List the causes of a sudden acute fall in systolic blood pressure to 50 mmHg one hour after an uneventful coronary artery bypass operation. Outline your principles of management for each cause.
A list of causes was requested, as were principles of management for each cause.
Potential causes are many, and more than one may co-exist. These could be listed according to causes of shock; one such approach to cover potential causes is: artefactual, hypovolaemic,obstructive, cardiogenic, and distributive. Principles of management are listed in brackets following each cause. Simple manoeuvres should always be considered early (eg. raise legs to autotransfuse). Artefactual: transducer error (check transducer: zero, level, calibration), damping of waveform (assess damping coefficient), malfunction of NIBP.
Hypovolaemic: blood loss (observe drain tubes, CXR, dressings; give fluid ± blood products), massive diuresis (observe urine output; give fluid).
Obstructive: pericardial tamponade (observe chest drainage ± clots, high filling pressures: may need to open chest), tension pneumothorax (observe expanded hemi-thorax, listen to chest: check
existing chest drains, may need needle thoracostomy and replace/insert ICC), elevated intrathoracic pressure (gas trapping: disconnect from ventilator; shivering/Valsalva/fighting: sedate ± paralyse; ensure ETT not blocked).
Myocardial: decreased contractility (ischaemia due to blockage/kinking/spasm: treat with GTN, inotropes &/or short term vasoconstrictor ± fix technical problem; sudden removal of inotropic drug: restart drug) or rhythm disturbance on monitor/ECG (brady-asystole: pace ± atropine/isoprenaline/adrenaline; SVT: eg. K/Mg/adenosine; AF eg. K/Mg/amiodarone, VT eg. K/Mg/lignocaine or amiodarone).
Distributive: anaphylaxis (rash/bronchospasm: remove hapten, adrenaline, fluids); vasodilator excess (recent boluses/infusion too high: stop responsible drug, ± titrated dose vasoconstrictor); sympathetic block (recent bolus of epidural Local Anaesthetic: titrated dose vasoconstrictor); too profound for a systemic inflammatory response.
Relevant reading includes:
- Approach to the haemodynamically unstable cardiac surgical patient
- Causes of shock in the cardiac surgical patient
- Definition and classification of shock
A systematic approach to this question would resemble this:
|Type of shock||Cause||Diagnostic strategy||Management|
|Artifact of measurement||Arterial blood pressure measurement is inaccurate||Compare with non-invasive measurement and physical examination||
|Cardiogenic||Post-operative stunning of the myocardium||TTE, ECG, cardiac output measurement by PiCCO or PA catheter||
|Myocardial infarction||TTE, ECG, cardiac enzymes||
|Obstructive||Cardiac tamponade||TTE, CVP trace||
|Massive pulmonary embolism||TTE, CVP trace, ECG, CTPA||
|Neurogenic||Infarction of spinal cord due to ischaemia or embolic events||Physical examination features, CT, MRI||
|Hypovolemic||Blood loss post operatively||Examination of drains, FBC,||
|Massive diuresis||Observation of fluid balance charts||
|Distributive||Vasoplegia||SVRI measurements by PiCCO||
|Anaphylaxis||Physical examination findings suggestive of angioedema||