QUESTION AAA Flashcards
Descriptions of appropriate anaesthetic strategies for surgery on the descending thoracic aorta include a:a.Right‐sided double lumen endotracheal tube.
b.Left‐sided radial arterial line.
c.Left internal jugular central venous catheter.
d.Temperature probe situated within the nasopharynx.
e.Transthoracic echo probe.
C
D
a. False. A left‐sided double lumen tube is ideally used. In the absence of compression of the left main bronchus, it is generally easier to position than a right‐sided double lumen tube.
b. False. Invasive blood pressure monitoring must be inserted at a location within the right upper limb, and therefore a right‐sided radial arterial line is preferable. A left‐sided line may become useless if the aortic clamp is applied proximal to the left subclavian artery.
c. True. A left internal jugular central venous catheter is preferable. In the semi‐lateral position required for the thoraco‐laparotomy, access to lines sited in the right internal jugular vein is limited.
d. True. The temperature measured in the nasopharynx has been shown to most accurately reflect the temperature of the brain. During cooling, careful monitoring of temperature is required in order to ensure an adequate reduction in temperature for cerebral protection and to prevent overheating during re‐warming.
e. False. Transoesophageal echocardiography is performed to allow assessment of: (i) valvular and ventricular function and (ii) the position of the venous pipe of the biypass circuit. The latter is often inserted via the femoral vein.
Question2
A 58 yr old man on the cardiac ICU has undergone elective surgery to his descending thoracic aorta yesterday. He is currently lightly sedated, and you have been asked to review the patient as he has developed new weakness of both lower limbs. Urgent steps that are likely to be taken include:
Select only the statements that you believe to be true. Leave the box blank if you believe the answer to be false.
a.
Transfusion of packed red cells to target a haemoglobin concentration >10 g dl–1.
b.Drainage of cerebrospinal fluid to target an ICP of 5 mm Hg.
c.Replacement of the spinal drain.
d.Administration of a vasopressor infusion to increase MAP to target a cerebral perfusion pressure (CPP) >60 mm Hg.
e.Titration of inspired oxygen to achieve an arterial oxygenation saturation >95%.
a. False. During the routine postoperative period, ahaemoglobin concentration >10 g dl–1isroutinelymaintained.Ifthereisevidenceof anewneurologicalimpairment, then a higherhaemoglobin concentration of 120 g dl–1istargeted.
b. True.Asthereisnewneurologicalimpairment,thepatientshouldbepositionedflat.Cerebrospinal fluid should be drainedin 10‐mlaliquots orno more than 20 ml h–1to target anICP of 5 mm Hg.
c. False. The spinal drain that isin situis likely to befunctioningeffectively and so another drainshould notbe inserted. Insertion of anew spinaldrain should be considered if: (i) surgery was performed as an emergency without a spinal drain and (ii) the spinal drain has been removed after surgery. It is unlikely that the drain has been removed at this point in the postoperative period.
d. False. A cerebral perfusion pressure greater than 80 mm Hg must be targeted.
e. True. Oxygen delivery must be optimised. Arterial oxygen saturation greater than 95% is targeted. This threshold may be achieved by increasing the inspired concentration of oxygen and optimising ventilation settings.
Question3
Appropriate statements regarding the physiological changes during surgery involving left heart bypass include:
Select only the statements that you believe to be true. Leave the box blank if you believe the answer to be false.
Correct Answer!
a.Surgery with left heart bypass is associated with a greater inflammatory response than full cardiopulmonary bypass.
b.
A core temperature below 24°C is performed for neurological protection.
c.My Response » Commencement of left heart bypass may be associated with a decrease in left ventricular afterload.
d.My Response » Anticoagulation to an activated clotting time (ACT) of 200–300 s is achieved.
e.My Response » Hypertension proximal to the clamp is likely to be attenuated by increasing flow through the bypass circuit.
C
D
E
False. Left heart bypass is associated with a less inflammatory response than full cardiopulmonary bypass. For this reason, the former is a preferableapproachtosituationswherethesurgicalclamp canbe applied distal to the left subclavian.
False. Cooling to a temperature within the deep hypothermic range is notroutinely performed during left heart bypass as end organ perfusion is maintained. The brain isperfused by the remaining cardiac outputof the heart, and the abdominal viscera areperfused by the bypasscircuit.Theperfusionistandanaesthetistworkclosely together to maintain a balance between the two circulations.
True. Application of the surgical cross‐clamp would lead to a marked increase in left ventricular afterload. Before application of the cross‐clamp, left heart bypass is likely to be commenced to prevent a rapid increase in afterload.
True. During left heart bypass there is no requirement for blood to pass through an oxygenator as blood still circulates via the native pulmonary circulation. For this reason, only partial heparinisation is required with an ACT target of 200–300 s.
True. The circulation proximal to the clamp supplies the brain and is measured using an arterial line sited in the right upper limb. An increase in pressure here increases left ventricular afterload and can eventually lead to myocardial ischaemia owing to increased cardiac work. By increasing bypass flow rates, a greater proportion of blood is diverted to the lower half the body distal to the clamp, thus offloading the left side of the heart.
Question 4
Appropriate statements regarding monitoring parameters during major aortic surgery include:
Select only the statements that you believe to be true. Leave the box blank if you believe the answer to be false.
If cerebral oxygen saturation measured using near‐infrared spectroscopy decreases by >25% from baseline, then you are likely to assess the cannulation sites. Consider an increase flow rate through bypass circuit and augment further hypothermia.
My Response
Cerebrospinal fluid pressure transduced via the spinal drain is likely to be <5 mm Hg.Motor evoked potentials (MEPs) are used to ensure that function within the posterior ascending columns remains intact.If the amplitude of MEPs decreases >50%, then the MAP of >80 mm Hg should be targeted.
My Response
The spinal drain should not remain in situ for more than 72 h.
a. True. A decrease in cerebral oxygen saturation of this degree could suggest cerebral hypoperfusion. If untreated, there could be cerebral ischaemia. The surgical team should assess cannulation sites to ensure optimal positioning. The perfusionist and anaesthetist should together assess arterial blood gas results to ensure sufficient haematocrit and consider increasing hypothermia and bypass flow rate.
b. False. During surgery, the CSF pressure should be maintained at 10–15 mm Hg.
c. False. Somatosensory evoked potentials monitor the posterior ascending sensory columns; MEPsmonitortheanteriordescendingmotorpathways.
d. True. AdecreaseinMEPamplitudeindicateshypoperfusion in the spinal cord. A MAP of at least 80 mmHg shouldbetargetedto achieve a cerebralperfusion pressure >70 mm Hg.
e. False. If there is no neurological deficitin the postoperative period, then the spinaldrain is often removed after 72 h. However, the draincanremainin situforupto 1weekifthereare concernssurroundingperfusioninspinalcord.
