4th year Anaesthesia MB ChB IV Fluids 4th year Anaesthesia MB ChB

The Human Body 60% total body weight (TBW) is water 40% of TBW is intracellular water 20% of TBW is extracellular water (ECF = interstitial and plasma) 5% of TBW is intravascular water i.e. ¼ of the ECF is found in the intravascular compartment as plasma

Osmols and tonicity 1 osmole = 1 mole nondissociable substance Osmolarity = osmoles per liter Osmolality = osmoles per kg Tonicity refers to effect on cell volume Normal plasma osmolarity is 280 - 290 mOsm/l

Oncotic pressure Plasma proteins remain intravascular and keep fluid within vessels Opposed by hydrostatic and interstitial oncotic pressure

Goals of perioperative fluids Maintain fluid volume and electrolytes Enable adequate renal excretion Provide energy substrates

Surgical stress response Fight or flight Circulatory changes trauma: haemorrhage, endothelial damage, tissue hypoxia, acidosis and loss of ATP Endocrine response: activation of SNS with release of adrenaline, cortisol, aldosterone and ADH Retention sodium and water Hyperglycaemia Preferential perfusion brain, heart and muscles

Types of Fluids Crystalloids - hypotonic - ± isotonic - hypertonic 5% dextrose GMS 10% dextrose Maintelyte 0.45% saline - ± isotonic Ringer’s Lactate () Plasmalyte L / B (Balsol) () 0.9% saline () - hypertonic 5% saline

Colloids - synthetic Starches: Voluven, Venofundin - blood products Gelatins: Haemacel, Gelofusin Dextrans - blood products Packed red blood cells (RBC’s) Platelets Fresh frozen plasma (FFP) Albumin (SHS: stabilised human serum)

Components Water Electrolytes - Na+, K+, Mg2+, Ca2+, Cl-, anions Glucose Proteins (synthetic and derived) Blood components

Commonly used IV fluids Na K Cl Ca / Mg Glucose (g/l) lactate bicarb Tonicity (mOsm/l) 5% dextrose 50 Hypo 253 N saline 154 Iso 308 Ringer’s Lactate 131 5.4 111 Ca = 2 29 273 Plas L 107 Mg 3

Indications for fluids Rehydration Resuscitation Replace losses Maintenance fluid balance Maintain / correct electrolytes Maintain / correct glucose

IV Fluids in theatre Rehydration Maintenance: 1 – 2 ml/kg/hour Hourly maintenance requirements x hours starved Don’t need to replace that much fluid though ... WHY? Increased requirements if high losses High temperature; nasogastric losses etc Maintenance: 1 – 2 ml/kg/hour Replacement of Ongoing Losses Clear fluids (crystalloid or colloid) Blood and blood products

How much? History Clinical Investigations Surgical losses – bleeding, exposure and “third space”

Too much! Pulmonary oedema Bowel oedema Tissue oedema Dilutional anaemia and coagulopathy

Crystalloids vs Colloids Expands intravascular space, but Need 3x volume (3:1) Physiologically similar to ECF (electrolytes) Cheap Long shelf life Easily transported + stored No anaphylaxis Colloid: No loss of oncotic pressure Volume for volume replacement (1:1) Expensive Anaphylaxis Coagulation defects Renal damage

Blood & Blood Products

Blood bank and its products Relies on donated blood Whole blood – in CPD-A Citrate, phosphate, dextrose and adenine Packed cells – in SAGM Sodium, adenine, glucose and mannitol Platelets, FFP’s, cryoprecipitate Storage and shelf life differs

Safety issues Correct labelling of blood for X-match and transfusion request Checking blood Warming blood Appropriate giving sets with FILTERS Patient monitoring STAT and uncrossed blood

Indications for blood transfusion: “transfusion triggers” GUIDELINES! consider physiology and pathophysiology of each patient as well as intended type of surgery 8 g/dl <6 – transfuse <10 g/dl ‘ischaemic cardiac & elderly’ Tolerate lower in chronic anaemia, chronic renal failure 4 ml/kg PRBC’s to increase Hb by 1 g/dl

Complications of transfusion Acute Hypothermia Electrolyte changes (esp K) Acidosis Incompatibility reactions Subacute Infections & Immunosuppression TRALI (tranfusion related acute lung injury) Alkalosis

Recognition of reaction Restless, anxious Nausea & Vomitting Pain in back, flank or praecordium Flushing, sweating, tingling, itching Abnormal bleeding Pyrexia, rigors Tachy/bradycardia, hypo/hypertension, clammy peripheries, anaemia Tachypnoea, bronchospasm Haemoglobinuria, oliguria Jaundice Coma, death

Management of transfusion reaction Stop transfusion Resuscitate – fluids, oxygen, adrenaline, antihistamines, steroids FBC, CEU, coag screen and urine Inform bloodbank ASAP Return all units of blood with blood and urine samples and reaction report form

Massive transfusion >10 units All the risks of single transfusions multiplied Hypothermia – need to warm units Decreased platelets, clotting factors Acidosis and alkalosis Hyperkalaemia and later hypokalaemia Citrate toxicity

Blood substitutes Oxygen carrying fluids Perfluorocarbons – Not currently used Haemoglobin-based Oxygen carriers e.g. Hemopure® (bovine haemoglobin)

Hemopure® Polymerised bovine haemoglobin molecules Acellular with low viscosity ‘oxygen bridge’ t1/2 life = 12 to 36 hours i.e. need daily infusions Expensive Despite being sourced from bovine blood it is apparently acceptable to most Jehovah’s Witnesses