Download Fluid therapy during anaesthesia

Fluid therapy
during anaesthesia
DR M.G. SENEKAL
DEPARTMENT OF ANAESTHESIOLOGY
3 MILITARY HOSPITAL
TEMPE
BLOEMFONTEIN
Fluid balance
 To maintain an effective circulating volume
 To preserve oxygen delivery to the tissues
 To maintain electrolyte homeostasis
On an individual patient basis
Fluid compartment physiology
Total body water (60% of total body weight)
Extracellular fluid
(20% of total body
weight)
Intravascular
fluid (5% of
total body
weight)
Red cells, white
cells and
platelets (2% of
total body
weight)
Intracellular fluid (40% of total body
weight)
Interstitial fluid (15% of total body weight)
Plasma (3% of total body
weight)
Fluid compartment physiology
Plasma:
solution in water
inorganic ions (e.g. sodium chloride)
simple molecules (e.g. urea)
larger molecules (e.g. albumin)
Capillary endothelium and blood vessel walls divide
the extracellular compartment into the intravascular
and interstitial compartments
Cell walls separate the intracellular compartment from
the extracellular compartment
Fluid compartment physiology
Water moves freely through cell and vessel walls and is
distributed throughout all the compartments
The Na⁺/K⁺/ATPase in the cell wall extrude Na⁺ and
maintains a sodium gradient across the cell
membrane
Capillary endothelium is freely permeable to small
ions such as Na⁺, but relatively impermeable to
larger molecules such as albumin
This helps to retain fluid in the plasma due to the
osmotic effect
Fluid compartment physiology
Jv α [(Pc-Pi)-σ(πc-πi)]
Jv – transcapillary fluid flux
Pc – capillary hydrostatic pressure
Pi – interstitial hydrostatic pressure
πc – intravascular oncotic pressure
πi – interstitial oncotic pressure
σ – the reflexion coefficient
Usually the net intracapillary pressures are more than
the interstitial pressures
This produces a slow flow to the interstitium
Many of the effects of different fluid solutions are
governed by their distribution within the
physiological compartments of the body
Normal fluid and electrolyte requirements
Normal fluid and electrolyte requirements
Adults lose 2.5-3 litres of water per day:
 1300-1800ml urine
 1000ml insensible loss from lungs and skin
 100ml in faeces
Normally fluid intake is orally and 200ml/day from
metabolism
Adults lose 1.5mmol/kg/day sodium ions and
1mmol/kg/day potassium ions
Assessment of hydration status and intravascular
volume
Present for surgery with conditions that result in
altered fluid balance
Decreased intake (fasting,
anorexia, altered conscious
level)
Increased losses (diarrhoea,
vomiting, bowel
preparation, burns, pyrexia)
Water
and
solute
depletion
Hydration status and intravascular volume is
determined by: history, examination, test results
and response to iv fluids
Assessment of hydration status and intravascular
volume
Dehydration:
loss of water from extracellular and
intracellular fluid
Abnormal losses are often from the gastrointestinal tract:
contains electrolytes
depletes the extracellular fluid
diarrhoea contain high [K⁺]
Pyrexia ↑ insensible losses by 20%/°C
Third space losses: from the intravascular compartment
secondary to increased capillary permeability
from the intestinal compartment
into the peritoneal compartment
into the pleural cavities
Assessment of hydration status and intravascular
volume: Physical examination
 Most reliable preoperatively
 Clinical signs of hypovolaemia more difficult to
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determine during anaesthesia due to drugs and
surgical stress
Anaesthesia and surgery affect fluid balance
General anaesthesia → vasodilatation and myocardial
suppression
Positive pressure ventilation → ↓ venous return and
cardiac output
Spinal and epidural anaesthesia → sympathetic
blockade → vasodilatation → ↓ preload and blood
pressure
Assessment of hydration status and intravascular
volume: Physical examination
Shock is defined as decreased oxygen delivery
or utilisation by tissues that may lead to
irreversible cellular damage if prolonged
Patients who present in a
state of shock require
immediate fluid therapy!
