Effects of positive end-expiratory pressure on renal function

The Complexity of Pulmonary Complications in Acute Kidney Injury

Background: Pulmonary complications often occur in patients with acute kidney injury, and represent an important cause of death.Objective: To analyze the complexity of lung disorders in patients with RIFLE class III acute kidney injury undergoing hemodialysis and the physiopathological mechanisms that cause the various pulmonary complications.Methods: Our study included 74 clinical cases of acute kidney injury of various etiologies (severe sepsis, trauma, post-surgery, toxic, etc.). The respiratory function of these patients was monitored from the clinical and radiological points of view. Deceased patients underwent autopsy.Results: Pulmonary complications occurred in 47.24% of cases. Most pulmonary complications (over 50%) occurred in sepsis-induced acute kidney injury.Regarding the clinical aspects of pulmonary complications, the most frequent were ARDS, atelectasisand bronchopneumopathies, determined by the etiological factors that had caused the acute kidney injury in the first place, and by the acute kidney injury-induced physiological effects.Conclusions: 1. The frequency of pulmonary complications in acute kidney injury is very high and has a negative impact on the evolution and prognosis. 2. The etiology of the pulmonary complications is complex, as these are caused by the agents that induced the acute kidney injury in the first place, most frequently by septic shock. 3. Along with clinical and radiological evidence of pulmonary damage, severe pulmonary histological lesions were found in deceased patients, with a high contribution to the increased mortality rate.

Neonatal non-invasive respiratory support: physiological implications

The introduction of assisted ventilation for neonatal pulmonary insufficiency has resulted in the successful treatment of many previously fatal diseases. During the past three decades, refinement of invasive mechanical ventilation techniques has dramatically improved survival of many high-risk neonates. However, as with many advances in medicine, while mortality has been reduced, morbidity has increased in the surviving high-risk neonate. In this regard, introduction of assisted ventilation has been associated with chronic lung injury, also known as bronchopulmonary dysplasia. This disease, unknown prior to the appearance of mechanical ventilation, has produced a population of patients characterized by ventilator or oxygen dependence with serious accompanying pulmonary and neurodevelopmental morbidity. The purpose of this article is to review non-invasive respiratory support methodologies to address the physiologic mechanisms by which these methods may prevent the pathophysiologic effects of invasive mechanical ventilation.

Mechanical ventilation and acute renal failure

OBJECTIVE

To review the current literature on possible mechanisms by which mechanical ventilation may initiate or aggravate acute renal failure.

DATA SOURCE

A Medline database and references from identified articles were used to perform a literature search relating to mechanical ventilation and acute renal failure.

DATA SYNTHESIS

Acute renal failure may be initiated or aggravated by mechanical ventilation through three different mechanisms. First, strategies such as permissive hypercapnia or permissive hypoxemia may compromise renal blood flow. Second, through effects on cardiac output, mechanical ventilation affects systemic and renal hemodynamics. Third, mechanical ventilation may cause biotrauma-a pulmonary inflammatory reaction that may generate systemic release of inflammatory mediators. The harmful effects of mechanical ventilation may become more significant when a comorbidity is present. In these situations, it is more difficult to maintain normal gas exchange, and moderate arterial hypoxemia and hypercapnia are often accepted. Renal blood flow is compromised due to a decreased cardiac output as a consequence of high intrathoracic pressures. Furthermore, the effects of biotrauma are not limited to the lungs but may lead to a systemic inflammatory reaction.

CONCLUSIONS

The development of acute renal failure during mechanical ventilation likely represents a multifactorial process that may become more important in the presence of comorbidities. Development of optimal interventional strategies requires an understanding of physiologic principles and greater insight into the precise molecular and cellular mechanisms that may also play a role.

