A comparison of the physiological effects of hypercapnia and hypoxia in the production of cardiac arrest

In the Nick of Time-Emergency Front-of-Neck Airway Access

Emergency front-of-neck access refers to all techniques that deliver oxygen into the airway lumen through the anterior neck structures and encompasses access both through the cricothyroid membrane and the tracheal wall. There has yet to be a universal agreement regarding the preferred technique. A surgical incision is currently the most common approach in prehospital and in-hospital care. This review intends to review and summarize the existing clinical, basic science, and societal guidelines for eFONA.

Continuous Heart Rate Dynamics Preceding In-Hospital Pulseless Electrical Activity or Asystolic Cardiac Arrest of Respiratory Etiology

INTRODUCTION

Respiratory failure is a common cause of pulseless electrical activity (PEA) and asystolic cardiac arrest, but the changes in heart rate (HR) pre-arrest is not well described. We describe HR dynamics prior to in-hospital cardiac arrest (IHCA) among PEA/asystole arrest patients with respiratory etiology.

METHODS

In this retrospective study, we evaluated 139 patients with 3-24 hours of continuous electrocardiogram data recorded preceding PEA/asystole IHCA from 2010-2017. We identified respiratory failure cases by chart review and evaluated electrocardiogram data to identify patterns of HR changes, sinus bradycardia or sinus arrest, escape rhythms, and development right ventricular strain prior to IHCA.

RESULTS

A higher proportion of respiratory cases (58/73, 79%) fit a model of HR response characterized by tachycardia followed by rapid HR decrease prior to arrest, compared to non-respiratory cases (30/66, 45%, p<0.001). Among the 58 respiratory cases fitting this model, 36 (62%) had abrupt increase in HR occurring 64 (IQR 23-191) minutes prior to arrest, while 22 (38%) had stable tachycardia until time of HR decrease. Mean peak HR was 123±21 bpm. HR decrease occurred 3.0 (IQR 2.0-7.0) minutes prior to arrest. Sinus arrest occurred during the bradycardic phase in 42/58 of cases; escape rhythms were present in all but 2/42 (5%) cases. Right ventricular strain ECG pattern, when present, occurred at a median of 2.2 (IQR -0.05-17) minutes prior to onset of HR decrease.

CONCLUSION

IHCAs of respiratory etiology follow a model of HR increase from physiologic compensation to hypoxia, followed by rapid HR decrease prior to arrest.

Development of a Translational Model to Assess the Impact of Opioid Overdose and Naloxone Dosing on Respiratory Depression and Cardiac Arrest

In response to a surge of deaths from synthetic opioid overdoses, there have been increased efforts to distribute naloxone products in community settings. Prior research has assessed the effectiveness of naloxone in the hospital setting; however, it is challenging to assess naloxone dosing regimens in the community/first-responder setting, including reversal of respiratory depression effects of fentanyl and its derivatives (fentanyls). Here, we describe the development and validation of a mechanistic model that combines opioid mu receptor binding kinetics, opioid agonist and antagonist pharmacokinetics, and human respiratory and circulatory physiology, to evaluate naloxone dosing to reverse respiratory depression. Validation supports our model, which can quantitatively predict displacement of opioids by naloxone from opioid mu receptors in vitro, hypoxia-induced cardiac arrest in vivo, and opioid-induced respiratory depression in humans from different fentanyls. After validation, overdose simulations were performed with fentanyl and carfentanil followed by administration of different intramuscular naloxone products. Carfentanil induced more cardiac arrest events and was more difficult to reverse than fentanyl. Opioid receptor binding data indicated that carfentanil has substantially slower dissociation kinetics from the opioid receptor compared to 9 other fentanyls tested, which likely contributes to the difficulty in reversing carfentanil. Administration of the same dose of naloxone intramuscularly from 2 different naloxone products with different formulations resulted in differences in the number of virtual patients experiencing cardiac arrest. This work provides a robust framework to evaluate dosing regimens of opioid receptor antagonists to reverse opioid-induced respiratory depression, including those caused by newly emerging synthetic opioids.

