Oximetry. Jan Bakker. Grants Hutchinson Pulsion.

Transcription

1 Oximetry Jan Bakker Grants Hutchinson Pulsion Postgraduate Workshop on Hemodynamic Monitoring ISICEM Brussels

2 Oximetry arterial (pulse oximetry) central/mixed venous (intravenous) tissue (Near InfraRed Spectroscopy)

3 Pulse oximetry Hbo 2 Red IR Hb technique 660nm Relies on two principles nm Figure 1: Absorption coefficient for two types of haemoglobin at red and infrared wavelength. Figure 1. Figure 2. Photodiode Figure 2: Basic idea of a pulse oximeter Absorption coefficient for two types Basic idea of a pulse oximeter of haemoglobin at red and infrared wavelength. 1. a pulsatile signal generated by arterial 12 blood relative to non-pulsatile signal related to capillary and venous blood 2. the different absorption spectra of oxygenated and deoxygenated blood are different

4 Pulse oximetry technique Red IR Photodiode An automatic gain control (AGC) is implemented into the system as the AGC controls the intensity of the LEDs. This is required in order to keep the DC level constant regardless of the thickness of the finger. Ideally, when a thick finger is placed between the photodiode and the LEDs, the intensity of the LEDs incident onto the measuring surface will be brighter but with a thin finger, the input intensity will be dimmer.

5 Pulse oximetry technique Red IR Photodiode Absorption and Light Output Red LED Spectrum 50% far red 0% (HHb) 100% (O 2 Hb) Wavelength (nm) IR LED Spectrum near infrared Red (660nm)and IR (910nm) light send into the tissue Nonabsorbed light is sensed by the opposite photodiode Absorption of each light is different for oxygenated and deoxygenated hemoglobin Calculated ratio can be converted to the actual hemoglobin saturation

6 Pulse oximetry limitations Red IR Photodiode Oxygen dissociation curve limits early detection of decreasing PaO2 when baseline is high Intravenous dyes (methylene blue, indocyanine green) can result in false low readings With 2 wavelength devices inaccuracy is increased carboxyhemoglobin and and methemoglobin Nail polish and skin pigmentation Ambient light (xenon light OR) 1.Anesthesiology 1986, 65: Acta Anaesthesiol Scand 1995, 89: Anesth Analg 1989, 67: Anesth Analg 1995, 81: J Clin Monit 1989, 5:

7 Pulse oximetry limitations Red IR Photodiode bias and precision related to true SaO 2 SaO2 >90% : bias <2% precision: <3% increases to >5% when SaO2 < 90% 1.Health Devices 1989, 18: Chest 1990, 97:

8 Pulse oximetry limitations Red IR Photodiode Anemia increases bias 0 O- 202 S,o 2 = 54.5 (range )%. * ~ / i -5-.,oso2 i -s BIAS and SD :" i i Hb, g/dl mas -T0- / / / / / t / p - /.s es S i,'" ~ Hb=12.9 g/dl, n=9 ~'"... & Hb=8 g/dl, n=r i t at t t =.t b 7b eb 9b 100 Sa02% 1.J Clin Monitoring 1990;6(3):85-88

9 Pulse oximetry limitations Red IR Photodiode Crit Care Med 1997, 25:

10 Comparison of two new generation pulse oximeters during emergency ambulance transportation Ulrike Weber, Elvira Tomschik, Irene Resch, Krista Adelmann, Matthias Hasun, Bruno Mora, Reinhard Malzer and Alexander Kober Eur J Anaesthesiol 2011;28:92 96 Table 3 Comparison of the two pulse oximeters all patients had vasoconstriction Radical 7 N 600 Significance BP > 100/60 Number of malfunctions per patient NS (minimum maximum) (0 1) (0 3) Mean duration per malfunction SD (s) NS Total number of malfunctions 3 3 BP 100/ NS Number of malfunctions per patient (minimum maximum) (0 4) (0 1) Mean duration per malfunction SD (s) NS Total number of malfunctions 8 4 All patients NS Number of malfunctions per patient (minimum maximum) (0 4) (0 3) Mean duration per malfunction SD (s) NS Total number of malfunctions 11 7 Conclusion Although number and duration of malfunctions did not differ significantly between the devices, they showed a very low number of malfunctions even in hypotensive patients with peripheral vasoconstriction. Oxygen saturation correlated significantly in the two devices investigated at time points. In addition, pulse rate also correlated significantly. The Masimo Radical 7 uses an algorithm that identifies the arterial signal in the presence of a non-arterial (venous) signal that occurs during motion The Nellcor N 600 attenuates incoming signals that do not occur synchronously with the average rhythm of the pulse rate and allows the parts of the waveform that are synchronous with the heart rate to remain unattenuated and, thus, contribute more to the calculated SpO2.

