As always assess and treat A & B first before moving on to circulation.

Look

Skin colour - blue / pale / flushed?

Skin appearance - mottled / clammy?

Listen

Low blood pressure or hypotension is a very common finding in patients who are acutely ill. Hypotension however is a relatively late sign in deterioration and so it is important that it is recognised and treated promptly. This chapter will discuss some of the common causes of hypotension, and how to assess and manage the hypotensive patient using the ABCDE approach.

What is blood pressure?

The main functions of circulation are to distribute blood around the body, delivering oxygen, nutrients and hormones to the cells, and to remove waste products. Blood pressure (BP) is the pressure exerted on the arterial walls by the volume of blood ejected from the heart.

The peak pressure is called systolic pressure and the minimum value is the diastolic pressure. The Mean Arterial Pressure (MAP) is the average pressure exerted by the cardiac cycle and is directly related to vital organ perfusion. The normal range of MAP is 70 – 105mmHg. For most patients a MAP of at least 70mmhg is needed to keep vital organs like the kidneys adequately perfused. Many elderly patients who are hypertensive will require a mean of 80 mmHg or more for adequate organ perfusion.

Fortunately automated blood pressure machines calculate and display MAP, although if you need to perform a manual blood pressure you can still calculate MAP using the equation below.

Although there are various definitions hypotension is most commonly defined as a systolic blood pressure of less than 100 mmHg or 90mmHg, but normal BP varies greatly among the population. Rather than relying solely on specific figures to define hypotension, where it is possible, it is a good idea to compare a previous blood pressure recording with the present value in order to determine “normal” pressures for that individual.

For example a patient may have had a systolic blood pressure of 160 mmHg for the previous few days. If their systolic blood pressure is now 115mmhg it is easy to consider this as still being 'normal', but it is significantly lower than what the patient is used to, and may not be high enough to adequately perfuse their organs.

Feel

Pulse - Rate, Volume, Rhythm

CRT - To obtain a capillary refill time, pressure is applied to the fingertip for 5 seconds (elevated above the level of the heart). The pressure is then released and the colour should return within 2 seconds. A prolonged time indicates poor peripheral circulation; the patient's fingers will feel cool and the most likely cause being due to hypovolaemia. Conversely, rapid capillary refill may indicate a hyperdynamic state, as seen in sepsis.

Temperature - Feel the patients temperature at the peripheries and gradual work your way up the limb noting any change in temperature or colour. Along with this you should also take a core temperature.

Shock is a generic term for any physiological state where there is inadequate delivery of oxygen to the tissues and organs. This can happen for a variety of reasons such as a 'pump problem' with the heart itself following a myocardial infarction, or an inflammatory / vasodilated state such as sepsis, or anaphylaxis. Shock states can still occur with a patient displaying a normal blood pressure, as the body will compensate initially to maintain it, but delivery of oxygen to the tissues can still be poor.

Don't assume a patient with a normal looking BP is not shocked.

Some patients with septic shock for example can have a normal blood pressure but they have high levels of lactate (an acid) in their blood showing that the tissues are not getting enough oxygen. Another example is patients who are bleeding, who do not begin to drop their blood pressure until they have lost around a third of their blood volume.

Types of shock:

• Hypovolaemic

• Cardiogenic

• Septic

• Neurogenic

• Anaphylactic

In many deteriorating patients with low blood pressure the cause is severe sepsis. Severe sepsis has a very high mortality but if treated promptly and aggressively survival can be greatly improved. It is very important, therefore, that you are able to recognise severe sepsis and treat it according to evidence based management guidelines.

Diagnosing severe sepsis

Sepsis = Infection (confirmed or suspected) with signs and symptoms of an infection also known as SIRS - systemic inflammatory response syndrome.

Sepsis is defined by the UK Sepsis Trust (2020) as "the body’s overwhelming and life-threatening response to infection that can lead to tissue damage, organ failure, and death. Medically, sepsis is the body's immune system overresponding to an infection".

Signs and symptoms of infection (SSI)

• Temperature > 38.3°c or < 36°c

• Heart rate > 90 beats per minute

• Respiratory rate > 20 breaths per minute

• White cell count < 4 g/L or > 12 g/L

• Altered mental status

• Hyperglycaemia (glucose > 6.6 mmol/L) unless diabetic

If the patient has 2 or more of these signs and a new infection then they are septic. Sepsis is a continuum so patients with sepsis alone may not be acutely ill. It becomes severe sepsis if there is also any evidence of organ dysfunction.

Signs of organ dysfunction

• Blood pressure < 90mmHg systolic or mean (MAP) < 65

• New or increased oxygen requirements to maintain SpO2 ≥ 92%

• Creatinine > 177 mmol/L or urine output < 0.5 ml/kg/hr for 2 hours

• Bilirubin > 34 micro mols/L

• Platelets < 100

• Lactate ≥ 2 mmol/L

• Coagulopathy INR > 1.5 or APPT > 60 s

Treating severe sepsis with the Sepsis 6

The Sepsis Six is six simple interventions that should be carried out in the first hour after diagnosis that can make a significant improvement to mortality.

