monitoring and interpreting medical investigations in icu

1. Monitoring and Interpreting
Medical Investigations in ICU
Hiba Anis
MPT 3rd Sem (Cardiopulmonary)
Jamia Millia Islamia

2. Monitoring
• Non Invasive
• Invasive

3. Non Invasive
• Commonly monitored parameters include
1. temperature,
2. heart rate,
3. blood pressure and
4. oxygen saturation.
5. Respiratory rate
• Displayed on a single monitor screen.
• Technical problems and artefacts can occur with the display of any of these parameters, so
the patient's clinical status must be checked before acting on a monitor display
abnormality.

4. Temperature
• monitored by means of
1. esophageal probe or
2. rectal probe
• This determines core temperature, which is usually at least 1°C higher than axillary
temperature
• Problems are rarely encountered with this method.
• The oesophageal temperature may be lower if the gases for respiratory support are
unwarmed
• the rectal probe may occasionally fall out without being noticed, leading to an
erroneously low temperature being displayed. A rectum full of faeces may also lead to
a lower temperature being recorded.

5. Heart rate
• measured from the electrocardiogram (ECG) trace.
• Artefacts are common.
• Interference, usually from patient movement may show the presence of a tachycardia
or arrhythmia
• Physiotherapy may also cause movement artefacts.
• On the ECG trace, large T waves may be interpreted as QRS complexes, leading to
the displayed heart rate being double the actual rate.
• Detached or dried-out electrodes will lead to asystole being displayed.

6. Blood pressure
• monitored with a pressure cuff around the upper arm.
• An oscillometric method is used to measure blood pressure, with automatic cuff
inflation and deflation.
• The accuracy of such systems is generally good, but the cuff needs to be applied
correctly and be of the appropriate size for the arm.
• The system also needs to be calibrated correctly against a mercury column.
• Non-invasive blood pressure monitoring is performed intermittently, but the interval
between readings may be as short as 1 minute.

7. Respiratory rate
• measured by making use of the changing impedance across the chest wall as it moves
with respiration.
• In systems which offer this parameter, the sensors are built into the ECG leads.
• The heart rate and other movements of the chest can cause overreading of respiratory
rate, while electrodes placed too far apart may not give a reading at all.
• Appropriate physiotherapy treatment (e.g. for lobar lung collapse) may reduce a rapid
respiratory rate, but it must be emphasized that an already tachypnoeic patient should
not be allowed to become exhausted during treatment as he may rapidly
decompensate. This may even necessitate emergency intubation..

8. Oxygen saturation
• measured by a pulse oximeter with a probe on a finger or ear lobe.
• There are two methods:
1. the functional method which measures the difference between oxyhaemoglobin and
deoxyhaemoglobin, and
2. the fractional method which measures all types of haemoglobin over a wide spectrum of light
absorption.
• The former method may record erroneously high saturations if there is a high concentration of
carboxyhaemoglobin (the combination of carbon monoxide and haemoglobin) in the blood, while the latter
method will be inaccurate if a light-emitting diode (LED) or ultraviolet light (including sunlight) is close to
the probe.
• Saturations are generally accurate between 100% and 80%, but may be inaccurate at lower levels.
• The saturation trace must be observed to correspond with the heart rate; if this is not so the reading may be
erroneous.
• and use of a sealed suction port (as used for fibreoptic bronchoscopy).

9. • Low saturations with either method may be due to poor peripheral perfusion, painted
or nicotine-stained fingernails, pierced ears, intravenous contrast medium, or injected
dyes.
• Hypoxaemia has been shown to occur both during and after chest physiotherapy
(Tyler 1982); awareness and careful monitoring are therefore important.
• A patient on a ventilator and on high inspired oxygen concentrations or positive end-
expiratory pressure may become dangerously hypoxaemic during tracheal suctioning.
• Strategies to limit this risk include preoxygenation

10. Invasive monitoring
• requires the use of an invasive catheter, inserted into an artery, a central vein, the
pulmonary artery or, in some neurosurgical centres, the extradural space (for intracranial
pressure (ICP) monitoring)
• Common invasively monitored parameters include
1. arterial blood pressure and
2. central venous pressure (CVP).
• Arterial cannulation allows continuous monitoring of blood pressure as well as easy
access for blood gas analysis.
• The radial artery on the non-dominant side is the most common site of insertion; other
sites include brachial, dorsalis pedis, and femoral arteries.
• The femoral artery is especially useful in states of shock, when peripheral pulses may be
impalpable. The catheter is usually inserted percutaneously, but may be introduced by
surgical cut-down.
• Complications of arterial cannulation are uncommon and include infection and, rarely,
thrombosis.

