Editorial I

The utility of pulmonary artery catheterization

Some of the most fascinating aspects of intensive care medicine are the controversies about patient management. A paradigm is the utility of the pulmonary artery catheter. Its use has been a matter of contention, more so since a paper by Connors and co-workers in 1996.1 This study of patients in a group of American teaching hospitals demonstrated an association between the use of pulmonary artery catheters in the first 24 h of intensive care and increased mortality. During the subsequent discussion, there were calls for a moratorium on the use of the pulmonary artery catheter and, more constructively, for randomized controlled trials to examine patient outcome after use of the device.2

In this issue of the journal, a study of apparently similar design to the Connors’ paper describes very different findings and will renew the flames of this debate.3 Before discussing these contrasting works, let us consider how to evaluate diagnostic and monitoring devices. I have used the framework described by Guyatt and colleagues4 (Table 1).


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Table 1 Framework for clinical evaluation of diagnostic technologies4
 
(1) Technological capability

Pulmonary artery catheters measure juxta-cardiac pressures, cardiac output and mixed venous oxygen saturation. Modern pressure transducers perform well in terms of their physical characteristics. However, the limitations of juxta-cardiac pressures in the clinical assessment of cardiac pre-load must be considered, and has been cogently discussed elsewhere.5

Thermodilution and Fick-derived cardiac outputs have been compared with varied results. Some studies demonstrated that thermodilution cardiac outputs were consistently less than those determined by the Fick method in low-flow states.6 This may be a result of heat transfer to the injectate during its passage down the catheter. The accuracy of the thermodilution system may be improved by the use of dual thermistors.7 The accuracy of continuous pulmonary arterial oxygen saturations has been confirmed by comparison with oximetric analysis of mixed venous blood samples.8

(2) Range of possible uses

Consensus statements from Europe and America have defined several situations in which the pulmonary artery catheter may provide useful information.9 10

(3) Diagnostic accuracy

Several observational studies have shown that data derived from pulmonary artery catheterization are poorly predicted by clinical skills alone.1113 For example, Connors and colleagues11 showed that pulmonary artery pressures and cardiac outputs of critically ill patients were only correctly predicted on ~ 40% of occasions, and concluded that pulmonary artery catheterization ‘results in a more accurate haemodynamic assessment’. Furthermore, doctors’ abilities to interpret haemodynamic data are incomplete,15 16 and it is worrying that the potential for such information to complement clinical findings may not be realised.

(4) Therapeutic impact

Therapeutic decisions are altered because of the data derived from pulmonary artery catheterization after 40–60% of insertions.1114

(5) Patient outcome

The ultimate patient outcome is survival to a reasonable lifestyle. But the assessment of the impact of a monitoring tool on survival is fraught with difficulties. Even if the device performs adequately, providing clinically relevant information which is interpreted correctly by the clinical team who invoke changes in patient treatment, it is by no means certain that any therapeutic regimen manipulating haemodynamic variables improves patient survival. While supra-normalization of oxygen transport, using data derived from a pulmonary artery catheter, may improve survival of patients with significant co-morbidity undergoing major elective surgery,17 18 this tactic does not improve survival of all-comers to intensive care19 and may even increase mortality.20

Survival from critical illness also depends on many other factors which will confound studies of this complex process. The two studies mentioned at the start have attempted to examine patient outcome after a period of critical illness during which the patients may have undergone pulmonary artery catheterization. By using a ‘propensity score’ they have attempted to adjust for potential confounders, which may influence both the likelihood of pulmonary catheterization and the chance of death.

Murdoch and colleagues3 examined the effect of pulmonary artery catheterization at any time on mortality in all patients admitted to a large intensive care unit in an English teaching hospital over a 7-yr period. Using stepwise logistic regression analysis, they devised a score of the propensity for pulmonary artery catheter insertion during the entire intensive care period. This propensity score was then used to account for the patients’ severity of illness in an analysis of use of the pulmonary artery catheter and intensive care mortality. In contrast to the case-matched Connors study,1 there was no increased mortality associated with the use of pulmonary artery catheters.

Why was there such a difference in the findings of two, apparently similar, studies? It may be that the propensity score used by Connors and colleagues1 did not adequately model the patients’ severity of illness. These authors calculated that a missing covariable would have to increase the risk of death six times to explain the difference in mortality, and considered the possibility as unlikely. However, they did not consider the possibility of several missing covariables. Perhaps some of the different covariables used by Murdoch and colleagues3 helped construct a more predictive model. These workers included important indices of severity of illness, such as presence of acute renal failure21 and physician’s prediction of outcome.22 They also considered concomitant treatments not included by Connors, for example use of vasoactive drugs and the need for artificial ventilation.

