Pulmonary artery catheter use — Refining the question *

T hree decades of critical care practice have been defined by the use of the pulmonary artery catheter (PAC). Initially a laboratory procedure used to aid diagnosis in heart disease, the introduction of balloon-tipped flow-directed catheters in 1970 allowed bedside use in the intensive care unit (ICU) for patients with all forms of heart disease, shock of any origin, sepsis, and respiratory failure and for preoperative use to optimize noncardiac surgical patients known to be at high risk. A generally accepted belief held by critical care practitioners was that fluid and drug therapy planned by using goals derived from the measurement of physiologic variable with PAC would improve outcomes. The PAC became an icon of critical care despite the absence of randomized controlled trials to show that this assumption of benefit was true. A large body of literature developed about PAC use that was generally considered to be inconclusive. Observational studies and small randomized controlled trials showed variable results: worse outcomes, no effect, or some benefit. However, the last decade of PAC use has been characterized by increasingly brisk debate (1) about the impact of PAC on patient outcomes. This debate has been stimulated by large observational studies (2, 3) that show an association between PAC use and increased mortality rate. These studies have challenged the assumption held by critical care practitioners that physiologic measurement could guide therapy with fluids and drugs to improve outcomes. This debate has played a useful role by stimulating critical care community to apply critical appraisal to the data that evaluate outcomes associated with PAC use. The consequence has been a consensus that randomized controlled trials are needed to assess outcomes associated with PAC use in clearly defined patient populations (4, 5). This issue of Critical Care Medicine contains an article by Dr. Chittock and colleagues (6) describing an observational cohort study that will continue to stimulate discussion about PAC use and about the design and conduct of further randomized controlled trials of PAC use. Their study occurred in a single ICU over 10 yrs and evaluated a total of 7,310 consecutive, eligible, critically ill patients. The main finding of the study is an association between PAC use at any time during their ICU stay and increased mortality rate when used in the least acutely ill patients and an association between PAC use and decreased mortality rate in the most acutely ill patients (Acute Physiology and Chronic Health Evaluation [APACHE] II 18: odds ratio, 2.47; 95% confidence interval, 1.27–4.81; APACHE II 18–24: odds ratio, 1.64; 95% confidence interval, 1.24–2.17; APACHE II 25–31: odds ratio, 1.00; 95% confidence interval, 0.80 –1.24; APACHE II 31: odds ratio, 0.80; 95% confidence interval, 0.64–1.00). These findings are in part congruent with the observational studies of Connors et al. (2) and Polanczyk et al. (3); both suggested an association between worse outcomes and PAC use that was most marked in the least acutely ill, but they did not show improved outcomes in any patient subgroup. However, the findings of Chittock et al. (6) are not similar to those of two large randomized controlled trials of PAC use that have been published within the last year. Sandham et al. (7) randomized 1,994 high-risk (American Society of Anesthesiologists class III and IV) geriatric surgical patients to preoperative ICU admission and PAC protocol guided therapy or ICU admission with central venous catheter insertion and therapy at the discretion of ICU staff. There were no differences in the primary outcome of mortality to hospital discharge, or at 6 and 12 months postrandomization, in length of hospital stay or organ dysfunction. In the study, patients were stratified for risk but not for acuity. Although there was an increase in mortality rate with PAC use suggested in the higher risk group (American Society of Anesthesiologists class IV), this difference was not statistically significant and disappeared on regression analysis. Richard et al. (8) randomized 681 acutely ill patients with early shock or the adult respiratory distress syndrome to use of PAC or not. There was no significant difference for outcome of the primary end point of the trial (mortality at 28 days) with and without PAC (59.4. vs. 61%; relative risk, 0.97; 95% confidence interval, 0.86 –1.10; p .67)) or for days in hospital, days in ICU, or days on mechanical ventilation. This trial demonstrates the feasibility of such a randomized controlled trial in this patient population, but it may be necessary to do a similar larger trial (9) to definitively exclude increased absolute risk of death of 5% with PAC use suggested by a previous observational study (2). Together, these two trials represent a spectrum of patient acuity and risk from moderate to high but do not detect differences in outcomes with PAC use. As such, they are in contrast to the findings of Chittock et al. (6). Despite efforts at case matching using a propensity score, or comparing acuity using APACHE II scores, the lack of randomization leads to the possibility of many unknown sources of bias that may have influenced the findings of this and other observational studies. In particular, the decision to use a PAC may have been a marker for greater severity of illness in some patients. Chittock et al. (6) quite rightly suggested the possibility of an unidentified confounder in their nonrandomized trial. Data not available from their study but that would help to clarify these differences include the timeliness of PACs in those who received them, differences in therapy (blood transfusions, vasoactive drugs, insulin therapy, mode of ventilation, corticosteroid use) offered to PAC and non-PAC patients, and refinement of the diagnostic groups beyond identification by most responsible organ system. *See also p. 911. Copyright © 2004 by Lippincott Williams & Wilkins