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CARDIOVASCULAR ANESTHESIA

Pulmonary Artery Catheter Placement for Elective Coronary Artery Bypass Grafting: Before or After Anesthetic Induction?

Departments of Anesthesiology (Sections on Critical Care and Cardiothoracic Anesthesia) and Medicine (Pulmonary and Critical Care Medicine), Wake Forest University School of Medicine, Winston-Salem, North Carolina

Address correspondence and reprint requests to Micheal H. Wall, MD, Department of Anesthesiology, Wake Forest University School of Medicine, Medical Center Blvd, Winston-Salem, NC 27157-1009. Address e-mail to mhwall{at}wfubmc.edu

	Abstract

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Pulmonary arterial catheters (PACs) are often used during and after coronary artery bypass grafting. We hypothesized that placement of a PAC would be faster in anesthetized patients. We further hypothesized that the presence or absence of a PAC during the induction of anesthesia would make no difference in hemodynamics, vasoactive drug use, or IV fluid administration during the induction. Patients (n = 200) undergoing elective coronary artery bypass grafting were assigned to PAC insertion either before or after the induction of anesthesia. Total time for PAC insertion, number of finder needle and venous catheter insertion attempts, incidence of carotid artery puncture, arrhythmias or ST segment changes, arterial blood gas analysis, hemodynamic variables, IV fluids, and vasoactive drugs required during and after the anesthetic induction were recorded. Thirty-two different physicians placed the PACs. PAC placement was faster (10 versus 12 min, P = 0.0003) and required fewer punctures with a finder needle (P = 0.0107) in anesthetized patients. There were no significant differences between groups in hemodynamic values or use of vasoactive or anesthetic drugs or IV fluids during the induction. There were also no significant differences between groups in the incidence of myocardial ischemia, arterial hypoxemia, or hypercarbia. Placement of a PAC before the induction of anesthesia consumes more time and fails to improve hemodynamic stability or lessen vasoactive drug use during the induction of anesthesia.

IMPLICATIONS: Insertion of pulmonary artery catheters (PACs) before the induction of anesthesia requires more needle sticks and takes longer than insertion after the induction of anesthesia; moreover, previous PAC insertion has no significant effect on hemodynamics or use of vasoactive drugs or IV fluid associated with the induction of anesthesia.

	Introduction

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Pulmonary artery catheters (PACs) are often inserted before the induction of anesthesia to obtain hemodynamic information that might guide the anesthetic induction. However, other data suggest that central venous catheter insertion may be faster and performed with fewer complications when performed in sedated or anesthetized patients (1–4). However, the stress of PAC placement with a local anesthetic in an awake but sedated patient could potentially induce or worsen myocardial ischemia. Additional risks of placing the PAC at this time potentially include increased difficulty of insertion and, thus, a theoretically larger number of complications. The lack of secure airway control in a sedated patient in the Trendelenburg position could compromise oxygenation and ventilation.

In patients having active angina coming to surgery from the coronary care unit or catheterization laboratory, our practice has been to place the PAC after the induction of anesthesia. This allows PAC placement in an anesthetized, unstressed, well oxygenated, and adequately ventilated patient. It had been our impression that the anesthetic induction in these acutely ischemic patients without PACs had been safe and hemodynamically uneventful, and placement of the PAC by our physician resident trainees seemed to go smoother in these anesthetized but critically ill patients. However, the potential negative aspect of placing the PAC after the induction of anesthesia is that significant changes in hemodynamics, myocardial ischemia, or both may be more likely to occur when information regarding ventricular filling pressures and cardiac output remains unavailable. We hypothesized that placement of a PAC after the induction of anesthesia would be faster. We also hypothesized that the presence or absence of a PAC would make no difference in hemodynamics, vasoactive drug use, or IV fluid administration during the anesthetic induction.

	Methods

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This study was approved by the IRB for Wake Forest University Baptist Medical Center and was designed to study 200 elective coronary artery bypass grafting (CABG) surgery patients over the course of two academic years, allowing us to include resident physicians with differing levels of experience during differing parts of their residency training.

Consenting patients were randomized using a modified block randomization technique. Patients were randomized separately by the physician who would be placing the PAC. The first patient enrolled onto the study for each individual physician was randomized to either PAC insertion before (Before group) or after (After group) the induction of anesthesia. All subsequent patients for that individual physician were then alternatively assigned into the Before or After group. This ensured that for each individual physician, the groups would be closely balanced.

All patients were premedicated with IM morphine (5–10 mg) and oral lorazepam (2–5 mg) approximately 1 h before their arrival in the operating room (OR). All patients received a similar IV induction with fentanyl (10–30 µg/kg) or sufentanil (1–10 µg/kg), midazolam (0.05–0.15 mg/kg), and pancuronium (0.1 mg/kg). Additional fluids, vasoactive medications, or anesthetics were administered as deemed required by the cardiac anesthesiologist consultant to maintain hemodynamic variables within ±10% of the baseline values.

