Unit 2 Fluids

Question 1

Surgical cardiovascular insufficiency

Answer 1

Caused by either induced loss of vasomotor tone and baroreceptor responsiveness from anesthesia

Or

Mechanical obstruction to blood flow

Surgical stress also causes a cytokine storm, combined with immune modulation alters micro circulation causing sub clinical injury

Question 2

Absolute minimum blood delivery to tissues required during surgery to avoid tissue dysoxia

Answer 2

600ml/min/m^2

Question 3

TBW Formula

Answer 3

0.6 X body weight (kg)

Question 4

Interstitial fluid is how much of ECF?

Answer 4

3/4

Question 5

Plasma is how much of ECF?

Answer 5

1/4

Question 6

How much trans cellular fluid?

Answer 6

0.5L
Fluid contained within epithelial lined spaces

Question 7

What determines Osmolarity? And what is normal level?

Answer 7

Determined by Na, K, Bun, Glucose
Normal 290 MOSM/Kg

Question 8

Osmotic pressure

Answer 8

Pressure across a semipermeable membrane exerted by a solute containing solution
Plasma osmotic pressure: 28mmHg (19mmHg protein)

Question 9

Plasma oncotic pressure

Answer 9

Proteins - only dissolved substance that doesn’t readily diffuse through capillary membranes

If they do diffuse for some reason, usually removed by lymphatic system under normal circumstances

Question 10

TBW Dynamics

Answer 10

60% of body weight, approx 40L
Men have more than women
It decereases with increasing age for everyone
It decreases in obesity (proportional to lean body mass) (inversely proportional to obesity)

Question 11

Total Body Weight by age/gender

Answer 11

Adult Male: 75ml/kg
Adult Female: 70ml/Kg
School age child: 75ml/Kg
Infant (1-12months): 80ml/Kg
Neonate: 85ml/Kg

Question 12

Pressures

Answer 12

Interstitial fluid pressure: 0mmHg
Arterial Inter capillary pressure: 35mmHg
Venous Inter capillary pressure: 15mmHg

Capillary Osmotic pressure: 25mmHg
Interstitial osmotic pressure: 4mmHg

Some movement out of capillary at arterial end and movement into capillary at venue end

Normally slight predominance of water efflux into tissues

Question 13

Preoperative considerations

Answer 13

Patients at risk of Hypovolemia
NPO and/or bowel prep
Chronic diuretic therapy
Chronic renal failure with or without dialysis
Chronic HTN (constant vasoconstriction > less intravascular volume > relative Hypovolemia with administration of anesthesia)
Trauma from blood loss
Burns from tissue loss > loss of protein and fluid
Sepsis from vasodilation
Liver failure from decreased plasma protein > intravascular hypovolemia from decreased intracapillary oncotic pressure > fluid leak out of vasculature

Question 14

Chronic gastric loss

Answer 14

Hypochloremic metabolic alkalosis

Consider 0.9% NS

Question 15

Chronic diarrhea (loosing bicarbonate)

Answer 15

Hyperchloremic metabolic acidosis
Consider LR (a bicarbonate substrate)

Question 16

Effects of anesthesia on fluid regulation

Answer 16

Anesthesia causes decreased vasomotor tone and baroreceptor responsiveness

Surgical stress > ADH release > fluid retention

Question 17

Other surgical considerations

Answer 17

Evaporative fluid loss with mechanical ventilation

Decreased atrial naturetic factor which produces Na to help retain fluids

Question 18

Clinical evaluation for preoperative hypvolemia

Answer 18

Positive tilt test:
HR ^ >20bpm and decrease of SBP >20mmHg

Oliguria
Weak peripheral pulses

Question 19

Laboratory evaluation for preoperative hypovolemia

Answer 19

BUN:CR ration > 20 indicates prerenal azotemia (hypovolemia)

Low urinary Na on UA

Minor hypovolemia: metabolic alkalosis
Major hypovolemia: metabolic acidosis

Increased hematocrit (after fluid replacement) it says the same during the acute blood loss.

