MONITORING OF CRITICALLY ILL PATIENT

INTRODUCTION

• "Repeated or continuous observations or measurements of the patient, his or her physiological function, and the function of life support equipment, for the purpose of guiding management decisions, including when to make therapeutic interventions, and assessment of those interventions".
• A patient monitor may not only alert caregivers to potentially life-threatening events; many provide physiologic input data used to control directly connected life-support devices.

CATEGORIES OF PATIENTS WHO NEED MONITORING

There are at least four categories of patients who need physiologic monitoring:

• Patients with unstable physiologic regulatory systems; for example, a patient whose respiratory system is suppressed by a drug overdose or anesthesia.
• Patients with a suspected life-threatening condition; for example, a patient who has findings indicating an acute myocardial infarction (heart attack).
• Patients at high risk of developing a life-threatening condition; for example, patients immediately post open-heart surgery, or a premature infant whose heart and lungs are not fully developed.
• Patients in a critical physiological state; for example, patients with multiple trauma or septic shock.

CARDIOVASCULAR MONITORING

• Cardiovascular monitoring include –
  • Continuous cardiac monitoring
  • 12-Lead ECG

Continuous cardiac monitoring

• Minimum standard for an ICU is availability of facilities for cardiovascular monitoring.
• Continuous cardiac monitoring allows for rapid assessment and constant evaluation.
• It is now common practice for five leads. The five electrodes are placed as follows:
  • Right and left arm electrodes—placed on each shoulder;
  • Right and left leg electrodes—placed on the hips or level with the lowest ribs on the chest;
  • V-lead views can be monitored—for V₁ place the electrode at the 4th intercostal space, right of the sternum; for V₆ place the electrode at the 5th intercostal space, left mid-axillary line.
  • The monitoring lead of choice is determined by the patient's clinical situation.

12-Lead ECG

• The Dutch physiologist Einthoven was one of the first to represent heart electrical conduction as two charged electrodes, one positive and one negative.
• The body can be likened to a triangle, with the heart at its centre, and this has been called Einthoven's triangle.
• ECG Leads - The 12-lead ECG consists of six limb leads and six chest leads.
  Limb Leads
  • The limb leads examine electrical activity along a vertical plane. The standard bipolar limb leads (I, II, III) record differences in potential between two limbs.
    • I = right arm–left arm (positive);
    • II = right arm–left leg (positive);
    • III = left arm–left leg (positive).
  • The three augmented unipolar limb leads (aVR, aVL, aVF) record activity between one limb and the other two limbs to increase the size of the potentials.
  Chest Leads (Precordial Leads)
  • The six unipolar chest leads (precordial leads) are designated V1–6 and examine electrical activity along a horizontal plane from the right ventricle, septum, left ventricle and the left atrium. They are positioned in the following way
    • V1 = 4^th intercostal space, to the right of the patient's sternum;
    • V2 = 4^th intercostal space, to the left of the patient's sternum;
    • V3 = equidistant between V2 and V4;
    • V4 = 5^th intercostal space on the midclavicular line;
    • V5 = 5^th intercostal space, anterior axillary line;
    • V6 = 5^th intercostal space on the mid-axillary line.

ECG Paper

• Amplitude (voltage) in the ECG is measured by a series of horizontal lines on the ECG. Each line is 1 mm apart and represents 0.1 mV.
• Duration of activity within the ECG is measured by a series of vertical lines. Each line is 1 mm apart and represents 0.04 sec.

ECG Waves And Intervals

• P wave: sequential depolarization of the right and left atria (P=0.08-0.1 Sec. 2-3 mm in amplitude)
• PR interval: time interval from onset of atrial depolarization (P wave) to onset of ventricular muscle depolarization (QRS complex) =0.12-0.2 sec
• QRS complex: right and left ventricular depolarization (Amplitude as high as 25 mm, duration (width of the QRS complex) with Normal Conduction 0.08 – 0.11 sec.)
• ST-segment: Time between completion of depolarization and onset of repolarization (Point where ST takes off from QRS= J point)
• T wave: ventricular repolarization
• QT interval: duration of ventricular depolarization and repolarization = 0.35 – 0.45 sec.
• U wave: origin of this wave is still being debated!
• PP interval: rate of atrial or sinus cycle
• RR interval: rate of ventricular cycle

