Respiratory monitoring

respiratory monitoring under anaesthesia

1. -BY DR.VYSHNAVI DR.DINESH -MODERATOR: DR.CHAITANYA ESIC MEDICAL COLLEGE & HOSPITAL, SANATH NAGAR, HYDERABAD RESPIRATORY MONITORING

2. CONTENTS Physical examination Pulsoximetry Mixed venous oxygen saturation Tissue oxygenation Capnography & ABG Static & Dynamic respiratory mechanics RR monitoring Imaging & point of care

3. INTRODUCTION Respiration : transport of O2 from the environment to the body cells and the transport of CO2 from those cells to the environment. Includes a component of cellular respiration. Respiratory monitoring : continuous or periodic assessment of processes involved with the exchange of respiratory gases between the environment and the subcellular pathways where those gases are utilized and produced

4. Respiratory monitoring includes assessment of convective and diffusive gas transport through the branching airway tree and alveoli equilibration of gases between alveoli and pulmonary capillary blood, regional ventilation and perfusion gases in arterial and mixed venous blood gas transport between the blood and body tissues through the microcirculation gas diffusion between tissues and mitochondria cellular respiration with O2 use and CO2 production

5. PHYSICAL EXAMINATION I nspection of the patient, either awake or during anesthesia. Assessment of the respiratory rate ,breathing pattern Anatomic signs :deformities of the chest wall and spine, goiter, tracheostomy scar, and tracheal deviation. Functional elements :inspiration and expiration (diaphragmatic versus thoracic), duration and difficulty of inspiration and expiration, paradoxical chest wall motion, use of accessory muscles, central and peripheral cyanosis, pallor, wheezing, stridor , cough and sputum, aphonia , splinting, and clubbed fingers.

6. Neck vein distension trauma patients: flail chest, pericardial tamponade , hemothorax , pneumothorax , pulmonary contusion and tension pneumothorax . Auscultation normal and abnormal breath sounds: vesicular sounds, rhonchi , wheezes, fine and coarse crackles, inspiratory stridor , and pleural friction.

7. PULSE OXIMETRY Arterial O2 content ,CaO2 is calculated as CaO2 = (1 . 34 × SaO2 × Hb) +0 . 0031 × PaO2 where 1.34 mL/g is the O2 binding capacity of Hb (i.e., Hüfner constant, theoretically equal to 1.39 mL/g (1.31 and 1.37 mL/g) SaO2 is the O2 saturation of Hb in the arterial blood 0.0031 is the solubility of O2 in blood PaO2 is the arterial partial pressure of O2 (mm Hg)

8. MEASUREMENT PRINCIPLES : Beer-Lambert law : transmission of light through a solution to the concentration of the solute in the solution. For each solute in a solution, I trans = I in e − DCε where Itrans is the intensity of transmitted light, Iin is the intensity of the incident light, e is the base of the natural logarithm, D is the distance the light is transmitted through the solution, C is the concentration of the solute, and ε is the extinction coefficient of the solute

9. Beer’s Law The intensity of transmitted light decreases exponentially as the concentration of the substance increases. Lambert’s Law The intensity of transmitted light decreases exponentially as the distance travelled through the substance increases.

10. Pulse oximetry takes advantage of the pulsatility of arterial blood flow to provide an estimate of SaO2 by differentiating light absorption by arterial blood from light absorption by other components Photoplethysmography : absorption of light is proportional to the amount of blood between the transmitter and photodetector , changes in the blood volume are reflected in the pulse oximeter trace

11. Changes in blood volume pulsations :depends on the distensibility of the vessel wall, intravascular pulse pressure. Variations in the amplitude of the pulse oximetry plethysmographic waveform (ΔPOP) : predict fluid responsiveness in mechanically ventilated patients. An index derived from the percent difference between the maximum and minimum amplitudes of the plethysmographic waveform during a respiratory cycle (PVI, Pleth Variability Index) :used to quantify ΔPOP and predict fluid responsiveness

12. Oxyhemoglobin absorbs infrared light (940 nm) > red light ( 660 nm) Deoxyhemoglobin absorbs red light >infrared light.

13. ISOSBESTIC POINT is the point at which two substances absorb a certain wavelength of light to the same extent. This point may be used as reference points where light absorption is independent of the degree of saturation.

