David N. Thrush

Are automated anesthesia records better

STUDY OBJECTIVE To determine whether data recorded by an information management system is significantly different from that recorded manually. DESIGN A comparison was made between 13 handwritten and 13 computer-generated anesthesia records by calculating the frequency with which recorded variables were outside predetermined acceptable ranges. Five physiologic variables [systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), end-tidal partial pressure of carbon dioxide (PETCO2), and oxygen saturation by pulse oximeter (SpO2)] were compared during the initial 1 1/2 hours of operation. SETTING Surgical suite at a university-affiliated hospital. PATIENTS Thirteen adult patients scheduled for operations that required general anesthesia for longer than 1 1/2 hours. INTERVENTION In addition to the traditional handwritten anesthesia records, an information management system (ARKIVE Patient Management System, DIATEK, San Diego, CA) was used to collect data from each case. MEASUREMENTS AND MAIN RESULTS No significant differences were found between the methods in the frequency of elevated SBP, elevated DBP, and tachycardia. However, the manual records showed low SBP, DBP, and HR with a significantly lower frequency (2%, 11%, 1%, respectively) than the automated records (6%, 26%, 5%, respectively; p < 0.01). The automated PETCO2 readings were higher than the upper limit (40 mmHg) with a higher frequency (18%) than the manual records (3%; p < 0.01). On the automated records, SpO2 was noted to be 90% or less on two occasions, but significant desaturation was noted only once on the manual charts. CONCLUSIONS Observer bias, missed readings, and errors of memory, which affect manual anesthetic records, may cause significant inaccuracy and may be avoided by using automated records generated by information management systems.

Cardiopulmonary resuscitation: effect of CPAP on gas exchange during chest compressions.

BACKGROUND Conventional cardiopulmonary resuscitation (CPR) includes 80-100/min precordial compressions with intermittent positive pressure ventilation (IPPV) after every fifth compression. To prevent gastric insufflation, chest compressions are held during IPPV if the patient is not intubated. Elimination of IPPV would simplify CPR and might offer physiologic advantages, but compression-induced ventilation without IPPV has been shown to result in hypercapnia. The authors hypothesized that application of continuous positive airway pressure (CPAP) might increase CO2 elimination during chest compressions. METHODS After appropriate instrumentation and measurement of baseline data, ventricular fibrillation was induced in 18 pigs. Conventional CPR was performed as a control (CPR(C)) for 5 min. Pauses were then discontinued, and animals were assigned randomly to receive alternate trials of uninterrupted chest compressions at a rate of 80/min without IPPV, either at atmospheric airway pressure (CPR(ATM)) or with CPAP (CPR(CPAP)). CPAP was adjusted to produce a minute ventilation of 75% of the animals baseline ventilation. Data were summarized as mean +/- SD and compared with Student t test for paired observations. RESULTS During CPR without IPPV, CPAP decreased PaCO2 (55+/-28 vs. 100+/-16 mmHg) and increased SaO2 (0.86+/-0.19 vs. 0.50+/-0.18%; P < 0.001). CPAP also increased arteriovenous oxygen content difference (10.7+/-3.1 vs. 5.5+/-2.3 ml/dl blood) and CO2 elimination (120+/-20 vs. 12+/-20 ml/min; P < 0.01). Differences between CPR(CPAP) and CPR(ATM) in aortic blood pressure, cardiac output, and stroke volume were not significant. CONCLUSIONS Mechanical ventilation may not be necessary during CPR as long as CPAP is applied. Discontinuation of IPPV will simplify CPR and may offer physiologic advantage.

Is Epinephrine Contraindicated During Cardiopulmonary Resuscitation

BACKGROUND Why pulmonary gas exchange deteriorates after administration of epinephrine during cardiopulmonary resuscitation (CPR) is unclear. METHODS AND RESULTS Forty-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. CONCLUSIONS During 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.

OBJECTIVE Cardiac outputs were determined with continuous thermodilution, bolus thermodilution, and the Fick method during pharmacologically varied hemodynamics. DESIGN Prospective comparison of techniques. SETTING University animal laboratory. PARTICIPANTS Swine. INTERVENTIONS Swine 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). MEASUREMENTS AND MAIN RESULTS Eighteen 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. CONCLUSION Automatic 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.

Cardiac Arrest after Oxymetazoline Nasal Spray

Oxymetazoline nasal spray is a potent alpha 1-adrenergic agonist commonly used to vasoconstrict blood vessels in the nasal mucosa. In this incident, oxymetazoline nasal spray 0.025% was administered to a 2-year-old patient during general anesthesia for nasal endoscopy. Severe hypertension with reflex bradycardia progressed to sinus arrest and was successfully treated with alropine and cardiopulmonary resuscitation. Decreasing the dose of oxymetazoline and pretreatment with an anticholinergic is recommended.

