Fontan circulation blue book article Flashcards
What’s a Fontan procedure for? Some indications? What happens to blood flow when the Fontan procedure is completed?
to palliate a congenital single functional ventricle
Most common indication= tricuspid atresia, multiple congenital cardiac defects could be offered a Fontan procedure, eg. hypo plastic left heart, double inlet LV or double outlet RV, ebstein’s anomaly
caval blood flows directly into the pulmonary artery
What are the different types of Fontan?
those performed prior to 1990s atrio-pulmonary
1990s lateral tunnel fontan
after 2000 almost all were extracardiac aka Total Cavo-pulmonary connection (TCPC)
What’s the “transpulmonary gradient” which is the driving force to maintain pulmonary blood flow?
It depends on the difference in pressure between the CVP & common atrial pressure
the Cavo-pulmonary flow is the “bottleneck” of the Fontan circulation, resulting in upstream venous congestion & downstream decreased flow
The Fontan circulation is unique in that PVR impacts preload but also afterload of the sole ventricle.
On what is the cardiac output highly dependent in Fontan patients? what ranges should these be kept at?
preload & pulmonary resistance
Keep Fontan pressure <20mmHg
Transpulmonary gradient <5mmHg
PVR <2WU/m2
for optimal circulation
what feature may pts with a lateral tunnel or extrapulmonary Fontan have to assist at times of high PVR?
a surgically-created fenestration or “pop-off”, allowing deoxygenated blood to bypass the pulmonary circulation & augment CO, which will allow blood to bypass the pulmonary circulation & increase preload & CO but the shunting of deoxygenated blood to the systemic circulation is at the expense of reducing systemic SaO2
what feature may pts with a lateral tunnel or extrapulmonary Fontan have to assist at times of high PVR?
a surgically-created fenestration or “pop-off”, allowing deoxygenated blood to bypass the pulmonary circulation & augment CO, which will allow blood to bypass the pulmonary circulation & increase preload & CO but the shunting of deoxygenated blood to the systemic circulation is at the expense of reducing systemic SaO2
By how much may the -ve intrathoracic pressure with inspiration contribute to increased systemic venous blood flow & CO?
Up to 30%
Anaesthetic considerations:
Higher perioperative risk, not only due to their complex haemodynamics & associated complications but due to potential for other significant congenital lesions/syndromes impacting management
PRE-OP:
-Assessment, particularly understand original pathology, type & timing of previous palliative formation surgery, interventions (eg. pacemaker) current Fontan complications & Rx
-functional tolerance- formally measure with cardiopulmonary testing or DASI (convert to METs)
ECG (arrhythmias poorly tolerated)
do they have a pacemaker? review it’s location, setting, dependence & response to magnet
SpO2: abnormal suggests pathology eg. raised PAP, ventricular dysfunction, requires further Ix
Hb & Fe stores, renal & hepatic function + coags. Ensure have cross-matched blood if high risk blood loss (multiple transfusion in the past may have Abs)
-consult specialists- their congenital heart disease cardiologist re: recent clinical summaries/investigations & current Rx
-multi-D discussion (eg. open vs laparoscopic)
-optimise
-medication advice (most on thromboprophylaxis, other cardiac meds likely to be continued although may consider withholding diuretics while fasting- liaise with cardiologist)
-risk stratify: MAIN ISSUE IS: ARE THEY A “WELL FONTAN” aka does their ventricle have adequate CO, or are they a “failing Fontan” with inadequate CO.
-informed consent, daylight at centre familiar with these pts, cardiac anaesthetist aware/available to assist, postop ICU
-limit fasting time (first on list) & dehydration- give IV hydration (thrombosis risk)
These pts at higher risk of: arrhythmias, heart failure increased Hb & relative Fe deficiency liver disease luminal protein loss thromboembolism common, they're often on anticoagulants & antiplatelets
expect SpO2 to be in the low 90s
INTRA-OP:
art line- radial may not be possible due to previous AV fistula or previous Blalock-Taussig shunt
Large-bore IV access- HIGH venous pressure to drive non-pulsatile flow through lungs
Need to ensure adequate venous return & preload to maintain pulmonary blood flow: replace blood & 3rd space losses in a timely manner, be aware of surgical techniques that may decrease venous return (eg. laparoscopy, thoracoscopy)
limit myocardial depressants & maintain myocardial contractility
Carefully consider placement of CVCs- the usual SVC-RA junction may be significantly altered- run risk of stenosis/clot formation
Want to maintain pulmonary blood flow: avoid hypoxia & hypercarbia & acidosis (all factors that incr PVR).
PPV: may cause haemodynamic instability (pulmonary blood flow decreased, limits CO) but avoidance of PPV must be weighed against clearance of CO2 as increased CO2 markedly increases PVR
Strategy for ventilation= avoid high peak inspiratory pressure, use low resp rates (<20/min) & short inspiratory times (exp flow near zero to limit breath stacking), avoid excessive PEEP
Arrhythmias: must be aggressively treated, arrhythmias are common in the Fontan population
POST-OP:
Aim for early extubation to limit PPV, re-establishing -ve Pip improves pulm blood flow
consider ICU
What happens to the ventricle with Fontan circulation?
Wall becomes thicker in response to reduction in preload, which reduces EDV & the diastolic impairment may reduce pulmonary blood flow & increase pulmonary artery pressure
Heart failure may occur due to pre-load limitation and increased afterload (single ventricle needs to pump against systemic & pulmonary vascular resistance), resulting in stiff, non-compliant hypertrophied ventricle with increased filling pressures & dilated atria.
What’s the usual SpO2 for Fontan pts? why?
low 90s, worsened with exercise
all have a mild degree of cyanosis- may be due to intracardiac shunting via coronary sinus blood +/- pulmonary shunting
What’s the Hb in most Fontan pts? consequences?
slightly elevated due to chronic mild hypoxia; this increases blood viscosity & may contribute to a relatively iron-deficient state
What accounts for 8% of mortality in the Fontan population?
thromboembolism
What may contribute to the high risk of thromboembolism in the Fontan population? consequences & management?
chronic low flow circulation
presence of prosthetic material
high blood viscosity
procoagulant state (altered concentration of AT, protein C&S)
chronic pulmonary embolic events may significantly increase pulmonary resistance
anticoagulation & anti platelet therapy is common in Fontan population
Is liver disease common in Fontan population? manifestations?
Yes- some extent is universal- chronic venous hypertension & low CO –> ultimately liver fibrosis
repeated ischaemic insult + chronic congestion causes fibrosis to develop to cirrhosis & clinical sequelae of portal HTN & HCC in some pts
pts may have hepatomegaly, raised liver enzymes, thrombocytopenia, synthetic dysfunction resulting in coagulopathy & hypoalbuminaemia
What 2 conditions of luminal protein loss are risk factors for late mortality in Fontan patients?
protein-losing enteropathy (via the GIT)- causes hypoalbuminaemia, decreased oncotic pressure, ascites & peripheral oedema. plastic bronchitis (bronchial loss)- proteinaceous material forms casts in bronchial tree which may worsen pulmonary HTN