Effect of mechanical ventilation on the kidney

Mechanical ventilation is a standard component of intensive care unit management of critically ill patients and is widely used for respiratory support. Recent animal and clinical studies have shown that positive pressure ventilation can worsen pre-existing lung injury and produce ventilator-induced lung injury, which has been linked with the development of systemic inflammation and multi-system organ dysfunction, including renal failure. Although the physiological consequences of mechanical ventilation on pulmonary and cardiovascular function have been extensively studied, its effects on renal function are not as well defined. Previous experimental studies and few clinical reports have shown a significant effect of mechanical ventilation on renal function. Interestingly, recent data are emerging which suggest that renal dysfunction also has a direct, adverse effect on pulmonary function. This chapter reviews the information in these areas and provides a framework for future investigation in this field.

Acute renal failure in the surgical setting

Acute renal failure (ARF) is an unwelcome complication of major surgical procedures that contributes to surgical morbidity and mortality. Acute renal failure associated with surgery may account for 18-47% of all cases of hospital-acquired ARF. The overall incidence of ARF in surgical patients has been estimated at 1.2%, although is higher in at-risk groups. Mortality of patients with ARF remains disturbingly high, ranging from 25% to 90%, despite advances in dialysis and intensive care support. Appreciation of at-risk surgical populations coupled with intensive perioperative care has the capacity to reduce the incidence of ARF and by implication mortality. Developments in understanding the pathophysiology of ARF may eventually result in newer therapeutic strategies to either prevent or accelerate recovery from ARF. At present the best form of treatment is prevention. In this review the epidemiology, pathophysiology, diagnosis, treatment and possible prevention of ARF will be discussed.

Mechanical ventilation and renal function: an area for concern?

Mechanical ventilation is a standard component of intensive care unit management of critically ill patients and widely used for respiratory support. Patients requiring ventilation often have renal dysfunction that can occur as a consequence of the underlying disease or be related to the therapy. Although the physiological consequences of mechanical ventilation on pulmonary and cardiovascular function have been extensively studied, its effects on renal function are not as well defined. Previous experimental studies and few clinical reports have shown a significant effect of mechanical ventilation on renal function. This review compiles the information in this area and provides a framework for future investigation in this field.

Perioperative renal dysfunction and cardiovascular anesthesia: concerns and controversies

In patients with renal disease undergoing cardiovascular surgery, perioperative management continues to be a challenge. Traditional answers have turned into new questions with the introduction of new agents and the redesign of old techniques. For ARF prevention, early recognition of pending deleterious compensatory changes is critical. Theoretically, therapeutic intervention designed to prevent ischemic renal failure should be designed to preserve the balance between RBF and oxygen delivery on one hand and oxygen demand on the other. Maintenance of adequate cardiac output distribution to the kidney is determined by the relative ratio of renal artery vascular resistance to systemic vascular resistance. Indeed, it should not be surprising to learn that norepinephrine (despite its vasoconstricting effect) has been reported to have no deleterious renal effects in patients with low systemic vascular resistance. Until recently, strategies for the treatment of ARF have been directed to supportive care with dialysis (to allow tubular regeneration). Various therapeutic maneuvers have been introduced in an attempt to accelerate the recovery of glomerular filtration, including dialysis, nutritional regimens, and new pharmacologic agents. A recent small prospective trial of low-dose dopamine in the prophylaxis of ARF in patients undergoing abdominal aortic aneurysm repair showed no benefit in those patients receiving dopamine. Conversely, the effects of intravenous atrial natriuretic peptide in the treatment of patients with ARF appear to offer benefit in patients with oliguria. Among 121 patients with oliguric renal failure, 63% of those who received a 24-hour infusion of atrial natriuretic peptide required dialysis within 2 weeks compared with 87% who did not. Whether this effect will be borne out in the future remains to be determined. The administration of epidermal growth factor after induction of ischemic ARF in rats has been shown to enhance tubular regeneration and accelerate recovery of kidney function. Human growth factor administration has been shown to increase GFR 130% greater than baseline in patients with chronic renal failure, but no data for clinical ARF have been reported. In addition, there have been significant improvements in dialysis technology in the treatment of ARF. Modern dialysis uses bicarbonate as a buffer as opposed to acetate, which reduces cardiovascular instability, and has more precise regulation of volume removal. Dialysate profiles and temperatures improve hemodynamics and reduce intradialytic hypotension. Techniques of hemodialysis without anticoagulation have reduced bleeding complications. Finally, dialysis membranes activate neutrophils and complement less with the biocompatible membranes used today that reduce recovery time and dialysis treatment. Evidence indicates that activation of complement and neutrophils by older dialysis membranes caused a greater incidence of hypotension, adding to ischemic renal injury. It remains to be determined whether early and frequent dialysis with biocompatible membranes, as well as other therapeutic interventions, will increase the survival of patients with perioperative ARF.

