Circulatory shock and IV fluid therapy Flashcards
Define shock
A clinical syndrome characterised by inadequate organ perfusion and tissue oxygenation due to an imbalance between oxygen delivery and tissue oxygen demand.
what is the normal physiology of tissue perfusion
Tissue perfusion is determined by the mean arterial pressure which means when blood pressure drops, hypoperfusion occurs
Mean arterial pressure = systemic vascular resistance x cardiac output
Cardiac output = heart rate x stroke volume
Stroke volume = end diastolic volume - end systolic volume
This depends on preload (ventricular filling), contractility and afterload (load against which the heart is working
what are the causes of shock
Cardiogenic shock - this is when there is failure of the ventricular pump so the problem is with the heart itself. Eg. MI, acute valve dysfunction, arrhythmia etc. this causes stroke volume to decrease which decreases cardiac output
Obstructive/mechanical shock - impaired ventricular filling or obstruction of the outflow tract eg. Pulmonary embolism or cardiac tamponade. This decreases stroke volume which decreases cardiac output
Distributive shock - reduced systemic vascular resistance with normal cardiac function eg. Sepsis, anaphylaxis, spinal trauma causing widespread vasodilation
Hypovolaemic shock- loss of circulating volume with normal cardiac function eg. Trauma, GI bleed, pancreatitis, burns, severe diarrhoea and vomiting. This decreases teh preload which therefore reduced stroke volume and cardiac output
It is possible for a patient to have more than one type of stroke at any point
what are the consequences of reduced tissue perfusion
Cell hypoxia Cells switch to anaerobic metabolism Accumulation of lactic acid Metabolic acidosis Cell membrane ion pump dysfunction Influx of sodium and water into cells Intracellular oedema Cell death and tissue damage
what compensatory mechanisms occur in shock?
Increasing cardiac output - stimulation of sympathetic nervous system to increase HR, SV and vascular resistance
Redistributing blood circulating to vital organs - vasoconstriction occurs and ADH and renin is released to reduce urine production
Increased oxygen delivery to cells - stimulation of the sympathetic nervous system to cause bronchoilation, increased respiration and tidal volume
Release of cortisol
Release of glucagon
Activation of complement and inflammatory cascade
what do you need to remember when taking a history from a patient in shock
Always have a high suspicion of shock in an acutely I’ll patient as no one sign or symptom is diagnostic
The aim of the history is to determine whether or not the patient is shocked and what the underlying cause is
It may not always be possible to take a history from an acutely unwell patient so remember to check the records and look at pre-existing conditions
Always measure vital signs
Follow ABCDE assesssment
Look out for mottling and cold peripheries (accept in septic shock which will have warm peripheries and a bounding pulse)
There are specific signs for each cause of shock
- cardiogenic - radioed JVP, pulmonary oedema, murmurs, arrhythmias
- obstructive - raised JVP, muffled heart sounds in cardiac tamponade, pulses paradoxes
- hypovolaemic - signs of bleeding, pulsation abdominal mass in AAA
- distributive - septic with have war peripheries, pyrexia/ hypothermia whereas anaphylactic will have bronchospasm, angioedema and rash
what investigations should be done in shock?
Blood
- FBC - infection markers, anaemia in bleeding
- clotting profile - bleeding, complications in liver
- renal function - perfusion injury to kidneys
- LFTs - perfusion injury to liber
- amylase - perfusion injury to pancreas - toxicology - shock may be caused by drugs
- group and save / cross match - may need to have transfusion
ABG - metabolic acidosis due to anaerobic metabolism casing increase in lactic acid, increased lactate, use serial ABGs to check progression
ECG - pulmonary embolism, cardiac tamponade, mi
CXR - infection, pulmonary oedema, cardiac tamponade
Echocardiogram - valvular lesions, pulmonary embolism , hypovolaemia
There are many more investigations which may be done depending on what you suspect the cause it
how is shock managed?
Prompt assessment and intervention is vital
Assess through ABCDE assessment
Further management
- make sure the patient is in an appropriate environment such as ITU so they can be closely monitored
- treat the cause
- do not forget analgesia
- may need organ support on iTU
how much fluid is in the average human and where is it found?
The average 70kg human has 42L total body water
This is mainly found within the cells as intracellular fluid
The remaining ⅓ is extracellular fluid
- Blood: 2L red blood cells and 3L plasma
- 8L of interstitial fluid - between blood vasculature and cells
- Transcellular fluid: CSF, Aqueous humour, Synovial fluid
what is the difference between intracellular and extracellular fluid
Normal body osmolality is 285mosmol/kg which is similar in both intracellular and extracellular fluid. The main difference is the predominant cation
Extracellular - sodium
Extracellular - potassium
what are the 2 types of IV fluid that can be given?
crystalloid fluids
large molecules in isotonic fluid
what is crystalloid fluid?
give some examples of crystalloid fluids
crystalloid fluid - these are small molecules dissolved in water which quickly redistribute throughout the fluid components. These are used to replace fluid eg. in shock and also for maintenance of body fluids. There are also special circumstances such as traumatic brain injury and metabolic acidosis secondary to renal failure.
examples
- Dextrose - glucose dissolved in water - the glucose is taken up by the cells which leaves behind pure water which is distributed evenly throughout total body water (⅔ intracellular and ⅓ extracellular)
- Saline - sodium and chloride ions dissolved in water. the sodium content is similar to that of the extracellular fluid - sodium distributes between interstitial fluid and plasma in a 3:1 ratio due to their volume - can result in hyperchloremic acidosis
- Hartmanns - similar make up to plasma - most ends up in extracellular space - lactate is taken up and metabolised by the cells
what is large molecules in isotonic solution?
give some examples
large molecules in isotonic fluid - molecules with a molecular weight of over 30,000 - used to quickly fill the intravascular space so are used in massive haemorrhage. Associated with kidney dysfunction and mortality.
examples
- Gelafusion
- Hydroxyethyl starch - can be used in critically ill, - sepsis or burns
- There is also blood. Blood is the most physiological fluid that can be given and is given in components (white cells taken out). This remains predominantly in intravascular space
Red cells - most common - red blood cells suspended in saline, adenine, glucose and mannitol
Platelets
Fresh frozen plasma
Albumin
Cryoprecipitate
what are the stages of haemorrhagic shock?
- Looses up to 15% of total blood - start of increased heart rate
- 15-30% - Increased heart rate
- 30-40% - heart rate increases further and blood pressure decreases as vasodilation can no longer compensate
- More than 40% - further heart rate increase and blood pressure decrease
what can you use to assess fluid status?
History and clinical situation Thirst Vital signs - HR, BPM RR, alertness Urine output Skin turgor Capillary refill Mucous membranes JVP Lung fields Oedema Daily weights