Cardiovascular effects of intravenous pimobendan in dogs with acute respiratory acidosis

OBJECTIVE

Acidosis decreases myocardial contractile and myofibrillar responsiveness by reducing the calcium sensitivity of contractile proteins, which could reduce the effectiveness of pimobendan. We aimed to assess the cardiovascular effects of pimobendan in dogs subjected to acute respiratory acidosis.

DESIGN

Randomized crossover study with a 2-week washout period.

SETTING

University Laboratory.

ANIMALS

Six healthy research Beagle dogs.

INTERVENTIONS

Anesthetized dogs were administered 2 doses of IV pimobendan during conditions of eucapnia (Paco2 35-40 mm Hg) and hypercapnia (Paco2 90-110 mm Hg). Eucapnia was maintained by positive pressure ventilation and hypercapnia was induced by adding exogenous CO2 to the anesthesia circuit. Heart rate (HR), systemic arterial blood pressure, cardiac output (CO), systemic and pulmonary vascular resistance (SVR and PVR, respectively), and pulmonary arterial pressure (PAP) were measured at baseline and 60 min after administering 0.125 mg/kg (low) and 0.25 mg/kg (high) pimobendan intravenously. Blood gas and biochemical analyses were performed at baseline and at the end of the experiment.

MEASUREMENTS AND MAIN RESULTS

The median baseline blood pH was 7.41 (range: 7.33-7.45) and 7.03 (range: 6.98-7.09) under conditions of eucapnia and hypercapnia, respectively. The serum concentrations of epinephrine and norepinephrine and the HR, CO, and PAP were higher, and SVR was lower at baseline in hypercapnic dogs. Pimobendan dose-dependently increased CO in eucapnia (baseline: 3.6 ± 0.2 L/kg/m2 [mean ± SE], low: 5.0 ± 0.4 L/kg/m2 , high: 5.8 ± 0.5 L/kg/m2 , P < 0.001) and hypercapnia (baseline: 4.9 ± 0.5 L/kg/m2 , low: 5.8 ± 0.5 L/kg/m2 , high: 6.2 ± 0.5 L/kg/m2 , P < 0.001), and increased HR and decreased SVR and PVR under both conditions (P < 0.001). In hypercapnia, the degree of increase or decrease of these cardiovascular measurements (except for PAP) by pimobendan was less than that in the eucapnic dogs.

CONCLUSIONS

Pimobendan maintains function as an inodilator in anesthetized dogs with induced respiratory acidosis.

Electrocardiographic right ventricular strain precedes hypoxic pulseless electrical activity cardiac arrests: Looking beyond pulmonary embolism

AIM

The role of the right ventricle (RV) in pulseless electrical activity (PEA) is poorly defined outside of pulmonary embolism. We aimed to (1) describe the continuous electrocardiographic (ECG) manifestations of RV strain (RVS) preceding PEA/Asystole in-hospital cardiac arrest (IHCA), and (2) determine the prevalence and clinical causes of RVS in PEA/Asystole IHCA.

METHODS

In this retrospective cross-sectional study, we evaluated 140 patients with continuous ECG data preceding PEA/Asystole IHCA. We iteratively defined the RVS continuous ECG pattern using the development cohort (93 patients). Clinical cause determination was blinded from ECG analysis in the validation cohort (47 patients).

RESULTS

The overall cohort had mean age 62.1 ± 17.1 years, 70% return of spontaneous circulation and 30% survival to discharge. RVS continuous ECG pattern was defined as progressive RV depolarization delay in lead V1 with at least one supporting finding of RV ischaemia or right axis deviation. Using this criterion, 66/140 (47%) cases showed preceding RVS. In patients with RVS, no pulmonary embolism was found in 9/13 (69%) autopsies and 8/10 (80%) CT chest angiograms. The positive and negative predictive value of RVS pattern for diagnosing a respiratory cause of PEA/Asystole in the validation cohort was 81% [95% CI 64-98%] and 58% [95% CI 36-81%], respectively.

