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Jonathan Wilson a Department of Anaesthetics, York District Hospital, York YO31
8HE, b Intensive Care Unit, York District
Hospital, c Pharmacy, York District Hospital
Correspondence to: Dr Wilson
jonathan{at}critbase.demon.co.uk
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Abstract |
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Objectives:
To determine whether preoperative
optimisation of oxygen delivery improves outcome after major elective
surgery, and to determine whether the inotropes, adrenaline and
dopexamine, used to enhance oxygen delivery influence outcome.
Design:
Randomised controlled trial with double
blinding between inotrope groups.
Setting:
York District Hospital, England.
Subjects:
138 patients undergoing major elective
surgery who were at risk of developing postoperative complications
either because of the surgery or the presence of coexistent medical conditions.
Interventions:
Patients were randomised into three
groups. Two groups received invasive haemodynamic monitoring, fluid,
and either adrenaline or dopexamine to increase oxygen delivery.
Inotropic support was continued during surgery and for at least 12 hours afterwards. The third group (control) received routine
perioperative care.
Main outcome measures:
Hospital mortality and morbidity.
Results:
Overall, 3/92 (3%) preoptimised patients
died compared with 8/46 controls (17%) (P=0.007). There were no
differences in mortality between the treatment groups, but 14/46 (30%)
patients in the dopexamine group developed complications compared with 24/46 (52%) patients in the adrenaline group (difference 22%, 95%
confidence interval 2% to 41%) and 28 patients (61%) in the control
group (31%, 11% to 50%). The use of dopexamine was associated with a
decreased length of stay in hospital.
Conclusion:
Routine preoperative optimisation of
patients undergoing major elective surgery would be a significant and
cost effective improvement in perioperative care.
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Key messages
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Introduction |
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Major elective surgery contributes to intensive care occupancy, with a significant mortality rate. 1 2 In the United Kingdom most patients are taken from the general ward directly to the operating theatre before major elective surgery. The extent of perioperative monitoring is dependent on the anaesthetist, and the site of postoperative care will depend on the anticipated development of complications and the availability of intensive care beds or high dependency beds.
The enhancement of oxygen delivery to the tissues, guided by data obtained with pulmonary artery catheters, has been shown to improve outcome of patients deemed to be at high risk from major surgery. 3 4
Oxygen delivery is dependent on the amount of oxygen in the blood and the cardiac index. Optimisation of cardiac index requires fluid and inotrope therapy to increase cardiac contractility. Inotropic agents, however, have different effects on circulation to the gut, which may possibly affect postoperative morbidity.5 Dopexamine (Dopacard, Ipsen, Maidenhead), is a peripheral vasodilator, which is associated with improved splanchnic oxygenation, 6 7 whereas adrenaline (epinephrine), commonly used in intensive care, may reduce splanchnic flow.8
Our study compared the outcome in a population of elective surgical
patients receiving either preoperative optimisation of oxygen delivery
(treatment groups) or undergoing current hospital practice (control
group). We also tested whether the inotrope dopexamine, given in a
double blind fashion, affects outcome.
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Subjects and methods |
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Approval for our study was obtained from the ethics committee of York District Hospital, and written consent was obtained from all the patients. We considered all patients undergoing major elective surgical procedures in general surgery, vascular surgery, and urology. Patients were identified as being at high risk of developing perioperative complications on the basis of either surgical criteria or the presence of coexisting medical conditions (table 1).
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The care of control patients was determined by the individual surgeon and anaesthetist according to their routine practices for the operation. Generally, the patients remained on the general surgical ward until surgery and were then returned to either intensive care, high dependency care, or the ward postoperatively. No routine preoperative fluid protocol was followed for these patients.
Patients in the adrenaline group and dopexamine group were admitted to either intensive care or high dependency care a minimum of 4 hours before surgery. A large intravenous cannula was inserted in the patient's forearm and an intra-arterial cannula was placed in the patient's radial artery for measurement of blood pressure and for blood sampling. A pulmonary artery catheter enabling continuous measurement of cardiac index (Baxter Swan Ganz IntelliCath, Baxter Healthcare, Irvine, CA) was inserted via a central vein. All line insertions were carried out under local anaesthesia, with sedation where required.
Oxygen delivery was measured using the standard formula: oxygen delivery (ml/min/m2) = cardiac index (l/min/m2) × oxygen content of blood (haemoglobin (g/l) × oxygen saturation × 1.34).
Optimisation of oxygen delivery consisted of two phases: fluid optimisation and inotrope optimisation.
