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Ann Thorac Surg 1997;64:134-141
© 1997 The Society of Thoracic Surgeons
Departments of Anesthesiology, Cardiothoracic Surgery, Medicine, Nursing, Preventive Medicine and Biometrics, University of Colorado Health Sciences Center, Denver Veterans Affairs Medical Center,Denver, Colorado
Accepted for publication January 20, 1997.
| Abstract |
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Methods. Time to extubation, hospital length of stay, perioperative morbidity, and mortality were studied in two consecutive cohorts undergoing cardiac operations requiring cardiopulmonary bypass before (pre-FT: n = 255, January 1992 to September 1993) and after (FT: n = 304, October 1993 to October 1995) institution of an FT protocol at a university-affiliated teaching Department of Veterans Affairs medical center. Preoperative risk factors, including a Department of Veterans Affairs risk-adjusted estimate of operative mortality, and perioperative surgical and anesthetic processes of care were evaluated.
Results. The mean Department of Veterans Affairs risk estimate of perioperative mortality was not different between the pre-FT and FT cohorts (3.5% versus 3.7%, p = 0.13). In the FT cohort, median time to extubation decreased significantly (19.2 versus 10.2 hours; p < 0.001) along with median surgical intensive care unit stay (96 versus 49 hours; p < 0.001) and total postoperative length of stay (222 versus 167 hours; p < 0.001). Median postoperative day of hospital discharge decreased from day 10 to 7 (p < 0.001). One patient (0.3%) required emergent reintubation directly related to early extubation. Reintubation for medical reasons was unchanged between pre-FT and FT groups (6.3% versus 5.0%; p = 0.48). Postoperative morbidity was similar between groups except for nosocomial pneumonia, the rate of which decreased significantly in the FT cohort (14.7% versus 7.3%; p < 0.005). Thirty-day (3.9% versus 4.6%; p = 0.69) and 6-month mortality (6.7% versus 6.9%; p = 0.91) were unchanged.
Conclusions. An FT cardiac surgery protocol has been instituted in a university-affiliated teaching Department of Veterans Affairs medical center, with decreased length of stay and no significant increase in postoperative morbidity, 30-day mortality, or 6-month mortality. It was associated with a lower rate of nosocomial pneumonia, a finding that must be validated in a prospective study.
| Introduction |
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In 1990, Krohn and colleagues [2] presented data on a clinical pathway using patient and family education, early extubation, pharmacologic adjuvants (including perioperative steroids), aggressive mobilization, ambulation, and early hospital discharge in 240 patients undergoing cardiac operation. The median postoperative LOS was 4 days, and only 2.5% of patients were readmitted within 6 months of discharge. However, this approach was not widely adopted until reports from the Baystate Medical Center using a similar protocol, now termed "fast-track" (FT) management, documented similar findings [3]. It now appears that economic forces are leading to routine use of FT management across the United States and Canada, despite relatively limited data on its safety and efficacy among different patient populations undergoing cardiac operations.
Approximately 7,000 cardiac surgical procedures are performed annually at 43 medical centers in the Department of Veterans Affairs (DVA) health care system [4]. These predominantly elderly, male patients have a high frequency of comorbid risk factors, particularly chronic obstructive pulmonary disease and current smoking, factors associated with postoperative pulmonary complications and considered by many to be contraindications to early postoperative extubation [5]. Other differences between this population and the private sector include lower socioeconomic status, lower functioning on quality of life scales, and impaired social support systems [6].
In the fall of 1993, an FT protocol similar to that of Engelman and associates [3] was implemented at the Denver Veterans Affairs Medical Center, a 276-acute care bed, university-affiliated teaching institution (see Appendix 1). In this report, observational data are presented on a retrospective cohort of cardiac surgery patients operated on before and after adoption of this protocol. The hypothesis of this investigation is that the FT protocol has resulted in a reduction in the duration of postoperative intubation and hospital LOS without significant change in morbidity or mortality.
| Material and Methods |
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Preoperative risk factors were selected based on previous risk models developed by the DVA's Continuous Improvement in Cardiac Surgery Program (CICSP) [4]. This CICSP model generates a "risk-adjusted" estimate of perioperative mortality. Perioperative processes of care specific to the FT protocol, as well as other processes known to independently influence patient outcome (such as surgical procedural details), were identified [7]. For the process of care and outcome variables chosen specifically for this study, a variety of sources were used, including the medical record, the DVA hospital computer system database, the national Beneficiary Indicator Records Locator System, the CICSP data set, and special software and reports developed by the hospital's Information Resources Management Service.
