Physiological monitoring of surgical patient

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Physiological monitoring of surgical patient

• Ahmad Al-Saleh
• Supervisor Dr. Abhay Patwari

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Introduction

• Physiological response to a stress is important
  in determining the outcome.
• Monitoring of physiological response
• Allows determination of physiological reserve
• Allows assessment of baseline of effective
  treatment
• It includes
• Maintenance of aerobic metabolism
• Maintenance of viable cell function
• Measurement of degree of tissue oxygenation

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Types of surgical stress

• Not only injury but includes
• Acute blood loss
• Shock
• Hypoxia
• Acidosis
• Hypothermia
• Altered microcirculatory blood flow
• Altered coagulation and immune system
• Pain
• Hypothalamic-pituitary axis Cortisol secretion
• Stimulation of sympathetic tone Catecholamines

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What do we mean by physiological monitoring?

• Homeostasis of
• Cardiovascular
• Respiratory
• Nervous
• Renal
• Hepatic
• Hematologic
• Scoring systems

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Cardiovascular

• Temperature
• Peripheral temperature Vs core temperature
• Peripheral temperature reflects tissue perfusion
  and affected by vasoconstriction and low cardiac
  output
• Core temperature tympanic membrane, oesophagus,
  bladder or rectum
• Increased gradient between the two in shock
  status
• Electrocardiogram (ECG)
• Useful information about ischaemia, arrhythmias,
  electrolyte imbalance, drug toxicity

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Cardiovascular

• Arterial blood pressure
• Affected by changes in the volume status of the
  patient, vasomotor tone and cardiac output
• If blood pressure is inadequate then tissue
  perfusion will be inadequate
• In critical illness autoregulatory mechanisms in
  vascular beds such as the brain and kidney may
  become impaired and perfusion to these organs
  will be pressure dependent

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Cardiovascular

• Arterial blood pressure
• Invasive through an intravascular cannula
• Common sites radial, femoral, dorsalis paedis or
  brachial
• Knowledge of the mean arterial pressure is also
  required for the calculation of systemic vascular
  resistance
• Cannulation can be associated with complications
  thrombosis, infection, bleeding, fistula
  pseudoaneurysm

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Cardiovascular

• Central Venous Pressure (CVP)
• Useful but not very accurate in assessing volume
  status
• Indications hypovolaemia following
• trauma
• shock
• burns
• Sepsis
• Normally CVP ranges between 6 and 12 mmHg

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Cardiovascular

• CVP
• Common sites
• External jugular vein,
• Internal jugular vein
• Subclavian vein
• Femoral vein
• Antecubital vein
• Seldinger technique most commonly used where the
  vein is punctured with a needle followed by
  insertion of a J-wire through the needle

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Cardiovascular

• CVP- Complications
• Pneumothorax
• Central line associated bloodstream infections
  Staphylococcus aureus and Staphylococcus
  epidermidis sepsis
• Air embolism
• Haemorrhage
• Nerve injury
• Arrhythmias

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Physiological monitoring

• Cardiovascular
• Respiratory
• Nervous
• Renal
• Hepatic
• Hematologic
• Scoring systems

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Respiratory

• Importance
• Assessing whether mechanical ventilation is
  needed
• Great importance in gas exchange and ensuring
  adequate oxygenation
• Optimising treatment response

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Respiratory

• Pulse Oximetry
• Ventilation Monitoring
• Gas monitoring

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Respiratory

• Pulse oximetry
• Measures haemoglobin saturation
• Estimate of arterial saturation can be made
• Critically ill patients usually have poor
  perfusion ? discrepancy in measurement
• Cannot distinguish between carboxyhaemoglobin and
  oxyhaemoglobin due to a similar absorption
  spectrum

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Respiratory- Ventilation

• Lung pressure- controlled by 3 forces
• Elastic nature of lungs
• Surfactant
• -ve intrapleural pressure
• Compliance ?V/?P
• Conditions lt compliance
• Fibrosis, pulmonary oedema, def. of surfactant,
  age, supine position.
• Conditions gt compliance
• emphysema

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Respiratory

• Gas monitoring
• Invasive
• Useful in assessing pulmonary function
• Should always be interpreted in relation to the
  inspired oxygen tension (FIO2)
• Patients with chronic pulmonary disease can
  tolerate abnormal blood gas values

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Respiratory

• Gas monitoring
• PaO2 value of less than 8.0kPa
• PaCO2 greater than 6.0kPa
• (while breathing 50 oxygen in the absence of
  COPD)

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Physiological monitoring

• Cardiovascular
• Respiratory
• Nervous
• Renal
• Hepatic
• Hematologic
• Scoring systems

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Nervous

• monitoring CNS function by Glasgow coma score and
  other assessments of routine neurological status
  is an essential part of the management of the
  critically ill patient
• Intracranial pressure (ICP)
• Electroencephalography (EEG)
• Cerebral function monitoring (CFM)

