FLUID MANAGEMENT AND ADMINISTRATION Flashcards
how much total body water is there in an a 70kg adult?
60% water (600ml/kg) = 42L in 70kg pt
how much total body water is intracellular vs extracellular?
2/3 of total body water is intracellular = 28L
1/3 of total body water is extracellular = 14L
OR 2:1 extra- to intra-cellular ratio
roughly how much of extracellular fluid is in plasma? in interstitial fluid?
plasma = 2.5L
interstitial fluid = 9L
OR roughly 1:4 plasma to interstitial fluid ratio
what is the ratio of plasma to blood volume?
1:2
plasma = 2.5L
total blood volume = 4-5L
describe the filtration system in capillaries in terms of hydrostatic and oncotic (colloid osmotic) pressures
net pressure = hydrostatic pressure – colloid osmotic pressure
- hydrostatic pressure (Pcap) forces fluid out of the capillary
- colloid osmotic pressure (π) of proteins within the capillary pulls fluid into the capillary
- as long as Pcap > π, net filtration out of the capillary occurs. when π > Pcap, net absorption occurs.
what is the net flow of fluid out of the capillaries per day?
net flow out = 2L/day
from what compartments are oncotic and hydrostatic pressures generated?
blood and interstitial fluid both contribute to hydrostatic and oncotic pressures, but inversely affect filtration.
* blood hydrostatic pressure induces filtration, while interstitial hydrostatic pressure induces absorption
what is the potential impact of preoperative fasting to perioperative fluid balance?
continued insensible and urinary losses causing hypovolemia
how long should children remain NPO before surgery?
3-4hr
what is the potential impact of vasodilation from general/regional anesthestic to perioperative fluid balance?
venodilation causing decreased preload
what is the potential impact of insensible losses from intraoperative surgical exposure to perioperative fluid balance?
hypovolemia
what is the potential impact of fluid shift from surgical trauma and inflammation to perioperative fluid balance?
can lead to third space fluid accumulation and/or increased interstitial fluid volume
what is the potential impact of blood loss to perioperative fluid balance?
reduced blood volume, decreased interstitial volume
what is the goal of perioperative fluid management?
to provide appropriate amount of parenteral fluid to maintain 1) intravascular volume and cardiac preload, 2) oxygen-carrying capacity, 3) coagulation status, 4) acid-base homeostasis, and 4) electrolyte balance
what is the basic approach to fluid management?
MDLEANS*
- provide MAINTENANCE fluid (type and rate)
- replace fluid DEFICITS
- monitor and replacing ongoing LOSSES
- consider ELECTROLYTES
- consider ACID-BASE status
- NUTRITIONAL needs
- SPECIAL patient or procedure considerations
how do the Na and Cl concentrations and pH of 0.9% NaCl compare to plasma?
plasma – Na: 140 Cl: 103 pH: 7.4
0.9% NaCl – Na: 154 Cl: 154 pH: 5.7
if given over long periods of time, will cause the plasma to become acidic => metabolic acidosis
how do the Na and Cl concentrations and pH of LR compare to plasma?
plasma – Na: 140 Cl: 103 pH: 7.4
LR – Na: 130 Cl: 109 pH: 6.4
why is LR the more preferred fluid for fluid management?
- NaCl concentrations closer to that of plasma
- LR is the only fluid with Ca (3 vs. 5 in plasma)
- contains lactate as a buffer; turned to bicarbonate in the liver, which is the natural buffer in plasma
- pH of lactated ringers closer to that of plasma; will not induce metabolic acidosis
what are the pros and cons of using plasmalyte or normosol
most physiologic; can mix with blood products (no Ca++)
>2x cost of LR or NS
what are the pros and cons of using LR?
closer to physiologic than NS (good choice for most patients), but because it contains Ca++, cannot be mixed with blood products
cannot be used in patients with serious lactic acidosis or live impairment
what are the pros and cons of using NS 0.9%?
good for neurosurgery/ICP, blood products, hypercalcemia, hypochloremia, hyponatremia; keep fluid normovolemic outside of vessels – prevents edema with fluid
high Na and Cl – at large volumes can cause acidosis
what is the best fluid to administer for cerebral edema?
hypertonic solutions – hypertonic saline (3%-23%)
* must use central line and pump
what are two ways to estimate maintenance rate?
2ml/kg/hr (acceptable for adults)
4:2:1 rule (use for pediatrics)
describe the 4:2:1 rule for maintenance fluid rate?