As discussed by Murdoch, Connors and co-workers constructed a propensity score more relevant to a patient’s condition on the first day of intensive care, while they used variables pertaining to the entirety of the intensive care stay. Thus, the propensity score used by Murdoch may have provided a better model for prediction of death following critical illness, so that the severity of disease and the process of intensive therapy explain the risk of mortality rather than the use of a monitoring device.

Cultural differences exist between American and British intensive care practice. An indicator of these differences is emphasized by the inclusion of years of education, income and type of medical cover as covariables in the propensity score of the Connors paper.1 Indeed, patients managed with a pulmonary artery catheter were more likely to be male and to have medical insurance. Thus, the patients considered suitable for pulmonary artery catheterization in this study may be different from such British patients. If the patient groups were too dissimilar, it is not surprising that the findings of the studies were different. Vincent and colleagues23 have suggested that medico-legal and even financial considerations may play a role in the inappropriate use of the pulmonary artery catheter.

The Connors study1 took place in five intensive units. It has also been suggested by Vincent and colleagues23 that the pulmonary artery catheters may have been used by physicians not specifically trained in intensive care. Observational studies have associated better patient outcome with management in closed units with intensive care-trained staff.24

The Connors study took place in 1989–1994, when the pursuit of supra-normal oxygen transport values was much in vogue. This therapeutic manoeuvre, which depends on pulmonary artery catheterization, has been demonstrated in one randomized controlled trial of ‘all-comers’ to intensive care to result in a higher mortality.20 Thus, the therapeutic changes invoked by the data derived from pulmonary artery catheterization may have led to the higher mortality, as acknowledged in the discussion of Connors’ paper. Therefore it is possible that differences in the use of haemodynamic data might explain the difference in the results of these two studies.

Given the difficulty in accounting for confounders in such cohort studies, there has been a clear need for randomized controlled trials into the utility of pulmonary artery catheterization. Such a trial was attempted in Canada, but interpretation was made impossible because of the high withdrawal rate of patients by their doctors and relatives resulting in a small sample size.25

However, the debate following the Connors paper1 has led to the setting up of at least two randomized controlled trials into the utility of pulmonary artery catheterization in North America and Great Britain. Are such trials likely to determine a true effect of a monitoring tool on patient survival, given the complexity of critical illness? Murdoch and colleagues do not think so, and I too remain sceptical. The reasons why have to do with the difficulty in setting up a very large, rigorously conducted trial. Essential features should include clear standards for the indications for pulmonary artery catheterization, the subsequent care of catheters, and assurances that accurate data are obtained with optimal interpretation. More problematically, any invoked change of treatment would have to be standardized, according to the best available information.

Even if such a thorough protocol was adhered to in a large number of patients, I am also sceptical about the validity of survival as an outcome in a trial of a monitoring device. Many factors determine survival from intensive care, and will confound all but the truly large randomized controlled trial. Is it not more meaningful to use so-called ‘surrogate markers’ in an evaluation of a monitoring tool? These may include duration of the shock state, and the incidences and durations of acute renal failure and multiple organ failure. After all, it is these occurrences that we are trying to avoid in the critically ill by employing invasive haemodynamic monitoring to help optimize oxygen transport.

It is now over 30 yr since the introduction of bedside pulmonary artery catheterization, and the debate about its usefulness continues. Other technologies are being introduced to help assess cardiac performance in critical illness. It is not possible to discuss these methods in this editorial, but one of the lessons from the use and study of pulmonary artery catheterization is that we ought to assess the utility of these devices in a thorough, efficient manner.

D. G. Swann

Consultant in Anaesthetics and Intensive Care

Royal Infirmary of Edinburgh

Scotland

EH3 9YW

UK

Conflict of interest

The author has received an educational grant from Baxter Healthcare plc.

References

1 Connors AF Jr, Speroff T, Dawson NV, et al. The effectiveness of right heart catheterization in the initial care of critically ill patients. JAMA 1996; 276: 889–97[Abstract]

2 Dalen JE, Bone RC. Is it time to pull the pulmonary artery catheter? JAMA 1996; 276: 916–8[ISI][Medline]

3 Murdoch SD, Cohen AT, Bellamy MC. Pulmonary artery catheterisation and mortality in critically ill patients. Br J Anaesth 2000; 85: K754

4 Guyatt GH, Tugwell PX, Feeny DH, Haynes RB, Drummond M. A framework for clinical evaluation of diagnostic technologies. Can Med Assoc J 1986; 134: 587–94[Abstract]

