Capnography
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This document discusses advanced capnography techniques. It begins by listing the objectives which include describing the physiology of carbon dioxide monitoring, differentiating between mainstream and sidestream capnography, interpreting normal and abnormal time-based and volume-based capnograms, and discussing several clinical applications of capnography. It then covers the physiology of carbon dioxide, monitoring technologies, key technological issues, differences between mainstream and sidestream sampling, phases of normal time-based and volume-based capnograms, abnormalities, artifacts, and clinical uses including ventilation monitoring, cardiac output measurement, pulmonary embolism detection, and more.
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Capnography
- 2. Objectives • List three indications for capnography. • Differentiate between mainstream and sidestream capnography. • Given a time-based capnogram, identify and distinguish between the phases. • Given a time-based capnogram, interpret any abnormality present. • Given a volume-based capnogram, identify and distinguish between the phases. • Given a volume-based capnogram, state the significance of each phase.
- 3. Objectives • Given a volume-based capnogram, interpret any abnormality present. • List two instances where volume-based capnography can lead to improved patient management. • State the formula used for the calculation of non-invasive cardiac output via the CO2 Partial-Rebreathing method. • Describe the set-up used to measure cardiac output via the CO2 Partial- Rebreathing method. • List two additional uses for capnography.
- 4. Physiology of Carbon Dioxide METABOLISM PERFUSION VENTILATION ALL THREE ARE IMPORTANT!
- 5. Carbon Dioxide Monitoring Technology • Mass Spectroscopy • Methods of Sampling • Mainstream • Sidestream • Microstream
- 7. Key Technological Issues • Calibration • Moisture Control • Sample flow rate • Transit time • Response time
- 9. The Normal Time Capnogram
- 10. Phases of the Time Capnogram • Phase I: Inspiration • No CO2 detected (hopefully) • Phase II: Appearance of CO2 in the system. • Mixed alveolar and deadspace gas. • Phase III: Plateau • Constant emptying of alveolar gas. • Presence of CO2 through the end of the breath. • Phase IV: Washout of CO2 from subsequent inspiration.
- 11. Abnormal Waveforms Sudden loss of PETCO2 to zero or near zero indicates immediate danger because no respiration is detected. •Esophageal intubation •Complete airway disconnect from ventilator •Complete ventilator malfunction •Totally obstructed/kinked endotracheal tube
- 12. Abnormal Waveforms Exponential decrease in PETCO2 reflects a catastrophic event in the patient’s cardiopulmonary system. •Sudden Hypotension/massive blood loss •Circulatory arrest with continued ventilation •Pulmonary embolism •Cardiopulmonary Bypass
- 13. Abnormal Waveforms Gradual decrease in PETCO2 indicates a decreasing CO2 production, or decreasing systemic or pulmonary perfusion. •Hypothermia •Sedation •Hyperventilation •Hypovolemia •Decreasing Cardiac Output
- 14. Artifacts with Time-Based Capnograms • Patient efforts • “Curare cleft” • Cardiac Oscillations
- 15. End-Tidal CO2
- 16. Clinical Uses of Capnography • Weaning • Hyperventilation monitoring • Use in Cardiac Arrest • Intubation verification • Restoration of Spontaneous Circulation • Easy Cap
- 18. The Normal Volume-Based Capnogram
- 20. Checklist for Interpreting a Volume- Based Capnogram • Phase I – Deadspace Gas • Rebreathing? (1) • Deadspace seem right? • Phase II – Transitional Phase • Transition from upper to lower airways. • Should be steep. (3) • Represents changes in perfusion. • Phase III – Alveolar Gas Exchange • Changes in gas distribution. • Increased slope = mal-distribution of gas delivery. (5) • End of Phase III is the PETCO2. (6) • Area under the curve represents the volume of expired CO2 (VCO2). • Exhaled volume (8)
- 21. The Normal Volume-Based Capnogram Vd
- 22. Waveform Phases % CO2 Exhaled Volume I: Deadspace II: Perfusion III: Gas Distribution
- 23. Clinical significance • Phase 1 • ↑ depicts an ↑ in airways dead space. • Phase 2 • ↓ slope depicts reducing perfusion. • Phase 3 • ↑ slope depicts mal-distribution of gas.
