S4C34 - Hemodynamic Monitoring

Question 1

MAP equation

Answer 1

MAP = diastolic BP + 1/3 of pulse pressure

Question 2

Estimates of systolic BP

Answer 2

• radial = 80 systolic
• femoral = 70 systolic
• carotid = 60 systolic

Question 3

In hypotension, Bp cuffs can underestimate systolic BP by..

Answer 3

> 30mmHg

Question 4

Advantages of Arterial LInes

Answer 4

• measure MAP, pulse pressure, CO and repeated blood sampling
• possible sites: radial, femoral, axillary , brachial, dorsalis pedis, ulnar, tibial psoterialis, temporal
• femoral is more accurate than radial, risk of infxn and limb ischemia the same
• useful for differentiating cardiac tamponade from respiration-induced changes in systolic pressure (in tamponade the pulse pressure reduces but diastolic remains constant, in respiration the systolic and diastolic reduce equally so that pulse pressure is constant)
• may need to flush system to remove air bubbles as these cause inaccurate BP measures

Question 5

Optimal BP

Answer 5

-organ perfusion becomes compromised at MAP 65mmHg

Question 6

CVP - central venous pressure

Answer 6

• CVP is the back pressure to systemic venous return
• a high value indicates large volumes returning to the herat from the systemic circulation
• factors affecting CVP: cetnral venous blood volume (venous return, CO, total blood volume), compliance of central compartment (heart/pericardial dz, tamponade), tricuspid valve dz, dysrhythmia, intrathoracic pressure (PEEP, tension pneumo)
• how to place: catheter inserted in IJ or SC vein proximal to R atrium with tip sitting in the SVC
• indications: pressors, fluid resusc, measure central venous oxygenation (ScvO2)
• how to measure: base of c-wave as this is the final pressure in the ventricle just before contraction which reflects preload, measure it at the end of expiration

Question 7

JVP

Answer 7

• estimates the CVP
• add 5cm to the measurement of the JVP above the sternal angle… eg. 4.5+5 = 9.5cm H20
• a-wave = atrial contraction (absent in a fib), enlarged in tricuspid stenosis, pulm HTN/stensosis
• c-wave = bulging of tricuspid valve into RA
• v-wave = rise in atrial pressure from venous return through the vena cava before the tricuspid valve opens (enlarged in tricuspid regurg)
• x-descent = atrial relaxation
• y-descent = atrial emptying into the ventricle
• u/s exam: jugular venous pulse is point where vein tapers resembling the neck of a wine bottle
• if JV is larger than the adjacent common carotid with pt in semi-upright position then the CVP >10cm H2O

Question 8

Optimal CVP

Answer 8

• 0-10mmHg in normal pts
• CVP measure CVP, then give 250cc NS over 15 mins, if CVP increases by >5, this indicates volume overload and one should discontinue fluids, if CVP increases

Question 9

Cardiac output monitoring: invasive

Answer 9

• invasive means using a pulmonary artery catheter, not currently recommended
• measures CVP, pulmonary artery wedge pressure (occlusion pressure), pulmonary/systemic vascular resistances, pulm artery pressure, L+R vetnricular stroke work, RV end-systolc and end-diastolic volume, mixed/central venous O2 sat, ssytemic oxygen delivery and consumption

-complications: same as central line but also cardiac perforation, pulm artery perf, tricuspid/pulmonary valve injury, dysrrhythmia, heart block, knotting of catheter

Question 10

Cardiac output monitoring: non-invasive

Answer 10

• thoracic electrical bioimpedence: measures blood flow w/in the aorta (eg. CO), good correlation with invasive methods however affected by any movement, can use bioreactance instead as it is less sensitive to mvmt
• esophageal dopller US: measures blood flow velocity in the aorta to dtermine stroke volume and CO, doppler transducer goes via mouth to esophagus, use in postoperative period decreasres complications and hospital length of stay - good as pulm art. catheter
• transcutaneous doppler US: applied to sternal notch, fairly accurate, requires a lot of training
• pulse pressure waveform analysis: indwelling intra-arterial catheter to measure CO, uses arterial pressure waveform and arterial vascular compliacne to derive CO, not use din ED yet

Question 11

Fluid resuscitation : some tips

Answer 11

-continuing fluid resusc until the pulse pressure variation b/w inspiration and expiration decreases to

Question 12

Central Venous Oxygen Saturation

Answer 12

• ideally measured in the pulm artery as a mixed venous sample (SmvO2)
• SmvO2 requires pulm artery catheter, central venous oxygen saturation (ScvO2) requires only central line
• ScvO2 is usually 3% less than SmvO2 (lower body extracts less O2 than upper body)
• in shock states ScvO2 is usually 5-10% higher than SmvO2 due to redistribution
• low ScvO2 represents inadequate O2 delivery relative to oxygen consumption, therefore must determine if pt is hypoxic, anemic, impaired CO, increased metabolic demand from fever/pain/seizure
• normal ScvO2=70%
• high ScvO2: problem with O2 extraction- hypothermia, shock, cyanid poisoning

Question 13

Causes of elevated lactate

Answer 13

• hypoxia
• shock
• seizure
• diabetic keoacidosis
• malignancy
• thiamine deficiency
• malaria
• HOV
• CO or cyanide poisoning
• mitochondrial myopathies
• drugs: metformin, simvastatin, lactulose, antiretrovirals, niacin, isoniazid, linezolid

Question 14

Do venous and arterial lactate levels correlate well?

Answer 14

-yes, however if the clinical picture does not fit then it should be confirmed with a arterial measurement

Question 15

Lactate >4

Answer 15

• assoc wtih increased ICU rate and mortality
• if persistent for >24h it is assoc with increased mortality as high as 90%
• lactate clearance w/in 6h in severe sepsis or septic shock is assoc with increased 60d survival

Question 16

Near-infrared spectroscopy

Answer 16

-uses near-infrared light to approximate the oxygen saturation of venous blood