Fluid optimisation
All patients received 1 litre of
Hartmann's solution during line insertion. Human albumin solution
4.5% was then infused until a pulmonary artery occlusion pressure of
12 mm Hg was achieved. If haemoglobin concentration was <110 g/l, red blood cells were transfused instead of the albumin solution. If
oxygen saturation was <94%, supplemental oxygen was
provided.
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Inotrope was commenced at a rate
(ml/hour) calculated from a chart according to the patient's weight
and equated to 0.025 µg/kg/min for adrenaline and 0.125 µg/kg/min for dopexamine. Blinding was achieved by administering the inotrope in
a syringe that had been preprepared in the pharmacy. The infusion was
increased by single multiples of the initial rate until the target
oxygen delivery of >600 ml/min/m2 was achieved or the
onset of side effects was noted (increase in heart rate >30% above
baseline or development of chest pain or a new dysrhythmia). If side
effects were noted, the infusion was decreased. All patients were
started on the study inotrope even if the target oxygen delivery had
been achieved after the fluid phase. The infusion was maintained at the
preoperative rate throughout the remainder of the perioperative period.
Intraoperative care was the responsibility of the anaesthetist,
including provision of additional inotropes if thought necessary.
After surgery, patients were returned to intensive care or high
dependency care. The study inotrope was continued at the preoperative rate for 12 to 24 hours postoperatively. The time of discontinuation of
the inotrope was at the discretion of the intensive care team. On a
routine clinical basis the intensive care and surgical teams determined
all other aspects of care including removal of the pulmonary artery
catheter and timing of discharge from intensive care or high dependency care.
Statistical analysis
We required 46 patients in each group, calculated by matching
reductions in mortality from 25% to 5% from the most similar previous
study, to give a study power of 80%.4 The randomisaton
sequence was generated from a Unix computer program. Allocation was
concealed until trial entry by sealed opaque envelope. Randomisation
was stratified into three subgroups: vascular surgery, surgery for
upper gastrointestinal malignancy, and others. This was to ensure even
distribution of these surgical subgroups across the three groups.
Outcome measures
Primary outcome measures were hospital mortality and morbidity
(number of patients developing one or more of a predefined range of
complications). Secondary measures were length of stay in hospital, use
of intensive care or high dependency care, and haemodynamic
measurements (for adrenaline and dopexamine groups). We analysed
hospital mortality by Kaplan-Meier survival estimates, using the
log-rank test for comparison, and by Fisher's exact test. The
differences in proportions of patients with morbidity were calculated.
Standardised ratios were constructed for morbidity and mortality,
comparing actual incidences to those predicted by the POSSUM score
(physiological and operative severity score for the enumeration of
mortality and morbidity).9 Where appropriate, we
calculated 95% confidence intervals.10 Kaplan-Meier
estimates were constructed for hospital length of stay, treating
non-survivors as censored values, and analysed using the log-rank
test.
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Results |
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Overall, 203 patients were identified and approached over a 16 month period; 65 did not enter the study either because of refusal to consent (40), lack of intensive care or high dependency care beds (16), or other reasons (9) (see website).
Table 1 shows the entry criteria for each group.
Table 2 outlines the variables for haemodynamics and oxygen transport obtained at the key stages of preoperative optimisation. One patient in the adrenaline group and three patients in the dopexamine group failed to reach target oxygen delivery owing to the development of side effects.
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According to the POSSUM scores, there were no differences in operative risk. One patient in the adrenaline group returned from theatre to the ward because of an inoperable lesion. One patient in the dopexamine group pulled out his pulmonary artery catheter immediately before surgery because he was confused. All other patients completed the minimum requirement of 12 hours' infusion of study inotrope postoperatively.
Overall, preoperative optimisation of oxygen delivery significantly reduced hospital mortality; 3/92 (3%) patients who were preoptimised died compared with 8/46 controls (17%, P=0.007; table 3). Compared with both the control and the adrenaline group, there was a significant reduction in morbidity in the dopexamine group (table 4). Optimisation with adrenaline alone did not significantly reduce morbidity compared with control. Compared with the value predicted from the POSSUM score, dopexamine is associated with a significantly reduced incidence of morbidity.
The length of hospital stay for the dopexamine group was significantly
reduced when individually compared with both the adrenaline group
(P=0.02) and the control group (P=0.009). There was no overall increase
in intensive care resources or high dependency care resources in the
treated groups compared with control, although only 32/46 (70%) of
control patients were admitted to these areas at any time during their
hospital stay.
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Discussion |
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Our study is a pragmatic one of the effect of a package of preoperative interventions on the outcome from major elective surgery in a typical UK hospital. The package comprises several components, each of which may have contributed to improvements in outcome.