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Nervous

• Intracranial pressure (ICP) monitoring
• Measures ventricular pressure directly or
  indirectly
• Supine position
• Normal ICP less than 10mmHg
• Variety of devices placed within the cranial
  vault via a small burr hole made in the parietal
  or frontal areas of the non-dominant hemisphere

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Nervous

• ICP Monitoring
• Increased ICP is most frequently seen following
  head injury
• Subarachnoid haemorrhage
• Hepatic encephalopathy
• Brain tumours
• Encephalitis

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Nervous

• ICP monitoring
• ICP above 20-25mmHg often amenable to therapeutic
  intervention including
• Control of hypercapnia (using mechanical
  ventilation to maintain a PaCO2 of 4kPa),
• Mannitol
• Slight head-up tilt
• Sedation with an intravenous anaesthetic agent
  such as propofol or thiopental

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Nervous

• EEG
• Measures voltage fluctuations resulting from
  ionic current flows within the neurons of the
  brain
• Epilepsy
• Coma
• Encephalitis
  
• Brain death

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Physiological monitoring

• Cardiovascular
• Respiratory
• Nervous
• Renal
• Hepatic
• Hematologic
• Scoring systems

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Renal

• Urine output
• Hourly urine output is a very useful guide to the
  adequacy of cardiac output, splanchnic perfusion
  and renal function
• Measurement of the specific gravity and
  osmolality of the urine is used to differentiate
  between pre-renal and renal failure.
• Normal urine output for an adult is 0.5ml/kg/hr.
  (30-40ml per hour in an average sized adult)

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Renal

• Plasma and Urine Electrolytes, Urea and
  Creatinine
• Useful for evaluating the progress of renal
  function
• Urea can rise in gastrointestinal bleeding, high
  protein intake and increased catabolism
• Urine / plasma osmolality ratio of lt1.2, urea
  ratio of lt10 and a urinary sodium of gt40mmol/l
  indicates acute renal failure
• Use of mannitol and loop diuretics should be
  taken into account as they can cause electrolyte
  abnormalities

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Renal

• GFR
• Creatinine clearance is the most reliable method
  for GFR assessment
• Measurements over 24hrs, but 2hr clearance
  reasonably accurate

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Renal

• Tubular Function Tests
• Primarily used in differential diagnosis of
  oliguria
• Differentiate pre-renal cause from intrinsic
  failure due to tubular dysfunction
• Fractional excretion of sodium most reliable lab
  test
• Value of lt1 suggests pre-renal
• gt2-3 compromised tubular function

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Physiological monitoring

• Cardiovascular
• Respiratory
• Nervous
• Renal
• Hepatic/ Gastric
• Hematologic
• Scoring systems

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Hepatic

• Wide range of functions including detoxification,
  protein synthesis and production of biochemicals
  necessary for digestion
• Has a high functional reserve
• Importance of monitoring LFTs to assess liver
  function
• Importance of differentiating between
  hepatocellular damage (? transaminases)
  obstructive picture (? alk phosph)

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Hepatic

• Albumin, clotting factors, anti-thrombin III and
  protein C all synthesised in the liver
• Usually albumin not used in assessing acute liver
  function due to its long half-life
• Clotting and prothrombin time are useful
  indicators of liver function
• Factor VII useful in assessing severity of
  coagulopathy even where fresh frozen plasma has
  been given (its half-life 4-8hrs)

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Gastric

• Acidosis within gastric mucosa can be a major
  factor contributing to stress ulceration
• Localised acidosis is due to either
• ? demand of O2 by mucosal cells
• impairment of oxygen utilisation within these
  tissues
• Direct measurement of mucosal pH may be performed
  since tissues are highly permeable to CO2
• The intramucosal pH (called pHi) can then be
  determined using the Henderson-Hasselbalch
  equation

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Physiological monitoring

• Cardiovascular
• Respiratory
• Nervous
• Hepatic/ Gastric
• Renal
• Hematologic
• Scoring systems

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Haematological

• Acquired coagulopathies such as disseminated
  intravascular coagulation are common in stress
• Main causes of deficiencies in clotting factors
  are
• liver disease
• vitamin K deficiency
• anti-coagulant drugs
• DIC
• massive blood transfusion
• Assessment of clotting function is by measurement
  of prothrombin time, activated partial
  thromboplastin time, fibrinogen concentration and
  either fibrin degradation products (FDPs) or
  D-dimer

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Physiological monitoring

• Cardiovascular
• Respiratory
• Nervous
• Hepatic/ Gastric
• Renal
• Hematologic
• Scoring systems

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APACHE system (Acute Physiological and Chronic
Health Evaluation
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Modified early warning score (MEWS)

• It is based on data derived from four
  physiological readings (systolic blood pressure,
  heart rate, respiratory rate, body temperature)
  and one observation (level of consciousness,
  AVPU)

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Take home message

• Physiological monitoring is essential in
  critically ill patients
• Basic simple tools are usually used in securing
  cardiorespiratory function
• GCS can be of great value in monotring nervous
  system
• Renal hepatic functions are important in
  assessing body metabolism
• MEWS similar systems are easy practical in
  surgical patients

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Thank you