Monitoring Cardiopulmonary Interactions: Where Are We Going?* Juliette Hunt, MD Pediatric Cardiac Intensive Care Unit Children’s Hospital of Orange County Orange County, CA; and Department of Pediatrics University of California Irvine, CA Nick Anas, MD Pediatric Intensive Care Unit Children’s Hospital of Orange County Orange County, CA; and David Geffen School of Medicine at UCLA Los Angeles, CA
T
he following editorial is written by a senior author (Dr. Anas) who completed his critical care training with extensive experience in the use of the pulmonary artery catheter (PAC). On the other hand, the junior author of this editorial (Dr. Hunt) recently completed her critical care fellowship training having never inserted a PAC nor having had the opportunity to interpret and apply the hemodynamic information generated from its placement. In recent years, this junior author’s experience in training does not seem to be unique. The use of PACs has dramatically decreased in ICUs across the country (1). However, despite the decreased use of PACs, ICU physicians continue to have the same responsibility of understanding the concepts of cardiopulmonary interactions and now must make clinical decisions without the ability to collect much of the real-time physiologic data that demonstrate the relationships. Most will agree that the role of PACs has fallen out of use not because the data generated from their use lacks merit or value but because few studies have demonstrated improved outcome and the risk-benefit ratio disfavors their use (2–4). Recent advances have tried to make use of less invasive means of obtaining the data that PACs once generated to assist the bedside clinician. Among them is ultrasound, a modality that has become much more widely used for a variety of indications in many areas of clinical
*See also p. 15. Key Words: cardiopulmonary interactions; goal-directed therapy; pediatric critical care medicine; pulmonary artery catheters; ultrasound cardiac output monitor Drs. Anas and Hunt are employed by the Children’s Hospital of Orange County. Dr. Anas has provided expert testimony, has lectured, and has stock options. Copyright © 2013 by the Society of Critical Care Medicine and the World Federation of Pediatric Intensive and Critical Care Societies DOI: 10.1097/PCC.0b013e31829f5a45
84
www.pccmjournal.org
practice, including the ICUs. The ultrasound cardiac output monitor (USCOM) is a specific technology that uses the ultrasound modality to provide noninvasive cardiac output monitoring by measuring flow using continuous wave Doppler through the aortic or pulmonary outflow tracts. It provides the ability to monitor real-time variables of cardiac function (cardiac index [CI], stroke volume index, systemic vascular resistance index, and oxygen delivery) (M. Richardson, J. Brierley: USCOM in the management of paediatric septic shock, hypovolaemia and myocardial dysfunction, unpublished observations, 2013). In this issue of Pediatric Critical Care Medicine, Ingaramo et al (5) described the use of USCOM to assess the impact of positive end-expiratory pressure (PEEP) on CI. The purpose of this study was to measure CI in pediatric patients using the USCOM at varying levels of PEEP. The hypothesis was that elevated levels of PEEP would not have significant impact on CI. Ingaramo et al (6) also wanted to show the effect of lung recruitment on the relationship between PEEP and CI. They concluded that an increase in PEEP between 0 and 12 cm H2O did have a statistically significant effect on decreasing CI in hemodynamically stable, mechanically ventilated children but suggest that this change in CI is unlikely to have clinical significance. Additionally, they concluded that the relationship between increasing PEEP and decreasing CI was similar even when the lung might be at optimal functional residual capacity. The secondary analysis looking at finding the level of PEEP that may offer optimal lung compliance (point of highest dynamic compliance) did not correlate to improved CI. Much data already exist on the various ways that positive pressure ventilation (PPV) affects the determinants of cardiac