Bradycardia during anesthesia in infants. An epidemiologic study.

BACKGROUND: The frequency and morbidity of bradycardia during anesthesia in infants are not well documented. This study sought to determine the frequency of bradycardia during anesthesia in infants (0 to 1 yr) compared to that in older children, describe causes and morbidity, and identify factors that influence its frequency. METHODS: Computerized information abstracted from 7,979 anesthetic records of patients ages 0-4 yr undergoing noncardiac surgery were examined for the presence or absence of intraoperative bradycardia. To study bradycardia in infants, 4,645 anesthetics in patients aged 0-1 yr were considered. Those with bradycardia to heart rates less than 100 beats/min were examined for causes, morbidity, and treatment of the bradycardia. For analysis of influencing factors, the frequency of bradycardia in infants was related to age, sex, race, ASA physical status, surgical site (body cavity), complexity (major or minor) and duration, type of primary anesthetist, type of supervising anesthesiologist, and anesthetic agents. Logistic regression was used to estimate the significance (P < 0.05) and odds ratios for each. RESULTS: The frequency of bradycardia was 1.27% in the 1st yr of life, but only 0.65% in the third and 0.16% in the 4th yr, a significant difference. Causes of bradycardia in infants included disease or surgery in 35%, the dose of inhalation agent in 35%, and hypoxemia in 22%. Morbidity included hypotension in 30%, asystole or ventricular fibrillation in 10%, and death in 8%. Treatment involved epinephrine in 30% and chest compression in 25%. Associated factors included an ASA physical status of 3-5 (vs. 1 or 2) and longer (vs. shorter) surgery. Bradycardia was less than half as likely when the supervising anesthesiologist was a member of the Pediatric Anesthesia Service as with other anesthesiologists (P < 0.001). CONCLUSIONS: Bradycardia is more frequent in infants undergoing anesthesia compared to older children and is associated with substantial morbidity. It is more likely in sicker infants undergoing prolonged surgery and less likely when a pediatric anesthesiologist is present.

Frequency of anesthetic cardiac arrests in infants: effect of pediatric anesthesiologists.

STUDY OBJECTIVE: To determine whether the presence of pediatric anesthesiologists decreases the frequency of anesthetic-related cardiac arrests in infants (children who are 1 year of age or younger). DESIGN: A comparative retrospective study of anesthetics and cardiac arrests during a 7-year period. SETTING: The main operating room (OR) suite of a large university hospital. PATIENTS: All patients age 1 year or less undergoing surgical anesthesia from July 1983 through March 1990. INTERVENTIONS: Computerized anesthetic and operative patients records were queried for patient age, ASA physical status, body weight, surgical procedure, intraoperative complications, and the identity of the attending anesthesiologist. In each case, it was determined whether a pediatric anesthesiologist was in attendance and whether a cardiac arrest due to anesthesia occurred. Pediatric anesthesiologists were identified as those with pediatric fellowship training or the equivalent. The study population was divided into two groups: (1) the pediatric anesthesiologist group, with 2,310 patients whose anesthetics were supervised by pediatric anesthesiologists; (2) the nonpediatric anesthesiologist group, with 2,033 patients. MEASUREMENTS AND MAIN RESULTS: Mean age and weight were comparable in the two groups, and the distribution of physical status did not differ. No anesthesia-related cardiac arrests occurred in the pediatric anesthesiologist group; four anesthetic cardiac arrests occurred in the nonpediatric anesthesiologist group, for a frequency of 19.7 per 10,000 anesthetics. This difference between provider groups is significant (Fisher's exact probability test, p = 0.048). CONCLUSIONS: The results suggest that the use of pediatric anesthesiologists for all infants 1 year of age or younger might decrease anesthetic morbidity in this age-group.

Decreasing frequency of anesthetic cardiac arrests.

STUDY OBJECTIVE: To determine whether the anesthetic cardiac arrest rate decreased following the introduction of enhanced respiratory monitoring and increased safety awareness during the past decade. DESIGN: Epidemiologic study of surgical anesthetic morbidity as represented by intraoperative cardiac arrests. SETTING: Operating room suite of a large university hospital. PATIENTS: 241,934 patients undergoing surgery over a period of 20 years. INTERVENTIONS: Anesthetic cardiac arrest rates from two decades were compared. The first decade (1969 to 1978) predated safety initiatives, while the second (1979 to 1988) included them. MEASUREMENTS AND MAIN RESULTS: Anesthetic cardiac arrests were identified, and their causes (respiratory vs nonrespiratory) and preventability (identifiable error) were determined shortly after their occurrence, as part of an ongoing study initiated in 1969. They provided numerators for rate calculations; total surgical anesthetics provided the denominators. The anesthetic cardiac arrest rate decreased by one-half from the first decade (2.1 arrests/10,000 anesthetics) to the second (1.0/10,000), a significant difference (p = 0.032, Fisher's Exact Test). The rate for preventable arrests due to respiratory causes declined significantly from 0.8/10,000 to 0.1/10,000 (p = 0.013) and accounted for most of the observed decrease in the overall anesthetic cardiac arrest rate. The rates for preventable nonrespiratory arrests and nonpreventable arrests did not change significantly. CONCLUSIONS: The results support the hypothesis that improved respiratory monitoring was effective in decreasing anesthetic morbidity.

