John B. Downs

Is Epinephrine Contraindicated During Cardiopulmonary Resuscitation

BACKGROUNDnWhy pulmonary gas exchange deteriorates after administration of epinephrine during cardiopulmonary resuscitation (CPR) is unclear.nnnMETHODS AND RESULTSnForty-four anesthetized swine received an infusion of six inert gases. Animals underwent ventricular fibrillation with CPR and intravenous administration of saline (control), epinephrine (15 microg/kg), or methoxamine (150 microg/kg). Cardiac output, aortic blood pressure, pH, and arterial oxygen saturation were recorded. Distributions of VA and Q were determined by the multiple inert gas elimination technique. Ventricular fibrillation and CPR caused significant decreases in cardiac output, aortic blood pressure, and arterial pH. With epinephrine (versus saline), diastolic blood pressure was significantly higher (23+/-7 versus 8+/-4 mm Hg), but the increase in shunt (from 7+/-4% to 29+/-17%) and the reduction in SaO2 (from 99.7% to 76.8%) were significantly larger. Also, the increase in dead space was greater and elimination of CO2 less. There were no differences between animals given methoxamine or saline, except for increased diastolic blood pressure.nnnCONCLUSIONSnDuring experimental ventricular fibrillation and CPR, epinephrine increased intrapulmonary shunt approximately 300% more than saline or methoxamine and significantly reduced arterial oxygen saturation. We suspect that the beta-adrenergic receptor activity of epinephrine attenuated hypoxic pulmonary vasoconstriction. Methoxamine is as effective a pressor as epinephrine for CPR and devoid of beta-adrenergic activity. We recommend that such an agent be considered, instead of epinephrine, for CPR.

Continuous thermodilution cardiac output: agreement with Fick and bolus thermodilution methods.

OBJECTIVEnCardiac outputs were determined with continuous thermodilution, bolus thermodilution, and the Fick method during pharmacologically varied hemodynamics.nnnDESIGNnProspective comparison of techniques.nnnSETTINGnUniversity animal laboratory.nnnPARTICIPANTSnSwine.nnnINTERVENTIONSnSwine were anesthetized, tracheally intubated, and instrumented to measure continuous (QTDC) and bolus (QTDB) thermodilution cardiac outputs and sample arterial and mixed venous blood. Continuous thermodilution of blood was facilitated by computer modulation of a thermal filament wrapped around the portion of the pulmonary artery catheter residing in the right atrium and ventricle. QTDC was computed from the thermodilution curve monitored by the thermistor. Bolus thermodilution was performed in triplicate by injecting 10 mL of 5% dextrose in water (0 to 4 degrees C). Oxygen consumption (VO2) was calculated as the averaged minute rate of disappearance of spirometer oxygen over a 6-minute steady state. Cardiac output was determined with the direct Fick method (QF) by dividing VO2 by the difference in arterial and mixed venous oxygen content. Basal QTDC was increased and decreased with an intravenous infusion of dobutamine or labetalol, respectively. Data are summarized as mean +/- SD or 95% confidence interval (CI 95%). Agreement between methods of determining cardiac output was assessed by calculating bias, percent bias, and percent coefficient of determination (100 r2).nnnMEASUREMENTS AND MAIN RESULTSnEighteen swine (38.9 +/- 1.2 kg) exhibited a range of QTDC from 2.2 to 14.8 L/min. Mean measurement variance of VO2, CaO2, CvO2, and QTDB was 1.5%, 1.5%, 2.0%, and 11.8%, respectively. Mean bias, percent bias, and 100 r2 was 0.004 +/- 1.05 L/min (CI 95%: 0.18 to 0.19 L/min), -0.37 +/- 13.8% (CI 95%: -2.75 to 2.01), and 89% between QTDC and QF, respectively. Bias, percent bias, and 100 r2 was 0.05 +/- 1.09 L/min (CI 95%: -0.14 to 0.23 L/min, 1.21 +/- 13.06% (CI 95%: -1.03 to 3.46%), and 91% between QTDC and QTDB, respectively. Bias, percent bias, and 100 r2 (Fig 6) was -0.04 +/- 0.69 L/min (CI 95%: -0.16 to -.08 L/min), -1.23 +/- 9.17% (CI 95%: -2.8 to 0.35%), and 94% between QTDB and QF, respectively.nnnCONCLUSIONnAutomatic cardiac output computed with continuous thermodilution appears accurate and reliable. Also, good agreement was confirmed between cardiac output derived by continuous and bolus thermodilution methods and bolus thermodilution and Fick methods.

