INTRAVENOUS FLUID INTRAVENOUS FLUID THERAPYTHERAPY

Anaesthesiology and Intensive Care DepartmentHospital Raja Permaisuri Bainun, Ipoh

Fluid Compartment

TOTAL BODY WATER = 60% Body Weight

42L40%

Intracellular28L

20%Extracellular

14L5%

Intravascular

4.6L

15%Interstitial

9.4L

*Based on a 70kg man

Total body water may vary with age, gender and body habitus

Types of fluidCrystalloids Colloids

Hypertonic

Isotonic

Hypotonic/Isoosmolar Natural Synthetic

Gelatin Starch

eg. Hypertonic saline

eg. 0.9% Saline,Hartmann solution,Sterofundin

eg. 0.18-0.45%saline With dextrose solution, Dextrose 5%

Albumin andBlood products

eg. Gelafusin,Haemacel

eg. Haesteril,Voluven, Volulytes,Venofundin,Tetraspan,Dextran 40/70

Crystalloids Solutions with low molecular weight particles/

solutes (<30kDa) either ionic (electrolytes) or non-ionic (mannitol, glucose)

Colloid oncotic pressure is by definition zero.

Hence, passes freely across capillary membranes with distribution determined by its tonicity (mainly Na content of the fluid).

Used as either maintenance or resuscitation fluid

Isotonic crystalloids

Fluid infused distribute in the extracellular compartment (¼ intravascular and ¾ interstitial) hence requiring 3-4 times the volume to resuscitate the intravascular compartment.

Eg. Normal Saline (0.9% NaCl), Balance solution- Hartmanns, sterofundin

Isotonic crystalloidsNS due to the high chloride content has a potential to induce

hyperchloraemic acidosis when infused in large volume.

The balance solutions are mildly hypotonic but is considered as part of the isotonic family

Lactate or acetate is added to balance solution to counter the development of acidosis

Lactate – Metabolism dependent on functional capacity of kidneys and liver

Acetate – Metabolised by all tissues. May be advantageous in shock state

Isotonic crystalloids are effective as:

Maintenance fluid

Plasma expander

Hypotonic crystalliods

Containing free water rendering it hypotonic

Eg 0.45% Saline, 0.18%Saline Detrose 5%, Dextrose solutions.

Glucose substrate is rapidly metabolised leaving a hypotonic solution that freely equilibrate throughout total body water content.

Eg. 1Litre Dextrose solutions will provide 1 L free water that will equilibrate leaving only 1/12 of the infused volume in intravascular space (83.3mls)

Commonly used as part of maintenance fluid in ward or as correction for hypertonic dehydration.

Hypertonic crystalloids

Salinity ranging from 1.5 – 7.5% (480 – 2400mOsm/L)

3% saline is commonly used for correction of severe hyponatremia

7.5% saline provides rapid volume expansion by mobilising the extravascular fluid into the IV compartment in small volume resuscitation concept.

HS benefit goes beyond intravascular volume expansion.

- helps improve cardiac contractility through improvement in the myocardial oedema sustained during the shock period.

- helps restore urine output through natiuresis

Also used in traumatic brain injury for ICP reduction where it acts as an osmotic agent

Colloids Solutions with high molecular weight solutes (usually

> 30kDa) that remains in the intravascular compartment, generating an oncotic pressure, effectively giving it a longer intravascular persistence as compared to crystalloids.

The degree of volume expansion is dependent on the MW but is generally accepted as 1:1

Used for rapid volume expansion

General problems include cost, allergic reaction and coagulopathy

Albumin – Use controversial

Dextran

Risk of anaphylactoid reaction 0.275%

Affected coagulation in various ways: Reduce platelet adhesion Induce fibrinolysis Decrease fibrinogen Lower blood viscosity

Gelatins:

Haemacel (Urea-bridged), Gelafusin (Succinyllated)

Relatively low MW, hence rapidly excreted through kidneys.

Anaphylactoid reaction incidence - 0.375%

Starches – Modified glycopectin with addition of hydroxyethyl group to resist degradation by endogenous amylase.

