Anesthesiology. First of two parts.

Sleep-induced apnea and disordered breathing refers to intermittent, cyclical cessations or reductions of airflow, with or without obstructions of the upper airway (OSA). In the presence of an anat...

Pathophysiology of Sleep Apnea

In mechanically ventilated patients with acute circulatory failure related to sepsis, we investigated whether the respiratory changes in arterial pressure could be related to the effects of volume expansion (VE) on cardiac index (CI). Forty patients instrumented with indwelling systemic and pulmonary artery catheters were studied before and after VE. Maximal and minimal values of pulse pressure (Pp(max) and Pp(min)) and systolic pressure (Ps(max) and Ps(min)) were determined over one respiratory cycle. The respiratory changes in pulse pressure (DeltaPp) were calculated as the difference between Pp(max) and Pp(min) divided by the mean of the two values and were expressed as a percentage. The respiratory changes in systolic pressure (DeltaPs) were calculated using a similar formula. The VE-induced increase in CI was >/= 15% in 16 patients (responders) and < 15% in 24 patients (nonresponders). Before VE, DeltaPp (24 +/- 9 versus 7 +/- 3%, p < 0.001) and DeltaPs (15 +/- 5 versus 6 +/- 3%, p < 0.001) were higher in responders than in nonresponders. Receiver operating characteristic (ROC) curves analysis showed that DeltaPp was a more accurate indicator of fluid responsiveness than DeltaPs. Before VE, a DeltaPp value of 13% allowed discrimination between responders and nonresponders with a sensitivity of 94% and a specificity of 96%. VE-induced changes in CI closely correlated with DeltaPp before volume expansion (r(2) = 0. 85, p < 0.001). VE decreased DeltaPp from 14 +/- 10 to 7 +/- 5% (p < 0.001) and VE-induced changes in DeltaPp correlated with VE-induced changes in CI (r(2) = 0.72, p < 0.001). It was concluded that in mechanically ventilated patients with acute circulatory failure related to sepsis, analysis of DeltaPp is a simple method for predicting and assessing the hemodynamic effects of VE, and that DeltaPp is a more reliable indicator of fluid responsiveness than DeltaPs.

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Relation between respiratory changes in arterial pulse pressure and fluid responsiveness in septic patients with acute circulatory failure.

Predicting Fluid Responsiveness in ICU Patients: A Critical Analysis of the Evidence

We applied a continuous positive airway pressure to 20 infants (birth weight 930 to 3800 g) severely ill with the idiopathic respiratory-distress syndrome. They breathed spontaneously. Pressure, up to 12 mm of mercury, was delivered through an endotracheal tube to 18 infants and via a pressure chamber around the infant's head to two. Arterial oxygen tension rose in all, permitting us to lower the inspired oxygen an average of 37.5 per cent within 12 hours. Minute ventilation decreased with increased continuous positive airway pressure, but this had little effect on arterial carbon dioxide tension, pH, arterial blood pressure and lung compliance. Sixteen infants survived, including seven of 10 weighing less than 1500 g at birth.

Treatment of the Idiopathic Respiratory-Distress Syndrome with Continuous Positive Airway Pressure

The hemodynamic effects of intermittent positive pressure ventilation were studied in lightly anesthetized dogs following recovery from implantation of pulsed ultrasonic flow transducers on the aorta and vena cava. A partial rebreathing system was utilized to maintain constant PaCO. Data were obtained during spontaneous respiration and using a respirator, with peak airway pressures of 10, 20 and 30 cm. of water, inspiratory to expiratory ratios of 1:2, 1:1 and 2:1. Maximum values for stroke volume and cardiac output occurred during spontaneous breathing. Cardiac output and aortic stroke volume decreased with increasing airway pressure and increasing inspiratory to expiratory ratios. Venous return was inhibited by increasing pressure, and changes in vena caval flow were reflected in changes in aortic flow within the time of two heart beats. The circulatory effects of positive pressure breathing are related to the mean intrathoracic pressure and the effect on venous return.

Hemodynamic Effects of Intermittent Positive Pressure Respiration

To assess the possibility that climbing to extremely high altitude may result in hypoxic injury to the brain, we performed neuropsychological and physiologic testing on 35 mountaineers bef...

The cost to the central nervous system of climbing to extremely high altitude.

