The Effects of On-Pump and Off-Pump Coronary Artery Bypass Surgery on Metabolic Profiles in the Early Postoperative Period

Morning or Afternoon Scheduling for Elective Coronary Artery Bypass Surgery: Influence of Longer Fasting Periods from Metabolic and Hemodynamic Perspectives

BACKGROUND

Prolonged preoperative fasting may worsen postoperative outcomes. Cardiac surgery has higher perioperative risk, and longer fasting periods may be not well-tolerated. We analysed the postoperative metabolic and hemodynamic variables in patients undergoing elective coronary artery bypass grafting (CABG) according to their morning or afternoon schedule.

METHODS

Single-centre retrospective study at University teaching hospital (1-year data collection from electronic medical records). Using a mixed-effects linear regression model adjusted for several covariates, we compared metabolic (lactatemia, pH, and base deficit [BD]) and haemodynamic values (patients on vasoactive support, and vasoactive inotropic score [VIS]) at 7 prespecified time-points (admission to intensive care, and 1st, 3rd, 6th, 12th, 18th, and 24th postoperative hours).

RESULTS

339 patients (n = 176 morning, n = 163 afternoon) were included. Arterial lactatemia and BD were similar (overall P = 0.11 and P = 0.84, respectively), while pH was significantly lower in the morning group (overall P < 0.05; mean difference -0.01). Postoperative urine output, fluid balance, mean arterial pressure, and central venous pressure were similar (P = 0.59, P = 0.96, P = 0.58 and P = 0.53, respectively). A subgroup analysis of patients with diabetes (n = 54 morning, n = 45 afternoon) confirmed the same findings. The VIS values and the proportion of patients on vasoactive support was higher in the morning cases at the 18th (P = 0.002 and p=0.04, respectively) and 24th postoperative hours (P = 0.003 and P = 0.04, respectively). Mean intensive care length of stay was 1.94 ± 1.36 days versus 2.48 ± 2.72 days for the afternoon and morning cases, respectively (P = 0.02).

CONCLUSIONS

Patients undergoing elective CABG showed similar or better metabolic and hemodynamic profiles when scheduled for afternoon surgery.

The Effects of On-Pump and Off-Pump Coronary Artery Bypass Surgery on Respiratory Function in the Early Postoperative Period

BACKGROUND:

Respiratory complications are common after cardiac surgery and the use of extracorporeal circulation is one of the main causes of lung injury. We hypothesized a better postoperative respiratory function in off-pump coronary artery bypass grafting (OPCABG) as compared with "on-pump coronary artery bypass grafting" (ONCABG).

METHODS:

This is a retrospective, single-center study at a cardiothoracic intensive care unit (ICU) in a tertiary university hospital. Consecutive data on 339 patients undergoing elective CABG (n = 215 ONCABG, n = 124 OPCABG) were collected for 1 year from the ICU electronic medical records. We compared respiratory variables (Pao2, Pao2/Fio2 ratio, Sao2, and Paco2) at 7 predefined time points (ICU admission, postoperative hours 1, 3, 6, 12, 18, and 24). We also evaluated time to extubation, rates of reintubation, and use of noninvasive ventilation (NIV). We used mixed-effects linear regression models (with time as random effect for clustering of repeated measures) adjusted for a predetermined set of covariates.

RESULTS:

The values of Pao2 and Pao2/Fio2 were significantly higher in the OPCABG group only at ICU admission (mean differences: 9.7 mm Hg, 95% confidence interval [CI] 3.1-16.2; and 27, 95% CI 6.1-47.7, respectively). The OPCABG group showed higher Paco2, overall ( P = .02) and at ICU admission (mean difference 1.8 mm Hg, 95% CI: 0.6-3), although mean values were always within normal range in both groups. No differences were seen in Sao2 values, time to extubation, rate of reintubation rate, and use of postoperative NIV. Extubation rate was higher in OPCABG only at postoperative hour 12 (92% vs ONCABG 82%, P = .02).

CONCLUSION:

The OPCABG showed only marginal improvements of unlikely clinical meaning in oxygenation as compared to ONCABG in elective low-risk patients.

Postoperative Compensatory Ammonium Excretion Subsequent to Systemic Acidosis in Cardiac Patients

Background

Postoperative acid-base imbalances, usually acidosis, frequently occur after cardiac surgery. In most cases, the human body, not suffering from any severe preexisting illnesses regarding lung, liver, and kidney, is capable of transient compensation and final correction. The aim of this study was to correlate the appearance of postoperatively occurring acidosis with renal ammonium excretion.

Materials and Methods

Between 07/2014 and 10/2014, a total of 25 consecutive patients scheduled for elective isolated coronary artery bypass grafting with cardiopulmonary bypass were enrolled in this prospective observational study. During the operative procedure and the first two postoperative days, blood gas analyses were carried out and urine samples collected. Urine samples were analyzed for the absolute amount of ammonium.

Results

Of all patients, thirteen patients developed acidosis as an initial disturbance in the postoperative period: five of respiratory and eight of metabolic origin. Four patients with respiratory acidosis but none of those with metabolic acidosis subsequently developed a base excess > +2 mEq/L.

Conclusion

Ammonium excretion correlated with the increase in base excess. The acidosis origin seems to have a large influence on renal compensation in terms of ammonium excretion and the possibility of an overcorrection.