Anesth Analg 2001;93:1546-1549
© 2001 International Anesthesia Research Society
CRITICAL CARE AND TRAUMA
The Safety of Immediate Extubation After Abdominal Aortic Surgery: A Prospective, Randomized Trial
Jonathan Cohen, FCP (SA)*,
Jacob Loewinger, MD
,
Karina Hutin, MD,
Jacqueline Sulkes, PhD
,
Avigdor Zelikovski, MD
, and
Pierre Singer, MD*
Departments of *General Intensive Care, Anesthesiology, Epidemiology, and General Vascular Surgery, Rabin Medical Center, Beilinson Campus, Petah Tikva, and Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel
Address correspondence and reprint requests to Dr. J. Cohen, Department of General Intensive Care, Rabin Medical Center, Beilinson Campus, Petah Tikva 49100, Israel.
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Abstract
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We performed this study to assess the safety of immediate extubation after elective abdominal aortic aneurysm surgery. Consecutive patients were prospectively randomized into two groups after surgery: Group 1 (n = 29) immediate extubation; and Group 2 (n = 21) delayed (at least 4 h) extubation. All patients were assessed by a senior anesthesiologist or intensivist before extubation. The following data were collected: preoperative—demographics, presence of comorbid disease, body mass index, hemoglobin level, heart rate, and blood pressure; intraoperative—duration of surgery and cross-clamping, blood loss, amount of crystalloids, colloids, and blood transfused, temperature at end of procedure, urine output, and complications; and postoperative—time to extubation, scores on the Acute Physiology and Chronic Health Evaluation-II and Therapeutic Intervention Scoring System, total fentanyl dose, and complications. Outcome variables were length of intensive care unit and hospital stay and 28-day mortality. The results showed no significant differences in preoperative or intraoperative variables between the groups, apart from a longer duration of surgery in Group 1 (P = 0.045). Group 2 patients had a significantly higher Therapeutic Intervention Scoring System score (P = 0.04) and required a significantly larger dose of fentanyl (P < 0.001). One patient in Group 2 required reintubation after a cerebrovascular accident. The overall mortality rate was 4% (2 patients in Group 2). There were no significant differences in any of the outcome variables. We conclude that immediate extubation can safely be performed after elective abdominal aortic aneurysm surgery.
IMPLICATIONS: In this prospective randomized study, we compared the outcome of patients undergoing elective aortic abdominal surgery who either were extubated immediately after surgery or after 4 h of stabilization in the intensive care unit. No significant differences were found in the length of intensive care unit or hospital stay, or 28-day mortality between the 2 groups.
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Introduction
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Patients undergoing elective abdominal aortic aneurysmectomy (AAA) frequently have coexisting cardiovascular, respiratory, and renal disease and are considered to be at increased risk for postoperative events. Thus, intensive postoperative monitoring is routinely provided, and typically includes admission to an intensive care unit (ICU) and mechanical ventilation for variable periods of time (1). This has also been standard practice at our institution. However, mechanical ventilation is personnel- and resource-intensive and may be associated with adverse effects. Our review of the literature failed to provide consistent recommendations regarding the optimal time for extubation. Indeed, one retrospective study suggested that early extubation might be safe (2) whereas another cautioned against it (3). Silbert et al. (4) reported that early extubation was successfully implemented for another group of patients considered at increased risk for postoperative morbidity and mortality, namely, patients undergoing elective cardiac surgery (4).
The present prospective, randomized trial was designed to assess whether immediate or delayed extubation after elective AAA surgery affects outcome.
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Methods
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All patients undergoing elective infrarenal AAA over a 1-yr period were included in the trial after approval was obtained from the local Ethics Committee and informed consent was obtained from all patients. Patients with morbid obesity (body mass index >35 kg/m2) or significant respiratory disease causing severe limitation of exercise tolerance (unable to perform activities of daily living) were excluded. The following preoperative data were collected: age, sex, presence of comorbid disease (namely, hypertension for patients receiving active oral medication; diabetes mellitus for patients receiving either oral medication or insulin treatment; ischemic heart disease (if there was a history of angina or a previous myocardial infarction or evidence of a myocardial infarction on the electrocardiogram); echocardiogram findings (if performed); body mass index, hemoglobin level, and immediate preoperative blood pressure and heart rate.
