Shannan K. Hamlin

Cardiovascular impact of manual and automated turns in ICU

Mechanically ventilated patients in the intensive care unit (ICU) are typically turned manually by nursing staff to reduce the risk of developing ventilator associated pneumonia and other problems in the lungs. However, turning can induce changes in the heart rate and blood pressure that can at times have a destabilizing effect. We report here on the early stage of a study that has been undertaken to measure the cardiovascular impact of manual turning, and compare it to changes induced when patients lie on automated beds that turn continuously. Heart rate and blood pressure data were analyzed over ensembles of turns with autoregressive models for comparing baseline level to the dynamic response. Manual turning stimulated a response in the heart rate that lasted for a median of 20 minutes and was of magnitude 5 to 13 bpm. The corresponding response in mean arterial pressure was 11 to 19 mm Hg, lasting for 8 to 21 minutes. There was no discernible response of either variable to automated turns.

Adverse hemodynamic effects of lateral rotation during mechanical ventilation.

Turning critically ill, mechanically ventilated patients every 2 hours is a fundamental nursing intervention to reduce the negative impact of prolonged immobility from preventable pulmonary complications such as ventilator-associated pneumonia and atelectasis. Unfortunately, when coupled with positive pressure ventilation, the benefits of turning may come at the expense of cardiovascular function. Clinicians should closely monitor the hemodynamic response to turning mechanically ventilated patients, and if compromise is observed, the degree and duration of compromise may provide guidance to the appropriate intervention.

Basic Concepts of Hemorheology in Microvascular Hemodynamics

Blood rheology, or hemorheology, involves the flow and deformation behavior of blood and its formed elements (ie, erythrocytes, leukocytes, platelets). The adequacy of blood flow to meet metabolic demands through large circulatory vessels depends highly on vascular control mechanisms. However, the extent to which rheologic properties of blood contribute to vascular flow resistance, particularly in the microcirculation, is becoming more appreciated. Current evidence suggests that microvascular blood flow is determined by local vessel resistance and hemorheologic factors such as blood viscosity, erythrocyte deformability, and erythrocyte aggregation. Such knowledge will aid clinicians caring for patients with hemodynamic alterations.

Microcirculatory Alterations in Shock States

Functional components of the microcirculation provide oxygen and nutrients and remove waste products from the tissue beds of the bodys organs. Shock states overwhelmingly stress functional capacity of the microcirculation, resulting in microcirculatory failure. In septic shock, inflammatory mediators contribute to hemodynamic instability. In nonseptic shock states, the microcirculation is better able to compensate for alterations in vascular resistance, cardiac output, and blood pressure. Therefore, global hemodynamic and oxygen delivery parameters are appropriate for assessing, monitoring, and guiding therapy in hypovolemic and cardiogenic shock but, alone, are inadequate for septic shock.

Microcirculatory Oxygen Transport and Utilization

The cardiovascular system (macrocirculation) circulates blood throughout the body, but the microcirculation is responsible for modifying tissue perfusion and adapting it to metabolic demand. Hemodynamic assessment and monitoring of the critically ill patient is typically focused on global measures of oxygen transport and utilization, which do not evaluate the status of the microcirculation. Despite achievement and maintenance of global hemodynamic and oxygenation goals, patients may develop microcirculatory dysfunction with associated organ failure. A thorough understanding of the microcirculatory system under physiologic conditions will assist the clinician in early recognition of microcirculatory dysfunction in impending and actual disease states.

Hemodynamic Changes With Manual and Automated Lateral Turning in Patients Receiving Mechanical Ventilation

BACKGROUND Lateral turning of critical care patients receiving mechanical ventilation can adversely affect hemodynamic status. OBJECTIVE To study hemodynamic responses to lateral turning. METHOD A time-series design with automated signal processing and ensemble averaging was used to evaluate changes in heart rate, mean arterial pressure, and pulse pressure due to lateral turning in 13 adult medical-surgical critical care patients receiving mechanical ventilation. Patients were randomly assigned to the manual-turn or the automated-turn protocol for up to 7 consecutive days. Heart rate and arterial pressure were measured every 6 seconds for more than 24 hours, and pulse pressure was computed. RESULTS A total of 6 manual-turn patients and 7 automated-turn patients completed the study. Statistically significant changes in heart rate, mean arterial pressure, and pulse pressure occurred with the manual turn. Return of the hemodynamic variables to baseline values required up to 45 minutes in the manual-turn patients (expected recovery time ≤ 5 minutes). However, clinically important changes dissipated within 15 minutes of the lateral turn. The steady-state heart rate response on the right side was slightly greater (3 beats per minute) than that on the back (P = .003). Automated turning resulted in no clinically important changes in any of the 3 variables. CONCLUSIONS In medical-surgical critical care patients receiving mechanical ventilation, manual lateral turning was associated with changes in heart rate, mean arterial pressure, and pulse pressure that persisted up to 45 minutes.