14. TYPES Transmission Pulse Oximetry emitter and photodetector are placed opposite of each other, measuring site is in-between the two. M.C Reflectance Pulse Oximetry : emitter and photodetector are side by side on the measuring site. The light gets reflected from the emitter to the detector across the site.

15. SITES FOR MEASUREMENT Fingers(Most common) Toe Pinna L obe of the ear in adults and children . Palm or Sole f or neonates and infants. Cheek and Tongue(Less common)

16. APPLICATIONS OF PULSE OXIMETRY Monitoring Oxygenation in OT, PACU, ICU and Transport . Neonatal Applications Neonatal Resuscitation Neonatal Screening for Congenital Heart Disease Monitoring Vascular Volume and Sympathetic Tone Monitoring Peripheral circulation Determining Systolic Blood Pressure Locating arteries Intrapartum Foetal Monitoring

17. PERFUSION INDEX Perfusion index is the numerical value of the plethysmograph waveform amplitude. It is the ratio of pulsatile to nonpulsatile blood flow through the peripheral capillary bed . It indicates the VASOMOTOR TONE . Higher the vasomotor tone(vasoconstriction ) lower is the PI and vice versa.

18. PLETH VARIABILITY INDEX PVI is an automatic measure of the dynamic change in PI that occurs during the respiratory cycle. G reater PVI => patient will respond to fluid administration Pleth variability index (PVI) = ( PLmax - PLmin ) × 100 PLmax where , PLmax : Maximum amplitude of plethysmograph wave PLmin : Minimum amplitude of plethysmograph wave.

19. ADVANTAGES Accuracy : W hen SaO2 is 90% or above. Deteriorates when SaO2 falls to 80% or less. Independence from gases and vapours Fast response time Non-invasive Continuous measurements Separate respiratory and circulatory variables Convenience Light weight and compactness Economy

20. OTHER CAPABILITIES OF PO Signal Strength Full strength signals => good perfusion. Low strength signals => vasoconstriction and low CO. Thus , it can help in the diagnosis of intraoperative hypotension . Pulse Beep All pulse oximeters emit a beep after detecting a plethysmographic pulse which coincides with heartbeat . The pitch of this beep is proportional to SpO2 .

21. SAFE AND UNSAFE LIMITATIONS SAFE LIMITATIONS Inaccuracy can be suspected and its cause is recognizable. D evice alarms and alerts the observer. Motion artifacts Poor perfusion Skin pigmentation, nail polish, and artificial nails Irregular rhythm Electromagnetic interference UNSAFE LIMITATIONS Inaccuracy is difficult to recognize, displayed SpO2 is incorrect. No alarm and warning to the observer Calibration assumptions Delay in detection of hypoxia Probe positioning Ambient light interference Abnormal hemoglobin molecules Venous pulsation Intravenous dyes

22. MOTION ARTIFACTS POOR PERFUSION NAIL POLISH, SKIN PIGMENTATION , ARTIFICIAL NAILS

23. IRREGULAR RHYTHMS

24. MASIMO Signal Extraction Technology, or Masimo SET, assumes that both the arterial and venous blood can move and uses parallel signal processing engines–DST, FST, SST, and MST–to separate the arterial signal from sources of noise (including the venous signal) to measure SpO 2  and pulse rate accurately, even during motion .

25. MIXED VENOUS OXYGEN SATURATION (SvO2) O2 saturation of blood at the proximal pulmonary artery: reflects the average O2 saturation of the blood returning from the body to the right heart Normal SvO2: between 65% and 80%. Values close to 40% are associated with tissue hypoxia, anaerobic metabolism, and lactate production . PvO2 can be derived from SvO2 values by utilizing the O2Hb dissociation curve adjusted to mixed-venous pH, PCO2, and temperature .

26. The normal value of PvO2 is 40 mm Hg Falsely increased in wedged pulmonary artery tip, mitral regurgitation, or left-to-right shunts. Venous saturations measured continuously by spectrophotometry -specialized fiberoptic catheters, which transmit infrared light and detect the amount of light reflected from red blood cells. USES: postoperative complications in major abdominal or cardiac surgeries

27. SCVO2 have been shown to reduce the length of stay, organ dysfunction, and mortality in patients undergoing major surgery and patients presenting with sepsis  used in GDT SCVO2 may be increased in sepsis - impaired tissue O2 extraction Direct measurement of SvO2 requires the insertion of a pulmonary artery catheter Mixed venous CO2 has been used to compute the arteriovenous CO2 difference (ΔPCO2 = PvCO2−PaCO2).

