A blinded, randomized controlled evaluation of an impedance threshold device during cardiopulmonary resuscitation in swine

Effects of Chest Compression on Ventilation Quality during Cardiopulmonary Resuscitation

Ventilation is an important part of cardiopulmonary resuscitation (CPR). The advanced airway mode and 30:2 mode are used for intubated and non-intubated patients, respectively. It is debatable that passive produced by 30 compressions can provide adequate tidal volume for 30:2 mode. In addition, the fragmented ventilation caused by continuous compression may result in ineffective ventilation. In the study, one pig was anaesthetized and intubated for 2 CPRs. Continuous chest compressions with ventilation and continuous chest compressions without mechanical ventilation were performed in 2 CPRs, respectively. Three 10-minute data segments including a period of normal ventilation (V segment), a period of only compressions without ventilation (C segment), and a period of compressions with ventilation (C-V segment) were used to analyze peek flow (PF), peek pressure (PP) and tidal volume. All the data was presented as mean ± standard deviation. Chest compression resulted in 14.90% increase in mean PP (2401.40 ± 94.75 Pa vs 2822.06 ± 291.10 Pa, p<0.05), 81.46% increase in average PF (319.58 ± 56.93 ml/s vs 579.92 ± 80.27 ml/s, p<0.05). The mean tidal volumes for C segment, V segment and C-V segment were 189.13 ml, 514.72 ml, and 429.26ml, respectively. Continuous compressions reduced the accumulative tidal volume, but when five compressions were made in one inspiratory phase, there is almost no loss of tidal volume (510.86 ± 47.24 ml vs 514.72 ± 29.25 ml, p<0.05). The study suggested the ventilator without feedback regulation might reduce the peek pressure during CPR and 5 compressions in 2 s inspiratory phase provided higher tidal volume.Clinical Relevance- This study shows that 150 chest compressions per minute provided greater tidal volume than 100 and 120 compressions per minute; continuous chest compressions could also provide a certain amount of oxygen supply.

An impedance threshold device did not improve carotid blood flow in a porcine model of prolonged cardiac arrest

BACKGROUND

An impedance threshold device (ITD) was developed to increase venous return to the heart and therefore increase cardiac output and organ blood flow during cardiopulmonary rescue (CPR). Basic CPR aims to maintain coronary and cerebral blood flow at the minimum level necessary for survival. The present study compared the effects of an ITD on cerebral blood flow assessed as blood flow in both carotid arteries to the blood flow of a control group during prolonged CPR.

METHODS

Fourteen anaesthetized pigs were monitored during 60 min of CPR after induced ventricular fibrillation. The primary outcome was blood flow in both carotid arteries, and the secondary outcomes were blood pressure, acid-base parameters, plasma potassium, and plasma lactate. The pigs were randomized to mechanical compressions and ventilation with an ITD added to the ventilation or to a control group treated only with mechanical compressions and ventilation. The time course for the parameters was tested using analysis of variance.

RESULTS

The cumulative carotid blood flow in the ITD group decreased from 64 to 42 ml/min, and it decreased from 69 to 51 ml/min in the control group during 60 min of CPR. The difference was not significant. The secondary outcome measures were also not significantly different.

CONCLUSIONS

This study did not show any beneficial effect of an ITD on carotid blood flow.

Blinded Evaluation of Combination Drug Therapy for Prolonged Ventricular Fibrillation Using a Swine Model of Sudden Cardiac Arrest

Despite experimental evidence supporting the use of resuscitation drugs in the treatment of sudden cardiac arrest (CA), there are no good human clinical data to support the decades-old practice of giving these medications during out-of-hospital CA resuscitation. We hypothesized that the lack of efficacy in clinical practice in ventricular fibrillation (VF) is the failure-based manner in which resuscitation drugs have historically been administered (one at a time interspersed with chest compressions and a defibrillation attempt, giving the next only if the previous one was ineffective). The aim of this study was to determine if giving and circulating a combination of commonly available, historically used resuscitation drugs together, prior to the first defibrillation attempt after prolonged VF, might improve short-term outcomes compared with the failure-based serial drug approach used in the past. We used a well-established swine model of sudden prolonged untreated VF. Animals were randomized to receive epinephrine (0.01 mg/kg), vasopressin (0.5 U/kg), amiodarone (4 mg/kg), and sodium bicarbonate (1.0 mEq/kg) in series (SERIES group [n = 53]) or a combination of epinephrine (0.01 mg/kg), vasopressin (0.5 U/kg), amiodarone (4 mg/kg), sodium bicarbonate (1.0 mEq/kg), and metoprolol (0.2 mg/kg) (COCKTAIL group) delivered in rapid succession at the beginning of the attempted resuscitation (n = 27). Data were analyzed descriptively. Baseline characteristics and chemistries between the two groups were the same. Termination of VF was statistically similar in the two groups: 88.7% (47/53) versus 85.2% (23/27) p = 0.66, with an adjusted relative risk ratio (RRR) of 0.94 (0.37, 1.15). However, ROSC was higher in the SERIES group (56.6% [30/53] versus 22.2% [6/27], adjusted RRR = 2.83; [1.16, 3.84] p = 0.029) as was 20-minute survival (52.8% [28/53] versus 18.5% [5/27], adjusted RRR = 3.15 [1.14, 4.54] p = 0.032). The combination of drugs studied, at these dosages, inexplicably worsened short-term outcomes after prolonged untreated VF.

