Bedside monitoring of tissue perfusion and oxygenation
BEDSIDE MONITORING OFTISSUE PERFUSION AND OXYGENATION Dr.Tushar Patil MD
Oxygen transport involves a series of convective and diffusive processes. Convective transport-bulk movement of oxygen in air or blood-active, energy consuming processes generating flow Diffusive transport- passive movement of oxygen down its concentration gradient across tissue barriers- across the extracellular matrix- depends on the oxygen tension gradient and the diffusion distance
Capillary blood to individual cells resting extraction ratio from capillary blood is about 25% may increase to 7080% during exercise Factors affecting O2 extraction from cappilary blood1. Rate of O2 delivery to capillary2. O2-Hb dissociation relation3. Size of capillary to cellular PO2 relation4. Diffusion distance to cells5. Rate of use of O2 by cells
Tolerance to hypoxia of various tissues Tissue Survival time1. Brain<3 min2. Kidney and liver15-20 min3. Skeletal muscle60-90 min4. Vascular smooth muscle24-72 h5. Hair and nails -Several days
Tissue Hypoxia in Critically Ill disordered regional distribution of blood Regional and microcirculatory distribution of cardiac output endothelial, receptor, neural, metabolic, and pharmacological factors small resistance arterioles and precapillary sphincters shunting and tissue hypoxia despite high global oxygen delivery and mixed venous saturation. reduce regional distribution, particularly to the renal and splanchnic capillary beds
EFFECTS OF HYPOXIA PaO2 level approaches 55mmHg-.short term memory loss, euphoria and impaired judgment PaO2 30-50mmHg -Progressive loss of cognitive and motor functions, increasing tachycardia PaO2 below 30mmHg-loss of consciousness
Clinical features of tissue hypoxia Dyspnoea Altered mental state Tachypnoea or hypoventilation Arrhythmias Peripheral vasodilatation Systemic hypotension Coma Cyanosis (unreliable) Nausea, vomiting, and gastrointestinal disturbance
Monitoring Tissue Perfusion and Oxygenation1. Clinical Evaluation2. Hemodynamic Monitoring3. Pulse Oximetry4. End Tidal CO2 Monitoring5. Monitoring Tissue Hypoxia6. Cerebral Oxygenation Monitoring
Clinical Evaluation HISTORY-Dyspnoea-Cough-Fever-Rash-Discolouration of digits/limbs-Palpitations-Altered sensorium-Convulsions
Clinical Evaluation Level of Consciousness Evaluation of Peripheral & Central Pulses Capillary Refill Time Cyanosis Respiratory Rate & Pattern Blood Pressure Systemic Examination
Monitoring arterial pressure Organ perfusion depends on the organ metabolic demand ,perfusion pressure,local vasomotor tone and cardiac output tissue perfusion is maintained through ‘‘autoregulation’’ Organ perfusion pressure cannot be measured directly at the bedside As a surrogate for tissue perfusion pressure, arterial blood pressure is monitored.
Noninvasive measurements of arterial pressure can be determined either manually or by oscillometric method . Oscillometric devices, determine MAP and then provide readings for systolic and diastolic pressures. Oscillometric devices tend to underestimate systolic and overestimate diastolic blood pressure noninvasive measurements less reliable with marked hypovolemia or abnormal cardiac function. Oscillometric measurements also limited by cycling delay of the device.