output, both positively and negatively (6). Classic experiments by Guyton et al (7) showed the basic principle that systemic venous return is the major determinant of left ventricular (LV) output. Others have also shown that the primary effect of PPV on cardiac output is by increasing right atrial pressure which reduces the driving pressure for venous return, thus decreasing preload and cardiac output (8, 9). Jardin et al (10) demonstrated that the increase in PEEP increased pulmonary vascular resistance, which impaired right ventricular (RV) function, resulting in increased RV end-diastolic volume. The distended RV pushes the intraventricular septum leftward thus impairing LV filling and hence cardiac output. Conversely, PPV has been shown to decrease LV wall stress in patients with impaired ventricular function, and hence, cardiac output increases with reduced afterload (11, 12). The secondary finding that the optimal lung compliance did not coincide with improved cardiac output, if corroborated, supports the notion that these cardiopulmonary relationships are complex and not intuitively obvious. January 2014 • Volume 15 • Number 1
Editorials
The strength of the study by Ingaramo et al (5) is that they have demonstrated the relationship between PEEP and CI using the USCOM, a noninvasive modality of determining cardiac output at a point in time when the use of PACs is very rare. Although there are not abundant data regarding the use of USCOM, the information available suggests that it may be a reliable alternative to the PAC. Phillips et al (13) have demonstrated that in sheep, the data generated by the use of the USCOM was actually superior to the use of the PAC in determining cardiac output measurements against an aortic flow probe. Richardson and Brierley (unpublished observations, 2013) have demonstrated how the USCOM can be used in the management of pediatric septic shock, hypovolemia, and myocardial dysfunction. The accuracy and reliability of all technologies employed in the care of the PICU patients is user dependent. Thus, training in the use of the USCOM, or similar technology, will be required to be standardized in order for various investigators to compare outcomes in their patient populations. It is also worth commenting that the USCOM does not have the capability of providing all the physiologic information that the PACs generated, including pulmonary artery pressure, pulmonary artery saturation, and pulmonary artery occlusion or left atrial pressure. The major limitation of this study is that the group of patients that require high levels of PEEP are those with severe cardiopulmonary dysfunction and those were not the patients studied in this report. In other words, we are most interested in the impact high levels of PEEP have on children with hemodynamic compromise. Assuming the USCOM provides reliable and reproducible measurements of cardiac output, the next study of the impact of PEEP must be done in those children with severe lung injury that require high levels of PEEP to achieve alveolar recruitment. For decades, ICU physicians have used the data generated from PACs to understand cardiopulmonary interactions and to employ goal-directed therapies in the care of their patients. The international guidelines for the management of surviving sepsis updated in 2012 continue to advocate for goal-directed therapy. This strategy requires central venous O2 saturation monitoring and recommends using high PEEP for lung recruitment in sepsis-induced lung disease (similar to the PEEP strategy recommended in the management of acute respiratory distress syndrome) (14). As the use of the PAC is nearly extinct, the advent of noninvasive modalities will allow
Pediatric Critical Care Medicine
this generation of ICU physicians to make informed goaldirected clinical decisions while monitoring cardiopulmonary interactions. The use of USCOM along with measuring central venous saturation may provide most of the data generated by the PAC and is worth investigating in the pediatric population with cardiac dysfunction. We congratulate Ingaramo et al (5) for pointing us in the right direction.
