PERIOPERATIVE FLUID THERAPY

• المقرر الدراسي: MEDI045

PERIOPERATIVE FLUID THERAPY

• Total Body Water (TBW)
• Varies with age, gender
• 55% body weight in males
• 45% body weight in females
• 80% body weight in infants
• Less in obese: fat contains little water
• Body Water Compartments
• Intracellular water: 2/3 of TBW
• Extracellular water: 1/3 TBW
  -  Extravascular water: 3/4 of extracellular water
  -  Intravascular water: 1/4 of extracellular water
• Fluid and Electrolyte Regulation
• Volume Regulation
  • Antidiuretic Hormone
  • Renin/angiotensin/aldosterone system
  • Baroreceptors in carotid arteries and aorta
  • Stretch receptors in atrium and juxtaglomerular aparatus
  • Cortisol
• Fluid and Electrolyte Regulation
• Plasma Osmolality Regulation
  • Arginine-Vasopressin (ADH)
  • Central and Peripheral osmoreceptors
• Sodium Concentration Regulation
  • Renin/angiotensin/aldosterone system
  • Macula Densa of JG apparatus
• Preoperative Evaluation
  of Fluid Status
• Factors to Assess:
  • h/o intake and output
  • blood pressure: supine and standing
  • heart rate
  • skin turgor
  • urinary output
  • serum electrolytes/osmolarity
  • mental status
• Orthostatic Hypotension
• Systolic blood pressure decrease of greater than 20mmHg from supine to standing
• Indicates fluid deficit of 6-8% body weight
  -  Heart rate should increase as a compensatory measure
  -  If no increase in heart rate, may indicate autonomic dysfunction or antihypertensive drug therapy
• Perioperative Fluid Requirements
  The following factors must be taken into account:
  1- Maintenance fluid requirements
  2- NPO and other deficits: NG suction, bowel prep
  3- Third space losses
  4- Replacement of blood loss
  5- Special additional losses: diarrhea
• 1- Maintenance Fluid Requirements
  • Insensible losses such as evaporation of water from respiratory tract, sweat, feces, urinary excretion.  Occurs continually.
  • Adults: approximately 1.5 ml/kg/hr
  • “4-2-1 Rule”
    -  4 ml/kg/hr for the first 10 kg of body weight
    -  2 ml/kg/hr for the second 10 kg body weight
    -  1 ml/kg/hr subsequent kg body weight
    -  Extra fluid for fever, tracheotomy, denuded surfaces
• 2- NPO and other deficits
• NPO deficit = number of hours NPO x maintenance fluid requirement.
• Bowel prep may result in up to 1 L fluid loss.
• Measurable fluid losses, e.g. NG suctioning, vomiting, ostomy output, biliary fistula and tube.
• 3- Third Space Losses
• Isotonic transfer of ECF from functional body fluid compartments to non-functional compartments.
• Depends on location and duration of surgical procedure, amount of tissue trauma, ambient temperature, room ventilation.
• Replacing Third Space Losses
• Superficial surgical trauma: 1-2 ml/kg/hr
• Minimal Surgical Trauma: 3-4 ml/kg/hr
  -  head and neck, hernia, knee surgery
• Moderate Surgical Trauma: 5-6 ml/kg/hr
  -  hysterectomy, chest surgery
• Severe surgical trauma: 8-10 ml/kg/hr (or more)
  -  AAA repair, nehprectomy
• 4- Blood Loss
• Replace 3 cc of crystalloid solution per cc of blood loss (crystalloid solutions leave the intravascular space)
• When using blood products or colloids replace blood loss volume per volume
• 5- Other additional losses
• Ongoing fluid losses from other sites:
  -  gastric drainage
  -  ostomy output
  -  diarrhea
• Replace volume per volume with crystalloid solutions
• Example
• 62 y/o male, 80 kg, for hemicolectomy
• NPO after 2200, surgery at0800, received bowel prep
• 3 hr. procedure, 500 cc blood loss
• What are his estimated intraoperative fluid requirements?
• Example (cont.)
• Fluid deficit (NPO): 1.5 ml/kg/hr x 10 hrs = 1200 ml + 1000 ml for bowel prep = 2200 ml total deficit: (Replace 1/2 first hr, 1/4 2nd hr, 1/4 3rd hour).
• Maintenance:  1.5 ml/kg/hr x 3hrs = 360mls
• Third Space Losses:  6 ml/kg/hr x 3 hrs =1440 mls
• Blood Loss:  500ml x 3 = 1500ml
• Total = 2200+360+1440+1500=5500mls
• Intravenous Fluids:
• Conventional Crystalloids
• Colloids
• Hypertonic Solutions
• Blood/blood products and blood substitutes
• Crystalloids
• Combination of water and electrolytes
  -  Balanced salt solution: electrolyte composition and osmolality similar to plasma; example: lactated Ringer’s, Plasmlyte, Normosol.