Effects of human atrial natriuretic peptide in patients after coronary artery bypass surgery

OBJECTIVES

To determine the effects of synthetic human atrial natriuretic peptide (ANP) on renal function, hemodynamics, and levels of vasoactive peptides when infused in the immediate postoperative period after coronary bypass surgery in patients with normal kidney function.

DESIGN

A prospective, randomized, double-blind, placebo-controlled study.

SETTING

The Department of Cardiothoracic Anaesthetics and Intensive Care of a university hospital.

PARTICIPANTS

Thirty patients with normal kidney function scheduled for elective coronary bypass surgery.

INTERVENTIONS

During the first 3 hours postoperatively, patients received an infusion of either ANP 7.5 pMol/kg/min (ANP) or vehicle alone (C).

MEASUREMENTS AND MAIN RESULTS

No differences were found between the two groups in respect to sex, degree of coronary disease, preoperative medical treatment, or duration of cardiopulmonary bypass and aortic occlusion. Plasma ANP levels increased nearly 10-fold from a mean of 7.0 +/- 1.1 pMol/L in ANP and remained at baseline levels in C, (p < 0.001). In ANP, there occurred significant increases in urine flow (p < 0.001), inulin clearance (p < 0.001), filtration fraction (p = 0.007), and fractional clearance of sodium (p < 0.001) and of osmoles (p < 0.001) compared with C. During the study, no differences in mean arterial pressure, heart rate, and right atrial or pulmonary capillary wedge pressure were detected between the groups. Cardiac index decreased by 5% in ANP compared with a 9% increase in C (p = 0.027). Vasopressin levels significantly increased in C but remained at baseline levels in ANP (p = 0.031). There were no changes in levels of catecholamines or angiotensin II.

CONCLUSIONS

The results of this study show that ANP increases diuresis, natriuresis, and glomerular filtration in the immediate postoperative period after coronary bypass surgery.

Low blood flow extracorporeal carbon dioxide removal (ECCO2R): a review of the concept and a case report

Despite advances in respiratory and critical care medicine, the mortality from ARDS remains unchanged. Recent research suggests current ventilatory therapy may produce additional lung injury, retarding the recovery process of the lung. Alternative supportive therapies, such as ECMO and ECCO2R, ultimately may result in less ventilator induced lung injury. Due to the invasiveness of ECMO/ECCO2R, these modalities are initiated reluctantly and commonly not until patients suffer from terminal or near-terminal respiratory failure. Low flow ECCO2R may offer advantages of less invasiveness and be suitable for early institution before ARDS becomes irreversible. We describe a patient with ARDS and severe macroscopic barotrauma supported with low flow ECCO2R resulting in significant CO2 clearance, reduction of peak, mean airway pressures and minute ventilation.

Renal and hemodynamic effects of diltiazem after elective major vascular surgery--a potential renoprotective agent?

