PERIOPERATIVE FLUID THERAPY

INTRODUCTION

Total Body Water (TBW) Varies with age, gender, body habitus 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 - Interstitial water: 3/4 of extracellular water - Intravascular water: 1/4 of extracellular water Water is present in plasma, interstitial and intracellular fluid volumes and passes freely between compartments, under the influence of osmotic pressure gradients. Total Body Water (TBW) in liters = Wt (Kg) x .6 (m) . 5 (f) =70 x .6 = 42 L

TBW 42 L Intracellular Fluid 2/3 of TBW 28 L Extracellular Fluid Intravascular Fluid 1/3 of ECF 5 L Interstitial Fluid 2/3 of ECF 9 L

NORMAL FLUID AND ELECTROLYTE REQUIREMENTS Average adults in temperate climates lose between 2.5 and 3 litres of water per day,(1300-1800mls urine, 1000mls insensible loss from lungs and skin, 100mls in the faeces). Normally fluid enters the body orally although around 200mls/day is produced from metabolic processes. Average adults lose about 1.5mmol/kg/day of sodium ions and 1 mmol/kg/day of potassium ions in the urine. If a patient is nil by mouth then normal daily requirements may be provided by: ◙ 1000mls Normal saline 0.9% ◙ 1500-2000mls Dextrose 5% ◙ 60 mmol KC1

AIMS OF FLUID THERAPY

Perioperative fluids are required to maintain adequate: Hydration Blood volume and oxygen delivery Renal function Electrolyte balance Splanchnic and hepatic circulation

Types Of Intravenous Fluids

IV fluids come in four forms: IV fluids are comprised of solutes dissolved in a solvent. • Crystalloids • Colloids • Blood and blood products • Oxygen-carrying solutions

Crystalloid Solutions

They are the primary fluid used for IV therapy. Crystalloids contain electrolytes (e.g. sodium, potassium, calcium, chloride) but lack the large proteins and molecules found in colloids. Crystalloids are classified according to their tonicity into: Hypertonic , Isotonic ,and Hypotonic

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Lactated Ringer’s and Normal Saline LR and NS : they contain sodium in similar concentrations as found in the plasma so they are the most common isotonic solutions used for fluid replacement because of their immediate ability to expand the volume of circulating blood. They are rapidly and evenly distributed throughout the extracellular space, with only 25-30% remaining in the intravascular compartment. So it is recommend that for every1 liter of blood lost, 3 liters of an isotonic crystalloid be administered for replacement.

5% Dextrose in water D5W : Is an isotonic carbohydrate that contains glucose as the solute. It is useful in supplying sugar, which is used by the cells to create energy. once D5W ( and other Crystalloids which contain a lower concentration of sodium than Plasma as 0.18% saline with 4% glucose) administered IV , they are distributed throughout the total body water after the glucose has been metabolised .

Colloid Solutions

They are IV fluids that contain solutes of high molecular weight particles derived from: gelatin (gelofusine, haemaccel), Protein (albumin solutions) starch (hetastarch) The high molecular weight particles are so large that they cannot pass onto the cells. Colloid solutions remain longer intravascularly and can significantly increase the intravascular volume. They should be given in a volume equivalent to the estimated blood loss also colloids have the ability to attract water from the cells into the blood vessels and this can cause cell dehydration.

Crystalloids colloids versus colloids

crystalloids colloids inexpensive and non-allergic greater expense, and allergic reactions (gelatins) not associated with transmission of infection, impairment of coagulation or cross matching. infection risk (HAS), coagulopathy (dextrans and starches), impaired cross matching (dextrans), and reduction in ionised calcium (HAS). They are more effective at replacing depleted ECF preferentially expand plasma volume rather than interstitial fluid volume Short lived haemodynamic effects Remain longer intravascularly When used for massive fluid resuscitation they invariably produce peripheral oedema and occasionally pulmonary oedema. In disease states associated with increased alveolar capillary permeability (sepsis, ARDS), infusion of colloid may aggravate pulmonary oedema. Similarly capillary leak of infused colloid in head injuries may cause increased cerebral oedema and increased intracranial pressure.

Blood and Blood Products

Oxygen delivery to the tissues is primarily a function of haemoglobin level, haemoglobin oxygen saturation and cardiac output. Ensuring an adequate haemoglobin level and intravascular volume is therefore vital for oxygen delivery. Transfusion of one unit of packed red cells (volume 300ml Hct 60-70%) will raise Hb by 1 to 1.5g/dl. blood products includes (platelets, packed red blood cells, plasma, cryoprecipitate)

Oxygen-Carrying Solutions

Synthetic fluids that carry and deliver oxygen to the cells. These fluids, remain experimental. It is hoped that oxygen-carrying solutions will be similar to crystalloid solutions in cost, storage capability, and ease of administration, and be capable of carrying oxygen, which presently can only be accomplished by blood or blood products.

ASSESSMENT OF HYDRATION STATUS AND INTRAVASCULAR VOLUME

Dehydration

reflects loss of water. This may come from extracellular fluid (ECF) and intracellular fluid (ICF) depletion. Hydration status and intravascular volume is assessed by the patient’s history, examination, test results and response to intravenous fluid administration. In perioperative care the emphasis is to use IV fluids to maintain the circulating volume and tissue oxygen delivery. The patients undergoing major surgery in a dehydrated, un-resuscitated state do worse than those who have received adequate IV fluid preoperatively.

PERIOPERATIVE FLUID MANAGEMENT

Fasting Policy

American society of Anaesthesiologists (ASA) guidelines: No solid food for 6 h preoperatively. No formula milk and non clear fluid for 4 h preoperatively. No clear fluids and breast milk for 2h preoperatively.

Perioperative fluid replacement

Perioperative fluid replacement is divided into maintenance fluids fluid deficit (pre-existing losses ) NPO and other deficits: NG suction, bowel preparation) third space losses replacement of intraoperative loss (Replacement of blood loss, and Special additional losses)

Maintenance Fluid Requirements Insensible losses such as evaporation of water from respiratory tract, sweat, feces, urinary excretion. 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

Deficits Fluid NPO deficit = number of fasting 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, colostomy output. ½ the amount given in the 1st hour ¼ in the 2nd hour ¼ in the 3rd hour

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, nephrectomy)

replacement of intraoperative loss Blood Loss : Replace 3 cc of crystalloid solution per 1 cc of blood loss When using blood products or colloids replace blood loss volume per volume Special additional losses: Ongoing fluid losses from other sites: - gastric drainage - colostomy output - diarrhea Replace volume per volume with crystalloid solutions

Example

62 y/o male, 80 kg, for hemicolectomy NPO after 2200, surgery at 0800 received bowel prep 3 hr. procedure 500 cc blood loss What are his estimated intraoperative fluid requirements?

1- maintenance fluid 4 x 10 +2 x 10 + 1 x 60 = 120 ml/hr = 360 ml/3hrs 2- deficit fluid 120 ml x 10hrs (fasting)+1000ml (bowel prep ) = 2200ml 1100 ml in the 1st hr 550 ml in the 2nd hr 550ml in the 3rd hr 3- Third Space Losses 6 ml/kg/hr x 3 hrs = 1440 mls 4- Blood Loss 500ml x 3 = 1500ml Total = 2200+360+1440+1500=5500mls crystalloid