PAC-Man: Pulmonary Artery Catheters in Critical Care (2005)

“We found no evidence that management with a PAC, as compared with standard care without a PAC, affects mortality or morbidity in a general population of critically ill adults.”

  • The PAC-Man Study Investigators

1. Publication Details

  • Trial Title: Pulmonary-Artery Catheters for Adult Patients in Intensive Care
  • Citation: Harvey S, Harrison DA, Singer M, 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. 2005;366(9484):472-477. DOI: 10.1016/S0140-6736(05)67061-4
  • Published: August 6, 2005, in The Lancet
  • Author: The PAC-Man study investigators
  • Funding: UK National Health Service Research and Development Programme.

2. Keywords

  • Pulmonary Artery Catheter (PAC), Hemodynamic Monitoring, Critical Care, ICU, Randomized Controlled Trial

3. The Clinical Question

  • In a general population of critically ill adult patients (Population), does management guided by a pulmonary artery catheter (PAC) (Intervention) compared to standard care without a PAC (Comparison) reduce in-hospital mortality (Outcome)?

4. Background and Rationale

  • Existing Knowledge: The pulmonary artery catheter (PAC), also known as the Swan-Ganz catheter, had been a cornerstone of hemodynamic monitoring in the ICU for over 30 years. It was used to measure cardiac output, pulmonary artery pressures, and other variables to guide fluid and vasopressor therapy.
  • Knowledge Gap: Despite its widespread and routine use, there was no high-quality evidence from a large, pragmatic randomized controlled trial to prove that the information provided by a PAC actually led to improved patient outcomes. There were also known risks associated with its insertion and use.
  • Proposed Hypothesis: The authors hypothesized that there would be no significant difference in in-hospital mortality between patients managed with a PAC and those managed with standard care.

5. Study Design and Methods

  • Design: A multicenter, pragmatic, randomized, controlled trial (used to test the effectiveness of interventions).
  • Setting: 65 intensive care units (ICUs) in the United Kingdom.
  • Trial Period: Enrollment ran from December 1999 to July 2004.
  • Population:
    • Inclusion Criteria: Adult patients admitted to a participating ICU for whom the treating clinician was substantially uncertain about whether or not to use a PAC.
    • Exclusion Criteria: Included patients for whom a PAC was considered either mandatory or contraindicated.
  • Intervention: Patients were randomized to have a pulmonary artery catheter (PAC) inserted for hemodynamic monitoring and management.
  • Control: Patients were randomized to standard care without a PAC. Other forms of monitoring (e.g., a central venous catheter) were permitted.
  • Management Common to Both Groups: All other aspects of ICU care were at the discretion of the treating clinicians. There was no protocol for how to use the information from the PAC.
  • Power and Sample Size: The authors calculated that a sample size of 1000 patients would provide 80% power to detect an 8% absolute risk reduction in mortality. (Power is a study’s ability to find a real difference between treatments if one truly exists; 80% is the standard accepted level for clinical trials).
  • Outcomes:
    • Primary Outcome: In-hospital mortality.
    • Secondary Outcomes: Included ICU and hospital length of stay, duration of organ support, and the incidence of complications.

6. Key Results

  • Enrollment and Baseline: 1014 patients were randomized (506 to the PAC group and 508 to the control group). The groups were well-matched at baseline.
  • Trial Status: The trial was completed as planned.
  • Primary Outcome: There was no significant difference in in-hospital mortality. 336 of 506 patients (66%) in the PAC group died, compared with 341 of 508 patients (67%) in the control group (p=0.79).
  • Secondary Outcomes: There were no significant differences between the groups in length of stay or duration of organ support.
  • Adverse Events: The incidence of catheter-related complications, particularly pulmonary embolism, was significantly higher in the PAC group.

7. Medical Statistics

  • Analysis Principle: The trial was analyzed using an intention-to-treat principle.
  • Statistical Tests Used: The primary outcome was analyzed using a chi-square test.
  • Primary Outcome Analysis: The primary outcome was a comparison of the proportions of death between the two groups.
  • Key Statistic(s) Reported: The key statistics were the absolute mortality rates and the associated P-value.
  • Interpretation of Key Statistic(s):
    • P-value: The p-value of 0.79 for the primary outcome is much higher than the 0.05 threshold, indicating that the result was not statistically significant and very likely due to chance (a result is conventionally considered statistically significant if the p-value is less than 0.05).
  • Clinical Impact Measures: As the trial was neutral, ARR and NNT are not applicable.
  • Subgroup Analyses: No significant differences were found in any of the pre-specified subgroups.