ECG Interpretation

• Heart rate:- Count the R waves on a 6 sec strip and multiply by 10 to calculate the rate.
• Rhythm (regularity) — To assess regularity, The R-R interval should not differ by more than 0.12 sec.
• Atrial activity — Observe for the presence or absence of P waves.
• AV node activity: — The duration of the P-R interval
• Ventricular activity: — Measure the QRS interval And Q wave (if present) = less than 0.04 sec.
• General notable aspects of ECG -
  • Observe whether the isoelectric line is present between the S and T waves.
  • Examine the T wave to see whether it is positive, and less than 0.16 sec.
  • Examine the duration of the Q-T interval.
• Heart Rate
  • Heart rate is a nonspecific parameter. It is usually measured by auscultation of the heart and palpation of an artery, automatically taken from an ECG or arterial pulse pressure wave.
  • Increase in heart rate (tachycardia) may be caused by hypovolemia (the tachycardia is a compensatory mechanism), fever, excitement, exercise and pain. Tachycardia is generally defined as a heart rate greater than 160 beats per minutes (bpm).
  • Decrease in heart rate (bradycardia) may be caused by high vagal tone, severe electrolyte disturbances and atrioventricular conduction blocks. Bradycardia is generally defined as a heart rate less than 60 bpm.
• Heart Rhythm
  • When irregularities in heart sounds are heard, the heart rate should be compared to pulse rate and the difference in rates are called pulse deficits. Pulse deficits are indicative of arrhythmias. Hypoxia, myocardial contusions and metabolic or acid base imbalance may cause arrhythmias.
  • Some examples of cardiac arrhythmias include- premature atrial contraction (PAC), atrial fibrillation, premature ventricular contraction (PVC) and ventricular tachycardia. All pulse abnormalities should be confirmed by a electrocardiogram (ECG).

HAEMODYNAMIC MONITORING

• The reasons for haemodynamic monitoring are -
  • To establish a precise health-related diagnosis;
  • To determine appropriate therapy; and
  • To monitor the response to that therapy.
• Hemodynamic monitoring can be –
  • Non-Invasive
  • Invasive

Non-invasive Monitoring

• Non-invasive monitoring does not require any device to be inserted into the body and therefore does not breach the skin.
• Directly measured non-invasive variables include –
  • Body Temperature,
  • Heart Rate,
  • Blood Pressure,
  • Respiratory Rate,
  • Urine Output,
  • Transcutaneous pulse oximetry and
  • Expired carbon monoxide monitors.

Invasive Monitoring

• Invasive monitoring requires the vascular system to be cannulated and pressure or flow within the circulation interpreted.
• Invasive haemodynamic monitoring technology includes:
  • Systemic arterial pressure monitoring;
  • Central venous pressure;
  • Pulmonary artery pressure; and
  • Cardiac output (Thermodilution).

Blood Pressure Monitoring

• Blood Pressure
  • Normal B.P. 18 + age = 100-120/60-80 mm Hg,
  • prehypertension = 120-139 /80- 90 mm Hg
  • Hypertension = >140/90 mm Hg
  • Hypotension = < 90/60 mm Hg
• Systemic arterial blood pressure can be measured by-
  • Indirectly or non-invasive
  • Directly or invasive
• Non-Invasive Blood Pressure Monitoring –
  • NIBP monitoring by the use of manual or electronic sphygmomanometer.
• Invasive Intra-Arterial Pressure Monitoring –
  • Arterial pressure recording is indicated when precise and continuous monitoring is required, such as in periods of instability of cardiac output and blood pressure.
  • Arterial cannula is placed in the artery. Most common site Radial Artery and other sites are The Brachial, Femoral, Dorsalis Pedis and Axillary Arteries.
  • Three main factor s are monitored –
    • Preload - preload is the filling pressure in the ventricles at the end of diastole. It is monitored by the - Central venous pressure (CVP) monitoring; Pulmonary artery pressure (PAP) monitoring; Pulmonary capillary wedge pressure (PCWP) monitoring; Left atrial pressure (LAP) monitoring.
    • Afterload - afterload is the pressure that the ventricle produces to overcome the resistance to ejection generated in the systematic or pulmonary circulation by the arteries and arterioles.
      It is calculated by cardiac output studies: left heart afterload is reflected as systemic vascular resistance (SVR), and right heart afterload is reflected as pulmonary vascular resistance (PVR)
      • Systemic vascular resistance is a measure of resistance or impediment of the systemic vascular bed to blood flow.
      • Pulmonary vascular resistance is a measure of resistance or the impediment of the pulmonary vascular bed to blood flow.
    • Contractility - Contractility reflects the force of myocardial contraction, and is related to the extent of myocardial fiber stretch (preload) and wall tension (afterload).
      It is important because it influences myocardial oxygen consumption.
      Contractility of the left side of the heart is measured by calculating the left ventricular stroke work index (LVSWI), and right side by Right ventricular stroke work index (RVSWI) can be similarly calculated.
      Contractility can decrease as a result of excessive preload or afterload, drugs such as negative inotropes, myocardial damage such as that occurring after MI, and changes in the cellular environment arising from acidosis, hypoxia or electrolyte imbalances.
      Increases in contractility arise from drugs such as positive inotropes.

