skin)
f) anaphylactic shock
■ see Emergency Medicine, ER3
g) drugs
■ vasodilators, high spinal anesthetic interfering with sympathetic outflow
h) other
■ transfusion reaction, Addisonian crisis, thyrotoxicosis, hypothyroid, aortocaval syndrome ■ see Hematology and Endocrinology
Causes of Intraoperative Hypertension
• inadequateanesthesiacausingpainandanxiety • pre-existingHTN,coarctation,orpreeclampsia • hypoxemia/hypercarbia
• hypervolemia
• increasedintracranialpressure
• fullbladder
• drugs(e.g.ephedrine,epinephrine,cocaine,phenylephrine,ketamine)andwithdrawal
• allergic/anaphylacticreaction
• hypermetabolicstates:malignanthyperthermia,neurolepticmalignantsyndrome,serotoninsyndrome,
thyroid storm, pheochromocytoma (see Endocrinology, E35) Fluid Balance and Resuscitation
• totalrequirement=maintenance+deficit+ongoingloss
• insurgicalsettings,thisformulamusttakeintoaccountmultiplefactorsincludingpre-operativefasting/
decreased fluid intake, increased losses during or before surgery, fluids given with blood products and
medications
• increasingly,EnhancedRecoveryAfterSurgeryprotocolsrecommendconsumptionofclearfluidsupto
two hours prior to surgery
• bothinadequatefluidresuscitationANDexcessivefluidadministrationincreasesmorbiditypost-
operatively
What is the Maintenance?
• averagehealthyadultrequiresapproximately2500mLwater/d ■ 200 mL/d GI losses
■ 800 mL/d insensible losses (respiration, perspiration)
■ 1500 mL/d urine (beware of renal failure)
• replacementof‘thirdspace’lossesisnotwarranted
• maintenanceshouldnotexceed3ml/kg/hr
• increasedrequirementswithfever,sweating,GIlosses(vomiting,diarrhea,NGsuction),adrenal
insufficiency, hyperventilation, and polyuric renal disease
• decreasedrequirementswithanuria/oliguria,SIADH,highlyhumidifiedatmospheres,andCHF
• maintenanceelectrolytes
■ Na+: 3 mEq/kg/d
■ K+: 1 mEq/kg/d
• 50kgpatientmaintenancerequirements
■ fluid=40+20+30=90mL/h=2160mL/d=2.16L/d
■ Na+ = 150 mEq/d (therefore 150 mEq / 2.16 L/d ≈ 69 mEq/L) ■ K+ = 50 mEq/d (therefore 50 mEq / 2.16 L/d ≈ 23 mEq/L)
• abovepatient’srequirementsroughlymetwith2/3D5W,1/3NS ■ 2/3 + 1/3 at 100 mL/h with 20 mEq KCl per litre
Anesthesia A13
BP=COxSVR,whereCO=SVxHR SV is a function of preload, afterload, and contractility
Intraoperative Shock
SHOCKED
Sepsis or Spinal shock Hypovolemic/Hemorrhagic Obstructive
Cardiogenic
anaphylactiK
Extra/other
Drugs