Management of Respiratory Failure in Hemorrhagic Shock.

Hemorrhagic shock results in acute respiratory failure due to respiratory muscle fatigue and inadequate pulmonary blood flow. Because positive pressure ventilation can reduce venous return and cardiac output, clinicians should use the minimum possible mean airway pressure during assisted or mechanical ventilation, particularly during episodes of severe hypovolemia. Hypoperfusion also worsens dead space fraction. Therefore, clinicians should monitor capnography during mechanical ventilation and recognize that hypercapnia may be treated with fluid resuscitation rather than increasing minute ventilation.

Automated expiratory ventilation assistance through a small endotracheal tube can improve venous return and cardiac output.

BACKGROUND: Positive pressure ventilation can decrease venous return and cardiac output. It is not known if expiratory ventilation assistance (EVA) through a small endotracheal tube can improve venous return and cardiac output. RESULTS: In a porcine model, switching from conventional positive pressure ventilation to (EVA) with - 8 cmH20 expiratory pressure increased the venous return and cardiac output. The stroke volume increased by 27% when the subjects were switched from conventional ventilation to EVA [53.8 ± 7.7 (SD) vs. 68.1 ± 7.7 ml, p = 0.003]. After hemorrhage, subjects treated with EVA had higher median cardiac output, higher mean systemic arterial pressure, and lower central venous pressure at 40 and 60 min when compared with subjects treated with conventional ventilation with PEEP 0 cmH20. The median cardiac output was 41% higher in the EVA group than the control group at 60 min [2.70 vs. 1.59 L/min, p = 0.029]. CONCLUSION: EVA through a small endotracheal tube increased venous return, cardiac output, and mean arterial pressure compared with conventional positive pressure ventilation. The effects were most significant during hypovolemia from hemorrhage. EVA provided less effective ventilation than conventional positive pressure ventilation.

Agreement of Bioreactance Cardiac Output Monitoring With Thermodilution During Hemorrhagic Shock and Resuscitation in Adult Swine.

OBJECTIVE: The study tests the hypothesis that noninvasive cardiac output monitoring based upon bioreactance (Cheetah Medical, Portland, OR) has acceptable agreement with intermittent bolus thermodilution over a wide range of cardiac output in an adult porcine model of hemorrhagic shock and resuscitation. DESIGN: Prospective laboratory animal investigation. SETTING: Preclinical university laboratory. SUBJECTS: Eight ~ 50 kg Yorkshire swine with a femoral artery catheter for blood pressure measurement and a pulmonary artery catheter for bolus thermodilution. INTERVENTIONS: With the pigs anesthetized and mechanically ventilated, 40 mL/kg of blood was removed yielding marked hypotension and a rise in plasma lactate. After 60 minutes, pigs were resuscitated with shed blood and crystalloid. Noninvasive cardiac output monitoring and intermittent thermodilution cardiac output were simultaneously measured at nine time points spanning baseline, hemorrhage, and resuscitation. MEASUREMENTS AND MAIN RESULTS: Simultaneous noninvasive cardiac output monitoring and thermodilution measurements of cardiac output were compared by Bland-Altman analysis. A plot was constructed using the difference of each paired measurement expressed as a percentage of the mean of the pair plotted against the mean of the pair. Percent bias was used to scale the differences in the measurements for the magnitude of the cardiac output. Method concordance was assessed from a four-quadrant plot with a 15% zone of exclusion. Overall, noninvasive cardiac output monitoring percent bias was 1.47% (95% CI, -2.5 to 5.4) with limits of agreement of upper equal to 33.4% (95% CI, 26.5-40.2) and lower equal to -30.4% (95% CI, -37.3 to -23.6). Trending analysis demonstrated a 97% concordance between noninvasive cardiac output monitoring and thermodilution cardiac output. CONCLUSIONS: Over the wide range of cardiac output produced by hemorrhage and resuscitation in large pigs, noninvasive cardiac output monitoring has acceptable agreement with thermodilution cardiac output.

