Computer based haemodynamic guidance system is effective and safe in management of postoperative cardiac surgery patients.

A circulatory guidance system, Navigator, was evaluated in a prospective, randomised control trial at six Australian university teaching hospitals involving 112 scheduled postoperative cardiac surgical patients with pulmonary artery catheters placed and receiving 1:1 nursing care. The guidance system was used to achieve and maintain physician-designated cardiac output and mean arterial pressure targets and compared these with standard post open-heart surgery care. The primary efficacy endpoint was the standardised unsigned error between the targeted and the actual values for cardiac output and mean arterial pressure, time averaged over the duration of cardiac output monitoring - the average standardised distance. This was 1.71 (SD=0.65) for the guidance group and 1.92 (SD=0.65) in the control group (P=0.202). Rates of postoperative atrial fibrillation, adverse events, intensive care unit and hospital length-of-stay were similar in both groups. There were no device-related adverse events. Guided haemodynamic therapy with the Navigator device was non-inferior to standard intensive care unit therapy. The study was registered with ClinicalTrials.gov Identifier NCT00468247.

Epinephrine-induced lactic acidosis following cardiopulmonary bypass.

OBJECTIVE: To determine if lactic acidosis occurring after cardiopulmonary bypass could be attributed to the metabolic or other effects of epinephrine administration. DESIGN: Prospective, randomized study. SETTING: Postsurgical cardiothoracic intensive therapy unit. PATIENTS: Thirty-six adult patients, without acidosis, requiring vasoconstrictors for the management of hypotension after cardiopulmonary bypass. INTERVENTIONS: Randomized administration of either epinephrine or norepinephrine by infusion. MEASUREMENTS AND MAIN RESULTS: Hemodynamic and metabolic data were collected before commencement of vasoconstrictor therapy (time 0) and then 1 hr (time 1), 6 to 10 hrs (time 2), and 22 to 30 hrs (time 3) later. Six of the 19 patients who received epinephrine developed lactic acidosis. None of the 17 patients receiving norepinephrine developed lactic acidosis. In the epinephrine group, but not in the norepinephrine group, lactate concentration increased significantly at times 1 and 2 (p = .01), while pH and base excess decreased (p < or = .01). Blood glucose concentration was higher in the epinephrine group at time 2 (p = .02), while the cardiac index (p < .03) and the mixed venous Po2 (p = .04) were higher at time 1. compared with the norepinephrine group, the patients receiving epinephrine had higher femoral venous lactate concentrations (p = .03), increased lower limb blood flow (p = .05), and increased femoral venous oxygen saturations (p = .04). CONCLUSIONS: The use of epinephrine after cardiopulmonary bypass precipitates the development of lactic acidosis in some patients. This phenomenon is presumably a beta-mediated effect, and is associated with an increase in whole-body and lower limb blood flow and a decrease in whole-body and transfemoral oxygen extraction. The phenomenon does not appear to be related to reduced tissue perfusion and does not have the poor outlook of lactic acidosis associated with shock.

Type B lactic acidosis following cardiopulmonary bypass.

