Cooling to Facilitate Metabolic Suppression in Healthy Individuals

BACKGROUND: Carbon dioxide (CO₂) toxicity could be catastrophic for astronauts. Suppressing metabolism by lowering body temperature decreases CO₂ production and may facilitate rescue in the event of a crippled ship. Lowering body temperature requires shivering suppression. We evaluated dexmedetomidine to facilitate cooling of healthy individuals.METHODS: Following consent, we administered a 1 mcg · kg^-1 bolus of dexmedetomidine followed by continuous infusion (0.5-1.4 mcg · kg^-1 · h^-1) for 3 h of cooling. We cooled subjects using a bolus of 30 cc · kg^-1 of 4°C saline followed by surface cooling. We measured vital signs, thermal and comfort scales, sedation, and shivering for 3 h and during recovery. ANOVA evaluated changes in measures over time.RESULTS: Nine subjects completed the study. Mean age was 31 (SD 8) yr, mean mass was 71 (SD 14) kg, height of 168 (SD 9) cm, and body mass index of 25 (SD 3). Median time to 1°C drop in core temperature was 16 (IQR 15, 32) min. Temperature changed over time with median lowest temperature being 33.1°C (IQR 32.8°C, 34.1°C). Neither heart rate nor diastolic blood pressures changed over time. Systolic blood pressure decreased over time. Subjects responded to verbal stimuli and completed tasks throughout the protocol. During cooling and maintenance, subjects reported discomfort and the sensation of being cold.CONCLUSION: Dexmedetomidine facilitates shivering suppression during prolonged cooling in healthy individuals. Subjects are easily roused, have mild decreases in systolic blood pressure, and note sensations of discomfort and cold. Cooling to suppress metabolism is a feasible countermeasure to prolong astronaut endurance.Rittenberger JC, Flickinger KL, Weissman A, Repine M, Elmer J, Guyette FX, Callaway CW. Cooling to facilitate metabolic suppression in healthy individuals. Aerosp Med Hum Perform. 2019; 90(5):475-479.

Preliminary experience with point-of-care EEG in post-cardiac arrest patients

OBJECTIVE

Abnormal electroencephalography (EEG) patterns are common after resuscitation from cardiac arrest and have clinical and prognostic importance. Bedside continuous EEGs are not available in many institutions. We tested the feasibility of using a point-of-care system for EEG acquisition.

METHODS

We prospectively enrolled a convenience sample of post-cardiac arrest patients between 9/2015-1/2017. Upon hospital arrival, a limited EEG montage was applied. We tested both continuous EEG (cEEG) and this point-of-care EEG (eEEG). A board-certified epileptologist and a board-certified neurointensivist jointly reviewed all EEGs. Cohen's kappa coefficient evaluated agreement between eEEG and cEEG and Fisher's exact test evaluated their associations with survival to hospital discharge and proximate cause of death.

RESULTS

We studied 95 comatose post-cardiac arrest patients. Mean age was 59 (SD17) years. Most (61%) were male, few (N = 22; 23%) demonstrated shockable rhythms, and PCAC IV illness severity was present in 58 (61%). eEEG was interpretable in 57 (60%) subjects. The most common eEEG interpretations were: continuous (21%), generalized suppression (14%), burst-suppression (12%) and burst-suppression with identical bursts (10%). Seizures were detected in 2 eEEG subjects (2%). No patient with seizure or burst-suppression with identical bursts survived. cEEG demonstrated generalized suppression (31%), burst-suppression with identical bursts (27%), continuous (18%) and seizure (4%). The eEEG and cEEG demonstrated fair agreement (kappa = 0.27). Neither eEEG nor cEEG was associated with survival (p = 0.19; p = 0.11) or proximate cause of death (p = 0.14; p = 0.8) CONCLUSIONS: eEEG is feasible, although artifact often precludes interpretation. eEEG is fairly associated with cEEG and may facilitate post-cardiac arrest care.

EAST Multicenter Trial on targeted temperature management for hanging-induced cardiac arrest

BACKGROUND

We sought to determine the outcome of suicidal hanging and the impact of targeted temperature management (TTM) on hanging-induced cardiac arrest (CA) through an Eastern Association for the Surgery of Trauma (EAST) multicenter retrospective study.