CONCLUSION

RVS continuous ECG pattern preceded 47% of PEA/Asystole IHCA and is predictive of a respiratory cause of cardiac arrest, not just pulmonary embolism. These suggest that rapid elevations in pulmonary pressures and resultant RV failure may cause PEA in respiratory failure.

Cardiovascular effects of intravenous colforsin in normal and acute respiratory acidosis canine models: A dose-response study

In acidosis, catecholamines are attenuated, and higher doses are often required to improve cardiovascular function. Colforsin activates adenylate cyclase in cardiomyocytes without beta-adrenoceptor. Here, six beagles were administered colforsin or dobutamine four times during eucapnia (partial pressure of arterial carbon dioxide 35–40 mm Hg; normal) and hypercapnia (ibid 90–110 mm Hg; acidosis) conditions. The latter was induced by CO₂ inhalation. Anesthesia was induced with propofol and maintained with isoflurane. Cardiovascular function was measured by thermodilution and a Swan-Ganz catheter at baseline and 60 min after 0.3 μg/kg/min (low), 0.6 μg/kg/min (middle), and 1.2 μg/kg/min (high) colforsin administration. The median pH was 7.38 [range 7.33–7.42] and 7.01 [range 6.96–7.08] at baseline in the Normal and Acidosis conditions, respectively. Endogenous adrenaline and noradrenaline levels at baseline were significantly (P < 0.05) higher in the Acidosis than in the Normal condition. Colforsin induced cardiovascular effects similar to those caused by dobutamine. Colforsin increased cardiac output in the Normal condition (baseline: 3.9 ± 0.2 L/kg/m² [mean ± standard error], low: 5.2 ± 0.4 L/kg/min², middle: 7.0 ± 0.4 L/kg/m², high: 9.4 ± 0.2 L/kg/m²; P < 0.001) and Acidosis condition (baseline: 6.1 ± 0.3 L/kg/m², low: 6.2 ± 0.2 L/kg/m², middle: 7.2 ± 0.2 L/kg/m², high: 8.3 ± 0.2 L/kg/m²; P < 0.001). Colforsin significantly increased heart rate and decreased systemic vascular resistance compared to values at baseline. Both drugs increased pulmonary artery pressure, but colforsin (high: 13.3 ± 0.6 mmHg in Normal and 20.1 ± 0.2 mmHg in Acidosis) may have lower clinical impact on the pulmonary artery than dobutamine (high: 19.7 ± 0.6 in Normal and 26.7 ± 0.5 in Acidosis). Interaction between both drugs and experimental conditions was observed in terms of cardiovascular function, which were similarly attenuated with colforsin and dobutamine under acute respiratory acidosis.

Cardiovascular, respiratory and metabolic responses to apnea induced by atlanto-occipital intrathecal lidocaine injection in anesthetized horses

OBJECTIVE

To determine physiologic responses to apnea-induced severe hypoxemia in anesthetized horses.

STUDY DESIGN

Prospective experimental study.

ANIMALS

Six university-owned horses with a median (range) body weight of 500 (220-510) kg and aged 13.5 (0.8-24.0) years scheduled for euthanasia.

METHODS

Xylazine-midazolam-ketamine-anesthetized horses breathing room air spontaneously were instrumented with a facial artery catheter for pressure measurement and blood sampling, and were made apneic with atlanto-occipital intrathecal lidocaine (4 mg kg^-1 ). Cardiopulmonary, biochemical and hematologic variables were recorded before (baseline) and every minute for 10 minutes after lidocaine injection.