Statistical Analyses
Univariate statistical analyses were performed to determine differences between the pre-FT and FT patient groups. For continuous variables, unpaired t tests or the Wilcoxon rank sum test (the nonparametric analogue to the unpaired t test) was used. For discrete variables, a
2 test or Fisher's exact test (for variables with small prevalence rates) was used. Deaths were censored in all postoperative time to event data elements, as appropriate. Kaplan-Meier survival analysis was used for selected variables measuring time to an event (eg, LOS). Statistical significance was accepted at a p value less than 0.05. Data were analyzed using the SAS, version 6.10 (SAS Institute, Cary, NC).
| Results |
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30°C, respectively) was used in nearly all patients. However, mild hypothermia was used in a greater percentage of the FT cohort (24% versus 8%, FT versus pre-FT; p < 0.001). Although our clinical practice generally uses both antegrade and retrograde cardioplegia administration, only data on the use of retrograde cardioplegia are presented, as it was not possible to determine exactly which patients had antegrade cardioplegia from the archival sources. The frequency of failed retrograde administration, usually from dislodgement of the catheter, was similar in both groups. Duration of time in the operating room, ischemic arrest time, and total CPB time have decreased modestly. The frequency of intraoperative complications related to surgical technique (either iatrogenic or attributable to underlying disease) was similar between cohorts.
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Also shown in Table 2
are several non-FT protocol, deliberate changes in our processes of care instituted in temporal association with the FT protocol. Most notable are our successful efforts to reduce intraoperative blood product use. Use of intraoperative transesophageal echocardiography continues to increase since acquisition of a dedicated operating room unit in March 1992.
Fast-track "specific" processes of care are presented in Table 3
. Intraoperative crystalloid administration (non-CPB) has decreased significantly, along with a more modest reduction in colloid use. The frequency of volatile anesthesia use, defined as 15 minutes or more of use (not including CPB), has increased to include 96% of patients in the FT cohort. Although opioids continue to be used in all patients, the doses have been reduced significantly. Use of midazolam has also decreased significantly, in part related to one attending physician's practice of substituting its use by the shorter-acting hypnotic agent propofol by continuous infusion. The dose of midazolam has decreased by 50%. Isoflurane use during CPB has increased significantly, as has the duration of administration (including its use during the rewarming period of CPB). The maximum inspired concentration has not changed significantly. Finally, our deliberate efforts to decrease use of the more expensive mixed venous pulmonary artery catheter are apparent.
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Neither the incidence of major nor minor complications (Table 4
) has changed significantly, with the exception of a significant reduction in the incidence of nosocomial pneumonia (50% decrease). Within the FT cohort the frequency of pneumonia was highest in patients remaining intubated 10 hours or more (9.2% versus 3.9%; p = 0.09). There was a trend toward a higher incidence of atrial fibrillation in the FT cohort, although it did not reach statistical significance (12.8 versus 18.2%; p = 0.08). There were no documented episodes of recall of intraoperative events in either group. Thirty-day (3.9% versus 4.6%; p = 0.69) and 6-month mortality (6.7% versus 6.9%; p = 0.91) were not significantly different.
Comparison of changes in duration of intubation and LOS variables stratified by CICSP risk estimate groups revealed significant changes, or a trend toward significance, within all strata between the pre-FT and FT cohorts (Table 5
). No significant changes were noted in either 30-day or 6-month mortality across these same groups (data not shown).
