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Ann Thorac Surg 1998;66:1306-1311
© 1998 The Society of Thoracic Surgeons

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Original articles: cardiovascular

Central venous catheter use in low-risk coronary artery bypass grafting

^a Division of Cardiothoracic Surgery, Beth Israel Deaconess Medical Center, West Campus, Harvard Medical School, Boston, Massachusetts, USA
^b Department of Anesthesia, Beth Israel Deaconess Medical Center, West Campus, Harvard Medical School, Boston, Massachusetts, USA

Accepted for publication May 7, 1998.

Address reprint requests to Dr Campos, Division of Cardiothoracic Surgery, Beth Israel Deaconess Medical Center, West Campus, Suite 2C, 110 Francis St, Boston, MA 02215

	Abstract

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
Background. To assess the impact of central venous pressure catheter monitoring in low-risk coronary artery bypass grafting (CABG), we compared the hospital course of patients undergoing CABG with central venous pressure catheter monitoring with that of similar patients undergoing CABG with pulmonary artery catheter monitoring.

Methods. All isolated primary CABG procedures (n = 312) performed between April 22 and October 31, 1996, were evaluated, and 194 patients meeting six central venous pressure catheter use criteria were identified. Of these 194 patients, 133 (68%) underwent CABG with central venous pressure catheter monitoring, and 61 (32%) had pulmonary artery catheter monitoring owing to surgeon or anesthesiologist preference.

Results. In-hospital mortality was similar. A trend toward increased overall complications was seen in the pulmonary artery catheter group. The total volume infused in the first 12 hours, the 24-hour weight gain, and the intubation time were significantly greater in the pulmonary artery catheter group. Increases in intensive care unit length of stay and in total hospital charges trended toward statistical significance in the pulmonary artery catheter group.

Conclusions. Pulmonary artery catheter use in low-risk patients undergoing CABG was associated with greater weight gain and longer intubation time and may be associated with increased morbidity and utilization of hospital resources.

	Introduction

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
Many clinical centers continue to perform coronary artery bypass graft (CABG) operations with routine use of a pulmonary artery (PA) catheter for continuous measurement of hemodynamic indices and assessment of myocardial function. Advocates of routine PA catheter use cite the advantages of early detection of hemodynamic deterioration [1–3], precise monitoring of the effects of therapeutic interventions, and evidence that mortality is related to indices of myocardial function, namely the cardiac index, measured with a PA catheter [4].

Occasional reports have suggested that CABG can be performed in selected patients with only central venous pressure (CVP) monitoring with equivalent outcomes [5–8]. However, the specific criteria to select patients who can undergo CABG safely with only CVP monitoring are not clear. Furthermore, there is little information on the impact of CVP rather than PA catheter use on CABG outcomes including length of stay and hospital costs. Although the direct cost of a PA catheter may not greatly exceed that of a CVP catheter, the additional costs related to the increased intensity of monitoring, the need to intervene therapeutically in cases of borderline hemodynamic function, and the potential to increase intensive care unit (ICU) length of stay may be considerable.

The impact of CVP catheter use on mortality, clinical morbidity, ICU outcomes, length of stay indices, and total hospital charges in patients undergoing isolated primary CABG at a single institution were examined in this analysis.

	Material and methods

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
Specific criteria were developed to preoperatively identify patients undergoing isolated primary CABG who would be candidates for CVP monitoring alone:

Left ventricular ejection fraction 0.40

Serum creatinine <2.0 mg/dL

No steroid- or oxygen-dependent chronic obstructive pulmonary disease

Nonemergent coronary artery bypass grafting

No preoperative intraaortic balloon pump

No "acutely" unstable angina, defined as angina within 24 hours of operation requiring the institution of intravenous heparin or nitroglycerin or an increase in the dose of intravenous nitroglycerin

These criteria were introduced as guidelines. The individual anesthesiologists and surgeons remained free to select either monitoring catheter according to personal preference.