• Fluid challenges

• Antibiotics

• Blood cultures prior to giving antibiotics

• Urinary catheter and hourly monitoring of urine output

• Measure Lactate and haemoglobin

• High flow Oxygen (15 L/min via reservoir mask)

Remember FABULO S(epsis)

For more detailed information see the Surviving Sepsis Campaign and UK Sepsis Trust for guidelines.

Following assessment of the circulatory system it maybe necessary to instigate treatment.

The majority of hypotensive patients require fluid; it is therefore appropriate to administer a fluid bolus.

To do this it will be necessary to establish venous access.

Many nurses are trained to cannulate, it may therefore be appropriate for the nurse to cannulate and take blood samples if there is going any delay in the doctor attending.

Blood samples

At the same time as cannulating the patient it is advisable to take routine bloods.

Consider:

• FBC

• Group and Save

• Clotting screen

• Full profile

• Blood Glucose

• Lactate

If you think the patient may be septic (signs of infection) then send blood cultures as well as the other routine blood tests.

Fluids

A fluid bolus is diagnostic. It will reveal if the patient is fluid responsive or not. If the patient responds to the fluid and blood pressure rises and pulse lowers this suggests the circulation needs filling up with more fluid. If there is no response at all to the fluid bolus this may mean that the circulation is already filled and further boluses are not indicated.

A fluid bolus can be delivered in a number of ways:

• Wide bore blood giving set and a pressure bag with the roller clamp opened fully on the giving set.

• A three way tap and a 50 ml syringe attached to the giving set allows fluid to be drawn from the bag of fluid into the syringe and then injected directly into the patient

• Via an infusion or volumetric pump set to 999 mls/hr

Video of fluid administration via giving set and pressure bag method.

Once a fluid bolus or fluid challenge has been given you should see a response right away if there is going to be one. Blood pressure and urine output should increase, capillary refill should shorten if it was prolonged and the patient should become more responsive if the cerebral perfusion was being affected. Do not wait for the fluid bolus / challenge to take effect, if it is going to work it will show an effect as soon as it is completed. If the blood pressure remains low contact the doctor to review the patient urgently. Further fluid bolus / challenges should be given up to 2 litres.

Continuous monitoring of RR, HR, BP, ECG, SpO2 and urine output is then required. If a myocardial cause for hypotension is suspected or the patient has a significant history of heart disease the doctor should auscultate the patient's chest after each bolus to look for signs of heart failure. Observe for signs of fluid overload developing in these patients such as a rising heart rate and respiratory rate and decreasing oxygen saturations in response to fluid boluses. See the algorithm below relating the fluid management (NICE 2017).

Failure to correct hypotension with repeated fluid bolus / challenges up to 2 Litres requires senior medical input as the patient may require further monitoring and treatment with drugs to help the heart muscle pump harder, or to vasoconstrict dilated blood vessels to improve BP.

The patient will usually need a Central Venous Catheter (CVC) line inserted to help diagnose the cause of hypotension and guide treatment. Transfer to an area where level 2 –3 care can be provided will be required. Liaise closely with the Critical Care Outreach Team or Hospital Out of Hours Team and keep them updated of the patient's condition.

What is a low urine output?

Historically a low urine output is defined by many doctors and nurses as less than 30 ml/hr and in practice it is usually only when urine output falls below this level that medical staff are informed. However, there are drawbacks to this because we all weigh a different amount, and we normally produce approximately 1 ml/kg/hr of urine.

Normal Urine Production requires 3 things:

1. Adequate blood supply ‘perfusion' to the kidneys:

This requires an adequate blood pressure. Mean blood pressure (MAP) needs to be at least 70mmHg to perfuse the kidney, although in the elderly hypertensive patient, the MAP will need to be higher than this, 80mHg or greater. The kidney is very sensitive to a reduction in perfusion or reduced oxygen levels. Normally about a quarter of the blood that the heart pumps round the body in a minute (cardiac output) goes to the kidney.

2. Normal functioning kidneys

3. No obstruction to urine flow

What happens if we don't recognise and respond to low urine output?

If a low urine output is allowed to persist, then acute kidney injury (AKI) can develop. Acute kidney injury (AKI) can be defined as an acute rise in blood urea and serum creatinine levels due to a sudden decline in the kidneys ability to filter waste products. This leads to fluid and electrolyte disorders, such as fluid overload, cardiac failure, metabolic acidosis, confusion and coma. Acute kidney injury can occur as an isolated problem, but it more commonly occurs secondary to a circulatory disturbance, for example, severe illness, sepsis, trauma or surgery. Acute kidney injury increases mortality and the length of hospital stay. NCEPOD (2009) carried out an independent enquiry into the care of all patients who die with an acute kidney injury to determine how we can best recognise, prevent and manage patients who have this experience this problem.

Acute kidney injury (AKI) is the sudden and (usually reversible) failure of the kidneys to excrete metabolic waste products.