  • Hypotonic salt solution: electrolyte composition lower than that of plasma; example: D5W.
  • Hypertonic salt solution: 2.7% NaCl.
• Colloids
• Fluids containing molecules sufficiently large enough to prevent transfer across capillary membranes.
• Solutions stay in the space into which they are infused.
• Examples: hetastarch (Hespan), albumin, dextran.
• Hypertonic Solutions
• Fluids containing sodium concentrations greater than normal saline.
• Available in 1.8%, 2.7%,3%, 5%, 7.5%, 10% solutions.
• Hyperosmolarity creates a gradient that draws water out of cells; therefore, cellular dehydration is a potential problem.
• Composition
• Clinical Evaluation of Fluid Replacement
  1. Urine Output: at least 1.0 ml/kg/hr
  2. Vital Signs:  BP and HR normal (How is the patient doing?)
  3. Physical Assessment:  Skin and mucous membranes no dry; no thirst in an awake patient
  4. Invasive monitoring;  CVP or PCWP may be used as a        guide
  5. Laboratory tests:  periodic monitoring of hemoglobin and hematocrit
• Summary
• Fluid therapy is critically important during the perioperative period.
• The most important goal is to maintain hemodynamic stability and protect vital organs from hypoperfusion (heart, liver, brain, kidneys).
• All sources of fluid losses must be accounted for.
• Good fluid management goes a long way toward preventing problems.
• Transfusion Therapy
  -  60% of transfusions occur perioperatively.
  -  responsibility of transfusing perioperatively is with the anesthesiologist.
• When is Transfusion Necessary?
• “Transfusion Trigger”:Hgb level at which transfusion should be given.
  -  Varies with patients and procedures
• Tolerance of acute anemia depends on:
  -  Maintenance of intravascular volume
  -  Ability to increase cardiac output
  -  Increases in 2,3-DPG to deliver more of the carried oxygen to tissues
• Oxygen Delivery
• Oxygen Delivery (DO2) is the oxygen that is delivered to the tissues
      DO2= COP x CaO2
• Cardiac Output (CO) = HR x SV
• Oxygen Content (CaO2):
  -  (Hgb x 1.39)O2 saturation + PaO2(0.003)
  -  Hgb is the main determinant of oxygen content in the blood
• Oxygen Delivery (cont.)
• Therefore: DO2 = HR x SV x CaO2
• If HR or SV are unable to compensate, Hgb is the major deterimant factor in O2 delivery
• Healthy patients have excellent compensatory mechanisms and can tolerate Hgb levels of 7 gm/dL.
• Compromised patients may require Hgb levels above 10 gm/dL.
• Blood Groups
                                            Antigen on         Plasma                                 Incidence
  Blood Group        erythrocyte     Antibodies         White   African-
                                                                                                                  Americans
  A                                        A                          Anti-B                 40%              27%
  B                                        B                          Anti-A                 11          20
  AB                       AB                       None                  4            4
  O                                       None                  Anti-A                 45          49
                                                                        Anti-B                                            
  Rh                                     Rh                                                   42          17
• Cross Match
• Major:
  -  Donor’s erythrocytes incubated with recipients plasma
• Minor:
  -  Donor’s plasma incubated with recipients erythrocytes
• Agglutination:
  -  Occurs if either is incompatible
• Type Specific:
  -  Only ABO-Rh determined; chance of hemolytic reaction is 1:1000 with TS blood
• Type and Screen
• Donated blood that has been tested for ABO/Rh antigens and screened for common antibodies (not mixed with recipient blood).
  -  Used when usage of blood is unlikely, but needs to be available (hysterectomy).
  -  Allows blood to available for other patients.
  -  Chance of hemolytic reaction: 1:10,000.
• Component Therapy
• A unit of whole blood is divided into components; Allows prolonged storage and specific treatment of underlying problem with increased efficiency:
  • packed red blood cells (pRBC’s)
  • platelet concentrate
  • fresh frozen plasma (contains all clotting factors)
  • cryoprecipitate (contains factors VIII and fibrinogen; used in Von Willebrand’s disease)
  • albumin
  • plasma protein fraction
  • leukocyte poor blood
  • factor VIII
  • antibody concentrates
• Packed Red Blood Cells
• 1 unit = 250 ml.Hct. = 70-80%.
• 1 unit pRBC’s raises Hgb 1 gm/dL.