Context Substance use disorders among physicians are important and persistent problems. Considerable debate exists over whether use of major opioids, especially among anesthesiologists, is associated with a higher relapse rate compared with alcohol and nonopioids. Moreover, the risk factors for relapse with current treatment and monitoring strategies are unknown. Objective To test the hypothesis that chemically dependent health care professionals using a major opioid (eg, fentanyl, sufentanil, morphine, meperidine) as drug of choice are at higher risk of relapse. Design, Setting, and Participants Retrospective cohort study of 292 health care professionals enrolled in the Washington Physicians Health Program, an independent posttreatment monitoring program, followed up between January 1, 1991, and December 31, 2001. Main Outcome Measure Factors associated with relapse, defined as the resumption of substance use after initial diagnosis and completion of primary treatment for chemical dependency. Results Twenty-five percent (74 of 292 individuals) had at least 1 relapse. A family history of a substance use disorder increased the risk of relapse (hazard ratio [HR], 2.29; 95% confidence interval [CI], 1.44-3.64). The use of a major opioid increased the risk of relapse significantly in the presence of a coexisting psychiatric disorder (HR, 5.79; 95% CI, 2.89-11.42) but not in the absence of a coexisting psychiatric disorder (HR, 0.85; 95% CI, 0.33-2.17). The presence of all 3 factors— major opioid use, dual diagnosis, and family history—markedly increased the risk of relapse (HR, 13.25; 95% CI, 5.22-33.59). The risk of subsequent relapses increased after the first relapse (HR, 1.69; 95% CI, 1.13-2.53). Conclusions The risk of relapse with substance use was increased in health care professionals who used a major opioid or had a coexisting psychiatric illness or a family history of a substance use disorder. The presence of more than 1 of these risk factors and previous relapse further increased the likelihood of relapse. These observations should be considered in monitoring the recovery of health care professionals.

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Risk factors for relapse in health care professionals with substance use disorders.

Quantitation of chemoreceptor activity: interrelation of hypoxia and hypercapnia.

The Growth of Knowledge About Air, Breathing, and Circulation as They Relate to High AltitudeCharles S. HoustonThe AtmosphereJohn B. WestThe PeopleSusan Niermeyer, Stacy Zamudio, and Lorna G. MooreCellular and Molecular Mechanisms of O2 Sensing with Special Reference to the Carotid BodySukhamay Lahiri and Neil S. CherniackMolecular/Metabolic Defense and Rescue Mechanisms for Surviving Oxygen Lack: From Genes to PathwaysPeter W. HochachkaControl of Breathing at High AltitudeCurtis A. Smith, Jerome A. Dempsey, and Thomas F. HornbeinMechanics of BreathingJoseph Milic-Emili, Bengt Kayser, and Henry GautierGas ExchangePeter D. WagnerThe Cardiovascular System at High Altitude: Heart and Systemic CirculationEugene E. Wolfel and Benjamin D. LevineThe Pulmonary Circulation at High AltitudeJohn T. Reeves and Kurt R. StenmarkCerebral Circulation at High AltitudeJohn W. SeveringhausThe High-Altitude BrainMarcus E. Raichle and Thomas F. HornbeinAutonomic Nervous SystemDouglas R. Seals, Pamela Parker Jones, and Kevin P. DavyThe Effects of Altitude on Skeletal MuscleHoward J. Green and John R. SuttonBloodRobert F. Grover and Peter B?rtschRenal Function and Fluid HomeostasisErik R. SwensonMetabolic Responses of Lowlanders to High-Altitude Exposure: Malnutrition Versus the Effect of HypoxiaGeorge A. Brooks and Gail E. ButterfieldThe Endocrine SystemJean-Paul RichaletHigh Altitude and Human Immune ResponsivenessRichard T. Meehan, Peter N. Uchakin, and Clarence F. SamsExercise and Hypoxia: Performance, Limits, and TrainingRobert Roach and Bengt KayserSleepJohn V. Weil and David P. WhiteAcute Mountain Sickness and High-Altitude Cerebral EdemaPeter B?rtsch, Robert. Roach, and Diana DeplaHigh-Altitude Pulmonary EdemaRobert B. Schoene, Herbert N. Hultgren, and Erik R. SwensonChronic Mountain Sickness in AndeansCarlos C. Monge, Fabiola L?on-Velarde, and Alberto ArreguiHigh Altitude and Common Medical ConditionsPeter H. Hackett

Thomas F. Hornbein

Papers

Hemodynamic Effects of Intermittent Positive Pressure Respiration

The cost to the central nervous system of climbing to extremely high altitude.

Risk factors for relapse in health care professionals with substance use disorders.

Quantitation of chemoreceptor activity: interrelation of hypoxia and hypercapnia.

High Altitude : An Exploration of Human Adaptation