Arterial CatheterisationINDICATIONS ABSOLUTE- As a guide to synchronization of intra-aortic balloon counter pulsation PROBABLE-1. Guide to management of potent vasodilator drug infusions2. Guide to management of potent vasopressor drug infusion3. As a port for the rapid and repetitive sampling4. As a monitor of cardiovascular deterioration in patients
Arterial CatheterisationUSEFUL APPLICATIONS Differentiating cardiac tamponade (pulsus paradoxus) from respiration-induced swings in systolic BP Differentiating hypovolemia from cardiac dysfunction as the cause of hemodynamic
Central venous pressure monitoringPressure in the large central veins proximal to the right atrium relative to atmosphere. METHODS- central venous line / Swan-Ganz catheter with distal tip connected to manometer/ pressure transducer- noninvasively as jugular venous pressure
Limitations of CVP Being wrongly used as a parameter/ goal for replacement of intravascular volume The validity as index of RV preload nonexistent Poor correlation with cardiac index, stroke volume, left ventricular end-diastolic volume, and right ventricular end-diastolic volume
Pulmonary artery catheterization Developed in the 1940s and later refined by Swan and Ganz in 1970INDICATIONS Diagnostic – Diagnosis of shock states – high- versus low-pressure pulmonary edema – primary pulmonary hypertension (PPH) – valvular disease, intracardiac shunts, cardiac tamponade, and pulmonary embolus (PE) – Monitoring complicated AMI – hemodynamic instability after cardiac surgery Therapeutic - Aspiration of air emboli
PACCONTRAINDICATIONS Tricuspid or pulmonary valve mechanical prosthesis Right heart mass (thrombus and/or tumor) Tricuspid or pulmonary valve endocarditis
Complications of PAC Venous access complications - include arterial puncture - hemothorax - Pneumothorax Arrhythmias - PVCs or nonsustained VT - Significant VT or ventricular fibrillation Right bundle-branch block (RBBB) PA rupture PAC related infection Pulmonary infarction
Measuring Cardiac Output1. Pulmonary Artery Catheter2. Pulse Contour Analysis -Lithium dilution -Transpulmonary Thermodilution -Without diluion calibration3. CO2 Rebreathing4. Trans thoracic Electrial Bioimpedence5. Trans Thoracic Echo6. Esophageal Doppler Monitoring
Pulse OximetryPRINCIPLE Displayed readings determined primarily by two components:1. The different absorption spectra of oxyhemoglobin and deoxyhemoglobin at different wavelengths2. Pulsatile arterial blood Probe (finger, ear, or forehead) contains two light- emitting diodes that emit light at 660 nm and 940 nm. Photoreceptor receives light, and compares absorption two wavelengths,
Pulse OximetryAPPLICATIONS indicated in circumstance where hypoxaemia May occur. should be included in the routine vital signs. . continuous monitoring. pattern of oxygenation can be recorded. can replace arterial blood gas analysis in cases where assessment of oxygenation is indication. Regulation of oxygen therapy Testing adequecy of circulation
Pulse Oximetry Improving oximeter signals• Warm and rub the skin• Apply a topical vasodilator• Try a different probe site, especially the ear• Try a different probe• Avoid motion artefact• Use a different machine
Pulse Oximetry PITFALLS1. Dyshemoglobinemias2. Poor function wiyh poor performance3. Difficulty in detecting high oxygen partial pressures4. Delayed detection of hypoxic events5. Erratic performance with irregular rhythms6. Nail polish and coverings7. Loss of accuracy at low values8. Electrical interference9. Failure to detect hypoventilation
Monitoring ventilation using end- tidal carbon dioxide provides information regarding alveolar ventilation. PetCO2 - concentration of carbon dioxide at end expiration . measured in both mechanically ventilated and spontaneously breathing patients. displayed as either numerical value (capnometry) or as a graphic waveform plotted against time (capnography). PetCO2 underestimatesPaCO2 by 2 to 5 mm Hg because of the influence of dead space ventilation relationship between PetCO2 and PaCO2 is unreliable in critically ill patients.