All patients were anesthetized and operated on by the same anesthesiologist and surgeon. Premedication consisted of midazolam 5–10 mg. A lumbar epidural catheter was inserted before the induction of anesthesia. The induction of anesthesia was achieved with midazolam 0.1–0.2 mg/kg, fentanyl 3 µg/kg, and vecuronium bromide 0.1 mg/kg. The trachea was intubated and the lungs mechanically ventilated. Immediately after the induction of anesthesia, 20 mL of bupivacaine 0.125% and fentanyl 0.1 mg were infused through the epidural catheter. Anesthesia was maintained with a nitrous oxide/oxygen mixture (50%:50%), isoflurane, and vecuronium. During aortic cross-clamping, all patients received dopamine 5 µg · kg-1 · min-1. ST segment monitoring was performed intraoperatively with a five-lead electrocardiogram; end-tidal carbon dioxide, oxygen saturation, central venous pressure, rectal temperature, and intraarterial blood pressure were monitored as well. Surgery was performed with standard techniques through a midline transperitoneal approach. The following intraoperative variables were recorded: duration of surgery, defined as the time from skin opening to closure; duration of aortic cross-clamping; estimated blood loss; amount of crystalloids, colloids, and blood transfused; temperature at the end of the operation; urine output; and complications, namely, hypotension (decrease in systolic blood pressure <90 mm Hg), tachycardia (increase in heart rate >110 bpm), bradycardia (decrease in heart rate <40 bpm), respiratory problems (decrease in oxygen saturation <90%), myocardial ischemia (ST segment depression of >2 mm), and renal problems (urine output of <60 mL/h).
Immediately after closure of the abdomen, patients were randomized into two groups. Group 1 underwent extubation in the operating theater, and Group 2 underwent extubation at least 4 h after surgery. Immediate extubation was performed only after assessment by the same senior anesthesiologist. Patients with a core (rectal) temperature of <35°C, hemodynamic instability (requirement for inotropic support at the end of surgery), (n = 2), or anticipated inability to maintain an unsupported airway (n = 1), and patients not admitted to the ICU because of lack of a bed (n = 5) were not randomized and were excluded from the study. The goals of postoperative ICU care were to maintain systolic blood pressure at >120 <160 mm Hg, heart rate at <90 bpm, oxygen saturation >92%, and urine output at >1 mL · kg-1 · h-1. All patients received Marcaine in titrated doses via the epidural catheter for pain control. Patients in Group 1 (immediate extubation) received bolus doses of IV fentanyl at the discretion of the attending intensivist. Patients in Group 2 received a continuous IV infusion of fentanyl titrated to maintain a Ramsay score of 4 or 5. The fentanyl was discontinued before extubation, which was performed only on approval of the senior intensivist. The following postoperative (ICU stay) variables were recorded: time to extubation; scores on the acute physiology and chronic health evaluation-II (5) and the therapeutic intervention scoring system (TISS) (6) after the first 24 h; total fentanyl dose required during the first 24 h; and complications, defined as any event requiring active intervention.
Patients were monitored in the ICU for at least 24 h after surgery and discharged to the vascular ward when their hemodynamic, respiratory, and renal status were considered stable. The main outcome measures were duration of ICU stay, duration of hospital stay, and 28-day mortality.
Student’s t-tests or Wilcoxon’s ranked sum test and median test were used to analyze statistically significant differences in mean continuous variables between the two groups of patients (immediate versus delayed extubation). 
2 Test was used to analyze statistically significant differences in categorical variables. A P value 
0.05 was considered statistically significant.
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Results
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The preoperative data are shown in Table 1. There were 29 patients in Group 1 (immediate extubation) and 21 in Group 2 (delayed extubation). No significant differences were found between the two groups for any of the preoperative factors assessed.
Intraoperative data are shown in Table 2. There were no significant differences between the two groups for any of the intraoperative variables except duration of surgery, which was significantly longer in Group 1 (115.7 ± 36.6 min versus 98.04 ± 21.24 min, P = 0.045). Intraoperative complications included hypotension in 22 patients (44%), oliguria in 8 (16%), tachycardia in 6 (12%), hypertension in 5 (10%), bradycardia in 2 (4%), and myocardial ischemia in 1 (2%). There were no significant differences in the distribution or incidence of these complications between the two groups.
By definition, time to extubation was significantly longer in Group 2 (340.00 ± 213.18 min versus 14.17 ± 8.26 min, P <0.001). This group also had a significantly higher score on the TISS (21.65 ± 4.6 versus 19.5 ± 2.56, P = 0.04) and received a significantly larger total dose of fentanyl (551.90 ± 348.93 µg versus 258.21 ± 228.65 µg, P <0.001) (Table 3). Complications in the ICU included hypertension in 23 patients (46%), tachycardia in 19 (38%), fluid overload in 4 (8%), oliguria in 2 (4%), hypotension in 2 (4%), cerebrovascular accident in 1 (2%), and atelectasis in 1 (2%). There were no significant differences in the incidence or distribution of complications between the two groups. Only one patient, from Group 2, required reintubation after a cerebrovascular accident.
There were no significant differences between the two groups for any of the outcome variables (Table 4). The overall mortality was 4% (2 patients in Group 2). Causes of death were cerebrovascular accident, and sepsis of undetermined cause that resulted in multi-organ dysfunction.
