Perioperative Managment and Complications, pt 2

Question 1

describe the important factors in myocardial ischemia

Answer 1

-management of oxygen supply and demand

Question 2

describe myocardial oxygen supply and demand imbalance

Answer 2

• increase in myocardial oxygen demand is of greater significance than a decrease in myocardial O2 supply
• simultaneous tachycardia and hypotension present greatest risk to pts. with a h/o IHD as it causes increased demand and decreased supply

Question 3

what populations are at risk for MI?

Answer 3

• MI within the past 6 months
• CHF
• previous h/o perioperative myocardial ischemia
• all cardiac pts. (40% ischemia postop; 60% intraop)

Question 4

what are major perioperative CV risk factors?

Answer 4

• unstable coronary syndromes: acute/recent MI, unstable angina
• decompensated heart failure
• significant dysrhythmias: high-grade AV block, symptomatic ventricular dysrhythmias in presence of heart disease; supraventricular dysrhythmias w/ uncontrolled ventricular rate
• severe valve disease

Question 5

what are intermediate perioperative CV risk factors?

Answer 5

• mild angina pectoris
• previous MI by h/o Q waves on ECG
• compensated or previous heart failure
• DM (esp. insulin dependent)
• renal insufficiency

Question 6

what are minor perioperative CV risk factors?

Answer 6

• advanced aged (> 70)
• abnormal ECG: LVH, LBBB, ST-T abnormalities
• rhythm other than sinus
• low functional capacity
• h/o stroke
• uncontrolled systemic HTN

Question 7

what contributes to myocardial ischemia?

Answer 7

• increased myocardial oxygen demand

- decreased myocardial oxygen supply

Question 8

what causes an increased myocardial O2 demand?

Answer 8

• increased HR (tachycardia)
• increased contractility
• increased LVEDV
• increased wall tension (afterload)
• SNS stimulation
• HTN
• increased preload

Question 9

what causes a decrease in myocardial O2 supply?

Answer 9

• decreased coronary blood flow (vasoconstriction, thrombosis, decreased diastolic time, decreased aortic diastolic pressure, increased ventricular end-diastolic pressure)
• decreased blood oxygen content: decrease Hct, anemia, decreased O2 sat
• tachycardia
• diastolic hypotension
• hypocapnia (coronary artery vasoconstriction)
• coronary artery spasm
• arterial hypoxemia
• shift of oxyhgb curve to the left

Question 10

describe TEE use in detecting ischemia

Answer 10

• abnormal regional wall motion via TEE is most reliable and most accepted standard for detection of intraoperative myocardial ischemia
• abnormal regional wall motion occurs prior to ECG changes

Question 11

describe PA catheters use in detecting ischemia

Answer 11

• unreliable
• acute increase in PAWP indicative of decreased LV compliance and performance
• V waves in PAWP tracing may indicate ischemia
• limited use b/c PAWP are only taken intermittently

Question 12

describe EKG ischemia detection

Answer 12

• most commonly utilized modality for detection of ischemia
• most perioperative myocardial ischemia and infarctions are subendocardial
• ST depression > 1mm or T wave inversion = subendocardial ischemia
• ST elevation indicates transmural ischemia

Question 13

what leads are best for ischemia detection?

Answer 13

• V5 is most sensitive lead for ischemia (detects 75%)

- combining V4 and V5 results in 85% detection

Question 14

what is important with leads for early detection of myocardial ischemia?

Answer 14

• proper 5 lead ECG placement

- three leads important to improve detection (Lead II, V4, V5)

Question 15

what area of the heart does Lead II detect ischemia?

Answer 15

RCA ischemia: inferior wall supplied 90% of time by RCA

Question 16

what are of the heart does Leads V4 and V5 detect ischemia?

Answer 16

LV ischemia: bulk of left ventricle is supplied by LAD

Question 17

in what ways can myocardial ischemia be prevented?

Answer 17

• minimize hypotension and HTN (maintain BP within 20% of baseline)
• continue beta blockers therapy
• avoid hyperventilation (hypocarbia may lead to coronary vasoconstriction)
• minimize SNS stimulation (pain, hypercarbia, hypovolemia)
• maintain normal blood oxygen content w/ CAD pts. (monitor excessive blood loss causing dec. hgb)
• early extubation if criteria met
• avoid intraoperative hypothermia
• utilize muscle relaxants that don’t effect HR (no Pavulon)
• reversal of NMB w/ anti-muscarinic w/ less chronotropic effect (use glycopyrrolate over atropine)
• short duration direct laryngoscopy (less than 15 sec)

Question 18

what should be considered with chronic HTN pts.

Answer 18

-usually volume depleted d/t meds and their autoregulation curve is shifted to the right (used to a higher BP)

Question 19

why is early extubation better with pts. at risk for cardiac ischemia?

Answer 19

deeper extubation to prevent increase in HR and BP on emergence which can lead to increased ischemia

Question 20

why should intraop hypothermia be avoided?

