Day 8 after CABG: progressing mobility within sternal precautions
Mr K is 66 years old, day 8 after elective three-vessel coronary artery bypass grafting through a median sternotomy (LIMA to LAD, vein grafts to RCA and circumflex). Pre-operative LVEF was 40%; he has hypertension, type 2 diabetes and a 40 pack-year smoking history, having stopped 3 weeks before surgery. Post-operatively he had atrial fibrillation treated with amiodarone and is now in sinus rhythm at 88 bpm. Current observations: SpO2 94% on 2 L/min nasal oxygen, BP 132/78 mmHg, respiratory rate 20, temperature 36.8 degrees Celsius, haemoglobin 92 g/L. The sternum is clinically stable with no clicking; chest drains were removed on day 5; the left leg wound is healing well. He mobilises 40 m with a wheeled frame and one assistant and stops with a Borg dyspnoea score of 5. He is anxious that the bone will split.
1. Is he safe to progress today? State the criteria and thresholds you will use and how you will advance him.
Read the worked answer
Yes - he meets readiness criteria, but progression should be incremental and criterion-based. Met criteria: haemodynamically stable in sinus rhythm at 88 bpm with BP 132/78, afebrile, clinically stable sternum, drains out, and a healing leg wound. Haemoglobin of 92 g/L is a mild post-operative anaemia that explains some fatigue and exertional breathlessness but is not a bar to mobilising; it does lower his reserve and should be noted.
What is not yet optimal: 40 m with a frame at day 8 is at the lower end of expected function, and the oxygen and his anxiety are both limiting.
Progression: walk with one assistant, then without the frame on a clear route; add 20-30 m per session and 2-3 sessions per day; target Borg 11-13 as the ceiling, not exhaustion. Thresholds to stop: SpO2 below 90% or a fall of more than 4%, heart rate rising more than 20-30 bpm above rest (about 110-115), chest pain, dizziness, new arrhythmia, or a Borg score above 13.
Anxiety: explain how the sternum is wired and how the precautions protect it - this improves adherence more than reassurance alone. Do not increase oxygen flow to force a longer walk; exertional desaturation needs assessment, not concealment.
2. Set out the sternal precautions you will teach, including load limits and functional retraining, and justify why early mobilisation is still appropriate.
Read the worked answer
Precautions for 6-8 weeks after median sternotomy: no lifting more than 5-8 kg; no pushing or pulling body weight through the arms (do not use the arms to rise from a chair, do not push a wheeled frame hard, avoid heavy resistance on the arms); no heavy unilateral arm work; no overhead or behind-the-back stretching; no driving until cleared; avoid sudden trunk rotation; splint the chest with a pillow when coughing.
Functional retraining: log-roll to sit up, nose-over-toes sit-to-stand with arms crossed, walking with arms relaxed, stair practice, and active shoulder range within pain limits to prevent posterior shoulder pain and stiffness.
Why early mobilisation is still right: complete immobilisation produces deconditioning, atelectasis, shoulder stiffness and posterior shoulder pain, and does not protect the sternum. Stability comes from the wires and bone healing, so the aim is to respect imposed load while maintaining function. Early walking, sitting out, breathing exercises and incentive spirometry are safe and reduce pulmonary complications.
Discharge readiness: he should manage at least 100 m and a flight of steps, have a safe home layout and a carer plan, and understand the precordial-pain action plan before going home.
3. Mid-session his SpO2 falls to 87%, heart rate rises to 130 bpm and he reports chest tightness. What do you do, and what does this change about his rehabilitation plan?
Read the worked answer
Recognise and act - this is an adverse event, not a training response. Stop the activity, sit him upright, and check the trace is adequate. Give prescribed oxygen to keep SpO2 at 90% or above. Re-measure heart rate, blood pressure and respiratory rate after 2-3 minutes, and look at the rhythm on the monitor. Note the character of the chest tightness: ischaemic pain is pressure-like, radiating, and associated with sweating or nausea - that is a different pathway from musculoskeletal wound pain.
Escalate: if chest tightness, desaturation or tachycardia persist after rest, call the cardiothoracic team immediately - he has a history of post-operative atrial fibrillation and a recent bypass, so new AF, ischaemia, effusion, atelectasis or anaemia (Hb 92) must be excluded. Do not simply shorten the walk and carry on.
If it resolves fully with rest and oxygen: document an incident note, inform the nurse in charge, and request medical review before the next session, with a 12-lead ECG and repeat full blood count.
Effect on the plan: reset his exercise ceiling to Borg 11 and a lower heart-rate cap, use interval walks with seated rests, and reassess oxygen prescription. Chest tightness of uncertain cause means no progression until medically cleared.