Emergency ventilatory management in hemorrhagic states: elemental or detrimental?

Prioritizing Circulation to Improve Outcomes for Patients with Exsanguinating Injury: A Literature Review and Techniques to Help Clinicians Achieve Bleeding Control

Prioritizing circulation in trauma care and delaying intubation in noncompressible cases improve outcomes. By prioritizing circulation, patient survival significantly improves, advocating evidence-based shifts in trauma care.

Acute overventilation does not cause lung damage in moderately hemorrhaged swine

Airway management is important in trauma and critically ill patients. Prolonged mechanical ventilation results in overventilation-induced lung barotrauma, but few studies have examined the consequence of acute (1 h or less) overventilation. We hypothesized that acute hyperventilation, as might inadvertently be performed in prehospital settings, would elevate systemic inflammation and cause lung damage. Female Yorkshire pigs (40-50 kg, n = 10/group) were anesthetized, instrumented for hemodynamic measurements and blood sampling, and underwent a 25% controlled hemorrhage followed by 1 h of 1) spontaneous breathing, 2) "normal" bag ventilation (4.8 L·min volume, ∼400 mL tidal volume, 12 breaths/minute), 3) bag hyperventilation (9 L·min volume, ∼750 mL tidal volume, 12 breaths/minute), 4) maximum hyperventilation (15 L·min volume, ∼750 mL tidal volume, 20 breaths/minute), or 5) mechanical ventilation. Pigs then regained consciousness and recovered for 24 h, followed by euthanasia and collection of blood and tissue samples. No level of manual ventilation had any significant impact on hemodynamic variables. Blood markers of tissue damage and plasma cytokines were not statistically different between groups with the exception of a transient increase in IL-1β; all values returned to baseline by 24 h. On pathological review, severity and distribution of lung edema or other gross pathologies were not significantly different between groups. These data indicate hyperventilation causes no adverse effects, to include inflammation and tissue damage, and that acute overventilation, as could be seen in the prehospital phase of trauma care, does not produce evidence of adverse effects on the lungs following moderate hemorrhage.NEW & NOTEWORTHY Appropriate airway management is essential in trauma and critically ill patients. Prolonged mechanical ventilation can result in overventilation-induced lung barotrauma, but few studies have examined the consequence of acute overventilation. We investigated the outcome of hemorrhage followed by 1 h of overventilation in swine. We found that acute overventilation, as could be seen in the prehospital phase of trauma care, does not produce evidence of adverse effects on otherwise healthy lungs following moderate hemorrhage.

Ventilation in Simulated Out-of-Hospital Cardiac Arrest Resuscitation Rarely Meets Guidelines

OBJECTIVE

The American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care recommend ventilation rates of eight to ten breaths per minute or two ventilations every 30 compressions, and tidal volumes between 500-600 ml. However, compliance with these guidelines is mainly unknown. The objective of this study is to estimate the proportion of simulated adult OHCA cases that meet guideline-based ventilation targets.

METHODS

We conducted a blinded prospective observational study of standardized simulated cases of EMS-witnessed adult OHCA. During scheduled training sessions, resuscitations were performed by high-quality CPR trained EMS teams composed of four on-duty, full-time EMT/Paramedics from a large urban fire-based EMS agency. A high-fidelity simulation center allowed complete audio and video monitoring from a control room. Rescuers were unaware of the study, or that ventilation practices were being observed. All interventions, including airway and ventilation strategies, were at the discretion of the clinical team. A calibrated Laerdal SimMan 3 G manikin and associated Laerdal Debrief Viewer software recorded ventilation rate, tidal volume, and minute ventilation. Simulations achieving median ventilation rate 7-10 breaths/min, tidal volume 500-600 ml, and minute ventilation 3.5-6 liters/min were considered meeting guideline-based targets.

RESULTS

A total of 106 EMS teams were included in the study. Only 3/106 [2.8% (95% CI: 0.6-8.0)] of the EMS teams demonstrated ventilation characteristics meeting all guideline-based targets. The median ventilation rate was 5.8 breaths/min (IQR 4.4-7.7 breaths/min) with 26/106 [24.5% (95% CI: 17.2-33.7)] between 7-10 breaths/min. The median tidal volume was 413.5 ml (IQR 280.5-555.4 ml), with 18/106 [17.0% (95% CI: 10.9-25.5)] between 500-600 ml. The median minute ventilation was 2.4 L/min (IQR 1.2-3.6 L/min) with 16/106 [15.1% (95% CI: 9.4-23.3)] between 3.5-6.0 L/min.

CONCLUSION

During simulated adult OHCA resuscitation attempts, ventilation practices rarely met guideline-based targets, despite being performed by well-trained EMS providers. Methods should be developed to monitor and ensure high-quality ventilation during actual OHCA resuscitation attempts.

A review of ventilation in adult out-of-hospital cardiac arrest

Out-of-hospital cardiac arrest continues to be a devastating condition despite advances in resuscitation care. Ensuring effective gas exchange must be weighed against the negative impact hyperventilation can have on cardiac physiology and survival. The goals of this narrative review are to evaluate the available evidence regarding the role of ventilation in out-of-hospital cardiac arrest resuscitation and to provide recommendations for future directions. Ensuring successful airway patency is fundamental for effective ventilation. The airway management approach should be based on professional skill level and the situation faced by rescuers. Evidence has explored the influence of different ventilation rates, tidal volumes, and strategies during out-of-hospital cardiac arrest; however, other modifiable factors affecting out-of-hospital cardiac arrest ventilation have limited supporting data. Researchers have begun to explore the impact of ventilation in adult out-of-hospital cardiac arrest outcomes, further stressing its importance in cardiac arrest resuscitation management. Capnography and thoracic impedance signals are used to measure ventilation rate, although these strategies have limitations. Existing technology fails to reliably measure real-time clinical ventilation data, thereby limiting the ability to investigate optimal ventilation management. An essential step in advancing cardiac arrest care will be to develop techniques to accurately and reliably measure ventilation parameters. These devices should allow for immediate feedback for out-of-hospital practitioners, in a similar way to chest compression feedback. Once developed, new strategies can be established to guide out-of-hospital personnel on optimal ventilation practices.

Meta-Analysis of Post-Intubation Hypotension: A Plea to Consider Circulation First in Hypovolemic Patients

Hypovolemic patients can develop postintubation hypotension (PIH). Our objective is to review the literature regarding PIH and the association with mortality. We searched MEDLINE from inception to February 2018. A meta-analysis was performed to assess the effect of PIH on mortality. The results of the meta-analysis were reported in forest plots of the estimated effects of the included studies with a 95 per cent confidence interval. Heterogeneity was evaluated using the I2 test, which corresponded to low (I2 < 25%), medium (I2 = 25–75%), and high (I2 > 75%) heterogeneity. We identified 243 records. Four studies were included in the meta-analysis. The studies reported 2044 patients with 36.8 per cent (n = 753) developing PIH. Data indirectly reflecting the hemodynamic status were available in three studies (n = 1117 patients). Overall mortality was 24.6 per cent (n = 503) and was significantly higher in patients that developed PIH [mortality, n (%): PIH = 250/753 (33.2%) vs 253/1291 (19.6%), P < 0.001]. Patients that develop PIH have an increased mortality. Considering a targeted resuscitation in hypovolemic patients is pivotal to minimize PIH.

