Platypnea-orthodeoxia related to aortic elongation.

An 80-year-old woman presented with progressive shortness of breath. There was no history of pulmonary or cardiac disease. Results of a physical examination were normal. She had significant oxygen desaturation while she was in an upright position. Admission to the hospital for workup followed, and evaluation included tilt-table transesophageal echocardiogram and cardiac catheterization. A massive right-to-left shunt through a patent foramen ovale was detected, and surgical intervention resulted in dramatic improvement of symptoms. In this patient, it seems that the syndrome of platypnea-orthodeoxia was related to aortic elongation, allowing significant right-to-left shunt.

Relationship between cardiac output and the end-tidal carbon dioxide tension.

STUDY OBJECTIVE: To further define the relationship between cardiac output (CO) and end-tidal carbon dioxide tension (ETCO2) at various levels of systemic flow. DESIGN: Prospective, controlled laboratory investigation. SETTING: Animal laboratory. TYPE OF PARTICIPANTS: Fourteen anesthetized, intubated sheep weighing 23 to 47 kg. INTERVENTIONS: One hundred seventy-two simultaneous measurements of thermodilution CO and ETCO2 were made during controlled arterial hemorrhage. After a 30-minute baseline control period, CO was sampled from approximately 0.6 to more than 8.0 L/min during a 60- to 90-minute period of controlled hemorrhage. MEASUREMENTS: Thermodilution CO; arterial pressure using fluid-filled plastic 14-gauge catheters; ETCO2 using an infrared analyzer. MAIN RESULTS: A plot of CO versus ETCO2 suggested that the relationship was logarithmic rather than linear. Linear regression showed that ETCO2 was significantly related (r = .91; P less than .001) to a logarithmic transformation of the CO. CONCLUSIONS: The relationship between CO and ETCO2 is logarithmic. Decreased presentation of CO2 to the lungs is the major, rate-limiting determinant of the ETCO2 during low flow. As the CO increases during resuscitation from shock or cardiac arrest, respiration becomes the rate-limiting controller of the ETCO2 (after the tissue washout of CO2 has occurred). Under such conditions, the ETCO2 provides useful information about the adequacy of ventilation provided that there is little ventilation/perfusion mismatch.

Dose-dependent vasopressor response to epinephrine during CPR in human beings.

The optimal dose of epinephrine during CPR in human beings is unknown. We studied ten prehospital cardiac arrest patients (six men and four women; mean age, 54 +/- 5 years) to determine the vasopressor response and change in the end-tidal carbon dioxide concentration (PetCO2) after incremental (1-, 3-, and 5-mg) doses of IV epinephrine given five minutes apart during closed-chest CPR. All patients were in ventricular fibrillation on arrival of the paramedics and did not respond to standard advanced cardiac life support. CPR was performed with a computerized Thumper; all patients were intubated and ventilated at 12 times a minute at an FiO2 of 0.8. Radial artery pressure was measured with a 20 angiocath inserted by radial artery cutdown. Paramedic response time was 4.3 +/- 0.5 minutes; elapsed time to emergency department arrival was 40.0 +/- 9.5 minutes. Initial blood gases were paO2, 241 +/- 50 mm Hg; pH, 7.23 +/- 0.08; paCO2, 27 +/- 5 mm Hg; and HCO3, 11 +/- 2 mEq/L. Baseline systolic and diastolic blood pressures were 47 +/- 5 mm Hg and 18 +/- 2 mm Hg, respectively. Systolic blood pressure was directly related to the dose of epinephrine (P less than .0001), rising to 69 +/- 7 mm Hg, 74 +/- 8 mm Hg, and 85 +/- 8 mm Hg after 1-, 3-, and 5-mg doses of epinephrine, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of applied chest compression force on systemic arterial pressure and end-tidal carbon dioxide concentration during CPR in human beings.