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These results must be considered in the context of our study limitations, which include retrospective data collection, limitation to a single medical center, small sample size, potential confounding changes in important processes of care (including, but not limited to, concurrent attempts to curtail perioperative blood product use and inherent trends over time in care patterns toward reduced resource use and cost containment), and sequential cohort analysis. Despite retrospective data extraction, we are relatively confident of the accuracy of our major study outcomes given use of the DVA's sophisticated computerized clinical information system (Decentralized Hospital Computer Program) from which many types of administrative, clinical, and laboratory data are accessible (including discharge summaries, operative dictations, and LOS data) [8]. Use of several redundant data sources, both archival at our medical center and in the DVA hospital computer system database, allowed us to triangulate in on incomplete data and verify any conflicting data.
Our analysis failed to demonstrate any significant difference in the CICSP risk estimate of operative mortality between cohorts, although several factors used to calculate the risk estimate changed, along with several independent factors (see Table 1
). The clinical significance of these differences is questionable given our small sample size and retrospective data collection. However, our observation that the frequency of three independent variables related to underlying pulmonary disease-clinical diagnosis of chronic obstructive pulmonary disease, actual forced expiratory volume in 1 second, and preoperative use of bronchodilators-were higher in the FT cohort would seem to negate any substantial bias against operating on "sicker" patients, particularly those with comorbid factors that might affect success of early extubation. Analysis of study outcomes by CICSP risk strata, with significant changes noted in nearly all strata between the pre-FT and FT cohorts (with no corresponding change in mortality), support our belief that "global changes" in our processes of care were successful.
Several different anesthetic agents and techniques are used by different anesthesiologist/resident physicians. It is tempting to speculate that a certain combination of agents or doses is more effective in facilitating early extubation than another. However, aside from the general conclusion noted by others, that "inhalation-based" techniques or "low-dose" opioid techniques are required, these issues cannot be determined from this study because of the small sample size and study design limitations [1]. Lack of a randomized, standardized anesthetic protocol, along with variable criteria for extubation based on different pulmonary consultants in the SICU, preclude any firm conclusions. Our current FT practice is geared toward earlier wake up and extubation, often within 2 to 3 hours after operation. Pharmacologic differences may be more important with this more aggressive strategy. Absence of intraoperative recall in either group suggests that our current anesthetic management is adequate to prevent this feared, although rare, complication [9].
An important issue is the safety of early extubation, with the potential for emergent reintubation in patients managed on an FT protocol. In our institution, this was a particular concern given absence of in-house anesthesia personnel after hours. As well, the practice of limiting extubation to the "daylight" hours was deeply ingrained. Although we considered these issues carefully, we elected to proceed with this protocol. We believe that the finding that only 1 FT patient, extubated on the day of operation, required emergent reintubation supports our practice. We now routinely extubate most patients during the late evening hours.
We noted a statistically significant reduction in the frequency of postoperative nosocomial pneumonia in the FT group as reported on the discharge summary. However, precisely defining nosocomial pneumonia, even in a prospective study, is difficult and controversial [10]. Given a strong presence by our Infection Control Team (with dedicated nurse specialists) incorporating mandatory sputum culture surveillance and Centers for Disease Control definitions for nosocomial pneumonia, it is likely that these data are accurate [11]. We hypothesize that early extubation is associated with less impairment of pulmonary defense mechanisms (eg, better ability to cough and raise secretions), as clinical studies have shown adverse effects on these parameters during mechanical ventilation [12]. However, this observation requires prospective evaluation because other changes in our processes of care (ie, respiratory therapy ventilator management, suctioning protocols, and equipment changes unrelated to our FT protocol) could be solely responsible.
An interesting observation was the increase in serum glucose levels noted on arrival in the SICU in the FT cohort. Although mild postoperative hyperglycemia is expected, as noted in the pre-FT cohort, the greater increase in the FT group is striking. We believe it is related to the use of intraoperative methylprednisolone, although increased catecholamine release related to lighter anesthesia or CPB effects cannot be discounted [13]. The mean levels observed are not life threatening, although potential adverse effects of hyperglycemia in the setting of cerebral ischemia, effects on electrolyte balance and urine output, and other factors make this issue worthy of further study [14].
As noted in Table 2
, the measures to reduce excessive blood product use instituted in close temporal association with the FT protocol were successful. This strategy could have had independent favorable effects on perioperative morbidity, including lower infection rates and improved pulmonary function due to avoidance of the potential adverse immunomodulatory effects of homologous transfusion [15].