OBJECTIVE: To describe, characterize, and identify the associations of postcardiac surgical lactic acidosis occurring in the absence of clinical evidence of tissue hypoperfusion. DESIGN: The preliminary study is a report of a series of observations in 12 patients. The prospective study is also observational, involving the structured collection of hemodynamic and metabolic variables in a prescribed series of patients. SETTING: Cardiac surgical intensive care unit of a university teaching hospital. PATIENTS: Twelve patients who developed an unexplained lactic acidosis after cardiac surgery are reported in the preliminary study. The prospective study involved observations in 112 consecutive patients undergoing cardiopulmonary bypass for cardiac surgery. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Preliminary study: Cardiac index was increased before, during and after recovery from lactic acidosis. Recovery from lactic acidosis was associated with a decrease in oxygen transport index and significant increases in oxygen consumption index and oxygen extraction ratio. PROSPECTIVE STUDY: Hemodynamic, oxygen transport, and oxygen consumption variables, together with arterial blood gas and lactate concentrations, were assessed every 6 hrs for 24 hrs after surgery. Sixteen patients developed lactic acidosis (peak lactate concentration > 5.0 mmol/L). Compared with the remainder of the patients, this subgroup had longer duration of cardiopulmonary bypass (116 +/- 31 vs. 76 +/- 31 mins, p < .01), greater intraoperative hypothermia (24.9 +/- 2.0 degrees vs. 26.6 +/- 2.3 degrees C, p < .01), more frequent requirement for vasopressor agents (14/16 vs. 35/96, p < .05) and a higher frequency of hyperglycemia (15/16 vs. 28/96, p < .01). Hemodynamic variables, including cardiac index, were remarkably similar in the acidotic and nonacidotic groups. All of the acidotic patients, in both parts of this study, recovered from their acidosis. Eleven of the patients in the preliminary study and all of the 16 acidotic patients in the prospective study were ultimately discharged from the hospital. CONCLUSIONS: This report documents the occurrence of lactic acidosis in a subgroup of patients undergoing cardiopulmonary bypass. The pathogenesis of this disorder is uncertain, but it appears to not relate to inadequate oxygen delivery. Systemic vasodilation and reduced oxygen extraction appear to be features of this disorder, which has an excellent prognosis.

The impact of heat and moisture exchanging humidifiers on work of breathing.

In this study the resistive work or breathing (WOB) associated with eleven commercially available heat and moisture exchangers (HMEs) was evaluated for gas flow rates of 20 to 60 l.min-1. The Gibeck Humid-Vent 2S Flex was also assessed after 24 hours patient usage (n = 50). The WOB associated with these devices was compared with that of standard endotracheal tubes and standard humidifying circuits with flex-tube connectors. The range of work imposed by the eleven HMEs approximated the range shown by water bath circuitry when used with two different commonly used flex-tube connectors. The excess WOB attributed to the HMEs was significantly less than that imposed by standard endotracheal tubes. After 24 hours of patient use, 96% of the Gibeck HMEs tested demonstrated a resistive WOB within the range of the two flex-tube connectors. To assess the clinical significance of this circuit-related WOB, we compared respiratory variables in 40 patients breathing on either CPAP or pressure support ventilation, using a variation in flex-tube resistance which imposed a range of WOB comparable to that shown by the HMEs. A small but statistically significant reduction was found for both the peak flow (48 +/- 1.4 vs 45 +/- 1.1 l.min-1, P < 0.0005) and the minute volume (8.6 +/- 0.35 vs 7.9 +/- 0.31, l, P < 0.0005). These data suggest that the range of resistive work imposed by commercially available HMEs has a small but potentially significant effect on clinical respiratory parameters.

Changes in myocardial blood flow rates during hyperdynamic sepsis with induced changes in arterial perfusing pressures and metabolic need.

OBJECTIVE: To determine whether hyperdynamic sepsis is associated with dysregulation in the control of myocardial blood flow rates unrelated to hypotension or the use of anesthetic agents. DESIGN: Prospective, nonrandomized, controlled trial. SETTING: Experimental laboratory. SUBJECTS: Fifteen mature male sheep (34 to 61 kg). INTERVENTIONS: Data were recorded in study subjects before and after the induction of sepsis following cecal ligation and perforation. Data were then recorded during: a) an infusion of prostaglandin E1 (PGE1), which decreased mean arterial perfusing pressure; and b) an infusion of zymosan-activated plasma, which increased mean pulmonary arterial pressures. MEASUREMENTS AND MAIN RESULTS: Myocardial blood flow rates were measured by the radiolabeled microsphere technique and cardiac index was measured by the thermodilution technique. Cardiac index (change delta) postcecal ligation and perforation minus baseline (+2.3 +/- 1.0 L/min/m2; p < .01) was increased in the septic study. Blood flow rate to the left ventricle was simultaneously increased, and was not further affected when the PGE1 infusion decreased the mean arterial perfusing pressures (-19 +/- 4%). During the infusion of zymosan-activated plasma, mean pulmonary arterial pressures increased (50 +/- 30%) and right ventricular blood flow was increased (zymosan minus postcecal ligation and perforation study: delta 17.8 +/- 50 mL/100 g/min; p < .01). CONCLUSIONS: In this model of hyperdynamic sepsis, increases in blood flow to both the left and right ventricles were positively coupled to changes in respective ventricular work. From the interventional PGE1 and zymosan-activated plasma infusion studies, we found no evidence to support previous suggestions that the regulation of myocardial blood flow rates according to changes in perfusing pressure and/or metabolic oxygen need is significantly altered during hyperdynamic sepsis.

