- Email: [email protected]
Monitoring during mechanical ventilation
PAEDIATRIC RESPIRATORY REVIEWS (2006) 7S, S37–S38
Monitoring during mechanical ventilation Dean R. Hess Associate Professor of Anesthesia, Harvard Medical School, Assistant Director of Respiratory Care, Massachusetts General Hospital, Boston, MA, USA
SUMMARY Monitoring is the continuous, or nearly continuous, evaluation of the physiologic function of a patient in real time to guide diagnosis and management decisions - including when to make therapeutic interventions and assessment of those interventions. Many physiologic parameters can be monitored during mechanical ventilation, including pulse oximetry, capnography, and ventilator graphics. Although its impact on patient outcomes has not been well studied, monitoring has become an integral part of the care of mechanically ventilated patients. Continuous pulse oximetry has become a standard of care for critically ill mechanically ventilated patients. Two wavelengths of light (660 nm and 940 nm) are passed through a pulsating vascular bed using two light-emitting diodes and a photodetector. This is translated into a plethysmographic waveform and the ratio of the amplitudes of these two plethysmographic waveforms is translated into a display of oxygen saturation. A number of limitations of pulse oximetry should be recognized, appreciated, and understood by everyone who uses pulse oximetry data. Most pulse oximeter errors can be explained as too little signal (e.g., low perfusion, improper probe placement) or too much noise (e.g., motion, ambient light). The newest generation of pulse oximeters is affected less by these potential errors. At saturations >80%, the accuracy of pulse oximetry is about 4–5%. Below 80%, the accuracy is worse, but the clinical importance of this is questionable. New pulse oximeters also measure carboxyhemoglobin and methemoglobin in addition to oxygen saturation.
E-mail address: [email protected] 1526-0542/$ – see front matter ß 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.prrv.2006.04.177
Capnometry is the measurement of CO2 at the airway opening during the ventilatory cycle. The relationship between the PaCO2 and end-tidal PCO2 will vary depending upon the relative contributions of various V/Q units of the lungs. Thus, caution should be exercised when extrapolating end-tidal PCO2 to PaCO2. End-tidal PCO2 is a standard of care to determine proper endotracheal tube position (no exhaled CO2 with esophageal placement). The slope of the capnogram is increased in patients with airway obstruction. Volume-based capnography can be used to assess carbon dioxide production (metabolic rate) and dead space ventilation. Using volume-based capnography, it is also possible to nonnvasively measure cardiac output with the partial CO2 rebreathing technique. Pulmonary mechanics is the expression of lung function through measures of pressure and flow. From these measurements, a variety of derived indices can be determined such as volume, compliance, resistance, and workof-breathing. Pulmonary graphics are derived when one of the parameters of pulmonary mechanics is plotted as a function of time or as a function of one of the other parameters. This produces scalar pressure-time, flowtime, and volume-time graphics as well as flow-volume and pressure-volume loops. Current generation ventilators provide monitoring of pulmonary mechanics and graphics in real time. Use of esophageal pressure allows assessment of pleural pressure changes during the respiratory cycle. The monitors readily available during mechanical ventilation provide important insights into the pathophysiology respiratory failure and are helpful to direct the care of mechanically ventilated patients. The entire January and February issues of Respiratory Care journal relate to assessment of respiratory mechanics and graphical waveforms during mechanical ventilation.
S38
FURTHER READING 1. Barker SJ. ‘‘Motion-Resistant’’ pulse oximetry: A Comparison of new and old models. Anesth Analg 2002; 95: 967–972. 2. Caples SM, Hubmayr RD. Respiratory monitoring tools in the intensive care unit. Curr Opin Crit Care 2003; 9: 230–235. 3. Davies G, Gibson AM, Swanney M et al. Understanding of pulse oximetry among hospital staff. N Z Med J 2003; 116: U297. 4. de Chazal I, Hubmayr RD. Novel aspects of pulmonary mechanics in intensive care. Br J Anaesth 2003; 91: 81–91. 5. DeNicola LK, Kissoon N, Abram HS Jr, Sullivan KJ, Delgado-Corcoran C, Taylor C. Noninvasive monitoring in the pediatric intensive care unit. Pediatr Clin North Am 2001; 48: 573–588. 6. Durbin CG, Rostow SK. More reliable oximetry reduces the frequency of arterial blood gas analyses and hastens oxygen weaning after cardiac surgery: a prospective, randomized trial of the clinical impact of a new technology. Crit Care Med 2002; 30: 1734–1740. 7. Gehring H, Nornberger C, Matz H et al. The effects of motion artifact and low perfusion on the performance of a new generation of pulse oximeters in volunteers undergoing hypoxemia. Respir Care 2002; 47: 48–60. 8. Giuliano KK, Higgins TL. New-generation pulse oximetry in the care of critically ill patients. Am J Crit Care 2005; 14: 26–37. 9. Goldman JM, Petterson MT, Kopotic RJ et al. Masimo signal extraction pulse oximetry. J Clin Monit 2000; 16: 475–483. 10. Harris RS, Hess DR, Venegas JG. An objective analysis of the pressurevolume curve in the acute respiratory distress syndrome. Am J Respir Crit Care Med 2000; 161: 432–439. 11. Hess D. An overview of noninvasive monitoring in respiratory care: Present, past, and future. Respir Care 1990; 35: 482–499. 12. Hess DR, Medoff MD, Fessler MB. Pulmonary mechanics and graphics during positive pressure ventilation. International Anesthesiology Clinics 1999; 37: 15–34.
