Physiological monitoring of surgical patient

1. Physiological monitoring of surgical patient Ahmad Al-Saleh Supervisor: Dr. Abhay Patwari

2. 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

3. 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

4. What do we mean by physiological monitoring? • Homeostasis of: • Cardiovascular • Respiratory • Nervous • Renal • Hepatic • Hematologic • Scoring systems

5. 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

6. 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

7. 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

8. 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

9. 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

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

12. Physiological monitoring • Cardiovascular • Respiratory • Nervous • Renal • Hepatic • Hematologic • Scoring systems

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

14. Respiratory • Pulse Oximetry • Ventilation Monitoring • Gas monitoring

15. 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

16. Respiratory- Ventilation • Lung pressure- controlled by 3 forces: • Elastic nature of lungs • Surfactant • -ve intrapleural pressure • Compliance: ∆V/∆P • Conditions < compliance: • Fibrosis, pulmonary oedema, def. of surfactant, age, supine position. • Conditions > compliance • emphysema

17. 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

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

19. Physiological monitoring • Cardiovascular • Respiratory • Nervous • Renal • Hepatic • Hematologic • Scoring systems

20. 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)

21. 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

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

24. 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

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

27. Physiological monitoring • Cardiovascular • Respiratory • Nervous • Renal • Hepatic • Hematologic • Scoring systems

28. 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)

29. 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 <1.2, urea ratio of <10 and a urinary sodium of >40mmol/l indicates acute renal failure • Use of mannitol and loop diuretics should be taken into account as they can cause electrolyte abnormalities

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

31. 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 <1 suggests pre-renal • >2-3 compromised tubular function Renal

32. Physiological monitoring • Cardiovascular • Respiratory • Nervous • Renal • Hepatic/ Gastric • Hematologic • Scoring systems

33. 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)

34. 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)

35. 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

36. Physiological monitoring • Cardiovascular • Respiratory • Nervous • Hepatic/ Gastric • Renal • Hematologic • Scoring systems

37. 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

38. Physiological monitoring • Cardiovascular • Respiratory • Nervous • Hepatic/ Gastric • Renal • Hematologic • Scoring systems

39. APACHE system (Acute Physiological and Chronic Health Evaluation

40. 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)

41. 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

42. Thank you