Central venous pressure

• Preload in the right ventricle is generally measured as CVP.
• Monitoring of central venous pressure by the insertion of central venous catheter in central vain of body.
• Central venous catheters are inserted to facilitate the monitoring of CVP, as well as facilitating the administration of large amounts of IV fluid or blood; providing long-term access for fluids, drugs, specimen collection; and/or parenteral feeding.
• Normal value of CVP is – 0 to +8 mm of Hg 'OR' 0 to +10 Cm H2O.
• A CVP less than 0 may be due to vasodilatation (increased volume capacitance) or hypovolemia. A CVP in a normal range but in the face of signs consistent with vasoconstriction may be due to hypovolemia.
• A CVP greater than 10 may be due to the heart's inability to function as a pump or fluid over-load, vasoconstriction (decreased volume capacitance), pericardial effusion and positive pressure ventilation.
• locations can be used for central venous access
  • The commonest sites in critically ill patients are –
    • Subclavian Vein Approaches
    • Internal Jugular Vein Approaches
  • Other less common sites are -
    • The antecubital Vein (may be used when the patient can't be positioned supine),
    • The femoral vein (associated with high infection risk),
    • The external jugular vein (the high incidence of anomalous anatomy).

Pulmonary Artery Pressure (PAP)

• It began in the 1970s, led by Dr's Swan, Ganz and colleagues
• PAP is monitored by using a pulmonary artery catheter (PAC)
• Pulmonary artery cauterization facilitates assessment of -
  • The preload or filling pressure of the left ventricle through the pulmonary artery wedge (occlusion) pressure.
  • By using a thermodilution PAC - cardiac output (CO) and other haemodynamic measurements can also be calculated.
• Complications of PACs,
  • all the complications of central lines
  • additionally associated with -
    • Higher incidence of dysrhythmia (particularly due to cold bolus injected, which irritates myocardium),
    • valve damage,
    • pulmonary vascular occlusion,
    • emboli/infarction (reported incidence of 0.1%–5.6%) and,
    • knotting of the catheter (very rarely).
• PAP monitoring is indicated for adults in severe hypovolaemic or cardiogenic shock, where there may be diagnostic uncertainty, or where the patient is unresponsive to initial therapy.
• The PAP is used to guide administration of fluid, inotropes and vasopressors.
• PAP monitoring may also be utilised in other cases of haemodynamic instability when
• diagnosis is unclear.
• It may be helpful when clinicians want to differentiate hypovolaemic from cardiogenic shock or, in cases of pulmonary oedema, to differentiate cardiogenic from non-cardiogenic origins.
• It has been used to guide haemodynamic support in a number of disease states such as shock, and to assist in assessing the effects of fluid management therapy.

Pulmonary Capillary Wedge Pressure

• Also known as Pulmonary artery occlusion pressure (PAOP),
• Measured by the pulmonary artery catheter balloon is inflated with 1–1.5 mL air
• The inflated balloon isolates the distal measuring lumen from the pulmonary arterial pressures, and measures pressures in the capillaries of the pulmonary venous system, and indirectly the left atrial pressure.
• Complication including all PAC completion associated with- Risk of air embolism and distal pulmonary vasculature ischemia and infarction.

Left Atrial Pressure Monitoring

• Left atrial pressure monitoring directly estimates left heart preload
• It requires an open thorax to enable direct cannulation of the atrium
• It is used only in the postoperative cardiac surgical setting

Respiratory Monitoring

• Respiratory insufficiency is one of the main reasons for admission to a critical care unit, as either a potential or actual problem, so comprehensive respiratory monitoring is essential.
• The respiratory monitoring include –
  • Pulse oximetry
  • Arterial Blood Gases Analysis
  • Ventilation monitoring

