Renal Function During Cardiopulmonary Bypass

Percutaneous Renal Access: Surgical Factors Involved in the Acute Reduction of Renal Function

INTRODUCTION AND OBJECTIVE

Studies in patients and experimental animals have shown that percutaneous nephrolithotomy (PCNL) can acutely impair glomerular filtration and renal perfusion, but the factors contributing to this decline in renal function are unknown. The present study assessed the contribution of needle puncture of the kidney vs dilation of the needle tract to the acute decline in renal hemodynamic and tubular transport function associated with PCNL surgery.

MATERIALS AND METHODS

Acute experiments were performed in three groups of anesthetized adult farm pigs: sham-percutaneous access (PERC), that is, no surgical procedure (n = 7); a single-needle stick to access the renal collecting system (n = 8); expansion of the single-needle access tract with a 30F NephroMax balloon dilator and insertion of a nephrostomy sheath (n = 10). The glomerular filtration rate (GFR), effective renal plasma flow (ERPF), and renal extraction of para-amino hippurate (EPAH, estimates tubular organic anion transporter [OAT] activity) were assessed before and 1 to 4.5 hours after sham-PERC or PERC surgical procedures.

RESULTS

Overall, GFR responses were similar in all three groups. Sham-treated PERC pigs showed no significant change in ERPF over the experimental observation period, whereas a single-needle stick to access the renal collecting system resulted in renal vasoconstriction (∼30% reduction in ERPF, p < 0.05). Dilation of the single-needle access tract to create the nephrostomy did not lead to a further decline in ERPF. PERC surgical procedure-mediated renal vasoconstriction was most evident at the 1-hour posttreatment time point. A reduction in EPAH was only observed in pig kidneys with a nephrostomy.

CONCLUSIONS

Needle puncture of the kidney for percutaneous access to the renal collecting system is the major driving force for the renal vasoconstriction observed after PCNL surgery, whereas creation of the nephrostomy appears to be largely responsible for decreasing tubular OAT activity.

Increasing mean arterial pressure during cardiac surgery does not reduce the rate of postoperative acute kidney injury

Introduction:

We hypothesized that the optimization of renal haemodynamics by maintaining a high level of mean arterial blood pressure (MAP) during cardiopulmonary bypass (CPB) could reduce the rate of acute kidney injury (AKI) in high-risk patients.

Methods:

In this randomized, controlled study, we enrolled 300 patients scheduled for elective cardiac surgery under cardiopulmonary bypass. All had known risk factors of AKI: serum creatinine clearance between 30 and 60 ml/min for 1.73m2 or two factors among the following: age >60 years, diabetes mellitus, diffuse atherosclerosis. After a standardized fluid loading, the MAP was maintained between 75-85 mmHg during CPB with norepinephrine (High Pressure, n=147) versus 50-60 mmHg in the Control (n=145). AKI was defined by a 30% increased of serum creatinine (sCr). We further tested others definitions for AKI: RIFLE classification, 50% rise of sCr and the need for haemodialysis.

Results:

The pressure endpoints were achieved in both the High Pressure (79 ± 6 mmHg) and the Control groups (60 ± 6 mmHg; p<0.001). The rate of AKI did not differ by group (17% vs. 17%; p=1), whatever the criteria used for AKI. The length of stay in hospital (9.5 days [7.9-11.2] vs. 8.2 [7.1-9.4]) and the rate of death at day 28 (2.1% vs. 3.4%) and at six months (3.4% vs. 4.8%) did not differ between the groups.

Conclusion:

Maintaining a high level of MAP (on average) during normothermic CPB does not reduce the risk of postoperative AKI. It does not alter the length of hospital stay or the mortality rate.

Regional oxygenation and systemic inflammatory response during cardiopulmonary bypass: influence of temperature and blood flow variations

OBJECTIVE

To evaluate the role of target temperature (28 degrees or 34 degrees C) in cardiac surgery on regional oxygenation during hypothermia and rewarming and systemic inflammatory response.

DESIGN

Prospective, controlled, and randomized clinical study.

SETTING

University hospital.

PARTICIPANTS

Elderly patients (mean age 70 +/- 2 years) with acquired heart disease with an anticipated bypass time exceeding 120 minutes (n = 30).

INTERVENTIONS

The patients were cooled to either 28 degrees C (n = 15) or 34 degrees C (n = 15). At hypothermia, bypass blood flow was reduced twice from full flow (2.4 L/min/m(2) body surface area [BSA]) to 2.0 L/min/m(2).

MEASUREMENTS AND MAIN RESULTS

Hepatic and jugular venous oxygen tension and saturation were higher at 28 degrees C than at 34 degrees C. In comparison with the preoperative values, at 28 degrees C hepatic venous values were higher; whereas at 34 degrees C, they were lower. The reduction of pump blood flow during hypothermia, from 2.4 to 2.0 L/min/m(2)was accompanied by reductions of central, jugular, and hepatic oxygenation at both target temperatures. During rewarming, central and regional venous oxygenation decreased irrespective of the preceding temperature. The decrease was most pronounced in hepatic venous blood, with the lowest individual values <10%. Serum concentrations of C3a and IL-6 increased during hypothermia and increased further during rewarming irrespective of the preceding temperature.

