Dr. Jeffrey Elliot Field HBSc,DDS, Diplomat of the National Dental Board of Anesthesia,Fellow of the American Dental Society of Anesthesia

 To understand and manage fluid balance for office based anesthesia.

 Accurate replacement of fluid deficits is based on an understanding of the distribution of water, sodium, and potassium.

 60% of the total body weight is water. Based on a 70 kg adult this is 42 kg  28 kg is intracellular(2/3)  14 kg is extracellular(1/3)  Intravascular volume is 5 liters and made up of plasma and red blood cell volume.  3 liters is plasma volume  2 liters is red blood cell volume

 Total body water  70 kg man has ~42 L (%60) body fluids. Distribution of fluid in the body is:  1/3 in extracellular fluid (14 L) Interstitial fluid 10L Plasma 3L  Transcellular fluid 1L Transcellular fluids include cerebrospinal fluid, synovial fluid, pleural fluid, ocular fluid, etc  2/3 in intracellular fluid Red blood cells 2L Other body cells outside the vasculature 26 L

 Fluid movement between these compartments is governed by osmotic and Starling forces

 Osmotic equilibrium at the cell membrane regulates the water balance between ECF and ICF. Osmotic forces depend on osmolality (Osmoles of solute per kilogram of solvent). Main solutes include charged (Na+, K+, Cl-, HCO3‐) and uncharged (urea, glucose) molecules.

 Starling equation illustrates movement of fluid across capillaries depending on three factors:  Hydrostatic forces that push fluid across membranes.  Oncotic pressure exerted by proteins in fluid that pulls water across membranes  Permeability of endothelium between plasma and interstitial fluid

 On the arterial side of capillary bed, intravascular fluid moves into interstitial space (higher intravascular hydrostatic force). On the venous side, fluid is reabsorbed into plasma (lower intravascular hydrostatic force).  When fluid is infused into plasma, hydrostatic forces increase and oncotic pressure decrease (dilution effect) until fluid is evenly distributed in ECF and Starling forces are in equilibrium.

 Aldosterone enhances sodium re-absorbption  ADH ( antidiuretic hormone) enhances water resorbption( a lack of ADH  diabetes insipidus see later module on diabetes).  Atrial natriuretic peptide enhances both sodium and water excretion (and increased levels are an indicator of poor left ventricular function ( leading to congestive heart failure) and an indicator of inability to get successful or sustained cardioversion when needed).

 Sodium is 140mEq/L and mostly in the extracellular fluid  Potassium is 150mEq/L and mostly in the intracellular fluid

 Daily Requirements  Water: 40 ml/kg/day (rough estimation, see 4,2 and 1 rule below for exact calculation)  Sodium ~ 100 mmol/day  Potassium ~60 mmol/day

 Intake: ~2500 ml  1500 ml – liquid intake  750 ml – food  250 ml – oxidative phosphorylation (The process by which ATP is produce in cells and of which H2O is a byproduct)  Output: ~ 2500 ml  1500 ml – urine*  100 ml – feces  900 ml – insensible loss (skin, lungs)  * Minimal volume of urine a healthy person needs to produce is 0.5 – 1 ml/kg/hr or else you have renal failure.

 In looking at fluid requirements one must make up for:  GI losses of 100 ml/day or 4.17 ml/hr.  Insensible losses ( respiratory and cutaneous) of 900 ml/day or 37.5 ml/hr.  Urine losses of 1500ml/day  Therefore total daily fluid requirements are around 2500ml/day.

 Sodium losses of 100 mEq/day.  Potassium of 60 mEq/day.  Note in the short term potassium, chloride,calcium and,magnesium do not need replacement.  Similarly in the short term glucose does not need replacement. Therefore glucose solutions are only indicated in infants( which we don’t do) and diabetics( to be discussed in a later module).

 There are several ways to calculate this.  1) For an average adult ( 70 kg) figure on 2500 ml/day or approximately 104 ml/hr.  A more sophisticated approach is to use the rule which takes into account body weight:  Give 4 ml/kg/hr for the 1 st 10kg (e.g. 40 ml/hr).  Give 2 ml/kg/hr for the next 10kg (e.g. 20 ml/hr).  Give 1 ml/kg/hr for the remaining kgs( 50 ml/hr).

 For surgical patients you must consider these additional factors in your fluid replacement calculations:  Blood loss for which you need to give 3 and some authors say 4 liters of normal saline for each liter of blood lost or 1 liter of colloid for each liter of blood loss.  Third space space losses ( water loss from intra and extracellular spaces secondary to tissue manipulation or damage).

 Calculating Blood Loss  Suction contents less irrigation fluid=blood loss  Blood contained in the gauze. Take the weight of a bloody gauze –the weight of the dry gauze or use a stock calculation for the blood contained on a saturated gauze swab if using scales to weigh gauzes are not practical.

