Matthew E. Cove

Bench to bedside review: Extracorporeal carbon dioxide removal, past present and future

Acute respiratory distress syndrome (ARDS) has a substantial mortality rate and annually affects more than 140,000 people in the USA alone. Standard management includes lung protective ventilation but this impairs carbon dioxide clearance and may lead to right heart dysfunction or increased intracranial pressure. Extracorporeal carbon dioxide removal has the potential to optimize lung protective ventilation by uncoupling oxygenation and carbon dioxide clearance. The aim of this article is to review the carbon dioxide removal strategies that are likely to be widely available in the near future. Relevant published literature was identified using PubMed and Medline searches. Queries were performed by using the search terms ECCOR, AVCO2R, VVCO2R, respiratory dialysis, and by combining carbon dioxide removal and ARDS. The only search limitation imposed was English language. Additional articles were identified from reference lists in the studies that were reviewed. Several novel strategies to achieve carbon dioxide removal were identified, some of which are already commercially available whereas others are in advanced stages of development.

Effects of fluid resuscitation with 0.9% saline versus a balanced electrolyte solution on acute kidney injury in a rat model of sepsis*.

Objective:To compare the acute effects of 0.9% saline versus a balanced electrolyte solution on acute kidney injury in a rat model of sepsis. Design:Controlled laboratory experiment. Setting:University laboratory. Subjects:Sixty adult, male Sprague-Dawley rats. Interventions:We induced sepsis by cecal ligation and puncture and randomized animals to receive fluid resuscitation with either 0.9% saline or Plasma-Lyte solution for 4 hours after 18 hours of cecal ligation and puncture (10 mL/kg in the first hour and 5 mL/kg in the next 3 hr). Blood and urine specimens were obtained from baseline, 18 hours after cecal ligation and puncture, immediately after 4 hours fluid resuscitation, and 24 hours later. We measured blood gas, plasma electrolytes, creatinine, interleukin-6, cystatin C, and neutrophil gelatinase-associated lipocalin concentrations. We also analyzed urine for cystatin C and neutrophil gelatinase-associated lipocalin. We used Risk, Injury, Failure, Loss and End-stage criteria for creatinine to assess severity of acute kidney injury. We observed all animals for survival up to 1 day after resuscitation. Surviving animals were killed for kidney histology. Finally, we carried out an identical study in 12 healthy animals. Measurements and Main Results:Compared with Plasma-Lyte, 0.9% saline resuscitation resulted in significantly greater blood chloride concentrations (p < 0.05) and significantly decreased pH and base excess. Acute kidney injury severity measured by RIFLE criteria was increased with 0.9% saline compared with Plasma-Lyte resuscitation (p < 0.05), and these results were consistent with kidney histology and biomarkers of acute kidney injury. Twenty-four-hour survival favored Plasma-Lyte resuscitation (76.6% vs 53.3%; p = 0.03). Finally, in healthy animals, we found no differences between fluids and no evidence of acute kidney injury. Conclusion:Volume resuscitation with Plasma-Lyte resulted in less acidosis and less kidney injury and improved short-term survival when compared with 0.9% saline in this experimental animal model of sepsis.

Clinical review: mechanical circulatory support for cardiogenic shock complicating acute myocardial infarction

Acute myocardial infarction is one of the 10 leading reasons for admission to adult critical care units. In-hospital mortality for this condition has remained static in recent years, and this is related primarily to the development of cardiogenic shock. Recent advances in reperfusion therapies have had little impact on the mortality of cardiogenic shock. This may be attributable to the underutilization of life support technology that may assist or completely supplant the patients own cardiac output until adequate myocardial recovery is established or long-term therapy can be initiated. Clinicians working in the intensive care environment are increasingly likely to be exposed to these technologies. The purpose of this review is to outline the various techniques of mechanical circulatory support and discuss the latest evidence for their use in cardiogenic shock complicating acute myocardial infarction.

