Vascular access Flashcards
:) What’s the benefit of peritoneal vs haemodialysis?
cons/main complications?
How’s Tenckhoff inserted?
Peritoneal dialysis may be done @ home most easily so has less impact on daily living/transport issues
Requires dexterity- better for younger/able pts
may be unable to site a PD catheter if prev abdo surg (scar/adhesions)
less efficient (not suitable for severe renal disease)
high risk of peritonitis (main complication of PD) & if get peritonitis, can’t have RRT again
Generally Tenckhoff best inserted under GA (often laparoscopic technique) but can be done under LA w US guidance. Removal is usually a simple superficial dissection but may be complicated by adhesions or infection so require a mini-laparotomy.
:) What are 5 modes of vascular access for renal pts? which are permanent types of vascular access & benefits? which has better outcomes- AVF or AV graft? Among the AVFs, what are the pros/cons of each approach preferred?
- AVF (for haemodialysis; requires maturation for 4-6wks) or an
- AV graft (prosthetic graft connecting A & V, tunnelled subcut), both are permanent types of vascular access for haemodialysis patients, given the risks of indwelling lines (eg. infection, thrombosis) with vascath or permacath.
Native AVF has better long-term patency rates & reduced rates of complications (steal, thrombosis, infection, M&M) vs grafts, AV grafts are used where it’s not possible to approximate an A&V or where previous fistulas have exhausted suitable vessels)
Ideally place distally as possible to preserve more proximal sites, require a minimum 2.5mm with a tourniquet to achieve a functional mature fistula.
1st line= radiocephalic (preserves proximal sites but has lowest flows of all)- between radial artery & cephalic vein @ level of wrist.
Brachiocephalic in proximal forearm, more proximal so higher flows but increased steal effect.
Brachiobasilic transposition in upper arm (brachial artery and basilica vein) in upper arm, is more difficult to create, deeper, often requires a 2nd superficialisation procedure, highest risk of steal & other complications incl inadequate maturation, stenosis, thrombosis & alterations in cardiac output, so often used after multiple failed distal fistulas.
pt shouldn’t have vascular access or BPs on the planned fistula limb. - Tenkhoff (for peritoneal dialysis)
- permacath (tunnelled, eg. subclavian portacath inserted in IR under fluoroscopic guidance)- may be used as bridging btwn peritoneal & haemodialysis or in the event of graft failure. usually subclavian.
- vascath (temporary- can be placed for urgent dialysis eg. in ICU, seldinger insertion, used for urgent CRRT)
What’s the flow rate through an Arrow 8.5Fr sheath (“cordis”, which is 11 or 23cm)?
1000mL in 1:05
What’s the flow rate through an Arrow 8.5Fr sheath introducer line (“cordis”)? cf the RIC line (8.5Fr but 6.4cm (shorter but same width))? cf 7Fr RIC line?
1000mL in 1:05 (this one is 11 or 23cm)
1000mL in 46 seconds (1.3L/min!)
1000mL in 1 min
Which lumen is the 14g on the quad lumen CVC? Speed to infuse 1000mL fluid?
Grey. The others are 2x 16Ga & 2x 18Ga.
1000mL in approx 5mins.
How long does a 14g IVC take to infuse 1L fluid?
16g? 18g?
PRODUCT INFO:
14g 250/400
16g 30mm 150/300
18g 100/150
20g 70/100
22 35/70
24 20mL/min
1 min 30 secs. ie. approx 666mL/min
2 min 20 so approx 400mL/min
18g 4 min 23 approx 230mL/min (ie. 5 mins)
20g 6:47 so approx 140mL/min (ie. 6-7mins)
What’s normal urea?
2.5-10.7mmol/L
How many mm is an 8Fr line?
2.7
How many lumens has a vascath? approx flow rate?
2, 600mL/min (depending on the French!)
What are 3 types of AV fistulas?
radio-cephalic- 1st line, distal so preserves more proximal sites, lowest flow
brachio-cephalic- more proximal so higher flows but also increased steal effect
brachio-basilic- more difficult to create, relative inaccessibility & reduced frequency of prior access the vein may be better preserved @ formation. does have the highest risk of steal so often used after failure of multiple distal fistulas.
What are some issues with brachio-basilic AVF? or AVF in general, over time?
brachio-basilic has the highest risk of steal (ie. high flow through fistula & decreased supply to the periphery, risk ischaemia), also with the very high flow rates, risk HF with such high venous return
fistulas increase in size over time, may become aneurysmal–> cosmetic objections. Also increased blood flow which, while good for dialysis efficacy, may–> cardiac failure (incr venous return to heart). steal syndrome: diversion of arterial flow through fistula, distal limb arterial insufficiency & ischaemia may put limb @ risk & require surgical intervention.
How long do AV fistulas need to mature? and AV grafts? what are some other advantages of AV grafts?
between 1 & 4 months, usually 4-6 weeks, for vessel thickening & enlargement, allowing for the repetitive cannulation for dialysis. should be within 1cm of skin & relatively accessible/straight for ease of access. usually in non-dominant hand.
grafts: immediately (the can be used on the day). along with short maturation time, grafts are also easier to cannulate, have large surface area
What are the problems with AV grafts vs fistulas?
inferior long-term potency; AV grafts have 4x incr risk salvage requirement & 6x thrombosis rate, 10x infection rate
SS_VS 1.4: What are the anaesthetic considerations for pts requiring vascular access surgery for renal dialysis?
