The haemodynamic effects of bolus versus slower infusion of intravenous crystalloid in healthy volunteers.

PURPOSE: This pilot study aimed to characterise the haemodynamic effect of 1L of IV normal saline (NS) administered as a rapid versus slow infusion on cardiac output (CO), heart rate (HR), systemic blood pressures, and carotid blood flow in six healthy volunteers. MATERIALS AND METHODS: Six healthy male volunteers aged 18-65years were randomized to receive 1L NS given over 30min or 120min. On a subsequent study session the alternate fluid regimen was administered. Haemodynamic data was gathered using a non-invasive finger arterial pressure monitor (Nexfin®), echocardiography and carotid duplex sonography. Time to micturition and urine volume was also assessed. RESULTS: Compared to baseline, rapid infusion of 1L of saline over 30min produced a fall in Nexfin®-measured CO by 0.62L/min (p<0.001), whereas there was a marginal but significant increase during infusion of 1L NS over 120min of 0.02L/min (p<0.001). This effect was mirrored by changes in HR and blood pressure (BP) (p<0.001). There were no significant changes in carotid blood flow, time to micturition, or urine volume produced. CONCLUSIONS: Slower infusion of 1L NS in healthy male volunteers produced a greater increase in CO, HR and BP than rapid infusion.

A Pilot Assessment of Carotid and Brachial Artery Blood Flow Estimation Using Ultrasound Doppler in Cardiac Surgery Patients.

OBJECTIVES: To estimate carotid and brachial artery blood flow with Doppler ultrasound in cardiac surgery patients and relate such estimates to cardiac index, lactate levels, and markers of renal function. DESIGN: A prospective observational study. SETTING: A teaching hospital. PARTICIPANTS: Twenty-five elective cardiac surgery patients. INTERVENTIONS: The authors measured bilateral carotid and brachial artery blood flows using Doppler ultrasound and, simultaneously, cardiac index using a pulmonary artery catheter; lactate and serum creatinine levels; and urine output. The relationship between these indices and biomarkers was assessed statistically. MEASUREMENTS AND MAIN RESULTS: Median carotid arterial blood flow was estimated at 0.323 L/min (interquartile ratio [IQR], 0.256-0.429 L/min) on the right and 0.308 L/min (IQR, 0.247-0.376 L/min) on the left at baseline. Median brachial arterial blood flow was estimated at 0.063 L/min (IQR, 0.039-0.115 L/min) on the right and 0.063 L/min (IQR, 0.039-0.081 L/min) on the left at baseline. There was a weak correlation between right- and left-sided flows (brachial: rho = 0.285; carotid: rho = 0.384) and between brachial and carotid flow (right: rho = 0.135, left: rho = 0.225). There also was a weak correlation between cardiac index and brachial flow (right: rho = 0.215; left: rho = 0.320) and carotid flow (left: rho = 0.159) immediately after surgery, and no correlation 1 day after surgery (right brachial: rho = -0.010; left brachial: rho = -0.064; left carotid: rho = -0.060). There were no significant correlations between carotid or brachial flows and lactate and serum creatinine levels or urine output. CONCLUSIONS: In cardiac surgery patients, Doppler-estimated carotid and brachial arterial blood flows have only a weak correlation with cardiac index and no correlation with lactate or creatinine levels or urine output. Thus, Doppler estimation of these blood flows cannot be used to provide noninvasive estimates of cardiac index in patients after cardiac surgery.

Clinical review: the role of the intensivist and the rapid response team in nosocomial end-of-life care.

In-hospital end-of-life care outside the ICU is a new and increasing aspect of practice for intensive care physicians in countries where rapid response teams have been introduced. As more of these patients die from withdrawal or withholding of artificial life support, determining whether a patient is dying or not has become as important to intensivists as the management of organ support therapy itself. Intensivists have now moved to making such decisions in hospital wards outside the boundaries of their usual closely monitored environment. This strategic change may cause concern to some intensivists; however, as custodians of the highest technology area in the hospital, intensivists are by necessity involved in such processes. Now, more than ever before, intensive care clinicians must consider the usefulness of key concepts surrounding nosocomial death and dying and the importance and value of making a formal diagnosis of dying in the wards. In this article, we assess the conceptual background, reference points, challenges and implications of these emerging aspects of intensive care medicine.