Surgical risk
The criteria for patient selection were as a result of
reviewing the elective surgical population for intensive care or high
dependency care in our own hospital; outcome of control patients would
seem to justify their use. We were unable to effect true blinding
between patients in the control and treatment groups, but we have no
evidence to suggest that this may have biased our results. The POSSUM
scoring system was specifically developed for, and validated in, a UK
general surgical population and can be used to explain differences in
surgical outcome on the basis of different risk.
9 12 13
The range of surgical procedures and POSSUM scores for surgical risk
would suggest that the three groups were evenly balanced. The hospital
mortality of 17% in the control group seems high, but two late deaths
contributed to this value (fig 1). POSSUM was derived from data
recorded for 6 weeks postoperatively; at that time our control group
mortality was 13%
exactly that predicted by POSSUM. After major
surgery a proportion of patients will still be in hospital at 6 weeks (fig 2) and, because of the serious morbidity delaying discharge, are
likely to have significant mortality.
Sixteen control patients went back to the general ward
after surgery (table 5). The location of postoperative care was the
decision of the clinical team responsible for the patient, and no
patient was denied access to intensive care or high dependency care
owing to lack of beds. The improvements we have shown, however, can
also be observed in study populations consisting exclusively of
patients in intensive care.
3 4
Oxygen delivery as a goal
High risk
surgery is one of the few areas in which reasonable evidence now exists
of the benefits of optimising oxygen delivery. When oxygen delivery
falls below 390 l/min/m2, tissue oxygenation becomes
physiologically inadequate in surgical patients at high
risk.14 This is a reduction of just 30% from the median
baseline measurements for oxygen delivery in our study groups. Because
of blood loss during surgery, reductions in haemoglobin concentration
and cardiac output are common occurrences in patients who are not
monitored, with consequent falls in tissue oxygenation and the
increased likelihood of complications.
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Fluid optimisation
Intraoperative fluid requirements were the same in all
groups. The treatment groups, however, received an average of 1500 ml
of additional fluid preoperatively, on the basis of measurements from
the pulmonary artery catheter. Considerable evidence exists that
provision of optimal fluid improves outcome after
surgery.
3 4 11 15 16
All of these studies, however, used additional "non-routine" monitoring to estimate fluid
requirements; it is therefore implicit that routine, less invasive
monitoring may leave patients relatively depleted of fluid and at
higher risk of adverse outcomes. Because of the low doses of inotropes used in our study, we suggest that fluid optimisation is the major contributor to improved oxygen delivery in our patients.
Choice of inotrope
Both inotropes produced the desired preoperative increase in
oxygen delivery and a similar decrease in mortality. Only dopexamine,
however, reduced morbidity and hospital stay. Although POSSUM scores
were equal, there is a suggestion that the patients who received
dopexamine may have had less pre-existing cardiovascular disease and a higher baseline oxygen delivery. In the
dopexamine group, however, there was a reduction in infective complications. Dopexamine has significant anti-inflammatory properties, reducing the release of toxic mediators in response to an infective challenge.17 This contrasts with the effects of inotropes
with
1 receptor activity such as adrenaline.18 Thus
dopexamine may confer an additional advantage to fluid optimisation by
reducing the effect of infective complications.
Conclusion
The incidence of morbidity in our control group suggests that
there is a substantial population of surgical patients in the United
Kingdom who are likely to benefit from the interventions described.
Only 5% of all planned elective surgical admissions to intensive care
are currently admitted preoperatively.2 Formal cost
benefit analysis was not performed in this study, but values for usage
of intensive carebeds or high dependency care beds (table 5) and length
of stay in hospital suggest there may be overall savings in hospital
costs when preoptimising patients for major elective surgery. An
initial investment in resources may lead to economic gains for
hospitals as well as a better outcome for surgical patients.
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Acknowledgments |
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We thank the patients, their surgeons, and the medical and nursing staff of the intensive care, anaesthetic, and operating theatre departments for their patience and cooperation. Andy Vale, senior medical statistician at the University of Leeds, gave advice on statistical analysis.
Contributors: JW and IW were responsible for the original concept of the study. JW analysed the data; he will act as guarantor for the paper. All authors were involved with the design and execution of the study and with writing the paper.
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Footnotes |
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Funding: Grant of £45 000 from the National Hospital Lotteries Fund.
Competing interests: York District Hospital's intensive care unit research fund was reimbursed by Ipsen, the manufacturer of dopexamine, after RJTW and IW spoke at meetings arranged by Ipsen.
website extra: Details of the flow of patients through the trial appear on the BMJ's website www.bmj.com
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