Answer 20

• postop shivering can increase oxygen consumption > 600%

- maintaining normothermia has been shown to reduce perioperative ischemia and subsequent cardiac mortality

Question 21

what NMB are good when you do not want an effect on HR?

Answer 21

• vecuronium
• rocuronium
• cisatracurium

Question 22

what can be utilized to blunt the SNS response and increased HR associated with intubation?

Answer 22

• LTA: lidocaine topical anesthesia
• IV lidocaine
• fentanyl
• esmolol

Question 23

what are the effects of ketamine that should be avoided?

Answer 23

• increased HR
• increased BP
• increased myocardial O2 requirements

Question 24

how can myocardial O2 supply and demand be optimized?

Answer 24

• volatile agents
• decrease myocardial oxygen requirements
• precondition myocardium to tolerate ischemic events in presence of decreased SBP and CPP (cardioprotectant)
• decreased coronary vascular resistance w/ iso
• coronary steal (no evidence w/ iso): dilates only normal vessels, stealing blood flow from stenotic vessels
• avoid tachycardia HR > 80 (use esmolol)

Question 25

describe sympathomimetic use for ischemia

Answer 25

- treat hypotension: restores coronary perfusion pressure (CPP) - inotropic support when hemodynamically instable (ischemia reduces CO and causes hypotension) - beta adrenergic agonist * beneficial: decrease LVEDV and increase aortic diastolic pressure * harmful: increase HR and contractility, decreased diastolic time

Question 26

describe alpha agonist use for ischemia

Answer 26

alpha adrenergic agonists... - increased myocardial oxygen supply by increasing aortic diastolic pressure - detrimental effects: increased myocardial O2 demand (arterial pressure increase associated with 60% increase in myocardial O2 consumption); coronary artery vasoconstriction - alpha 2 agonists can decrease SNS outflow and decrease HR and BP (dexmetatomidine)

Question 27

describe nitrate use for ischemia

Answer 27

- nitroglycerin (NTG): utilized when ischemia by increased BP; coronary vasodilation (increases supply); decreases preload improving subendocardial blood flow - nipride: much like NTG but with afterload reduction; controversial use in myocardial ischemia (possible coronary steal)

Question 28

describe beta blocker use for ischemia

Answer 28

- mixed research regarding reduction in post of cardiac mortality - decrease myocardial demand and increase supply - decrease HR and contractility but may cause cardiac depression

Question 29

describe calcium channel blocker use for ischemia

Answer 29

- decrease myocardial O2 demand and increase supply | - shown to reduce coronary artery vasospasm

Question 30

describe phosphodiesterase inhibitor use for ischemia

Answer 30

-systemic and pulmonary vasodilation w/o increase in HR (usually get a rebound increase in HR)

Question 31

define oliguria

Answer 31

urine output less than 0.5 ml/kg/hr

Question 32

what are causes of oliguria?

Answer 32

- prerenal: decreased CO, renal perfusion, fld. volume - intrarenal: acute tubular necrosis (ATN), glomerulonephritis, toxins (all leads to improper functioning nephrons) - postrenal: obstruction, stones, prostate, neurogenic bladder, catheter obstruction

Question 33

describe management for oliguria

Answer 33

- rule out mechanical obstruction such as block F/C - restore perfusion: correct hypotension, increase CO, possible low dose DA infusion - correct fluid volume deficit: crystalloids and colloids - intraop diuretics: Lasix 2-20 mg IV, mannitol

Question 34

describe cause of pulmonary aspiration

Answer 34

- depressed/absent airway reflexes cant protect the trachea - acidic aspirate can damage alveoli in 12-18 seconds - pH 0.4 ml/kg can cause: alveolar hemorrhage, collapse, edema, increased airway resistance, hypoxia, large particles can cause obstruction, inflammatory response

Question 35

what populations are at risk for pulmonary aspiration?

Answer 35

- extreme age (decreased airway reflexes) - emergency or trauma (inadequate NPO time) - hiatal hernia, GERD (check if symptomatic) - morbid obesity - full stomach or decreased NPO time - pregnancy - DM (slowed gastric emptying) - neuromuscular diseases - GI tract diseases - altered mental status (decreased airway reflexes) - small bowel obstruction - increased pain - h/o N/V

Question 36

how can pulmonary aspiration be recognized?

Answer 36

- 90% have symptoms within 1 hour - awake: cough, cyanosis, wheezing, tachypnea, rales - anesthetized: laryngospasm, bronchospasm, wheezing, increased PIPs, decreased BP, VR, and O2 sat * CXR may detect pulmonary infiltrates (delayed 6-24 hrs) * CXR only definitive diagnosis

Question 37

how should pulmonary aspiration be managed?

Answer 37

* IV PPIs, H2 antagonists, prokinetics * po antacids, antiemetics - turn head to side to prevent aspirate from falling into trachea * RSI for pts. at risk for aspiration - immediate suction and 100% FiO2 * take control of airway w/ severe cases: tracheal intubation - administer PEEP and adequate Vt * antibiotics, steroids, bronchodilators - bronchoscopy may be indicated for removal of large particles obstructing airway