Assessment of hydration status and intravascular
volume: Physical examination
Table 1: Grades of hypovolaemic shock secondary to intravascular
volume loss
Class l
Class ll
Class lll
Class lV
Blood loss (ml)
Up to 750
750-1500
1500-2000
>2000
% blood loss
Up to 15%
15-30%
30-40%
>40%
Pulse rate (/min)
<100
>100
>120
>140
Blood pressure
Normal
Normal
Decreased
Decreased
Pulse pressure
Normal
Decreased
Decreased
Decreased
Respiratory rate
Normal
Increased
Increased
Rapid
Urine output (ml/hour)
>30
20-30
5-15
Negligible
CNS/mental state
Slight
anxiety
Mild
anxiety
Anxious,
confused
Confused,
lethargic
Assessment of hydration status and intravascular
volume: Physical examination
Table 2: Grades of dehydration, relating to the % body weight lost and
the resulting physical signs
Mild <5%
Moderate 5-10%
Severe >10%
Pulse rate
Normal
Increased
Increased
Blood pressure
Normal
Normal
Decreased
Respiratory rate Normal
Normal
Rapid
Capillary return <2 seconds
3-4 seconds
>5 seconds
Urine output
Normal
Decreased
Negligible/absent
Mucous
membranes
Moist
Dry
Parched
CNS/mental
state
Normal/restless
Drowsy
Lethargic/comatose
Assessment of hydration status and intravascular
volume: Physical examination
Assessment of hydration status and intravascular
volume: Laboratory evaluation
To evaluate intravascular volume and adequacy of
tissue perfusion:
 Serial hematocrits
 Arterial blood pH
 Urinary specific gravity or osmolality
 Urinary sodium or chloride concentration
 Serum sodium
 The serum creatinine to blood urea nitrogen (BUN) ratio
Assessment of hydration status and intravascular
volume: Hemodynamic measurements
 Central venous pressure monitoring
 Pulmonary artery pressure monitoring
 Transesophageal monitoring
Intravenous fluids
Three types of intravenous fluids:
 Crystalloids
 Colloids
 Blood products
Different fluids influences:
The magnitude and duration of intravascular volume expansion
Hemorrheology
Hemostasis
Vascular integrity
Inflammatory cell function
Intravenous fluids: Crystalloid solutions
 Inorganic ions and small organic molecules in water
 The main solute is glucose or sodium chloride
 Isotonic, hypotonic or hypertonic compared to
plasma
 Potassium, calcium or lactate may be added to more
closely replicate plasma
 Crystalloids with an ionic composition close to that
of plasma is referred to as “balanced” or
“physiological”
Intravenous fluids: Crystalloid solutions
A crystalloid with [Na⁺] similar to plasma rapidly
distribute through the extracellular space – only 2530% of 0.9% saline or Ringer’s remains in the
intravascular compartment
A crystalloid with a lower [Na⁺] than plasma distribute
throughout the total body water – less than 10% of
5% glucose or 0.18% saline with 4% glucose remains
in the intravascular compartment after the glucose
has been metabolised
Crystalloids exerts short lived haemodynamic effects
Intravenous fluids: Colloid solutions
 Suspensions of high molecular weight particles, derived
from gelatine, protein or starch in solutions of saline or
glucose
 Remain longer intravascularly and expand plasma volume
 Divided into semisynthetic colloids (gelatins, dextrans and
hydroxyethyl starches) and human plasma derivatives
(human albumin solutions and fresh frozen plasma)
 Vary in magnitude and duration of plasma volume
expansion, effects on hemorrheology and hemostasis,
interaction with endothelial and inflammatory cells,
adverse drug reactions and cost
Intravenous fluids: Colloid solutions
 Duration of plasma volume expansion is dependent on the
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rate of molecule loss from the circulation and their
metabolism – determined by molecular size and surface
charge characteristics
Reduce blood viscosity by hemodilution
Semisynthetic colloids influence plasma viscosity and red cell
aggregation
Affect hemostasis because of hemodilution of clotting factors
and because of effects on the hemostatic mechanism
The dextrans are effective antithrombotic agents
Anaphylaxis has been described
The human derived colloids is expensive and there is a risk
infection
