IOP and Succinylcholine: The Real Risk

If you're like me, you've been taught that succinylcholine is "contraindicated" in open globe injury and then spent years watching attendings give it anyway. The reality is more nuanced — and the boards will test whether you understand the actual physiology rather than the reflex teaching. The succinylcholine-IOP question is a trap designed to see if you know the relative magnitude of the risks, not just the dogma.

The clinical scenario is always some version of the same dilemma: penetrating eye injury, full stomach, potentially difficult airway. You need rapid, reliable conditions. Every approach has a trade-off. The consultant's job is to weigh them correctly and defend the choice.

The Core Logic

Succinylcholine increases intraocular pressure by 5-10 mmHg, primarily through sustained contraction of the extraocular muscles. This effect lasts 5-10 minutes. The concern in an open globe is that a sudden IOP elevation could force vitreous humor, lens, or uveal tissue through the wound — catastrophic but theoretically possible.

Here's the competing risk: laryngoscopy without adequate paralysis, a struggling patient, or a cough on emergence can spike IOP by 40 mmHg or more. A single cough during an inadequate intubation attempt produces far greater IOP elevation than succinylcholine does — and does so at exactly the moment when the globe is most vulnerable (unparalyzed, awake enough to react). Choosing rocuronium to avoid the 5-10 mmHg succinylcholine spike, and then having a difficult intubation with a moving patient, is worse by an order of magnitude.

How the Examiner Tests This

Classic scenario: a 35-year-old with a nail gun injury through the right eye. Full stomach. Mallampati II. "How do you plan to intubate?" The examiner is watching whether you reflexively say "no succinylcholine" or whether you actually reason through it.

If you say rocuronium 1.2 mg/kg: good. Explain why — high-dose rocuronium provides similar onset time to succinylcholine and is your alternative for RSI in open globe. If you say succinylcholine: defensible, with the explicit reasoning that the risk of a smooth intubation with succinylcholine is less than the risk of inadequate conditions with any other agent. The key is defending the logic, not the drug name.

The Board Trap

The absolute contraindication trap: stating that succinylcholine is "absolutely contraindicated" in open globe injury. This is outdated and overly rigid. The ASA difficult airway guidelines acknowledge that in a full-stomach, potentially difficult airway scenario, the aspiration and hypoxia risk from a failed intubation may outweigh the theoretical IOP risk from succinylcholine. Blanket contraindications without clinical context will get you a logic probe.

The emergence trap: even if the intubation is perfect, the IOP risk continues through the case. An awake extubation with coughing and bucking is dangerous. The consultant has a smooth emergence plan — deep extubation or IV lidocaine 1-1.5 mg/kg — before the patient wakes up enough to strain.

Lead-In Phrases

• "My primary goal in this open globe patient is a smooth, rapid, controlled intubation — a cough or struggling patient creates far greater IOP spikes than succinylcholine, and that's my primary concern."
• "I will use rocuronium 1.2 mg/kg as my relaxant of choice — it provides onset conditions similar to succinylcholine and avoids the 5-10 mmHg IOP rise from extraocular muscle fasciculations."
• "I will supplement my induction with adequate topical anesthetic to the cords and ensure deep anesthesia before laryngoscopy — the response to laryngoscopy is as important as the drug choice."
• "My emergence plan includes deep extubation or IV lidocaine before the patient is awake — a single cough at emergence is the most dangerous IOP event in the entire case."
• "If this were a full-stomach patient with a known difficult airway and no time for an awake fiberoptic, I would use succinylcholine — the risk of a failed RSI with inadequate conditions exceeds the IOP risk from succinylcholine in that specific scenario."

FAQs

What actually causes IOP elevation with succinylcholine?

The extraocular muscles don't relax with succinylcholine the way skeletal muscles do — they instead enter a state of contracture (prolonged, non-fasciculating contraction). This squeezes the globe from the outside, raising IOP for several minutes. Pre-treatment with non-depolarizers (defasciculating doses) reduces but does not eliminate this effect.

If the airway looks easy and the stomach is full, can I use succinylcholine?

Yes, with the explicit understanding that the IOP rise is a potential risk and your technique is optimized to minimize it. Adequate induction depth, smooth laryngoscopy, and no patient movement are more important than the drug choice. Succinylcholine in a perfectly executed RSI on an easy airway is safer for the eye than rocuronium in a technically poor intubation attempt.

What's the approach for a pediatric open globe with a full stomach?

The same logic applies, with weight-adjusted dosing. High-dose rocuronium (1.2 mg/kg in children) provides the best balance. The smaller airway in a child means adequate paralysis is even more critical to avoid the coughing and straining that cause the real IOP spikes. Sugammadex 16 mg/kg for emergency reversal should be available.

The open globe IOP question is a test of proportional thinking, not rote contraindication. Practice defending your drug choice with the relative magnitudes — 5-10 mmHg from succinylcholine versus 40 mmHg from a cough — in Boards Bot until the logic is instinctive.