Circulation first - the time has come to question the sequencing of care in the ABCs of trauma; an American Association for the Surgery of Trauma multicenter trial

Background

The traditional sequence of trauma care: Airway, Breathing, Circulation (ABC) has been practiced for many years. It became the standard of care despite the lack of scientific evidence. We hypothesized that patients in hypovolemic shock would have comparable outcomes with initiation of bleeding treatment (transfusion) prior to intubation (CAB), compared to those patients treated with the traditional ABC sequence.

Methods

This study was sponsored by the American Association for the Surgery of Trauma multicenter trials committee. We performed a retrospective analysis of all patients that presented to trauma centers with presumptive hypovolemic shock indicated by pre-hospital or emergency department hypotension and need for intubation from January 1, 2014 to July 1, 2016. Data collected included demographics, timing of intubation, vital signs before and after intubation, timing of the blood transfusion initiation related to intubation, and outcomes.

Results

From 440 patients that met inclusion criteria, 245 (55.7%) received intravenous blood product resuscitation first (CAB), and 195 (44.3%) were intubated before any resuscitation was started (ABC). There was no difference in ISS, mechanism, or comorbidities. Those intubated prior to receiving transfusion had a lower GCS than those with transfusion initiation prior to intubation (ABC: 4, CAB:9, p = 0.005). Although mortality was high in both groups, there was no statistically significant difference (CAB 47% and ABC 50%). In multivariate analysis, initial SBP and initial GCS were the only independent predictors of death.

Conclusion

The current study highlights that many trauma centers are already initiating circulation first prior to intubation when treating hypovolemic shock (CAB), even in patients with a low GCS. This practice was not associated with an increased mortality. Further prospective investigation is warranted.

Trial registration

IRB approval number: HM20006627. Retrospective trial not registered.

Ventilation rate in adults with a tracheal tube during cardiopulmonary resuscitation: A systematic review

AIM

The optimal ventilation rate during cardiopulmonary resuscitation (CPR) with a tracheal tube is unknown. We evaluated whether in adults with cardiac arrest and a secure airway (tracheal tube), a ventilation rate of 10min^-1, compared to any other rate during CPR, improves outcomes.

METHODS

A systematic review up to 14 July 2016. We included both adult human and animal studies. A GRADE (Grades of Recommendation, Assessment, Development and Evaluation) approach was used to evaluate the quality of evidence for each outcome.

RESULTS

We identified one human observational study with 67 patients and ten animal studies (234 pigs and 30 dogs). All studies carried a high risk of bias. All studies evaluated for return of spontaneous circulation (ROSC). Studies showed no improvement in ROSC with a ventilation rate of 10 min-1 compared to any other rate. The evidence for longer-term outcomes such as survival to discharge and survival with favourable neurological outcome was very limited.

CONCLUSION

A ventilation rate recommendation of 10 min-1 during adult CPR with a tracheal tube and no pauses for chest compression is a very weak recommendation based on very low quality evidence.

Preliminary report of a mathematical model of ventilation and intrathoracic pressure applied to prehospital patients with severe traumatic brain injury

BACKGROUND

Inadvertent hyperventilation is associated with poor outcomes from traumatic brain injury (TBI). Hypocapnic cerebral vasoconstriction is well described and causes an immediate and profound decrease in cerebral perfusion. The hemodynamic effects of positive-pressure ventilation (PPV) remain incompletely understood but may be equally important, particularly in the hypovolemic patient with TBI.

OBJECTIVE

Preliminary report on the application of a previously described mathematical model of perfusion and ventilation to prehospital data to predict intrathoracic pressure.

METHODS

Ventilation data from 108 TBI patients (76 ground transported, 32 helicopter transported) were used for this analysis. Ventilation rate (VR) and end-tidal carbon dioxide (PetCO2) values were used to estimate tidal volume (VT). The values for VR and estimated VT were then applied to a previously described mathematical model of perfusion and ventilation. This model allows input of various lung parameters to define a pressure-volume relationship, then derives mean intrathoracic pressure (MITP) for various VT and VR values. For this analysis, normal lung parameters were utilized. Separate analyses were performed assuming either fixed or variable PaCO2-PetCO2 differences. Ground and air medical patients were compared with regard to VR, PetCO2, estimated VT, and predicted MITP.

RESULTS

A total of 10,647 measurements were included from the 108 TBI patients, representing about 13 minutes of ventilation per patient. Mean VR values were higher for ground patients versus air patients (21.6 vs. 19.7 breaths/min; p < 0.01). Estimated VT values were similar for ground and air patients (399 mL vs. 392 mL; p = NS) in the fixed model but not the variable (636 vs. 688 mL, respectively; p < 0.01). Mean PetCO2 values were lower for ground versus air patients (30.6 vs. 33.8 mmHg; p < 0.01). Predicted MITP values were higher for ground versus air patients, assuming either fixed (9.0 vs. 8.1 mmHg; p < 0.01) or variable (10.9 vs. 9.7 mmHg; p < 0.01) PaCO2-PetCO2 differences.

CONCLUSIONS

Predicted MITP values increased with ventilation rates. Future studies to externally validate this model are warranted.

Effects of socio-emotional stressors on ventilation rate and subjective workload during simulated CPR by lay rescuers

Several studies have documented the occurrence of high ventilation rates during cardiopulmonary resuscitation, but to date, there have been no scientific investigation of the causes of hyperventilation. The objective of the current study was to test the effects of socio-emotional stressors on lay rescuers' ventilation rate in a simulated resuscitation setting using a manikin model. A within-subjects experiment with randomized order of conditions tested lay rescuers' ventilation rate on an intubated manikin during exposure to socio-emotional stressors and during a control condition where no external stressors were present. Ventilation rates and subjective workload were significantly higher during exposure to socio-emotional stressors than during the control condition. All but one of the nine participants ventilated at a higher ventilation rate in the experimental condition. All nine participants rated the subjective workload to be higher during exposure to socio-emotional stressors. Hence, exposure to socio-emotional stressors is associated with increased ventilation rates performed by lay rescuers during simulated cardiac arrest using a manikin model. These findings might have implications for the understanding of the type of situations which hyperventilation may occur. Awareness of these situations may have implications for training of lay rescues.