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Discussion
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Our prospective, randomized trial revealed no significant differences in length of ICU or hospital stay or 28-day mortality between patients undergoing immediate or delayed (more than four hours) extubation after elective AAA.
Elective AAA is associated with significant postoperative mortality, ranging from 8% in Europe and North America to 10% in Britain (7). It has been standard practice not to extubate the trachea immediately after surgery, but to admit these patients to an ICU for intensive monitoring and continuation of mechanical ventilation until a period of stability has been established (1). Intensive postoperative monitoring may well be advantageous for patients who are elderly and have significant cardiovascular and respiratory disease. We sought to determine whether prolonged mechanical ventilation also provides an outcome advantage.
AAA induces both nonspecific and specific changes in the pulmonary system. The nonspecific changes are those seen after any type of surgery involving the upper abdomen, and are caused by splinting from pain and the inability to take a deep breath resulting in atelectasis (8). The now widespread use of postoperative epidural analgesia after AAA has significantly improved pain control. The specific changes in the respiratory mechanics include an increased elastance and resistance when surgical retractors are placed, and a decrease in lung elastance after aortic cross-clamping (9). These changes may be attributable to an increase in thoracic blood volume. Other possible mechanisms include release of interleukin-8, pulmonary microembolism, and the effects of ischemia and reperfusion of the lower extremities. After unclamping, elastance decreases almost to baseline.
A stronger argument for delaying extubation is based on the results of a study that assessed the relationship of the organizational characteristics of ICUs, specifically the presence or absence of an ICU physician, to patient outcome after elective abdominal aortic surgery (3). The authors found that routine extubation by anesthesiologists and surgeons in the operating room was associated with increased hospital length of stay as well as an increased risk of reintubation and postoperative complications. However, the criteria for extubation were not described, and the authors suggested that the presence of intensivists could modify such patient outcomes.
In our study, all patients were assessed before extubation by either a senior anesthesiologist or intensivist. In addition, extubation was performed only under well-defined conditions (normothermia, ability to maintain unaided airway, and hemodynamic stability), and two patients were, in fact, excluded from the study because of hemodynamic instability. For the purpose of this study, all of our patients were admitted to the ICU where the postoperative care was goal directed to ensure optimal hemodynamic conditions. In our previous study (10), complications after AAA were related to a longer duration of surgery which, in turn, was associated with the performance of additional procedures and/or intraoperative complications. It is probable that in the absence of these events, patients could be monitored in the recovery room.
Only a single retrospective chart review study has been performed to evaluate the safety of early extubation (less than two hours after surgery) in patients undergoing AAA (2). Time to extubation was dependent on clinical factors and was not protocol directed. Early extubation was performed in 86% of the patients at a median time of 12 minutes after skin closure. The authors found that 4.8% of the patients required reintubation. The only death in the early extubation group occurred in a patient with cardiac arrest. The factors associated with failure of early extubation were obesity, abnormal preoperative chest radiograph, prior myocardial infarction, and previous coronary revascularization. Although the authors concluded that early extubation seemed to be safe in these patients, they acknowledged that the statistical validity of their results was compromised by the lack of prospective randomization.
Our study included consecutive patients undergoing elective AAA surgery. The patients were prospectively randomized into two groups—immediate postoperative extubation or extubation after at least four hours. The groups were well matched for preoperative and intraoperative variables. None of the patients in the early extubation group required reintubation. As expected, the ventilated group had a higher TISS score because of the points assigned for mechanical ventilation, and a larger requirement for fentanyl because of the need for sedation. However, there were no between-group differences in any of the outcome variables, namely, ICU, hospital stay, and 28-day mortality. This finding suggests that there was no advantage gained by the additional hours of ventilation. Indeed, delaying extubation has practical and potential disadvantages. Mechanical ventilation requires specialized equipment and personnel. Indeed, a TISS score of >20, as was the case in the ventilated group in our series, indicates an intensity of intervention requiring ICU nursing (5). However, ICU beds are scarce and expensive. In addition, mechanical ventilation, even of short duration, may be associated with morbidity including an increased risk of pneumonia, whereas the use of drugs such as fentanyl may result in hypotension, and excessive sedation may prolong the requirement for ventilation.
We acknowledge that the findings of this study are based on a relatively small number of patients. However, this is the first prospective randomized trial examining this topic; moreover, it is a single center study in which consecutively enrolled patients were treated by the same surgical, anesthetic, and ICU teams. Despite the unequivocal results of the study, we recommend that larger multicenter studies are required to validate our findings.
In conclusion, this study suggests that immediate extubation after major elective abdominal surgery is safe, and it may allow for decreased use of the ICU and specialized personnel without altering morbidity or mortality.
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References
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Accepted for publication August 21, 2001.
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Abstract
Introduction