As well, the use of mild hypothermia (usually 32°C) increased modestly in the FT cohort. However, the role of temperature as a predictor of success of early extubation has not yet been specifically addressed in our analyses. Given that the vast majority of our patients are normothermic (or nearly so) on arrival in the SICU (Table 2
), the lowest temperature on CPB may not be as important. The similar success of an FT protocol implemented at two centers reported by Engelman and colleagues [3], one using normothermic CPB and the other using hypothermic CPB (although the exact degree is not reported), supports this contention.
An important consideration in evaluating the efficacy of this protocol is the potential for early readmission due to medical or surgical complications, and even death, after discharge. Given the high percentage of veterans from outside our metropolitan area, many of whom do not return to our center for postoperative follow-up, we were unable to verify all hospital readmissions. However, any patients requiring surgical sternal debridement do return to our institution. We did not observe any difference in this complication between cohorts. We also noted no differences between cohorts in 30-day and 6-month mortality. However, our observation of 1 patient in the FT cohort with sudden ventricular fibrillation arrest on postoperative day 7 just before planned hospital discharge (resulting in implantable defibrillator placement) raises concerns that the absolute safety of rapid hospital discharge has not been defined precisely.
Our data suggest, but do not prove, that comorbidities and social factors may have hampered efforts to decrease LOS. We have observed that the greater reduction in monitored LOS relative to overall postoperative LOS is at times related to either slowly resolving "minor" physiologic problems (ie, prolonged nasal oxygen requirements attributable to atelectasis) or problems in discharge planning and transportation. Given that more than half of our patients live more than 50 miles from our center (many in isolated rural areas), this may complicate discharge planning. Other factors seen in the DVA system include a high percentage of care delivered by resident physicians and constrained financial resources [16]. We believe that our demonstration that an FT protocol can be successfully implemented in the DVA suggests that these factors are not insurmountable in effecting changes to increase efficiency, while maintaining the quality of patient care delivered.
| Appendix 1. Protocols |
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Administration of preoperative cardiac medications is continued up until the time of operation and patients are premedicated with intramuscular morphine supplemented by lorazepam or scopolamine. All patients are monitored with indwelling radial artery catheters. Pulmonary artery catheterization through the right internal jugular vein is performed before or after induction of anesthesia at the discretion of the anesthesia attending physician. Anesthesia technique before institution of the FT protocol used high-dose opioids (fentanyl or sufentanil) supplemented by midazolam, with limited use of volatile anesthetics. After institution of the FT protocol, doses of intravenous opioids and benzodiazepines were reduced and use of volatile anesthetic agents or short-acting intravenous agents was increased. Routine use of isoflurane during cardiopulmonary bypass, by way of a vaporizer on the CPB machine, was encouraged. In contrast to previous practice, it is continued during the rewarming period, up to 5 to 10 minutes before weaning. Long-acting muscle relaxants, commonly used before, were discouraged in favor of intermediate-duration agents (ie, vecuronium, rocuronium). Cardiopulmonary bypass is performed using nonpulsatile bypass with a centrifugal pump and a membrane oxygenator. Myocardial preservation is accomplished using varying combinations of retrograde and antegrade cold crystalloid and blood cardioplegia after institution of either mild or moderate hypothermia.
Adjuvant intraoperative pharmacologic agents administered intravenously include methylprednisolone sodium succinate (500 mg), metoclopramide (10 mg), digoxin (0.5 mg),
-aminocaproic acid (5 g), and vitamin K (10 mg). The dose of methylprednisolone was increased in June 1994 from 100 to 500 mg (except in insulin-dependent diabetics, who receive 250 mg). Postoperative methylprednisolone administration (125 mg intravenously every 8 hours for three doses) was sporadic until April 1994, but is now routine, along with intravenous metoclopramide (10 mg every 8 hours for three doses) and digoxin (0.25 mg intravenously or by mouth once a day, continued for 4 weeks postoperatively). Efforts to decrease total time in the operating room, including surgical and CPB times, were emphasized to all clinical staff. Efforts to minimize total fluid administration and blood product administration where appropriate, as well as increasing use of less expensive nonprotein colloids (eg, hetastarch), were also emphasized.