8. Strengths of the Study

  • Study Design and Conduct: The large, multicenter, pragmatic, randomized design provided high-quality evidence on a real-world clinical question.
  • Generalizability: The pragmatic “uncertainty principle” for enrollment and the inclusion of 65 diverse ICUs make the findings highly generalizable to a broad population of critically ill patients.
  • Statistical Power: The study was large and adequately powered to confidently rule out a modest but clinically important mortality difference.
  • Patient-Centered Outcomes: The primary outcome of in-hospital mortality is a robust and patient-centered endpoint.

9. Limitations and Weaknesses

  • Internal Validity (Bias): The study was unblinded, which introduces a risk of performance bias. A key limitation is that the trial did not protocolize the interventions based on the PAC data, so it was a trial of the monitor itself, not a specific PAC-guided therapy algorithm.
  • External Validity (Generalizability): The findings are highly generalizable to the routine use of PACs in a general ICU population.
  • Other: The overall mortality rate in the trial was very high (over 65%), reflecting a very sick patient population.

10. Conclusion of the Authors

  • The authors concluded that the use of a PAC in a general population of critically ill patients does not reduce mortality and may be associated with an increase in complications.

11. To Summarize

  • Impact on Current Practice: This was a profoundly practice-changing trial. It provided definitive evidence that the routine, untargeted use of this invasive and expensive monitoring device was not beneficial and could be harmful. It led to a dramatic global decline in the use of the pulmonary artery catheter.
  • Specific Recommendations:
    • Patient Selection: For the broad population of adult ICU patients.
    • Actionable Intervention: Do not routinely use a pulmonary artery catheter for hemodynamic monitoring.
  • What This Trial Does NOT Mean: This trial does NOT mean that the PAC has no role in the ICU. It may still be useful in highly selected, complex patients (e.g., those with severe pulmonary hypertension or right heart failure) where the specific information it provides is needed to guide a specific therapy.
  • Implementation Caveats: The key takeaway is that invasive monitoring without a clear plan for how to act on the data does not improve outcomes.

12. Context and Related Studies

  • Building on Previous Evidence: The PAC-Man trial (2005) was designed to provide a definitive answer to a question that had been debated for decades, following a famous observational study by Connors et al. (1996) that suggested PACs were associated with increased mortality.
  • Influence on Subsequent Research: The definitive neutral-to-harmful result of this trial, along with other similar trials, effectively ended the era of routine PAC use. It has spurred the development and evaluation of less invasive hemodynamic monitoring technologies.

13. Unresolved Questions & Future Directions

  • Unresolved Questions: The key unresolved question is whether there is a specific, well-defined subgroup of critically ill patients who might still benefit from PAC-guided therapy.
  • Future Directions: Future research in hemodynamic monitoring is focused on less invasive technologies and on trials that link the monitoring to a specific, protocolized treatment algorithm.

14. External Links

15. Framework for Critical Appraisal

  • Clinical Question: The research question was of the highest relevance, testing a ubiquitous, invasive, and expensive technology that had become a standard of care without high-quality evidence.
  • Methods: The large, multicenter, pragmatic RCT design was appropriate and robust. The main methodological weakness is the open-label design. The “uncertainty” enrollment criterion is a key strength that enhances real-world applicability.
  • Results: The study reported a clear neutral finding for its primary outcome of mortality, but a statistically significant increase in harm (complications).
  • Conclusions and Applicability: The authors’ conclusion is strongly supported by the data. The trial is a landmark in evidence-based medicine and a classic example of how a high-quality trial can be profoundly practice-changing by providing strong evidence to de-adopt a long-standing and deeply entrenched clinical practice.

16. Disclaimer and Contact

  • This summary is provided by the Academic Committee of ESBICM (ACE) to facilitate the understanding of this study; readers are advised to refer to the original trial document for a deeper understanding. If you find any information incorrect, or missing, or it needs an update or have a request for a specific critical care trial summary, kindly write to us at academics[at]esbicm.org.
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