28. In conditions of steady-state CO2 production, ΔPCO2 changes inversely and nonlinearly with cardiac output ( Fick equation) ΔPCO2 is an indicator of the adequacy of cardiac output to provide adequate clearance of tissue CO measurement of venous O2 saturation can be performed intermittently by co-oximetry from the distal tip of a pulmonary artery catheter (SvO2) or a central venous catheter (SCVO2).

29. TISSUE OXYGENATION Arterial and venous O2 saturations are measures of DO2 and uptake by the whole body. do not provide information regarding organ or tissue oxygenation  reflects local balance between O2 supply and demand noninvasive methods for the assessment of microcirculatory oxygenation use reflectance spectroscopy using light either in the visible spectrum (VLS) or in the near-infrared spectrum (NIRS)

30. Reflectance spectroscopy probes have light emitters and receivers positioned in line. When placed on a tissue surface, light transmission through the tissue is affected by reflection, absorption, and scatter. Based on Beer lamberts law VLS makes use of white light with wavelengths of 500 to 800 nm, whereas NIRS employs light in the 700 to 1100 nm range. NIRS can penetrate tissue to a depth of several centimeters and allows sampling of a larger volume of tissue includes arteries, capillaries, and veins, and has a predominantly venous weighting .

31. USES : Buccal microvascular Hb saturation: survival in sepsis monitoring flap viability : reconstructive surgery GI & esophageal sx : reductions in gastrointestinal tissue saturation, anastomotic complications, mesentric ischaemia NIRS: frontal cortical oxygenation (rSO2). open thoracoabdominal aortic aneurysm repair for continuous monitoring of spinal cord oxygenation carotid endarterectomy cardiovascular, abdominal, thoracic, and orthopedic surgery: POCD

32. CAPNOMETRY AND CAPNOGRAPHY The presence CO2 in exhaled breath reflects the fundamental physiologic processes of ventilation, pulmonary blood flow, and aerobic metabolism. Exhaled CO2 :ventilation & adequacy of cardiac output Bohr equation

33. Capnometry : measurement and quantification of inhaled or exhaled CO2 concentrations at the airway opening. Capnography : graphic display as a function of CO2 time or volume. Capnometer is simply a device that measures CO2 concentrations, display a numeric value for inspired or exhaled CO2. Capnograph : a device that records and displays CO2 concentrations, as a function of time. Capnogram : graphic display that the capnograph generates.

34. MEASUREMENT PRINCIPLES : mass spectrometry, Raman spectrometry, photoacoustic measurement, gas chromatography M.C method : nondispersive infrared Gaseous CO2 absorbs light over a very narrow bandwidth centered around 4.26 μm . WORKING: infrared-light source is focused on a chopper disk that rotates at approximately 60 rev/ sec. The chopper allows the beam to be alternately directed through (1) the sample cell with the gas to be analyzed and (2) a reference cell with no detectable CO2.

35. the light source is completely blocked at various points during the revolution of the chopper disk. The photodetector and associated circuitry process these three signals to estimate the changes in CO2 concentration continuously in the sample cell.

36. CO2 concentration may be estimated with solid-state technology, using a beam splitter instead of a chopper wheel. The splitter allows for the measurement of infrared energy at wavelengths within and outside the absorption spectrum of CO2 . The measured CO2 is displayed as either volume percent or as partial pressure (mm Hg) Capnometers types: sidestream (diverting) mainstream ( nondiverting ).

37. Mainstream Sidestream

38. MAINSTREAM SIDESTREAM No gas removed from circuit Increase in mechanical dead space H eavy (can cause kinking or disconnection of circuit) Sensor may be damaged or lost Waveform in real time Difficult to adapt to nonintubated patients. Gas is constantly aspirated from circuit via a 6 feet sampling tube Minimal dead space Light weight adapter Sampling line may clog Waveform is delayed (1–4 seconds) due to transportation of gases from the patient’s airway to the unit containing the sensor Easily adapted to nonintubated patients

39. END-TIDAL CO2 (PETCO2 ) PetCO2 is the best reflection of alveolar CO2 ( PACO2 ) . Normal lungs have a high CO2 diffusion coefficient, hence alveolar CO2 [ PACO2 ] closely reflects the arterial CO2 [PaCO2] concentration. The difference between PetCO2 and PaCO2 (PaCO2–PetCO2) is usually 3–5 mm Hg . It is an indirect measure of physiological dead space .