End Tidal Carbon DioxideAPPLICATIONS Confirming endotracheal tube placement detecting endotracheal tube dislodgment detecting ventilator malfunction assessing the success of cardiopulmonary resuscitation evaluation of weaning from mechanical ventilation determining the optimal level of PEEP
End Tidal CO2 sudden loss of the capnogram waveform –ET obstruction -extubation - ventilator malfunction –cardiac arrest sudden drop of the waveform -partial obstruction of ET -an airway leak -hypotension
End Tidal CO2 Capnography can be used to monitor patients in whom hypercarbia may be detrimental PetCO2 values greater than 40 mm Hg correlate with equal or higher value of PaCO2 Elevated PetCo2 indicate sthe need for alterations in management
Monitoring Tissue Hypoxia Global markers of tissue hypoxia - serum lactate -central venous oxygen saturation (ScvO2) Monitoring regional hypoxia -Sublingual Capnometry –Gastric Tonometry - Orthogonal Polarization Spectroscopy (OPS) - Near Infra Red Spectroscopy (NIRS) -Trans cutaneous Oxygen Tension -Resonance Raman Spectroscopy
Serum Lactate byproduct of anaerobic metabolism, resulting from the inabilityof pyruvate to enter the Krebs cycle. The normal serum value - less than 2 mmol/L. lactate levels above 4mmol/L strongly associated with worse outcome. more important is the time to normalization of lactateLevels- ‘‘lactate clearance time.’’ Prolonged lactate clearance time(>48hrs)-significantly higher rates of infection, organ dysfunction, and death Better survival correlates with a lactate clearance time <24 hrs.
Central venous oxygen saturation Mixed venous oxygen saturation (SvO2) - a measure of tissue hypoxia. o Obtained with pulmonary artery catheter. FACTORS INFLUENCING SvO2- arterial oxygen saturation- hemoglobin concentration- cardiac output- tissue oxygen consumption.-NORMAL VALUES- 70% to 75%.- Values below 60% indicate cellular oxidative impairment- values below50% associated with anaerobic metabolismpulmonary artery catheters not placed routinely ScvO2 - surrogate For SvO2
ScvO2 venous oxygen saturation near the junction of the superior vena cava and right atrium. obtained from subclavian or internal jugular central venous catheter. Because ScvO2 neglects venous return from the lowerbody, values for ScvO2 typically are 3% to 5% less than SvO2 values < 65% -ongoing oxidative impairment. values > 80% - cellular dysfunction with impaired oxygen consumption. - seen in late stages of shock To be used in context with other markers of tissue perfusion (eg, lactate).
Sublingual capnometry studies perfusion of the splanchnic circulation. sensor placed under the tongue measures partial pressure of carbon dioxide in the sublingual tissue (PslCO2). Normal values for PslCO2 - 43 to 47 mmHg PslCO2 >70 mm Hg - correlates with elevated arterial lactate levels more important is the ‘‘PslCO2 gap.’’- difference between PslCO2 and PaCO2 A PslCO2 gap of> 25 mm Hg identifies patients at a high risk of mortality.
Gastric Tonometry Offers an index of aerobic metabolism in gut mucosa. Based on increase in tissue CO2 A balloon in stomach,measures intramucosal pCO2 Using this and arterial (HCO3), gastric intramucosal PH is calculated
Orthogonal polarization spectroscopy uses polarized light to visualize the microcirculation directly. hemoglobin absorbs polarized light real-time images reflected to videomicroscope functional capillary density measured. sensitive marker of tissue perfusion and an indirect measurement of oxygen delivery. Tissues evaluated- oral mucosa, sublingual mucosa, rectal mucosa,and vaginal mucosa. LIMITNG FACTORS- -movement artifacts -presence of saliva -observer related bias
Near-infrared spectroscopy measures the concentrations of hemoglobin, oxygen saturation,and cytochrome aa3 Cytochrome aa3- final receptor in the electron transport chain - responsible for 90% cellular O2 consumption - remains in a reduced state during hypoxia used primarily to evaluate the perfusion of skeletal muscles.PROBLEMS-signal contamination by light scatter-variable interpretations of the data-lack of a reference standard for comparison
Transcutaneous oxygen tension measure transcutaneous oxygen or carbon dioxide. Use heated probes placed on the skin•markers of regional tissue hypoperfusion increased mortality in patients with low transcutaneous oxygen orhigh CO2•LIMITATIONS-Tissue trauma from probe insertion,- thermal injury if probes are not moved every4 hours- lack of established critical values to guide resuscitation .