Twelve adult (nine men and three women) cardiac arrest patients were studied as they received CPR by a computerized Thumper to determine the influence of the applied chest compression force on blood flow (as assessed by the end-tidal carbon dioxide concentration) and arterial pressure. At the end of a resuscitation when the decision was made by the senior physician to cease resuscitative efforts, the applied force on the CPR Thumper was decreased from 140 to 0 pound-force (lbf) in 20-lbf increments at 30-second intervals. Radial artery cutdown blood pressure and end-tidal carbon dioxide (ETCO2) were recorded continuously. Arterial systolic blood pressure was linearly related (r = .59, P less than .0001) to applied force (systolic blood pressure, 31 +/- 6 mm Hg at 20 lbf to 60 +/- 7 mm Hg at 140 lbf). ETCO2 (r = .42, P less than .0001) was also linearly related to applied force (ETCO2, 0.7 +/- 0.1% at 20 lbf to 1.5 +/- 0.2% at 140 lbf). Diastolic pressure did not change significantly with change in applied force (17 +/- 2 mm Hg from 20 to 140 lbf). Our findings indicate that higher compression force than that currently recommended may improve arterial systolic pressure and flow in human beings receiving closed-chest compression during CPR.

Capnographic waveforms in esophageal intubation: effect of carbonated beverages.

Capnography is a useful tool in differentiating tracheal from esophageal intubation. It may be an especially useful tool in emergency airway management by rescue squads or in the emergency department. However, in clinical practice the question has arisen as to whether prior ingestion of carbonated beverages can generate false-positive capnographic evidence of endotracheal intubation when in fact esophageal intubation has occurred. To answer this question, we compared the difference between tracheal and esophageal capnographic waveforms in dogs in the setting of recent ingestion of carbonated beverages. Esophageal capnographic recordings from three of five dogs undergoing esophageal ventilation were strikingly positive for exhaled carbon dioxide; however, the waveforms were significantly different from waveforms of tracheal ventilation. We conclude that esophageal intubation, after recent ingestion of carbonated beverages, may give false-positive waveforms suggestive of tracheal intubation. Rapidly diminishing CO2 concentrations, however, help differentiate esophageal from tracheal ventilation in this setting.

Hypercarbic arterial acidemia following resuscitation from severe hemorrhagic shock.

Arteriovenous pH and PCO2 gradients can develop during low cardiac output states. We have seen a transient rise in arterial PCO2 and a fall in arterial pH in humans receiving closed-chest cardiopulmonary resuscitation immediately following restoration of spontaneous circulation. Using a hemorrhagic shock model in sheep, serial arterial and mixed venous blood gases were sampled and CO2 elimination was measured. When cardiac output was less than 30% of the baseline value and the arteriovenous PCO2 difference was greater than 20 mmHg, the animals were rapidly resuscitated with intravenous 0.9% NaCl and dopamine. Following resuscitation, there was a transient arterial acidosis and hypercarbia due to passage of venous blood with a high CO2 content into arterial blood. The clinical implications in the setting of hemorrhagic shock are that (1) arterial blood gases are poor indicators of the systemic acid-base state, (2) arterial blood gases drawn immediately following volume resuscitation may be misinterpreted and should probably not be used to guide therapy and (3) there is a transient hypercarbic arterial acidosis following volume resuscitation that may have deleterious effects on cardiac and cerebral function in the early post-resuscitative period.

Treatment of paroxysmal supraventricular tachycardia in the emergency department by clinical decision analysis.

Vagal maneuvers terminate new onset, catheter-induced paroxysmal supraventricular tachycardia (PSVT) in up to 92% of patients. The risk and benefit of vagal maneuvers for treating PSVT in the emergency department (ED) is inadequately defined. The purpose of this study was to determine the efficacy of nonpharmacological vagal interventions in converting spontaneous episodes of PSVT in adult patients and to derive a treatment plan for such patients based on clinical decision analysis. Seventeen adult patients who presented to the ED because of PSVT were treated with carotid sinus massage, Valsalva maneuver, and head-down tilt (alone and in combination). Only three patients converted out of PSVT with vagal intervention. The remainder received verapamil, which converted 12 of the 14 patients (86%) who received the drug (one required digoxin, one required synchronized cardioversion). Vagal maneuvers are safe in young, otherwise healthy patients but problems have been documented in the literature in older patients, who have a higher likelihood of coronary and/or cerebrovascular disease. Clinical decision analysis indicates that young patients should be treated initially with vagal maneuvers but that older patients (above approximately 65 years of age) should be treated initially with verapamil.

Effect of cardiopulmonary resuscitation compression rate on end-tidal carbon dioxide concentration and arterial pressure in man.