5 Gomez CM, Palazzo MG. Pulmonary artery catheterization in anaesthesia and intensive care. Br J Anaesth 1998; 81: 945–56[Free Full Text]

6 Sherman MS, Kosinski R, Paz HL, Campbell D. Measuring cardiac output in critically ill patients: disagreement between thermodilution-, calculated-, expired gas-, and oxygen consumption-based methods. Cardiology 1997; 88: 19–25[ISI][Medline]

7 Lehmann KG, Platt MS. Improved accuracy and precision of thermodilution cardiac output measurement using a dual thermistor catheter system. J Am Coll Cardiol 1999; 33: 883–91[ISI][Medline]

8 Baele PL, McMichan JC, Marsh H, Sill JC, Southorn PA. Continuous monitoring of mixed venous oxygen saturation in critically ill patients. Anesth Analg 1982; 61: 513–7[Abstract]

9 European Society of Intensive Care Medicine. Expert panel: the use of the pulmonary artery catheter. Intens Care Med 1991; 17: I–VIII[Medline]

10 Anonymous. Pulmonary artery catheter consensus conference: consensus statement. Crit Care Med 1997; 25: 910–25[ISI][Medline]

11 Connors AF Jr, McCaffree DR, Gray BA. Evaluation of right-heart catheterization in the critically ill patient without acute myocardial infarction. New Engl J Med 1983; 308: 263–7[ISI][Medline]

12 Connors AF Jr, Dawson NV, Shaw P, Montenegro HD, Nara AR, Martin L. Hemodynamic status in critically ill patients with and without acute heart disease. Chest 1990; 98: 1200–6[Abstract]

13 Steingrub JS, Celoria G, Vickers-Lahti M, Teres D, Bria W. Therapeutic impact of pulmonary artery catheterization in a medical/surgical ICU. Chest 1991; 99: 1451–5[Abstract]

14 Mimoz O, Rauss A, Rekik N, Brun-Buisson C, Lemaire F, Brochard L. Pulmonary artery catheterization in critically ill patients: a prospective analysis of outcome changes associated with catheter-prompted changes in therapy. Crit Care Med 1994; 22: 573–9[ISI][Medline]

15 Iberti TJ, Fischer EP, Leibowitz AB, Panacek E, Silverstein J, Albertson TE. A multicenter study of physicians’ knowledge of the pulmonary artery catheter. Pulmonary Artery Catheter Study Group. JAMA 1990; 264: 2928–32[Abstract]

16 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; 25: 213–20[ISI][Medline]

17 Wilson J, Woods I, Fawcett J, et al. Reducing the risk of major elective surgery: randomised controlled trial of preoperative optimisation of oxygen delivery. BMJ 1999; 318: 1099–103[Abstract/Free Full Text]

18 Boyd O, Grounds RM, Bennett ED. A randomized clinical trial of the effect of deliberate perioperative increase of oxygen delivery on mortality in high-risk surgical patients. JAMA 1993; 270: 2699–707[Abstract]

19 Gattinoni L, Brazzi L, Pelosi P, et al. A trial of goal-oriented hemodynamic therapy in critically ill patients. New Engl J Med 1995; 333: 1025–32[Abstract/Free Full Text]

20 Hayes MA, Timmins AC, Yau EH, Palazzo M, Hinds CJ, Watson D. Elevation of systemic oxygen delivery in the treatment of critically ill patients. New Engl J Med 1994; 330: 1717–22[Abstract/Free Full Text]

21 Chertow GM, Christiansen CL, Cleary PD, Munro C, Lazarus JM. Prognostic stratification in critically ill patients with acute renal failure requiring dialysis. Arch Intern Med 1995; 155: 1505–11[Abstract]

22 Marks RJ, Simons RS, Blizzard RA, Browne DRG. Predicting outcome in intensive care units – a comparison of Apache II with subjective assessments. Intensive Care Med 1991; 17: 159–63[ISI][Medline]

23 Vincent JL, Dhainaut JF, Perret C, Suter P. Is the pulmonary artery catheter misused? A European view. Crit Care Med 1998; 26: 1283–7[ISI][Medline]

24 Reynolds HN, Haupt MT, Thill-Baharozian MC, Carlson RW. Impact of critical care physician staffing on patients with septic shock in a university hospital medical intensive care unit. JAMA 1988; 260: 3446–50[Abstract]

25 Guyatt G. Ontario Intensive Care Study Group. A randomized control trial of right-heart catheterisation in critically ill patients. J Intensive Care Med 1991; 6: 91–5[Medline]





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