CARDIAC HEMODYNAMICS: THE PULMONARY ARTERY CATHETER AND THE MEANING OF ITS READINGS

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CHAPTER 82 CARDIAC HEMODYNAMICS: THE PULMONARY ARTERY CATHETER AND THE MEANING OF ITS READINGS

The pulmonary artery catheter (PAC) is a physical object creating a conundrum. Since its introduction in the 1970s, the PAC has been simultaneously hailed for its ability to provide physiological data not easily obtainable by other means, and condemned as a useless and potentially harmful invasive monitor. Very little hard data support continued use of the PAC, and some data support avoiding it altogether. Despite considerable controversy over the clinical utility and safety of the PAC, which has intermittently led to confusion and conjecture regarding its use and future, the PAC remains a mainstay of invasive intensive care unit (ICU) monitoring. In this chapter, we aim to provide a concise history of right-heart catheterization. We will then examine the basis of insertion, data collection, interpretation, and troubleshooting. Finally, we will reexamine the clinical data for and against the use of PA catheterization and determination of resuscitation in critically ill surgical patients.

HISTORY OF CONTROVERSY

The PAC was introduced in the late 1960s, approved for clinical use in 1970 and quickly became the de facto tool of the critical care physician. By 1999, 1.5 million catheters were sold, and presumably used, each year in the United States. Due to its introduction prior to a 1976 policy change, which mandated the testing of medical devices, the PAC was grandfathered by the Food and Drug Administration (FDA), and has to date never been required to undergo safety testing. Even as considerable controversy and political debate over its utility continues, the catheter has never been considered a life-saving device and, as a result, is exempt from licensing and required study.¹

Since its invention, the PAC has enjoyed growing use and acceptance as a monitoring tool. Indeed, its popularity has followed closely the advent of critical care as a specialty, and thus is considered by many a primary tool of the critical care physician. After years of use with little data supporting benefits, concerns about the overall utility and safety of the PAC first appeared in several papers written in the late 1980s.¹ Gore et al. examined 3000 patients with acute myocardial infarction (MI) and the relationship of outcome to PA catheterization.² This study of over 3000 patients with acute MI reported higher mortality in patients with hypotension who received a PAC (42% vs. 32%). Higher mortality was also reported in the subgroup or patients with CHF who received a PAC (44% vs. 25%). In addition, patients who received a PAC had longer hospital stay. Several observational and retrospective studies quickly followed with similar concerning results.³ Many in the critical care community discounted these trials, believing that PAC placement was more common in patients with greater illness, which would explain the higher mortality rates. A 1990 Canadian trial was the first to attempt to prospectively study the use of PAC in critically ill patients. In what was to become a recurring theme, however, the study failed due to a 35% exclusion rate as many clinicians refused to randomize their patients, arguing instead that it was unethical not to use a PAC (which had become the de facto tool of the ICU physician). A lack of clinical agreement regarding PAC use or perhaps just a lack of interest in the problem followed, and the PAC enjoyed continued widespread use until the debate was reignited by Connors et al., who studied PAC use in 5735 critically ill ICU patients. The Connors group was careful to attempt to match illness severity and other confounding variables between the PAC and control groups. Ultimately, his group found that patients treated with PAC had increased 30-day mortality, mean cost, and ICU stay. Subgroup analysis identified no groups of patients who benefited from PAC.⁴

As a result of these and similar data, in the same issue of the Journal of the American Medical Association, Bone and Drhen called for a National Heart, Lung, and Blood Institute (NHLBI) randomized prospective clinical trail to test the efficacy and safety of the PAC. They went on to spark considerable controversy by suggesting that the FDA issue a moratorium on the use of the pulmonary catheter until such time that the safety and use be measured in an appropriate clinical trial. In response to this call for a moratorium, both a National Heart, Lung, and Blood Institute (NHLBI) and a Society of Critical Care Medicine (SCCM) consensus conference were convened in 1997. The Pulmonary Artery Catheter Consensus Conference Consensus Statement was published that same year. According to the statement, there was no need of a moratorium on PACs, given adequate level-IV evidence to support the possibility of benefit of PAC in patient groups including MI and trauma, but conceded that appropriate clinical trials should be undertaken to measure its use and safety.^5,⁶ The NHLBI conference came to similar findings.⁷ Many trials followed, all with limited numbers of patients or low randomization rates.

In 2003, a Canadian group published the first prospective randomized study with sufficient patient enrollment to have statistical power and authority.⁸ In this study, 1994 patients were randomized to surgery without a pulmonary catheter versus with a PAC. The authors found that there were no differences in hospital survival, and in 6- and 12-month survival. There was however, an increase in the number of pulmonary embolism (PE) events with eight reported in the catheter group versus 0 in the observation group. The authors concluded that no benefit from PA catheterization could be found in elderly high-risk surgical patients. While this study was important in that it was the first to randomize a significant cohort of patients, the randomization rate remained a low 52%. Furthermore, it represented a subset of older critically ill patients, while excluding younger trauma or septic patients. Other trials have followed and shown mixed results.⁹^–¹² More recently Shah et al. performed a meta-analysis of 13 randomized clinical trials between 1985 and 2005.¹³ This study totaling 5051 patients was performed using a random effects model to estimate the odds ratio for death, hospital days, and pressors and found no difference between patients with and without a PAC.

No randomized prospective trial to date, however, has shown a definite benefit to PA catheterization in critically injured patients. In data limited to trauma patients, there is some recent evidence to show a benefit for PAC use in the injured. A database study of over 53,000 patients drawn from the National Trauma Data Bank showed a reduction in mortality in older patients and patients with higher injury severity scores. Overall, PAC use was shown to be beneficial in patients with severe shock with a base deficit of 11 or more, injury severity scores higher than 25, and age over 61. This large cohort database study is the first and only study to show a clear benefit from PAC use in the severely injured patient.¹⁴

One bias confounding PAC use and study are disparate factors that affect which patients are treated with the PAC. In 2000, Rapoport et al. reported a comprehensive look at the characteristics of PAC use.¹⁵ This group retrospectively examined 10,217 patients in 34 ICUs in the United States and showed that full-time ICU staffing was associated with a decreased likelihood of PAC use. Catheter use was associated with white race/ethnicity and private insurance. Patients admitted to a surgical ICU were two times more likely to have a PAC. This study is revealing in that it is indicative of the lack of an established protocol and the presence of an established bias in PAC placement.