Considerations:
-Patient:
(preop Consent-Hx/Ex/Ix, Optimise, Premed/planning, explain/consent, disposition)
consider the indications for RRT & complications of the underlying disease, stability of the renal function.
temporal relation to haemodialysis (has profound effect on fluid volume & distribution & electrolytes)- preferable for them to have dialysis close to the OT (intermittent HD usually 3 days/week, PD every night)
does the pt produce urine?
what fluid restrictions do they have?
find out “dry weight” to gauge excess fluid volume - may avoid IVT in OT
consider high risk cardiovascular complications (IHD incidence 2x > in pts with RRT, their commonest cause of mortality)
end-stage renal failure considerations: increased mortality risk, worsens as eGFR falls. RRT is an independent mortality risk factors.
IHD may be asymptomatic (sedentary life, DM)
Consider HTN, PVD, IHD, CCF, DM, peripheral & ANS neuropathies, immunocompromised due to disease & drugs, anaemia, chronic hyperK, acidosis & other electrolyte/fluid shifts @ the time of dialysis
ECG for all
FBC (anaemia, electrolytes esp K, eGFR)- bear in mind the pts “normal”- they may have developed tolerance to chronic electrolyte abnormalities & anaemia
Pts with CKD 5 or less severe class but rapidly deteriorating function are often offered RRT
medication R/V & planning:
often anticoagulants & antiplatelets
chemo & DMARDs
steroids
antihypertensives
hypoglycaemic agents
-Pathology:
Fluid overload, altered GFR will modify the Pk of anaes drugs
-depending on timing of dialysis, may be volume overloaded which –> higher VD of hydrophilic drugs, less plasma proteins available for drug binding (diluted), while if recent dialysis may be intravascularly deplete, exaggerated CV instability, lower apparent VD
chronic metabolic acidosis impacts degree of ionisation, combined with hypoalbuminaemia & reduced PPs, this may increase free drug availability (should reduce BZD & thio doses by 30-50%)
Propofol generally pk generally unaltered by renal disease but care with CV instability
inhalational agents ideal for maintenance of GA as excreted via lungs
most opioids metabolised in liver so Pk & Pd unaffected by renal disease ASIDE FROM morphine (M6G active metabolite renal excreted)- fentanyl more appropriate- rapid onset/offset & lack of active metabolites. buprenorphine can be used in normal doses (liver metabolism)
care with rise in serum K+ with sux
reduce doses of NDMRs given may accumulate with maintenance doses (most NDMRs excreted by kidneys unchanged)- actrac Hoffman elimination (independent of renal & hepatic function), roc has partial renal excretion so may have prolonged action.
sugammadex not recommended if CrCl <30mL/min (drug & sugammadex/roc complex are renally excreted)
LAs: metabolic acidosis reduces duration of action & protein binding, higher free drug portion & lower seizure threshold make renal pts at higher risk of LAST however LA fantastic for RRT- just reduce maximum doses by 25%. esters are hydrolysed in plasma, amides hepatic metabolism so renal failure doesn’t impact clearance.
platelet dysfunction common in chronic renal failure (altered adhesion & aggregation), pts may often take anti-platelets, theoretical risk of residual heparin effect causing ongoing anticoagulation after dialysis- neuraxial & some regional blockade may be contraindicated.
-Procedure:
-Potential complications:
Intraop plan:
consider pt/surgeon/anaes factors-
can be done under LA- least physiologically intrusive but poorest tolerance by pts, some procedures it’s not feasible due to location or extent of incisions or depth of surgery.
regional anaesthesia +/- light sedation= my preferred in appropriate scenarios as advantages for pt (avoid unpredictable drug pK/pD, airway, haemodynamic & other consequences of GA, less requirement for intra & post-op analgesia which may speed recovery- if other factors OK may be day case), surgeon (sympatholysis increases vessel diameter, improves surgical ease, longer-term patency & likelihood of fistula success as increases vein diameter & vessel flow rate (both predictors of successful fistula formation)).
pitfalls= supraclavicular particularly good (VD) but technically challenging, risks PTx, noncompressible site, ulnar sparing possible; infraclav also technically challenging & poorly compressible, extensive distribution of analgesia though), or axillary block (risks radial & musculocutaneous sparing). none cover intercostobrachial (but tourniquet often not used), patchy blocks may need topup by surgeons, often supplemented with IV sedation, check coagulation status
If GA, consider CV comorbidities & potential for instability, risk ANS neuropathy (DM common), potential for GORD related to gastroparaesis w DM (low threshold for intubation), try & avoid combo of GA & RA (given excessive hypoT may compromise fistula formation.
Monitoring- BP cuff on opposite arm or leg to current fistulas
avoid art line unless absolutely necessary (preserve arteries for future surgery)
Assistant
Drugs
Equipment: US stuff
Airway
Ventilation
Circulation
AVOID accessing fistulas. generally don’t need wide bore access (source control of bleeding in most fistula sites is easy). preference for cannulation= preferred site= back of hand, avoid multiple attempts (use US guidance). Avoid using indwelling dialysis lines (often have high-dose heparin, risks of line failure or complications)
Disability
Environment
Fluids
Glucose
What are the 4 modes of renal replacement therapy?
peritoneal dialysis
home haemodialysis
haemodialysis. Haemodialysis requires wide-bore vascular access as large volumes are exchanged.
transplant