The evolution and current use of invasive hemodynamic monitoring for predicting volume responsiveness during resuscitation, perioperative, and critical care.

Traditional hemodynamic monitors such as pulmonary artery and central venous catheters provide continuous data and secure intravenous access, but their diagnostic efficacy has been criticized. Dynamic arterial waveform monitoring is promising, but studies suggest it is reliable only within narrow ventilation and rhythm parameters. Newer algorithm-based hemodynamic monitors have emerged; they, too, are limited in their accuracy and applicability. Intravascular monitors are used to predict fluid responsiveness and need for alternative therapies, such as vasomotor or inotropic support. Recent efficacy data, along with other important clinical findings, are reviewed with regard to invasive monitors. We caution against over-generalizing from existing studies, and provide guidance for clinicians wishing to target monitoring techniques for appropriate patients.

Development of a rapid, safe, fiber-optic guided, single-incision cricothyrotomy using a large ovine model: a pilot study.

STUDY AIM: We present a pilot study in which we use an ovine model to develop a rapid, safe cricothyrotomy technique using a Melker cuffed 5.0 cricothyrotomy catheter loaded over a fiberoptic stainless steel optical stylet. The technique requires a single incision. The stylet allows easy placement and facilitates visual, tactile, and transillumination confirmation of intratracheal placement. We recorded this process on video to facilitate the development of the procedure and to allow others to replicate it for further research or refinement. All devices used in this technique are currently employed in clinical practice. METHODS: We performed the procedure in four anesthetized sheep, varying the technique to maximize speed, demonstrate pitfalls, and optimize video recording of confirmation methods. We recorded each case using a 4-channel digital video recorder. RESULTS: After making a single scalpel incision we inserted the stylet and confirmed placement by visualization, transillumination, "click" palpation, and gentle stylet-driven tracheal displacement. We passed the cricothyrotomy tubes without difficulty and easily ventilated the animals. CONCLUSION: The procedure is rapid, incorporates redundant safety features, and uses equipment increasingly available to anesthesiologists, emergency physicians, intensivists and surgeons. The promising outcome of this pilot study should be verified in a larger controlled, comparative trial.

Increasing ventilator surge capacity in disasters: ventilation of four adult-human-sized sheep on a single ventilator with a modified circuit.

OBJECTIVE: Recent manmade and natural disasters have focused attention on the need to provide care to large groups of patients. Clinicians, ethicists, and public health officials have been particularly concerned about mechanical ventilator surge capacity and have suggested stock-piling ventilators, rationing, and providing manual ventilation. These possible solutions are complex and variously limited by legal, monetary, physical, and human capital restraints. We conducted a study to determine if a single mechanical ventilator can adequately ventilate four adult-human-sized sheep for 12h. METHODS: We utilized a four-limbed ventilator circuit connected in parallel. Four 70-kg sheep were intubated, sedated, administered neuromuscular blockade and placed on a single ventilator for 12h. The initial ventilator settings were: synchronized intermittent mandatory ventilation with 100% oxygen at 16 breaths/min and tidal volume of 6 ml/kg combined sheep weight. Arterial blood gas, heart rate, and mean arterial pressure measurements were obtained from all four sheep at time zero and at pre-determined times over the course of 12h. RESULTS: The ventilator and modified circuit successfully oxygenated and ventilated the four sheep for 12h. All sheep remained hemodynamically stable. CONCLUSION: It is possible to ventilate four adult-human-sized sheep on a single ventilator for at least 12h. This technique has the potential to improve disaster preparedness by expanding local ventilator surge capacity until emergency supplies can be delivered from central stockpiles. Further research should be conducted on ventilating individuals with different lung compliances and on potential microbial cross-contamination.

Manual in-line stabilization for acute airway management of suspected cervical spine injury: historical review and current questions.