40. CLINICAL SIGNIFICANCE The measurement of CO2 in expired gases reflects alterations in Respiration Metabolism Circulation Breathing system

41. TIME CAPNOGRAM Phase I: exhalation of dead space gas from the central conducting airways or any equipment distal to the sampling site Phase II: a sharp rise in PCO2 to a plateau indicates the sampling of transitional gas between the airways and alveoli. Phase III : plateau region of the capnogram : PCO2 in the alveolar compartment Phase 0 :a sharp downstroke of PCO2 occurs as fresh inspired gas moves past the sampling site and washes out the remaining CO2. Phase IV or IV′: a sharp upstroke in PCO2 is at end of phase III

42. Alpha angle is the angle between phase II and III and is usually 100–110°. It decreases as the slope of phase III increases as seen in chronic obstructive pulmonary disease (COPD). The slope also indirectly represents the ventilation/perfusion (V/Q) status of the lung. Beta angle is the angle between phase III and phase 0 and is usually 90°. This angle increases during rebreathing.

43. RESPIRATION Gives information about rate, depth and frequency of respiration Evaluates patient’s ability to breathe, effect of bronchodilator, nitric oxide therapy, or altered ventilator parameters. Detection of esophageal intubation Determine the position of DLT Accidental bronchial intubation

44. Progressive slanting/slant of phase 3 inspiration starts before expiration ends  decreased ETCO2 Seen in Bronchospasm(asthma), Upper airway obstruction, COPD, partially obstructed ETT.

45. METABOLISM To monitor patient’s metabolism by increased or decreased CO2 elimination in mechanically ventilated patients only Increased  Hyperthermia, shivering, convulsions, excessive catecholamine production, bicarbonate administration, release of torniquet . Decreased  Hypothermia, increased muscle relaxation Malignant hyperthermia  CO2 increases before rise in temperature .

46. NORMAL WAVEFORM WITH ELEVATED ETCO2 Baseline zero => No CO2 in inspired mixture Elevated ETCO2 => Increased CO2 production or decreased clearance Malignant hyperthermia Absorbtion during laparoscopy Torniquet release Increased muscle (during reversal) Shivering Convulsions

47. CIRCULATION Increased CO  Increased ETCO2 and vice versa Reduced flow to lungs (surgical manipulations of heart or thoracic vessels, wedging of PA catether , pulmonary embolus Effectiveness of resuscitation(not associated with mechanical artifacts seen with ECG,BP or PR) Predicting resolution of pulmonary embolus

48. BREATHING SYSTEM Incompetent Inspiratory valves Incompetent Expiratory valve Faulty or exhausted absorbents Disconnections Low FGF Rebreathing over facemask in RA Inspiratory valve defect  CO2 in inspiratory limb rebreathed  slowed downslope(phase 0)

49. NORMAL WAVEFORM WITH ELEVATED BASELINE Incompetent expiratory valve Exhausted absorbent Low FGF Rebreathing under drapes in spontaneously breathing

50. NORMAL WAVEFORM WITH DECREASED ETCO2 Baseline Zero => No CO2 in inspired mixture Low ETCO2 can be due to Hyperventilation Increased dead space ventilation

51. CURARE NOTCH Caused due to lack of synchronous action between intercostal muscles and diaphragm Causes:- 1) Inadequate muscle relaxation(most common) 2) Cervical transverse lesions 3) Flail chest 4) Hiccups 5) Pneumothorax

52. SPONTANEOUS RESPIRATORY EFFORTS DURING MV Small breaths during exhalation and inhalation Inadequate muscle paralysis Hypoventilation Severe hypoxia Pressure on patient’s chest

53. BIPHASIC EXPIRATORY PLATEAU due to variation in compliance, airway resistance or V/Q ratio of one lung from the other. Severe Kyphoscoliosis One lung ventilation After single lung transplant

54. CARDIOGENIC OSCILLATIONS At end of expiration when flows become zero beating heart empties different portion of lungs back and forth motion between exhaled and fresh gas.