A postoperative study was done of the effects of an infusion of diltiazem (DTZ), 1 microgram.kg-1.min-1 after a bolus dose of 0.28 mg.kg-1 on renal function and hemodynamics in 10 patients who were operated with insertion of an abdominal aortic graft. Urine flow, glomerular filtration rate (GFR) by inulin clearance, and renal plasma flow (RPF) by PAH clearance and fractional excretion of electrolytes and osmols were measured for three periods of 20 min during infusion of DTZ, in the morning after surgery. Systemic hemodynamic studies were conducted and serum levels of catecholamines were measured. GFR increased during the initial period of DTZ infusion. There were no significant changes during the study period in any of the other parameters, compared to baseline, except for a decrease in heart rate from 84 to 77 beats per minute. The absence of a sustained increase in GFR and a natriuretic and diuretic effect may possibly be ascribed to a preexisting nonconstricted status of the renal vasculature. The authors conclude that the dose of DTZ used in this study can be safely used for further investigations to elucidate the effects of peroperative infusion of DTZ on renal function in connection with major vascular surgery.

Renal effects of human atrial natriuretic peptide in patients after major vascular surgery

The effects were studied postoperatively of an infusion of atrial natriuretic peptide (ANP) 7.5 pMol.kg-1.min-1 on renal function and haemodynamics in seven patients who had been operated with insertion of an abdominal aortic graft. Urine flow, glomerular filtration rate (GFR), renal plasma flow (RPF) and excretion of electrolytes and osmoles were measured for three periods of 20 minutes during infusion of ANP, in the morning of the day after surgery. Haemodynamic studies were conducted, and serum levels of ANP, catecholamines and plasma renin activity were measured. ANP levels increased from 52 to approximately 250 pMol.L-1 during ANP infusion and decreased after infusion to a level equal to baseline. GFR increased from 92 mL.min-1 by 58, 20 and 21%, respectively. RPF was unchanged. Urine flow rate increased from 1.99 mL.min-1 by 81, 151 and 173%, respectively. Fractional clearances of sodium, chloride and osmoles were increased during the second and third ANP periods whereas fractional potassium clearance did not change during the study. There were no changes in catecholamine levels or plasma renin activity during the study. Heart rate, mean arterial pressure and calculated systemic and pulmonary vascular resistance did not change whereas reductions occurred in cardiac index, mean pulmonary artery pressure, pulmonary artery wedge pressure and mean right atrial pressure. We conclude that infusion of ANP also in the postoperative situation increases GFR, diuresis and sodium excretion.

Donor treatment after pronouncement of brain death: a neglected intensive care problem

The need for cadaveric organs for transplantation is increasing. To decrease the shortage of organs, identification of potential donors and conditioning of these donors must improve. We present a review of relevant data on body and tissue alterations due to brain death and summarize the recent literature covering experimental and clinical studies on optimal donor management.

Physiologic implications of mechanical ventilation on pharmacokinetics

Numerous factors present in the critically ill patient decrease drug clearance. The contribution of one factor, mechanical ventilation, to this decrease is largely unknown and unquantified. This article attempts to review the physiologic effects of mechanical ventilation and to propose theoretical changes in the pharmacokinetics of concomitantly administered drugs. Mechanical ventilation with or without positive end-expiratory pressure is a well-documented cause of decreases in cardiac output, hepatic and renal blood flow, glomerular filtration rate, and urine flow. The mean airway pressure delivered, the pathophysiologic state of the patient, and coexisting therapeutic interventions affect the degree of hemodynamic alteration. Theoretically, these hemodynamic changes can decrease the clearance of several drugs frequently administered to critically ill patients. Decreased hepatic blood flow decreases the clearance of nonrestrictively cleared drugs. The pharmacokinetics of drugs predominantly renally cleared, by either glomerular filtration or tubular secretion, are affected by a decrease in renal blood flow or glomerular filtration rate. Also, the clearance of agents for which tubular reabsorption is important may decrease because the reduction in urine flow resulting from mechanical ventilation allows increased time for drug reabsorption. Interventions that minimize the decrease in cardiac output and organ blood flow and, theoretically, the risk of the adverse drug reactions from decreased drug clearance include expansion of intravascular volume, administering positive inotropic agents, and decreasing mean airway pressure. Monitoring serum concentration of critical and toxic agents suspected to have altered clearance in patients receiving mechanical ventilation is recommended. We hope that our article will stimulate future research in this area to give clinicians guidelines for drug dosing in patients receiving mechanical ventilation.