A critique of fluid bolus resuscitation in severe sepsis.

Resuscitation of septic patients by means of one or more fluid boluses is recommended by guidelines from multiple relevant organizations and as a component of surviving sepsis campaigns. The technique is considered a key and life-saving intervention during the initial treatment of severe sepsis in children and adults. Such recommendations, however, are only based on expert opinion and lack adequate experimental or controlled human evidence. Despite these limitations, fluid bolus therapy (20 to 40 ml/kg) is widely practiced and is currently considered a cornerstone of the management of sepsis. In this pointof-view critique, we will argue that such therapy has weak physiological support, has limited experimental support, and is at odds with emerging observational data in several subgroups of critically ill patients or those having major abdominal surgery. Finally, we will argue that this paradigm is now challenged by the findings of a large randomized controlled trial in septic children. In the present article, we contend that the concept of large fluid bolus resuscitation in sepsis needs to be investigated further.

Totem and taboo: fluids in sepsis.

The need for early, rapid, and substantial fluid resuscitation in septic patients has long been an article of faith in the intensive care community, a tribal totem that is taboo to question. The results of a recent multicenter trial in septic children in Africa, published in The New England Journal of Medicine, powerfully challenge the fluid paradigm. The salient aspects of the trial need to be understood and reflected upon. In this commentary, we discuss the background to and findings of the trial and explain why they will likely trigger a re-evaluation of our thinking about fluids in sepsis, a re-evaluation that is already happening in the treatment of acute respiratory distress syndrome and acute kidney injury and in postoperative care.

Nutritional support in adult patients receiving extracorporeal membrane oxygenation.

BACKGROUND: Patients receiving extracorporeal membrane oxygenation (ECMO) are some of the most critically ill in the intensive care unit. In such patients, malnutrition is associated with increased morbidity and mortality. OBJECTIVES: To describe the use, methods and adequacy of nutritional support in a consecutive group of patients receiving ECMO; to determine differences between the periods during and after ECMO support; and to determine differences in nutritional adequacy between ECMO survivors and ECMO non-survivors. DESIGN, SETTING AND PARTICIPANTS: We conducted a retrospective study of patients who received ECMO at the Alfred Hospital between January 2005 and December 2007. Patients who received venoarterial (VA) or venovenous (VV) ECMO had their case notes reviewed for clinical and nutritional outcomes. Nutritional adequacy was defined as the ratio of delivered nutrition to target nutrition, expressed as a percentage. RESULTS: Of 48 patients included in our analysis, 35 had VA ECMO and 13 had VV ECMO. Overall, the mean nutritional adequacy achieved for all patients over the periods during and after ECMO support was 62% (SD, 19%). Nutritional adequacy was lower during ECMO support (55%) than after ECMO removal (71%) (P = 0.003). Survivors did not achieve better nutritional adequacy than non-survivors (52% v 61%; P = 0.345). CONCLUSIONS: Patients receiving ECMO received inadequate nutritional support, with only 55% of their nutritional targets being achieved while receiving ECMO. Optimal nutritional support should be a major goal in the care of these patients, and measures to improve nutritional delivery require careful consideration.

Avoiding common problems associated with intravenous fluid therapy.