Between April 22 and October 31, 1996, 312 cases involving isolated primary CABG were performed and are the basis for this review. Patient-specific data were obtained through comprehensive retrospective chart review. Standard definitions of medical comorbidities were used [9]. Extent of coronary artery disease was determined from the cardiac catheterization report and was defined according to Coronary Artery Surgery Study criteria [10]. Left ventricular ejection fraction (EF) was calculated by left ventriculography in 252 patients and by echocardiography in 40 patients without ventriculograms. An EF of 0.40 or greater was assumed if "normal" or "preserved" left ventricular function was noted. Of the remaining 20 patients without ventriculograms or echocardiograms, 6 failed to meet criteria other than ventricular function for use of a CVP catheter and were excluded, and 14 were considered to have an EF of at least 0.40 based on the absence of a history of previous myocardial infarction or congestive heart failure.

The use of either a PA or CVP catheter was determined from the anesthesia record. Details of the operative procedure were obtained from the perfusion record and from the operative note. The ICU outcome variables (total crystalloid and colloid volume infused during the initial 12 hours after CABG, intubation time, and weight gain through the first postoperative day) were derived from the ICU flowsheet. In-hospital mortality, major morbidity (mediastinitis, cerebrovascular accident, reoperation for postoperative bleeding, reintubation, and renal failure defined as a rise in creatinine to a level greater than 2.0 mg/dL or the institution of dialysis after the operation), and need to change from a CVP catheter to a PA catheter were determined through chart review. Total hospital charges were obtained from the institutional computerized billing database. Because these patients were drawn from a single institution during the same fiscal year, hospital charges are an appropriate surrogate for hospital costs. Overall length of stay, and the lengths of stay in the ICU, in the step-down unit, and on the general care ward were determined according to the daily room charges. All lengths of stay and hospital charges are calculated from the date of operation.

During the study period, standardized anesthetic and extubation protocols were followed. Induction was achieved with sodium pentothal (3 mg/kg), midazolam (2 mg), and pancuronium (0.1 mg/kg). Patients received fentanyl (10 to 20 µg/kg) and were maintained throughout the operation on a titrated dose of isoflurane. Additional midazolam (2 to 4 mg) was given during the operation and at the start of rewarming. With rewarming, a propofol infusion (1 mg · kg^-1 · h^-1) was started and continued in the ICU until all vital signs were stable, the core body temperature reached 36°C (96.8°F), and no evidence of significant mediastinal bleeding was present. At this point, the propofol infusion was discontinued, and the patient was weaned rapidly from the ventilator using standard extubation criteria.

Statistical analyses were performed using STATA statistical software (Stata Corporation, College Station, TX). Continuous data are presented as the mean ± the standard deviation and are compared using Student’s t tests for normally distributed data or Wilcoxon rank sum tests for nonparametric results. Categorical data are compared with ² or Fisher’s exact tests when appropriate. Univariate and multivariate linear regression analyses were performed to examine the relationship between preoperative patient characteristics, including the choice of monitoring line, and the ICU outcomes. Variables with a p value less than 0.15 in the univariate analysis and other factors acknowledged to be important correlates of CABG outcome that did not meet this level of statistical significance (eg, sex, hypertension, peripheral vascular disease, history of prior myocardial infarction, and diabetes) were considered potential confounders and were included in the multivariate linear regression model. Statistical significance was defined as a two-sided p value less than 0.05.

	Results

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
Retrospective chart review determined that 194 (62%) of the 312 patients undergoing isolated primary CABG met all six criteria for placement of a CVP catheter. One hundred thirty-three of these patients (68%) actually had a CVP catheter placed (CVP group) and, despite meeting all CVP use criteria, 61 patients (32%) had a PA catheter placed (PA group) based on surgeon or anesthesiologist preference.

The clinical characteristics and the comorbid medical conditions of the CVP and PA groups are summarized in Table 1. The PA group patients were slightly older and had a greater prevalence of a past history of congestive heart failure (13% versus 2%; p = 0.01). However, at the time of CABG, no patient in either group was in active congestive heart failure, and all patients had a left ventricular EF of at least 0.40.

View larger version (14K): [in this window] [in a new window]   Fig 1. Twelve-hour volume infused, weight gain on the first postoperative day, and total intubation time in the central venous pressure (CVP) and pulmonary artery (PA) groups. Data are presented as the mean ± the standard error.

View larger version (11K): [in this window] [in a new window]   Fig 2. Intensive care unit (ICU), step-down unit (SDU), general care ward (Ward), and total length of stay results in the central venous pressure (CVP) and pulmonary artery (PA) groups. Data are presented as the mean ± the standard error.

