Critical Care Trailblazers: The PAC-Man Trial

The concept of the floatation catheter

On a bright autumn afternoon of 1967, Jeremy Swan stood by the beach at Santa Monica, watching sailboats pass by. He was a cardiologist at the Cedars of Lebanon Hospital, Los Angeles, and had taken time off following a particularly difficult cardiac catheterization just a few days ago. As the sail boats cruised along, propelled by wind, an inspirational thought dawned upon him. Could he guide a catheter from the right heart through to the pulmonary artery, driven by the direction of blood flow? A sail or parachute-type appendage attached to the tip of the catheter could enable floatation of the catheter along the direction of flow. 

He joined hands with a colleague, William Ganz, to refine the concept and contrived the balloon-tipped pulmonary artery catheter (PAC), creating the eponymous device that turned out to be a milestone in the history of medicine.  

The early years of the Swan…

In the years that followed, the novel device was extensively used in operating rooms and ICUs. Although no controlled trial had evaluated its impact on clinical outcomes, clinicians were swayed by the information on hemodynamic variables offered by the catheter and its ready availability by the bedside. Although the usage of the PAC rose, no tangible outcome benefits were demonstratable during the same period. On the contrary, similar or higher mortality rates and a longer duration of hospital stay were observed among those who underwent PAC-based management (1). Furthermore, catheter-related complications began to surface; this included thrombosis of the internal jugular vein and the pulmonary artery, pulmonary artery rupture, pulmonary hemorrhage, infective endocarditis, knotting of the catheter, and occasionally, fatal arrhythmias (2,3). 

The SUPPORT investigators rock the boat 

A quarter of a century had elapsed since its introduction to clinical practice when Connors et al. designed a prospective cohort study to evaluate clinical outcomes among ICU patients who underwent PAC-based management (4). A randomized controlled trial (RCT) on the use of the PAC seemed unrealistic in that era – such was the deep-rooted faith clinicians seemed to pin on the device. A previous RCT (5) had to be aborted following refusal of many treating clinicians to participate as they considered it unethical not to use a PAC!  

The SUPPORT study by Connors et al. evaluated 5735 patients who were admitted to the ICU of five hospitals in the US (4); of these, 2184 patients underwent PAC insertion within the first 24 hours of ICU admission. On unadjusted analysis, the PAC was associated with a significantly higher mortality 30, 60, and 180 days. The duration of stay in the ICU and hospital was also longer in patients who underwent pulmonary artery catheterization. On propensity-matched analysis, higher mortality was consistently observed with PAC-based care. Furthermore, the cost of care was higher, the duration of ICU stay longer, and the intensity of care higher in patients who underwent pulmonary artery catheterization compared to those who did not.

The study was limited by its observational design, and the likelihood of confounding variables that may have led to bias. It was confined to five hospitals and lacked generalizability to other settings. The study evaluated PAC use within the first 24 hours of ICU admission; hence, the possibility of a beneficial effect with later use could not be excluded. The authors recommended an RCT considering the adverse outcomes noted in their retrospective observational study. An accompanying editorial proposed a moratorium on the use of the PAC if an RCT was considered infeasible. 

Background to the PAC-Man trial

Despite the findings of the SUPPORT study, PAC use continued in many ICUs through the late 1990s and into the new millennium. Proponents continued to argue for its merits, including the relative ease of cardiac output monitoring once the catheter was in place and other potentially useful hemodynamic parameters. Detractors raised questions about the accuracy of the measured variables, the lack of evidence supporting improved clinical outcomes, and most of all, concerns regarding safety. The PAC-Man trial was conceptualized as a pragmatic RCT to test the hypothesis whether PAC-based management of critically ill patients leads to reduced hospital mortality.

Population and design

The PAC-Man trial was conducted between October 2001, and March 2004 across 65 ICUs in the UK (6). Adult patients admitted to the ICU who were considered to require pulmonary artery catheterization based on clinician judgment were enrolled. The ICUs included could choose not to use an alternative, less invasive cardiac output monitoring device (stratum A) or retain the option of using such a device (stratum B). 

