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 animal's 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.

Does significant arterial hypoxemia alter vital signs?

STUDY OBJECTIVE: To determine the cardiovascular and respiratory effects of arterial hypoxemia in adult volunteers. DESIGN: Prospective, subject-controlled. SETTING: University-affiliated hospital. SUBJECTS: 16 awake, unsedated, unanesthetized adult volunteers. INTERVENTIONS: Inspired 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%. MEASUREMENTS AND MAIN RESULTS: Heart 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. CONCLUSIONS: HR, 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.

Spirometric versus Fick-derived oxygen consumption: which method is better?

OBJECTIVE: Oxygen consumption (VO2) is often measured in critically ill patients using the Fick equation: VO2 = cardiac output x arterial-venous oxygen content difference. To determine if this method is accurate, it was compared with a spirometric technique. DESIGN: Prospective study. SETTING: University laboratory. SUBJECTS: Nineteen large adult pigs. INTERVENTIONS: Cardiac output, measured with bolus thermodilution technique, and arterial and venous oxygen content values, determined with the galvanic fuel cell method, were used to determine VO2 with the Fick equation. The spirometrically determined VO2 was the rate of disappearance of oxygen from a water-sealed spirometer. Dobutamine and labetalol were titrated to vary VO2 (range 204 to 584 mL/min). MEASUREMENTS AND MAIN RESULTS: The bias between the Fick and spirometrically determined VO2 values was 58 mL/min. The precision (SD of the bias) between the Fick and spirometrically determined Vo2 was 35 mL/min. Fick-derived Vo2 was greater than Vo2 measured spirometrically. The correlation coefficient was 0.90. CONCLUSIONS; Despite all attempts to reduce measurement error, there was an unexplained difference in Fick-derived and spirometrically measured Vo2. Therefore, I feel that the two methods are not interchangeable, and that calculations of Vo2 using the Fick method should be used cautiously when therapeutic maneuvers are based on these data.

Cardiopulmonary bypass temperature does not affect postoperative euthyroid sick syndrome?

STUDY OBJECTIVE: To determine if temperature during cardiopulmonary bypass (CPB) has an effect on perioperative and postoperative thyroid function. DESIGN: Prospective study comparing thyroid function during and after hypothermic and normothermic CPB. SETTING: Cardiac surgical unit at a university-affiliated hospital. PATIENTS: Twelve patients scheduled to undergo cardiac operations with normothermic (n = 6) or hypothermic (n = 6) CPB. INTERVENTIONS: Blood was analyzed for serum concentration of total thyroxine (TT4), total triiodothyronine (TT3), free T3 (fT3), reverse T3 (rT3), and thyroid stimulating hormone (TSH) preoperatively, 60 min after CPB was initiated, 30 min after discontinuing CPB, and on postoperative days (POD) 1, 3, and 5. MEASUREMENTS AND RESULTS: Patients who underwent either cold (26 degrees +/- 5 degrees C) or warm (35 degrees +/- 1 degree C) CPB were comparable with regard to age, body weight, duration of CPB, cross-clamp time, use of inotropes, total heparin dose, and length of hospital stay. Incidence of postoperative myocardial infarction, congestive heart failure, and death were similar. In both groups, TT4 and TT3 were reduced below baseline values beginning with CPB and persisting for up to 5 days after CPB (p < 0.05), free T3 was reduced for up to 3 days after CPB (p < 0.05), mean serum rT3 was elevated on POD 1 and POD 3 (p < 0.05), and TSH remained unchanged. CONCLUSION: The results of this study suggest that normothermic CPB does not prevent the development of the "euthyroid sick syndrome" during and after CPB. Despite these changes in thyroid function, most patients in both groups had a normal postoperative recovery.

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.

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.

Blood pressure after cardiopulmonary bypass: which technique is accurate?

To evaluate the accuracy with which a patient's 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 surgeon's 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 surgeon's 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.

Ketorolac as a premedicant for coronary artery bypass surgery patients with normal ventricles.

