Monitoring of Respiratory Parameters, EIT

Question 1

Electrical Impedance Tomography

Answer 1

• Imaging of regional lung function – electrodes placed around thorax with current applied to two, voltage measured by others
• Calculation of impedance changes –> varying gas, fluid content in the thorax –> regional changes in ventilation distribution within lung

Question 2

Advantages of EIT

Answer 2

• Noninvasive, no radiation exposure, more dynamic than CT

Question 3

Respiratory Parameters

Answer 3

Respiratory rate widely varies, limited value as a respiratory parameter – change in breathing rate is sensitive indicator of change in underlying status of patient

Question 4

Estimation of Ventilation Vol

Answer 4

visual observation of chest, RBB or measured with ventilometry

Question 5

Normal VT

Answer 5

6-15mL/kg

Question 6

Normal minute ventilation in awake patients

Answer 6

150-250mL/min

Question 7

Ventilometry

Answer 7

measure total volume ventilation, cannot measure proportion distributed to dead space vs functional alveoli

Question 8

Physiologic Dead Space

Answer 8

(alveolar + anatomic): btw 30-50% of total VT, minute ventilation in normal patient breathing normal VT
 Remaining balance = functional alveolar ventilation
 Physiologic dead space higher with rapid, shallow breathing; lower with shallow, deep breathing

Question 9

Bohr’s Dead Space Equation

Answer 9

Vd/Vt = dead space vol/tidal vol = (PaCO2-PeCO2)/(PaCO2-PiCO2)

o Dead space (%) x measured VT or minute ventilation calculates absolute values (mL/kg) for dead space
 Vt – VD = Valv

Question 10

Effective alveolar minute ventilation

Answer 10

typically defined by PaCO2
o High measured total minute ventilation in combination with normal PaCO2 = increased alveolar dead space ventilation

Question 11

Static Compliance

Answer 11

measurements made after inspiratory pause value

Question 12

Dynamic Compliance

Answer 12

measurements made during cyclic breathing process with peak pressure, calculated value

Question 13

Compliance

Answer 13

Compliance = expired VT/change in pressure

Change in airway pressure during PPV calculated as peak or pause pressure - end expiratory pressure
SpV: change in transpulmonary pressure requires measurement of plural pressure via balloon tipped catheter placed in lower esophagus

Question 14

PPV

Answer 14

during airway pressurization some of volume that left in ventilator taken up by compression of gases within anesthetic circuit and by breathing circuit expansion
o Volume never reaches patient, but measured as part of expired tidal volume
o Many ventilators do not compensate for this effect – high VT result in erroneous assumptions about patient

Question 15

Vol of Compression/Expansion for Given Circuit Calculation

Answer 15

 Disconnect patient
 Record measured VT at same PIP observed while ventilating patient with patient port of wye piece plugged
 Subtract that volume from measured tidal volume prior to calculating compliance