Pulse oximetry

• To assess the efficiency of the patient's gas transfer mechanisms
• Pulse oximetry is a non-invasive device that measures peripheral (capillary) saturation of haemoglobin by oxygen along with the heart rate.
• It works by using select wavelengths of infrared light absorption by blood. Well-oxygenated blood absorbs light differently from deoxygenated blood, with the oximeter determining the amount of light absorbed by the vascular bed and calculating the saturation of oxygen in those capillaries (SpO2).
• Normal SpO2 is greater than 97%.
• The probes used to emit the infrared light source can be sited on a finger, toe or ear.
• Pulse oximetry alone, does not provide all the information needed on ventilation status and acid–base balance. It is important that when SpO2 appears to be abnormal, the arterial blood is sampled and gases are checked. Therefore, arterial blood gases are also needed periodically to assess other parameters.
• Other limitations arise with oximetry monitoring:
  • Peripheral vasoconstriction results in poor perfusion, causing poor flow and less accurate signals.
  • Cardiac dysrhythmias can impair perfusion and flow.
  • Shivering and other movements may give poor or inaccurate readings.
  • The presence of high levels of bilirubin, dark skin and nail varnish may cause underestimation of SpO2, as light is absorbed in these circumstances.
  • External light can overestimate SpO2, especially fluorescent light and heat lamps; ear probes in particular may detect overhead lighting.
  • Dyshaemoglobins such as carboxyhaemoglobin levels above 3% cause overreading, making SpO2 monitoring unreliable.
  • When hypercapnia is present (e.g. in patients with COPD), SpO2 monitoring alone is unreliable.

Arterial Blood Gases Analysis

• Arterial blood gases (ABGs) are one of the most commonly performed laboratory tests in ICUs and other critical care areas.
• ABG measurements are essential for assessing oxygenation/gas exchange and ventilation.
• ABGs are measured to determine the status of the acid–base balance and oxygenation, and include measurement of the PaO₂, PaCO₂, acidity (pH) and bicarbonate (HCO₃^-).
• Blood for ABG analysis is sampled by arterial puncture or from an arterial catheter in the radial or femoral artery.
• Continuous blood gas monitoring is possible if a fibreoptic sensor or an oxygen electrode is inserted into the arterial catheter system. The advantage of the arterial catheter is that it facilitates ABG sampling without repeated arterial punctures.

Measurements	Description	Normal Value
Temperature (T)	Default setting is 37°C. No consensus on analysis according to patient temperature. Consistency of greater importance.	37°C
Haemoglobin (Hb)	Samples need to be fully mixed so should be constantly agitated until analysed.	Females 115–165 g/L Males: 130–180 g/L
Acid–base status (pH)	Overall acidity or alkalinity of blood.	7.36–7.44
Carbon dioxide (PaCO2)	Partial pressure of arterial CO2.	4.5–6.0 kPa 35–45 mmHg
Oxygen (PaO2)	Partial pressure of arterial oxygen.	11–13.5 kPa 80–100 mmHg (varies with age)
Bicarbonate (HCO3 )	Standard bicarbonate is usually used to assess metabolic function; this is calculated by removing the respiratory component from the HCO3 .	22–32 mmol/L
Base excess (BE)	The number of molecules of acid or base that are needed to return 1 litre of blood to the normal pH (7.4): it measures acid–base balance. As with HCO3 , standard BE is more useful for accurate assessment of metabolic components.	3 to +3 mmol/L
Saturation (SaO2)	Haemoglobin saturation by oxygen in arterial blood.	>94%

Ventilation Monitoring

• Mechanical ventilation is a common intervention used in ICUs for patients with respiratory failure or who require respiratory support.
• The recent major advances in ventilation technology use as ventilation monitor and display these readings in integrated graphic displays as waveforms.

Neurological Monitoring

• Neurological Monitoring in critical care units including –
  • Neurological observation
  • Cerebral function monitoring
  • Intracranial pressure monitoring

Neurological observation

It includes -

• Consciousness
• Glasgow Coma Scale
• Pupillary Assessment
• Limb Movement

• Consciousness
  • Consciousness is the most sensitive indicator of neurological change and is usually the first to be noted in neurological signs
  • A state of general awareness of oneself & the environment, including the ability to orientate towards new stimuli (Hickey, 2003)
  • Level of Consciousness
    • There are three properties of consciousness which can be individually affected by the disease process. These are:
      • Arousal or wakefulness (i.e. eyes open to command)
      • Alertness and awareness (i.e. orientation and communication)
      • Appropriate voluntary motor activity (i.e. obeying commands)
• Common methods of assessing conscious level are:
  • AVPU
  • Glasgow Coma Scale (GCS)
  Note: Both are potential tools for assessing the conscious level, and either can be used in the Early Warning Score
• AVPU

