Intraoperative Hemodynamic Predictors of Mortality, Stroke, and Myocardial Infarction After Coronary Artery Bypass Surgery

Treating pulmonary hypertension post cardiopulmonary bypass in pigs: milrinone vs. sildenafil analog

Procedures using cardiopulmonary bypass (CPB) and aortic cross-clamping are associated with a variable degree of ischemia/reperfusion of the lungs, leading to acute pulmonary hypertension (PHT). The purpose of this study was to compare the effects of the sildenafil analog (UK343-664), a phosphodiesterase type V(PDEV) inhibitor, with milrinone, a PDE type III inhibitor, in a porcine model of acute PHT following CPB. After the pigs were anesthetized, pressure-tipped catheters were placed in the right ventricle and carotid and pulmonary arteries. Cardiac output was measured with an ultrasound probe on the ascending aorta. After heparinization and placement of aortic and right atrial cannulae, non-pulsatile CPB was instituted and cardioplegia administered following aortic cross-clamping. After 30 minutes, the clamp was removed and the animals re-warmed and separated from CPB in sinus rhythm. The animals were randomized to 3 groups, and 16 animals were studied to completion: milrinone (n=5) 50 μg/kg; sildenafil-analog (n=5) 500 μg/kg; and normal saline (NS) (n=6). Hemodynamic data were collected at baseline pre-CPB and, following termination of CPB, at baseline, 5, 10 and 30 minutes after administration of the drug. Pulmonary hypertension was present in all groups following CPB. After administration of the drugs, mean pulmonary artery pressure decreased in all 3 groups; however, only in the sildenafil-analog group did pulmonary vascular resistance(PVR) decrease by 35%, from 820 to 433 dynes · cm · sec-5at 5 minutes (p<0.05), and continued to be decreased at 10 minutes by 26% (P<0.05). Pulmonary selectivity was demonstrated with sildenafil-analog, because there were no similar changes in systemic vascular resistance(SVR) and no significant changes in systemic hemodynamics. Sildenafil-analog, a PDEV inhibitor, shows a promising role for managing the PVR increases that occur following CPB.

Does the Surgical Apgar Score measure intraoperative performance?

OBJECTIVE

To evaluate whether Surgical Apgar Scores measure the relationship between intraoperative care and surgical outcomes.

SUMMARY BACKGROUND DATA

With preoperative risk-adjustment now well-developed, the role of intraoperative performance in surgical outcomes may be considered. We previously derived and validated a 10-point Surgical Apgar Score--based on intraoperative blood loss, heart rate, and blood pressure--that effectively predicts major postoperative complications within 30 days of general and vascular surgery. This study evaluates whether the predictive value of this score comes solely from patients' preoperative risk or also measures care in the operating room.

METHODS

Among a systematic sample of 4119 general and vascular surgery patients at a major academic hospital, we constructed a detailed risk-prediction model including 27 patient-comorbidity and procedure-complexity variables, and computed patients' propensity to suffer a major postoperative complication. We evaluated the prognostic value of patients' Surgical Apgar Scores before and after adjustment for this preoperative risk.

RESULTS

After risk-adjustment, the Surgical Apgar Score remained strongly correlated with postoperative outcomes (P < 0.0001). Odds of major complications among average-scoring patients (scores 7-8) were equivalent to preoperative predictions (likelihood ratio (LR) 1.05, 95% CI 0.78-1.41), significantly decreased for those who achieved the best scores of 9-10 (LR 0.52, 95% CI 0.35-0.78), and were significantly poorer for those with low scores--LRs 1.60 (1.12-2.28) for scores 5-6, and 2.80 (1.50-5.21) for scores 0-4.

CONCLUSIONS

Even after accounting for fixed preoperative risk--due to patients' acute condition, comorbidities and/or operative complexity--the Surgical Apgar Score appears to detect differences in intraoperative management that reduce odds of major complications by half or increase them by nearly 3-fold.

Cardiac surgery patients present considerable variation in pre-operative hemodynamic variables

BACKGROUND

It is essential to control hemodynamics in cardiac surgery. Patients are often monitored extensively in order to optimize hemodynamic performance. However, pre-operative values are normally unknown. Furthermore, hemodynamic goals may seem arbitrary and the lack of an evidence-based consensus may lead to both under- and over-treatment. The aim of this study was to evaluate the variables most commonly used for hemodynamic guidance in the post-operative period.

METHODS

Ten patients scheduled for elective cardiac surgery were followed with invasive hemodynamic monitoring the night before surgery. All data were recorded automatically and electronically.

RESULTS

We found considerable inter-patient differences and intra-patient variation. The greatest intra-patient variation was found in the cardiac index (CI), ranging from 1.9 to 5.3 l/min/m(2). Four patients had periodic CI <2.4 l/min/m(2). Eight patients showed SpO2 values < or =92, four of them in more than 15% of the observations. Six patients had an SvO2 <70% in more than 40% of the observations and two an SvO2 < 64% in more than 20% of the observations.