- 24. ↑ phase 1 Phase 1 – relatively short Phase 1 - prolonged
- 25. Phase 2 assessment If ↓ in phase 2 – Assure stable minute ventilation • Assess PEEP level • ↑ intrathoracic pressure may cause ↓ venous return • Assess hemodynamic status • Is minute ventilation stable? • Volume resuscitation or vasopressors may be indicated
- 26. ↓ Phase 2 Decreased Perfusion Baseline
- 27. ↓ Phase 2 • When minute ventilation is stable, indicative of a ↓ in perfusion.
- 28. Phase 3 assessment If ↑ or absent phase 3 mal-distribution of gas at alveolar level exists • Assess for appropriate PEEP level • Inadequate PEEP may be present • Bronchospasm • Bronchodilator tx my be indicated • Structure damage at alveolar level may be present • Pnuemothorax?
- 29. ↑Phase 3 CO2 Exhaled Volume increased phase 3
- 30. ↑ or absent phase 3 •Slope of phase 3 present and level •Phase 3 absent
- 31. Airway - Alveolar Volume % CO2 VD VALV Exhaled Tidal Volume
- 32. Effective Tidal Volume • The volume of gas between the end of Phase I and the end of Phase III. • Phase I represents the volume of gas being delivered from the ventilator which doesn’t participate in gas exchange. • Monitoring of the effective tidal volume can indicate on a breath-by-breath basis when PaCO2 changes will be occurring before they actually rise.
- 33. Area X = Vol CO2 Allows determination of VCO2 in one min. (200 mL/min.) Exhaled Volume % CO2 Volume CO2 (Area X)
- 34. VCO2 • VCO2 represents the volume of CO2 eliminated. • This is usually the same as what is produced. • CO2 balance is dependent on four factors: • Production • Transportation (cell to blood & blood to lungs) • Storage (conversion to CO2 containing substances in the muscle, fat and bone) • Elimination • Monitoring VAand VCO2 allows for evaluation of a successful weaning process.
- 35. Waveform Regions Z = anatomic VD; Y = VD Alveolar % CO2 VD VALV %CO2 in Arterial Blood Z X Y Exhaled Tidal Volume
- 36. Sum of VDanat (Z) and VDalv (Y) is Physiologic VD X Y Z PaCO2 - PeCO2 PaCO2 Y + Z X + Y + Z =• Phys VD / VT • Alveolar Ventilation • Min. Vol. CO2 ( VCO2 )
- 37. Uses of Volumetric Capnography • Assess work of breathing during weaning trial.
- 38. EXPECTED
- 39. Using Vtalv and VCO2 to Recruit Alveoli in a Postoperative CABG Patient Suffering from Hypoxemia HOSAM M ATEF
- 40. Using Vtalv and VCO2 to Recruit Alveoli • Patient Profile • 72 yo male, post-op CABG, MV • Clinical Challenge • Developed a low SpO2 within 2 hours of arrival into the ICU • FIO2 and PEEP increased, no acceptable change in PaO2 and SpO2 • Clinical Intervention • Lung recruitment
- 41. •Clinical Course •PEEP increased by 2 cm H2O every 10 minutes •Observed Vtalv, VCO2 and SpO2 •Monitoring Data •Red arrows show PEEP increases •No deterioration in VCO2, oV/Q stable •Vtalv starts to increase at 16 cm H2O, alveoli are being recruited •SpO2 responded at 20 cm H2O Using Vtalv and VCO2 to Recruit Alveoli
- 42. • Summary • Vtalv is an ideal parameter to show alveolar recruitment • VCO2 indicates V/Q status during the procedure • SpO2 did not show improvement until best PEEP • Vtalv combined with VCO2 were best to indicate increased PEEP levels were working Using Vtalv and VCO2 to Recruit Alveoli
- 43. Uses of Volumetric Capnography • Optimal PEEP • Overdistension leads to increased Vdanat and reduced perfusion. • Increased Vdanatcan be assessed by an increase in Phase I volume. • Reduced perfusion can be assessed by a decrease in Phase II slope combined with a decrease in VCO2.