Anesthesia advanced circulatory life support

PURPOSE

The constellation of advanced cardiac life support (ACLS) events, such as gas embolism, local anesthetic overdose, and spinal bradycardia, in the perioperative setting differs from events in the pre-hospital arena. As a result, modification of traditional ACLS protocols allows for more specific etiology-based resuscitation.

PRINCIPAL FINDINGS

Perioperative arrests are both uncommon and heterogeneous and have not been described or studied to the same extent as cardiac arrest in the community. These crises are usually witnessed, frequently anticipated, and involve a rescuer physician with knowledge of the patient's comorbidities and coexisting anesthetic or surgically related pathophysiology. When the health care provider identifies the probable cause of arrest, the practitioner has the ability to initiate medical management rapidly.

CONCLUSIONS

Recommendations for management must be predicated on expert opinion and physiological understanding rather than on the standards currently being used in the generation of ACLS protocols in the community. Adapting ACLS algorithms and considering the differential diagnoses of these perioperative events may prevent cardiac arrest.

The relationship between out-of-hospital airway management and outcome among trauma patients with Glasgow Coma Scale Scores of 8 or less

BACKGROUND

Airway management remains a fundamental component of optimal care of the severely injured patient, with endotracheal intubation representing the definitive strategy for airway control. However, multiple studies document an association between out-of-hospital intubation and increased mortality for severe traumatic brain injury.

OBJECTIVES

To explore the relationship between out-of-hospital intubation attempts and outcome among trauma patients with Glasgow Coma Scale (GCS) scores ≤ 8 across sites participating in the Resuscitation Outcomes Consortium (ROC).

METHODS

The ROC Epistry-Trauma, an epidemiologic database of prehospital encounters with critically injured trauma victims, was used to identify emergency medical services (EMS)-treated patients with GCS scores ≤ 8. Multiple logistic regression was used to explore the association between intubation attempts and vital status at discharge, adjusting for the following covariates: age, gender, GCS score, hypotension, mechanism of injury, and ROC site. Sites were then stratified by frequency of intubation attempts and chi-square test for trend was used to associate the frequency of intubation attempts with outcome.

RESULTS

A total of 1,555 patients were included in this analysis; intubation was attempted in 758 of these. Patients in whom intubation was attempted had higher mortality (adjusted odds ratio [OR] 2.91, 95% confidence interval [CI] 2.13-3.98, p < 0.01). However, sites with higher rates of attempted intubation had lower mortality across all trauma victims with GCS scores ≤ 8 (OR 1.40, 95% CI 1.15-1.72, p < 0.01).

CONCLUSIONS

Patients in whom intubation is attempted have higher adjusted mortality. However, sites with a higher rate of attempted intubation have lower adjusted mortality across the entire cohort of trauma patients with GCS scores ≤ 8. Coma Scale score.

Predictors of Intubation Success andTherapeutic Value of Paramedic Airway Management in a Large, Urban EMS System

BACKGROUND

Endotracheal intubation (ETI) is commonly used by paramedics for definitive airway management. The predictors of success and therapeutic value with regard to oxygenation are not well studied.

OBJECTIVES

1) To explore the relationship between intubation success and perfusion status, Glasgow Coma Scale (GCS) score, and end-tidal carbon dioxide (EtCO2); 2) to describe the incidence of unrecognized esophageal intubations with use of continuous capnometry; and 3) to document the incremental benefit of invasive versus noninvasive airway management techniques in correcting hypoxemia.

METHODS

This was a prospective, observational study conducted in a large urban emergency medical services system. Paramedics completed a telephone debriefing interview with quality assurance personnel following delivery of all patients in whom invasive airway management had been attempted. Continuous capnometry was used for confirmation of tube position in all patients. Descriptive statistics were used to document airway management performance, including first-attempt ETI success, overall ETI success, and Combitube insertion (CTI) success. In addition, the incidence of unrecognized esophageal intubation was recorded. The relationship between intubation success and perfusion status, GCS score, and initial EtCO2 value was explored using logistic regression. Finally, recorded SpO2 values and the incidence of hypoxemia (SpO2 < 90%) at baseline, following noninvasive airway maneuvers, and after invasive airway management were compared for perfusing patients.

RESULTS

A total of 703 patients were enrolled over 12 months. First-attempt ETI success was 61%, and overall ETI success was 81%; invasive airway management (ETI or CTI) was unsuccessful in 11% of patients. A single unrecognized esophageal intubation was observed (0.1%). A clear relationship between airway management success and perfusion status, GCS score, and initial EtCO2 value was observed. Only EtCO2 demonstrated an independent association with ETI success after adjusting for the other variables. Significant improvements in mean SpO2 and the incidence of hypoxemia over baseline were observed with both noninvasive and invasive airway management techniques in 168 perfusing patients.

CONCLUSIONS

A relationship between intubation success and perfusion status, GCS score, and initial EtCO2 value was observed. Capnometry was effective in eliminating unrecognized esophageal intubations. Both noninvasive and invasive airway management strategies were effective in increasing SpO2 values and decreasing the incidence of hypoxemia, with additional benefit observed with invasive airway maneuvers in some patients.

Smaller self-inflating bags produce greater guideline consistent ventilation in simulated cardiopulmonary resuscitation

Background

Suboptimal bag ventilation in cardiopulmonary resuscitation (CPR) has demonstrated detrimental physiological outcomes for cardiac arrest patients. In light of recent guideline changes for resuscitation, there is a need to identify the efficacy of bag ventilation by prehospital care providers. The objective of this study was to evaluate bag ventilation in relation to operator ability to achieve guideline consistent ventilation rate, tidal volume and minute volume when using two different capacity self-inflating bags in an undergraduate paramedic cohort.

Methods

An experimental study using a mechanical lung model and a simulated adult cardiac arrest to assess the ventilation ability of third year Monash University undergraduate paramedic students. Participants were instructed to ventilate using 1600 ml and 1000 ml bags for a length of two minutes at the correct rate and tidal volume for a patient undergoing CPR with an advanced airway. Ventilation rate and tidal volume were recorded using an analogue scale with mean values calculated. Ethics approval was granted.

Results

Suboptimal ventilation with the use of conventional 1600 ml bag was common, with 77% and 97% of participants unable to achieve guideline consistent ventilation rates and tidal volumes respectively. Reduced levels of suboptimal ventilation arouse from the use of the smaller bag with a 27% reduction in suboptimal tidal volumes (p = 0.015) and 23% reduction in suboptimal minute volumes (p = 0.045).

Conclusion

Smaller self-inflating bags reduce the incidence of suboptimal tidal volumes and minute volumes and produce greater guideline consistent results for cardiac arrest patients.

