Anaesthetic Risks — GA, Spinal and Nerve Blocks

Part of The Joint Replacement Guide — Phase 3: Understanding the Risks · Article 14 of 44 · Hip & Knee

Key Points

  • The two main options for hip or knee replacement are a spinal anaesthetic or a general anaesthetic.
  • NICE recommends offering a choice between regional and general anaesthesia, normally with additional local pain relief, when both options are clinically suitable.[1]
  • Current evidence does not show that one technique is best for every patient.
  • Sedation can be given with a spinal anaesthetic if you would prefer to feel relaxed or sleepy.
  • Local infiltration analgesia and selected nerve blocks can improve pain relief and reduce the need for opioid medicines.
  • Your anaesthetist will recommend a plan based on the operation, your health, your preferences and the facilities available.

The Different Parts of an Anaesthetic Plan

Several techniques may be used during joint replacement, and their names can be confusing:

  • A general anaesthetic produces a controlled, deep sleep-like state.
  • A spinal anaesthetic numbs the lower part of the body.
  • Sedation can make you relaxed or sleepy while a spinal is working.
  • A peripheral nerve block numbs selected nerves to provide pain relief.
  • Local infiltration analgesia involves the surgeon placing local anaesthetic around the operated joint.

A nerve block or local infiltration usually supplements a spinal or general anaesthetic. It does not normally provide enough anaesthesia for a hip or knee replacement by itself.[3]

General Anaesthesia

A general anaesthetic uses medicines to produce a controlled state of unconsciousness. You will not be aware of the operation. The anaesthetic team monitors your heart rate, blood pressure, breathing and oxygen level throughout.

Your breathing may be supported using an airway device, oxygen and, where necessary, a breathing machine. The exact approach depends on the procedure and your individual needs.

Temporary effects can include:

  • nausea or vomiting;
  • a sore throat or hoarse voice;
  • shivering;
  • dizziness;
  • drowsiness; and
  • temporary confusion, particularly in some older or more vulnerable patients.

More serious complications—such as severe allergic reaction, breathing difficulties, dental damage, awareness during anaesthesia or serious heart problems—are uncommon or rare. Your individual risk depends more on your health and the nature of the operation than on a population average.

Spinal Anaesthesia

A spinal anaesthetic involves injecting local anaesthetic through a fine needle in the lower back. It temporarily numbs the lower half of the body, including the operated leg.

You can remain fully awake, but many people choose sedation so that they feel relaxed or sleepy. Depending on the depth of sedation, you may remember everything, something or nothing about the time in theatre.[3]

You should not feel pain during the operation, although you may be aware of movement, pressure or activity around you. Screens prevent you from seeing the surgery, and headphones or music may sometimes be available.

Possible effects and complications include:

  • a temporary fall in blood pressure;
  • itching, nausea or shivering;
  • temporary difficulty passing urine;
  • a headache after the spinal;
  • the spinal not working fully or lasting long enough; and
  • very rare bleeding, infection or nerve injury.

If the spinal is incomplete, cannot be inserted or wears off unexpectedly, additional medication or a general anaesthetic may be required. The anaesthetist will discuss this possibility with you.

Is a Spinal Better Than a General Anaesthetic?

Neither technique is best for everyone. NICE’s evidence review concluded that regional and general anaesthesia were similarly effective for elective hip and knee replacement and recommended that patients be offered a choice when appropriate.[1,2]

Some large observational studies report lower rates of certain complications or a shorter hospital stay with spinal anaesthesia.[4] However, these studies cannot completely remove differences between the patients selected for each technique. For example, people receiving general anaesthesia may have health conditions or technical factors that made a spinal unsuitable.

The choice should therefore not be presented as “safe spinal” versus “riskier general anaesthetic”. Both are established options, and the advantages and disadvantages depend on the individual patient and clinical circumstances.

When Might a Spinal Be Unsuitable or Difficult?

Factors that may affect whether a spinal can be offered include:

  • certain blood-thinning medicines;
  • a bleeding or clotting disorder;
  • infection near the injection site;
  • some neurological or spinal conditions;
  • previous surgery or significant deformity of the spine;
  • inability to maintain the position needed for the injection; and
  • the anticipated duration or complexity of the operation.

Previous spinal surgery does not automatically rule out a spinal anaesthetic, but it may make placement more difficult. The anaesthetist will assess the particular circumstances.

Sedation

Sedation is often used with a spinal anaesthetic. It can range from light relaxation to a deeper sleep-like state.

Sedation is not exactly the same as general anaesthesia. With lighter sedation, you may hear sounds or remember parts of your time in theatre. Deeper sedation can affect breathing and requires close monitoring.

Tell the anaesthetist what concerns you—for example, whether you would prefer to be alert, would like music, or strongly wish to avoid awareness of the operating environment. They can explain what is realistically possible and safe.