REFERENCES
1. Wiener RS, Welch HG: Trends in the use of the pulmonary artery catheter in the United States, 1993-2004. JAMA 2007; 298:423–429 2. Rajaram SS, Desai NK, Kalra A, et al: Pulmonary artery catheters for adult patients in intensive care. Cochrane Database Syst Rev 2013; 2:CD003408 3. Harvey S, Stevens K, Harrison D, et al: An evaluation of the clinical and cost-effectiveness of pulmonary artery catheters in patient management in intensive care: A systematic review and a randomised controlled trial. Health Technol Assess 2006; 10:iii–iv, ix 4. Perkin RM, Anas N: Pulmonary artery catheters. Pediatr Crit Care Med 2011; 12:S12–S20 5. Ingaramo OA, Ngo T, Khemani RG, et al: Impact of Positive EndExpiratory Pressure on Cardiac Index Measured by Ultrasound Cardiac Output Monitor. Pediatr Crit Care Med 2013; 14:15–20 6. Bronicki RA, Anas NG: Cardiopulmonary interaction. Pediatr Crit Care Med 2009; 10:313–322 7. Guyton AC, Jones CE, Coleman TG: Mean circulatory pressure, mean systemic pressure and mean pulmonary pressure and their effects on venous return. In: Circulatory Physiology: Cardiac Output and Its Regulation. Second Edition. Guyton AC, Jones CE, Coleman TG (Eds). Philadelphia, WB Saunders, 1973, pp 205–221 8. Jardin F, Brun-Ney D, Hardy A, et al: Combined thermodilution and two-dimensional echocardiographic evaluation of right ventricular function during respiratory support with PEEP. Chest 1991; 99:162–168 9. Jardin F: PEEP, tricuspid regurgitation, and cardiac output. Intensive Care Med 1997; 23:806–807 10. Jardin F, Farcot JC, Boisante L, et al: Influence of positive end-expiratory pressure on left ventricular performance. N Engl J Med 1981; 304:387–392 11. Buda AJ, Pinsky MR, Ingels NB Jr, et al: Effect of intrathoracic pressure on left ventricular performance. N Engl J Med 1979; 301:453–459 12. Mathru M, Rao TL, El-Etr AA, et al: Hemodynamic response to changes in ventilatory patterns in patients with normal and poor left ventricular reserve. Crit Care Med 1982; 10:423–426 13. Phillips RA, Hood SG, Jacobson BM, et al: Pulmonary artery catheter (PAC) accuracy and efficacy compared with flow probe and transcutaneous Doppler (USCOM): An ovine cardiac output validation. Crit Care Res Pract 2012; 2012:621496 14. Dellinger RP, Levy MM, Rhodes A, et al; Surviving Sepsis Campaign Guidelines Committee including The Pediatric Subgroup: Surviving Sepsis Campaign: International guidelines for management of severe sepsis and septic shock, 2012. Intensive Care Med 2013; 39:165–228
www.pccmjournal.org
85
T
he following editorial is written by a senior author (Dr. Anas) who completed his critical care training with extensive experience in the use of the pulmonary artery catheter (PAC). On the other hand, the junior author of this editorial (Dr. Hunt) recently completed her critical care fellowship training having never inserted a PAC nor having had the opportunity to interpret and apply the hemodynamic information generated from its placement. In recent years, this junior author’s experience in training does not seem to be unique. The use of PACs has dramatically decreased in ICUs across the country (1). However, despite the decreased use of PACs, ICU physicians continue to have the same responsibility of understanding the concepts of cardiopulmonary interactions and now must make clinical decisions without the ability to collect much of the real-time physiologic data that demonstrate the relationships. Most will agree that the role of PACs has fallen out of use not because the data generated from their use lacks merit or value but because few studies have demonstrated improved outcome and the risk-benefit ratio disfavors their use (2–4). Recent advances have tried to make use of less invasive means of obtaining the data that PACs once generated to assist the bedside clinician. Among them is ultrasound, a modality that has become much more widely used for a variety of indications in many areas of clinical
*See also p. 15. Key Words: cardiopulmonary interactions; goal-directed therapy; pediatric critical care medicine; pulmonary artery catheters; ultrasound cardiac output monitor Drs. Anas and Hunt are employed by the Children’s Hospital of Orange County. Dr. Anas has provided expert testimony, has lectured, and has stock options. Copyright © 2013 by the Society of Critical Care Medicine and the World Federation of Pediatric Intensive and Critical Care Societies DOI: 10.1097/PCC.0b013e31829f5a45
84
www.pccmjournal.org