There are 3 groups of causes:

1) Pre-renal:

Refers to inadequate perfusion of the kidneys which results usually from periods of low blood pressure or hypoxia. Pre renal is the most common cause of acute renal failure in patients admitted to ICU and HDU. If periods of poor perfusion from low blood pressure or hypoxia are prolonged this will eventually damage the tubules in the kidney causing a condition known as acute tubular necrosis or ATN for short. Once this occurs the kidneys will stop working for a few weeks or more and kidney function has to be supported by a kidney machine which mimics the filtration process that occurs normally in the glomeruli in the nephrons. The good news however is that pre renal failure secondary to low blood pressure is potentially reversible if recognised early and treated promptly.

2) Intrinsic Renal Failure:

Refers to damage caused to the kidney tissue from prolonged periods of low blood pressure or hypoxia (ATN) it can also occur due to damage resulting from diseases such as glomerulonephritis or pyelonephritis. Drugs can also damage the kidneys causing acute kidney injury. Think about the drugs you are giving and question the safety of giving them – drugs such as NSAIDs, some antibiotics such as gentamycin and media contrast used in some x-rays.

3) Post Renal Failure:

Refers to anything that obstructs the flow of urine. This may be caused by renal stones, a tumour outside of the renal tract pressing onto a ureter, or from a blocked catheter. Untreated these can lead to renal failure.

Recognising low urine output

The trend of decreasing urine output must be identified early to ensure timely intervention. Not all patients who deteriorate will have a urinary catheter in situ and if they do it may not have a urometer to allow hourly readings. Acutely ill patients, particularly those with low blood pressure will require close monitoring of their urine output with a urinary catheter that has an hourly urometer.

Treatment of a low urine output

1. Give high flow oxygen as the kidneys are very susceptible to hypoxia.

2. Take bloods for FBC, U&E, and Clotting. U&E will give important information about kidney function. Deteriorating kidney function will be shown by raised urea and creatinine, raised serum potassium and a low bicarbonate level. If a patient has a low urine output they need to be reviewed urgently by medical staff, and if they do not respond to treatment they need to be reviewed by a more senior doctor.

3. The next question to ask in a patient with a low urine output is ‘Is perfusion adequate?'

This means assessing the blood pressure to ensure it is adequate for the individual patient to perfuse their kidneys. Consider the patients normal BP, for example a BP of 115/ 67 may not cause concern, but in a patient who is normally hypertensive this may not produce adequate perfusion of the kidneys.

If perfusion is not adequate give fluid challenges of 250 – 500mls, up to a total of 2 litres if there is no response. Aim for a MAP of at least 70 mmHg or a systolic of > 100 mmHg (remember to consider the patients norm).

If a patient is anuric (there is no urine output or virtually none) rather than oliguric, then this could mean that there is a urinary tract obstruction, from a blocked urinary catheter for example. In an anuric patient exclude catheter blockage by performing a bladder washout (flushing the catheter under aseptic conditions using 50mls sterile normal saline). If the catheter is patent give fluid challenges if perfusion is inadequate. If urinary tract obstruction is suspected then once the patient is stable they may require further investigations such as an abdominal ultrasound scan.

4. Check the patient's prescription chart and ensure that drugs which are potentially damaging are reviewed.

For further guidance on the preventing, detecting and managing AKI, see National Institute for Health and Care Excellence (NICE) guidance (2019).

In acutely ill patients, especially those that have been transferred from critical care and who have been in hospital for a long period, it is often difficult to accurately assess fluid balance status. For example previous days charts may show a large negative balance which would support treatment with fluids, or they may show a large positive balance which in the presence of clinical signs of fluid overload (chest auscultation, raised jugular venous pressure (JVP), ankle oedema) may support treatment with Frusemide.

Frusemide should only be used where there are clear signs of fluid overload.

Such patients with low urine output may have some signs of fluid overload whilst actually lacking fluid in their circulation. Oedema and a positive fluid balance doesn't always mean there is too much fluid in the circulation. It can be the result of many factors, for example, a patient may have a low albumin which will cause oedema or they can have leaky capillaries which may cause fluid shifts. This group of complex patients need senior medical input and may require insertion of a Central Venous Catheter to help assess and guide treatment for low urine output.

• NCEPOD (2009) Adding insult to injury. NCEPOD, London

• NICE (2017) Intravenous fluid therapy in adults in hospital. NICE clinical guideline [CG174]. Retrieved from https://www.nice.org.uk/guidance/cg174/chapter/introduction

• NICE (2019) Acute kidney injury: prevention, detection and management. NICE Quality Standard No 148. Retrieved from https://www.nice.org.uk/guidance/ng148

• NICE (2019b) Hypertension in adults: diagnosis and management. NICE guideline [NG136]. Retrieved from https://www.nice.org.uk/guidance/ng136/chapter/Recommendations#measuring-blood-pressure

• UK Sepsis Trust (2020) About Sepsis. Retrieved from https://sepsistrust.org/about/about-sepsis/