Intraoperative Management Flashcards
Hypothermia temp
<36
Hyperthermia temp
37.5 - 38.3
Causes of hypothermia
- 90% of intraoperative heat loss is transcutaneous
- OR environment (cold room, IV fluids, instruments)
- open wound
Causes of hyperthermia
- Drugs (ex. atropine)
- Blood transfusion reaction
- Infection/sepsis
- Medical disorder (ex. thyrotoxicosis)
- Malignant hyperthemia
- Over-zealous warming efforts
Impact of hypothermia
- 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
Which cardiac rhythms can cause pulseless cardiac arrest? Which are shockable and which are non-shockable?
■ shockable: ventricular fibrillation (VF) and ventricular tachycardia (VT)
■ non-shockable: asystole and pulseless electrical activity (PEA)
Key for survival in VF/VT
good early CPR and defibrillation
Key for survival in asystole/PEA
key to survival is good early CPR and exclusion of all reversible causes
Reversible causes of PEA arrest
■ 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)
Causes of sinus tachycardia
■ 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
Causes of sinus bradycardia
■ 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
Concerning types of bradycardia
2nd degree Mobitz type II and 3rd degree heart block, which can both degenerate into asystole
Causes of intraoperative shock and usual presentation
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
Causes of intraoperative hypertension
- 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
Maintenance fluids composition and calculation
• 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
What conditions cause increased requirements for maintenance fluids
fever, sweating, GI losses (vomiting, diarrhea, NG suction), adrenal insufficiency, hyperventilation, and polyuric renal disease
What conditions cause decreased requirements for maintenance fluids
anuria/oliguria, SIADH, highly humidified atmospheres, and CHF
Maintenance electrolytes required
■ Na+: 3 mEq/kg/d
■ K+: 1 mEq/kg/d
What is the breakdown of total body water in an adult approx 70 kg
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
What determines ECF volume
Total Na content
What determines ICF volume
[Na]
What are etiologies of hypovolemia due to volume contraction
■ 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
Mild dehydration percentage loss, signs and symptoms
3%
Decreased skin turgor, sunken eyes, dry mucous membranes, dry tongue, reduced sweating
Moderate dehydration percentage loss, signs and symptoms
6%
Oliguria, orthostatic hypotension, tachycardia, low volume pulse, cool extremities, reduced filling of peripheral veins and CVP, hemoconcentration, apathy
Severe dehydration percentage loss, signs and symptoms
9%
Profound oliguria or anuria and compromised CNS function with or without altered sensorium
Iv fluids improve ___ but not ___ of blood
IV fluids improve perfusion but NOT O2 carrying capacity of blood
What is a crystaolloid infusion
salt containing solutions that distribute only within ECF
Crystalloid volume replacement ratio
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
If large volumes needed what crystalloid infusions do you use and why
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
What do colloid infusions include and where do they distribute
• includes protein colloids (albumin and gelatin solutions) and non-protein colloids (dextrans and starches e.g. hydroxyethol starch [HES]) • distributes within intravascular volume
Colloid replacement ratio
• 1:1 ratio (infusion:blood loss) only in terms of replacing intravascular volume
Why are colloid fluids controversial
• 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
Colloids vs crystalloids for fluid resuscitation in critically ill patients
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.
How to calculate acceptable blood loss
• 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
Na mEq/L in ECF, RL, 0.9% NS, 0.45% NS in D5W, 2/3 D5W + 1/3 NS, plasmalyte
142
130
154
77
-
51
140
K mEq/L in ECF, RL, 0.9% NS, 0.45% NS in D5W, 2/3 D5W + 1/3 NS, plasmalyte
4
4
-
-
-
-
5