Patients were randomly assigned to PAC-based monitoring or no PAC in a 1:1 ratio. Randomization was stratified by age, the underlying clinical syndrome, and the surgical status. 


The study excluded patients admitted to the ICU for preoperative optimization and those who already had a PAC in place on ICU admission. Potential organ donors undergoing hemodynamic optimization were also excluded. 

Intervention – the PAC group

The PAC was inserted as soon as possible post-randomization and was retained for as long as considered appropriate by the treating clinician. Assessment of hemodynamic status and management was entirely at clinician discretion. No specific treatment algorithm was followed based on PAC data. 

The control group

Patient management was based on clinician judgment. An alternative method of hemodynamic monitoring could be used instead of the PAC among patients in stratum B. 

Sample size 

Assuming a mortality of 50% in patients managed with a PAC, an initial sample size of 5673 patients was calculated to detect a 5% difference in hospital mortality. As the study progressed, the mortality in the control group was noted to be 69% – higher than initially estimated. Hence, the sample size was revised to 1281 patients to allow detection of a 10% mortality difference with 90% power at a 5% level of significance. 


The study randomized a total of 1041 patients – 519 to the PAC group and 522 to the control group. In the control group, 24 patients (5%) underwent PAC insertion; 34 patients (7%) in the PAC group did not receive the intervention. PAC insertion was withheld due to a change in the clinical situation (3%) or the potential for complications (1%). Attempts at insertion were unsuccessful in 14 (3%) patients.  

Most patients were medical (66%), followed by those who underwent emergency (28%) or elective surgical procedures (6%); there was no significant difference between groups.  In most patients, the PAC was considered necessary to guide the titration of vasoactive medication (>70%). Multiorgan dysfunction was present in 65% of patients in the PAC group and 66% of patients in the control group. Patients had a high baseline severity of illness – the mean APACHE II score was 22.1 (6.6) in the PAC group and 22.7 (6.5) in the control group.  

A change in the management strategy within 2 hours of PAC insertion occurred in 80% of patients – mainly related to additional fluid administration and commencement or increased dosage of vasoactive medication. The median duration of PAC-based management was 3 (2–4) days.

The primary outcome – hospital mortality

Among patients managed with a PAC, 346/506 (68%) died in hospital, compared with 333/507 (66%) in the control group; the difference was non-significant. 

Secondary outcomes 

ICU and 28-d mortality

The ICU and 28-day mortality were also similar in both groups. The ICU mortality was 60% and 57%, respectively, in the PAC and the control groups. In the PAC group, 62% of patients had died by day 28, compared with 60% in the control group.

Other outcomes 

The in-hospital survival up to 90 days was similar in both groups. The ICU length of stay and the number of days of organ support were also similar.  

Subgroup analysis 

On subgroup analysis, there was no significant difference based on the APACHE II scores, the underlying clinical syndrome, and regardless of an alternative method of cardiac output measurement. 

Adverse events

Complications directly related to PAC insertion occurred in 10% of patients. These included hematoma at the insertion site, arterial puncture, and arrhythmias requiring treatment. Pneumothorax occurred in two patients, while one patient sustained a hemothorax. There were two instances of lost guidewires that had to be retrieved from the femoral vein and the inferior vena cava. 

Strengths of the study

The PAC-Man trial was a pragmatic RCT that compared the outcomes of patients who were managed with or without a PAC. No specific treatment strategy was followed based on the information obtained from PAC, reflecting real-world practice. The study was conducted across 65 ICUs in the UK, thus providing external validity. There was high compliance to the assigned treatment strategy, and follow-up was complete. Analysis was by intention to treat, adding further strength to the study. 


