1. Fluid therapy during anaesthesia
Dr M.G. Senekal
Department of Anaesthesiology
3 Military Hospital
Tempe
Bloemfontein

2. Fluid balance To maintain an effective circulating volume
To preserve oxygen delivery to the tissues
To maintain electrolyte homeostasis
On an individual patient basis

3. 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)
Plasma (3% of total body weight)
Interstitial fluid (15% of total body weight)
Intracellular fluid (40% of total body weight)

4. 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

5. 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

6. 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

7. Normal fluid and electrolyte requirements

8. Normal fluid and electrolyte requirements
Adults lose litres of water per day:
ml 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

9. Assessment of hydration status and intravascular volume
Present for surgery with conditions that result in altered fluid balance Hydration status and intravascular volume is determined by: history, examination, test results and response to iv fluids
Water and solute depletion
Decreased intake (fasting, anorexia, altered conscious level)
Increased losses (diarrhoea, vomiting, bowel preparation, burns, pyrexia)

10. 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

11. Assessment of hydration status and intravascular volume: Physical examination
Most reliable preoperatively
Clinical signs of hypovolaemia more difficult to 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

12. 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!

13. 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
>2000
% blood loss
Up to 15%
15-30%
30-40%
>40%
Pulse rate (/min)
<100
>100
>120
>140
Blood pressure
Normal
Decreased
Pulse pressure
Respiratory rate
Increased
Rapid
Urine output (ml/hour)
>30
20-30
5-15
Negligible
CNS/mental state
Slight anxiety
Mild anxiety
Anxious, confused
Confused, lethargic

14. 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
Blood pressure
Decreased
Respiratory rate
Rapid
Capillary return
<2 seconds
3-4 seconds
>5 seconds
Urine output
Negligible/absent
Mucous membranes
Moist
Dry
Parched
CNS/mental state
Normal/restless
Drowsy
Lethargic/comatose

15. Assessment of hydration status and intravascular volume: Physical examination

16. 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

17. Assessment of hydration status and intravascular volume: Hemodynamic measurements
Central venous pressure monitoring
Pulmonary artery pressure monitoring
Transesophageal monitoring

18. Crystalloids Colloids Blood products 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

19. 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”

20. Intravenous fluids: Crystalloid solutions
A crystalloid with [Na⁺] similar to plasma rapidly distribute through the extracellular space – only 25-30% 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

21. 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

22. Intravenous fluids: Colloid solutions
Duration of plasma volume expansion is dependent on the 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

23. 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

24. 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

25. Intravenous fluids: Crystalloids versus Colloids
Infusion of water expand all compartments in proportion 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

26. 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

27. 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

28. 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

29. 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

30. Peri-operative fluid management: Replacement of pre-existing deficits
Stabilise the patient before the anaesthetic is performed
Fluid deficits, electrolyte and acid-base imbalances 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

31. 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

32. 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

33. Peri-operative fluid management: Blood transfusion
Oxygen delivery is a function of haemoglobin level, 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

34. 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 x 10⁹/l
The initial therapeutic dose of Fresh Frozen Plasma is usually 10-15ml/kg

35. The end is near

36. 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

37. How fluids should be administered/Assessment of fluid administration
Adverse outcomes is associated with inadequate or 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

38. 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)

39. 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

40. 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

41. 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