View larger version (7K): [in this window] [in a new window]   Fig 3. Total hospital charges in the central venous pressure (CVP) and pulmonary artery (PA) groups. Data are presented as the mean ± the standard error.

	Comment

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

Performance of CABG with only CVP monitoring is not without precedent. In 1983, Loop and colleagues [5] reported a 10% reduction in total hospital charges, a decrease in total and ICU length of stay, and no increase in mortality or morbidity for CABG after introduction of a combined strategy of same day admission, limiting ICU stay, reducing blood usage, and eliminating PA catheters in patients with multivessel coronary artery disease with left ventricular EFs equal to or greater than 0.35. Bashein and associates [6] reported a retrospective analysis of 698 patients undergoing isolated CABG with left ventricular EFs of at least 0.40, with no history of congestive heart failure, and with a normal blood pressure response during exercise testing who underwent operation with CVP monitoring. This represented 54.7% of the total number of CABG procedures performed at the University of Washington during a 3-year period. The mortality rate (0.72%) and the perioperative myocardial infarction rate (3.2%) were acceptably low when compared with the results of the multicenter Coronary Artery Surgery Study [11], and a $216,000 cost savings based on the costs attributable to the PA catheter alone was estimated. Only 4.7% of patients required a change to a PA catheter, most commonly for postoperative management of hemodynamic instability.

Tuman and coworkers [7] examined the impact of CVP catheter use in 1,094 patients undergoing CABG who were allocated to a CVP or PA catheter based on anesthesiologist assignment. No significant differences in mortality or morbidity were noted. In patients in the highest of three mortality risk groups, the duration of ICU stay and the use of vasoactive infusions to support systemic blood pressure or cardiac output were significantly greater in the PA catheter groups. Seven percent of CVP group patients required a PA catheter after cardiopulmonary bypass for the evaluation and management of inadequate perfusion without experiencing a significant increase in mortality or morbidity.

In the only randomized, prospective study comparing CVP catheter use with use of either a standard or an oximetric PA catheter in patients undergoing elective cardiac operation, Pearson and associates [8] observed no significant differences in mortality, ICU length of stay, or vasodilator or vasopressor use. Costs of the catheters plus postoperative ICU and monitoring costs were significantly greater in the PA catheter groups. However, owing to anesthesiologist preference, 64.5% of patients randomized to a CVP catheter actually underwent surgery with a PA catheter in place limiting the interpretation of these results.

After the introduction of the CVP catheter use criteria at the Beth Israel Deaconess Medical Center, West Campus, 62% of all patients undergoing isolated primary CABG were candidates for CVP catheter use. Sixty-eight percent of these patients, or 42% of our overall isolated primary CABG population, actually underwent CABG with only CVP monitoring. It is likely that the introduction of these criteria as guidelines, with surgeons and anesthesiologists free to select a PA catheter based on personal preference, resulted in excessive conservatism. Only 2 patients (2%) required a change from a CVP to a PA catheter in the postoperative period without experiencing mortality or morbidity.

The CVP group, when compared with the CVP candidates who actually received a PA catheter, were less likely to leave the operating room at the conclusion of the CABG procedure with inotropic support, received significantly less volume in the first 12 hours after operation, were extubated significantly sooner, and gained significantly less weight by the first postoperative day. Volume infused in the first 12 hours was significantly correlated with weight gain by the first postoperative day, and volume infused and weight gain were significantly correlated with total intubation time. Trends toward reduced ICU (22% lower) and overall (7% lower) length of stay were observed that did not achieve statistical significance but, nevertheless, may be of clinical relevance. A 7.7% lower total hospital charge was noted in the CVP group. This also did not achieve statistical significance but may be of significant clinical importance.

How should these results be interpreted and can they be generalized? There are three possible interpretations. First, the observed differences may not be real but may be caused by chance. Second, catheter selection bias may have created two groups with substantial risk differences that may account for the differences in outcomes. Third, the choice of monitoring line may actually account for the differences observed.

