Intraoperative Management

Question 1

Hypothermia temp

Answer 1

<36

Question 2

Hyperthermia temp

Answer 2

37.5 - 38.3

Question 3

Causes of hypothermia

Answer 3

• 90% of intraoperative heat loss is transcutaneous
• OR environment (cold room, IV fluids, instruments)
• open wound

Question 4

Causes of hyperthermia

Answer 4

• Drugs (ex. atropine)
• Blood transfusion reaction
• Infection/sepsis
• Medical disorder (ex. thyrotoxicosis)
• Malignant hyperthemia
• Over-zealous warming efforts

Question 5

Impact of hypothermia

Answer 5

• Increased risk of wound infections due to impaired immune function
• increases period of hospitalization by delaying healing
• reduces platelet function and impairs activation of coagulation cascade increasing blood loss and transfusion requirements
• triples incidence of VT and morbid cardiac events
• decreases the metabolism of anesthetic agents prolonging post-operative recovery

Question 6

Which cardiac rhythms can cause pulseless cardiac arrest? Which are shockable and which are non-shockable?

Answer 6

■ shockable: ventricular fibrillation (VF) and ventricular tachycardia (VT)

■ non-shockable: asystole and pulseless electrical activity (PEA)

Question 7

Key for survival in VF/VT

Answer 7

good early CPR and defibrillation

Question 8

Key for survival in asystole/PEA

Answer 8

key to survival is good early CPR and exclusion of all reversible causes

Question 9

Reversible causes of PEA arrest

Answer 9

■ 5 Hs: hypothermia hypovolemia, hypoxia, hydrogen ions (acidosis), hypo/hyperkalemia

■ 5 Ts: tamponade (cardiac), thrombosis (pulmonary), thrombosi (coronary), tension pneumothorax, toxins (overdose/poisoning)

■ when a patient sustains a cardiac arrest during anesthesia, it is important to remember that there are other causes on top the Hs and Ts to consider (i.e. local anesthetic systemic toxicity (LAST), excessive anesthetic dosing and others)

Question 10

Causes of sinus tachycardia

Answer 10

■ shock/hypovolemia/blood loss ■ anxiety/pain/light anesthesia ■ full bladder ■ anemia ■ febrile illness/sepsis ■ drugs (e.g. atropine, cocaine, dopamine, epinephrine, ephedrine, isoflurane, isoproterenol, pancuronium) and withdrawal ■ Addisonian crisis, hypoglycemia, transfusion reaction, malignant hyperthermia

Question 11

Causes of sinus bradycardia

Answer 11

■ increased parasympathetic tone vs. decreased sympathetic tone ■ must rule out hypoxemia ■ arrhythmias (see Cardiology and Cardiac Surgery, C16) ■ baroreceptor reflex due to increased ICP or increased BP ■ vagal reflex (oculocardiac reflex, carotid sinus reflex, airway manipulation) ■ drugs (e.g. SCh, opioids, edrophonium, neostigmine, halothane, digoxin, β-blockers) ■ high spinal/epidural anesthesia

Question 12

Concerning types of bradycardia

Answer 12

2nd degree Mobitz type II and 3rd degree heart block, which can both degenerate into asystole

Question 13

Causes of intraoperative shock and usual presentation

Answer 13

SHOCKED
Sepsis or Spinal shock
■ decreased sympathetic tone
■ hypotension without tachycardia or peripheral vasoconstriction (warm skin)

Hypovolemic/Hemorrhagic
■ most common form of shock, due to decrease in intravascular volume

Obstructive
■ obstruction of blood into or out of the heart
■ increased JVP, distended neck veins, increased systemic vascular resistance, insufficient cardiac output (CO)
■ e.g. tension pneumothorax, cardiac tamponade, pulmonary embolism (and other emboli – i.e. fat, air)

Cardiogenic
■ increased JVP, distended neck veins, increased systemic vascular resistance, decreased CO
■ e.g. myocardial dysfunction, dysrhythmias, ischemia/infarct, cardiomyopathy, acute valvular dysfunction

anaphylactiK

Extra/other
■ transfusion reaction, Addisonian crisis, thyrotoxicosis, hypothyroid, aortocaval syndrome

Drugs
■ vasodilators, high spinal anesthetic interfering with sympathetic outflow

Question 14

Causes of intraoperative hypertension

Answer 14

• inadequate anesthesia causing pain and anxiety
• pre-existing HTN, coarctation, or preeclampsia
• hypoxemia/hypercarbia
• hypervolemia
• increased intracranial pressure
• full bladder
• drugs (e.g. ephedrine, epinephrine, cocaine, phenylephrine, ketamine) and withdrawal
• allergic/anaphylactic reaction
• hypermetabolic states: malignant hyperthermia, neuroleptic malignant syndrome, serotonin syndrome, thyroid storm, pheochromocytoma

Question 15

Maintenance fluids composition and calculation

Answer 15

• average healthy adult requires approximately 2500 mL water/d
■ 200 mL/d GI losses
■ 800 mL/d insensible losses (respiration, perspiration)
■ 1500 mL/d urine (beware of renal failure)

• 4:21 rule to calculate maintenance requirements (applies to crystalloids only)
■ 4 mL/kg/h first 10 kg
■ 2 mL/kg/h second 10 kg
■ 1 mL/kg/h for remaining weight >20 kg