55. VOLUME CAPNOGRAM graphic display of CO2 concentration or partial pressure versus exhaled volume. Inspiratory phase: not defined Advantages: allows for estimation of the relative contributions of anatomic and alveolar components of physiologic dead space more sensitive in detecting subtle changes in dead space caused by alterations in PEEP, pulmonary blood flow, or ventilation heterogeneity numeric integral of PCO2 as a function of volume- determination of the total mass of CO2 exhaled during a breath and provides for the estimation of˙VCO2

56. A, Alterations in phases II and III with corresponding changes in PEEP(0, 3, 6, 9, and 12 cm H2O) during positive-pressure ventilation. B, Alterations in phases II and III with corresponding changes in pulmonary perfusion (increasing numbers correspond to decreasing pulmonary blood flow). C, Pronounced positive slope of phase III duringacute bronchospasm (day 1). Following resolution (day 5), a noticeable reduction in the slope of phase III occurs.

57. Sudden hypotension Circulatory arrest Pulmonary embolus

58. BLOOD GAS ANALYSIS used to assess oxygenation, ventilation , and acid-base status. This section focuses on the use of arterial blood gases to assess oxygenation and ventilation. Oxygenation is reflected in the PaO2, which is a function of the alveolar partial pressure of O2 (PAO2) and the efficiency of O2 transfer from alveoli to the pulmonary capillary blood .

59. five physiologic causes of hypoxemia: (1) hypoventilation (2) V/ Qmismatching (3) right-to-left shunt (4) diffusion limitation (5) diffusion-perfusion mismatch PRINCIPLE : PaO2 is measured using a Clark electrode. The electrode :cathode (either platinum or gold) and an anode in an electrolytic bath, surrounded by a thin O2 permeable membrane.

60. The electrode is inserted into the sample, and O2 diffuses through the membrane and is reduced by the cathode, generating a current. The current is proportional to the PO2 in the sample The PCO2 electrode measures the change in pH brought about by the equilibration of blood with a bicarbonate solution TEMPERATURE : At lower temperatures, solubility is increased, leading to a reduction in partial pressure. measure gas partial pressures at 37°C. As blood from a hypothermic patient is warmed to 37°C by the analyzer, CO2 and O2 will come out of solution, leading to PaCO2 and PaO2 higher than those present in the patient.

61. DYNAMIC RESPIRATORY MECHANICS the mechanical behavior of the respiratory system during breathing or ventilation can be described according to the simple equation of motion that encompasses its resistive (R), elastic (E), and inertial (I) properties: P= RV+EV+IV+Po where V is volume, V denotes volume acceleration (i.e., the first time-derivative of flow or the second time-derivative of volume ), and Po is the distending pressure at end expiration .

62. STATIC RESPIRATORY MECHANICS quasi-static PV curves of the lungs or total respiratory system : nonlinear Compliance : local slope ( dP / dV ) of the PV curve , varies with lung volume. PV curves described using single exponential or sigmoidal functions . upper inflection point ( UIP) and lower inflection point (LIP ) The UIP :the point at which lung overdistention occurs, as during parenchymal strain-stiffening The LIP :reflect the process of maximum alveolar recruitment .

63. During protective ventilation, one seeks to ventilate a patient in the most linear region of the PV curve . Enough PEEP needs to be applied to avoid the LIP, where cyclic recruitment and derecruitment occur, along with lower VTs to avoid the UIP and overdistention . PV curves exhibit hysteresis: the biophysical properties of surfactant, time-dependent recruitment or derecruitment , contact friction among various connective tissue elements

64. MONITORING OF RESPIRATORY PRESSURES M.C. used Pressure measured in the trachea or at the airway opening, exclusive of any distortions from airway devices or breathing circuits Transrespiratory pressure :pressure drop across the lungs and chest wall, during PPV - difference between airway pressure and atmospheric pressure . transpulmonary pressure : distending pressure across the lungs alone. measurement of airway opening pressure, but also estimates of the pressure within the pleural space.

65. Noninvasively: esophageal balloon catheter catheters are typically 100 cm long, with side holes in the distal tip covered by a thin-walled balloon Peak and plateau pressuresare obtained from the transrespiratory pressure. limiting transrespiratory plateau pressures to 26 to 30 cm H2O, to minimize alveolar overdistension .

66. Auto-PEEP or intrinsic-PEEP : positive pressure present within the alveoli at end-exhalation in ventilated patients with COPD, who demonstrate dynamic airway compression and expiratory flow limitation , as well as a significant portion of patients with ARDS , sepsis, and respiratory muscle weakness difference between end-occlusion to preocclusion airway pressures esophageal balloon G auge configuration & piezoresistive transducers: pressure-sensing diaphragm whose electrical resistance changes when it is deformed in response to a differential pressure.