A comparison between direct and calculated oxygen saturation in intensive care.

We investigated the discrepancy between calculated and spectrophotometrically determined oxygen saturation, and the corresponding effect of this difference on calculated oxygen uptake in 46 arterial-venous sample pairs from 28 critically ill patients. The range of discrepancy between the two methods showed limits of agreement (mean +/- 2SD) of -2.26 to +0.70% for arterial samples, and -5.52 to +4.96% for the corresponding venous samples. The effect of this variation on oxygen uptake showed limits of agreement of -43.2 to 36.0 ml/min when the discrepancy between oxygen uptake, calculated using the direct measure of saturation, was compared to that using the derived value. Multiple regression analysis showed that PCO2, temperature and 2,3 diphosphoglycerate were significantly related to saturation discrepancy with an R-squared value of 0.64 (P < 0.0001) for a subgroup of 25 venous samples. The precision of the PO2 electrode was also found to be a major contributory component to the discrepancies, particularly at venous PO2 values. Thus the use of calculated oxygen saturation may result in clinically significant inaccuracies in the assessment of some oxygen flux variables.

Increased right ventricular compliance in response to continuous positive airway pressure.

The right ventricular hemodynamic effects of incremental continuous positive airway pressure (CPAP) were assessed in 16 studies in nine unanesthetized, spontaneously breathing sheep. In seven sheep, studies were performed before and after the induction of sepsis. CPAP was applied in four increments of 4 mm Hg via a cuffed tracheostomy tube. Cardiac output, right ventricular ejection fraction (RVEF) and right ventricular end-diastolic volume (RVEDV) were assessed by thermodilution. In this model, incremental CPAP produced similar effects in septic and nonseptic studies. Cardiac output was preserved by a progressive increase in heart rate (106 +/- 25 to 126 +/- 29, p less than 0.05) in spite of a significant decline in stroke volume index (49 +/- 7 to 43 +/- 7, p less than 0.05). Transmural pulmonary artery pressure and pulmonary vascular resistance index increased with incremental CPAP whereas RVEF declined (0.38 +/- 0.05 to 0.31 +/- 0.05, p less than 0.05). Transmural right atrial pressure declined significantly (7.7 +/- 1.7 to 4.8 +/- 2.9, p less than 0.05) whereas RVEDV was unchanged. In this study incremental CPAP was associated with an enhancement of right ventricular compliance. Further, right ventricular preload was preserved in spite of the measured increase in intrathoracic pressure and cardiac output was maintained in the face of a CPAP-related increase in right ventricular afterload by compensatory increases in heart rate and right ventricular work.

Alterations in anion gap following cardiopulmonary bypass.

