Contrast Prophylaxis Before an Urgent Catheterization: Saline, Bicarbonate, or Neither
A single patient with CKD stage 3b needing urgent coronary angiography for NSTEMI. The disagreement is whether any specific prophylactic regimen beyond straightforward isotonic saline actually changes her risk.
N.S., a 63-year-old retired accountant, has spent the last four years balancing her own books with the same discipline she once applied to other people's — a spreadsheet for blood pressure readings, another for the low-sodium meals she has learned to actually enjoy, since a nephrologist told her four years ago that her kidneys were “something to watch.” That watching has held her fairly steady at an eGFR in the low 30s, attributed to long-standing hypertension rather than diabetes, which she has never had, until this morning, when crushing chest pressure while gardening brought her to the emergency department with dynamic ST depressions and a troponin already climbing. Cardiology wants her in the catheterization lab within the next few hours, not tomorrow, and that timeline is the actual constraint the team is working inside.
Her baseline creatinine, confirmed against a lab drawn three weeks ago at her last nephrology visit, is 1.6 mg/dL, eGFR 32 — real, established CKD, not a today-only fluctuation. The question is not whether contrast carries risk for her; that much everyone agrees on. It is whether anything beyond straightforward hydration meaningfully changes that risk, and the honest answer, per the PRESERVE trial — 5,177 patients randomized, with an eGFR stratum of 15 to 44.9 that her own 32 sits inside regardless of her non-diabetic status — is that neither sodium bicarbonate nor oral N-acetylcysteine outperformed straightforward isotonic saline for the composite renal endpoint, and neither reduced death, need for dialysis, or persistent kidney impairment. Her kidney matches that trial; the rest of her does not. PRESERVE excluded emergency angiography outright, and she is going to the lab within hours for an infarct still in progress — so the study describing her renal risk most precisely is one she would have been screened out of. That cuts less than it sounds like it should: a negative result crosses that gap in a way a positive one would not, because what it establishes is what the team can safely decline to add, not how long they have in which to add it.
Emergency department, three hours before the cath lab
She is having a heart attack in progress, and every hour we spend optimizing prophylaxis is an hour of ongoing myocardial injury. I want isotonic saline running now, at whatever rate her volume status tolerates, and I want to go to the lab as soon as she has had a reasonable bolus — not wait for a bicarbonate protocol or a dose of oral NAC to finish absorbing.
I am not going to ask you to delay a heart attack for kidney prophylaxis, and I want to say clearly that the evidence supports you here rather than just deferring to urgency. PRESERVE, the largest trial to test this head to head at her degree of renal risk, found no advantage for sodium bicarbonate over saline and none for oral NAC over placebo on the composite renal outcome. I should be straight that it excluded emergency angiography, so she would not have been enrolled — but a negative finding survives that gap better than a positive one would, and the direction it points is the one that helps you. There is no bicarbonate regimen or NAC dose I can offer that the evidence says will outperform what you are already planning to run.
This is a genuine case where the evidence and the time pressure point the same direction, not one where I am conceding urgency over what I'd otherwise recommend.
The one thing I would add is contrast volume itself, since that is the variable PRESERVE did not test directly but that his own procedural planning controls. Minimizing total contrast load and using a low-osmolar agent are both supported independently of the prophylaxis question, and they cost nothing in time.
Neither the nephrologist's nor my point is an argument for adding bicarbonate or NAC on top of saline — PRESERVE's finding was a genuine negative, not an untested combination waiting to be tried; the actionable levers here are volume expansion, already planned, and contrast minimization, not an additional prophylactic agent.
Agreed, without real disagreement once the PRESERVE data were on the table: isotonic saline started immediately, catheterization proceeding on cardiology's timeline without waiting for a bicarbonate or NAC protocol, and contrast volume minimized procedurally.
The team's shared read, stated explicitly rather than left implicit: this was not a case of medical urgency overriding better renal prophylaxis available elsewhere — the evidence itself did not support a better option, which made the time-pressured and the evidence-based path the same path.