67. MONITORING OF RESPIRATORY FLOWS Hot wire anemometers : rely on temperature-dependent changes in the electrical resistance of a current carrying wire. When gas flows past the wire, the corresponding temperature drop changes the conductivity of the filament, which can be sensed with appropriate electronic circuits . Limitation: single wire filament cannot sense the direction of flow Pneumotachographs Orifice Flowmeters MONITORING OF RESPIRATORY VOLUME: electrically or numerically integrating the corresponding flow signal

68. PLETHYSMOGRAPHIC MONITORING Respiratory inductance plethysmography (RIP ): non invasive respiratory monitoring technique quantifies changes in the cross-sectional area of the chest wall and the abdominal compartments . used to assess VT, respiratory rate, adequacy of HFOV, lung volume changes during tracheobronchial suctioning, and thoracoabdominal synchrony.

69. Principle : current applied through a loop of wire generates a magnetic field normal to the orientation of the loop (Faraday’s law) and that a change in the area enclosed by the loop creates an opposing current within the loop directly proportional to the change in the area (Lenz’s law ) USES : monitor VT and respiratory rate, building on the advantage that a facemask, LMA, or ETT is not required for measurements LIMITATIONS : cannot be used during thoracic and abdominal surgery

70. RESPIRATORY RATE MONITORING M ain types of apnea central and obstructive Central apnea :failure of the CNS to drive respiration Obstructive apnea: upper airway obstruction Chest wall expansion is usually measured as follows: Changes in thoracic electrical impedance (impedance pneumography ) of the chest wall . based on the changes in electrical conductivity of the chest to an electrical current as air moves in and out of the lungs during breathing and blood volume changes in the same period .

71. 2 . Inductive plethysmography 3. Abdominal and chest fiberoptic and resistive strain gauges (a pressure pad placed alongside the infant’s rib cage , pneumatic abdominal sensors) are used. 4. Electromyographic signal of respiratory muscles is not frequently used because of the low signal-to-noise ratio . drawback of techniques based on chest expansion: inaccuracy in the presence of movement. O bstructive apnea: falsely assessed as normal respirations Gas flow methods are based on measurements of different variables directly related to the presence of air flow in the airway:

72. 1. Pressure gradients along the breathing circuit. Uses the Poiseuille principle (ΔP=k × V) and differential pressure transducers to detect flow 2 . Temperature of the breathed air in the nose or mouth 3. Rapid response hygrometer : assessment of humidity in the exhaled air . Techniques based on gas exchange : Capnography : early detection of respiratory depression before O2 desaturation , particularly when supplemental O2 is administered.Infrared sensors : M.C technique. Respiratory rate measurements

73. IMAGING FOR RESPIRATORY MONITORING Chest radiography: interstitial infiltrates, hyperinflation, pneumothorax , pleural effusion, and consolidation Ultrasonography I-AIM (Indication, Acquisi tion , Interpretation, Medical Decision-Making) framework BLUE protocol, A/B/C and PLUS protocol

74. POINT OF CARE TESTS POCT: analysis of arterial blood gases (PaO2, PaCO2, pH), Hb, and lactate. Hb is measured using either conductivity-based meth ods where hematocrit is assessed and the Hb concentration calculated (Hb [g/ dL ] = hematocrit × 0.34) or with optical methods, such as using the azide-metHb reaction and photometry

75. ADDITIONAL MONITORED VARIABLES Nitrogen washout and end-expiratory lung volume: step change in the inspired air (room air to 100% O2, a nitrogen washout/wash-in method with 10% to 20% change in FIO2) mass balance equations for the lung volume Transcutaneous measurements of Partial pressures of O2 & CO2 based on the diffusion of O2 and CO2 through the skin Lung water

76. Indicator Dilution Methods: cold saline as the single indicator injected in a central venous line. EVLW and additional hemodynamic parameters (i.e., cardiac output) are computed from the curve of temperature in the peripheral artery.

77. DNB QUESTIONS Pulseoximeter – physical principle, applications and limitations Recent advances What is capnography ? Principles Labelled diag. of normal capnograph Importance in anaesthesia Various methods of oxygen monitoring in anaesthesia practice

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