The effects of QuikClot Combat Gauze on hemorrhage control in the presence of hemodilution and hypothermia

Hemorrhage is the leading cause of death from trauma. Intravenous (IV) fluid resuscitation in these patients may cause hemodilution and secondary hemorrhage. In addition, hypothermia may interfere with coagulation. The purposes of this study were to compare the effectiveness QuikClot Combat Gauze (QCG) to a control group on hemorrhage in a hemodiluted, hypothermic model, and to determine the effects of IV volume resuscitation on rebleeding. This was a prospective, between subjects, experimental design. Yorkshire swine were randomly assigned to two groups: QCG (n = 13) or control (n = 13). The subjects were anesthetized. Hypothermia (temperature of ≤34.0 °C) was induced; 30% of their blood volume was exsanguinated. A 3:1 replacement of Lactated Ringer's was administered to dilute the remaining blood. The femoral artery and vein were transected. After 1 min of uncontrolled hemorrhage, QCG was placed into the wound followed by standard wound packing. The control group underwent the same procedures without QCG. After 5 min of manual pressure, a pressure dressing was applied. Following 30 min, the dressings were removed, and blood loss was calculated. For subjects achieving hemostasis, up to 5 L of IV fluid was administered or until bleeding occurred, which was defined as >2% total blood volume. The QCG had significantly less hemorrhage than the control (QCG = 30 ± 99 mL; control = 404 ± 406 mL) (p = .004). Further, the QCG group was able to tolerate more resuscitation fluid before hemorrhage (QCG = 4615 ± 1386 mL; control = 846 ± 1836) (p = .000).

Outcomes by rescue shock number during the metabolic phase of porcine ventricular fibrillation resuscitation

BACKGROUND

Optimal resuscitation duration before the first rescue shock (RS) to maximize the probability of success after prolonged ventricular fibrillation (VF) cardiac arrest remains unknown. The purpose of this study was to determine the occurrence of return of spontaneous circulation (ROSC) and survival by RS attempt after 12 minutes of untreated VF.

METHODS

This was a secondary analysis of prospectively collected data from an institutional animal care and use committee-approved protocol. Fifty-three swine (30-35 kg) were instrumented under anesthesia. Ventricular fibrillation was electrically induced. After 12 minutes of untreated VF, cardiopulmonary resuscitation (CPR) was initiated (and continued as necessary (prn)) and a standard dose of epinephrine (0.01 mg/kg) was given (and repeated every 3 (q3) minutes prn). The first RS was delivered after 3 minutes of CPR (and q3 minutes thereafter prn). Each failed RS was followed (in series) by vasopressin (0.57 mg/kg), amiodarone (4.3 mg/kg), and sodium bicarbonate (1 mEq/kg) prn. Resuscitation continued until ROSC or 20-minute elapsed time. The primary outcomes were ROSC and 20-minute survival. Data were analyzed using descriptive statistics.

RESULTS

After 3 minutes of resuscitation, 1 animal (1.9% [95% confidence interval {CI, 0.3-10.0]) achieved ROSC on RS1 and survived. After 6 minutes of resuscitation, 17 animals (32.1% [95% CI, 21.1-45.5]) achieved ROSC on RS2 and 15 (28.3% [95% CI, 18.0-41.6]) survived. Twelve additional animals had ROSC and survival with continued resuscitation. In 23 animals, ROSC was never achieved and efforts were terminated per protocol.

CONCLUSION

Our data suggest that during the metabolic phase of VF, 3 minutes of CPR and 1 standard dose of epinephrine may be insufficient to achieve ROSC on the first RS attempt. A longer duration of CPR and/or additional vasopressors may increase the likelihood of successful defibrillation.

Oxygenation, ventilation, and airway management in out-of-hospital cardiac arrest: a review

Recently published evidence has challenged some protocols related to oxygenation, ventilation, and airway management for out-of-hospital cardiac arrest. Interrupting chest compressions to attempt airway intervention in the early stages of OHCA in adults may worsen patient outcomes. The change of BLS algorithms from ABC to CAB was recommended by the AHA in 2010. Passive insufflation of oxygen into a patent airway may provide oxygenation in the early stages of cardiac arrest. Various alternatives to tracheal intubation or bag-mask ventilation have been trialled for prehospital airway management. Simple methods of airway management are associated with similar outcomes as tracheal intubation in patients with OHCA. The insertion of a laryngeal mask airway is probably associated with worse neurologically intact survival rates in comparison with other methods of airway management. Hyperoxemia following OHCA may have a deleterious effect on the neurological recovery of patients. Extracorporeal oxygenation techniques have been utilized by specialized centers, though their use in OHCA remains controversial. Chest hyperinflation and positive airway pressure may have a negative impact on hemodynamics during resuscitation and should be avoided. Dyscarbia in the postresuscitation period is relatively common, mainly in association with therapeutic hypothermia, and may worsen neurological outcome.