OBJECTIVES: To evaluate the changes in the anion gap and their relation to hyperlactatemia and alterations in plasma proteins after cardiopulmonary bypass. DESIGN: Prospective study. SETTING: Cardiothoracic intensive therapy unit. PATIENTS: One hundred eleven consecutive patients after cardiopulmonary bypass. MEASUREMENTS AND MAIN RESULTS: Data were collected before cardiopulmonary bypass and every 6 hrs for 24 hrs after cardiopulmonary bypass. Results were analyzed for the entire cohort and for hyperlactatemic subgroups. The major finding of this study was that the anion gap decreased significantly at all sampling periods relative to precardiopulmonary bypass values, despite the presence of clinically important hyperlactatemia. No correlation between the decrease in plasma protein concentrations and the decrease in anion gap could be demonstrated. CONCLUSIONS: The decrease in anion gap after cardiopulmonary bypass appears to represent a balance between the influences of increased serum chloride and lactate concentrations and reduced plasma protein concentrations. This analysis demonstrates the limitations of the anion gap in the evaluation of a metabolic acidosis after cardiopulmonary bypass.

The 'cuff-leak' test for extubation.

The 'cuff-leak' test, which involves demonstrating a leak around a tracheal tube with the cuff deflated, has been advocated to determine the safety of extubation in patients with upper airway obstruction. In 62 such patients we were able safely to extubate all patients with a cuff leak. Two patients extubated without cuff leak required reintubation and in five patients who repeatedly failed the test, tracheostomy was performed. Subsequently, we extubated 10 patients who were stable on spontaneous ventilation and did not have cuff leak; three later required tracheostomy and seven were uneventfully extubated. While the presence of cuff leak demonstrates that extubation is likely to be successful, a failed cuff-leak test does not preclude uneventful extubation and if used as a criterion for extubation may lead to unnecessarily prolonged intubation or to unnecessary tracheostomy.

Effect of PGE1 on altered distribution of regional blood flows in hyperdynamic sepsis.

Since the sepsis syndrome is associated with depressed vascular reactivity, it may be incorrect to assume that pharmacologically mediated changes in cardiac output will be proportionately distributed at the regional level of the circulation. We examined the effect of hyperdynamic sepsis and the concurrent administration of the vasodilatory prostaglandin (PGE1) on the regional distribution of blood flows (Q) in unanesthetized sheep rendered septic by cecal ligation and perforation. Systemic Q progressively increased throughout a 48-h study period after cecal ligation and perforation. Simultaneously, organ Q, measured by the radioactive microsphere technique, was depressed to the pancreas, but increased to the heart, gallbladder, brain, and colon; the increased Q to both heart and gallbladder was greater than the simultaneous increase in systemic Q in this septic study. With the infusion of PGE1 (1 microgram/kg/min), mean arterial perfusing pressures fell, while the cardiac index increased further over that recorded during the 48-h septic study. Despite this depression in arterial pressures, the only significant effect of PGE1 on the interorgan distribution of Q was in the renal circulation, where it was demonstrated that kidney Q fell. We conclude that (1) hyperdynamic and normotensive sepsis exerted nonhomogeneous effects on the distribution of organ Q, and (2) an increased systemic Q during PGE1 infusion was proportionately distributed to all organs, except the kidneys, where Q paradoxically fell. The latter finding suggests that the regulation of kidney Q may be depressed across the normal range of arterial perfusing pressures in the sepsis syndrome. Further investigation is essential to understand the effect of clinical interventions on the control of tissue O2 flux at both the regional and microregional levels of the circulation.

Withdrawing and withholding treatment in intensive care. Part 2. Patient assessment.

In order to allocate resources fairly in intensive care units, and to avoid treatment which only prolongs dying, accurate prediction of outcome is necessary. Most systems that have been developed to predict the outcome of treatment are flawed and are little better than the guesses of experienced medical and nursing staff. The likelihood of survival must then be weighed against a subjective assessment of quality of life. The perception that intensive care wastes resources on patients who have little chance of survival should be reassessed in the light of our limited ability to detect hopelessly ill patients before embarking upon treatment.

Withdrawing and withholding treatment in intensive care. Part 1. Social and ethical dimensions.