4ml/kg/hr for the FIRST 10kg
+ 2ml/kg/hr for the SECOND 10kg
+ 1ml/kg/hr for EACH ADDITIONAL kg
what are the two major sources of fluid deficit?
- fasting, prolonged NPO
2. other preoperative losses (bleeding, emesis, diarrhea, bowel prep
define blood loss in terms of hemorrhage class I-IV as well as CV response
- class I – 40% (>2L) blood loss – critical HR and BP
how is fasting fluid deficit estimated?
multiply maintenance fluid rate x NPO time
how is bowel prep fluid deficit estimated
500-1500ml
what is the typical approach for correcting fluid deficit?
correct 50% in first hour; correct remaining 50% over next two hours (3hr total)
which fluid type is more effective in replacing intravascular losses?
colloids
which fluid type increases the risk of tissue edema, airway edema and bowel edema?
crystalloids – requires more total fluid correct deficits
what is the rational approach to determining the fluid type for correcting fluid deficit?
- replace total body deficits with crystalloid
* replace intravascular deficits with colloid
how much blood does a fully soaked 4” surgical sponge hold? a fully soaked 12” gauze laparotomy tape?
4” surgical sponge = 10ml
12” gauze laparotomy tape = 100-150ml
what is the replacement ratio of crystalloid:blood loss? colloid:blood loss? blood products:blood loss?
crystalloid – 3:1
colloid – 1:1
blood products –1:1
what is the protocol for administering blood products for blood loss replacement?
- PRBC when transfusion threshold reached
- FFP if giving ≥ 4u PRBC (plus labs)
- platelets if giving ≥ 6u PRBC (plus labs)
- cryoprecipitate based on coats (fibrinogen
what is meant by third-spacing?
fluids shifting from intravascular space to interstitial space, causing edema
how much replacement is typically necessary for evaporation/insensible losses?
- 5-1ml/kg/hr
* increases with increasing temperature
define ascites
accumulation of fluid in the peritoneal cavity, causing abdominal swelling
how is ascites fluid loss managed?
replace with 25% albumin; 5-8g/L over 5L
how is excessive urine output (i.e., inadvertent mannitol administration) managed?
monitor for hypovolemia; replace as needed.
what are the three primary ways of diagnosing hypovolemia?
BP, HR, CVP
labs
UOP
PPV, SPV, delta down, SVV
how are CVP and blood volume related?
there is no association between CVP and circulating blood volume; CVP does not predict fluid responsiveness across a wide spectrum of clinical conditions
what lab values are useful in diagnosing hypovolemia?
lactate, base deficit, hematocrit
below what UOP can you reasonably assume hypovolemia?
what are the requirements for using PPV and SPV for diagnosing hypovolemia?
- arterial line
- no sustained arrhythmia
- controlled mechanical ventilation
- 8ml/kg tidal volume
how is PPV interpreted in terms of diagnosing hypovolemia?
PPV > 10 or > 12% indicates fluid responsiveness
*
how is SPV interpreted in terms of diagnosing hypovolemia?
SPV > 7.5 or ? 10 indicates fluid responsiveness
what types of cases require fluid restriction approach?
- liver resection (low CVP) – keep dry until resection is complete
- intrathoracic surgery – keep lungs dry
- renal failure/dialysis, heart failure – avoid fluid overload
what types of cases require liberal fluid approach?
- kindey transplant (donor and recipient) – typically 3L crystalloid
- outpatient same day surgery (20/30ml/kg)
what is meant by “goal directed” fluid therapy?
use of a monitor to guide fluid administration
how is fluid responsiveness assessed by stroke volume measurements?
- fluid responsive if fluid bolus leads to > 10% increase SV
- not fluid responsive if fluid bolus does not lead to > 10% increase SV
- the increase in stroke volume decreases as fluid status is optimized
- cardiac output will fall with severe fluid overload
what is the fluid challenge for EDM fluid optimization protocol?
250mll 5% albumin over 5min
how is fluid responsiveness predicted by pulse pressure variation?
- PPV ≥ 13% predicts fluid responsiveness
- PPV 8-12% is indeterminate (some pts fluid responsive)
- PPV
what is the fluid challenge for PPV fluid optimization protocol?
250ml 5% albumin or 300-500ml LR/PLyte over 5-10min.
how should you approach fluid management for pediatrics?
- meticulous attention to detail required
- less room for error
- calculate everything to patient’s weight
- use buretrol to avoid fluid overdose
- blood products are also dosed based on weight
- neonates may require dextrose
give two criteria for selecting maintenance fluid
- 0.9% NaCl for neurosurgery patients
2. otherwise, LR or Plasmalyte for most pts
