Chapter 153 - Air embolism

Question 1

with venous access, what anatomic sites have increased risk of air embolism?

Answer 1

gravitationally above the heart

Question 2

what patient subset has reduced tolerance for small amounts of embolised air?

Answer 2

patients with right-to-left cardiac shunting

Question 3

what single dose of air is probably tolerated before cardiovascular collapse in the dog?

Answer 3

2ml/kg - extrapolated from pig data

Question 4

do pigs or dogs have more efficient removal of air during infusion?

Answer 4

dogs

Question 5

what gas is used for inflation for laparoscopic procedures?

Answer 5

carbon dioxide

Question 6

list 3 advantages of carbon dioxide over nitrogen if embolised?

Answer 6

1. absorbed rapidly into tissues so larger amounts needed to cause clinical problems
2. does not produce bronchoconstriction to the same degree
3. does not cause changes in pulmonary compliance in the same degree

Question 7

what is the most sensitive diagnostic modality for diagnosis of air emboli?

Answer 7

transesophageal echocardiography

Question 8

what % of patients had evidence of emboli in the R heart during laparoscopic hysterectomy in 1 human study?

Answer 8

100% (RA, RV, RV outflow tract - 37% had grade III - occupied half the structures)

Question 9

incidence of clinical problems from air embolism in human laparoscopy?

Answer 9

0.001-0.59%

Question 10

what pressure conditions are needed for air to enter the vascular bed during abdominal insufflation?

Answer 10

pressure of gas is between the intravenous pressure and that needed to cause vascular collapse

Question 11

what intraabdominal inflation pressure cut-off is recommended during laparoscopy? Why?

Question 12

what patient subset has reduced tolerance for small amounts of embolised air?

Answer 12

patients with right-to-left cardiac shunting

Question 13

what change in ETCO2 is expected with air embolism? under what circumstance may the change be in the opposite direction?

Answer 13

rapid drop in the face of constant ventilation - exception is if the embolism is comprised of CO2

Question 14

what venous air delivery rate is associated with air in the arterial system in dogs?

Answer 14

0.35ml/kg/min

Question 15

dead space ventilation is expected to increase with increasing abolition of blood flow through the lungs - how is % dead space calculated from capnography and arterial blood gas data?

Answer 15

100 x [(PaCO2-ETCO2)/PaCO2]

Question 16

what gas is used for inflation for laparoscopic procedures?

Answer 16

carbon dioxide

Question 17

list 3 advantages of carbon dioxide over nitrogen if embolised?

Answer 17

1. absorbed rapidly into tissues so larger amounts needed to cause clinical problems
2. does not produce bronchoconstriction to the same degree
3. does not cause changes in pulmonary compliance in the same degree

Question 18

what is the most sensitive diagnostic modality for diagnosis of air emboli?

Answer 18

transesophageal echocardiography

Question 19

what % of patients had evidence of emboli in the R heart during laparoscopic hysterectomy in 1 human study?

Answer 19

100% (RA, RV, RV outflow tract - 37% had grade III - occupied half the structures)

Question 20

incidence of clinical problems from air embolism in human laparoscopy?

Answer 20

0.001-0.59%

Question 21

what pressure conditions are needed for air to enter the vascular bed during abdominal insufflation?

Answer 21

pressure of gas is between the intravenous pressure and that needed to cause vascular collapse

Question 22

what intraabdominal pressure causes venous collapse?

Answer 22

> 20-30mmHg

Question 23

what intraabdominal inflation pressure cut-off is recommended during laparoscopy? Why?

Question 24

list 3 strategies that can help reduce the risk of air embolisation during surgery

Answer 24

1. minimise elevated above heart
2. fill surgical site with isotonic fluids
3. elevate CVP with PEEP/volume loading

Question 25

list some signs of air embolism in an at risk patient

Answer 25

neurologic deficits, changes in ETCO2, development of a murmur, hypotension, increased dead space ventilation on serial blood gas measurements

Question 26

what change in ETCO2 is expected with air embolism? under what circumstance may the change be in the opposite direction?

Answer 26

rapid drop in the face of constant ventilation - exception is if the embolism is comprised of CO2

Question 27

what is the name of the murmur that may be heard near the time of cardiac arrest due to air embolism?

Answer 27

mill-wheel murmur - harsh, churning, splashing & metallic

Question 28

dead space ventilation is expected to increase with increasing abolition of blood flow through the lungs - how is % dead space calculated from capnography and arterial blood gas data?

Answer 28

100 x [(PaCO2-ETCO2)/PaCO2]

Question 29

if gas entrainment is detected, what should be done immediately to prevent further entrainment?

Answer 29

remove insufflated gas from abdomen if dt laparoscopy
ligate transected vasculature
increase CVP (PEEP, volume)
position heart apex up to allow blood flow to bypass the air bubble
manual reduction if able

Question 30

if gas entrainment is detected, what changes should be made to inhaled gases?

Answer 30

100% oxygen (for hypoexmia and to provide a diffusion gradient if the embolized is not O2), d/c nitrous oxide

Question 31

what are 3 theoretic advances of hyperbaric O2 therapy for reversing gas emboli?

Answer 31

can compress bubble size (esp air emboli, less helpful with CO2)
reduces ICP
increases dissolved O2 in plasma

Question 32

if gas entrainment is detected, what IVF strategies may help?

Answer 32

hemodilution w colloids to 30% may help with neurologic recovery
don’t exceed 1/4 shock doses of crystalloids to avoid exacerbating cerebral edema

Question 33

if gas entrainment is detected and seizures occur, what AED is recommended and why?

Answer 33

barbiturates>benzos - better inhibition of catecholamines, reduced O2 consumption and reduced ICP

Question 34

if gas entrainment is detected, what IV medication may improve cerebral function and decrease infarct size?

Answer 34

lidocaine