Question 20

Main goal of fluid therapy??

Answer 20

provide adequate delivery of oxygen to tissues

Maintain environment necessary for proper function of cells and organ systems

Question 21

One way to reduce PNV?

Answer 21

Adequate fluid replacement

Question 22

Complications of too much fluid replacement on bowel and lungs?

Answer 22

If bowel is edematus will have slow return of bowel function
Pulmonary edema

Question 23

If you fail to give enough fluids during surgery?

Answer 23

Can have Increased release of stress hormones

Question 24

LR

Answer 24

Most commonly used in OR

Caution in metabolic/resp alkalosis
already have increased levels of bicarbonate/lactate

Caution in severe hepatic failure
impaired utilization of lactate may lead to accumulation

Caution with severe renal failure
risk of Hyperkalemia

Na content is too high and K too low for normal maintained fluid???

Question 25

Balanced salt solutions

Answer 25

LR (don’t use with blood products because it has calcium) Plasmalyte (more expensive) (does not have Ca, so it can be given with blood products) Normal Saline

Question 26

“Normal Saline”

Answer 26

When compared to plasma: lower pH, higher osmolarity, higher chloride content With excessive administration: can cause hyperchloremic metabolic acidosis can take days to resolve in pts with renal failure/insufficiency

Question 27

Hypertonic Solutions

Answer 27

Usually used to treat deficit I.e. dextrose for glucose deficiency or hypertonic saline for Na deficiency

Question 28

Hypertonic Saline Contents and Considerations

Answer 28

NaCl 513 mEq/L Osmolarity of 1025 mosm/L Risk of hypernatremia, hyperchloremia, & cellular dehydration Consider giving through a central line Gradual admin to achieve Na of 145-155 Increase no more than 10-20mEq/L in 24hrs (risk of cerebellar pontine demyelination) Uses: severe symptomatic hyponatremia fluid resuscitation increased ICP; neurosurgery

Question 29

D5W

Answer 29

Hypertonic in the bag Hypotonic in patient as glucose is rapidly metabolized, essentially resulting in free water

Question 30

Look at Nagelhout chart with fluid compositions

Answer 30

D5W 0.9% NS LR Plasmalyte D5W 1/4 NS

Question 31

Albumin

Answer 31

Human albumin that is plamapheresed, and pasteurized to decrease risk of anaphylaxis, infection, or coagulopathy (aside from hemodilution) 25% (salt poor) albumin pulls H20 intravascular lay unpredictable effects 5% albumin Used in OR hypothetically stays intravascular longer than crystaloid (16hrs) isotonic to plasma Will have opposite effect with capillary leak as it will mostly go interstitial and then pull fluid interstitial as well.

Question 32

Hetastartch

Answer 32

Dilutional effect on coagulation factors Direct inhibition of clot formation (reduced platelet aggregation) Binds Factor VIII, VWF, fibrinogen FDA black box warning, rarely used anymore Increased risk of mortality and renal failure

Question 33

Crystalloid vs colloid

Answer 33

Contraversial research In general: Start with crystalloid, hetastarch, then protein colloid

Question 34

When to use colloids?

Answer 34

Only specific patient populations

Question 35

4-2-1 Rule

Answer 35

Not evidence based, but need to know it. Based on patient weight. For the first 10Kg 4ml/Kg/hr Second 10Kg add 2ml/Kg/hr For the remainder add 1ml/Kg/hr Also account for bowel prep and NG loss bowel prep: add 1000ml to fluid plan. Typically replace upfront first 1-2 or 1-3 hrs depending on length of case

Question 36

NPO replacement

Answer 36

Number of hours NPO x hourly maintince requirement (4-2-1 rule) Replace over the first 2-3 hours of the surgery

Question 37

Types Surgical loss

Answer 37

Evaporative or third space losses (based on potential tissue trauma) minimal 0-2ml/kg/hr moderate 2-4 ml/kg/hr severe 4-8 ml/kg/hr True surgical loss replace with crystalloid on a 3:1 basis replace with colloid on a 1:1 basis