- 44. Increasing PEEP – •Expanded Airways increase Vdanat.(zone Y) •Expanded alveoli restrict perfusion so increased Vdalv. (Zone Z) Exhaled Volume 0 3 6 9 12 15 cmH2O
- 45. VCO2 to Determine Optimal PEEP • Patient Profile • 25 yo male, motorcycle accident • Head injury, rib fractures • Pentobarbital induced coma • Clinical Challenge • Developed acute lung injury • Low PaO2, SpO2
- 46. • Clinical Intervention • Maximize lung recruitment • Determine optimal PEEP • Without aversely affecting intracranial pressures • Clinical Course • Monitor VCO2 and VA • Increase PEEP in 2 cm H2O increments VCO2 to Determine Optimal PEEP
- 47. •Results •PEEP increased from 14 to 20 •Each step increased VA, VCO2 initially decreased but recovered •At PEEP of 22, VA did not increase, VCO2 did not recover •PEEP reduced to 20, VCO2 recovered 22 cmH20 Optimal PEEP VCO2 to Determine Optimal PEEP
- 48. • Determining Optimal PEEP • VA Showed sharp rises after initial PEEP settings A result of alveolar recruitment • VCO2 Initial decrease after PEEP increase, recovered quickly Confirmed that pulmonary perfusion was not compromised VCO2 to Determine Optimal PEEP
- 49. Improvement in Distribution of Ventilation in Asthma • Asthma – Day 1 (dark) Day 5 (blue)
- 50. Which graph represents ARDS? •Graphs show PECO2 vs. Volume (hatched line). •VAE represents the “alveolar ejection volume” (true alveolar gas mixing volume).
- 51. Uses of Volumetric Capnography • Pulmonary Embolism • 650,000 cases/year in US • 50,000 to 200,000 die. • Most deaths occur within first hour. • Prompt therapy can reduce mortality from 30% to 2.5 to 10%. • 70% of deaths from PE identified by autopsy were not identified before death. • Methods of PE detection • Evaluation of Vd/Vt • PaCO2-PETCO2 gradient with maximum exhalation. • Late deadspace fraction (Fdlate)
- 53. Uses of Volumetric Capnography •Non-Invasive Cardiac Output •Fick Principle (1870) OR 22 2 OvCCaO OV QC − = • 22 2 CaCOCOvC COV QC − = •
- 55. Calculation involved with NICO 22 2 CaCOCOvC COV QC − = • 2 2 PetCO COV QC ∆ ∆ = •
- 57. Other uses for Capnography • During Apnea Testing in Brain-dead patients. • Eur J Anaesthesia Oct 2007, 24(10):868-75 • Evaluating DKA in children. • No patients with a PETCO2 >30 had DKA. • J Paeditr Child Health Oct 2007, 43(10):677-680 • Vd/Vt ratio and ARDS Mortality • Elevated Vd/Vt early in the course of ARDS was correlated with increased mortality. • Chest Sep 2007, 132(3): 836-842 • PCA Administration • “Continuous respiratory monitoring is optimal for the safe administration of PCA, because any RD event can progress to respiratory arrest if undetected.” • Anesth Analg Aug 2007, 105(2):412-8
Editor's Notes
- Summarize the phases
- …the slope of phase II is eliminated and a clear separation of deadspace is established.
- Area under the SBCO2 curve IS the volume of CO2 in a single breath. Sum all the Co2 volumes in a minute and you get the same results as a Douglas Bag collection
- If we add a horizontal line representing %CO2 in arterial blood, 4 distinct regions of the curve are established: 1 – Area X represents the actual amount of CO2 exhaled in the breath. 2 – Area Y represents the amount of CO2 that was NOT eliminated because we have some alveolar deadspace 3 – Area Z represents the amount of CO2 that was NOT eliminated because we have a certain anatomic structure 4 – Area X, Y and Z in total represent the maximum volume of CO2 possible to exhale in a single breath IF we have no airway deadspace AND no alveolar deadspace (or shunt). This would represent the perfect situation. The relationship between the areas (with the added Arterial Blood line) gives us some very important parameters for analysis.
- Three very important ventilation assessment parameters emerge and mimic the action of the douglas bag… The ratios of the areas created in the SBCO2 curve are the same as the relationship seen in the Enghoff modified Bohr equation. Keep in mind here that the elimination of CO2 volume (VCO2) is necessary to balance CO2 produced in the metabolism process. Alveolar ventilation details how much ventilation is required to eliminate the CO2 volume that is presented to the alveoli by perfusion.