Intensive care is an expensive resource. The medical profession has been criticised for applying technology indiscriminately and at vast expense to a relatively small group of patients. The desire of governments to reduce the cost of health care has made rationing of health services a topic of open discussion rather than an implicit activity as it has been in the past. The appropriate response of doctors to these problems is to provide leadership in promoting public awareness and debate of the effects of rationing, and to provide rational allocation of therapy to individual patients. The major issues involving resource allocation in society and to individuals are discussed.

Withdrawing and withholding treatment in intensive care. Part 3. Practical aspects.

A major goal of intensive care units should be to provide an environment in which death may occur with dignity if cure is impossible. The key issues in providing such an environment are the establishment of consensus that cure is impossible, and the provision of a resource person who has been a major participant in efforts to cure the patient. This person leads discussion with the patient or relatives, seeking concurrence rather than permission when the withdrawing or withholding of care is under consideration. We present problems which may arise in facilitating a dignified demise, and a practical approach to these problems.

Constancy of air-oxygen mixtures in intensive care.

The performance of ten high-flow Bird blenders (3M Company) was assessed to ascertain the stability of the oxygen delivery both over time and within a single respiratory cycle. Blended oxygen concentrations were assessed for both continuous low flow and for intermittent flow with variable tidal volumes as is seen with mechanical ventilation. Studies were repeated after the addition of a high flow bleed from the blender via a T-piece. We observed clinically significant variations in the oxygen concentrations delivered by several blenders when the relationship between air and oxygen supply pressures varied. This variability was greatest when the air and oxygen pressures were nearly equal. When the line pressures were stable, mixed oxygen concentrations were constant but variations in oxygen delivery were found within individual breath cycles. This could be explained by postulating that at the initiation of flow from the blender a small pocket of unblended gas (pure air or pure oxygen) was issued by the blender before the balancing mechanism stabilised to deliver the desired oxygen concentration. This variability of oxygen delivery may have considerable impact on the measurement of oxygen consumption using the open circuit technique. The addition of a high flow bleed completely ablated this blender-derived variation in oxygen delivery.

The optimization of renal function in acute illness.

The development of acute renal failure increases the morbidity, the mortality and the duration of hospital stay of all patients who are treated in intensive-care units. Consequently, the prevention of renal failure, and especially that of oliguric acute renal failure, has a high priority in the management of patients who are seriously-ill. The identification of risk factors, the pretreatment of patients who are in high-risk categories and the maintenance of adequate hydration, oxygenation, cardiac output and renal blood flow are the first-line priorities in management. The use of loop diuretic agents, mannitol and dopamine, separately or in combination, probably are effective prophylactic measures. They also may have therapeutic benefit in the maintenance of a non-oliguric state in the presence of acute renal failure, although there is less scientific support for this role. Such manoeuvres are worthy of trial before an oliguric state is accepted. They are more likely to be efficacious if they are instituted early.

The effects of coronary artery disease on cardiac function in nonhypotensive sepsis.

To assess the effects of coronary artery disease on cardiac function in the presence of sepsis, we compared several hemodynamic indices in two groups of septic patients. Group 1 (n = 69) consisted of patients with nonhypotensive sepsis without coronary artery disease. Group 2 (n = 25) comprised septic patients who had clinical evidence of coronary artery disease. All patients were hemodynamically stable and normotensive at the time of the study. None required inotropic support. While the two groups had similar mean heart rates, mean blood pressures, and biventricular filling pressures, the mean cardiac index was significantly lower in group 2 (3.5 +/- 0.9 L/min/m2 vs 4.4 +/- 1.2; p less than 0.05). This lower cardiac index was related to significantly lower end-diastolic volume indices in group #2, not to differences in contractility between groups. Since the ventricular filling pressures of the groups were similar, the differences in end-diastolic volumes indicate differences in the biventricular compliance. In the presence of hyperdynamic, nonhypotensive sepsis, coronary artery disease was associated with a clinically significant impairment of biventricular compliance, which resulted in a reduction in cardiac output and systemic oxygen transport.