Central Extracorporeal Membrane Oxygenation for Septic Shock in an Adult With H1N1 Influenza

Extracorporeal membrane oxygenation has been used as rescue therapy for respiratory failure caused by pandemic hemagglutanin-1 and neuroaminadase-1 (H1N1) influenza, but it is unclear as to whether it can be also used for refractory circulatory failure. A previously healthy 29-year-old woman presented with pneumonitis and septic shock. She deteriorated, despite multiple pharmacologic and ventilatory strategies, so she was placed on central (atrio-aortic) extracorporeal membrane oxygenation for 4 days. After a protracted intensive care stay, she recovered and is undergoing rehabilitation. In particularly severe cases of H1N1 influenza, central extracorporeal membrane oxygenation can completely supplant both cardiac and pulmonary function until the patient recovers from the infection.

Ethical Dilemmas of Adult ECMO: Emerging Conceptual Challenges

From the Department of Cardiothoracic Intensive Care Unit, Dept of Cardiac, Thoracic and Vascular Surgery, National University Heart Centre, National University Hospital, Singapore. Presented at the First Asia Pacific Extracorporeal Life Support Organization meeting at Beijing, October 10-12, 2013. Supported in part by New Clinician Scientist Unit, National University Health System, Singapore (MEC). Address reprint requests to Ramanathan Kollengode, Department of Cardiothoracic and Vascular Surgery, National University Heart Centre, 1 E Kent Ridge Road, Tower Block, Level 9, National University Hospital, Singapore 119228. E-mail: ram_ramanathan@nuhs. edu.sg

Infectious Complications of Cardiac Surgery: A Clinical Review

INFECTIOUS COMPLICATIONS after cardiac surgery occur in 5% to 21% of cases.1,2 Major infectious complications increase postoperative mortality by more than 5 times and prolong recovery.2,3 Forty-seven percent of these patients require more than 14 days in the hospital compared with 5.9% (p < 0.0001) of patients without a major infection.3 As a result, infectious complications substantially increase the cost of care.4 However, infectious complications can be reduced with many simple interventions, starting with risk factor modification at the first anesthetic preoperative screening visit right through to postoperative risk factor vigilance in the intensive care unit (ICU). The most common sites of infection are the respiratory tract (45.7%-57.8%), the surgical site (27.7%), and catheters or devices (20.5%-25.2%).2 This review describes the incidence, impact, treatment, and prevention of infections occurring perioperatively or within the first 12 months of surgery, focusing on interventions in which the anesthesiologist and intensivist play a key role, as well as those infections in which optimum management has been controversial.

Perioperative hemodynamic monitoring

Hemodynamic monitoring is the cornerstone of perioperative anesthetic monitoring. In the unconscious patient, hemodynamic monitoring not only provides information relating to cardiac output, volume status and ultimately tissue perfusion, but also indicates depth of anesthesia and adequacy of pain control. In the 21st century the anesthesiologist has an array of devices to choose from. No single device provides a complete assessment of hemodynamic status, and the use of all devices in every situation is neither practical nor appropriate. This article aims to provide the reader with an overview of the devices currently available, and the information they provide, to assist anesthesiologists in the selection of the most appropriate devices for any given situation.

Disrupting differential hypoxia in peripheral veno-arterial extracorporeal membrane oxygenation

Patients receiving circulatory support with peripheral veno-arterial extracorporeal membrane oxygenation (VA-ECMO) are at risk of developing differential hypoxia. This phenomenon occurs in patients with concomitant respiratory failure. Poorly oxygenated blood, ejected into the ascending aorta from the left ventricle, competes with retrograde flow from the ECMO circuit, potentially causing myocardial and cerebral ischaemia. In a recent Critical Care article, Hou et al. use an animal model of peripheral VA-ECMO to study the physiology of differential hypoxia. Their findings support a dual circuit hypothesis, and show how different cannulation strategies can disrupt the two circuits. In particular, strategies that increase venous oxygen saturations in the pulmonary artery can have a large effect on oxygenation saturation in the ascending aorta. The authors provide evidence supporting the use of veno-arterial-venous ECMO in patients who require peripheral VA-ECMO but have simultaneous respiratory failure.