Direct laryngoscopy with manual in-line stabilization is standard of care for acute trauma patients with suspected cervical spine injury. Ethical and methodologic constraints preclude controlled trials of manual in-line stabilization, and recent work questions its effectiveness. We searched MEDLINE, Index Medicus, Web of Knowledge, the Cochrane Database, and article reference lists. According to this search, we present an ancestral review tracing the origins of manual in-line stabilization and an analysis of subsequent studies evaluating the risks and benefits of the procedure. All manual in-line stabilization data came from trials of uninjured patients, cadaveric models, and case series. The procedure was adopted because of reasonable inference from the benefits of stabilization during general care of spine-injured patients, weak empirical data, and expert opinion. More recent data indicate that direct laryngoscopy and intubation are unlikely to cause clinically significant movement and that manual in-line stabilization may not immobilize injured segments. In addition, manual in-line stabilization degrades laryngoscopic view, which may cause hypoxia and worsen outcomes in traumatic brain injury. Patients intubated in the emergency department with suspected cervical spine injury often have traumatic brain injury, but the incidence of unstable cervical lesions in this group is low. The limited available evidence suggests that allowing some flexion or extension of the head is unlikely to cause secondary injury and may facilitate prompt intubation in difficult cases. Despite the presumed safety and efficacy of direct laryngoscopy with manual in-line stabilization, alternative techniques that do not require direct visualization warrant investigation. Promising techniques include intubation through supraglottic airways, along with video laryngoscopes, optical stylets, and other imaging devices.

Percutaneous transcricoid jet ventilation compared with surgical cricothyroidotomy in a sheep airway salvage model.

BACKGROUND: We developed a large animal model of the "cannot intubate/cannot ventilate" (CNI/V) scenario to compare percutaneous transcricoid manual jet ventilation (MJV) with surgical cricothyroidotomy (SC). METHODS: Twelve sheep weighing 40-80 kg were assigned to MJV or SC groups. After sedation, intubation, and line placement, CNI/V was simulated by removing the tracheal tube and inducing paralysis with vecuronium. When SaO2 reached 80% (t=0), MJV catheter insertion or SC was initiated. Upon successful airway placement, ventilation began using 100% oxygen at 20 breaths/min. MJV was administered at 50 psi. HR, BP, SaO2, pH, PCO2, and PO2 were recorded at t=0, 30, 60, 90, 120, 150, 180, 300, 600, and 1200 s. Data were reported as mean+/-S.E.M. over the whole observation period. Baseline values were compared using Student's t-tests. Repeated-values ANOVA was used for post-procedure group comparisons. Statistical tests were two-tailed and alpha was set at 0.05. RESULTS: Body weights were not significantly (P=0.08) different between MJV (65+/-6 kg) and SC (52+/-3 kg) groups. Baseline respiratory and hemodynamic variables were also not significantly different. Median procedure time for MJV (20 s) and SC (24 s) was not significantly (P=0.69) different. Post-procedure values were not significantly different for SaO2 (P=0.65), pH (P=0.70), PCO2 (P=0.47), PO2 (P=0.84), MAP (P=0.09), or HR (P=0.16) over the entire 20 min resuscitation period. CONCLUSION: Using a realistic model of CNI/V we found no difference in respiratory or hemodynamic variables between MJV and SC. Adequate ventilation and perfusion was maintained solely by MJV for up to 20 min.

Social bias and injustice in the current health care system.

This paper reflects upon historical and modern events and challenges emergency physicians to affirm a genuine commitment to social justice. Such an affirmation does not allow the physician to rest in the belief that the system is inherently just. Rather, it challenges the practitioner to recognize the widespread and inherent injustices that are present. It is probable that significant strides have been made toward protecting the rights and dignity of our patients. Even so, much remains to be done. Poor and minority patients are still less than optimally treated, and increasing marketplace competitiveness may jeopardize some of the recent gains in caring for the uninsured. Future generations may look upon some of the current discriminatory practices of our professional lifetimes with the condemnation that we hold for past abuses.