You are asked by your consultant to arrange preoperative workup for a 75 year old man who is booked for open Abdominal Aortic Aneurysm resection and graft. The consultant wants to get the surgery done as soon as possible, as the aneurysm measures 8cm in diameter and is a little tender to palpation – he is concerned about imminent rupture.
The patient is an ex-smoker of 30 pack-years; he has hypertension treated with Ramipril and Metoprolol; Type 2 diabetes for 14 years, currently treated with insulin, protaphane 22 units in the morning and 12 units at dinner time; he says he is quite active but on questioning, his only real activity is a 1km round-trip level walk to the TAB 4 days a week, after which he feels quite tired and normally has a sleep; he denies any symptoms suggestive of ischaemic heart disease.
His blood tests done yesterday by the surgeon show normal FBC; K of 5.5, Urea 10.0 mmol/l and Creatinine 140 micromol/l.
Questions
1. Over and above those issues pertinent to all patients, what are the particular preoperative issues for this man?
High risk surgery (major vascular. Other high-risk includes thoracic, upper abdominal)
Urgent surgery (as distinct from emergent) - a tender 8cm AAA is a condition at great risk of rupture and sudden death. There is time for preop evaluation of cardiac risk but not over weeks, more like a day or 2, and the testing should be arranged as an inpatient
Coronary artery disease risk - He is at high risk of having coronary artery disease
Renal function - His Renal function is abnormal and there is considerable risk to it during and after the proposed surgery
Diabetes - Needs special consideration
Respiratory function - He has a long smoking history and his respiratory function will be an important determinant of post-op recovery after this major upper abdominal surgery
Analgesia options - Discussion of analgesia options is important at the preoperative assessment by the anaesthetist, perhaps not so much by the surgical team members
2. Discuss a plan for preoperative cardiac evaluation, given that this is a patient undergoing high-risk surgery who has limited functional reserve.
A slow walk 1km after which he is exhausted suggests 4 METS of activity – quite limited. Unless emergency surgery, he should have more extensive workup even in the absence of other symptoms. DM2 is associated with "silent" myocardial ischaemia and RBBB and Beta-blockade make resting and stress ECG uninterpretable.
Options for assessment:
Aim is to assess risk of perioperative adverse cardiac event (AMI, CCF, death) and to monitor appropriately
To do this, assess coronary circulation, and myocardial function – preferably myocardial function while myocardium is being stressed
If good functional reserve, no symptoms, normal resting ECG, reasonable to proceed
Otherwise, either Dipyridamole-Sestamibi Scan or Dobutamine Stress Echo
DSE gives more assessment of cardiac function; the jury seems to be out
Coronary angio as a screening tool - risks outweigh benefit
3. What is the current role of preoperative beta-blockade in a patient like this?
A number of small studies and one larger (POISE) over the last 10 years or so of periop beta blockers and high-risk patients. Inconsistent results for various reasons, largely methodological.
This man is already on Metoprolol, well beta-blocked with HR 52/min. He should remain on it up to and including the morning of surgery.
4. Discuss some possible options for his perioperative diabetes management.
Management of Ramipril:
His Ramipril should be withheld – certainly on the morning of surgery and probably from now, at least until renal artery stenosis can be excluded
It may be contributing to his impaired renal function
Advice from a nephrologist should be obtained, as well as to warn the team of the possibility of post-op renal failure
Possible causes of renal impairment:
Vascular disease
Diabetes
Hypertension
Others
Renal protection measures:
Meticulous attention to haemodynamics intra and post operatively
Avoidance of nephrotoxins, eg IV contrast, aminoglycosides, NSAIDs
Avoidance of preop dehydration by giving IV fluids while fasting
Diabetes management options:
Aims: prevent hypoglycaemia, and prevent complications of hyperglycaemia. In DM1, prevent ketoacidosis. Not a risk in DM2
Conflicting evidence of benefits of "tight" (4-6) vs "conventional" (5-10) glucose control
For DM2 (simplest): No insulin morning of surgery, also no oral hypoglycaemics. Check BGL intraop and if necessary run infusion of soluble insulin to keep BGL < 8 or so. If insulin is given, also need IV of 5% Dextrose available
For DM1: Need some insulin otherwise get ketoacidosis. Either ½ normal am dose, given as soluble insulin, along with 5% D infusion, or run Glucose/Insulin +/-Potassium infusion – there are institutional protocols
If in doubt call patient's endocrinologist
Important: Always stop Metformin 1-2 days preop especially with fasting