Intravenous fluids: Blood
Transfusions
Packed red blood cells
Complications:
Haemolytic reactions
Anaphylaxis
Fever
Urticaria
Pulmonary oedema (TRALI)
Graft-versus-host disease
Purpura
Immune suppression
Infections
Coagulopathy
Citrate toxicity
Hypothermia
Acid-base balance disturbances
Hyperkalaemia
Intravenous fluids: Crystalloids versus Colloids
 Water is “pulled” along osmotic gradients
 Solute distribution determines the water content of
each compartment
 Solute distribution is determined by the properties of
the membranes separating the compartments
 Solutes that pass freely across a semipermeable
membrane do not generate any osmotic pressure
 The volume of distribution of infused fluids is
therefore dictated by their solute content
 Plasma volume expansion = Volume infused/Volume of distribution
Intravenous fluids: Crystalloids versus Colloids
 Infusion of water expand all compartments in proportion
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to their total volume
Only 7% of infused water remain in the intravascular
space
Infusion of isotonic glucose solution (5% glucose) is
rapidly equivalent to infusion of water
Infusion of isotonic crystalloid solution (0.9% saline or
Ringer’s) expand the extracellular volume
Only 20% of the infused volume remain in the
intravascular space
Infusion of an “ideal colloid”, containing large molecules
that do not escape from the circulation, will expand the
intravascular volume by 100% of the volume infused
Intravenous fluids: Crystalloids versus Colloids
 Significant plasma volume expansion requires large
volume crystalloid infusion → significant expansion of
the extracellular volume → tissue oedema → increasing
diffusion distances and compression of small vessels and
capillaries → compromised end organ perfusion and
oxygenation
 Colloid may result in less oedema and better recovery in
the postoperative period due to less tissue oedema
 Hypertonic crystalloid and colloid solutions draw tissue
fluid into the intravascular space and provide a
significant plasma volume expansion with minimal tissue
oedema
Intravenous fluids: Crystalloids versus Colloids
When prescribing fluid replacement, it
is important to identify which
compartment is depleted
Specific losses should be
replaced with the
appropriate fluid
Peri-operative fluid management
 Provision of maintenance fluids
 Replacement of pre-existing deficits
 Replacement of intra-operative losses
To maintain the circulating volume and tissue oxygen
delivery
Fluid regimes must be individualised for each patient
Fluids should be warmed to help maintain a normal
body temperature
Peri-operative fluid management: Maintenance
 Normal maintenance requirements: 1.5ml/kg/hour
 Usually 0.9% saline or Ringer’s and 5% glucose
Patients undergoing elective minor surgery often do not need
supplementary intravenous fluids
Peri-operative fluid management: Replacement
of pre-existing deficits
 Stabilise the patient before the anaesthetic is performed
 Fluid deficits, electrolyte and acid-base imbalances
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should be corrected
The fluid deficit is the maintenance requirement (x hours
since last oral intake) + preoperative external and third
space losses
Hard to measure accurately
Replacement should be based on response
10-20ml/kg fluid boluses in dehydration followed by
reassessment and further fluids guided by clinical signs
Peri-operative fluid management: Replacements
of intra-operative and postoperative losses
Maintenance of an effective intravascular
volume to maintain tissue perfusion and
cellular oxygenation
 Inaccuracy in the observation of blood and other
fluid losses
 The physiological stress response to surgery or
trauma results in water and sodium retention - more
water than sodium is retained with a risk of
hyponatraemia
Peri-operative fluid management: Replacements
of intra-operative and postoperative losses
 Postoperatively maintenance requirements,
abnormal insensible losses, visible external losses,
third space loss and concealed blood loss should be
measured or estimated.