A – Alert	Responds spontaneously
V – Verbal	Responds to voice
P – Pain	Responds to pain stimuli
U - Unresponsive	No response to verbal or pain stimuli

• Glasgow Coma Scale (GCS)
  • The GCS Is a simple & standardised system to detect changes in level of consciousness. It should be quick, easy, objective & accurate
  • The GCS was originally devised in 1974 by Teasdale and Jennett to establish the prognosis of a patient with a brain injury.
  • In 2003, the UK National Institute for Clinical Excellence stipulated the use of the GCS for assessment and classification of all head-injured patients.
  • The GCS includes scoring of separate subscales related to eye opening, verbal response and motor response.

• An example of the Glasgow Coma Scale (G.C.S.)
• Below are some GCS chart wording variations:
• Head injuries can be classified into three categories according to GCS scores: minor, moderate, and severe.
  

  	Head injury classification
  	Severe head injury	GCS score of 8 or less
  	Moderate head injury	GCS score of 9–12
  	Minor head injury	GCS score of 13–15

  
  

• Pupillary Assessment
• Pupil size
  • Normal pupils are round and equal in size, with an average size of 2–5 mm in diameter.
  • Pupil size scale on the neurological observation chart
  
• Reaction to light
  • The immediate constriction of the pupil when light is shone into the eye is referred to as the direct light reflex.
  • Withdrawal of the light should produce an immediate and brisk dilation of the pupil. Introduction of the light into one eye should cause a similar constriction to occur in the other pupil (consensual light reaction).
  
• Pupil Documentation
  • Pupil size should be recorded before proceeding to test pupil response to direct light.
  • + is used to indicate a brisk response
  • - is used to indicate no response
  • SL is used to indicate a 'sluggish' response
  • C is used to indicate closed eyes due to periorbital oedema.
• Torch position for testing light reflex
  • Approach from the side. Do not move in from directly in front.
  
• Limb Movement
• In this section you are assessing all limbs as opposed to the best response in a limb, as in the GCS section.
• It is a combination of active and active resisted movements.

Cerebral Function Monitoring

• The electroencephalogram has been used for the assessment of neurological function by recording electrical signals emitted from the brain, particularly those impulses from the surface of the brain that reflect the current awareness state (e.g. awake, asleep or sedated). Waves produced by the electrical impulses are displayed on a monitor and can then be interpreted by examining the frequency and morphology of each wave or series of waves.
• Use of continuous EEG monitoring to assess and monitor a patient with brain injury or acute ischemia enables prevention of further complications.

Intracranial Pressure Monitoring

• The primary goals of intracranial pressure (ICP) monitoring are identification of intracranial pressure trends and evaluation of therapeutic interventions in order to minimize ischemic injury in the brain-injured patient.
• Normal ICP is between 0 and 15 mm Hg.
• Intracranial pressure (ICP) monitoring is commonly used in patients with -
  • Severe traumatic brain injury
  • Intracranial hemorrhage
  • Cerebral edema
  • Post-craniotomy
• Contraindications
  • Central nervous system infection
  • Coagulation defects
  • Anticoagulant therapy
  • Scalp infection
  • Severe midline shift resulting in ventricular displacement
  • Cerebral edema resulting in ventricular collapse
• Complications
  • Intracranial infection
  • Intracerebral hemorrhage
  • CSF leakage
  • Over drainage of CSF leading to ventricular collapse and herniation

Fluids monitoring (in-put & out-put)

• Urinary output is an excellent reflection of tissue perfusion. If the kidneys are producing urine then the other organs are probably being perfused. The normal urinary output is 1 - 2 ml/kg/hr. Ideally its important to quantitate the urine output.
• In addition to quantitation of urine, it is also helpful to quantitate defecation and emesis, this can provide you with a better picture of your total fluid balance. Weight gains and losses should be monitored on a daily basis if not more frequently. Acute changes in weight are usually a result of fluid changes and not muscle mass.
• The fluid losses should be compared to fluid intake, they should just about balance out. Any big discrepancy in the "ins and outs" should be brought to the attention of the clinician.

Laboratory Investigations

• Laboratory Investigations includes -
  • Arterial blood gases
  • Full blood count
  • Biochemistry
  • Cardiac enzymes
  • Coagulation profiles

Diagnostic Procedures

• Diagnostic Procedures in ICU includes -
  • X-Ray
  • Ultrasound