Newer generation of starches usually has a lower MW (140kDa), degree of substitution ( 0.4/ 0.42) and C2/C6 ratio giving it a shorter t½ and less risk of accumulation, hence increasing its recommended daily volume to 50mls/kg

Much lower incidence of anaphylactoid reaction

Assessing Fluid Status•Patients more likely to have deranged fluid balance:

•Extremes of ages

•Patients with abnormal losses such as blood/ plasma loss, loss from GIT (vomiting, diarrhoea, NGT aspirate, stoma losses), diuresis and perspiration.

•Patients with reduced intake – debilitated, cachexic or comatose and GIT pathology

•Patients at risk of fluid overloading such as CCF, ESRF

•Diabetics with poor sugar control

Assessing Fluid Status

Clinical assessment:

Clinical history of poor intake or excessive fluid loss associated with patients' pathological conditions.

Physical examination will usually elicit the degree of dehydration

Degree of dehydrationDegree of dehydrationSigns Mild (5% body

weight)Moderate (10%) Severe (>15%)

Mucous membrane

Sensorium

Postural Changes in heart rate and blood

pressure

Urine Output

Pulse rate

Blood Pressure

Dry

Normal

Absent or Mild

Mildly decreased

Normal or increased

Normal

Very Dry

Lethargic

Present

Decreased

Increased

Mildly decreased

Parched

Obtunded

Marked

Markedly Decreased

Markedly increased

Decreased

Other signs to watch for: Skin turgor, Anterior fontanelle tension, pulse volume, capillary reperfusion time

Laboratory investigations:Gives added values to physical examination but it should not cause delay in much needed fluid resuscitation.

Full blood count – Hb, Hct

BUSE – Disproportionate rise in urea, deranged sodium level

ABG – Metabolic Acidosis, Lactate level

Urine – SG > 1.010 or [Na]urine < 20 mmol/l indicating water conservation

Invasive Haemodynamic Monitoring:

Central venous pressure:

Measures the right atrial pressure to imply the left ventricular filling pressure (LVEDP)Accurate at extreme of values ( <2mmHg indicates undervolume and >15mmHg overvolume in a normal heart)

Serial reading is more useful to assess adequacy of fluid therapy

CVP changes after 250mls fluid challenge

< 3mmHg 3-5mmHg > 5mmHg

Volume Status Undervolume Adequately filled Over-volume

Pulmonary artery wedge pressure:

Static measurement to imply LVEDP hence LVEDV

Serial measurement provides more useful information

Other parameters may be measured to optimise shock state resuscitation

Other useful monitoring toolsArterial blood pressure

Waveform may be analysed to give an indication of the intravascular volume status.(respiratory swing usually indicates hypovolaemia)

Pulse contour analysis relates stroke volume assessment to measurement of haemodynamic parameters

Transoesophageal doppler

ECHO and IVC USG imaging

Fluid Therapy During the Perioperative Period

Total Fluid =

Maintenance +

Deficit +

On-going loss

Maintenance Fluid

Replaces daily losses through urine, gastrointestinal tract, respiratory tract and skin.

Estimation of total maintenance by 4-2-1 rule: First 10kg: 4mls/kg/hr Second 10kg: 2mls/kg/hr Subsequent kg: 1ml/kg/hr

Maintenance requirement may need to be increased in patients with excessive GI/GU loss, fever, hypermetabolic states or tachypnoea.

Deficit

• Deficit may be estimated through clinical assessment as demonstrated earlier.

• In patients who are fasted in preparation for surgery, the deficit is calculated by the hours of fasting multiplied by the maintenance volume per hour

• Replacement of deficit may need to be guided by invasive monitoring in severely dehydrated and ill patients

On-Going Loss

Includes: blood loss drainage of ascitic or cystic fluid gastric fluid aspirated through NGT Evaporative loss through exposed surgical

field

Type of fluid given should reflect the nature of loss.

Evaporative loss may be estimated based on the degree of surgical site exposure:

Superficial 1-2mls/kg/hrModerate 3-4mls/kg/hrSevere 6-8mls/kg/hr

Invasive haemodynamic monitoring should be used in major surgery with expected massive fluid shift and blood loss.

Close monitoring and repeated assessment is required to ensure adequate intravascular volume and hence vital organs perfusion.

Postoperative fluid therapy•Oral intake should be resumed as soon as possible

•If the surgery involves gastrointestinal tract, current recommendation would still be early feeding but decision will usually be at the discretion of the operating surgical team.

•Patients who are unlikely to resume oral intake should be placed on maintenance fluid of crystalloids.