|
Shock = Acute circulatory failure with inadequate or inappropriately distributed tissue perfusion resulting
in generalised cellular hypoxia
- Cardiogenic shock
- Pump failure often due to myocardial infarction
- Obstructive shock
- Mechanical impedance to ventricular outflow - pulmonary embolus, cardiac tamponade
- Hypovolaemic shock
- Loss of circulating blood volume - blood loss, burns, pancreatitis etc.
- Distributive shock
- Abnormalities of peripheral circulation - sepsis or anaphylaxis
Acute blood loss
- Haemoglobin and PCV remain normal for first 3-4 hours
- Plasma volume then expands and the haemoglobin and PCV fall
- Associated with increase in neutrophils and platelets
- Reticulocyte count increases on day 2 or 3
- Reaches maximum of 10-15% by day 8 to 10
- Without treatment haemoglobin begins to rise by day 7
Cardiovascular monitoring
The cardiovascular system can be monitored by measuring:
- Blood pressure
- Central venous pressure
- Pulmonary capillary wedge pressure
- Oesophageal doppler
- Assessment of tissue perfusion
- Core-peripheral temperature gradient
- Urine output
- Acid base status - arterial gases / arterial lactate
- Gastric tonometry
Cardiovascular support
- Need to achieve adequate cardiac output and tissue perfusion
- Aim for a mean arterial pressure of at least 80 mmHg
- For this to be achieved it requires:
- Preload optimisation with volume replacement
- Inotropic support
- Some patients require inotropes and vasopressors
- Others require inodilators to redistribute blood flow
- Choice of inotrope depends on actions on relative actions on sympathetic nervous system
Properties of commonly used inotropic and vasopressor agents
|
Beta-1 |
Beta-2 |
Alpha-1 |
Alpha-2 |
DA-1 |
DA-2 |
| Adrenaline |
|
|
|
|
|
|
| Low dose |
+ |
+ |
+ |
+ |
NA |
NA |
|
High dose
|
+++ |
+++ |
++++ |
+++ |
NA |
NA |
| Noradrenaline |
++ |
0 |
+++ |
+++ |
NA |
NA |
| Isoprenaline |
+++ |
+++ |
0 |
0 |
NA |
NA |
| Dopamine |
|
|
|
|
|
|
| Low dose |
+ |
0 |
+ |
+ |
++ |
+ |
| High dose |
+++ |
++ |
++ |
+ |
++ |
+ |
| Dopexamine |
+ |
+++ |
0 |
0 |
++ |
+ |
| Dobutamine |
++ |
+ |
+ |
? |
0 |
0 |
Inotropic support of shock states
Cardiogenic shock
- Patients have low cardiac output with high filling pressure and vascular resistance
- Dobutamine is an inotrope that reduces vascular resistance
- Inodilators such as dopexamine are also useful
- Pure vasodilators such as nitrates or nitroprusside may also be useful
Obstructive shock
- Inotropes may be useful to support myocardium until definitive treatment available
High output states
- In severe cases vasodilatation is resistant to vasoconstrictors
- Perfusion pressure can be restored with noradrenaline
- Dobutamine can be added to increase cardiac output
- Adrenaline aggravates splanchnic ischaemia
Bibliography
Barnard M J, Linter S P K. Acute circulatory support. Br Med J 1993; 307: 35-41.
Dellinger R P. Cardiovascular management of septic shock. Crit Care Med 2003;
31: 946-955
Hinds C J, Watson D. Circulatory support. Br Med J 1999; 318: 1749-1752. |