RESULTS

PaO₂ values were: baseline, 55 mmHg (7.3 kPa); 1 minute, 28 mmHg (3.8 kPa); 2 minutes, 18 mmHg (2.4 kPa); 3 minutes, 15 mmHg (2.0 kPa), and 4-10 minutes, (8-11 mmHg (1.1-1.5 kPa). PaCO₂ values were: baseline, 50 mmHg (6.7 kPa); 1 minute, 61 mmHg (8.1 kPa), and 2-10 minutes, 64-66 mmHg (8.5-8.8 kPa). Base excess values at baseline, 1 minute and 2-10 minutes were 5.3 mmol L^-1 , 6.5 mmol L^-1 and 7.0-8.1 mmol L^-1 , respectively. Pulse rates at baseline, 1 minute and 2-7 minutes were 36, 53 and 54-85 beats minute^-1 , respectively. Asystole occurred at 8 minutes. Pulse pressures were 50 mmHg at baseline and 1 minute, and 39 mmHg, 31 mmHg, 22 mmHg, 17 mmHg and 1-9 mmHg at 2, 3, 4, 5 and 6-10 minutes, respectively. Lactate was 0.9 mmol L^-1 at baseline, progressively increasing to 1.7-2.4 mmol L^-1 at 7-10 minutes. Packed cell volume increased after 7 minutes of apnea. There were no other major changes.

CONCLUSIONS AND CLINICAL RELEVANCE

Apnea immediately exacerbated hypoxemia and hypercapnia and rapidly caused hemodynamic instability. Apnea in hypoxemic anesthetized horses is associated with a serious risk for progress to cardiovascular collapse.

Olfactory Hallucinations without Clinical Motor Activity: A Comparison of Unirhinal with Birhinal Phantosmia

Olfactory hallucinations without subsequent myoclonic activity have not been well characterized or understood. Herein we describe, in a retrospective study, two major forms of olfactory hallucinations labeled phantosmias: one, unirhinal, the other, birhinal. To describe these disorders we performed several procedures to elucidate similarities and differences between these processes. From 1272, patients evaluated for taste and smell dysfunction at The Taste and Smell Clinic, Washington, DC with clinical history, neurological and otolaryngological examinations, evaluations of taste and smell function, EEG and neuroradiological studies 40 exhibited cyclic unirhinal phantosmia (CUP) usually without hyposmia whereas 88 exhibited non-cyclic birhinal phantosmia with associated symptomology (BPAS) with hyposmia. Patients with CUP developed phantosmia spontaneously or after laughing, coughing or shouting initially with spontaneous inhibition and subsequently with Valsalva maneuvers, sleep or nasal water inhalation; they had frequent EEG changes usually ipsilateral sharp waves. Patients with BPAS developed phantosmia secondary to several clinical events usually after hyposmia onset with few EEG changes; their phantosmia could not be initiated or inhibited by any physiological maneuver. CUP is uncommonly encountered and represents a newly defined clinical syndrome. BPAS is commonly encountered, has been observed previously but has not been clearly defined. Mechanisms responsible for phantosmia in each group were related to decreased gamma-aminobutyric acid (GABA) activity in specific brain regions. Treatment which activated brain GABA inhibited phantosmia in both groups.

Unrecognized severe postoperative hypercapnia: a case of apneic oxygenation

Transcutaneous pulse oximetry is increasingly being used to supplant arterial blood gas measurement as a means to monitor oxygenation. Previous studies have demonstrated that, despite inadequate ventilation, oxygenation can be maintained during delivery of supplemental oxygen by a process known as diffusion respiration. In this setting, severe hypercapnia and acidosis rapidly develop. This case report demonstrates that pulse oximetry is an unreliable means to monitor adequacy of ventilation. A 75-year-old woman in good health suffered a fracture of the right hip that necessitated arthroplasty. During postoperative recovery, she remained unresponsive while receiving 100% oxygen through an endotracheal tube; mechanical ventilation was not used. Pulse oximetry indicated a blood oxygen saturation of 94 to 96%; however, results of blood gas studies 3 1/2 hours postoperatively revealed profound hypercapnia (arterial carbon dioxide tension, 265 mm Hg) and acidosis (pH, 6.65) but confirmed normal oxygen levels (arterial oxygen tension, 213 mm Hg). Assisted ventilation resulted in normalization of the blood gases and an improved level of consciousness. The patient was then transferred to Mayo Clinic Rochester and had an uneventful recovery.