Effects of ephedrine on renal function in patients after major vascular surgery

The haemodynamic and renal effects of ephedrine were studied in 11 mechanically ventilated patients on the first day after major vascular surgery. Ephedrine, a sympathomimetic agent with alpha-1, beta-1, and beta-2 agonistic activity, was infused into 11 patients to achieve a 20% rise in systolic blood pressure. The doses used were 2-6 micrograms/kg/min, and in six of these 11 patients the dose was then doubled, 4-12 micrograms/kg/min for another renal function test. Blood pressure, heart rate, and cardiac output increased at both dose-ranges. Systolic pulmonary arterial pressure increased by 10% at the first dose-range. Systemic vascular resistance was unchanged and plasma catecholamine levels were unaltered in the present study. Plasma renin activity diminished by 18% and 6%, respectively. Clearance of para-aminohippuric acid increased by 20% and 6%, at the two dose-ranges, while clearance of inulin and urine flow rate increased by 24% and 29%, respectively, at the first dose-range, without further increase during the second dose-range. Fractional chloride excretion, and fractional osmolar clearance were unaltered. Fractional Na+ clearance rose by 30% and 36%, respectively. Fractional free water clearance diminished by 8% at the second dose-range. When comparing the two dose-ranges, HR, systolic and mean BP rose by 8%, 13% and 11%, respectively. Fractional K+ excretion diminished by 30%. We conclude that ephedrine given as a continuous infusion seems to have beneficial effects on renal function in patients after elective major vascular surgery.

PEEP and CPAP

Positive end-expiratory pressure (PEEP) maintains airway pressure above atmospheric at the end of expiration, and may be used with mechanical ventilation or spontaneous breathing. CPAP, or continuous positive airway pressure, refers to spontaneous ventilation with a positive airway pressure being maintained throughout the whole respiratory cycle. PEEP/CPAP primarily improves oxygenation by increasing functional residual capacity, and may increase lung compliance and decrease the work of breathing. PEEP/CPAP may be applied using endotracheal tubes, nasal masks or prongs, or face masks or chambers to treat a wide range of adult and paediatric respiratory disorders. Complications associated with their use relate to the pressures applied and include pulmonary barotrauma, decreased cardiac output and raised intracranial pressure.

Physiological aspects of intermittent positive pressure ventilation

The mechanical properties of the lungs and chest wall dictate the relationship between tidal volume, flow rate and airway pressure developed during intermittent positive pressure ventilation (IPPV). The increase in intrathoracic pressures associated with IPPV has consequences for the intrapulmonary distribution of ventilation and perfusion (hence gas exchange), cardiac output and regional blood flows. Barotrauma is a potential hazard. IPPV also affects the homeostatic mechanisms that keep the air spaces dry. Strategies to maximise the benefits and minimise the side effects of IPPV include positive end-expiratory pressure, intermittent mandatory ventilation, differential lung ventilation and high frequency ventilation. Understanding the physiological effects of IPPV and associated therapies allows a rational approach to the adjustment of ventilation against pulmonary, cardiovascular and systemic responses so as to optimise gas exchange and peripheral oxygen delivery.

