Chapter 153 - Air embolism Flashcards
with venous access, what anatomic sites have increased risk of air embolism?
gravitationally above the heart
what patient subset has reduced tolerance for small amounts of embolised air?
patients with right-to-left cardiac shunting
what single dose of air is probably tolerated before cardiovascular collapse in the dog?
2ml/kg - extrapolated from pig data
do pigs or dogs have more efficient removal of air during infusion?
dogs
what gas is used for inflation for laparoscopic procedures?
carbon dioxide
list 3 advantages of carbon dioxide over nitrogen if embolised?
- absorbed rapidly into tissues so larger amounts needed to cause clinical problems
- does not produce bronchoconstriction to the same degree
- does not cause changes in pulmonary compliance in the same degree
what is the most sensitive diagnostic modality for diagnosis of air emboli?
transesophageal echocardiography
what % of patients had evidence of emboli in the R heart during laparoscopic hysterectomy in 1 human study?
100% (RA, RV, RV outflow tract - 37% had grade III - occupied half the structures)
incidence of clinical problems from air embolism in human laparoscopy?
0.001-0.59%
what pressure conditions are needed for air to enter the vascular bed during abdominal insufflation?
pressure of gas is between the intravenous pressure and that needed to cause vascular collapse
what intraabdominal inflation pressure cut-off is recommended during laparoscopy? Why?
what patient subset has reduced tolerance for small amounts of embolised air?
patients with right-to-left cardiac shunting
what change in ETCO2 is expected with air embolism? under what circumstance may the change be in the opposite direction?
rapid drop in the face of constant ventilation - exception is if the embolism is comprised of CO2
what venous air delivery rate is associated with air in the arterial system in dogs?
0.35ml/kg/min
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?
100 x [(PaCO2-ETCO2)/PaCO2]
what gas is used for inflation for laparoscopic procedures?
carbon dioxide
list 3 advantages of carbon dioxide over nitrogen if embolised?
- absorbed rapidly into tissues so larger amounts needed to cause clinical problems
- does not produce bronchoconstriction to the same degree
- does not cause changes in pulmonary compliance in the same degree
what is the most sensitive diagnostic modality for diagnosis of air emboli?
transesophageal echocardiography
what % of patients had evidence of emboli in the R heart during laparoscopic hysterectomy in 1 human study?
100% (RA, RV, RV outflow tract - 37% had grade III - occupied half the structures)
incidence of clinical problems from air embolism in human laparoscopy?
0.001-0.59%
what pressure conditions are needed for air to enter the vascular bed during abdominal insufflation?
pressure of gas is between the intravenous pressure and that needed to cause vascular collapse
what intraabdominal pressure causes venous collapse?
> 20-30mmHg
what intraabdominal inflation pressure cut-off is recommended during laparoscopy? Why?
list 3 strategies that can help reduce the risk of air embolisation during surgery
- minimise elevated above heart
- fill surgical site with isotonic fluids
- elevate CVP with PEEP/volume loading
list some signs of air embolism in an at risk patient
neurologic deficits, changes in ETCO2, development of a murmur, hypotension, increased dead space ventilation on serial blood gas measurements
what change in ETCO2 is expected with air embolism? under what circumstance may the change be in the opposite direction?
rapid drop in the face of constant ventilation - exception is if the embolism is comprised of CO2
what is the name of the murmur that may be heard near the time of cardiac arrest due to air embolism?
mill-wheel murmur - harsh, churning, splashing & metallic
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?
100 x [(PaCO2-ETCO2)/PaCO2]
if gas entrainment is detected, what should be done immediately to prevent further entrainment?
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
if gas entrainment is detected, what changes should be made to inhaled gases?
100% oxygen (for hypoexmia and to provide a diffusion gradient if the embolized is not O2), d/c nitrous oxide
what are 3 theoretic advances of hyperbaric O2 therapy for reversing gas emboli?
can compress bubble size (esp air emboli, less helpful with CO2)
reduces ICP
increases dissolved O2 in plasma
if gas entrainment is detected, what IVF strategies may help?
hemodilution w colloids to 30% may help with neurologic recovery
don’t exceed 1/4 shock doses of crystalloids to avoid exacerbating cerebral edema
if gas entrainment is detected and seizures occur, what AED is recommended and why?
barbiturates>benzos - better inhibition of catecholamines, reduced O2 consumption and reduced ICP
if gas entrainment is detected, what IV medication may improve cerebral function and decrease infarct size?
lidocaine
