Post-Operative Day 1 Total Knee Replacement: Dizziness During First Mobilisation
A 68-year-old woman is assessed on post-operative day 1 following an uncomplicated left total knee replacement under spinal anaesthesia. Comorbidities: type 2 diabetes, hypertension, and a body mass index of 33. Pre-operatively she walked independently with a stick. Current observations at rest, supine: heart rate 88 bpm, blood pressure 138/82 mmHg, oxygen saturation 96% on room air, respiratory rate 16, temperature 37.4 C. Haemoglobin is 9.8 g/dL (pre-operative 12.6 g/dL). The wound drain was removed 2 hours ago. She has a femoral nerve block infusion running, quadriceps strength is grade 1/5, hamstring grade 3/5, and the knee is held in 15 degrees flexion with a bulky dressing. She has an indwelling urinary catheter and a patient-controlled analgesia pump. She reports pain 3/10 at rest. The surgeon has ordered full weight bearing as tolerated. On sitting to the edge of the bed she becomes pale and reports feeling light-headed; heart rate rises to 112 bpm and blood pressure falls to 104/60 mmHg.
1. Interpret the observations during sitting. What is the most likely cause, and how does the femoral nerve block and recent blood loss change your reasoning and immediate plan?
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The response is consistent with symptomatic orthostatic intolerance (a symptomatic drop of >20 mmHg systolic and >10 mmHg diastolic, with heart rate rising ~24 bpm and light-headedness).
Differential and weighting:
- Orthostatic hypotension from deconditioning and bed rest - plausible in anyone on day 1, but the magnitude of the drop and pallor suggest more than simple deconditioning.
- Post-operative anaemia - Hb has fallen from 12.6 to 9.8 g/dL, a drop of ~2.8 g/dL, which is a meaningful contributor to reduced orthostatic reserve and reduced oxygen-carrying capacity. This should be flagged to the surgical team.
- Residual sympathetic blockade from spinal anaesthesia - spinal anaesthesia can cause vasodilatation and blunted baroreflex responses; this typically resolves within hours but contributes on day 1.
- Opioid-related vasodilatation and sedation - PCA use can lower vascular tone.
- Hypovolaemia - drain removal 2 hours ago and possible ongoing losses should prompt a check for bleeding and fluid status.
Why the femoral nerve block matters: quadriceps grade 1/5 means the knee cannot be actively stabilised. If she stands and the knee buckles, she is at high risk of a fall and of disrupting the prosthesis or wound. A block also masks pain that would otherwise warn of excessive loading, so she may over-reach her tolerance without feedback.
Immediate plan:
- Return her to supine with legs elevated; do not attempt standing.
- Recheck heart rate, blood pressure, oxygen saturation, and consciousness; observe until symptoms resolve.
- Escalate: report the symptomatic drop, the Hb fall, and drain status to the surgical team for review of blood loss, hydration, and analgesia.
- Defer standing until she is symptom-free on sitting and has an acceptable orthostatic profile. Meanwhile, progress bed-based exercises, seated knee extension with support, and respiratory care.
- When re-attempting, use a tilt-table or graded sitting-to-standing progression, two-person assist, a walking frame, and a knee immobiliser or therapist-provided knee support if quadriceps remains grade 1/5.
- Document the event and the revised mobilisation plan.
2. The patient asks why she cannot just push through the dizziness to get to the bathroom. How do you explain the risk and negotiate a plan?
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Explain in plain language: the dizziness is a signal that blood pressure is falling when she sits up, and if she stands and her knee gives way because the nerve block has switched off the thigh muscle, she could fall and damage the new joint or the wound. Pushing through does not train the body faster; it increases the chance of a fall.
Negotiate a concrete, time-bound plan:
- Agree that the therapist will sit her up in stages (30 degrees, then 60, then upright) and check her blood pressure at each stage before any standing.
- Agree a 'stop rule': if she feels light-headed, has visual changes, or her systolic pressure falls more than 20 mmHg, she returns to lying flat and the team is called.
- Offer alternatives for dignity and safety now: commode at the bedside with two staff, rather than a walk to the bathroom.
- Reassure her that mobilisation remains the goal and will resume as soon as her observations are stable, likely the same day if the team addresses the anaemia and fluids.
- Confirm understanding with teach-back and document the agreed plan and her consent.