Question 16

What conditions cause increased requirements for maintenance fluids

Answer 16

fever, sweating, GI losses (vomiting, diarrhea, NG suction), adrenal insufficiency, hyperventilation, and polyuric renal disease

Question 17

What conditions cause decreased requirements for maintenance fluids

Answer 17

anuria/oliguria, SIADH, highly humidified atmospheres, and CHF

Question 18

Maintenance electrolytes required

Answer 18

■ Na+: 3 mEq/kg/d

■ K+: 1 mEq/kg/d

Question 19

What is the breakdown of total body water in an adult approx 70 kg

Answer 19

TBW 42 L

2/3 ICF - 28 L
1/3 ECF - 14 L

Breakdown of ECF:
3/4 Interstitial - 10.5 L
1/4 Intravascular - 3.5 L

Question 20

What determines ECF volume

Answer 20

Total Na content

Question 21

What determines ICF volume

Answer 21

[Na]

Question 22

What are etiologies of hypovolemia due to volume contraction

Answer 22

■ extra-renal Na+ loss ◆ GI: vomiting, NG suction, drainage, fistulae, diarrhea ◆ skin/resp: insensible losses (fever), sweating, burns ◆ vascular: hemorrhage ◆ renal Na+ and H2O loss ◆ diuretics ◆ osmotic diuresis ◆ hypoaldosteronism ◆ salt-wasting nephropathies ◆ renal H2O loss ◆ diabetes insipidus (central or nephrogenic) ◆ hypovolemia with normal or expanded ECF volume ◆ decreased CO ◆ redistribution – hypoalbuminemia: cirrhosis, nephrotic syndrome – capillary leakage: acute pancreatitis, rhabdomyolysis, ischemic bowel, sepsis, anaphylaxis

Question 23

Mild dehydration percentage loss, signs and symptoms

Answer 23

3%

Decreased skin turgor, sunken eyes, dry mucous membranes, dry tongue, reduced sweating

Question 24

Moderate dehydration percentage loss, signs and symptoms

Answer 24

6%

Oliguria, orthostatic hypotension, tachycardia, low volume pulse, cool extremities, reduced filling of peripheral veins and CVP, hemoconcentration, apathy

Question 25

Severe dehydration percentage loss, signs and symptoms

Answer 25

9%

Profound oliguria or anuria and compromised CNS function with or without altered sensorium

Question 26

Iv fluids improve ___ but not ___ of blood

Answer 26

IV fluids improve perfusion but NOT O2 carrying capacity of blood

Question 27

What is a crystaolloid infusion

Answer 27

salt containing solutions that distribute only within ECF

Question 28

Crystalloid volume replacement ratio

Answer 28

maintain euvolemia in patient with blood loss: 3 mL crystalloid infusion per 1 mL of blood loss for volume replacement (i.e. 3:1 replacement

Question 29

If large volumes needed what crystalloid infusions do you use and why

Answer 29

if large volumes are to be given, use balanced fluids such as Ringer’s lactate or Plasmalyte®, as too much normal saline (NS) may lead to hyperchloremic metabolic acidosis

Question 30

What do colloid infusions include and where do they distribute

Answer 30

• includes protein colloids (albumin and gelatin solutions) and non-protein colloids (dextrans and starches e.g. hydroxyethol starch [HES]) • distributes within intravascular volume

Question 31

Colloid replacement ratio

Answer 31

• 1:1 ratio (infusion:blood loss) only in terms of replacing intravascular volume

Question 32

Why are colloid fluids controversial

Answer 32

• the use of HES solutions is controversial because of recent RCTs and meta-analyses highlighting their renal (especially in septic patients) and coagulopathic side effects, as well as a lack of specific indications for their use ■ colloids are being used based on mechanistic and experimental evidence but there is a paucity of definitive studies investigating their safety and efficacy; routine use of colloids should be avoided

Question 33

Colloids vs crystalloids for fluid resuscitation in critically ill patients

Answer 33

There is no evidence that use of colloids improves survival in trauma patients, burn patients, or post-operative patients when compared to crystalloid solutions. Given the increased cost of colloids as compared to crystalloids, it is recommended that crystalloids be the fluid of choice in these patients.

Question 34

How to calculate acceptable blood loss

Answer 34

• Blood volume
term infant 80 mL/kg
adult male 70 mL/kg
adult female 60 mL/kg

• Calculate estimated blood volume
(EBV) (e.g. in a 70 kg male, approx. 70 mL/kg)
EBV = 70 kg x 70 mL/kg = 4900 mL

• Decide on a transfusion trigger, i.e. the Hb level at which you would begin transfusion, (e.g 70 g/L for a person with Hb(i) = 150 g/L)
Hb(f) = 70 g/L

• Calculate
ABL = {[Hb(Hi) – Hb(Hf)] / Hb(Hi)} x EBV

= 150 – 70 x 4900 150
= 2613 mL

• Therefore in order to keep the Hb level above 70 g/L, RBCs would have to be given after approximately 2.6 L of blood has been lost

Question 35

Na mEq/L in ECF, RL, 0.9% NS, 0.45% NS in D5W, 2/3 D5W + 1/3 NS, plasmalyte

Answer 35

142

130

154

77

-

51

140

Question 36

K mEq/L in ECF, RL, 0.9% NS, 0.45% NS in D5W, 2/3 D5W + 1/3 NS, plasmalyte

Answer 36

4

4

-

-

-

-

5