Effects of dobutamine on renal function in normal man

The effects of graded doses of dobutamine on renal function were studied in eight male volunteers. The infusion rates were 2.5, 5 and 10 micrograms/kg/min. Systolic blood pressure increased by 19% (P less than 0.01), 31% (P less than 0.01), and 44% (P less than 0.01), respectively, while diastolic blood pressure decreased by 17% (P less than 0.02), 17% (P less than 0.02) and 25% (P less than 0.01), respectively. Heart rate increased at the highest dosage by 32% (P less than 0.01). Glomerular filtration rate (GFR) diminished at all three infusion speeds by 10% (P less than 0.02), 9% (P less than 0.05) and 14% (P less than 0.02), respectively, while renal blood flow (RBF) was unchanged. Urine flow rate (UF) decreased by 36% (P less than 0.05) and fractional free water clearance (CH2O/CIn) diminished by 37% (P less than 0.05) at the rate of 10 micrograms/kg/min. Fractional potassium excretion (CK/CIn) decreased by 34% (P less than 0.01) and 44% (P less than 0.01) at the two highest rates. Fractional sodium excretion (CNa/CIn) and fractional chloride excretion (CCl/CIn) were unchanged. Catecholamine levels were unaltered. Plasma renin activity (PRA) rose significantly (P less than 0.05) at the highest infusion rate of dobutamine. It is concluded that dobutamine influences GFR, the clinical significance of which, however, is difficult to evaluate.

Renal function in tetanus

In twenty-eight patients suffering from tetanus, renal function was evaluated from admission for a period of 2 weeks. Investigations included daily blood urea, osmolality and creatinine and urinary osmolality and sodium. Free water clearance (CH2O) was calculated. The patients were divided into those requiring tracheostomy and sedation alone (Group I) and those with more severe tetanus requiring total muscle paralysis and IPPV (Group II). The latter group also had evidence of sympathetic nervous overactivity (SOA). Daily blood urea, serum creatinine and osmolality showed no significant difference between the two groups except during the phase of uremia. Mean urinary sodium was significantly different between the two groups (p less than 0.001). Four patients in Group II developed an abnormal plasma urea (Group IIb). In one patient the rise in urea followed resuscitation from cardiac arrest and the remaining three patients had in common severe cardiovascular instability associated with SOA. All four patients were non-oliguric during the phase of uremia. Only one patient with renal failure survived, compared with a 75% survival in the patients with SOA without renal failure and a 100% survival in Group I. Tetanus complicated by renal failure has a poor prognosis.

Facilitation of renal function by intermittent mandatory ventilation

The effects of intermittent mandatory ventilation (IMV) and controlled mechanical ventilation (CMV) on excretory function and the hemodynamics of the kidneys were studied in two groups of anaesthetized dogs during periods of 3 and 4 h. IMV was associated with statistically significant improved urinary output and renal plasma flow of approximately 50 and 35%, respectively. Graphical and statistical analysis revealed certain cross-over effects indicating that the beneficial effect of IMV was more pronounced if it was used following CMV. The improvements in renal function were interpreted as consequences of decreased mean intrathoracic pressures during IMV as compared to CMV. A correlation to global hemodynamic changes could not be established. IMV does facilitate kidney function and hence may successfully counteract the retention of water and salt which occurs during prolonged mechanical ventilation.

Anaesthesia for the patient with impaired renal function

Patients with renal disease are at risk of further deterioration of renal function and acute tubular necrosis when subjected to anaesthesia and surgery. Optimal fluid loading and careful selection of anaesthetic techniques and agents, appropriate monitoring and the use of mannitol and dopamine assist in the maintenance of renal blood flow and help preserve renal function in these patients. In association with renal failure, physiological changes in other systems result in reduced oxygen supply to the tissues, metabolic disturbances, impairment of the coagulation and immune defence mechanisms and an increased risk of cardiac and cerebrovascular catastrophe. Although many anaesthetic techniques including regional analgesia may be used successfully in these patients caution with most drugs, especially pethidine, phenoperidine, suxamethonium and all non-depolarising neuromuscular relaxants is recommended. Of the volatile anaesthetics currently available, halothane is the agent of choice. Oxygen therapy and close monitoring of cardiorespiratory function are necessary postoperatively.

Complications of acute respiratory failure

Acute respiratory failure is frequently fatal. Attempts to decrease mortality must include attention to pulmonary and extrapulmonary complications. Pulmonary complications include pulmonary emboli, barotrauma, fibrosis, and pneumonia. Swan-Ganz catheters, tracheal intubation, and mechanical ventilation can also result in pulmonary complications. Extra-pulmonary complications such as gastrointestinal hemorrhage, renal failure, infection, and thrombocytopenia may increase mortality. Early diagnosis, aggressive treatment, and prophylaxis of complications should increase survival.