The optimal rate of chest compression during CPR in man has been debated. Recently, the end-tidal carbon dioxide concentration (PetCO2) has been shown to correlate with cardiac output during CPR in experimental animals. Eighteen prehospital cardiac arrest patients were studied to determine the effect of external chest compression rate on the PetCO2 and BP in man when ventilation rate, ventilation inspiration time, applied compression force, and a 50:50 downstroke:upstroke ratio were held constant using a microprocessor-controlled CPR Thumper. Compression rate was increased from 60 to 140/min in 20 beat/min increments. The PetCO2 was 1.7 +/- 0.2% at a compression rate of 60/min and did not change significantly at increased rates. Systolic BP fell progressively from 59 +/- 5 mm Hg at 60/min to 46 +/- 4 mm Hg at 140/min. Diastolic BP remained approximately 23 mm Hg at all rates studied. Using a CPR manikin, we found that greater Thumper compression force was necessary to sustain the same sternal displacement and to achieve the same applied sternal pressure when the rate was increased due to a rate-limited fall in the compression duration.

Cost-effectiveness of defibrillation by emergency medical technicians.

Effective emergency systems using emergency medical technicians (EMTs) trained to defibrillate or paramedics can save more lives from out-of-hospital cardiac arrest due to ventricular fibrillation than can emergency systems staffed with basic EMTs who cannot defibrillate. This article focuses on the cost-effectiveness of systems staffed with each type of EMT. Data were collected from all 50 states and from the District of Columbia to determine the number of hours and estimated cost of initial training for the three types of EMTs in the United States in 1986. The median initial training hours for basic EMTs, EMTs trained in defibrillation, and paramedics were 110, 129, and 700, respectively. Median costs for initial training at each EMT level were +123, +150, and +1580/student. According to published survival data for emergency medical systems staffed with EMTs at each level, the total initial training personnel and equipment cost per life saved from ventricular fibrillation was +7687, +2126, and +2289 for systems staffed by the respective EMTs. The initial cost per life saved from ventricular fibrillation is more than three times greater in systems staffed by basic EMTs than in systems staffed by EMTs trained in defibrillation or paramedics. From a medical and a cost-effective standpoint, all communities served by basic EMTs should consider upgrading them to at least the defibrillation-trained EMT level.

End-tidal carbon dioxide monitoring during cardiopulmonary resuscitation.

The end-tidal carbon dioxide (CO2) concentration has been found to correlate with cardiac output during and after cardiopulmonary resuscitation (CPR) in animal models. We monitored end-tidal CO2 values continuously during cardiac resuscitation in 23 humans while ventilation was held constant with a computer-controlled CPR Thumper. This report focuses on ten of the 23 patients who experienced return of spontaneous circulation (ROSC) during monitoring. There was no significant difference in the end-tidal CO2 value of patients without ROSC (1.8% +/- 0.9%) and the end-tidal CO2 value of patients before ROSC in patients who had ROSC (1.7% +/- 0.6%). The end-tidal CO2 concentration increased immediately in all patients who had ROSC, from 1.7% +/- 0.6% to 4.6% +/- 1.4%, then gradually returned to a new baseline (3.1% +/- 0.9%). Change in the end-tidal CO2 value was often the first clinical indicator that ROSC had occurred. Our findings suggest that end-tidal CO2 monitoring may provide clinically useful information that can be used to guide therapy during CPR.

Bacterial contamination of ambulance oxygen humidifier water reservoirs: a potential source of pulmonary infection.

The risk and benefit of oxygen humidification during ambulance transport is unknown. We cultured the water in plastic multiple-use bottles of humidifiers on 30 randomly selected area ambulances during November 1985. There were 22 positive cultures. Potentially pathogenic bacteria (four Pseudomonas maltophilia, three Pseudomonas aeruginosa, one Klebsiella pneumoniae, and one Staphylococcus epidermidis) were found in nine samples. Assuming that the water in ambulance humidifiers should have been sterile, the findings are statistically significant (P less than .01). Because there is no evidence that humidification is of benefit for nonintubated patients receiving oxygen at flow rates of 4 L/min or less when environmental humidity is adequate, we suggest that such patients should receive oxygen without humidification during ambulance transport. All other patients requiring oxygen during ambulance transport should continue to receive humidified oxygen. If a multiple-use humidifier reservoir is to be used, a written policy for its use must be developed and there must be appropriate documentation of compliance with the policy. An alternative is to replace the multiple-use humidifier reservoir with single-use sterile disposable devices, which cost approximately $2.00 per unit.