To reduce LOS, early transfer from the SICU to the intermediate care unit ("stepdown unit") on the day after operation (postoperative day 1) was instituted in patients who had been successfully extubated the day of operation (postoperative day 0) and in whom mediastinal drains and the pulmonary artery catheter were removed. Rapid mobilization and ambulation were emphasized with transfer to the surgical ward on postoperative day 2 and hospital discharge by postoperative day 5 in patients with stable hemodynamics, adequate mental status, ability to ambulate and eat, afebrile status, and adequate family or social support systems. Same-day admission was not used in this cohort. To reduce costs, criteria for the use of the more expensive mixed venous oxygen saturation pulmonary artery catheter were agreed on by the anesthesia and surgical staff, substantially reducing its previous routine use. Use of intraoperative transesophageal echocardiography is at the discretion of the anesthesiology attending physician, unless requested by the surgeon. Postoperatively, selective ordering of laboratory tests, chest radiographs, and electrocardiograms based on patient condition alone was encouraged.
Several months after institution of the protocol, a formal, written clinical pathway was finalized and adopted. This pathway addresses patient assessment, consultations, diagnostic testing, specific therapeutic treatments, medications, nutrition, patient activity, patient education, and discharge planning throughout each phase of the perioperative period.
Ventilator Management and Weaning Protocol
In the initial phases of the protocol's institution early postoperative extubation of low-risk patients was emphasized. Upon arrival in the SICU, the anesthesia attending physician relayed that the patient was a suitable candidate based on a favorable preoperative risk profile, use of a "low-dose" anesthetic regimen, and an uncomplicated intraoperative course. Management of postoperative mechanical ventilation and the actual timing of extubation is directed by pulmonary/critical care medicine consultation with a fellow/attending physician team with input from the anesthesia and surgical staff.
Over time, a protocol emphasizing synchronized intermittent mandatory ventilation was instituted in favor of assist control ventilation. Initial tidal volumes range from 10 to 15 mL/kg depending on clinical factors (eg, stretch on internal mammary artery graft, degree of preoperative obstructive lung disease). Initial inspired oxygen settings (70% to 80% in uncomplicated cases) are recommended by the anesthesiologist, based on arterial blood gas results and pulse oximetry before CPB on arrival in the SICU.
Based on the patient's time to awakening, body temperature greater than 36°C, hemodynamic stability on minimal inotropic support, chest radiograph results, and lack of excessive mediastinal bleeding, the patient is rapidly advanced to lower ventilator rates and inspired oxygen concentration using pulse oximetry and selective arterial blood gas analysis. Neuromuscular blocker reversal agents (edrophonium or neostigmine) are routinely administered after the patient has a stable temperature of more than 36°C. The patient is advanced to a T-piece or to continuous positive airway pressure spontaneous ventilation. After a period of 20 to 30 minutes of spontaneous ventilation, an arterial blood gas measurement is obtained and if adequate (ie, based on the specific patient's preoperative pulmonary function tests and room air oxygen saturation), the patient is extubated. Supplemental oxygen (40% to 60%) is administered initially through a humidified face tent and nasal prongs. The patient is weaned to room air during the following 24 hours based on pulse oximetry measurements.
After the first several months, higher risk patients were considered for early extubation, including those undergoing redo procedures, patients with impaired preoperative pulmonary function results, those with impaired ejection fraction, and those requiring moderate inotropic support. Patients leaving the operating room with an intraaortic balloon pump or those receiving high doses of inotropic agents were not considered candidates, although all are treated with FT pharmacologic adjuvants and are initially managed with a "light" anesthetic. Unstable patients after CPB are given additional doses of opioids as tolerated and muscle relaxants before leaving the operating room.
| Acknowledgments |
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This study was funded in part by Cooperative Study in Health Services No. 5 ("Processes, Structures and Outcomes of Care in Cardiac Surgery") from the Department of Veterans Affairs Health Services Research and Development Service.
| Footnotes |
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| References |
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