Question 38

Calculating blood loss

Answer 38

Not an exact science Saturated lap pad holds 100ml Raytek 10-20ml During the case keep track of the blood loss in canisters as well as the # of saturated sponges

Question 39

Allowable blood loss formula

Answer 39

[EBV X (HCT initial - HCT final)] / HCT initial When you hit the allowable blood loss you need to draw a hgb to evaluate blood loss/status

Question 40

Do fluid loss calculation

Answer 40

Do it and check the results

Question 41

Physiologic variable affected by fluid administration

Answer 41

Temperature: can exacerbate hypothermia and acidosis. Typically warm fluids, but especially if giving more than 2L. pH: especially NS, but LR can also lead to acidosis with large volumes RBCs: hemodilution, temp, and pH all affect RBC concentration and function. WBCs: artificial colloids and LR activate neutrophils - may be related to resuscitation injury Platlets/coagulation: hypothermia and acidosis = decreased plt function and coagulopathy

Question 42

Variables affecting decisions for fluid replacement

Answer 42

Patient Anesthetic technique Type of surgery Intraoperative course

Question 43

Special neurosurgical patient considerations

Answer 43

Never give glucose containing fluids, it will make intercranial ischemia worse

Question 44

ARDS patient special considerations

Answer 44

Fluid restriction shown to decrease morbidity complication is we still need to maintain euvolemia in order to perfuse kidneys etc.

Question 45

CHF special considerations

Answer 45

Judicious fluid management Risk of post-op third space redistribution causing increased cardiac work (diastolic HF)

Question 46

Lung resection special considerations

Answer 46

Postpneumonectomy pulmonary edema (excess fluids make this worse) Minimize fluids, use pressors if necessary Avoid blood products (inflammatory response)

Question 47

Liver failure/transplant special considerations

Answer 47

Multiple co-morbid conditions confound fluid management cerebral edema, hepatorenal syndrome, electrolyte disturbances Consider use of colloids replacement early Replace paracentesis >4L with albumin

Question 48

Burn special considerations

Answer 48

Initial replacement is formula guided. E.G parkland formula Consider albumin after the first 24 hrs

Question 49

Parkland formula

Answer 49

BSA% X WT X4 = total volume in first 24hrs Give 1/2 in the first 8 hours

Question 50

Laparoscopy special considerations

Answer 50

Transient intraoperative oliguria The gastric insufflation puts pressure on kidneys so blood flow goes down and they are not perfused, kidneys think there is not enough blood volume so they retain fluid (RAAS activation) these patients may not make urine a lot of the time, DONT USE URINE OUTPUT AS A GUIDE FOR FLUID REPLACEMENT IN LAPAROSCOPIC CASES Be careful with too much volume - post pneumoperitoneum redistribution

Question 51

Sepsis special considerations

Answer 51

Early and aggressive fluid replacement is important

Question 52

Massive trauma special considerations

Answer 52

Lethal triad of acidosis, hypothermia, and coagulopathy

Question 53

Plasmapheresis special considerations

Answer 53

Replace volume with albumin

Question 54

Liposuction

Answer 54

Tumescent technique (most common) can have large fluid shifts with > 5L of liposuction resulting in cardiopulmonary complications. Most keep track of how much is removed during these procedures.

Question 55

Renal patient special considerations

Answer 55

Tendency to have hyperchloremic metabolic acidosis can be made worse with NS admin dilution of bicarb by large volumes of buffer free solution Acidosis can contribute to decreased splanchnic blood flow Hyperchloremia may contribute to renal vascular constriction Anuric: judicious fluid management Nephrotic syndrome: albumin for fluid resucitation

Question 56

How do we know we achieved our goal?

Answer 56

Normal cardiac indicies Adequate hemoglobin Normothermia Prevention of fluid loss/excess Met unique needs of the patient Normal lab values: pH, lactate, anion gap, coagulation profile, electrolyte levels, glucose