None of the present studies found any positive impact of PAC use on outcome variables. However, prospective, randomized studies in which the PAC was used as part of a management algorithm have shown improved outcomes in high-risk surgical patients [15, 16], although it should be noted that these studies did not provide an explicit protocol for care based on PAC-generated data. Assessment of a monitoring technology in a vacuum is unlikely to demonstrate benefit. Efficacy (PAC linked to explicit treatment protocols dictated by the study) cannot therefore be assessed at present.
What, then, is the evidence regarding the broader issue of PAC use in the ICU? The data collected to date do not support routine use of the PAC in any patient group, justifying withdrawal of the PAC from routine use. The only trial as yet to evaluate a strategy guided by PAC use in patients with ARDS was recently completed (results are yet to be published) [17]. The trial compared a 'fluid conservative' approach with a 'fluid liberal' strategy. If a positive result attributable to PAC is demonstrated, then a specific 'niche' for the technology may remain in critical care. If the results demonstrate no benefit, then PAC use will become limited to rescue therapy in a small number of select patients. Among these, complex cases associated more with right than with left ventricular failure within the context of ARDS secondary to severe sepsis or septic shock may benefit from guidance of therapy with PAC-derived data.
The previous consensus conference on PAC use must then be revisited in light of the most recently published trials and meta-analyses. In critical care and/or perioperative settings, two major reports must be considered: the consensus conference from the SCCM [6] and the guidelines from the American Society of Anesthesiologists [2]. The recent publication of guidelines for diagnosis and treatment of cardiac failure provides an opportunity to define better the position of PAC use in this setting as well [18].
Indications for pulmonary artery catheter use in cardiac failure
Myocardial infarction complicated by cardiogenic shock or progressive hypotension is a class I indication for PAC use in the formulated American College of Cardiology/American Heart Association guidelines [19]. This recommendation is also included in the PAC consensus conference convened by the SCCM in 1997 [6]. It is based on expert opinion, and there is no conclusive proof that PAC use improves outcomes in this patient population [6]. The SCCM consensus conference also indicated that PAC use was appropriate in patients with congestive heart failure refractory to empirical therapy.
The European Society of Cardiology guidelines [18] published in 2005 insist that invasive monitoring of patients with acute heart failure (AHF) should be initiated as soon as possible after they arrive at the emergency unit, concurrent with ongoing diagnostic measures to determine the primary aetiology. Those guidelines based on expert opinion also indicate that although PAC insertion for diagnosis in AHF is usually unnecessary, it could be used to distinguish between a cardiogenic and a noncardiogenic mechanism in complex patients with concurrent cardiac and pulmonary disease. The use of PAC is a class IIb recommendation (level C evidence) in haemodynamically unstable patients who are not responding in a predictable manner to traditional treatment, and in patients with a combination of congestion and hypoperfusion. In these cases, the PAC is inserted to ensure optimal fluid loading of the ventricles and to guide vasoactive therapies and inotropic agents.
It is recommended that, in cardiogenic shock and prolonged severe low output syndrome, the mixed venous oxygen saturation from the PA be measured and maintained above 65% in patients with AHF [6].
Experts have stated that direct measurement of haemodynamics can be helpful in patients for whom the physical examination with symptoms is unrevealing or discordant. It may be particularly useful for determining the contribution of heart failure to a complex clinical picture, such as sepsis, acute renal failure, or acute coronary syndrome, in the setting of chronic heart failure. Another common setting in which PAC insertion may be helpful is in the evaluation of dyspnoea and elevated right heart pressures in patients with concomitant pulmonary and cardiac disease.
Concerning right heart failure, catheterization of the PA is more invasive than echocardiography, but it is useful in evaluating right ventricular function and in confirming the presence of right ventricular failure in patients in the ICU [20].
Indications for severe sepsis or septic shock
Based largely on expert opinion, the consensus conference of 1997 [6] concluded that PAC use may be appropriate in patients with septic shock who are unresponsive to early resuscitative measures. Maintenance of normal haemodynamics in this group appeared to be the most appropriate goal. Research is needed to determine the proper role of the PAC in patients with sepsis or sepsis shock.