practice, including the ICUs. The ultrasound cardiac output monitor (USCOM) is a specific technology that uses the ultrasound modality to provide noninvasive cardiac output monitoring by measuring flow using continuous wave Doppler through the aortic or pulmonary outflow tracts. It provides the ability to monitor real-time variables of cardiac function (cardiac index [CI], stroke volume index, systemic vascular resistance index, and oxygen delivery) (M. Richardson, J. Brierley: USCOM in the management of paediatric septic shock, hypovolaemia and myocardial dysfunction, unpublished observations, 2013). In this issue of Pediatric Critical Care Medicine, Ingaramo et al (5) described the use of USCOM to assess the impact of positive end-expiratory pressure (PEEP) on CI. The purpose of this study was to measure CI in pediatric patients using the USCOM at varying levels of PEEP. The hypothesis was that elevated levels of PEEP would not have significant impact on CI. Ingaramo et al (6) also wanted to show the effect of lung recruitment on the relationship between PEEP and CI. They concluded that an increase in PEEP between 0 and 12 cm H2O did have a statistically significant effect on decreasing CI in hemodynamically stable, mechanically ventilated children but suggest that this change in CI is unlikely to have clinical significance. Additionally, they concluded that the relationship between increasing PEEP and decreasing CI was similar even when the lung might be at optimal functional residual capacity. The secondary analysis looking at finding the level of PEEP that may offer optimal lung compliance (point of highest dynamic compliance) did not correlate to improved CI. Much data already exist on the various ways that positive pressure ventilation (PPV) affects the determinants of cardiac output, both positively and negatively (6). Classic experiments by Guyton et al (7) showed the basic principle that systemic venous return is the major determinant of left ventricular (LV) output. Others have also shown that the primary effect of PPV on cardiac output is by increasing right atrial pressure which reduces the driving pressure for venous return, thus decreasing preload and cardiac output (8, 9). Jardin et al (10) demonstrated that the increase in PEEP increased pulmonary vascular resistance, which impaired right ventricular (RV) function, resulting in increased RV end-diastolic volume. The distended RV pushes the intraventricular septum leftward thus impairing LV filling and hence cardiac output. Conversely, PPV has been shown to decrease LV wall stress in patients with impaired ventricular function, and hence, cardiac output increases with reduced afterload (11, 12). The secondary finding that the optimal lung compliance did not coincide with improved cardiac output, if corroborated, supports the notion that these cardiopulmonary relationships are complex and not intuitively obvious. January 2014 • Volume 15 • Number 1
Editorials
The strength of the study by Ingaramo et al (5) is that they have demonstrated the relationship between PEEP and CI using the USCOM, a noninvasive modality of determining cardiac output at a point in time when the use of PACs is very rare. Although there are not abundant data regarding the use of USCOM, the information available suggests that it may be a reliable alternative to the PAC. Phillips et al (13) have demonstrated that in sheep, the data generated by the use of the USCOM was actually superior to the use of the PAC in determining cardiac output measurements against an aortic flow probe. Richardson and Brierley (unpublished observations, 2013) have demonstrated how the USCOM can be used in the management of pediatric septic shock, hypovolemia, and myocardial dysfunction. The accuracy and reliability of all technologies employed in the care of the PICU patients is user dependent. Thus, training in the use of the USCOM, or similar technology, will be required to be standardized in order for various investigators to compare outcomes in their patient populations. It is also worth commenting that the USCOM does not have the capability of providing all the physiologic information that the PACs generated, including pulmonary artery pressure, pulmonary artery saturation, and pulmonary artery occlusion or left atrial pressure. The major limitation of this study is that the group of patients that require high levels of PEEP are those with severe cardiopulmonary dysfunction and those were not the patients studied in this report. In other words, we are most interested in the impact high levels of PEEP have on children with hemodynamic compromise. Assuming the USCOM provides reliable and reproducible measurements of cardiac output, the next study of the impact of PEEP must be done in those children with severe lung injury that require high levels of PEEP to achieve alveolar recruitment. For decades, ICU physicians have used the data generated from PACs to understand cardiopulmonary interactions and to employ goal-directed therapies in the care of their patients. The international guidelines for the management of surviving sepsis updated in 2012 continue to advocate for goal-directed therapy. This strategy requires central venous O2 saturation monitoring and recommends using high PEEP for lung recruitment in sepsis-induced lung disease (similar to the PEEP strategy recommended in the management of acute respiratory distress syndrome) (14). As the use of the PAC is nearly extinct, the advent of noninvasive modalities will allow
Pediatric Critical Care Medicine
this generation of ICU physicians to make informed goaldirected clinical decisions while monitoring cardiopulmonary interactions. The use of USCOM along with measuring central venous saturation may provide most of the data generated by the PAC and is worth investigating in the pediatric population with cardiac dysfunction. We congratulate Ingaramo et al (5) for pointing us in the right direction.