Left ventricular thrombus development during ventricular fibrillation and resolution during resuscitation in a swine model of sudden cardiac arrest

BACKGROUND

Intracardiac thrombus is a well-known complication of low-flow cardiac states including acute myocardial infarction and atrial fibrillation. Little is known, however, about the formation of intracardiac (left ventricular [LV]) thrombus during the extreme low-flow state of cardiac arrest.

OBJECTIVE

Using a swine model of sudden cardiac arrest, we examined the sonographic development of LV thrombus over time after induction of ventricular fibrillation (VF) and resolution of thrombus with cardiopulmonary resuscitation (CPR).

METHODS

This observational study was IACUC approved. Forty-five Yorkshire swine were sedated, intubated, and instrumented under general anesthesia before VF was electrically induced. Sonographic data was collected immediately after VF induction and at 2-min intervals thereafter. Following 12min of untreated VF, resuscitation was initiated with closed chest compressions using an oxygen-powered mechanical resuscitation device. Observations were continued during attempted resuscitation. At the end of the experiment, the animals were euthanized while still at a surgical depth of anesthesia. The data was analyzed descriptively.

RESULTS

Sonographic evidence of LV thrombus was observed in 43/45 animals (95.6% [95%CI: 85.2%, 98.8%]). Thrombus was detected within 6min in 39/45 (86.7% [95%CI: 73.8%, 93.8%]) animals that developed thrombus. Thrombus resolved within 2min after initiation of chest compressions in 31/43 (72.1% [95%CI: 57.3%, 83.3%]) animals.

CONCLUSION

Similar to other low-flow cardiac states, LV thrombus develops early in the natural history of VF arrest and resolves quickly once forward flow is re-established by chest compressions. Institutional protocol number: 154600-8.

A trial of an impedance threshold device in out-of-hospital cardiac arrest

BACKGROUND

The impedance threshold device (ITD) is designed to enhance venous return and cardiac output during cardiopulmonary resuscitation (CPR) by increasing the degree of negative intrathoracic pressure. Previous studies have suggested that the use of an ITD during CPR may improve survival rates after cardiac arrest.

METHODS

We compared the use of an active ITD with that of a sham ITD in patients with out-of-hospital cardiac arrest who underwent standard CPR at 10 sites in the United States and Canada. Patients, investigators, study coordinators, and all care providers were unaware of the treatment assignments. The primary outcome was survival to hospital discharge with satisfactory function (i.e., a score of ≤3 on the modified Rankin scale, which ranges from 0 to 6, with higher scores indicating greater disability).

RESULTS

Of 8718 patients included in the analysis, 4345 were randomly assigned to treatment with a sham ITD and 4373 to treatment with an active device. A total of 260 patients (6.0%) in the sham-ITD group and 254 patients (5.8%) in the active-ITD group met the primary outcome (risk difference adjusted for sequential monitoring, -0.1 percentage points; 95% confidence interval, -1.1 to 0.8; P=0.71). There were also no significant differences in the secondary outcomes, including rates of return of spontaneous circulation on arrival at the emergency department, survival to hospital admission, and survival to hospital discharge.

CONCLUSIONS

Use of the ITD did not significantly improve survival with satisfactory function among patients with out-of-hospital cardiac arrest receiving standard CPR. (Funded by the National Heart, Lung, and Blood Institute and others; ROC PRIMED ClinicalTrials.gov number, NCT00394706.).

Use of the impedance threshold device in cardiopulmonary resuscitation

Although approximately one million sudden cardiac deaths occur yearly in the US and Europe, cardiac arrest (CA) remains a clinical condition still characterized by a poor prognosis. In an effort to improve the cardiopulmonary resuscitation (CPR) technique, the 2005 American Heart Association (AHA) Guidelines for CPR gave the impedance threshold device (ITD) a Class IIa recommendation. The AHA recommendation means that there is strong evidence to demonstrate that ITD enhances circulation, improves hemodynamics and increases the likelihood of resuscitation in patients in CA. During standard CPR, venous blood return to the heart relies on the natural elastic recoil of the chest which creates a transient decrease in intrathoracic pressure. The ITD further decreases intrathoracic pressure by preventing respiratory gases from entering the lungs during the decompression phase of CPR. Thus, although ITD is placed into the respiratory circuit it works as a circulatory enhancer device that provides its therapeutic benefit with each chest decompression. The ease of use of this device, its ability to be incorporated into a mask and other airway devices, the absence of device-related adverse effects and few requirements in additional training, suggest that ITD may be a favorable new device for improving CPR efficiency. Since the literature is short of studies with clinically meaningful outcomes such as neurological outcome and long term survival, further evidence is still needed.