“My Oxygen Dropped and Nobody Told Me”: When Colonoscopy Sedation Goes Wrong

Surgical and hospital care guides · 15 min read · Published 10 November 2026 · Reviewed 10 November 2026 · Next review May 2027

By Dr Rosemary Listing, PhD (Law) · Medical negligence lawyer since 2014 · Of Counsel, Peter Evans & Associates

If you are reading this after a colonoscopy that didn’t go the way it should have, I want you to know that asking what happened is entirely reasonable. Sedation is very safe for most people, which is why it can be easy to overlook the people for whom it isn’t. You were entitled to be assessed, monitored and told.

This guide is for anyone who has had a colonoscopy in Australia, and for the families who drive them home. It covers how sedation should be planned, what Australian standards say, the risks of the procedure itself, the warning signs, what your records should show, and how the law looks at it.

Start with your question

• What are the risks of sedation for colonoscopy?
• Should an anaesthetist have been there?
• Why would my blood pressure or oxygen drop during a colonoscopy?
• How common is a bowel perforation?
• Should I have been told if something went wrong?
• When should I worry after a colonoscopy?
• Could this be medical negligence?

Colonoscopy and sedation

A colonoscopy uses a flexible camera to look inside the large bowel. More than 800,000 were performed in Australia in 2016–17, about one for every 32 Australians.¹ Sedation or a light anaesthetic is used to reduce pain and discomfort, and most people don’t remember the procedure. Afterwards you may feel sleepy, need someone to take you home, and shouldn’t drive or sign legal documents for the rest of the day.²

Before the procedure

The Australian Commission on Safety and Quality in Health Care updated its national Colonoscopy Clinical Care Standard in 2025. It says that, before bowel preparation starts, you should receive information about the preparation, the colonoscopy and sedation, be able to discuss the reasons, risks, benefits, costs and alternatives, and have your consent to sedation and the procedure documented.³

Questions to ask before your colonoscopy

• Who will give the sedation, and will someone be watching only my sedation?
• Do my heart, lung or sleep conditions change the plan?
• Should an anaesthetist assess me first?
• What are the risks of sedation, and of the procedure itself, for me?
• What happens if my blood pressure or oxygen drops?
• Will you tell me if anything goes wrong?

Assessment on the day

Under the national standard, you should be assessed before your colonoscopy by an appropriately trained clinician to identify any increased cardiovascular, respiratory or airway risk, and sedation should be planned to match. Sedation must be given by a credentialed clinician working within their scope. Anaesthetists are needed for deep sedation or general anaesthesia, and if increased risk is identified, an anaesthetist or other suitably trained practitioner should assess you and be present.³

The Australian and New Zealand College of Anaesthetists’ guideline on procedural sedation explains that higher-risk patients need a fuller assessment, including heart, breathing and sleep apnoea history. For patients with significant medical conditions, a suitably trained practitioner should be exclusively present to manage sedation, and when a proceduralist also gives propofol sedation, two additional staff are essential.⁴

During sedation

You should be monitored throughout the procedure and recovery in line with the college’s guidelines.³ The college strongly recommends waveform capnography, which measures the carbon dioxide you breathe out, for moderate sedation.⁴

Low blood pressure and low oxygen

Sedation medicines can lower blood pressure and slow breathing. Bowel preparation can also leave you dehydrated.² For most people any dip is brief and managed quickly. But in people with heart disease, lung disease or sleep apnoea, or in older people, the effects can be greater. That is why the standard requires assessment beforehand and the right person in the room.

Risks of the procedure itself

Colonoscopy can cause bleeding, especially if polyps are removed, which can start straight away or up to two weeks later. Rarely, it can cause a perforation, a hole in the bowel wall. Infection and reactions to the bowel preparation are also possible, and a polyp or cancer can be missed.² Perforation occurs in about one in every 1,000 screening colonoscopies.¹

Being told what happened

The national standard says that, before you leave, you should be told verbally and in writing about the preliminary outcome of the colonoscopy, including any interventions or adverse events, when to restart activities and medicines, and the follow-up plan. You should go home with a responsible adult. Adverse events such as perforation, bleeding after polyp removal and sedation-related heart or breathing problems must be recorded, and you must be told if one occurred and how it was managed.³

Expected, worth a call, or emergency

A general guide only. Your clinic’s instructions come first.