Local Infiltration Analgesia

Local infiltration analgesia, or LIA, involves the surgeon injecting local anaesthetic and sometimes other pain-relieving medicines into tissues around the joint during the operation.

It can be used with either spinal or general anaesthesia and is an important part of pain management after many hip and knee replacements. NICE recommends regional or general anaesthesia in combination with LIA for primary elective hip and knee replacement.[1]

LIA usually has less effect on muscle power than some peripheral nerve blocks, which can support earlier mobilisation.

Peripheral Nerve Blocks

A peripheral nerve block involves placing local anaesthetic near one or more nerves supplying the operated area, often using ultrasound guidance. It can provide pain relief for several hours and sometimes longer.

For knee replacement, an adductor-canal block may be used because it is intended to preserve more quadriceps strength than a traditional femoral nerve block. Other blocks may also be considered according to local practice and individual circumstances.

Some nerve blocks can temporarily weaken the leg as well as numb it. This may delay safe walking or increase the risk of falling until the block wears off. NICE therefore advises considering blocks that do not significantly impair motor function.[1,2]

A nerve block may reduce—but will not necessarily eliminate—the need for opioid painkillers. Patients still require a balanced pain-relief plan and should ask for help if pain is not adequately controlled.

Possible complications include failure of the block, bruising, bleeding, infection, temporary nerve symptoms and, very rarely, serious reaction to local anaesthetic or lasting nerve injury.

Multimodal Pain Relief

Modern joint-replacement care usually combines different types of pain relief rather than relying on one medicine or procedure. Depending on your health, this may include:

  • local infiltration analgesia;
  • a selected nerve block;
  • paracetamol;
  • an anti-inflammatory medicine, when suitable;
  • ice and positioning;
  • early movement; and
  • an opioid medicine when required.

Combining treatments can improve pain control while limiting opioid-related effects such as nausea, constipation, drowsiness and slowed breathing.

Choosing an Anaesthetic

The anaesthetist will consider:

  • your medical conditions and previous anaesthetic experiences;
  • medicines, allergies and blood-thinning treatment;
  • spinal anatomy or previous spinal surgery;
  • the type and expected duration of the operation;
  • your preferences and concerns;
  • the surgeon’s pain-relief plan; and
  • the staff, equipment and techniques available locally.

You should be able to ask questions and express a preference. A particular technique cannot always be guaranteed because the final plan must remain clinically appropriate, and circumstances can change on the day.

Useful questions include:

  • What options are suitable for me?
  • What are the important benefits and risks of each?
  • If I have a spinal, what level of sedation can I have?
  • What additional pain relief will be used?
  • Could the technique weaken my leg or affect mobilisation?
  • What is the backup plan if the spinal or nerve block does not work as intended?

The Bottom Line

Spinal and general anaesthesia are both accepted options for elective hip and knee replacement. A spinal can be combined with sedation; either principal technique can be supplemented by local infiltration analgesia or an appropriate nerve block.

The best plan is not determined by a universal preference for one technique. It is an individual decision made after discussing your health, the operation, the relevant benefits and risks, and what matters to you. Many hospitals use enhanced recovery pathways in which spinal anaesthesia is commonly preferred, although practices vary; your anaesthetist will discuss whether this approach is suitable for you and what alternatives are available.

This article provides general information and does not replace your individual discussion with an anaesthetist. Follow your hospital’s instructions about medicines, fasting and preparation for surgery. Do not stop blood-thinning medication unless your clinical team tells you to do so.

References

  1. National Institute for Health and Care Excellence. Joint replacement (primary): hip, knee and shoulder. NICE guideline NG157. London: NICE; 2020. Recommendations 1.3.1–1.3.2. Available from: https://www.nice.org.uk/guidance/ng157/chapter/Recommendations
  2. National Institute for Health and Care Excellence. Joint replacement (primary): rationale and impact—anaesthesia and analgesia. London: NICE; 2020. Available from: https://www.nice.org.uk/guidance/ng157/chapter/Rationale-and-impact
  3. Royal College of Anaesthetists. Anaesthetic choices for hip or knee replacement. 7th ed. London: RCoA; 2026. Available from: https://www.rcoa.ac.uk/patients/patient-information-resources/patient-information-leaflets-video-resources/anaesthetic-choices-hip-or-knee-replacement
  4. Wang R, Liu X, Lang Z, Liu Y, Zhang Y. Comparison of spinal anesthesia and general anesthesia in total hip and total knee arthroplasty: a meta-analysis and systematic review. Minerva Anestesiol. 2025;91. doi:10.23736/S0375-9393.25.19043-3. Available from: https://pubmed.ncbi.nlm.nih.gov/40658191/
  5. Royal College of Anaesthetists. Risks associated with general anaesthesia. London: RCoA. Available from: https://www.rcoa.ac.uk/patients/patient-information-resources/anaesthesia-risk/risks-associated-general-anaesthesia

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