11. • Disconnection of the catheter from the line can easily occur with
movement of the patient; vigorous bleeding will follow and
exsanguination is a real risk.
• These lines should always therefore remain visible and care should be
taken when moving the patient.
• Should disconnection occur, reconnection should be quickly
performed; should displacement occur, firm pressure should be applied
to the bleeding site

12. Central Venous Pressure (CVP) measurement
• involves placement of a catheter into a central vein (generally the superior vena cava),
usually via the subclavian or internal jugular vein.
• The basilic, external jugular, and femoral veins may also be used for access
• the advantage of these sites is mat there is no risk of pneumothorax and that bleeding is
easier to control.
• Disadvantages of these routes include difficulty with accurate placement and a higher
incidence of thrombosis.
• The CVP represents the state of filling of the vasculature and heart, more specifically the
right side of the heart.
• If correctly interpreted, it can yield valuable diagnostic information and guide fluid
therapy.
• .

13. • The complications associated with all central venous catheters are; they include
vascular erosion, air embolism, bleeding, thrombosis, and infection
• Disconnection can occur with movement.
• Bleeding will occur if the end of the catheter is below the level of the heart while air
may be sucked into the system and air embolism may result if the end of the catheter
is above that level.
• Air embolism is a very serious event and can result in immediate collapse and death

14. Left atrial pressure measurement
• may be measured directly by means of a catheter inserted into the left atrium at the
time of cardiac surgery.
• The catheter is brought out through the chest wall and monitoring takes place in the
conventional way.
• All the above mentioned complications may occur; in addition, displacement may
occasionally result in pericardial tamponade.

15. Intracranial pressure monitoring
• may be performed in patients with head injuries, brain surgery,
intracranial and subarachnoid haemorrhage, and cerebral oedema from
other causes.
• Such monitoring may give an indication of a rise in ICP before it
becomes clinically evident, thus allowing therapeutic manoeuvres
(hyperventilation, mannitol, surgery) to be initiated before cerebral
damage occurs.

16. • The importance of ICP measurement is that it provides an estimate of cerebral perfusion
pressure (cerebral perfusion pressure = mean arterial pressure — ICP) which in turn relates
to cerebral blood flow (CBF).
• Raised ICP causes reduced CBF which leads to tissue hypoxia and acidosis, raised PCO2,
cerebral vasodilatation, and oedema, all of which cause a further rise in ICP.
• ICP may be measured by means of an extradural or subarachnoid bolt, an intraventicular
catheter (inserted through the skull into the lateral ventricle), or an epidural catheter.
• The former methods are the most widely used.
• The intraventricular catheter has the additional advantage of being able to drain
cerebrospinal fluid, thereby relieving raised ICP.
• All these methods are invasive and the potential complications are not insignificant, the
most serious being infection.

17. ECG Monitoring
• Monitors arrythmias or irregular heart rhythm
• the more common arrhythmias are
1. Sinus bradycardia: is a sinus rhythm below 60 beats /min.
• The common causes are drugs .
• Vagal stimuli from tracheal suctioning may also be implicated.
• Care with suctioning and generous preoxygenation may be necessary;
occasionally it is reassuring to have atropine drawn up and ready to inject.

18. • Sinus tachycardia: is a sinus rhythm above 100 beats/min.
• Pain and anxiety are common causes, but occasionally it may be precipitated by
haemodynamic instability or respiratory distress.
• Procedures should be carefully explained to the patient, and adequate analgesia
should be given before physiotherapy begins.
• Atrial fibrillation: It is a totally irregular rhythm that may reach a ventricular rate of
up to 200 beats/min and cause haemodynamic instability.
• It may be paroxysmal.
• The cause is usually multifactorial, but common precipitating factors include
hypokalaemia, hypoxaemia, dehydration or overhydration, ischaemic heart
disease, and cardiac surgery.

19. INTERPRETING MEDICAL
INVESTIGATIONS
• A number of blood and microbiological tests are regularly performed on patients
in hospital
• It is clearly vital to know the normal values for these tests, which abnormalities
are important and which are not, and how to respond to any abnormalities which
need treatment.
• Normal values depend on the test technique, the units in which the result is given,
and the local reference values
• The more commonly performed haematological, biochemical, and microbiological
tests are

20. Haematology
• Full blood count: Included in most analysers are the following
• Haemoglobin (Hb).
• is easy to measure (it can be measured in the ward with a Spencer haemoglobinometer)
and is an indirect measure of the number of RBCs in the circulation and, therefore, of the
total red cell mass.
• In states of dehydration or overhydration Hb may be falsely raised or lowered.
• A reduced red cell mass is referred to as ' anaemia', while an increased red cell mass is
known as 'polycythaemia' or 'erythrocytosis’.
• most commonly seen causes of anemia are acute or chronic blood loss, iron deficiency,
and chronic illness or inflammation.
• Polycythaemia may be primary (from a disorder of the bone marrow) or secondary (owing
to chronic hypoxaemic lung disease or cyanotic heart disease, renal carcinoma, cerebellar
haemangioblastoma, or uterine fibroids).