 Calculating Blood Loss Each swab ( 10X10 Cm gauze) weighs 2.0 gms Each lap sponge weighs 36 gms Each gm of blood equals 1 ml of blood  Weigh the bloody gauzes or lap sponges  If no scale available then an approximate estimate is as follows: Soaked lap sponge =30ml of blood loss Soaked 10X10 cm gauze = 10ml of blood loss

         So we have 16 saturated 10X 10 gauzes for a total blood loss on the gauzes of 160 ml ( 10 ml per saturated 10X 10 cm gauze)  

 These are replaced based on the degree of tissue trauma/damage.  Minimal tissue damage ( dental surgery, surgeries of the extremities etc) are replaced at 4ml/kg/hr  Moderate tissue damage ( abdominal surgery) are replaced at 6ml/kg/hr  Severe tissue damage ( 3 rd degree burns) are replaced at 8 ml/kg/hr

 Remember all are patients are fasting. So you calculate their fluid requirements from the time they started fasting.  Usually midnight for all morning patients)(i.e. NPO midnight)  Replace ½ the NPO deficit in the first hr and rest in the second hr

Solution mmol/L Na+K+HC03-Cl-Ca+ Normal saline 154 Hartmans /Ringers % Dextrose 4% dextrose and 0.18% saline 30

 The choices are:  1)Crystalloids like normal saline, Hartman's/called Ringers lactate in the US) and glucose or a combination of glucose and normal saline.  2)Colloids like albumin, starches and Gelatins like gelofusin.  blood or blood products( RBC/packed cells,fresh frozen plasma, factor specific blood ).  The jury is still out as to how helpful colloids or hypertonic saline are in long term survival rates.  Blood or blood products have the real potential for cross infection and allergic reactions.  Crystalloids alone are used unless over 3.0 L of replacement fluid is needed acutely. At this point colloids are introduced.  In the office environment the only choices are crystalloids.

 So from the above we can see that for 90% of our patients normal saline is the fluid of choice.  Hartmans/Ringers could be considered if you believe there might be some minor electrolyte deficit in your patient.  Examples might be that the patient is on diuretics which can lead to low K+  The patient was not taking much orally for a day or 2 secondary to pain. As a result they may be electrolyte depleted and would benefit from the small amount of electrolytes in Hatrmans/Ringers.

 first look at blood loss based on a classification system from class I to class IV This classification system considers the volume of blood lost as a percentage each individual patients estimated blood volume.  next look at hemoglobin and platelet levels that the patient needs to be maintained at or above.( outside the scope of this presentation)  We will look at the classification system only so that you know when to transport to hospital based on blood loss.

 First thing to know is what your patients blood volume ( based on age) is.

 Premature neonates 95 ml/kg  Full term neonates 85 ml/kg  Infants-8yr olds 80 ml/kg  Adult males 75 ml/kg ( over the age of 8 yrs)  Adult Females 65 ml/kg ( over the age of 8 yrs)  So for Australian in office sedation the last 2 ( adult male and female) is all you have to know because that’s the only age groups we see.

 class one blood loss is when less than 15% of circulating blood volume is lost  resuscitate with crystalloids and colloids only  only transfuse if there was a pre-existing anemia such that the patient’s hemoglobin carrying capacity is reduced to the point that clinical signs and symptoms are evident. [e.g., dizziness, shortness of breath, new worsening angina]  class II use is when less than 30% of the circulating blood volume is lost.  resuscitate with crystalloids and colloids only

 class III is when less than 30-40% of the circulating blood volume is lost  rapid value replacement with both crystaloid and colloids is indicated.  these patients will also require transfusion in order to maintain an appropriate hemoglobin.  class IV is when of over 40% of circulating blood volume is lost  rapid fluid replacement with both crystaloid and colloids  these patients will also require transfusion in order to maintain an appropriate hemoglobin level.

 Prior to the start of case calculate the EBV and what volumes of blood loss represent class I-IV blood loss. From this you will know when you are reaching the threshold values for the use of colloid and the need for transfusion and transfer.

 clear fluids may be taken up till two hours preop.  Breast milk may be taken up until four hours preop  a light meal( toast and clear fluids), infant formula and other milk or milk products require a fasting period of six hours preop.  Milk is considered a solid because when mixed with gastric juices if thickens and congeals into a solid.  Solids require 8 or more hours of fasting

 Note in certain patients these times must be increased As certain metabolic diseases, medications will cause delayed gastric emptying.  it should be noted that the delayed gastric emptying refers to solids and does not apply to clear liquids.

 the conditions, and medications associated with delayed gastric emptying are as follows:  Diabetics secondary to gastroparesis  Patients with GER  Obesity secondary to both gastroparesis and GER  opioid use  in all these cases it is possible that greater than eight hours of fasting is required.

 conditions which will decrease gastric motility and therefore gastric emtying are as follows:  head injury  pyloric stenosis  patients at risk of regurgitation are as follows:  pregnant patients  obese patients  in all these cases it is possible that greater than eight hours of fasting is required and all of these patients should have rapid sequence inductions performed.( see discussion on airway management later)

 Take into account all of the following  GI + insensible losses ( 50 ml/day for 70 kg adult)  Maintenance requirements ( rule)  NPO deficit  Acute Blood loss  Third space losses

 76 kg male having wisdom teeth removed  Fasting from midnight  Appoint at 10 am  HOW MUCH FLUID dose he need by 1100 am

 76 kg  4=40ml  2=20ml  1=56 ml  Total maintenance=116ml/hr  NPO deficit = 1200am till 1100 am or 11 hrs at 116/hr=1276 ml  Third space loss 304/hr  Total fluid required by 11 am is 2130 ml of NS

 At 1030 am he looses 200 ml of blood  How much and what type of fluid does he need by 1100 am?

 76 kg  4=40ml  2=20ml  1=56 ml  Total maintenance=116ml/hr  NPO deficit = 1200am till 1100 am or 11 hrs at 116/hr=1276 ml  3 rd space loss of 304/hr  Replace blood loss 3 to one so ml  Total fluid required by 1100 am is ml  Options are:  Give NS( ½ of required fluid) in the first hour and 1/2of normal saline in the second hour  Give NS( ½ of required fluid) in the first hour and 1/2 of hartmans in the second hour  Give hartmans( ½ of required fluid) in the first hour and hartmans ( ½ of required fluid) in the second hour  Since he is under the three liters no colloid will be required

 Thank you for your commitment to continuing education.