Effects of interventional lung assist on haemodynamics and gas exchange in cardiopulmonary resuscitation: a prospective experimental study on animals with acute respiratory distress syndrome

Introduction

Interventional lung assist (ILA), based on the use of a pumpless extracorporeal membrane oxygenator, facilitates carbon dioxide (CO₂) elimination in acute respiratory distress syndrome (ARDS). It is unclear whether an ILA system should be clamped during cardiopulmonary resuscitation (CPR) in patients with ARDS or not. The aim of our study was to test the effects of an ILA on haemodynamics and gas exchange during CPR on animals with ARDS and to establish whether the ILA should be kept open or clamped under these circumstances.

Methods

The study was designed to be prospective and experimental. The experiments were performed on 12 anaesthetised and mechanically ventilated pigs (weighing 41 to 58 kg). One femoral artery and one femoral vein were cannulated and connected to an ILA. ARDS was induced by repeated bronchoalveolar lavage. An indwelling pacemaker was used to initiate ventricular fibrillation and chest compressions were immediately started and continued for 30 minutes. In six animals, the ILA was kept open and in the other six it was clamped.

Results

Systolic and mean arterial pressures did not differ significantly between the groups. With the ILA open mean ± standard deviation systolic blood pressures were 89 ± 26 mmHg at 5 minutes, 71 ± 28 mmHg at 10 minutes, 63 ± 33 mmHg at 20 minutes and 83 ± 23 mmHg at 30 minutes. The clamped ILA system resulted in systolic pressures of 77 ± 30 mmHg, 90 ± 23 mmHg, 72 ± 11 mmHg and 72 ± 22 mmHg, respectively. In the group with the ILA system open, arterial partial pressure of CO₂ was significantly lower after 10, 20 and 30 minutes of CPR and arterial partial pressure of oxygen was higher 20 minutes after the onset of CPR (191 ± 140 mmHg versus 57 ± 14 mmHg). End-tidal partial pressure of CO₂ decreased from 46 ± 23 Torr (ILA open) and 37 ± 9 Torr (ILA clamped) before intervention to 8 ± 5 Torr and 8 ± 10 Torr, respectively, in both groups after 30 minutes of CPR.

Conclusions

Our results indicate that in an animal model of ARDS, blood pressures were not impaired by keeping the ILA system open during CPR compared with the immediate clamping of the ILA with the onset of CPR. The effect of ILA on gas exchange implied a beneficial effect.

Influence of ventilation strategies on survival in severe controlled hemorrhagic shock

OBJECTIVE

To investigate the effect of different ventilation settings on hemodynamic stability in severe controlled hemorrhagic shock.

DESIGN

Prospective, randomized, controlled animal study.

SETTING

Research laboratory in a university hospital.

SUBJECTS

Approximately 35-45 kg domestic pigs.

INTERVENTIONS

Twenty-four domestic pigs were bled 45 mL/kg (estimated 65% of their calculated blood volume) and then ventilated with either 0 cm H2O positive end-expiratory pressure and a respiratory rate of 14 ventilations/min (positive end-expiratory pressure 0 respiratory rate 14), or with 5 cm H2O positive end-expiratory pressure, a respiratory rate of 28 ventilations/min, and a tidal volume reduced by half (positive end-expiratory pressure 5 respiratory rate 28), or with 5 cm H2O positive end-expiratory pressure and a respiratory rate of 14 ventilations/min (positive end-expiratory pressure 5 respiratory rate 14). After 1 hr study phase surviving animals, received fluid resuscitation and were monitored for further 1 hr.

MEASUREMENTS AND MAIN RESULTS

Pulmonary variables, hemodynamic variables, and short-term survival. There were no significant differences in mean arterial blood pressure and cardiac index after hemorrhage. After 20 mins of different ventilation strategies mean arterial blood pressure was 40 +/- 3 mm Hg in the positive end-expiratory pressure 0 respiratory rate 14 group, vs. 24 +/- 6 mm Hg the positive end-expiratory pressure 5 respiratory rate 28 group (p < 0.05) vs. 19 +/- 3 mm Hg in the positive end-expiratory pressure 5 respiratory rate 14 group (p < 0.01). Cardiac index was 65 +/- 5 mL/min/kg in the positive end-expiratory pressure 0 respiratory rate 14 group vs. 37 +/- 5 mL/min/kg in the positive end-expiratory pressure 5 respiratory rate 28 group(p < 0.01) and 20 +/- 3 mL/min/kg in the positive end-expiratory pressure 5 respiratory rate 14 group (p < 0.01). Mean airway pressure and positive end-expiratory pressure correlated strongly with mean arterial blood pressure and cardiac index. None of the positive end-expiratory pressure 0 respiratory rate 14 animals died in the study phase, whereas six of seven positive end-expiratory pressure 5 respiratory rate 28 animals, and all seven positive end-expiratory pressure 5 respiratory rate 14 animals died.

CONCLUSIONS

In this porcine model of severe hemorrhagic shock, reduction of positive end-expiratory pressure was the most important ventilation strategy component influencing hemodynamic stability. Reducing mean airway pressure by decreasing tidal volumes and increasing respiratory rates seemed to have less influence on cardiopulmonary function and survival than 0 cm H2O positive end-expiratory pressure.

Early ventilation in traumatic brain injury

While airway and ventilatory compromise are significant concerns following traumatic brain injury (TBI), there is little data supporting an aggressive approach to airway management by prehospital personnel, and a growing number of reports suggesting an association between early intubation and increased mortality. Recent clinical and experimental data suggest that hyperventilation is an important contributor to these adverse outcomes in TBI patients. Various mechanisms appear to be responsible for the worsened outcomes, including hemodynamic, cerebrovascular, immunologic and cellular effects. Here, relevant experimental and clinical data regarding the impact of ventilation on TBI are reviewed. In addition, experimental data regarding potential mechanisms for the adverse effects of hyperventilation and hypocapnia on the injured brain are presented. Finally, the limited data regarding the impact of hypoventilation and hypercapnia on outcome from TBI are discussed.

Influence of the mode of ventilation on ketamine/xylazine requirements in rabbits

OBJECTIVE

To evaluate the effect of the mode of mechanical ventilation (MV) on the dose of intravenous anesthetic during 3 hours of ketamine/xylazine anesthesia.

STUDY DESIGN

Prospective laboratory study.

ANIMALS

Sixty-one adult male New Zealand White rabbits.

