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Hypotension post-cardiac surgery
Acronym?
PROVED?
Pump, rhythm, obstruction, volume, (endocrine), distributive, ? = artefactual
Hypotension post-cardiac surgery
Possible sources of error/artefacts (7)
- examine the patient for pulses and check for symmetry
- transducer error: check transducer, zero, level, calibrate, NIBP
- damping of waveform: assess damping co-efficient, replace
- NIBP malfunction: check cuff (size, fit, connection)
- check inotrope infusions into patient
- Radial/ central arterial monitoring discrepancy with severe vasoconstriction
- Upper limb vascular disease (radial arterial line) or obstruction (e.g. dissection or aorto-occlusive disease: femoral arterial line)
Causes of hypovolaemia post cardiac-surgery
Two main categories?
Approach to each?
Bleeding
Check drains, dressings, CXR, give fluids/blood products, correct coagulopathy/temperature
Diuresis
Check urine output and sodium
Give fluids
Approach to haemodynamic instability post-op
Four categories
Heart rate & rhythm
Preload
Afterload
Contractility
Causes of heart rate/rhythm issues leading to hypotension
(2 categories, 2+3 examples)
Tachydysrhythmia
- Pacing malfunction
- Electrolyte imbalance
Bradydysrhythmia
- Pacing malfunction
- Electrolyte imbalance
- Ischaemia
Causes of altered preload leading to hypovolaemia
4 categories
3,2,1,2examples
Hypovolaemia
- Bleeding
- Diuresis (esp post bypass)
- Rewarming/vasodilator therapy
Increased intrathoracic pressure
- Excessive PEEP
- Pneumothorax
Increased intra-pericardial pressure
- Tamponade
RV failure
- Contractility
- Increased RV afterload
Causes of altered afterload leading to hypovolaemia
3 categories
3,4,4 examples
Increased LV afterload
- Aortic valve dysfunction
- Excessive vasoconstrictor therapy
- Dynamic outflow tract or mid-cavity obstruction
Decreased LV afterload
- SIRS
- Post CPB vasoplegia
- Anaphylaxis
- Excessive vasodilator therapy
Increased RV afterload
- Acidosis
- Hypoxia
- Excessive PEEP
- Thromboembolism
Causes of altered contractility leading to hypotension post-op
3 categories
2, 1, 1 examples
Ischaemia
- Acute graft dysfunction
- Air embolus (particularly RCA)
Inadequate myocardial protection on CPB
- Inadequate cardioplegia or ventricular dilatation
Pre-existing ventricular dysfunction
Initial priorities following handover
10 categories
Aims for each category
Tasks for each category
Ventilation
Aim: Ensure initial settings adequate
Tasks
- Check PIP waveforms + patient ventilator synchony
- Check ETT size and position at teeth
Monitor
Aim: Display all relevant information
Tasks
- Zero all pressure
- Ensure correct channel display
- Set up cardiac output monitor
Examination
Aim: Rapid assessment
Tasks
- Pupils, GCS, Temp, Peripheral perfusion, Neck veins, Breath sounds, Heart sounds, Mediastinal/pleural drain outputs, Urine output
Infusions
- Check infusion pumps, check volume remaining
Investigations
- Blood gas, Formal bloods, CXR
Fluids and electrolytes
- Chart fluid bolus
Drugs
- Antiemetics/analgesia
- Electrolyte replacemnt
Pacing
Glucose
Documentation
Main cardiovascular complications of cardiac surgery (6)
- Cardiac tamponade
- Low CO/organ dysfunction
- Periperative MI
- Arrhythmias
- Stroke
- Peripheral/mesenteric ischaemia
Cardiac tamponade
Frequency
Signs (7)
Prevention (3)
Treatment (3)
0.5–6% of the patients within the first 24–48 postoperative hours
Hypotension, tachycardia, elevated CVP, reduced UO, pulsus paradoxus, dyspnoea, mental confusion
Administer prophylactic drugs to reduce bleeding risk/haemostasis, frequent suction of chest drains
Evacuation of pericardial space via pericardiocentesis or re-sternotomy, fluids, vasopressors
Most common mechanism of acute LV dysfunction (3)
What is myocardial stunning? Frequency? Treatment?
The most common mechanisms of the acute LV systolic dysfunction are myocardial ischaemia, acute myocardial infarction (AMI), and myocardial stunning.
Myocardial stunning occurs in about 45% of the patients undergoing elective cardiac surgery. It is represented by viable myocardium that has suffered from prolonged coronary hypoperfusion
during heart surgery. Therefore, the causal mechanism of stunning is the ischaemic reperfusion injury. The systolic dysfunction correlated with myocardial stunning is generally transient and responsive to positive inotropes with a complete recovery of the heart function in the early postoperative hours
Which risk model is used to calculate risk of death following a heart operation?
EuroSCORE II
What are the benefits of cardioplegia?
What are the effects of temperature of cardioplegic solutions?
What are the two main types of solution?
What are the two main types of delivery?
Hypothermic cardioplegia is commonly employed
in cardiac surgery to provide heart standstill. It reduces myocardial oxygen demand and it reverses the ischaemic injury-carrying oxygen and metabolic substrates.
Hypothermic marginally reduces MvO2 but increases plasma viscosity and activates cold agglutinins. No difference in adverse effects between warm and cold but better recovery after warm.
Blood vs crystalloid solutions. Blood may be better but no mortality benefit.
Can be delivered antegrade (through aortic root/coronary ostia) and retrograde (through coronary sinus).