 0.9% saline or Ringer’s because of the risk of
hyponatraemia
Peri-operative fluid management: Blood
transfusion
 Oxygen delivery is a function of haemoglobin level,
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haemoglobin oxygen saturation and cardiac output
Ensuring an adequate haemoglobin level and
intravascular volume is vital
Haematocrit or Hb may reduce after fluid replacement
Blood loss is replaced initially with 3ml of 0.9% saline or
Ringer’s per ml blood lost
Transfusion is indicated when Hb falls to 7.5g/dl in fit
patients
Patients with ischaemic heart disease may need levels of
more than 9g/dl
Peri-operative fluid management: Blood
transfusion
The volume of red cells to be transfused:
 Calculate the patient’s blood volume (patient’s weight in
kg x 65ml/kg)
 Calculate the red blood cell volume at the ideal
hematocrit (ideal hematocrit in % x patient’s blood
volume) A
 Calculate the red blood cell volume at the current
hematocrit (hematocrit in % x patient’s blood volume) B
 A – B = red cell volume to be transfused (x 1.5 if
transfusing packed red blood cells or x 3 if transfusing
whole blood)
A unit of platelets may be expected to increase the count by 5000-10000 x 10⁹/l
The initial therapeutic dose of Fresh Frozen Plasma is usually 10-15ml/kg
The end is near
How fluids should be administered/Assessment
of fluid administration
The “recipe book” approach is a continuous
predetermined rate of fluid infusion with additional
replacement of observed losses
However, different magnitudes of
surgical insult require very
different amounts of fluid therapy
How fluids should be administered/Assessment
of fluid administration
 Adverse outcomes is associated with inadequate or
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excessive fluid administration
Fluids should be titrated to physiological end-points
that can be monitored and responded to
Fluids should therefore be administered with
adequate monitoring
Avoid underuse of fluid resulting in hypovolaemia
and inadequate tissue perfusion
Avoid the administration of excess fluid with the risk
of pulmonary and peripheral oedema
How fluids should be administered/Assessment
of fluid administration
 Maintain a mean arterial blood pressure above a
level defined by an individual’s pre-operative mean
arterial blood pressure
 Variations in systolic blood pressure and pulse
pressure with positive pressure ventilation predict
circulatory responses to a fluid challenge
(A decrease in systolic pressure of >5mmHg during a positive pressure
mechanical breath is predictive of a positive response to a colloid
volume challenge)
How fluids should be administered/Assessment
of fluid administration
The response of CVP to a fluid challenge:
 A volume of colloid (200ml) is infused over 10-15min
 No change in CVP or a decrease suggests
hypovolaemia and the fluid challenge should be
repeated
(The combination of an increase in intravascular volume without a
related increase in pressure indicates that vascular compliance
has increased, suggesting a reduction in vasoconstrictor tone)
 A sustained increase of >3mmHg suggests that the
limits of intravascular compliance have been reached
and fluid challenges should be discontinued
How fluids should be administered/Assessment
of fluid administration
Physiological goals:
 Normal pulse rate (<100/min)
 Normal blood pressure (within 20% of normal)
 Urine output 0.5-1ml/kg/hour
 CVP 6-12cmH₂O
 Normal pH, PaO₂, base excess, serum lactate
 Haemoglobin >7.5g/dl in fit patients, >9g/dl in
patients with ischaemic cardiac disease
 Where advanced monitoring is used, fluids may be
targeted to maintain cardiac output
How fluids should be administered/Assessment
of fluid administration
 Knowledge of fluids should guide their
administration
 Correct dosage of fluid improves
patient outcome
 Accurate dosing of fluid in major
surgery requires monitoring of arterial
blood pressure and blood flow