The PACs were inserted by 1 of 32 physicians who ranged in experience from resident physicians in their second year of anesthesia training to consultants with 18 yr of cardiac anesthesia experience. Resident physicians placed all PACs in patients where the anesthetic team included resident physicians and consultants, whereas consultant anesthesiologists placed PACs when the anesthesia team included a consultant and a certified registered nurse anesthetist. All patients had central venous access obtained in the Trendelenburg position, which is usually in the right internal jugular (IJ) vein, but when attempts at that site failed, the left IJ vein was used. Patients underwent subclavian vein cannulation only when attempts at right and left IJ vein cannulation were unsuccessful. After sterile skin preparation, all physicians followed the same basic procedure of using a 21-gauge finder needle to locate the vein followed by the use of an 18-gauge venous catheter or 18-gauge thin-wall arteriotomy needle to access the vein for placement of the guidewire. After a stab wound was made at the insertion site, the introducer sheath was inserted, and the PAC was floated through the introducer sheath and into the pulmonary artery.

Careful documentation of times began with entry of the patient into the operating suite. We recorded times for the start of skin site preparation, initial finder needle insertion, venous catheter (or thin-walled arteriotomy needle) insertion, completed placement of introducer sheath, and completed floatation of PAC. Introducer sheath time was the time from the start of skin preparation to placement of the introducer sheath. PAC time was the duration of time from the initial start of skin preparation to completed floatation of the PAC. All times were documented by a research nurse who observed the entire procedure and was not part of the surgical or anesthetic team.

Hemodynamic data collected included heart rate (HR), systolic, diastolic, and mean arterial blood pressures (MAP) (recorded from an arterial catheter that had been placed in the holding room before entry into the OR), and SpO₂. These hemodynamic variables were recorded at 5-min intervals and whenever there was a substantial change.

Preinduction hemodynamic values were measured less than 2 min before the injection of anesthetic drugs; hemodynamic values after the induction were mea-sured less than 2 min after tracheal intubation. Similarly, the hemodynamic variables were measured immediately preceding skin preparation and recorded immediately after the PAC was positioned in the pulmonary artery.

SpO₂ was monitored throughout the study, and supplemental oxygen was adjusted to ensure SpO₂ remained 90%. Arterial blood samples were obtained from the radial artery catheter before the first procedure (PAC placement or induction), after PAC insertion, and after the anesthetic induction (intubation) for blood gas analysis.

For detection of myocardial ischemia, patients were monitored continuously (qMed Inc, Clark, NJ) starting the day before surgery and continuing until surgical skin preparation using modified leads II and V5. Analysis of the electrocardiogram was performed with the use of ECGraph software (qMed Inc) by a physician blinded to the timing of PAC placement. We defined a greater than 1-mm depression or increase of the ST segment at the J-point plus 60 ms that lasted more than 1 min as diagnostic of significant myocardial ischemia. The analysis period was split into two groups. The time from placement of the monitor until arrival in the OR was termed the preoperative period. The period from arrival in the OR to the end of all recording was termed the intraoperative period.

Analyses using either the exact ² or t-tests were used to test whether the preoperative and patient demographics were reasonably balanced between the treatment groups. Outcome variables required more complex analyses that adjusted for the random effects caused by the individual physician providing the group treatment. Binomial outcomes were analyzed using generalized linear models (Proc Genmod, SAS 8.1, SAS Institute, Cary, NC) with a logit-link, fixed effect for the physician training level and a random effect for the physician. Throughout the manuscript, odds ratio refers to the odds of the outcome for the Before group:odds of the outcome for the After group. Likewise, mixed effect models (Proc Mixed, SAS 8.1, SAS Institute) were used to analyze continuous outcome variables. Introducer sheath and PAC times were normalized using log-transformed times before analysis using mixed effect models. Outcome variables requiring log-transformation were reported as geometric least squares mean with their 95% confidence intervals (95% CI). Discrete quantitative outcomes such as insertion attempts were analyzed using a modification of Fisher’s sign test with pairing between groups with each physician. First, each physician’s set of patients (both treatment groups combined) was ranked according to outcome variable size. Then, under each physician, the average ranks of the Before and the average ranks of the After group were determined. Finally, using the average ranks for each physician’s treatment group, the Fisher’s sign test with pairing by physician was applied to test for group differences. A power analysis was performed to determine the number of patients necessary to detect differences between CA-2 (clinical anesthesia year 2 residents) PAC placement times of the Before and After treatment groups. The placement times were assumed to be log-normal in distribution with a geometric mean of 15 and 10 min in the Before and After groups, respectively. Assuming that 95% of the placement times ranged from 25% to 400% of their treatment group’s geometric mean, detection of significant treatment group differences with 80% power requires sample sizes of 85 patients per group.