The symptoms in the middle card are those healthdirect lists as reasons to call your doctor immediately after a colonoscopy.²

Afterwards

If you had a frightening reaction, a procedure that couldn’t be finished, or a complication, ask for a meeting to go through what happened. If your oxygen dropped for a long time, ask whether there could be lasting effects. Our guide to hypoxic brain injury during surgery covers the most serious outcome. If you felt brushed off, see when being dismissed by a doctor becomes a legal issue.

What to look for in the records

Your records are often where the story becomes clear. You have a right to access your own health information. In NSW the Health Records and Information Privacy Act 2002 covers both public and private providers, and the Information and Privacy Commission explains how to ask.⁵ Our step-by-step guide to getting your medical records in Australia walks you through it.

How the law looks at it

A drop in blood pressure or oxygen during sedation, or a perforation, is not, on its own, negligence. These are known risks even with excellent care. The legal questions are whether the care, from assessment to discharge, met the standard expected, and whether any shortfall caused harm.

A claim usually turns on three questions: whether the care fell below what peers would widely accept as competent practice (section 5O of the Civil Liability Act 2002 (NSW))⁶, whether that shortfall probably caused harm you wouldn't otherwise have had (Tabet v Gett)⁷, and, where it matters, whether you were told the material risks first (Rogers v Whitaker)⁸⁹. Our guide to how a medical negligence claim works explains each one in plain terms.

In a colonoscopy case, the questions might be: were your risks assessed and was sedation planned to match, with an anaesthetist involved if needed? Were you monitored by someone whose role was your sedation? Was a problem recognised and managed promptly? Were you told what happened?

In plain terms, the question is whether proper assessment, monitoring or response would probably have avoided the harm you suffered, such as a lasting injury or a further procedure.

For colonoscopy, that would usually include the risks of sedation, bleeding, perforation and a missed lesion, and the option of a different level of sedation or none at all where appropriate.

Who can claim, and when

The person who had the procedure can claim. If someone died, members of their family may be able to bring a claim. In NSW, time usually runs from when you knew, or ought to have known, enough to claim, not from the treatment itself, and courts can sometimes extend it, so an old injury may still count. See time limits in NSW or other states, and ask early.

More: complaint or claim? · how a claim is paid for · what a claim can cover

In my practice

In files about procedural sedation, I often find that the important information was there all along, just not in the right place. A referral that mentions sleep apnoea or a heart condition. A pre-procedure checklist that says “nil”. A sedation chart that shows oxygen levels falling and an airway being supported. And then a discharge note that says “procedure incomplete” and nothing more. The patient goes home not knowing anything happened, except a feeling that something did. These are small failures of communication, not dramatic errors. But the standard asks for honesty about adverse events precisely because people need to know what happened to their own bodies.

Both things can be true

The team may have responded quickly and well when your oxygen dropped, and the assessment beforehand may still have missed something important. Sedation may be safe for almost everyone, and you may still have been one of the people for whom it needed more care. You can be grateful to the staff who helped you and still want to know why it happened.

The bigger picture

Australia introduced a national Colonoscopy Clinical Care Standard in 2018, partly in response to wide variation in quality and the potential for avoidable harm, and updated it in 2025.¹³ The anaesthetists’ college updated its procedural sedation guideline in 2023.⁴

You can check any practitioner’s registration on the Ahpra public register,¹⁰ and complaints about care in NSW can go to the Health Care Complaints Commission.¹¹ If a cancer or polyp was missed, see our guide to missed and delayed diagnosis.

Support

You don't have to work through this alone. These services can help:

• Lifeline, 24-hour crisis support: 13 11 14 (listed on healthdirect's helplines page)¹²
• Beyond Blue, anxiety and depression support: 1300 22 4636
• Medicare Mental Health, help finding mental health support: 1800 595 212
• healthdirect, 24-hour nurse advice: 1800 022 222
• Health Care Complaints Commission (NSW): 1800 043 159

A man who sat in the passenger seat wondering what happened in that room found out, at his own dining table, with his granddaughter beside him. You deserve that clarity too.

With care,
Rosemary

Frequently asked questions