Critics would continue to posit that the utility of any monitoring device would depend on a structured, algorithmic therapeutic approach based on the data that it offers. However, the PAC-Man study adopted a pragmatic methodology and reflected evaluation of real-world practice. Cardiologists and their surgical colleagues continue to aver that among their patient population with heart failure, the PAC provides invaluable information and titration of therapeutic interventions, including the use of inotropes. 

The study was conducted in an era when ultrasonography was not widely used to guide catheter insertion. Perhaps some of the complications may have been attributable to the blind approach of catheter insertion.  

The ability of ICU staff in identifying waveforms and data from the PAC may also be questionable based on evidence from previous studies (7,8).  The PAC-Man trial did not assess the adequacy of catheter use or interpretation of data. However, the level of experience of study centers with the use of the PAC did not appear to influence outcomes.


The PAC-Man trial was an eye-opener regarding the role of the PAC in the management of critically ill patients. This large, adequately powered RCT reflected the real-world practice of the time, and conclusively demonstrated no added benefit with the use of the PAC. Needless to say, the lack of a protocolized approach continues to remain a thorn in the flesh in the management of critically ill patients with shock. However, several newer, less-invasive modalities of cardiac output monitoring have been increasingly used in the management of hemodynamically unstable patients, including bedside echocardiography and pulse contour analysis (9,10). 

The once iconic “Yellow Snake” as it is often alluded to, appears to be on the verge of extinction after having lived a charmed life for over half a century.  

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1.         Gore JM, Goldberg RJ, Spodick DH, Alpert JS, Dalen JE. A community-wide assessment of the use of pulmonary artery catheters in patients with acute myocardial infarction. Chest. 1987 Oct;92(4):721–7. 

2.         Chastre J, Cornud F, Bouchama A, Viau F, Benacerraf R, Gibert C. Thrombosis as a complication of pulmonary-artery catheterization via the internal jugular vein: prospective evaluation by phlebography. N Engl J Med. 1982 Feb 4;306(5):278–81. 

3.         Rowley KM, Clubb KS, Smith GJ, Cabin HS. Right-sided infective endocarditis as a consequence of flow-directed pulmonary-artery catheterization. A clinicopathological study of 55 autopsied patients. N Engl J Med. 1984 Nov 1;311(18):1152–6. 

4.         Connors AF, Speroff T, Dawson NV, Thomas C, Harrell FE, Wagner D, et al. The effectiveness of right heart catheterization in the initial care of critically ill patients. SUPPORT Investigators. JAMA. 1996 Sep 18;276(11):889–97. 

5.         Guyatt G. A randomized control trial of right-heart catheterization in critically ill patients. Ontario Intensive Care Study Group. J Intensive Care Med. 1991;6(2):91–5. 

6.         Harvey S, Harrison DA, Singer M, Ashcroft J, Jones CM, Elbourne D, et al. Assessment of the clinical effectiveness of pulmonary artery catheters in management of patients in intensive care (PAC-Man): a randomised controlled trial. Lancet Lond Engl. 2005 Aug 6;366(9484):472–7. 

7.         Iberti TJ, Daily EK, Leibowitz AB, Schecter CB, Fischer EP, Silverstein JH. Assessment of critical care nurses’ knowledge of the pulmonary artery catheter. The Pulmonary Artery Catheter Study Group. Crit Care Med. 1994 Oct;22(10):1674–8. 

8.         Gnaegi A, Feihl F, Perret C. Intensive care physicians’ insufficient knowledge of right-heart catheterization at the bedside: time to act? Crit Care Med. 1997 Feb;25(2):213–20. 

9.         Schmidt S, Westhoff TH, Hofmann C, Schaefer JH, Zidek W, Compton F, et al. Effect of the venous catheter site on transpulmonary thermodilution measurement variables. Crit Care Med. 2007 Mar;35(3):783–6. 

10.       Chaney JC, Derdak S. Minimally invasive hemodynamic monitoring for the intensivist: current and emerging technology. Crit Care Med. 2002 Oct;30(10):2338–45. 

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