• Mixed with saline:LR has Calcium which may cause clotting if mixed with pRBC’s.
• Platelet Concentrate
• Treatment of thrombocytopenia
• Intraoperatively used if platlet count drops below 50,000 cells-mm3 (lab analysis).
• 1 unit of platelets increases platelet count 5000-10000 cells-mm3.
• Risks:
  -  Sensitization due to HLA on platelets
  -  Viral transmission
• Fresh Frozen Plasma
• Plasma from whole blood frozen within 6 hours of collection.
  • Contains coagulation factors except platelets
  • Used for treatment of isolated factor deficiences, reversal of Coumadin effect, TTP, etc.
  • Used when PT and PTT are >1.5 normal
• Risks:
  • Viral transmission
  • Allergy
• Complications of Blood Therapy
• Transfusion Reactions:
  -  Febrile; most common, usually controlled by slowing infusion and giving antipyretics
  -  Allergic; increased body temp., pruritis, urticaria.  Rx: antihistamine,discontinuation.  Examination of plasma and urine for free hemoglobin helps rule out hemolytic reactions.
• Complications of Blood Therapy (cont.)
•  Hemolytic:
  • Wrong blood type administered (oops).
  • Activation of complement system leads to intravascular hemolysis, spontaneous hemorrhage.
  • Signs: hypotension,fever, chills, dyspnea, skin flushing, substernal pain. Signs are easily masked by general anesthesia.
  • Free Hgb in plasma or urine
  • Acute renal failure
  • Disseminated Intravascular Coagulation (DIC)
• Complications (cont.)
• Transmission of Viral Diseases:
  • Hepatitis C; 1:30,000 per unit
  • Hepatitis B; 1:200,000 per unit
  • HIV;1:450,000-1:600,000 per unit
  • 22 day window for HIV infection and test detection
  • CMV may be the most common agent transmitted, but only effects immuno-compromised patients
  • Parasitic and bacterial transmission very low
• Other Complications
  • Decreased 2,3-DPG with storage: ? Significance
  • Citrate: metabolism to bicarbonate; Calcium binding
  • Microaggregates (platelets, leukocytes): micropore filters controversial
  • Hypothermia: warmers used to prevent
  • Coagulation disorders: massive transfusion (>10 units) may lead to dilution of platelets and factor V and VIII.
  • DIC: uncontrolled activation of coagulation system
• Treatment of Acute Hemolytic Reactions
• Immediate discontinuation of blood products and send blood bags to lab.
• Maintenance of urine output with crystalloid infusions
• Administration of mannitol or Furosemide for diuretic effect
• Autologous Blood
• Pre-donation of patient’s own blood prior to elective surgery
• 1 unit donated every 4 days (up to 3 units)
• Last unit donated at least 72 hrs prior to surgery
• Reduces chance of hemolytic reactions and transmission of blood-bourne diseases
• Not desirable for compromised patients
• Administering Blood Products
  • Consent necessary for elective transfusion
  • Unit is checked by 2 people for Unit #, patient ID, expiration date, physical appearance.
  • pRBC’s are mixed with saline solution (not LR)
  • Products are warmed mechanically and given slowly if condition permits
  • Close observation of patient for signs of complications
  • If complications suspected, infusion discontinued, blood bank notified, proper steps taken.
• Alternatives to Blood Products
• Autotransfusion
• Blood substitutes
• Autotransfusion
• Commonly known as “Cell-saver”
• Allows collection of blood during surgery for re-administration
• RBC’s centrifuged from plasma
• Effective when > 1000ml are collected
• Blood Substitutes
  • Experimental oxygen-carrying solutions: developed to decrease dependence on human blood products
  • Military battlefield usage initial goal
  • Multiple approaches:
    • Outdated human Hgb reconstituted in solution
    • Genetically engineered/bovine Hgb in solution
    • Liposome-encapsulated Hgb
    • Perflurocarbons
• Blood Substitutes (cont.)
• Potential Advantages:
  • No cross-match requirements
  • Long-term shelf storage
  • No blood-bourne transmission
  • Rapid restoration of oxygen delivery in traumatized patients
  • Easy access to product (available on ambulances, field hospitals, hospital ships)
• Blood Substitutes (cont.)
• Potential Disadvantages:
  -  Undesirable hemodynamic effects:
  • Mean arterial pressure and pulmonary artery pressure increases
• Short half-life in bloodstream (24 hrs)
• Still in clinical trials, unproven efficacy
• High cost
• Transfusion Therapy Summary
• Decision to transfuse involves many factors
• Availability of component factors allows treatment of specific deficiency
• Risks of transfusion must be understood and explained to patients
• Vigilance necessary when transfusing any blood product