METHODS

Rabbits were anesthetized (ketamine/xylazine 35 + 5 mg kg(-1), IM), the trachea was intubated and randomized to four groups - (1) CMV-1 (n = 14), ventilated with traditional conventional volume-cycled MV [V(T) = 12 mL kg(-1), RR = 20, positive end-expiratory pressure (PEEP) = 0 cmH(2)O]; (2) CMV-2 (n = 13), ventilated with a modern lung-protective regimen of volume-cycled MV (V(T) = 6 mL kg(-1), RR = 40, PEEP = 5 cmH(2)O); (3) HFPV (n = 17) ventilated with high-frequency percussive ventilation [high-frequency oscillations (450 minute(-1)) superimposed on 40 minute(-1) low-frequency respiratory cycles, I:E ratio = 1:1], oscillatory continuous positive airway pressure (CPAP) of 7-10 cmH(2)O, and demand CPAP of 8-10 cmH(2)O. (4) A fourth group, spontaneously ventilating (SV, n = 17), was anesthetized, intubated, but not ventilated mechanically. FiO(2) in all groups was 0.5. Anesthesia was maintained at a surgical plane by IV administration of a ketamine/xylazine mixture (10 + 2 mg kg(-1), as necessary) for 3 hours after intubation. Total dose of xylazine/ketamine administered and the need for yohimbine to facilitate recovery were quantitated.

RESULTS

The total dose of xylazine/ketamine was significantly higher in the HFPV and SV groups compared with CMV-1 (p < 0.01). Fewer animals required yohimbine to reverse anesthesia in the HFPV than CMV-1 group (p < 0.05).

CONCLUSIONS

The HFPV mode of MV led to higher doses of ketamine/xylazine being used than the other modes of MV.

CLINICAL RELEVANCE

In rabbits, anesthetic dose for the maintenance of anesthesia varied with the mode of MV used. Investigators should be aware of the possibility that changing the mode of ventilation may lead to an alteration in the amount of drug required to maintain anesthesia.

Hyperventilation following aero-medical rapid sequence intubation may be a deliberate response to hypoxemia

BACKGROUND

Recent studies document a high incidence of hyperventilation by prehospital providers, with a potentially detrimental effect on outcome in traumatic brain injury (TBI).

PURPOSE

To document the incidence of hyperventilation by aero-medical providers and explore a possible relationship between hyperventilation episodes and desaturations or impending hypoxemia.

METHODS

This was a prospective, descriptive study using TBI patients undergoing prehospital RSI by aero-medical crews. Continuous data regarding end-tidal CO2 (EtCO2), ventilatory rate, and oxygen saturation (SpO2) were downloaded from hand-held oximeter-capnometer devices. Two investigators independently assessed oximetry/capnometry data to identify the following occurrences: desaturation during RSI (SpO2 < 90%), impending hypoxemia (SpO2 decrease by >or=3% to a value <95%) following intubation, loss of SpO2 signal, hyperventilation (EtCO2<30 mm Hg), and severe hyperventilation (EtCO2 < 25 mm Hg). Covariate analysis was used to explore the possible association between hyperventilation episodes and either desaturation, impending hypoxemia, or loss of SpO2 signal.

RESULTS

A total of 32 aero-medical patients were enrolled with a mean duration of ventilation monitoring of 14.8 min. The incidence of hyperventilation or severe hyperventilation was substantially lower than previously documented with ground paramedics. A total of 28 hyperventilation episodes were identified in 16 patients; 13 of these were associated with impending hypoxemia following intubation, five were associated with desaturation during RSI, and seven were associated with loss of SpO2 signal. The remaining three occurred immediately following intubation without desaturation during RSI. Desaturation was observed in 62% of patients; of note, desaturation was recorded on the quality improvement document in only 23% of these. Covariate analysis revealed an association between hyperventilation episodes and either desaturatios during RSI, impending hypoxemia following intubation, or loss of SpO2 signal.

CONCLUSIONS

The incidence of hyperventilation by aeromedical crews was lower than reported for ground paramedics and appears to occur in response to desaturation, impending hypoxemia, or loss of SpO2 signal.

Do we hyperventilate cardiac arrest patients?

INTRODUCTION

Hyperventilation during cardiopulmonary resuscitation is detrimental to survival. Several clinical studies of ventilation during hospital and out-of-hospital cardiac arrest have demonstrated respiratory rates far in excess of the 10 min(-1) recommended by the ERC. We observed detailed ventilation variables prospectively during manual ventilation of 12 cardiac arrest patients treated in the emergency department of a UK Hospital.

METHODS

Adult cardiac arrest patients were treated according to ERC guidelines. Ventilation was provided using a self-inflating bag. A COSMOplus monitor (Respironics Inc.) was inserted into the ventilation circuit at the beginning of the resuscitation from which ventilation data were downloaded to a laptop.

RESULTS

Data were collected from 12 patients (7 male; age 47-82 years). The maximum respiratory rate was 9-41 breaths per minute (median 26). The median tidal volume was 619 ml (374-923 ml) and the median respiratory rate was 21 min(-1) (7-37 min(-1)). The corresponding median minute volume was 13.0 l/min (4.6-21.3 min(-1)). Median peak inspiratory pressures were 60.6 cmH(2)O (range 46-106). Airway pressure was positive for 95.3% of the respiratory cycle (range 87.9-100%).

CONCLUSIONS

Hyperventilation was common, mostly through high respiratory rates rather than excessive tidal volumes. This is the first study to document tidal volumes and airway pressures during resuscitation. The persistently high airway pressures are likely to have a detrimental effect on blood flow during CPR. Guidelines on respiratory rates are well known, but it would appear that in practice they are not being observed.

Effects of face mask ventilation in apneic patients with a resuscitation ventilator in comparison with a bag-valve-mask

Bag-valve-mask ventilation in an unprotected airway is often applied with a high flow rate or a short inflation time and, therefore, a high peak airway pressure, which may increase the risk of stomach inflation and subsequent pulmonary aspiration. Strategies to provide more patient safety may be a reduction in inspiratory flow and, therefore, peak airway pressure. The purpose of this study was to evaluate the effects of bag-valve-mask ventilation vs. a resuscitation ventilator on tidal volume, peak airway pressure, and peak inspiratory flow rate in apneic patients. In a crossover design, 40 adults were ventilated during induction of anesthesia with either a bag-valve-mask device with room air, or an oxygen-powered, flow-limited resuscitation ventilator. The study endpoints of expired tidal volume, minute volume, respiratory rate, peak airway pressure, delta airway pressure, peak inspiratory flow rate and inspiratory time fraction were measured using a pulmonary monitor. When compared with the resuscitation ventilator, the bag-valve-mask resulted in significantly higher (mean+/-SD) peak airway pressure (15.3+/-3 vs. 14.1+/-3 cm H2O, respectively; p=0.001) and delta airway pressure (14+/-3 vs. 12+/-3 cm H2O, respectively; p<0.001), but significantly lower oxygen saturation (95+/-3 vs. 98+/-1%, respectively; p<0.001). No patient in either group had clinically detectable stomach inflation. We conclude that the resuscitation ventilator is at least as effective as traditional bag-valve-mask or face mask resuscitation in this population of very controlled elective surgery patients.