CONCLUSION

During cardiopulmonary bypass, hypothermia at 28 degrees C increases regional and central venous oxygenation better than at 34 degrees C. In contrast, venous oxygenation decreases during rewarming irrespective of the preceding temperature. No significant difference in the systemic inflammatory response associated with target temperature was detected.

Impact of cardiopulmonary bypass management on postcardiac surgery renal function

OBJECTIVE

Cardiac surgery on cardiopulmonary bypass (CPB) is associated with postoperative renal dysfunction and up to 4% of patients with normal preoperative renal function develop acute renal failure (ARF) requiring dialysis. According to recent investigations, CPB management is not evidence-based and, thus, current clinical CPB practice may favor renal dysfunction. The purpose of our study was to investigate if postcardiac surgery renal dysfunction is influenced by CPB management.

METHODS

We selected three groups of patients with normal preoperative renal function who had been subjected to cardiac surgical procedures on CPB: 44 patients with postoperative ARF requiring hemofiltration/dialysis (ARF group), 51 patients with postoperative renal dysfunction not requiring hemofiltration/dialysis (serum creatinine increase > 0.5 mg/dl within 48 h postsurgery: CREA group), and 48 patients with normal postoperative renal function (Control group). The patients' on-line CPB records were analyzed for CPB duration, CPB perfusion pressure, CPB flow, and periods on CPB at a perfusion pressure <60 mmHg. On-CPB diuretic and vasoconstrictor medication was recorded.

RESULTS

Patient demographics were similar for the three groups. In the ARF group, CPB duration was longer (166 +/- 77 [standard deviation, SD] min) compared to CREA (115 +/- 41 min; p < 0.001) and to Control groups (107 +/- 40 min; p < 0.001), and mean CPB flow was lower (2.35 +/- 0.36 l/min/m2) compared to CREA (2.61 +/- 0.35 l/min/m2; p = 0.0015) and to Control groups (2.51 +/- 0.33 l/min/m2; p = 0.09). Mean arterial pressure on CPB (ARF: 61 +/- 10; CREA: 60 +/- 7;

CONTROL

63 +/- 9 mmHg; p = 0.19) as well as furosemide and norepinephrine medication on CPB were similar for the groups. Compared to Control (46 +/- 26 min), CPB duration at arterial pressures <60 mmHg was longer in ARF (78 +/- 60 min; p = 0.034) and in CREA (62 +/- 36 min;p = 0.048).

CONCLUSIONS

Our data suggest that current clinical CPB management impacts postoperative renal function. We found that patients with normal preoperative renal function who developed postoperative ARF had longer CPB duration, lower CPB perfusion flow, and longer periods on CPB at pressures < 60 mmHg compared to patients with no post CPB ARF. However, our data do not allow us to separate these CPB-related factors from the potential influence of perioperative low cardiac output syndrome as a cause for postoperative ARF. Thus, future clinical studies are required to elucidate CPB-induced ARF and to optimize CPB management for ARF prevention.

Acute renal failure in hospitalized patients: part II

BACKGROUND

Acute renal failure (ARF) is a common condition in hospitalized patients. Research has been unable to identify the optimal target for therapeutic intervention; hence, effective prevention of and/or treatment for ARF remain elusive.

OBJECTIVE

To examine the usefulness of current and potential pharmacologic treatments in seriously ill, hospitalized patients.

DATA SOURCES

A MEDLINE search (1996-June 2002) was conducted using the search terms kidney (drug effects) and acute kidney failure (drug therapy). Bibliographies of selected articles were also examined to include all relevant investigations.

STUDY SELECTION AND DATA EXTRACTION

Review articles, meta-analyses, and clinical trials describing prevention of and treatment for hospital-acquired ARF were identified. Results from prospective, controlled trials were given priority when available.

CONCLUSIONS

Appropriate management of ARF includes prospective identification of at-risk patients, fluid administration, and optimal hemodynamic support. Drug treatments, including low-dose dopamine and diuretics, have demonstrated extremely limited benefits and have not been shown to improve patient outcome. Experimental agents influence cellular processes of renal dysfunction and recovery; unfortunately, relatively few drugs show promise for the future.

Insulin (GIK) improves central mixed and hepatic venous oxygenation in clinical cardiac surgery

OBJECTIVE

Insulin is a vasodilating agent and it was hypothesized that insulin (GIK) could improve systemic and regional oxygenation in cardiac surgery with cardiopulmonary bypass (CPB). Two questions were addressed: 1) Does insulin improve central mixed and hepatic venous oxygenation during CPB? and 2) Does this treatment reduce systemic levels of the proinflammatory mediators C3a and IL-6?

DESIGN

Prospective, randomized, controlled study at a university hospital. Thirty patients were included and 16 of these received an infusion of insulin, glucose and potassium (GIK) using an euglycemic clamp technique. The insulin infusion was started during hypothermia, 15 min before rewarming. Blood gases and hemodynamic parameters were measured during hypothermia (before the insulin infusion was started), during rewarming at 35 degrees C, and 30 min after CPB was discontinued. Inflammatory markers were measured: preoperatively, during hypothermia and 2 h after CPB.