	Results

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One-hundred-ninety-nine of 200 patients enrolled were analyzed. One patient was excluded because, despite the patient being randomized to the Before group, the consultant anesthesiologist decided to place the PAC after the induction. Each consultant placed a mean of 5.3 PACs (range, 1–10); each resident placed a mean of 4.3 PACs (range, 1–11). The size of the two groups was not equal because of the randomization and sequencing procedures that were used (Table 1).

The introducer sheath (P = 0.0005) and PAC (P = 0.0003) were placed significantly faster in the After group (Table 2). Table 3 shows the differences in times by experience. Overall, the introducer sheath insertion and PAC insertion times decreased significantly as experience increased (overall effect, P = 0.0001 each). The differences in times between placement before or after the induction were most evident in the physician groups with less experience. Locating the IJ vein required significantly fewer attempts with the finder needle when the PAC was placed after the induction (P = 0.0107) (Table 4). These differences were also the most evident in physician groups with the least experience. In patients requiring greater than six finder needle attempts, two patients in the Before group and one in the After group had a left IJ catheter placed; two patients in each group had a subclavian catheter placed.

There was no difference between the Before or After groups in the timing (medians, 85 versus 82 min before arrival in the OR), in the doses of morphine (8 versus 7.5 mg) or lorazepam (3 versus 3 mg) premedication, or in the doses of fentanyl (1500 versus 2000 µg), sufentanil (500 versus 225 µg), or midazolam (5 versus 5 mg) used for the induction of anesthesia. There were no significant differences in changes in MAP between groups (Table 5). However, the Before group had a small but statistically significantly greater change in HR during the induction (102% ± 16% versus 99% ± 12%) (Table 5).

Patients with impaired left ventricular function (ejection fraction 40% or left ventricular end-diastolic pressure >20 mm Hg; n = 14 in Before group; n = 21 in After group) or left main coronary artery disease (stenosis 60% by area; n = 15 in Before group; n = 5 in After group) were analyzed separately. There were no significant differences between groups in ischemia during the induction, changes in MAP or HR, or vasoactive drug use.

	Discussion

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Our data show that placement of a PAC in elective CABG patients is faster and takes fewer punctures with a finder needle in anesthetized patients. In this study of 199 patients, we found no significant differences in ST segment changes, vasoactive drug or IV fluid use, changes in MAP, or clinically significant changes in HR during the anesthetic induction in patients with the PAC placed before or after the anesthetic induction.

The use of PACs during cardiac surgery remains controversial (5–7), as does the timing of their placement (3,4). Some physicians advocate placing a PAC before the induction of anesthesia to permit optimum control and treatment of hemodynamic alterations during the induction (8). Others counter that placement of PACs in awake patients can lead to pain and stress, which may lead to adverse changes in hemodynamics or ischemia (9). Ours is the only study that has prospectively evaluated this issue. This study clearly has shown that placement of a PAC is 17% faster in anesthetized patients and requires fewer insertion attempts. These differences are most pronounced for the physicians with the least experience. We speculate that eliminating the need for local anesthesia and for a cooperative patient with a stable degree of conscious sedation increase the confidence of the inexperienced operator. Further, we speculate that the 17% savings in time may be a surrogate marker for teaching other techniques in the OR. This time saving may have important implications for OR teaching and scheduling issues.

It is interesting that the presence of a PAC made no difference in the amount of anesthetic drugs (sufentanil, fentanyl, or midazolam) or vasoactive drugs (phenylephrine or nitroglycerin) used during the anesthetic induction in our study. This was surprising because we expected that the additional hemodynamic information available with the PAC would have influenced anesthetic and hemodynamics management.

In the intensive care unit, Sznajder et al. (2) demonstrated that both complications and failures of central venous catheter placement were twice as common for physicians with limited experience versus those with more experience with invasive procedures. Regardless of the level of experience, there were fewer complications and failures if the central venous catheters were attempted in patients who were unconscious at the time of insertion (2). The reasons our results differ from Sznajder et al. may include 1) different patient populations (intensive care unit versus elective cardiac surgery patients), 2) unconscious versus fully anesthetized and mechanically ventilated patients, and 3) the level of training (interns versus CA-2 and CA-3 residents). However, we did show that fewer insertion attempts were required, and the introducer sheath and PAC were placed faster in the After group. These differences in times are most pronounced in the groups with the least experience. Our study also showed that as experience increases, time to place the introducer and PAC decreases in both awake and anesthetized patients. Both of these studies suggest that in academic medical centers, where central venous catheters and PACs are sometimes inserted by inexperienced trainees, these procedures can be performed faster after the induction of anesthesia.