Inappropriate intravenous fluid therapy is a significant cause of patient morbidity and mortality and may result from either incorrect volume (too much or too little) or incorrect type of fluid. Fluid overload has no precise definition, but complications usually arise in the context of pre-existing cardiorespiratory disease and severe acute illness. Insufficient fluid administration is readily identified by signs and symptoms of inadequate circulation and decreased organ perfusion. Administration of the wrong type of fluid results in derangement of serum sodium concentration, which, if severe enough, leads to changes in cell volume and function, and may result in serious neurological injury. In patients whose condition is uncomplicated, we recommend a restrictive approach to perioperative intravenous fluid replacement, with initial avoidance of hypotonic fluids, and regular measurement of serum concentration of electrolytes, especially sodium.

Reliable suction detection for patients with rotary blood pumps.

All rotary blood pumps (RBPs) are prone to the harmful effects of ventricular collapse or "suction events" because of over-pumping, because they are inherently preload insensitive devices, yet RBP controllers do not comprise a clinically reliable suction detector. We therefore investigated the clinical performance of seven expertly selected time domain indices of suction based on the observed positive spike induced in the RBP impeller speed waveform. Using expert panel classifications, a balanced set of 404 five-second speed snapshots of normal and suction events was created from the impeller speed 25 Hz data in 12 VentrAssist implant patients. Initially, suction index threshold levels were set differently for each patient, giving best sensitivity 95% and specificity 99%. However, analysis of paired combinations of suction indices with fixed thresholds identified one pair giving an acceptable sensitivity of 99.5% and specificity 97.5%; the low number of high speed data samples relative to the speed snapshot mean and maximum OR the largest increase in successive speed maxima. The additional precondition of RBP speed amplitude exceeding a low threshold level allows its more general application to patients with low cardiac contractility. This gives a suction detector with high clinical utility; requiring three index threshold settings only.

Echocardiography is the best cardiovascular 'monitor' in septic shock.

Haemodynamic instability and respiratory failure are common in critically ill patients, with sepsis being a frequent cause. Echocardiography is a useful, practical and safe bedside tool for diagnosis and management of these problems. It provides real-time two-dimensional structural and functional imaging of the heart and vascular system. With Doppler techniques, it provides blood and tissue velocity information from which to derive haemodynamic data equivalent to those provided by conventional invasive haemodynamic monitoring. Its use can help determine whether, and when, continuous haemodynamic monitoring should be instituted. It is the best monitor for the management of sepsis because of its broad clinical utility and as a reference for the judicious use of invasive monitoring.

Effects of positive-pressure ventilation, pericardial effusion, and cardiac tamponade on respiratory variation in transmitral flow velocities.

OBJECTIVE: To determine the effects of positive-pressure ventilation and experimentally induced pericardial effusion and tamponade on transmitral flow velocities in dogs. DESIGN: Descriptive. SETTING: University laboratory. PARTICIPANTS: Eleven tracheally intubated and mechanically ventilated dogs. INTERVENTIONS: Experimental pericardial effusion and cardiac tamponade were created by pericardial injection of warm saline. MEASUREMENTS AND MAIN RESULTS: Hemodynamic parameters and pericardial pressures were monitored in the 11 dogs. Pulsed-wave Doppler tracings of mitral valve flow were obtained at the leaflet tips along with hemodynamic measurements at 4 stages: control, effusion (no decrease in mean arterial pressure), tamponade (>or=40% decrease in mean arterial pressure), and tamponade relief (after evacuation of pericardial fluid). Maximal variation (36%) in transmitral flow velocity over the respiratory cycle during positive-pressure ventilation was seen in the control stage. In the effusion and tamponade stages, variation in transmitral flow velocity decreased progressively to 29% (p = 0.1804, not significant) and 16% (p < 0.0001), respectively. CONCLUSION: Intrathoracic pressure and lung volume changes caused by positive-pressure ventilation influence transmitral flow velocity patterns. Respiratory variation in transvalvular flow is pronounced during standard positive-pressure mechanical ventilation, decreases in the presence of pericardial effusion, and becomes almost nonexistent when cardiac tamponade is present. These findings show that the echocardiographic criteria used to diagnose cardiac tamponade based on mitral valve inflow patterns are different during positive-pressure ventilation from spontaneously breathing subjects.