CONCLUSIONS

This study is unique because hemodynamic reference data in cardiac surgery patients have not been published previously. The intra-patient variations were unexpectedly high in most hemodynamic variables and demonstrate the difficulties of using hemodynamic parameters as a guidance for treatment and indicate that goal-oriented therapy using currently accepted values may result in over-treatment in some patients.

Xenon or propofol anaesthesia for patients at cardiovascular risk in non-cardiac surgery

BACKGROUND

The results of two European multi-centre trials on xenon anaesthesia led to the hypothesis that a xenon-based anaesthetic would keep left ventricular (LV) and circulatory function more stable than a propofol-based anaesthetic, in patients with coronary artery disease (CAD).

METHODS

In a prospective, randomized design, 40 patients of ASA classes III and IV with known CAD were anaesthetized for elective non-cardiac surgery with either xenon (n=20) or propofol (n=20), each combined with remifentanil. Target criteria were intraoperative LV function as evaluated by transoesophageal echocardiography (TOE: Tei index, circumferential fibre shortening), arterial pressure, and heart rate (HR).

RESULTS

Mean arterial pressure was decreased with propofol but was stable at pre-anaesthetic level with xenon (P<0.02) and HR was lower with xenon (P<0.01). The Tei index (also known as myocardial performance index) improved from 0.53 (0.14) to 0.45 (0.10) after 1 h with xenon and changed from 0.50 (0.14) to 0.55 (0.20) with propofol anaesthesia [means (SD); P=0.01 between the groups]. Deviation of circumferential fibre shortening from expected value after 1 h was -2 (14)% with xenon and -14 (18)% with propofol [means (SD); P=0.03]. There were no perioperative signs of acute myocardial ischaemia (TOE, ECG, and troponin T release).

CONCLUSIONS

Xenon anaesthesia provided a higher arterial pressure level than propofol, with no signs of cardiovascular compromise, in patients with CAD. Echocardiographic indices showed better LV function with xenon.

Anesthetic management of children with pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is associated with significant perioperative risk for major complications, including pulmonary hypertensive crisis and cardiac arrest. Several mechanisms of hemodynamic deterioration, including acute increases in pulmonary vascular resistance (PVR), alterations of ventricular contractility and function and coronary hypoperfusion can contribute to morbidity. Anesthetic drugs exert a variety of effects on PVR, some of which are beneficial and some undesirable. The goals of balanced and cautious anesthetic management are to provide adequate anesthesia and analgesia for the surgical procedure while minimizing increases in PVR and depression of myocardial function. The development of specific pulmonary vasodilators has led to significant advances in medical therapy of PAH that can be incorporated in anesthetic management. It is important that anesthesiologists caring for children with PAH be aware of the increased risk, understand the pathophysiology of PAH, form an appropriate anesthetic management plan and be prepared to treat a pulmonary hypertensive crisis.

The Effects of Systemic Phenylephrine and Epinephrine on Pedicle Artery and Microvascular Perfusion in a Pig Model of Myoadipocutaneous Rotational Flaps

BACKGROUND

Anesthesiologists and reconstructive surgeons have differing views regarding the control of rotational flap perfusion. Anesthesiologists view the entire body as having flow that is dependent on systemic perfusion pressure, whereas plastic surgeons conjure that systemic administration of vasoactive agents causes vasoconstriction of the pedicle artery and the microvasculature. The aim of this study was to investigate the effects of systemically administered phenylephrine and epinephrine on rotational myocutaneous flap perfusion.

METHODS

After institutional animal care and use committee approval, seven vertical rectus abdominal myocutaneous (VRAM) flaps were created in six pigs. Under 1.0 minimum alveolar concentration isoflurane anesthesia, pedicle artery blood flow (transit time flow probe) and microvascular perfusion (laser Doppler flow probe) were recorded at baseline and after achieving steady hemodynamics with the systemic intravenous administration of phenylephrine (20, 40, and 80 microg/minute) and epinephrine (0.5, 1, and 2 microg/kg/minute).

RESULTS

Under stable physiologic conditions, phenylephrine consistently decreased the pedicle artery blood flow and the microvascular perfusion of porcine VRAM rotational flaps, whereas epinephrine consistently increased both flows across the entire dose range studied. Furthermore, epinephrine-induced increases in cardiac output correlated well with the observed increases in pedicle artery blood flow and microvascular perfusion.

CONCLUSIONS

With the systemic delivery of phenylephrine, rotational myocutaneous flaps react in a manner described by the surgeon. In contrast, the anesthesiologist's model of the hemodynamics is correct for low to moderate doses of epinephrine. Therefore, epinephrine may be the vasoactive agent of choice for treating perioperative hypotension without harming the rotational flap blood flow.