METHODS

We analyzed hanging patient data and TTM variables from January 1992 to December 2015. Cerebral performance category score of 1 or 2 was considered good neurologic outcome, while cerebral performance category score of 3 or 4 was considered poor outcome. Classification and Regression Trees recursive partitioning was used to develop multivariate predictive models for survival and neurologic outcome.

RESULTS

A total of 692 hanging patients from 17 centers were analyzed for this study. Their overall survival rate was 77%, and the CA survival rate was 28.6%. The CA patients had significantly higher severity of illness and worse outcome than the non-CA patients. Of the 175 CA patients who survived to hospital admission, 81 patients (46.3%) received post-CA TTM. The unadjusted survival of TTM CA patients (24.7% vs 39.4%, p < 0.05) and good neurologic outcome (19.8% vs 37.2%, p < 0.05) were worse than non-TTM CA patients. However, when subgroup analyses were performed between those with an admission Glasgow Coma Scale score of 3 to 8, the differences between TTM and non-TTM CA survival (23.8% vs 30.0%, p = 0.37) and good neurologic outcome (18.8% vs 28.7%, p = 0.14) were not significant. Targeted temperature management implementation and post-CA management varied between the participating centers. Classification and Regression Trees models identified variables predictive of favorable and poor outcome for hanging and TTM patients with excellent accuracy.

CONCLUSION

Cardiac arrest hanging patients had worse outcome than non-CA patients. Targeted temperature management CA patients had worse unadjusted survival and neurologic outcome than non-TTM patients. These findings may be explained by their higher severity of illness, variable TTM implementation, and differences in post-CA management. Future prospective studies are necessary to ascertain the effect of TTM on hanging outcome and to validate our Classification and Regression Trees models.

LEVEL OF EVIDENCE

Therapeutic study, level IV; prognostic study, level III.

The effects of caffeine on heart rate variability in newborns with apnea of prematurity

OBJECTIVE

Apnea of prematurity is a common complication in premature newborns and caffeine is a widespread medication used to treat this complication. Caffeine may have adverse effects on the cardiovascular and central nervous system, yet its effects on the autonomic nervous system modulation of heart rate have not been studied in premature newborns, which was the objective of our study.

STUDY DESIGN

We prospectively studied 21 premature newborns who were treated with caffeine. We analyzed heart rate variability by power spectral density and by dynamic nonlinear analyses methods.

RESULT

There were no changes in heart rate, blood pressure or the autonomic nervous system tone following administration of caffeine, nor were the nonlinear dynamical properties of the system altered by caffeine.

CONCLUSION

Caffeine does not have detrimental effects on heart rate variability, heart rate or blood pressure in conventional doses given to premature newborns.

The effects of meperidine and epidural analgesia in labor on maternal heart rate variability

BACKGROUND

Epidural and parenteral opioid analgesia are two common methods of pain relief in labor that may influence the autonomic nervous system. However, these effects on laboring women have not yet been adequately studied. The aim of our study was to assess the effects of these two methods of analgesia on autonomic nervous system modulation of maternal heart rate variability in laboring women.

METHODS

A prospective observational study was conducted on 64 laboring women; 33 received epidural analgesia with bupivacaine and fentanyl and 31 intravenous meperidine and promethazine. Power spectral analysis and nonlinear methods were applied to digitized electrocardiograms performed before and after administration of analgesia, to assess maternal heart rate variability and autonomic equilibrium.

RESULTS

Maternal heart rate significantly increased in women who received meperidine compared to those who had epidural analgesia. There was a significant increase in the low-frequency to high-frequency ratio (3.7+/-3.9 vs. 1.8+/-1.6, P<0.05), and a significant decrease of high-frequency spectral power in women who had meperidine compared to those who received epidural analgesia (163+/-91 vs. 98+/-100 ms(2)/Hz, P<0.05).

CONCLUSIONS

Meperidine caused an autonomic nervous system shift towards sympathetic activation with abolition of respiratory sinus arrhythmia high-frequency spectral band. Conversely epidural analgesia had no significant effect on autonomic nervous system control of heart rate.

Standard vs atraumatic Whitacre needle for diagnostic lumbar puncture: a randomized trial

In order to define the impact of needle type on post-lumbar puncture headache (PLPH), we performed a prospective, randomized trial comparing the incidence of PLPH in patients undergoing lumbar punctures (LPs) with traumatic vs atraumatic 22-gauge needles. Fifty-eight patients underwent 85 LPs. The incidence of PLPH was 36% in the traumatic vs 3% in the atraumatic group (p = 0.002).