Intraoperative correction of low cardiac output to normal values improves outcome in patients with elective abdominal surgery

Introduction

Clinically unrecognised hypovolemia [1], low stroke volume and/or cardiac output [1,2] during the intraoperative period represent risk factors for unfavourable postoperative outcome. Several prospective randomized clinical studies have shown a decreased postoperative morbidity and mortality linked to perioperative cardiac output or DO₂ stimulation to so-called supranormal values (CI > 4.5 l/min/m² or DO₂I > 600 ml/min/m²) [3]. The objective of our study was to find out whether intraoperative maintenance of at least normal values of cardiac output (i.e. 5-7 l/min) would influence postoperative outcome in a group of elective abdominal surgery patients. The reason to choose normal range of cardiac output as a therapeutic goal was the observation, that average values of intraoperatively measured cardiac output are frequently found in a range lower than normal values in a group of patients with unfavourable postoperative outcome [2].

Methods

Forty-nine consecutive adult patients, undergoing extensive elective abdominal surgery with expected duration of more than 90 min, were included in this prospective observational study (37 male and 12 female; average age: 61.6 ± 11 years; 84% - abdominal surgery for tumour, 14% - bowel resection for inflammatory disease, 2% - abdominal aortic surgery; average length of surgery: 172 ± 64 min). They were divided into two groups: the first group of consecutive 24 patients managed with oesophageal doppler and the second consecutive group of 25 patients managed according to usual intraoperative monitoring. In the first group of patients (doppler group [D]; n = 24, male: 67%, female: 33%; average age: 61.4 ± 13 years; 79% - abdominal surgery for tumour) intraoperative hemodynamic management was based on the continual CO monitoring using oesophageal doppler (HEMOSONIC- 100, Arrow International, Inc.). Doppler probe was inserted on an average 15 min after induction of general anesthesia. Whenever during surgery there was a drop in cardiac output below 5 l/min, usual diagnostic and therapeutic intervention were carried out to reach its normal range 5-7 l/min. Cardiac output values, for data processing, obtained from oesophageal dopplerometry, were collected in 30 min interval (Fig. 1). Intraoperative hemodynamic management in the second group of patients (non-doppler group [ND]; n = 25, male: 84%, female: 16%; average age: 61.8 ± 9 years; 84% - abdominal surgery for tumour) was based on the monitoring of commonly used parameters: ECG, non-invasive blood pressure or invasive pressures (arterial blood pressure, central venous pressure), ETCO₂, SpO₂. Operating theatre staff, both anesthesiologic and surgical personnel, were blinded to patients' study inclusion. The postoperative management of both patient's groups was carried out in the Department of Surgery. Likewise the operating theatre staff, staff of the surgical department was also blinded to patients' study inclusion. In both D and ND group of patients we analysed and compared these data: ASA score, duration of surgery, blood units administered and fluid management intraoperatively, hemodynamic or respiratory instability occurrence during surgery, need for postoperative artificial ventilation longer than 24 hours, length of ICU stay, occurrence of postoperative complications (cardiovascular, respiratory, renal, gastrointestinal, coagulation, CNS and wound complication) total length of hospital stay and mortality. For statistic data processing following tests were used: Wilcox, Mann-Whitney and ?²-test. Statistical significance was determined as P < 0.05. Values are shown as mean ± SE.

Figure 1

Average CO values during surgery in doppler group. ?, Initial CO value (15 min after general anesthesis induction). ^*P < 0.05, compared with initial CO value

Results

Significantly lower frequency of postoperative complications (number of patients with complications: D: 5/24 vs ND: 14/25; total frequency of complications: D: 8/186 vs ND: 31/175; average frequency of complications per patient: D: 0.33 ± 0.63 vs ND: 1.24 ± l.69; the greatest difference in occurrence of complications was found for gastrointestinal and wound complications), shorter ICU stay (D: 3.9 ± 1.8 days vs ND: 5.8 ± 3.2 days) and total hospital stay (D 14.8 ± 7.3 days vs ND: 19.4 ± 8.1 days) were found in the group of patients with intraoperative cardiac output maintained in normal range (46% of cases needed beyond fluid administration also inotropic support with dobutamin and 25% of cases needed administration of isosorbid-dinitrate). In the rest of observed parameters there was found no significant difference (Table 1).

Table 1 Average values of parameters that did not reach statistical significance

Conclusion

Intraoperative correction of low cardiac output to normal range is linked to improvement of postoperative outcome in elective abdominal surgery patients. Randomly collected data with high comparability between both groups of patients (namely age, ASA score, duration of surgery, intraoperative blood units administered and fluid management, frequency of intraoperative complications), allow us to state that clinically unrecognised low cardiac output or drop of cardiac output during intraoperative period participates, in a crucial way, in postoperative unfavourable development.