- P R O F I L E This is a 72-year-old male patient, status post open heart surgery for four vessel CABG. The patient was taken to the Open Heart Cardiac Surgery Intensive Care Unit post procedure. Ventilator settings: SIMV 12, DP 22 cmH2O, IT 1.1 seconds, FIO2 40%, PEEP 5 cmH2O, PS 5 cmH2O. The ventilator settings were based on protocol and the anesthesia settings. Clinical problem: The patient developed a low SpO2 within two hours of arrival into the ICU. FIO2 was increased to 60%, PEEP increased to 10 cmH2O, DP increased to 28 cmH2O. A subsequent blood gas revealed a PaO2 of 61 mmHg. The patient’s compliance was 41 cmH2O/mL. Clinical intervention: The Health Care Team (HCT) decided to utilize the NICO2 monitor to optimize PEEP and maximize lung recruitment. Advanced Lung Recruitment Technology (ALuRT)
- CLINICAL COURSE Patient was set up on the NICO2 monitor and baseline Vtalv, VCO2, and SpO2 was measured. PEEP was increased by 2 cmH2O every 10 minutes to observe increases in Vtalv and SpO2. If the lung overdistends, VCO2 will drop significantly (greater than 20%). At a PEEP level of 14 cmH2O, Vtalv, VCO2, and SpO2 did not change significantly. PEEP was increased by 2 cmH2O up to 20 cmH2O. Within 15 minutes, Vtalv, VCO2 and SpO2 increased. Subsequent PaO2 increased to 151 mmHg. Compliance increased to 81 cmH2O/ml. The DP and IT was decreased to maintain the same minute ventilation. FIO2 was decreased to 40%. Over the next 24-36 hours, the patient’s PEEP was weaned utilizing the Vtalv parameter.
- DISCUSSION Most patients undergoing heart/lung bypass have adequate lung re-expansion from aggressive manual bagging by the clinician in the operating room prior to transfer to the ICU. If the procedure is not adequate, the patient can suffer from alveolar collapse and poor ventilation in the hours after the surgery. Using NICO2 to monitor Vtalv, VCO2, and SpO2 served two purposes: 1) increase the PEEP while monitoring for over distension 2) continuous monitoring of Vtalv to demonstrate the alveolar recruitment moment. In this case, the lung was never “over distended” at anytime, no cardiac compromise was noted. The reduction in DP, IT, and FIO2 facilitated a minimal support ventilation strategy. Additional note: Notice as the PEEP levels increased there was no deterioration in VCO2 indicating that V/Q was maintained. Vtalv was most sensitive to showing that alveoli were being recruited. SpO2 lagged until optimal PEEP was achieved.
- Another example is in this increasing PEEP model…phase II shifts right due to expanding airways (increasing PEEP stints the airways open more). Notice that slope of phase II decreases as well. This is a result of lower CO2 concentration occurring at a identical volume point (in a less/more PEEP setting). This demonstrates the need to manage alveolar volume in changing PEEP conditions…you must compensate for the loss of gas exchange volume
- P R O F I L E A 25-year-old male motorcycle operator struck a tree head-on. He sustained a massive head injury requiring ventriculostomy and eventually a pentobarbital-induced coma to control intracranial pressures. Patient rapidly developed acute lung injury due to multiple rib fractures and bilateral lung contusions. Ventilator settings were PCV-AC, RR of 14 breaths/minute, DP of 25 cmH2O, FIO2 80%, PEEP 14 cmH2O. The patient’s arterial PO2 was 78 mmHg.
- In light of the patient’s lung injury, the Health Care Team sought to maximize lung recruitment and determine the patient’s optimal PEEP without adversely affecting intracranial pressures.
- C L I N I CA L C O U R S E A baseline VCO2 trend was gathered. The NICO® Monitor was utilized to trend •VCO2 while PEEP was increased in 2 cmH2O increments. VCO2 was monitored for approximately five to seven minutes after each increase in PEEP. A decrease in VCO2 occurred immediately when PEEP was increased to 16 cmH2O. Over the next two minutes, sharp rises in MValv occurred and the VCO2 returned to baseline. An increase in PEEP to 18 cmH2O resulted in a decrease in VCO2 and no change in MValv. Over the next two minutes, sharp rises in MValv occurred and the VCO2 returned to baseline. The trial continued until the PEEP level reached 22 cmH2O. At this point, VCO2 decreased by over 40 ml/min and did not rise. PEEP was decreased to 20 cmH2O and VCO2 increased. The subsequent blood gas resulted in an arterial PO2 of 120 mmHg. The FIO2 was decreased over the next hour to 50%. The NICO Monitor was utilized over the next 24 to 48 hours to assist in weaning PEEP.
- The NICO Monitor was instrumental in determining optimal PEEP. The sharp rises in MValv and VCO2 after the initial two PEEP changes were a result of lung recruitment. Once the patient was receiving 22 cmH2O of PEEP, the alveoli were over-distended and pulmonary capillaries were compressed preventing adequate CO2 diffusion across the alveolar-capillary membrane. Determining optimal PEEP and fully recruiting the alveoli dramatically reduced the FIO2 requirement.