Chance may have played a role as the p values exceed 0.05 for the length of stay and the total hospital charge differences. However, the differences in ICU outcomes are highly significant. These differences in ICU outcome may be associated with prolonged length of stay and increased total hospital charges. It is reasonable to conclude that the lack of statistical significance for differences in length of stay and total hospital charges may be caused by a type II error. For an 8% reduction in total hospital charges or a 0.4-day (22%) decrease in ICU length of stay to be detected with a power of 80%, sample sizes of 778 and 694 patients, respectively, would be required.

Catheter selection bias may also explain the observed differences. The choice of monitoring catheter was not randomized. Therefore, selection bias may have been introduced when the surgeon or the anesthesiologist selected a PA rather than a CVP catheter. There are measurable differences between the two groups in age, left ventricular EF, and a history of congestive heart failure, and there are statistically nonsignificant differences in other risk indicators. However, the magnitude of the statistically significant differences is small—only 4 years for age and only 0.04 for left ventricular EF. No patient was in active congestive heart failure, and all had left ventricular EFs of at least 0.40 at the time of CABG. Any unmeasured selection bias resulting in the PA group being significantly sicker than the CVP group is limited by the general well-being of the patients. In contrast to the small differences in CABG mortality risk indicators, the observed differences in outcomes were large. The 12-hour volume infused was 33% less, the weight gain measured on the first postoperative day was 21% less, and the intubation time was 28% shorter in the CVP group. The CVP group had a 22% shorter ICU length of stay, and total hospital charges were 7.7% lower in the CVP group. When the potential confounding variables (including age, left ventricular EF, and a history of congestive heart failure) were included in a multivariate linear regression model (see Table 4), all ICU outcome differences remained significant. Furthermore, the regression coefficients were remarkably similar to the outcome differences observed in the crude analysis (eg, 12-hour volume infused: 1.3-L difference by crude analysis versus 1.08 L by multivariate linear regression analysis).

The third possible explanation for these findings is that the observed differences in outcome between the CVP and PA groups are real and are explained by the choice of monitoring line. Inotropic drug use in the PA group was significantly greater in this analysis as has previously been noted by Tuman and colleagues [7]. Patients with PA catheters received significantly more volume in the initial hours after CABG, presumably to treat low diastolic filling pressures or borderline cardiac output. It is plausible that this would be associated with longer intubation times, greater postoperative weight gain, longer ICU and total length of stay, and increased total hospital charges without any recognizable benefit in terms of reduced mortality or morbidity as has been observed previously by others [5–8].

Finally, a combination of all three of these possible interpretations may explain the differences observed between the CVP and PA groups. The nonrandomized, retrospective design of this analysis limits the ability of this study to differentiate between these interpretations. However, application of these criteria for CVP catheter use led to a 42% reduction in the use of PA catheters for isolated primary CABG without any associated increase in morbidity or in-hospital mortality.

The trend toward an increase in nonfatal major complications (10% versus 4%, p = 0.10) that was observed in patients undergoing CABG with a PA catheter (see Table 3) is an intriguing and potentially worrisome finding. In the recent report by Connors and associates [12] of the Study to Understand Prognoses and Preferences for Outcomes and Risks of Treatments, increases in mortality, in ICU and total length of stay, and in total hospital costs were observed in ICU patients managed with PA catheters compared with a matched group of ICU patients treated without PA catheters. Previous reports have suggested that the relative risk of death may be greater in the elderly [13] and in patients with acute myocardial infarction [14–16] who are managed with PA catheters. Clearly, the nonrandomized, retrospective, observational design of the present analysis and its insufficient statistical power to detect significant differences in the incidence of nonfatal major complications limit any conclusions that can be reached. However, the significant differences in ICU outcomes that were observed and the trends toward increased nonfatal major complications, prolonged ICU length of stay, and greater total hospital charges raise concerns regarding the role of PA catheters in patients undergoing CABG that argue strongly for the performance of a prospective, randomized clinical trial.

	Acknowledgments

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
This work was supported, in part, by a Faculty Research Fellowship from the American College of Surgeons, Chicago, Illinois, to Dr Campos.

	Footnotes

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
This article has been selected for the open discussion forum on the STS Web site: http://www.sts.org/annals

	References

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Robert D. Stewart Stephen J. Lahey Sidney Levitsky Christian T. Campos Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Stewart, R. D. Articles by Campos, C. T. Search for Related Content PubMed PubMed Citation Articles by Stewart, R. D. Articles by Campos, C. T.