In 2004, the American College of Critical Care Medicine reported an update to their recommendations on practice parameters for haemodynamic support of sepsis in adult patients [21]. The authors of the report highlighted the principles that clinicians using haemodynamic therapies should define specific goals and end-points, titrate therapies to achieve these end-points, and evaluate the results of their interventions on an ongoing basis by monitoring a combination of variables that reflect global and regional perfusion and, if possible, the microcirculation. The assessment of cardiac filling pressures may require a central venous catheter or a PAC. With a level D recommendation, invasive haemodynamic monitoring should be considered in those patients who do not respond to initial resuscitative efforts; this monitoring should be combined with fluid infusion titrated to a goal-directed level of filling pressure associated with the greatest increase in cardiac output and stroke volume. For most patients, this will correspond to a PA occlusion pressure in the 12–15 mmHg range.
It is likely that the question of whether the PAC offers potential benefit for patients with septic shock will only be answered by a randomized, prospective trial in which both education on proper measurements and consensus treatment protocols are used.
In a case-control study, nested within a prospective cohort study, Yu and coworkers [22] examined the relationship between PAC use and patient outcomes, including mortality rates and resource utilization, in patients with severe sepsis in eight academic medical centres. They stratified a random sample of 1010 adult admissions with severe sepsis. Among patients with severe sepsis, they found that PAC placement was not associated with a change in mortality rate or resource utilization, although there was a small nonsignificant trend toward lower resource utilization in the PAC group. However, PAC use was associated with an increased risk for renal failure within 28 days after sepsis onset but not with increased risks for other complications, including ARDS, shock, disseminated intravascular coagulation, liver failure, or central nervous dysfunction.
Indications in acute lung injury/acute respiratory distress syndrome
The 1997 consensus conference convened by the SCCM [6] indicated that the optimal role of the PAC as a diagnostic and monitoring device in different types of respiratory failure has not been clearly defined. Research is needed to determine the role of the PAC in very carefully defined groups of patients with respiratory failure. The trial reported by Richard and coworkers [4] failed to find any benefit for PAC use in the subgroup of patients with ARDS.
In their retrospective study, Connors and colleagues [1] found an increased relative risk for death in the 1789 patients who had ARDS. The authors provided the following explanations for the observed lack of benefit. First, direct catheter-related complications during PAC use, such as catheter-related sepsis, might have outweighed any potential benefit of PAC placement. Second, PAC data might have been improperly obtained, leading to spurious haemodynamic profiles and resulting treatment. Finally, even if PAC data had been carefully obtained, the data may have been inaccurate and imprecise (for example, intravascular pressure values do not represent the transmural values, the only one able to inform on heart filling; tricuspid regurgitation may give inaccurate cardiac output measurements; mixed SvO2 might be artificially high in the presence of left to right shunt. These conditions may change the accuracy even though the technique for measurement is good). Another explanation for these results was given by Richard and coworkers [4], who hypothesized that the study by Connors and colleagues might have overestimated the mortality in the PAC group because of limitations associated with retrospective matching of patients. Connors and colleagues chose to use a propensity score, but this score did not take into account the intensity of treatment used to sustain haemodynamics. This approach could have masked a greater severity of illness in the patients undergoing PAC placement. In any case, all of these possibilities will have to be evaluated in a prospective, randomized controlled trial.
Interestingly, a study addressed predictors of mortality in acute respiratory failure [23]. The authors examined a retrospective cohort study of consecutive ARDS patients admitted to two medical ICUs of tertiary care hospitals in whom two different approaches to haemodynamic monitoring were used: PAC on demand and no use of PAC. The study evaluated risk factors for death and the influence of PAC, with adjustment to haemodynamic support as a confounding factor, in 98 patients in whom the delay between onset of ARDS, use of vasopressors and PAC placement did not exceed 48 hours. The authors identified only two independent predictors of death: an extrapulmonary cause of ARDS and need for maximal haemodynamic support with epinephrine/norepinephrine to control circulatory failure. The results did not permit detection of either a benefit or an adverse effect of invasive monitoring through the PAC. In 2003, Richard and coworkers [4] found no difference in morbidity and mortality at both 14 and 28 days.