11 Pulse oximetry new technology Red IR Photodiode Forehead Fingers Ear Reduced O 2 The MAX-FAST Forehead Sensor detects changes in SpO 2 faster than finger sensors, and with accuracy that more closely tracks to arterial blood data. SaO 2, SpO 2 (%) Radial Artery FIO 2 (%) FIO :04:00-0:02:00 0 0:00:00 0:02:00 0:04:00 0:06:00 0:08:00 0:10:00 Elapsed Time (h:mm:ss) Cold Room Vasoconstriction Blood Study Subject 403

12 Knowledge about pulse oximetry among medical and nursing staff If a patient s saturation is unacceptably low, what are your immediate actions? - none would check airway, breathing or circulation - 10% of the nurses and 20% of the doctors would check the waveform - 50% of the doctors would order a blood gas analysis A patient with tension pneumothorax and central cyanosis is in the ED. The SpO2 on the monitor reads 100% What are the implications of this reading? - 87% of the doctors and 57% of the nurses would ignore the reading and treat on clinical signs What happens to the SpO2 reading right after cardiac arrest? - 7% of the nurses and 17% of the doctors correctly stated that as the pulseoximeter requires a pulsatile signal an alarm would sound - all the others thought the saturation would fall gradually or suddenly What happens to the SpO2 reading right after respiratory arrest? - 83% of the doctors and 63% of the nurses correctly answered that the saturation would fall until cardiac arrest occurred Lancet 1994, 344:

13 Pulse oximetry does the patient benefit? Red IR Photodiode Very obvious advantages of having an indicator of SaO2 When correctly understood the limitations of the technique may also contain important information No RCT in ICU patients Large RCT in surgery failed to prove benefit to patients although it increased confidence levels of health care workers and decreased the incidence of low SaO2 levels Continuous SpO2 monitoring when used on a postcardiac surgery floor was costeffective. It changed the reason for ICU admission but not the rate of ICU admission was. 1.Anesth Analg 2003;96: Anesth Analg 2006;102: Anesthesiology 1993;78:

14 venous oximetry technique The emitted light illuminates the blood within the vessel s lumen and is backscattered and refracted by the different blood cells and by the vessel s wall and absorbed by the hemoglobin. As for absorption during transmission spectrophotometry, the reflection characteristics of hemoglobin and oxyhemoglobin are a function of wavelength and oxygen saturation is assumed to be a function of the ratio of reflected light at different selected wavelengths.

15 venous oximetry Table 4. Clinical Studies Examining Accuracy of Svoz Monitoring B Baele Rouby Woerkens Scuderi wong Vaughn Armaganidis References (1992P (1990)55 (1992)55 ( (1993P (198W (1994P Referenced bench bench bench blood bench blood blood methods oxymetry oxymetry oxymetry gases oxymetry gases gases Number of studied eters cath- Number of studied patients Patient popula- surgical ICU surgical ICU perioperative ICU ICU CHF, ARF, medical ICU tion Comparison Analysis Correlation to to preoperative Bias (96) to to 1.3 Precision 1%) to to Abbreviations: ARF, acute respiratory failure; CHF, congestive heart failure; ICU, intensive care unit. J Crit Care 1998;4:

16 venous oximetry limitations Blood flow velocity Hemoglobin level Blood coagulability Distance to the vessel wall Refractive index of the plasma Erythrocyte shape and position in the flowing stream Degree of rouleaux formation J Crit Care 1998;4:

17 venous oximetry limitations (cont d) Global indicator no direct regional indicator of flow Balance between oxygen demand and oxygen supply Not an indicator of the adequacy of oxygen supply Multimodal parameter CaO2 (Hemoglobin and arterial saturation) Oxygen consumption Cardiac Output 1.J Crit Care 1998;4: Crit Care Med 2005; 33:

18 venous oximetry trouble shooting Problems Potential Causes Interventions Svo, PA value higher or lower than Svo, measured on blood gases No Svo, PA available Problem with signal pulsatility (catheter wedging) Problem with signal intensity (catheter kinking, debris on the tip, hemodilution) input values of hematocrit and/or hemoglobin differ by more than 1.8 g/dl or 6% Fault in the in vitro calibration procedure Catheter not free floating Wall contact artifact Update input values with actual hematocrit and/or hemoglobin values Repeat in vivo calibration procedure Chest radiograph verification of catheter position: Ensure that catheter insertion distance is consistent with heart size Use chest radiograph to verify proper catheter position Confirm that catheter is not against the endocardial surface Replace catheter well positioned but with persistent poor signal quality (or use alternative method of monitoring Svo,) Abbreviations: CO, cardiac output; PA, pulmonary artery; Svo?, venous oxygen saturation. J Crit Care 1998;4:

19 venous oximetry ScvO2 vs SvO2 Normal: ScvO2 is higher then SraO2 and SvO2 Differences may increase in states of (septic)shock

20 venous oximetry ScvO2 vs SvO2 90# 85# 80# 75# 70# 65# 60# 55# 50# SVC# RA# PA# Crit Care Med 1998; 26:

21 venous oximetry ScvO2 vs SvO2 SvO2 (%) SraO2 (%) 1.Crit Care Med 2009;37: Shock 2009;31:

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23 venous oximetry ContinuousCentral Venous Oxygen Saturation During Human CPR % Patients with return of spontaneous circulation 74 (19) (11) (25) 1OO (16) When Hb, SaO2 and Oxygen Demand do not change much, ScvO2 is indicative of blood flow (18) O (19) (6) o ~ r Maximal ScvO2 (%) Maximal mixed venous oxygen saturation (%) 90 Ann Ernerg Med 1992;21:

24 venous oximetry regional circulation Jugular bulb C2 Internal jugular vein British Journal of Anaesthesia 97 (1): (2006) J Cereb Blood Flow Metab 1998; 18: Neurosurgery 1994; 34: J Neurosurg 1996; 85: Facial vein Catheter Indicator of the balance between oxygen delivery and oxygen demand of the global brain (not regional ischemia of the brain) only monitoring of one side asymmetry of cerebral venous drainage best side to monitor cannot be predicted right side is preferred as it usually is the dominant vessel place above C2 to prevent sampling of extra-cranial venous drainage continuous monitoring or intermittent sampling (slow aspiration of the blood to prevent retrograde extra-cranial contamination) frequent calibration of continuous SjO2 catheter is required

25 venous oximetry regional circulation Jugular bulb C2 Internal jugular vein Facial vein Catheter Good indicator of vasospasm in SAH Good correlation with SNIRSO2 of the brain When oxygen content of the blood is stable and oxygen demand of the brain is coupled to flow and not changing, SjO2 is a good indicator of cerebral blood flow Can J Neurol Sci 2004;31:80-86 Ann Thoracic Surg 1996;61(3):

26 venous oximetry Interventions Crit Care Med 2005; 33:

27 venous oximetry does the patient benefit Early studies on goal directed SvO 2 showed no benefit N Engl J Med1995;333(16): Early goal directed ScvO 2 monitoring improved outcome N Engl J Med 2001;345: Goal directed ScvO 2 not superior to goal directed lacate in improving outcome JAMA 2010;303(8): Goal directed lactate and ScvO 2 improved outcome Am J Respir Crit Care Med 2010;182:

28 Near InfraRed Spectroscopy technique With 4 wavelength probe: total hemoglobin, optical path length, and optical scattering have little effect Since signal intensity is inversely proportional to the square of the pathlength, 5 cm separation appears to be the functional maximal optode spacing. This provides a mean depth of NIR light penetration ~1.7 cm Journal of Biomedical Optics 10(3), (May/June 2005) Neuroimage 2006;29:

29 Near InfraRed Spectroscopy technique Light sent into tissue is compared to light received in order to measure the amount of light lost (attenuation) Both absorbance and scattering events cause attenuation of light Muscle HHb Microvessel RBC HbO 2 HbO 2 HHb MbO 2 Objective is to measure light lost due to absorption events, not scattering in the non-pulsatile signal

30 Near InfraRed Spectroscopy technique Multiple-depth probes (different spaced receiving probes) can measure hemoglobin saturation at different depths can separate signal from different layers by subtracting the signal received by the two separately spaced probes and thus eliminate confounding effect of non-relevant layers (extra cerebral tissue)

31 Near InfraRed Spectroscopy advantages Multiple spots possible (muscle, brain, stoma, mouth) Reflects balance between local oxygen demand and oxygen supply Thus in stable oxygen content and demand related to flow Cold (vasoconstriction) does not impair the reading Critical Care 2009 Vol 13(suppl 1):P237 Crit Care 2010;14(suppl 1):S43 Br J Anaesth 2009; 103 (Suppl. 1): i3 i13 Ann Surg. 2009;249(5):

32 Peripheral vasoconstriction influences thenar oxygen saturation as measured by NIRS Lima et al. Intensive Care Med 2012 (in press) Baseline Cold 30 Rewarmed 30 HR (b/min) MAP (mmhg) SV (ml) CO (L/min) Core Temp ( o C) 76 [70-83] 67 [58-73] 70 [67-74] 93 [88-101] 100 [92-107] 95 [87-100] 110 [76-125] 139 [ ] 114 [ ] 8,6 [8,0-9,4] 10,1 [8,9-12,2] 7,9 [7,3-10,1] 36,8 [36,6-36,9] 36,6 [36,4-36,9] 36,6 [36,4-36,9] median [IQR]

33 Peripheral vasoconstriction influences thenar oxygen saturation as measured by NIRS Lima et al. Intensive Care Med 2012 (in press) Baseline Cold 30 Rewarmed 30 StO2 (%) RincStO2 (%/sec) Tskin-diff ( o C) CRT (sec) PI (%) 82 [80-87] 72 [70-77] * 80 [79-85] 3,0 [2,8-3,3] 1,7 [1,1-2,0] * 3,2 [3,0-4,2] 1,0 [-1,6-1,8] 3,1 [1,8-4,3] * 1,2 [-0,3-2,7] 2,5 [2,0-3,0] 8,5 [7,2-11,0] * 4,0 [3,0-5,7] 10,0 [9,1-11,7] 2,5 [2,0-3,8] * 9,1 [8,2-11,7] median [IQR]

34 Near InfraRed Spectroscopy limitations Edema is confounding factor (thenar muscle has low variance) Increased bilirubin levels (trending is preserved) Hemoglobin levels Extra- or intracracranial hematoma Changes in distribution of blood volume between arterial/capillary/venous compartment Skull thickness, extra-cerebral tissue 1.Intensive Care Med (2006) 32: Br J Anaesth 2009; 103 (Suppl. 1): i3 i13 3.Anesthesiology 2007;106:458 62

35 Near InfraRed Spectroscopy limitations SthenarO 2 is not related to ScvO2 unless flow is impaired Group A: LV failure 1.Surgical Infections 2008;9(5): Critical Care 2007,11:R6