Veno-venous extracorporeal CO2 removal for the treatment of severe respiratory acidosis.

We read with interest the article by Karagiannidis and colleagues reporting the effects of extracorporeal CO2 removal (ECCO2R) in a pig model of severe respiratory acidosis [1]. However, their conclusion that blood flow rates between 750 and 1,000 ml/minute are necessary to correct severe acidosis using ECCO2R may have been biased by limitations in experimental methodology. Firstly, the authors report CO2 removal rates for various blood flow rates using 19Fr and 14Fr catheters. However, the data clearly demonstrated blood recirculation using the 14Fr catheter, reducing CO2 removal efficiency. Although the authors mention this limitation, it is curious why the 14Fr data were presented at all, since recirculation confounds meaningful interpretation. Secondly, a 15-minute equilibration time was used between experimental set points, but no evidence is provided that equilibrium was achieved. It is reasonable to expect equilibration within 15 minutes when the entire cardiac output participates in gas exchange, but in this study blood flow rates of only 200 to 1,000 ml/minute passed through the gas exchanger. Longer equilibration times may have resulted in continued pH correction, as demonstrated in a human ECCO2R pilot study using approximately 450 ml/minute blood flows [2]. Finally, this study demonstrates reductions of partial pressure of CO2 from 107.9 to 76.9 mmHg with blood flows of 500 ml/minute. In clinical practice this may be sufficient, a reduction from 80-85 to 60-65 mmHg in chronic obstructive pulmonary disease patients with respiratory acidosis normalized pH, allowing intubation to be avoided [2]. Although ECCO2R with higher blood flows clearly increases CO2 removal, lower flows with appropriately designed catheters may provide sufficient support for severe hypercapnic respiratory failure.

Age related inverse dose relation of sedatives and analgesics in the intensive care unit

Sedative and analgesic practices in intensive care units (ICUs) are frequently based on anesthesia regimes but do not take account of the important patient related factors. Pharmacologic properties of sedatives and analgesics change when used as continuous infusions in ICU compared to bolus or short-term infusions during anesthesia. In a prospective observational cohort study, we investigated the association between patient related factors and sedatives/analgesics doses in patients on mechanical ventilation (MV) and their association with cessation of sedation/analgesia. We included patients expected to receive MV for at least 24 hours and excluded those with difficulty in assessing the depth of sedation. We collected data for the first 72 hours or until extubation, whichever occurred first. Multivariate analysis of variance, multivariate regression as well as logistic regression were used. The final cohort (N = 576) was predominantly male (64%) with mean (SD) age 61.7 (15.6) years, weight 63.4 (18.2) Kg, Acute Physiology and Chronic Health Evaluation II score 28.2 (8) and 30% hospital mortality. Increasing age was associated with reduced propofol and fentanyl doses requirements, adjusted to the weight (p<0.001). Factors associated with higher propofol and fentanyl doses were vasopressor use (Relative mean difference (RMD) propofol 1.56 (95% confidence interval (CI) 1.28–1.90); fentanyl 1.48 (1.25–1.76) and central venous line placement (CVL, RMD propofol 1.64 (1.15–2.33); fentanyl 1.41 (1.03–1.91). Male gender was also associated with higher propofol dose (RMD 1.27 (1.06–1.49). Sedation cessation was less likely to occur in restrained patients (Odds Ratio, OR 0.48 (CI 0.30–0.78) or those receiving higher sedative/analgesic doses (OR propofol 0.98 (CI 0.97–0.99); fentanyl 0.99 (CI 0.98–0.997), independent of depth of sedation. In conclusion, increasing age is associated with the use of lower doses of sedative/analgesic in ICU, whereas CVL and vasopressor use were associated with higher doses.