21. • Mean corpuscular volume (MCV).
• This is a measure of the size of the RBCs.
• A low MCV (small RBCs) is referred to as 'microcytosis': the most common
cause is iron deficiency.
• A high MCV is referred to as 'macrocytosis', and is most often caused by vitamin
B12 or folate deficiency.
• The MCV is useful in narrowing down th differential diagnosis of anaemia and
other blood disorders
• Mean corpuscular haemoglobin (MCH).
• This is calculated by dividing the Hb by the total red cell count It reflects the
amount of Hb in the RBCs.

22. • White cell count (WCC).
• Their major role is to defend the body against infection
• The neutrophils (the predominant type of leukocyte) perform the immediate
response to infection by phagocytosing offending organisms.
• Platelet count (Pit).
• They are part of the first-line reaction to a breach in the vascular endothelium.
• A reduction in the platelet count is known as 'thrombocytopenia' while an
increase is called ' thrombocytosis’.

23. • Differential count
• This looks primarily at the white cells in the blood, but at the same time the
morphology of the red blood cells and the platelets may be commented upon.
• The different cells are counted in a high power field and the numbers are given as
a percentage.
• Absolute numbers of cells will thus depend upon the total white cell count. The
differential count may be useful in diagnosis of specific infections or infiltrations,
allergic or parasitic disorders, and assessing immune status

24. • Clotting profile
• This is generally performed in a patient who is either bleeding or is at
high risk of developing a bleeding problem.
• Indices measured include
1. prothrombin time,
2. partial thromboplastin time (PTT),
3. platelets, fibrinogen, and fibrin degradation products (FDPs).

25. Biochemistry
• Arterial blood gases
• measure only pH, PO, and PC02 , and extrapolate from these values the
bicarbonate and oxygen saturation.
• In acidosis the pH is always low (normal pH is 7.36-7.44) and in alkalosis the
pH is always high

26. • Electrolytes
• Sodium and potassium are often measured as part of an automated biochemistry
run
• Hyponatremia has a variety of causes, but is more commonly caused by relative
excess of water than deficiency of sodium. This is often iatrogenic, following
excessive administration of hypotonic fluids.
• Hypernatremia is most often caused by water depletion. A true sodium excess is
uncommon and is always iatrogenic.
• Hypokalaemia, on the other hand, is potentially far more dangerous. It may
predispose to cardiac arrhythmias, especially if combined with hypoxaemia.
• Hyperkalemia may predispose to ventricular tachycardia and fibrillation.
• Physiotherapy treatment may have to be postponed until these abnormalities have
been corrected.

27. • Glucose
• This needs to be regularly monitored in diabetics and in all critically ill
patients.
• Blood glucose can easily be measured in the ward by means of reagent
strips.
• A very high blood glucose level is almost always caused by diabetes
mellitus or an intravenous infusion of high glucose content while a slightly
raised value may be caused by stress.
• The causes of a low blood glucose include starvation, liver failure (failure to
produce glucose), insulin therapy, or an insulin-secreting tumour

28. • Renal function tests
• These include urea and creatinine.
• Urea is formed mainly from protein breakdown and creatinine mainly from
muscle breakdown;
• there are obligatory amounts of both of these that need to be handled by the
kidneys daily.
• If formation increases or excretion decreases, serum levels will rise.
• Renal failure causes both urea and creatinine to rise, though often at different
rates.
• In hypovolemic or low cardiac output states, urea rises more than creatinine,
whilst in rhabdomyolysis (breakdown of skeletal muscle) creatinine rises
faster than urea.

29. • Liver function tests
• raised enzymes reflect damage to cells and raised bilirubin may reflect a
variety of abnormalities, not all of which actually occur in the liver.
• Enzymes such as lactate dehydrogenase (LDH) and aspartate aminotransferase
(AST) are not specific to liver tissue, and even when they are produced by
damaged liver cells give little clue to the underlying pathology.
• Gamma glutamyl transferase (GGT) and alanine aminotransferase (ALT) are
found in few other tissues, but again do not reflect causation.
• Alkaline phosphatase (ALP) is also not specific to liver cells, but that fraction
which comes from the liver is concentrated in bile ducts and, as such, gives a
clue to biliary disease or obstruction.

30. • Cardiac enzymes
• Cardiac enzyme estimations are performed to confirm myocardial damage,
usually caused by a myocardial infarct but occasionally caused by chest
trauma.
• There is a characteristic pattern of enzyme rise, with creatine kinase (CK)
rising first, followed by aspartate aminotransferase (AST) and then LDH.
• For more specificity, isoenzymes (specific fractions of the enzymes) of CK
and LDH may be measured.
• CK is also present in skeletal muscle, so the myocardial fraction is measured
to exclude skeletal muscle damage (from surgery, trauma)
• LD1 and LD2 fractions are specific for cardiac muscle or red blood cells (the
distinction is easily made clinically).

31. Thank you!