Anesthetic complications in the horse

The basis for management of all complications is early recognition, preparation, and a problem-solving approach. Some anesthetic complications, such as equipment malfunction and injuries from endotracheal intubation or misplaced drug injections, are common to all animals and can be prevented almost entirely by careful management. Other problems, such as pulmonary dysfunction and cardiovascular depression, seem to occur more often in healthy horses than in healthy members of other domestic species. Postoperative myopathy-neuropathy, sometimes a devastating complication, seems to be peculiar to the horse, and its incidence has been linked to hypotensive inhalant anesthesia. Careful positioning and padding, monitoring of anesthetic depth, and treating of cardiovascular depression may prevent most cases of postanesthetic myopathy. Idiosyncratic drug reactions, such as MH, are entirely unpredictable and can be rapidly fatal unless recognized early and treated vigorously and specifically.

Stability of brain intracellular lactate and 31P-metabolite levels at reduced intracellular pH during prolonged hypercapnia in rats

The tolerance of low intracellular pH (pHi) was examined in vivo in rats by imposing severe, prolonged respiratory acidosis. Rats were intubated and ventilated for 10 min with 20% CO2, for 75 min with 50% CO2, and for 10 min with 20% CO2. The maximum PaCO2 was 320 mm Hg. Cerebral intracellular lactate, pHi, and high-energy phosphate metabolites were monitored in vivo with 31P and 1H nuclear magnetic resonance (NMR) spectroscopy, using a 4.7-T horizontal instrument. Within 6 min after the administration of 50% CO2, pHi fell by 0.57 +/- 0.03 unit, phosphocreatine decreased by approximately 20%, and Pi increased by approximately 100%. These values were stable throughout the remainder of the hypercapnic period. Cerebral intracellular lactate, visible with 1H NMR spectroscopy in the hyperoxic state, decreased during hypercapnia, suggesting either a favorable change in oxygen availability (decreased lactate production) or an increase in lactate clearance or both. All hypercapnic animals awakened and behaved normally after CO2 was discontinued. Histological examination of cortical and hippocampal areas, prepared using a hematoxylin and eosin stain, showed no areas of necrosis and no glial infiltrates. However, isolated, scattered, dark-staining, shrunken neurons were detected both in control animals (no exposure to hypercapnia) and in animals that had been hypercapnic. This subtle histological change could represent an artifact resulting from imperfect perfusion-fixation, or it could represent subtle neurologic injury during the hypercapnia protocol. In summary, extreme hypercapnia and low pHi (approximately 6.5) are well tolerated in rats for periods up to 75 min if adequate oxygenation is maintained.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of arterial oxygenation during anaesthesia

The clinical or physiological signs of hypoxaemia have limited value during anaesthesia. In the absence of surgical bleeding, the best signs are probably cyanosis and/or bradycardia-although neither is sensitive or specific. A moderate degree of hypoxaemia can be present without clinical signs! In the presence of surgical bleeding, the best sign may be darkening of fresh blood in the surgical field. The only reliable indicators of arterial oxygenation available for routine anaesthesia are the laboratory measurements of PaO2 and SaO2. Unfortunately, these measurements are intermittent and delayed. The modern Hewlett Packard and Biox ear oximeters can provide an immediate and continuous estimate of arterial oxygen saturation in anaesthetized humans. These instruments are extremely useful in clinical practice when the risks of hypoxaemia or hypoxaemic injury are high. Unfortunately, cost precludes their general use. The safety of anaesthesia would no doubt be improved with an inexpensive reliable monitor of arterial oxygenation.

Management of the patient with a prosthetic heart valve

Approximately 20,000 heart valve prostheses are inserted yearly in the United States. Even after successful heart operations, the patients who receive them cannot be regarded as healthy individuals but are a special group with special problems who need close medical attention for the rest of their lives. They are susceptible to many unusual complications because of their implanted foreign body, and it is a challenge to all physicians in contact with them to be aware of their peculiar problems in order to prevent complications if possible and to treat them immediately if they occur. General therapy, surgical complications, infection, and mechanical problems are reviewed, with means for management outlined. These difficulties can be dealt with only by careful follow-up and well-coordinated teamwork between the family physician and the institution where the operation was performed.

ACID-BASE CHANGES AND TISSUE RESPIRATION IN EXTRACORPOREAL CIRCULATION

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