Premedication of patients requiring cardiac surgery should provide adequate analgesia, sedation and anxiolysis for the stress and pain associated with preoperative preparation and placement of monitoring catheters. Ideally, these effects would be achieved without producing respiratory depression and hypoxia, which could be life-threatening to patients at risk for myocardial ischemia. Ketorolac, a nonsteroidal, antiinflammatory agent, has previously been shown to provide postoperative pain relief comparable to that provided by morphine, without respiratory depression. This study compared the incidence of arterial blood desaturation, respiratory depression, and patient comfort after preoperative medication with scopolamine and ketorolac versus scopolamine and morphine. Scopolamine and ketorolac premedication provided sedation and analgesia comparable to that provided by scopolamine and morphine, without significant respiratory depression. Since ketorolac has no central respiratory depressant effect, it may be a useful alternative to morphine for premedication in the cardiac surgical patient.

Direct or modified Seldinger guide wire-directed technique for arterial catheter insertion.

Percutaneous radial artery cannulation is widely used for direct continuous arterial blood pressure measurement and sampling of arterial blood. We compared the success rate of arterial catheter placement in patients undergoing aortocoronary bypass operations using the direct and the modified Seldinger techniques. The effects of gender and quality of the pulse were also investigated. Our study group consisted of 42 female and 96 male patients. The overall success rate with the guide wire was 82% compared with that of the direct method of 65% (P = 0.02). The success rate for arterial cannulation in male patients was high whether direct cannulation or a guide wire was used. In female patients, on the other hand, the failure rate with the direct technique was high (57%) and was significantly lower (14%) when the guide wire was used (P < 0.001). We conclude that the success rate for cannulation is high in male patients, and patients with a bounding pulse regardless of the use of the direct or guide-wire techniques. The guide wire is recommended as the initial technique for cannulating the radial artery of female patients. In patients with a thready pulse, no significant advantage could be obtained by using a guide wire, but in salvaging an arterial line the guide wire is efficacious.

Comparison of low-dose sufentanil and fentanyl in balanced intravenous anesthesia for orthotopic cardiac transplantation.

A retrospective review was made of the records of 118 patients who received orthotopic heart transplant. Anesthetic techniques, drugs, dosage, hemodynamic profiles, intubation time, and intensive care unit stay were evaluated. The efficacy of sufentanil was compared to fentanyl in a balanced anesthetic when given in lower doses. Patients were given adequate anesthesia with total opioid doses of sufentanil, 6.5 +/- 2.9 micrograms.kg-1, or fentanyl, 58.9 +/- 24.9 micrograms.kg-1. Midazolam was used in all patients (mean dose 7.6 +/- 3.8 mg). There were no differences between the groups in complications, requirements for inotropic support, or time to extubation. A significantly higher pulmonary artery pressure was noted in patients who received sufentanil, but not fentanyl, pretransplant. The pulmonary artery pressures were not significantly elevated posttransplant. This review indicated that patients can be safely anesthetized with either combination of drug in lower doses than previously recommended.

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.

Incidence of arterial oxygen desaturation in cardiac patients premedicated with intramuscular scopolamine and morphine.

The effect of a standard preoperative medication combination, morphine and scopolamine, on arterial oxyhemoglobin saturation was measured continuously in 29 patients scheduled for elective coronary artery bypass grafting procedures. On the morning of operation, both before and after administration of preoperative medication, each patient was monitored continuously with a pulse oximeter (SpO2). Patients received 0.05 to 0.11 mg/kg of morphine (mean = 6.0 +/- 2.1 mg) intramuscularly (IM) and 0.2 to 0.4 mg of scopolamine (mean = 0.30 +/- 0.07 mg) IM. The mean arterial blood oxyhemoglobin saturation decreased from 92.0 +/- 1.8% before preoperative medication to 89.0 +/- 3.8% (P greater than .001) after preoperative medication. Forty-five percent of the patients had SpO2 less than 90% for at least 2 minutes, and 21% below 85%. In conclusion, significant arterial oxyhemoglobin desaturation occurred in this group of cardiac surgical patients after preoperative medication with morphine and scopolamine. Prophylactic administration of oxygen with preoperative medication might reduce the incidence of hypoxemia in this group of patients at risk for myocardial ischemia.

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.

Automated anesthesia records and anesthetic incidents.

A case report is presented in which the cause of an anesthetic mishap would have remained a mystery had it not been for an automated anesthesia record.