The problem with and benefit of ventilations: should our approach be the same in cardiac and respiratory arrest?

PURPOSE OF REVIEW

Recent advances in cardiopulmonary resuscitation have led to greater understanding of cardio-cerebral-pulmonary interactions during the process. The purpose of this discussion is to update the physiologic understanding of these interactions during cardiopulmonary resuscitation, review the detrimental and beneficial effects of ventilation, and identify implications for clinical practice.

RECENT FINDINGS

There is an inversely proportional relationship between mean intrathoracic pressure, coronary perfusion pressure, and survival from cardiac arrest. Increased ventilation rates and increased ventilation duration impede venous blood return to the heart, decreasing hemodynamics and coronary perfusion pressure during cardiopulmonary resuscitation. It has also been shown that there is a direct and immediate transfer of the increase in intrathoracic pressure to the cranial cavity with each positive pressure ventilation, also reducing cerebral perfusion pressure. The reduced amount of blood flowing through the pulmonary bed during cardiopulmonary resuscitation tends to be overventilated, compromising hemodynamics to both the heart and brain and resulting in ventilation/perfusion mismatch.

SUMMARY

The fundamental hemodynamic principle of intrathoracic pressure defines cardio-cerebral-pulmonary interactions during cardiopulmonary resuscitation. Further research is essential to optimize these interactions during treatment of profound shock.

Early ventilation and outcome in patients with moderate to severe traumatic brain injury

OBJECTIVES

An increase in mortality has been reported with early intubation in severe traumatic brain injury, possibly due to suboptimal ventilation. This analysis explores the impact of early ventilation on outcome in moderate to severe traumatic brain injury.

DESIGN

Retrospective, registry-based analysis.

SETTING

This study was conducted in a large county trauma system that includes urban, suburban, and rural jurisdictions.

PATIENTS

Nonarrest trauma victims with a Head Abbreviated Injury Score of > or =3 were identified from our county trauma registry.

INTERVENTIONS

Intubated patients were stratified into 5 mm Hg arrival PCO(2) increments. Logistic regression was used to calculate odds ratios for each increment, adjusting for age, gender, mechanism of injury, year of injury, preadmission Glasgow Coma Scale score, hypotension, Head Abbreviated Injury Score, Injury Severity Score, PO(2), and base deficit. Increments with the highest relative survival were used to define the optimal PCO(2) range. Outcomes for patients with arrival PCO(2) values inside and outside this optimal range were then explored for both intubated and nonintubated patients, adjusting for the same factors as defined previously. In addition, the independent outcome effect of hyperventilation and hypoventilation was assessed.

MEASUREMENTS AND MAIN RESULTS

A total of 890 intubated and 2,914 nonintubated patients were included. Improved survival was observed for the arrival PCO(2) range 30-49 mm Hg. Patients with arrival PCO(2) values inside this optimal range had improved survival and a higher incidence of good outcomes. Conversely, there was no improvement in outcomes for patients within this optimal PCO(2) range for nonintubated patients after adjusting for all of the factors defined previously. Both hyperventilation and hypoventilation were associated with worse outcomes in intubated but not nonintubated patients. The proportion of arrival PCO(2) values within the optimal range was lower for intubated vs. nonintubated patients.

CONCLUSIONS

Arrival hypercapnia and hypocapnia are common and associated with worse outcomes in intubated but not spontaneously breathing patients with traumatic brain injury.

Out-of-hospital endotracheal intubation: where are we?

While remaining prominent in paramedic care and beneficial to some patients, out-of-hospital endotracheal intubation has not clearly improved survival or reduced morbidity from critical illness or injury when studied more broadly. Recent studies identify equivocal or unfavorable clinical effects, adverse events and errors, interaction with other important resuscitation interventions, and challenges in providing and maintaining procedural skill. We provide an overview of current data evaluating the overall effectiveness, safety, and feasibility of paramedic out-of-hospital endotracheal intubation. These studies highlight our limited understanding of out-of-hospital endotracheal intubation and the need for new strategies to improve airway support in the out-of-hospital setting.

Pre-hospital endotracheal intubation and positive pressure ventilation is associated with hypotension and decreased survival in hypovolemic trauma patients: an analysis of the National Trauma Data Bank

BACKGROUND

Studies of pre-hospital endotracheal intubation (ETI) from single EMS systems have shown contradictory results, which may represent local differences in paramedic training and experience. An alternative hypothesis is that positive pressure ventilation increases mortality because positive pressure ventilation causes hypotension in severely injured hypovolemic patients.

METHODS

A national sample (National Trauma Data Bank, 1994-2002) was used to minimize effects of local paramedic training and experience. All patients with pre-hospital GCS < 8 (most likely to warrant early ETI) and ISS > 16 (most likely to be hypovolemic) were included. Patients intubated in the field (pre-hospital group, n = 871) and in the emergency department (ED group, n = 6581) were compared. To determine whether pre-hospital ETI was an independent predictor of hypotension and mortality, logistic regression was used to control for potential confounders, including age, ISS, body region injured, AIS scores, pre-hospital IV fluids, and other variables. Physiologic variables were not used, as they may be influenced by ETI and positive pressure ventilation, and were therefore considered outcomes, rather than predictors.

RESULTS

Groups were comparable in age, gender, anatomic distribution of injuries, likelihood of at least one severe injury (AIS >3) and other variables, except for head injury (ED 83%, pre-hospital 71%, p < 0.001) and ISS (ED 33 +/- 0.2, pre-hospital 36 +/- 0.6, p < 0.001). Patients intubated in the field were more likely to be hypotensive upon arrival in the ED (SBP < or = 90 mm Hg; ED 33%, pre-hospital 54%, p < 0.001), and had worse survival (ED 45% versus pre-hospital 24%, p < 0.001). Even after controlling for potential confounders, pre-hospital ETI was still an independent predictor of hypotension upon arrival in ED (OR 1.7, 95% CI 1.46 -2.09, p < 0.001) and decreased survival (OR 0.51, 95% C.I. 0.43-0.62, p < 0.001).

CONCLUSIONS

Pre-hospital endotracheal intubation in trauma patients is associated with hypotension and decreased survival. This may be mediated by the effect of positive pressure ventilation during hypovolemic states.

Maskenbeatmung als Rückzugsstrategie zur endotrachealen Intubation

The goal of ventilation in an unprotected airway is to optimize oxygenation and carbon dioxide elimination of the patient. This can be achieved with techniques such as mouth-to-mouth ventilation, but preferably with bag-valve-mask ventilation. Securing the airway with an endotracheal tube is the gold standard, but excellent success in emergency airway management depends on initial training, retraining, and actual frequency of a given procedure in the routine. "Patients do not die from failure to intubate; they die from failure to stop trying to intubate or from undiagnosed oesophageal intubation" (Scott 1986). Therefore, adequate face mask ventilation has absolute priority in airway management by an unexperienced rescuer. During ventilation of an unprotected airway, stomach inflation and subsequent severe complications may result. Careful ventilation can be performed with low inspiratory pressure and flow, and subsequently with a low tidal volume at a high inspiratory fraction of oxygen. This could be a strategy to achieve more patient safety.