D. R. HESS
13. Hess DR, Medoff MD, Fessler MB. Pulmonary mechanics and graphics during positive pressure ventilation. International Anesthesiology Clinics 1999; 37: 15–34. 14. Hess DR, Capnometry IN, Tobin MJ. Principles and practice of intensive care monitoring. New York: McGraw-Hill, 1998. 15. Hess DR. Monitoring during mechanical ventilation. in: Mosenifar Z, Soo Hoo GW. Practical pulmonary and Critical Care Medicine. Respiratory Failure. Lung Biology in Health and Disease, Volume 213, 2006. 16. Jensen LA, Onyskiw JE, Prasad NGN. Meta-analysis of arterial oxygen saturation monitoring by pulse oximetry in adults. Heart Lung 1998; 27: 387–408. 17. Nadkarni UB, Shah AM, Deshmukh CT. Non-invasive respiratory monitoring in paediatric intensive care unit. J Postgrad Med 2000; 46: 149–152. 18. Numa AH, Newth CJ. Assessment of lung function in the intensive care unit. Pediatr Pulmonol 1995; 19: 118–128. 19. Salyer JW. Neonatal and pediatric pulse oximetry. Respir Care 2003; 48: 386–398. 20. Stenqvist O. Practical assessment of respiratory mechanics. Br J Anaesth 2003; 91: 92–105. 21. Tachibana K, Imanaka H, Takeuchi M et al. Noninvasive cardiac output measurement using partial carbon dioxide rebreathing is less accurate at settings of reduced minute ventilation and when spontaneous breathing is present. Anesthesiology 2003; 98: 830–837. 22. Verschuren F, Liistro G, Coffeng R et al. Volumetric capnography as a screening test for pulmonary embolism in the emergency department. Chest 2004; 125: 841–850. 23. Walsh TS. Recent advances in gas exchange measurement in intensive care patients. Br J Anaesth 2003; 91: 120–131. 24. Yem JS, Tang Y, Turner MJ et al. Sources of error in noninvasive pulmonary blood flow measurements by partial rebreathing. A computer model study. Anesthesiology 2003; 98: 881–887.
Monitoring during mechanical ventilation Dean R. Hess Associate Professor of Anesthesia, Harvard Medical School, Assistant Director of Respiratory Care, Massachusetts General Hospital, Boston, MA, USA
SUMMARY Monitoring is the continuous, or nearly continuous, evaluation of the physiologic function of a patient in real time to guide diagnosis and management decisions - including when to make therapeutic interventions and assessment of those interventions. Many physiologic parameters can be monitored during mechanical ventilation, including pulse oximetry, capnography, and ventilator graphics. Although its impact on patient outcomes has not been well studied, monitoring has become an integral part of the care of mechanically ventilated patients. Continuous pulse oximetry has become a standard of care for critically ill mechanically ventilated patients. Two wavelengths of light (660 nm and 940 nm) are passed through a pulsating vascular bed using two light-emitting diodes and a photodetector. This is translated into a plethysmographic waveform and the ratio of the amplitudes of these two plethysmographic waveforms is translated into a display of oxygen saturation. A number of limitations of pulse oximetry should be recognized, appreciated, and understood by everyone who uses pulse oximetry data. Most pulse oximeter errors can be explained as too little signal (e.g., low perfusion, improper probe placement) or too much noise (e.g., motion, ambient light). The newest generation of pulse oximeters is affected less by these potential errors. At saturations >80%, the accuracy of pulse oximetry is about 4–5%. Below 80%, the accuracy is worse, but the clinical importance of this is questionable. New pulse oximeters also measure carboxyhemoglobin and methemoglobin in addition to oxygen saturation.
E-mail address: [email protected] 1526-0542/$ – see front matter ß 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.prrv.2006.04.177
Capnometry is the measurement of CO2 at the airway opening during the ventilatory cycle. The relationship between the PaCO2 and end-tidal PCO2 will vary depending upon the relative contributions of various V/Q units of the lungs. Thus, caution should be exercised when extrapolating end-tidal PCO2 to PaCO2. End-tidal PCO2 is a standard of care to determine proper endotracheal tube position (no exhaled CO2 with esophageal placement). The slope of the capnogram is increased in patients with airway obstruction. Volume-based capnography can be used to assess carbon dioxide production (metabolic rate) and dead space ventilation. Using volume-based capnography, it is also possible to nonnvasively measure cardiac output with the partial CO2 rebreathing technique. Pulmonary mechanics is the expression of lung function through measures of pressure and flow. From these measurements, a variety of derived indices can be determined such as volume, compliance, resistance, and workof-breathing. Pulmonary graphics are derived when one of the parameters of pulmonary mechanics is plotted as a function of time or as a function of one of the other parameters. This produces scalar pressure-time, flowtime, and volume-time graphics as well as flow-volume and pressure-volume loops. Current generation ventilators provide monitoring of pulmonary mechanics and graphics in real time. Use of esophageal pressure allows assessment of pleural pressure changes during the respiratory cycle. The monitors readily available during mechanical ventilation provide important insights into the pathophysiology respiratory failure and are helpful to direct the care of mechanically ventilated patients. The entire January and February issues of Respiratory Care journal relate to assessment of respiratory mechanics and graphical waveforms during mechanical ventilation.