REFERENCES
1. Wiener RS, Welch HG: Trends in the use of the pulmonary artery catheter in the United States, 1993-2004. JAMA 2007; 298:423–429 2. Rajaram SS, Desai NK, Kalra A, et al: Pulmonary artery catheters for adult patients in intensive care. Cochrane Database Syst Rev 2013; 2:CD003408 3. Harvey S, Stevens K, Harrison D, et al: An evaluation of the clinical and cost-effectiveness of pulmonary artery catheters in patient management in intensive care: A systematic review and a randomised controlled trial. Health Technol Assess 2006; 10:iii–iv, ix 4. Perkin RM, Anas N: Pulmonary artery catheters. Pediatr Crit Care Med 2011; 12:S12–S20 5. Ingaramo OA, Ngo T, Khemani RG, et al: Impact of Positive EndExpiratory Pressure on Cardiac Index Measured by Ultrasound Cardiac Output Monitor. Pediatr Crit Care Med 2013; 14:15–20 6. Bronicki RA, Anas NG: Cardiopulmonary interaction. Pediatr Crit Care Med 2009; 10:313–322 7. Guyton AC, Jones CE, Coleman TG: Mean circulatory pressure, mean systemic pressure and mean pulmonary pressure and their effects on venous return. In: Circulatory Physiology: Cardiac Output and Its Regulation. Second Edition. Guyton AC, Jones CE, Coleman TG (Eds). Philadelphia, WB Saunders, 1973, pp 205–221 8. Jardin F, Brun-Ney D, Hardy A, et al: Combined thermodilution and two-dimensional echocardiographic evaluation of right ventricular function during respiratory support with PEEP. Chest 1991; 99:162–168 9. Jardin F: PEEP, tricuspid regurgitation, and cardiac output. Intensive Care Med 1997; 23:806–807 10. Jardin F, Farcot JC, Boisante L, et al: Influence of positive end-expiratory pressure on left ventricular performance. N Engl J Med 1981; 304:387–392 11. Buda AJ, Pinsky MR, Ingels NB Jr, et al: Effect of intrathoracic pressure on left ventricular performance. N Engl J Med 1979; 301:453–459 12. Mathru M, Rao TL, El-Etr AA, et al: Hemodynamic response to changes in ventilatory patterns in patients with normal and poor left ventricular reserve. Crit Care Med 1982; 10:423–426 13. Phillips RA, Hood SG, Jacobson BM, et al: Pulmonary artery catheter (PAC) accuracy and efficacy compared with flow probe and transcutaneous Doppler (USCOM): An ovine cardiac output validation. Crit Care Res Pract 2012; 2012:621496 14. Dellinger RP, Levy MM, Rhodes A, et al; Surviving Sepsis Campaign Guidelines Committee including The Pediatric Subgroup: Surviving Sepsis Campaign: International guidelines for management of severe sepsis and septic shock, 2012. Intensive Care Med 2013; 39:165–228
www.pccmjournal.org
85