Thermodilution cardiac output: Comparison between automated and manual injection of indicator

In clinical practice, cardiac output (CO) is usually reported as the average of thermodilution determinations with injection of the thermal indicator performed at end-exhalation. However, an average of multiple determinations with injections equally dispersed throughout the respiratory cycle has been shown to provide the best estimate of mean CO. This study sought to determine the reproducibility of CO determinations obtained with manual injections of indicator solution performed at end-exhalation, compared with those determined by computer-controlled injections equally dispersed throughout the breathing cycle of 27 patients undergoing cardiac operations. Mean CO was calculated by averaging the four determinations obtained with each technique before induction of anesthesia, after induction of anesthesia, after sternotomy, after cardiopulmonary bypass, and after sternal closure. A total of 130 pairs of mean CO estimations were obtained with manual and automated injections. Mean CO values obtained with manual injections were significantly lower than those obtained with the dispersed injection technique (5.0 +/- 1.4 L/min vs 5.3 +/- 1.6 L/min, P = 0.002). The bias between CO values measured with the manual technique was -0.25 +/- 0.47 L/min lower than those obtained with the dispersed technique. The mean relative bias for the group was 7 +/- 18% with 95% confidence intervals of +/- 26%. During mechanical ventilation, the thermodilution technique with manual injection of indicator solution significantly underestimated CO. Variability in the manual injection technique and inappropriate representation of the mean CO by injections timed to occur at end-exhalation contributed to the disparity. These results indicate that the manual technique of determining CO at end-exhalation may not accurately reflect the average CO.

Radial nerve injury after routine peripheral vein cannulation

The dorso-radial aspect of the wrist and hand is a common location for intravenous (IV) cannulation prior to anesthesia. The sensory branch of the radial nerve lies superficially in this area, and it can be injured during routine insertion of IV catheters. In this case, the nerve was lacerated during insertion and a painful neuroma developed after elective surgery and anesthesia. Knowledge of this complication may help with its recognition and treatment.

Vagotonia and cardiac arrest during spinal anesthesia

SUDEN cardiac arrest during spinal anesthesia can occur in otherwise healthy patients. 1-6 Although respiratory depression secondary to excessive sedation is responsible in some cases, sudden cardiac arrest can occur without overt signs of respiratory depression in hemo-dynamically stable patients. Vasovagal reactions have been reported to cause cardiac arrest during spinal and epidural anesthesia. 5,6 Increased vagal tone, or vagotonia, is present in approximately 7% of the population. 7 Such individuals frequently have a history of recurrent reactions precipitated by emotional or physical stress. Vagotonic manifestations can include nausea, sweating, pallor, bradycardia, hypotension, and syncope. 7,8 If a patient who is prone to have vasovagal reactions is exposed to emotional stress during spinal anesthesia, what might otherwise be a benign or transient reaction may progress to cardiac arrest Two incidents of syncope and asystole, during two separate spinal anesthetics, are described in a patient with a history of recurrent vasovagal reactions.

Blood pressure after cardiopulmonary bypass: Which technique is accurate?

To evaluate the accuracy with which a patients aortic blood pressure can be estimated upon separating from cardiopulmonary bypass (CPB), simultaneously recorded radial artery pressure, oscillometric brachial artery pressure, pressure in the CPB circuit, and the surgeons estimate of blood pressure by aortic palpation were compared to directly measured aortic root pressure. After obtaining institutional approval and written informed consent, 20 patients requiring CPB for cardiac operations were studied. General anesthesia was induced and maintained with fentanyl, vecuronium, and enflurane. Blood pressure measurements were made before CPB and repeated 2, 5, and 10 minutes after discontinuation of CPB. Radial artery systolic pressure before CPB and radial artery mean pressure 10 minutes after CPB were different from the aortic root pressures (P < 0.05). Although the other radial artery pressures and the surgeons estimate of systolic aortic pressure were statistically similar to the aortic root pressures, the range of differences was clinically significant. The oscillometric technique and CPB line were poor estimates of aortic root pressure. Of the techniques used to estimate aortic blood pressure, including radial arterial, oscillometric, aortic line of the CPB circuit, and digital palpation, the radial arterial was the best, and the aortic line from the CPB machine and palpation by the surgeon were the worst. When a clinician is unsure of the blood pressure during separation from CPB, direct measurement of central aortic blood pressure is advised.

Weaning with end-tidal CO2 and pulse oximetry

STUDY OBJECTIVE To 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. DESIGN Prospective study comparing SpO2 and P(ET)CO2 to calculated arterial oxygen saturation (SaO2) and arterial carbon dioxide tension (PaCO2) obtained from blood gas analysis. SETTING Cardiac surgical intensive care unit at a university-affiliated hospital. PATIENTS Ten patients requiring elective coronary artery bypass grafting (CABG) were studied in the postoperative period during weaning from mechanical ventilation. INTERVENTIONS Continuous monitoring of SpO2 and P(ET)CO2 was used to wean patients from mechanical ventilation. MEASUREMENTS AND MAIN RESULTS The 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. CONCLUSIONS Continuous 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.