RESULTS

GIK was associated with reduced systemic vascular resistance (p = 0.02 vs the control group), higher bypass pump flow (p = 0.001). higher central mixed oxygen saturation (p = 0.036) and oxygen tension (p = 0.001) and higher hepatic venous oxygen saturation (p = 0.04) and oxygen tension (p = 0.006). C3a and IL-6 increased during surgery in both groups but there were no differences between the groups.

CONCLUSION

1) GIK infusion improved central mixed and hepatic venous oxygenation in patients undergoing heart surgery. 2) During the conditions of this study, this had no effect on the proinflammatory mediators C3a and IL-6.

New pharmacologic options for renal preservation

The understanding of the cause and pathophysiology of renal failure has guided the rational development of pharmacologic renoprotective strategies. Although traditionally anesthesiologists have focused on renal hemodynamic derangements, newer information suggests that cellular interactions amplify and perpetuate the insult. Consequently, the potential renoprotective armamentarium not only encompasses the more traditional vasoactive agents but also therapeutic approaches that may modify the cellular response to injury. Although few of these agents have reached the clinical arena, preliminary work suggests that this new approach to renal injury and protection may be promising.

Renal hypoxanthine balance in cardiac surgery: effects of felodipine

OBJECTIVE

To test the hypothesis that felodipine, a renal vasodilator, can prevent a release of hypoxanthine during rewarming after moderate hypothermic cardiopulmonary bypass and that this is related to improved renal oxygen supply.

DESIGN

A prospective, randomized, and controlled study.

SETTING

Operating room in the cardiothoracic surgery department of a university hospital.

PARTICIPANTS

Twenty-two patients submitted to elective first-time coronary bypass surgery.

INTERVENTIONS

A catheter was placed in the left renal vein for thermodilution renal blood flow (RBF) measurement and blood sampling. In 11 patients, felodipine was infused during the hypothermic period of cardiopulmonary bypass.

MEASUREMENTS AND MAIN RESULTS

Renal uptake (renal arteriovenous concentration difference x RBF) of hypoxanthine was maintained during rewarming in felodipine-treated patients but not in control patients (55+/-28 v. -39+/-1 nmol/min, p<0.05). Oxygen consumption was higher after felodipine infusion despite unchanged total RBF. A positive correlation between renal oxygen consumption and hypoxanthine uptake and release (r = 0.74, p<0.01) was observed.

CONCLUSIONS

Felodipine maintained renal uptake of hypoxanthine during rewarming after hypothermic cardiopulmonary bypass. This maintenance is the effect of improved renal oxygen supply secondary to improved nutritive blood flow at the expense of nonnutritive renal blood flow.

Mechanisms of the systemic inflammatory response

The purpose of inflammation is to combat various agents that may injure the tissues. Conditions such as CPB can often cause systemic inflammation and dysfunction of major organs. Pulmonary, renal, myocardial and intestinal function may suffer various degrees of impairment during and after cardiac surgery. Although changes in major organs usually remain clinically insignificant, severe organ failure is not uncommon. The process of systemic inflammation proceeds through activation of serum proteins, activation of leucocytes and endothelial cells, secretion of cytokines, leucocyte-endothelial cell interaction, leucocyte extravasation and tissue damage. Several anti-inflammatory strategies have already been used, some of which have given promising results pertaining to further reduction in the rate of the inflammation-related complications in cardiac surgical patients.

Chronic angiotensin converting inhibition does not influence renal hemodynamic and function during cardiac surgery

PURPOSE

Treatment with angiotensin-converting enzyme (ACE) inhibitors affects the autoregulation of renal blood flow and glomerular filtration and provides renal protective effects. The purpose of this case-control study was to investigate the effects of chronic ACE inhibition on perioperative renal hemodynamics and function.

METHOD

We prospectively studied renal function in two groups of patients, chronically treated or not, with ACE inhibitors (ACEI and control; n = 16, in each group) who underwent elective cardiac surgery under hypothermic cardiopulmonary bypass. Glomerular filtration rate, effective renal plasma flow, osmolar clearance and fractional excretion of sodium and potassium were determined before, during and after CPB. Additional measurements included plasma atrial natriuretic factor (ANF) as well as plasma and urinary cyclic GMP (cGMP), thromboxane B2 (TxB2) and 6-keto-PGF1.

RESULTS

Renal functional and hemodynamic variables did not differ between the two groups, at any period. Cardiopulmonary bypass induced increases in urinary flow, osmolar clearance and fractional excretion of sodium and potassium in both groups. Plasma and urinary ratio of 6-keto-PGF to TxB2 increased markedly and reflected a predominant systemic and renal release of vasodilatory prostaglandins. Intraoperatively, ANF was higher in ACEIs than in control patients.

CONCLUSIONS

Long term treatment with ACE inhibitors does not influence the perioperative changes in renal hemodynamics and function. During cardiopulmonary bypass, a transient impairment in solute reabsorption is associated with renal release of vasodilatory mediators (nitric oxide and prostacyclin).