S38
FURTHER READING 1. Barker SJ. ‘‘Motion-Resistant’’ pulse oximetry: A Comparison of new and old models. Anesth Analg 2002; 95: 967–972. 2. Caples SM, Hubmayr RD. Respiratory monitoring tools in the intensive care unit. Curr Opin Crit Care 2003; 9: 230–235. 3. Davies G, Gibson AM, Swanney M et al. Understanding of pulse oximetry among hospital staff. N Z Med J 2003; 116: U297. 4. de Chazal I, Hubmayr RD. Novel aspects of pulmonary mechanics in intensive care. Br J Anaesth 2003; 91: 81–91. 5. DeNicola LK, Kissoon N, Abram HS Jr, Sullivan KJ, Delgado-Corcoran C, Taylor C. Noninvasive monitoring in the pediatric intensive care unit. Pediatr Clin North Am 2001; 48: 573–588. 6. Durbin CG, Rostow SK. More reliable oximetry reduces the frequency of arterial blood gas analyses and hastens oxygen weaning after cardiac surgery: a prospective, randomized trial of the clinical impact of a new technology. Crit Care Med 2002; 30: 1734–1740. 7. Gehring H, Nornberger C, Matz H et al. The effects of motion artifact and low perfusion on the performance of a new generation of pulse oximeters in volunteers undergoing hypoxemia. Respir Care 2002; 47: 48–60. 8. Giuliano KK, Higgins TL. New-generation pulse oximetry in the care of critically ill patients. Am J Crit Care 2005; 14: 26–37. 9. Goldman JM, Petterson MT, Kopotic RJ et al. Masimo signal extraction pulse oximetry. J Clin Monit 2000; 16: 475–483. 10. Harris RS, Hess DR, Venegas JG. An objective analysis of the pressurevolume curve in the acute respiratory distress syndrome. Am J Respir Crit Care Med 2000; 161: 432–439. 11. Hess D. An overview of noninvasive monitoring in respiratory care: Present, past, and future. Respir Care 1990; 35: 482–499. 12. Hess DR, Medoff MD, Fessler MB. Pulmonary mechanics and graphics during positive pressure ventilation. International Anesthesiology Clinics 1999; 37: 15–34.
D. R. HESS
13. Hess DR, Medoff MD, Fessler MB. Pulmonary mechanics and graphics during positive pressure ventilation. International Anesthesiology Clinics 1999; 37: 15–34. 14. Hess DR, Capnometry IN, Tobin MJ. Principles and practice of intensive care monitoring. New York: McGraw-Hill, 1998. 15. Hess DR. Monitoring during mechanical ventilation. in: Mosenifar Z, Soo Hoo GW. Practical pulmonary and Critical Care Medicine. Respiratory Failure. Lung Biology in Health and Disease, Volume 213, 2006. 16. Jensen LA, Onyskiw JE, Prasad NGN. Meta-analysis of arterial oxygen saturation monitoring by pulse oximetry in adults. Heart Lung 1998; 27: 387–408. 17. Nadkarni UB, Shah AM, Deshmukh CT. Non-invasive respiratory monitoring in paediatric intensive care unit. J Postgrad Med 2000; 46: 149–152. 18. Numa AH, Newth CJ. Assessment of lung function in the intensive care unit. Pediatr Pulmonol 1995; 19: 118–128. 19. Salyer JW. Neonatal and pediatric pulse oximetry. Respir Care 2003; 48: 386–398. 20. Stenqvist O. Practical assessment of respiratory mechanics. Br J Anaesth 2003; 91: 92–105. 21. Tachibana K, Imanaka H, Takeuchi M et al. Noninvasive cardiac output measurement using partial carbon dioxide rebreathing is less accurate at settings of reduced minute ventilation and when spontaneous breathing is present. Anesthesiology 2003; 98: 830–837. 22. Verschuren F, Liistro G, Coffeng R et al. Volumetric capnography as a screening test for pulmonary embolism in the emergency department. Chest 2004; 125: 841–850. 23. Walsh TS. Recent advances in gas exchange measurement in intensive care patients. Br J Anaesth 2003; 91: 120–131. 24. Yem JS, Tang Y, Turner MJ et al. Sources of error in noninvasive pulmonary blood flow measurements by partial rebreathing. A computer model study. Anesthesiology 2003; 98: 881–887.