A Follow-Up Analysis of Factors Associated with Head-Injury Mortality After Paramedic Rapid Sequence Intubation

BACKGROUND

The San Diego Paramedic Rapid Sequence Intubation (RSI) Trial documented an increase in mortality after paramedic RSI, with hyperventilation identified as a contributing factor in a small subgroup analysis. Here we explore factors affecting outcome in the entire cohort of patients undergoing paramedic RSI to confirm previous findings. This also represents a synthesis of findings from previous analyses

METHODS

Adult trauma patients with severe head injury (Glasgow Coma Scale score, 3-8) who could not be intubated without RSI were prospectively enrolled in the trial. This analysis excluded patients without traumatic brain injury (head/neck abbreviated injury score <2 or failure to meet Major Trauma Outcome Study criteria) or death in the field or within 30 minutes of arrival. Each remaining trial patient was matched to two nonintubated historical controls from the county trauma registry based on: age, sex, mechanism, abbreviated injury scores for each body system, and Injury Severity Score. Logistic regression, cohort analysis, mean least squares regression, and discordant group analysis were used to explore the impact of various factors on outcome.

RESULTS

Of the 426 trial patients, 352 met inclusion criteria for this analysis and were hand-matched to 704 controls. Trial patients and controls were identical with regard to all matching variables. Mortality was increased in RSI patients versus matched controls (31.8 versus 23.7%; odds ration, 1.5; 95% confidence interval, 1.1-2.0; p < 0.01). Hyperventilation was associated with an increase in mortality, whereas transport by aeromedical crews after paramedic RSI was associated with improved outcomes. The reported incidence of aspiration pneumonia was higher for the RSI patients.

CONCLUSION

Paramedic RSI was associated with an increase in mortality compared with matched historical controls. The association between hyperventilation and mortality was confirmed. In addition, patients transported by helicopter after paramedic RSI had improved outcomes. Paramedic RSI did not seem to prevent aspiration pneumonia.

The detrimental effects of ventilation during low-blood-flow states

PURPOSE OF REVIEW

In recent years, it has become increasingly apparent that resuscitative ventilatory procedures, classically thought to be life saving, may have profound detrimental effects.

RECENT FINDINGS

Most assisted breathing techniques during resuscitation involve the provision of intermittent positive pressure ventilation to inflate lung zones for erythrocyte oxygenation and clearance of carbon dioxide. A growing number of studies involving low-flow states, however, have demonstrated that provision of overzealous (or even 'normal') ventilatory rates with intermittent positive pressure ventilation can significantly diminish both systemic and coronary circulation, most likely through inhibition of venous return. Recent laboratory studies of hemorrhage have shown not only a direct detrimental impact of each positive pressure ventilation breath on coronary perfusion, but also how dramatic improvements in blood flow can be achieved, without loss of oxygenation, by delivering breaths infrequently during such low-flow states. Likewise, in cardiac arrest models, studies have shown that interrupting chest compressions, even to provide breaths, can be extremely deleterious by abruptly (and continually) lowering the aortic pressure head to the coronary arteries, thus impairing restoration of spontaneous circulation. Even with endotracheal intubation and uninterrupted chest compressions, frequent positive pressure ventilation still inhibits circulation during cardiopulmonary resuscitation. Despite directed training, paramedics (and other rescuers) have been shown to still excessively ventilate during cardiac arrest resuscitations.

SUMMARY

Ventilation can have profound detrimental hemodynamic effects in low-flow states, exacerbating the circulatory compromise. This underappreciated confounding variable may be one of the reasons many clinical trials of resuscitative interventions have failed despite dramatic successes in the laboratory.

The Impact of Prehospital Endotracheal Intubation on Outcome in Moderate to Severe Traumatic Brain Injury

BACKGROUND

Although early intubation to prevent the mortality that accompanies hypoxia is considered the standard of care for severe traumatic brain injury (TBI), the efficacy of this approach remains unproven.

METHODS

Patients with moderate to severe TBI (Head/Neck Abbreviated Injury Scale [AIS] score 3+) were identified from our county trauma registry. Logistic regression was used to explore the impact of prehospital intubation on outcome, controlling for age, gender, mechanism, Glasgow Coma Scale score, Head/Neck AIS score, Injury Severity Score, and hypotension. Neural network analysis was performed to identify patients predicted to benefit from prehospital intubation.

RESULTS

A total of 13,625 patients from five trauma centers were included; overall mortality was 22.9%, and 19.3% underwent prehospital intubation. Logistic regression revealed an increase in mortality with prehospital intubation (odds ratio, 0.36; 95% confidence interval, 0.32-0.42; p < 0.001). This was true for all patients, for those with severe TBI (Head/Neck AIS score 4+ and/or Glasgow Coma Scale score of 3-8), and with exclusion of patients transported by aeromedical crews. Patients intubated in the field versus the emergency department had worse outcomes. Neural network analysis identified a subgroup of patients with more significant injuries as potentially benefiting from prehospital intubation.

CONCLUSION

Prehospital intubation is associated with a decrease in survival among patients with moderate-to-severe TBI. More critically injured patients may benefit from prehospital intubation but may be difficult to identify prospectively.

Die Behandlung des hämorrhagischen Schocks

The future of shock treatment depends on the importance of scientific results, and the willingness of physicians to optimize, and to reconsider established treatment protocols. There are four major potentially promising approaches to advanced trauma life support. First, control of hemorrhage by administration of local hemostatic agents, and a better, target-controlled management of the coagulation system. Second, improving intravascular volume by recruiting blood from the venous vasculature by preventing mistakes during mechanical ventilation, and by employing alternative spontaneous (i.e. use of the inspiratory threshold valve) or artificial ventilation strategies. In addition, artificial oxygen carriers may improve intravascular volume and oxygen delivery. Third, pharmacologic support of physiologic, endogenous mechanisms involved in the compensation phase of shock, and blockade of pathomechanisms that are known to cause irreversible vasoplegia (arginine vasopressin and K(ATP) channel blockers for hemodynamic stabilization). Fourth, employing potentially protective strategies such as mild or moderate hypothermia. Finally, the ultimate vision of trauma resuscitation is the concept of "suspended animation" as a form of delayed resuscitation after protection of vital organ systems.