Stimulation induced variability of pulse plethysmography does not discriminate responsiveness to intubation

BACKGROUND

Hypnotic depth but not haemodynamic response to painful stimulation can be measured with various EEG-based anaesthesia monitors. We evaluated the variation of pulse plethysmography amplitude induced by an electrical tetanic stimulus (PPG variation) as a potential measure for analgesia and predictor of haemodynamic responsiveness during general anaesthesia.

METHODS

Ninety-five patients, ASA I or II, were randomly assigned to five groups [Group 1: bispectral index (BIS) (range) 40-50, effect site remifentanil concentration 1 ng ml(-1);Group 2: BIS 40-50, remifentanil 2 ng ml(-1); Group 3: BIS 40-50, remifentanil 4 ng ml(-1); Group 4: BIS 25-35, remifentanil 2 ng ml(-1); Group 5: BIS 55-65, remifentanil 2 ng ml(-1)]. A 60 mA tetanic stimulus was applied for 5 s on the ulnar nerve. From the digitized pulse oximeter wave recorded on a laptop computer, linear and non-linear parameters of PPG variation during the 60 s period after stimulation were computed. The haemodynamic response to subsequent orotracheal intubation was recorded. The PPG variation was compared between groups and between responders and non-responders to intubation (anova). Variables independently predicting the response were determined by logistic regression.

RESULTS

The probability of a response to tracheal intubation was 0.77, 0.47, 0.05, 0.18 and 0.52 in Groups 1-5, respectively (P<0.03). The PPG variability was significantly higher in responders than in non-responders but it did not improve the prediction of the response to tracheal intubation based on BIS level and effect site remifentanil concentration.

CONCLUSION

Tetanic stimulation induced PPG variation does not reflect the analgesic state in a wide clinical range of surgical anaesthesia.

Hypotension caused by extracorporeal circulation: serotonin from pump-activated platelets triggers nitric oxide release

BACKGROUND

Cardiopulmonary bypass and hemodialysis often cause hypotension. We investigated a possible role of pump-induced platelet activation with consequent serotonin release.

METHODS AND RESULTS

In rats, a heparin-coated extracorporeal shunt was placed between the proximal part of a carotid artery and the distal part of a femoral artery. Autoperfusion did not affect platelets or hemodynamics. Pump perfusion, however, immediately elicited strong platelet aggregation, whereas aortic pressure rapidly fell to 60+/-12% (mean+/-SD) of its prepump value, partially recovered, and then progressively decreased to 70+/-12% at 2 hours. Femoral resistance doubled and then decreased to 59+/-11%. The initial changes in aortic pressure and femoral resistance were proportional to the amount of platelet aggregation, were accompanied by a rise (6-fold) in plasma serotonin levels downstream of the pump, but not in the aorta, and could be mimicked by serotonin-infusion into the leg. All hemodynamic changes were prevented or largely reduced by blockade of 5-hydroxytryptamine (5-HT)2 receptors with pizotifen or ritanserin. The hypotension and femoral resistance decrease could also be prevented or abolished by inhibiting the production of nitric oxide (NO), an intermediate in 5-HT(2B) receptor-induced vasodilation. When the extracorporeal blood was pumped into the aortic arch instead of the femoral artery, the hypotensive effect was similar and also NO dependent, but it was absent with venous return.

CONCLUSIONS

Pump perfusion with arterial return of the blood causes hypotension by endothelial NO-release, which in turn is triggered by serotonin from activated platelets.

Rapacuronium and the risk of bronchospasm in pediatric patients

We conducted this study to determine the risk factors for the development of bronchospasm after the administration of rapacuronium and to determine if children with bronchospasm on induction of anesthesia were more likely to have received rapacuronium compared with other muscle relaxants. In a retrospective cohort study, all anesthetic records in which rapacuronium was administered were reviewed to determine which patients developed bronchospasm during induction of anesthesia. Two-hundred-eighty-seven patients were identified, of whom 12 (4.2%; 95% confidence interval [CI], 2.2%--7.2%) developed bronchospasm during induction of anesthesia. Significant risk factors for the development of bronchospasm with administration of rapacuronium included rapid sequence induction (relative risk [RR], 17.9; 95% CI, 2.9--infinity) and prior history of reactive airways disease (RR, 4.6; 95% CI, 1.5--14.3). In a case-control study, all cases of bronchospasm during induction of anesthesia in the 5-mo time period that rapacuronium was available for clinical use were identified. Aside from the 12 cases of bronchospasm with rapacuronium, 11 additional cases of bronchospasm were associated with the use of other muscle relaxants. Four controls were randomly selected for each of the 23 cases of bronchospasm. Children with bronchospasm during induction of anesthesia were several times more likely (odds ratio, 10.1; 95% CI, 3.5--28.8) for having received rapacuronium compared with other muscle relaxants.

IMPLICATIONS

In a retrospective cohort study, significant risk factors for the development of bronchospasm with the administration of rapacuronium on induction of anesthesia included rapid sequence induction and prior history of reactive airways disease. In a case-control study, children with bronchospasm during induction of anesthesia were several times more likely to have received rapacuronium compared with other muscle relaxants.