Cerebral Perfusion and Oxygenation monitoring1. Jugular venous bulb oximetry2. Direct brain tissue oxygen tension3. Near inrared spectroscopy4. Cerebral Microdialysis5. Cerebral Blood Flow Monitoring6. Oxygen-15 PET
Jugular venous oxygen saturation(SjvO2) Retrograde placement of jugular venous catheter with oximeter cannulate dominant IJV catheter tip positioned in jugular bulb compatible with MRI. SjvO2 - result of the difference between cerebral oxygen delivery (supply) and cerebral metabolic rate of oxygen (demand) Low SjvO2 (!50% for O10 minutes) -hypoperfusion / increased . cerebral metabolism.APPLICATIONS - comatose patients (GCS <8) -treatment of SAH- - neurosurgical procedures
SjvO2LIMITATIONS- changes in arterial oxygen content- hemodilution- prone position of catheter- necessity for frequent calibrations- infection- increase in ICP- thrombosis- arterial Puncture- pneumothorax- reflects global cerebral oxygenation and does not detect regional ischemia in smaller regions ipsilateral or in contralateral hemisphere
Brain tissue oxygen pressure(PBO2) Small flexible microcatheter inserted into brain parenchyma. marker of the balance between regional oxygen supply and use. ICP, brain temperature (Licox, Integra Neurosciences) or tissue partial pressure of carbon dioxide (PBCO2) and pH (Neurotrend, Johnson & Johnson) can be monitored Licox device uses polarographic technique by Clark electrode Neurotrend uses ‘‘optimal luminescence’’ catheter should pass through gray matter into white matter tunneled after craniotomy or placed through a double or triple lumen bolt measured tissue volume 17 mm3. PBO2 levels highest in dense population of neurons and lower in white matter PBO2 and amplitude of changes lower with Neurotrend than Licox compatible with MRI
Near infrared spectroscopy monitoring of transmittance across the brain at two or more wavelengths optical attenuation of the spectra converted into changes of cerebral oxygenation methods include time-resolved, spatially resolved, and phase-resolved spectroscopy INVOS system provides a numerical value for oxygen saturation using rSO2 normal range-60-80% NIRO oximeters present values for oxygenated and total Hb concentration, cytochrome aa3, and a tissue oxyge index
NISAPPLICATIONS detection of changes during carotid cross-clamping during carotid endarterectomy & cardiac surgery to detect cerebral vasospasm causing delayed cerebral ischemic deficit after SAH assessment of perfusion reductions in stroke Reconstruction of a three-dimensional image using optical tomography attractive because applied by attaching pads to the forehead or other regions of interest.
NISLIMITATIONS limited and variable penetration of infrared light through the skull (2–3 mm, limited to gray matter) contamination by extra- and intracranial sources (mixture of capillary, venous,and arterial blood), and uniform distribution of infrared light in the CSF layer. degree of scatter unpredictable inconsistent impact of monitoringof decreased oxygenation on neurologic outcome
Cerebral Microdialysis bedside monitor to provide on-line analysis of brain tissue biochemistry during neurointensive care. The principles and clinical double-lumen probe, lined at it tip with dialysis membrane. perfused by an inlet tube with fluid isotonic to the tissue interstitium perfusate passes along the membrane before exiting collecting chamber. catheter acts as an artificial blood capillary. Measures microdialysate concentrations of glucose, lactate, pyruvate, glycerol, and glutamateThe concentration of these substances in the microdialysate does not correspond to their true extracellular fluid concentration proportion of the extracellular fluid concentration the ‘‘relative recovery”
Applications of MD Most clinical experience with TBI and SAH Severe cerebral hypoxia /ischemia associated with marked increases in the lactate-pyruvate ratio Ratio greater than 20 to 25 associated with poor outcome Glycerol is a marker of ischemic cell damage Increased MD glycerol concentrations associated with poor outcome Increased excitatory amino acids and reduced brain ECF glucose associated with metabolic catastrophes after acute brain injury.