Weaning with end-tidal CO2 and pulse oximetry

STUDY OBJECTIVEnTo determine whether continuous measurement of arterial oxyhemoglobin saturation (SpO2) and end-tidal carbon dioxide (P(ET)CO2) can be used to wean patients safely and efficiently from postoperative mechanical ventilation after cardiac surgery.nnnDESIGNnProspective study comparing SpO2 and P(ET)CO2 to calculated arterial oxygen saturation (SaO2) and arterial carbon dioxide tension (PaCO2) obtained from blood gas analysis.nnnSETTINGnCardiac surgical intensive care unit at a university-affiliated hospital.nnnPATIENTSnTen patients requiring elective coronary artery bypass grafting (CABG) were studied in the postoperative period during weaning from mechanical ventilation.nnnINTERVENTIONSnContinuous monitoring of SpO2 and P(ET)CO2 was used to wean patients from mechanical ventilation.nnnMEASUREMENTS AND MAIN RESULTSnThe patients were weaned from mechanical ventilation in an average time of 6.5 +/- 1.5 hours (mean +/- SD). A plot of SaO2 versus SpO2 indicated a high correlation (r = 0.84) with sensitivity (100%) for hypoxemia (SaO2 less than 90%). P(ET)CO2 was a good indicator of PaCO2 (r = 0.76); its sensitivity to detect hypercarbia (PaCO2 less than 45 mmHg) was 95%. The gradient between SpO2 and SaO2 was not significantly affected by the weaning process, but the PaCO2-P(ET)CO2 gradient decreased significantly as the ventilator rate was decreased (p less than 0.001). The weaning process was discontinued on four separate occasions because of metabolic acidosis. Ninety-five percent of arterial blood samples confirmed the weaning recommendations based on the continuous monitoring of SpO2 and P(ET)CO2.nnnCONCLUSIONSnContinuous monitorin of SpO2 and P(ET)CO2 can be used to wean patients safely and effectively after CABG when adjustment of minute ventilation compensates for an increased PaCO2-P(ET)CO2 gradient during controlled ventilation.

Does significant arterial hypoxemia alter vital signs

STUDY OBJECTIVEnTo determine the cardiovascular and respiratory effects of arterial hypoxemia in adult volunteers.nnnDESIGNnProspective, subject-controlled.nnnSETTINGnUniversity-affiliated hospital.nnnSUBJECTSn16 awake, unsedated, unanesthetized adult volunteers.nnnINTERVENTIONSnInspired oxygen concentration (FIO2) was decreased in decrements to reduce pulse oximeter values to a range of 95% to 90%, 89% to 85%, 84% to 80%, and 79% to 70%.nnnMEASUREMENTS AND MAIN RESULTSnHeart rate (HR), blood pressure (BP), respiratory rate (RR), arterial blood pH, gas tensions, and oxyhemoglobin saturation were determined during normoxia and each level of oxyhemoglobin desaturation. FIO2 was reduced from 21% to 10%. Arterial blood oxyhemoglobin saturation and oxygen tension ranged from 100% to 71% and 103 to 35 mmHg, respectively. There were no significant changes in RR, BP, or HR during the study.nnnCONCLUSIONSnHR, BP, and RR are not reliable indicators of arterial hypoxemia in awake volunteers. If this finding is also true for sedated or anesthetized patients, then continuous monitoring with pulse oximetry should be used whenever patients are at risk for arterial hypoxemia. Stable HR, BP, and RR may not eliminate the possibility of significant arterial hypoxemia and impending catastrophic events.

The human immunodeficiency virus: Knowledge and precautions among anesthesiology personnel

STUDY OBJECTIVEnTo compare actual infectious disease precautions with current recommendations and to determine the influence of age, clinical experience, human immunodeficiency virus (HIV) knowledge, previous personal HIV exposure, and education on practices.nnnDESIGNnDirect clinical observations of infectious precautions and preeducation and posteducation surveys of clinical practices and general knowledge of the HIV.nnnSETTINGnUniversity teaching hospital.nnnPARTICIPANTSnForty-six anesthesia department members completed a preeducation survey, and 24 completed a posteducation survey.nnnMEASUREMENTS AND MAIN RESULTSnThe survey showed that adequate precautions were used during less than 50% of the routine procedures. Significant positive correlations were found between years of clinical practice and precautions used while inserting vascular catheters. Significant positive correlation was found between years of clinical practice and precautions taken while handling soiled laryngoscopes. Knowledge about the HIV and HIV transmission was limited. We noted a negative correlation between knowledge and precautions during vascular cannulation procedures, emergency department resuscitation, and tracheal suction. More precautions were taken with patients who had proven HIV infections and those at high risk of infection. The posteducation survey demonstrated a significant increase only in the use of gloves during routine procedures. Knowledge scores were only slightly improved and did not significantly reflect infection control practices.nnnCONCLUSIONSnAdequate infectious disease precautions were not taken by anesthesia personnel. An HIV educational program resulted in only a small increase in precautionary measures.

Life-threatening postoperative hypoventilation after bariatric surgery

Life-threatening postoperative hypoventilation after bariatric surgery Scott F. Gallagher, M.D., F.A.C.S.*, Krista L. Haines, M.A.B.M.H., Lynn Osterlund, M.D., Michel Murr, M.D., F.A.C.S., John B. Downs, M.D., F.C.C.M. Department of Surgery, University of South Florida College of Medicine, University of South Florida Health, Tampa, Florida Department Anesthesiology, University of South Florida College of Medicine, University of South Florida Health, Tampa, Florida Received April 7, 2009; revised April 8, 2009; accepted April 8, 2009 Surgery for Obesity and Related Diseases 6 (2010) 102–104

Rebreathing improves accuracy of ventilatory monitoring

AbstractObjective. Our objective was to determine if rebreathing would reduce the gradient between arterial and end-tidal CO2 tension during positive-pressure ventilation.Methods.Design: Experimental investigation.Setting: Anesthesiology laboratory.Subjects: A total of 10 dogs of either sex.Interventions: Anesthesia (sodium pentobarbital) and muscle relaxation (pancuronium) were induced and animals were tracheally intubated and ventilated with a standard anesthesia ventilator and breathing circuit with CO2 absorber and then with a Mapleson D circuit with a fresh gas flow rate (n

Physiologic Effects of Raised Airway Pressure

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