Death by hyperventilation: A common and life-threatening problem during cardiopulmonary resuscitation

CONTEXT

This translational research initiative focused on the physiology of cardiopulmonary resuscitation (CPR) initiated by a clinical observation of consistent hyperventilation by professional rescuers in out-of-hospital cardiac arrest. This observation generated scientific hypotheses that could only ethically be tested in the animal laboratory.

OBJECTIVE

To examine the hypothesis that excessive ventilation rates during performance of CPR by overzealous but well-trained rescue personnel causes a significant decrease in coronary perfusion pressure and an increased likelihood of death.

DESIGN AND SETTING

In the in vivo human aspect of the study, we set out to objectively and electronically record rate and duration of ventilation during performance of CPR by trained professional rescue personnel in a prospective clinical trial in intubated, adult patients with out-of-hospital cardiac arrest. In the in vivo animal aspect of the study, to simulate the clinically observed hyperventilation, nine pigs in cardiac arrest were ventilated in a random order with 12, 20, or 30 breaths/min, and physiologic variables were assessed. Next, three groups of seven pigs in cardiac arrest were ventilated at 12 breaths/min with 100% oxygen, 30 breaths/min with 100% oxygen, or 30 breaths/min with 5% CO2/95% oxygen, and survival was assessed.

MAIN OUTCOME MEASURES

Ventilation rate and duration in humans; mean intratracheal pressure, coronary perfusion pressure, and survival rates in animals.

RESULTS

In 13 consecutive adults (average age, 63 +/- 5.8 yrs) receiving CPR (seven men) the average ventilation rate was 30 +/- 3.2 breaths/min (range, 15 to 49 breaths/min) and the average duration of each breath was 1.0 +/- 0.07 sec. The average percentage of time in which a positive pressure was recorded in the lungs was 47.3 +/- 4.3%. No patient survived. In animals treated with 12, 20, and 30 breaths/min, the mean intratracheal pressures and coronary perfusion pressures were 7.1 +/- 0.7, 11.6 +/- 0.7, 17.5 +/- 1.0 mm Hg/min (p < .0001) and 23.4 +/- 1.0, 19.5 +/- 1.8, 16.9 +/- 1.8 mm Hg (p = .03) with each of the different ventilation rates, respectively (p = comparison of 12 breaths/min vs. 30 breaths/min for mean intratracheal pressure and coronary perfusion pressure). Survival rates were six of seven, one of seven, and one of seven with 12, 30, and 30 + CO2 breaths/min, respectively (p = .006).

CONCLUSIONS

Despite seemingly adequate training, professional rescuers consistently hyperventilated patients during out-of-hospital CPR. Subsequent hemodynamic and survival studies in pigs demonstrated that excessive ventilation rates significantly decreased coronary perfusion pressures and survival rates, despite supplemental CO2 to prevent hypocapnia. This translational research initiative demonstrates an inversely proportional relationship between mean intratracheal pressure and coronary perfusion pressure during CPR. Additional education of CPR providers is urgently needed to reduce these newly identified and deadly consequences of hyperventilation during CPR. These findings also have significant implications for interpretation and design of resuscitation research, CPR guidelines, education, the development of biomedical devices, emergency medical services quality assurance, and clinical practice.

Increased myocardial matrix metalloproteinases in hypoxic newborn pigs during resuscitation: effects of oxygen and carbon dioxide

BACKGROUND

Perinatal asphyxia is associated with cardiac dysfunction, and it is important to prevent further tissue injury during resuscitation. There is increasing evidence that myocardial matrix metalloproteinases (MMPs) are involved in myocardial hypoxaemia-reoxygenation injury.

OBJECTIVE

To assess MMPs and antioxidant capacity in newborn pigs after global ischaemia and subsequent resuscitation with ambient air or 100% O(2) at different PaCO(2)-levels.

METHODS

Newborn pigs (12-36 h of age) were resuscitated for 30 min by ventilation with 21% or 100% O(2) at different PaCO(2) levels after a hypoxic insult, and thereafter observed for 150 min. In myocardial tissue extracts, MMPs were analyzed by gelatin zymography and broad matrix-degrading capacity (total MMP). Total endogenous antioxidant capacity in myocardial tissue extracts was measured by the oxygen radical absorbance capacity (ORAC) assay.

RESULTS

Matrix metalloproteinase-2 more than doubled from baseline values (P < 0.001), and was higher in piglets resuscitated with 100% O(2) than with ambient air (P = 0.012). The ORAC value was considerably decreased (P < 0.001). In piglets with elevated PaCO(2), total MMP-activity in the right ventricle was more increased than in the left ventricle (P = 0.008). In the left ventricle, total MMPactivity was higher in the piglets with low PaCO(2) than in the piglets with elevated PaCO(2) (P = 0.013).

CONCLUSION

In hypoxaemia-reoxygenation injury the MMP-2 level was highly increased and was most elevated in the piglets resuscitated with 100% O(2). Antioxidant capacity was considerably decreased. Assessed by total MMP-activity, elevated PaCO(2) during resuscitation might protect the left ventricle, and probably increase right ventricle injury of the myocardium.

Hyperventilation-Induced Hypotension During Cardiopulmonary Resuscitation

Background— A clinical observational study revealed that rescuers consistently hyperventilated patients during out-of-hospital cardiopulmonary resuscitation (CPR). The objective of this study was to quantify the degree of excessive ventilation in humans and determine if comparable excessive ventilation rates during CPR in animals significantly decrease coronary perfusion pressure and survival.

Methods and Results— In humans, ventilation rate and duration during CPR was electronically recorded by professional rescuers. In 13 consecutive adults (average age, 63±5.8 years) receiving CPR (7 men), average ventilation rate was 30±3.2 per minute (range, 15 to 49). Average duration per breath was 1.0±0.07 per second. No patient survived. Hemodynamics were studied in 9 pigs in cardiac arrest ventilated in random order with 12, 20, or 30 breaths per minute. Survival rates were then studied in 3 groups of 7 pigs in cardiac arrest that were ventilated at 12 breaths per minute (100% O 2 ), 30 breaths per minute (100% O 2 ), or 30 breaths per minute (5% CO 2 /95% O 2 ). In animals treated with 12, 20, and 30 breaths per minute, the mean intrathoracic pressure (mm Hg/min) and coronary perfusion pressure (mm Hg) were 7.1±0.7, 11.6±0.7, 17.5±1.0 ( P <0.0001), and 23.4±1.0, 19.5±1.8, and 16.9±1.8 ( P =0.03), respectively. Survival rates were 6/7, 1/7, and 1/7 with 12, 30, and 30+ CO 2 breaths per minute, respectively ( P =0.006).

Conclusions— Professional rescuers were observed to excessively ventilate patients during out-of-hospital CPR. Subsequent animal studies demonstrated that similar excessive ventilation rates resulted in significantly increased intrathoracic pressure and markedly decreased coronary perfusion pressures and survival rates.