In a study comparing placement of a PAC in a small group of anesthetized versus sedated patients undergoing elective cardiac surgery, O’Connor et al. (10) showed no significant differences in hemodynamics and no differences in the stress response to PAC placement between groups. Our study showed that there was no difference in percentage change of MAP during PAC placement between groups. Statistically, the HR increased more in the Before group, although this difference has no clinical importance (95% CI for group differences in total percentage change in HR, 0.15%–3.6%).

The present study has several limitations. We could not blind the physicians caring for the patient to the presence or absence of the PAC. This makes the lack of an effect even more convincing. The PAC we used did not use continuous cardiac output or continuous mixed venous oximetry (SO₂) technology. Continuous measurements (especially of SO₂) might have prompted changes in anesthetic or vasoactive drug use that pulmonary artery pressures or intermittent bolus cardiac outputs did not. This study included only patients undergoing elective CABG surgery, so these results may not apply to other patient populations; however, in other populations with significant coronary artery disease presenting for noncardiac surgery, the management of the anesthetic induction is similar, so we predict that the results would be similar as well. Our patients were induced using relatively large doses of opioids. Induction regimens using smaller doses of opioids combined with other drugs (volatile or IV) could yield different results. The study design allowed for the use of sufentanil or fentanyl during the induction of anesthesia because at the time of the study that reflected clinical practice at our institution, with some consultant cardiac anesthesiologists preferring to use sufentanil. We felt that at the time there was no scientific reason to favor one drug over the other (11–13), and because the anesthetic doses of all drugs were titrated to effect, we felt it was reasonable to allow both to be used. Post hoc analysis of our data, excluding the 16 patients who received sufentanil, made no difference in any of our results. The two groups differed in their use of calcium channel blockers, and this may have influenced their hemodynamic responses to the anesthetic induction. This study is also underpowered in evaluating patients with left-main disease or decreased left ventricular function, and, as such, the lack of difference found in these groups needs to be interpreted with caution.

It is difficult to use PAC measurements to compare our two groups. When the catheter was placed in anesthetized patients, the first set of hemodynamic measurements was confounded by the effects of general anesthesia and positive pressure ventilation. These are not comparable to the same measurements obtained in the Before group, who were sedated and spontaneously ventilating. Nevertheless, we did measure mixed pressure versus PO₂ after completion of both the induction and PAC placement in both groups (immediately after intubation in the Before group and immediately after PAC placement in the After group). There were no significant differences between groups (PO₂; Before, 49 ± 7.7 mm Hg versus After, 46 ± 8.2 mm Hg). This implies that there were no differences in the ratio of total body oxygen supply and demand at the first time point the groups could have been reasonably compared.

Finally, another weakness of this study is that it is underpowered to determine if presence of a PAC before the induction (versus after induction) could decrease the incidence of serious (and rare) adverse events, such as death or myocardial infarction, during the anesthetic induction. Such a study would require many thousands of patients. Because the common arguments for placing a PAC before the induction are to treat unexpected hemodynamic abnormalities (with fluids or drugs) and have a hemodynamically smoother induction, we looked at several secondary, intermediate outcome variables (i.e., IV fluid and vasoactive drug use and MAP and HR changes), and have reported odd ratios and 95% CIs for our findings.

In conclusion, placement of the PAC before the anesthetic induction in a teaching hospital takes longer and requires more needle sticks to localize the IJ vein. Furthermore, placement of a PAC before the induction of anesthesia for elective CABG surgery did not reduce hemodynamic alterations, myocardial ischemia, or vasoactive drug use during the induction of anesthesia when performed by a consultant in cardiac anesthesiology. This study suggests that the induction of anesthesia can be performed safely without a PAC in patients presenting for elective cardiac surgery, although small differences in the incidence of rare events could not be excluded. Whether PACs contribute to outcome after CABG surgery is a more significant question and one that has not been completely answered.

Addendum
The timing of PAC placement with respect to the anesthetic induction before conducting this study was very controversial within our cardiac anesthesia group. The standard practice had been to place the PAC before the induction. However, by the conclusion of the study, all of the residents and faculty, even the most vocal proponents of placing the PAC before induction, preferred placing the PAC after the induction. In fact, since the study was completed, our practice has now changed with almost 100% of PACs for cardiac surgery, including valve surgery, placed after the induction of anesthesia.

	Acknowledgments

 
The authors would like to thank Judy Bennett, RN, for her assistance with completing this study.

	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 Services Email this article to a colleague Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by Wall, M. H. Articles by Royster, R. L. Search for Related Content PubMed PubMed Citation Articles by Wall, M. H. Articles by Royster, R. L. Related Collections Anesthetic Techniques Cardiovascular Heart Monitoring (Cardiac)

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