Effects of prenalterol on renal function in normal man

The effects of prenalterol infusion, 0.5 microgram/kg/min, on renal function were studied in 10 male volunteers. Systolic blood pressure increased by 22 mmHg (P less than 0.01) and diastolic pressure decreased by 11 mmHg (P less than 0.01). Heart rate increased by 11 beats/min (P less than 0.01). Plasma catecholamine levels and plasma renin activity were not altered. Renal haemodynamics were unchanged. Urine flow rate and fractional free water excretion decreased by 29% and 45%, respectively (P less than 0.01). Fractional sodium excretion increased by 19% (P less than 0.01) and fractional potassium excretion fell by 33% (P less than 0.05).

Enhanced renal function associated with intermittent mandatory ventilation in acute respiratory failure

In ten patients suffering from acute respiratory failure (ARF) renal function was evaluated during 2-h periods of intermittent mandatory ventilation (IMV) or controlled mechanical ventilation (CMV). Urine flow, osmolal and creatinine clearances were significantly lower during CMV in comparison to both IMV phases and the free water clearance was less negative. Potassium excretion declined with CMV but remained reduced during the second IMV phase. There was no change in sodium excretion. This study suggests that in order to maintain renal function and prevent water retention the use of IMV should be considered whenever a sufficient mechanical reserve for partial spontaneous ventilation is present.

[The effect of PEEP ventilation on hemodynamics and regional blood flow (author's transl)]

The beneficial effects of PEEP on lung function may be counteracted by its hemodynamic sequelae induced by a reduction of venous return due to the elevated intrathoracic pressure, and by an increased right ventricular afterload secondary to the rise of pulmonary vascular resistance. PEEP redistributes cardiac output in favor of brain, heart, adrenals and intestines, whereas the perfusion of stomach, pancreas and thyroid is diminished out of proportion to the fall of cardiac output. Total renal blood flow is relatively little affected; however, redistribution of intrarenal blood flow will result in a marked salt-water-retention. Reduction of hepatic artery flow, at higher levels of PEEP, may jeopardize liver tissue oxygenation. - Under clinical conditions, individual differences regarding preexisting cardiopulmonary and peripheral-vascular diseases may modify the PEEP-induced hemodynamic alterations in a wide range.

Heart surgery in patients under haemodialysis

Several cases of open-heart surgery on patients with severe chronic renal failure have been reported in the last few years. The present study reviews the main problems posed by this situation and analyses our recent experience of three successfully managed patients. Emphasis is made on preoperative preparation, drugs employed in anaesthesia, and postoperative management. We conclude that the prognosis of these patients is good, and that their management is quite similar to that of nephrologically healthy patients.

Hemodynamics and renal function during low frequency positive pressure ventilation with extracorporeal CO2 removal. A comparison with continuous positive pressure ventilation

Six lambs were anesthetized and connected venovenous mode to a Membrane Lung for Extracorporeal CO2 removal. The animals underwent several hours periods of continuous positive pressure ventilation (CPPV), at 5 cmH2O positive end expiratory pressure (PEEP), alternated with several hours periods of low frequency positive pressure ventilation (5 cmH2O PEEP, 2 b.p.m.) with extracorporeal CO2 removal (LFPPV-ECCO2R). During LFPPV-ECCO2R compared with CPPV, cardiac output increased by 26%, pulmonary vascular resistances and systemic vascular resistances decreased by 28% and 22% respectively. The renal function improved significantly during LFPPV-ECCO2R compared with CPPV, i.e. urinary flow, creatinine clearance and osmolar clearance increased by 50%, 37% and 52% respectively. In these experiments LFPPV-ECCO2R, a form of completely artificial ventilation, seems to prevent hemodynamic and renal complications of CPPV.