The Physiologic Role of Erythrocytes in Oxygen Delivery and Implications for Blood Storage

Erythrocytes are not just oxygen delivery devices but play an active metabolic role in modulating microvascular blood flow. Hemoglobin and red blood cell morphology change as local oxygen levels fall, eliciting the release of adenosine triphosphate and nitric oxide to initiate local vasodilation. Aged erythrocytes undergo physical and functional changes such that some of the red cells most physiologically helpful attributes are diminished. This article reviews the functional anatomy and applied physiology of the erythrocyte and the microcirculation with an emphasis on how erythrocytes modulate microvascular function. The effects of cell storage on the metabolic functions of the erythrocyte are also briefly discussed.

Tumor Lysis Syndrome: A Unique Solute Disturbance

Tumor lysis syndrome (TLS) is a life-threatening disorder that is an oncologic emergency. Risk factors for TLS are well-known, but the current literature shows case descriptions of unexpected acute TLS. Solid tumors and untreated hematologic tumors can lyse under various circumstances in children and adults. International guidelines and recommendations, including the early involvement of the critical care team, have been put forward to help clinicians properly manage the syndrome. Advanced practice nurses may be in the position of triaging and initiating treatment of patients with TLS, and need a thorough understanding of the syndrome and its treatment.

Microvascular Fluid Resuscitation in Circulatory Shock

The microcirculation is responsible for blood flow regulation and red blood cell distribution throughout individual organs. Patients with circulatory shock have acute failure of the cardiovascular system in which there is insufficient delivery of oxygen to meet metabolic tissue requirements. All subtypes of shock pathophysiology have a hypovolemic component. Fluid resuscitation guided by systemic hemodynamic end points is a common intervention. Evidence shows that microcirculatory shock persists even after optimization of macrocirculatory hemodynamics. The ability for nurses to assess the microcirculation at the bedside in real-time during fluid resuscitation could lead to improved algorithms designed to resuscitate the microcirculation.

MORTALITY REDUCTION ASSOCIATED WITH SURVEILLANCE USING AN EMR-BASED ACUITY SCORE AT AN ACADEMIC MEDICAL CENTER

Background Early detection of subtle changes in a patients condition is critical to patient safety, but is difficult to achieve, even with electronic medical records. Objectives To identify at-risk patients and reduce in-hospital mortality through the implementation of surveillance protocols based upon a patient acuity score. Methods The Rothman Index (RI) is a validated patient acuity score, integrated into the EHR, updated in real-time, computed using: vital signs, laboratory values, and nursing assessments. In a nurse-driven initiative at Houston Methodist Hospital, a surveillance system based on RI was implemented on 11 clinical units. On each unit, RI-time-graphs, one for each patient, color-coded by severity, organized so that patients with poor or deteriorating scores were highlighted, were displayed. Graphs were reviewed by nurses at shift-change, during safety huddles, at least 5 times per day. Nurse practitioners rounded on those patients whose RI graphs were highlighted as high risk. Protocols were established for bedside nurses, and charge nurses, specifying actions (e.g. increased monitoring, notification of physicians) required upon triggering of a high risk alert level. Results Risk adjusted mortality (using the UHC mortality model) fell 32% in the 9-months following the intervention as compared to prior 9-months (historical control). Also there was a coincident control group, the remainder of the hospital, where risk-adjusted mortality was unchanged during the 18-months. Conclusions Enhanced surveillance reduced mortality, and the nursing-based protocols were subsequently implemented throughout the hospital, and are being implemented throughout the 8-hospital system. Implications are that this approach will also aid in improving the general quality of care. Figure 1 Monitoring protocols by clinician role fore patient surveillance at Houston Methodist Hospital “Graphs” below refer to Rothman Index graphs displayed on kiosks (monitors) at each nursing station, and in the EMR. Figure 2 Houston Methodist alert rules and required nursing action. Rothman Index graphs are updated whenever new data is entered into the electronic medical record and a customized set of rules are evaluated to determine if a patient meets the criteria for an alert. Figure 1a A Rothman Index (RI) graph for a single patient. RI is on the y-axis, scale 0-100. For calibration: 100 is unimpaired, 65 is the acuity level typical for a patient discharged to a SNF, 40 is the acuity level when a physician might consider moving the patient to an ICU. Each dot reflects the score and the time when a new piece of data has been entered into the EMR and the RI was recalculated. Graphs are color-coded by the most recent score; below 40 the background of the graph is red, 40-65 it is yellow, and above 65 it is blue. Vertical lines are at midnights. This patient graph shows a 5-day history. RI has just fallen below 20, which triggered a “Very High Risk” alert. Figure 1b Nursing unit or array view of seven RI graphs. Each graph shows a patients condition over the previous 5-days. Note that the graph for any patient who has triggered a Very High Risk alert is displayed in a special area at the top of the screen. Figure 2 Mortality Index for 11 nursing units as computed with the University HealthSystem Consortium mortality model for the 9-months prior to initiation of surveillance protocols (historical control) and for the 9-months intervention period. Also shown is a second concurrent control, the mortality index from non-intervention nursing units (20 units) through the entire 18-month period. Risk-adjusted mortality decreased 32% (0.7 to 0.48), p-value < 0.001. The study included 33,797 patient visits from Houston Methodist Hospital (889 beds).