36 Near InfraRed Spectroscopy dynamic measurements Vascular Occlusion Test 3 min 30 mm Hg above SAP

37 Peripheral vasoconstriction influences thenar oxygen saturation as measured by NIRS Lima et al. Intensive Care Med 2012 (in press) Baseline Cold 30 Rewarmed 30 StO2 (%) RincStO2 (%/sec) Tskin-diff ( o C) CRT (sec) PI (%) 82 [80-87] 72 [70-77] * 80 [79-85] 3,0 [2,8-3,3] 1,7 [1,1-2,0] * 3,2 [3,0-4,2] 1,0 [-1,6-1,8] 3,1 [1,8-4,3] * 1,2 [-0,3-2,7] 2,5 [2,0-3,0] 8,5 [7,2-11,0] * 4,0 [3,0-5,7] 10,0 [9,1-11,7] 2,5 [2,0-3,8] * 9,1 [8,2-11,7] median [IQR]

38 Near InfraRed Spectroscopy dynamic measurements In sepsis non-survival is associated with persistent abnormal recovery slope in a VOT In peripherally cooled healthy volunteers and in critically ill an abnormal recovery slope is related to peripheral vasoconstriction Administration of Norepinephrine can improve the recovery slope associated with a decrease in lactate levels 1.Intensive Care Med 2007;33: Lima et al. Intensive Care Med 2012 (in press) Crit Care Med 2011;39(7): J. Int Care Med. 2009;35(Suppl 1):S80

39 Near InfraRed Spectroscopy interventions In sepsis norepinephrine can improve SthenarO2 In major surgery and cardiac surgery therapeutic interventions to optimize arterial oxygen content, blood flow, perfusion pressure and to limit cerebral oxygen demand have been associated with improved ScerebralO2 1.Intensive Care Med 2010;36: Semin Cardiothorac Vasc Anesth 2007; 11:

40 Near InfraRed Spectroscopy does the patient benefit In carotid endarterectomy a decrease in ScerebralO2 > 12% is indicative of cerebral ischemia secondary to ICA clamping requiring interventions to preserve cerebral blood flow Use of ScerebralO2 traumatic brain injury has shown mixed results poor correlation with ICP and Sjugular bulbo2 in trauma good sensitivity in the detection of intracranial hematoma 1.Br J Anaesth 2009; 103 (Suppl. 1): i3 i13 2.Zentralbl Neurochir 2000;61: J Trauma 2006;61: Prog Brain Res 2007;161:207 16

41 Near InfraRed Spectroscopy does the patient benefit In multiple trauma patients SthenarO2 measured during early resuscitation is related to organ failure In high risk surgical patients and cardiac surgery patients prevention of low ScerebralO2 is associated with improved outcome In critically ill patients, low SthenarO2 is frequently present and associated with a worse outcome Dynamic measures of SthenarO2 following vascular occlusion are associated with outcome in sepsis J Trauma 2007;62:44 55 Anesth Analg 2005;101:740 7 Anesth Analg!2007;104:!51 8 Critical Care 2009, 13(Suppl 5):S13 Crit Care 2010;14(suppl 1):S750 Anesthesiology 2009;111:

42 Near InfraRed Spectroscopy does the patient benefit SmuscleO2 can predict development of compartment syndrome SmuscleO2 can predict need for blood transfusion in trauma patients Use of SthenarO2 may limit the use of blood transfusion in cardiac surgery patients Routine use of ScerebralO2 monitoring in post cardiac surgery patients remains a subject of debate J Pediatr Orthop 2007;27: Am Surg 2008;74: A Loukas et al. Crit Care 2011;Suppl 1 (abstract) Semin Thorac Cardiovasc Surg Pediatr Card Surg Ann 13:51-54 Semin Thorac Cardiovasc Surg Pediatr Card Surg Ann 13:44-50

43 Oximetry conclusions SpulseO 2 Scentral venouso2 and Smixed venouso2 and SNIRSO2 all use the difference in (infrared)(red)-light absorption of oxygenated and deoxygenated hemoglobin to estimate the oxygen saturation of the hemoglobin in the different compartments All techniques suffer from limitations Advanced algorithms and techniques have been shown to limit these limitations Trending is usually preserved All techniques deliver very relevant information in the treatment of critically ill patients when correctly used and understood When associated with appropriate protocols these techniques have been shown to improve outcome or may improve outcome but yet to prove