Stable xenon versus radiolabeled microsphere cerebral blood flow measurements in baboons.

Regional cerebral blood flow was simultaneously determined using the stable xenon computed tomographic and the radioactive microsphere techniques over a wide range of blood flow rates (less than 10-greater than 300 ml/100 g/min) in 12 baboons under conditions of normocapnia, hypocapnia, and hypercapnia. A total of 31 pairs of determinations were made. After anesthetic and surgical preparation of the baboons, cerebral blood flow was repeatedly determined using the stable xenon technique during saturation with 50% xenon in oxygen. Concurrently, cerebral blood flow was determined before and during xenon administration using 15-microns microspheres. In Group 1 (n = 7), xenon and microsphere determinations were made repeatedly during normocapnia. In Group 2 (n = 5), cerebral blood flow was determined using both techniques in each baboon during hypocapnia (PaCO2 = 20 mm Hg), normocapnia (PaCO2 = 40 mm Hg), and hypercapnia (PaCO2 = 60 mm Hg). Xenon and microsphere values in Group 1 were significantly correlated (r = 0.69, p less than 0.01). In Group 2, values from both techniques also correlated closely across all levels of PaCO2 (r = 0.92, p less than 0.001). No significant differences existed between the slopes or y intercepts of the regression lines for either group and the line of identity. Our data indicate that the stable xenon technique yields cerebral blood flow values that correlate well with values determined using radioactive microspheres across a wide range of cerebral blood flow rates.

Unilateral high-frequency jet ventilation during one-lung ventilation for thoracotomy.

One-lung ventilation is indicated during thoracic operations for bronchopleural fistula, pulmonary abscess, and pulmonary hemorrhage in spite of the possibility of the development of severe hypoxemia. To evaluate methods for improving oxygen transport during one-lung ventilation, we applied high-frequency jet ventilation (HFJV) and continuous positive airway pressure (CPAP) to the nondependent lung following deflation to atmospheric pressure in each procedure, and measured the effects on cardiac output and arterial oxygenation. In each case, the dependent lung was ventilated with conventional intermittent positive pressure ventilation (IPPV). Eight patients were studied during posterolateral thoracotomy using double-lumen endobronchial tubes. HFJV or CPAP to the nondependent lung improved arterial oxygenation significantly during both closed and open stages of the surgical procedures (p less than 0.008). When the chest was open, HFJV maintained satisfactory cardiac output, whereas CPAP usually decreased cardiac output (p less than 0.008). There were no significant differences in mean partial pressure of arterial carbon dioxide between HFJV, CPAP, and deflation to atmospheric pressure. In conclusion, HFJV to the nondependent lung provides not only satisfactory oxygenation but also good cardiac output, thereby maintaining better oxygen transport than CPAP or deflation to atmospheric pressure, while the dependent lung is ventilated with IPPV during one-lung ventilation for thoracotomy.

A method of rapid-sequence induction using high-dose narcotics with vecuronium or vecuronium and pancuronium in patients with coronary artery disease.

A method of rapid-sequence induction was studied in 18 patients undergoing coronary artery bypass grafting (CABG) to assess the adequacy of relaxation for endotracheal intubation without resulting in major changes in heart rate (HR). Ten patients received vercuronium, 0.2 mg/kg (V); and eight patients received vecuronium, 0.1 mg/kg, and pancuronium, 0.1 mg/kg (V + P). All patients then received fentanyl, 50 to 70 microg/kg, or sufentanil, 5 to 7 microg/kg, followed 60 seconds later by intubation. Patients were assessed for ulnar and mandibular nerve response to train-of-four (TOF) and tetanic (T) stimulation at 60 seconds; presence or absence of coughing or bucking; degree of vocal cord relaxation (1=none, 2=some, 3=complete relaxation); ability to intubate at 60 seconds; and changes in HR. At the time of intubation, 17 patients had four twitches to TOF and a positive response to T stimulation of the ulnar nerve, while all 18 patients had zero or one twitch to TOF and only four had a positive response to T stimulation of the mandibular nerve (P < .0001 for T and TOF, ulnar v mandibular). Coughing and bucking were not observed in any patient. Vocal cord position was "3" in 14 patients and "2" in four patients. All patients were intubated without difficulty. The mean change in HR was -4.1 beats/min for patients receiving V and +16.4 beats/min for those receiving V + P (P < .002 for change in HR), with two V + P patients developing tachycardia. It is concluded that the onset of neuromuscular blockade is more rapid in the distribution of the mandibular nerve than at the ulnar nerve; mandibular nerve stimulation is a better predictor of adequate intubating conditions; good intubating conditions can be attained with either V or V + P; and, rapid-sequence induction with V is safe from a cardiac standpoint as measured by changes in HR, but the addition of pancuronium is unnecessary.

Xenon/computed tomography cerebral blood flow measurements. Methods and accuracy.

We performed a series of five baboon experiments to compare cerebral blood flow measured with an improved stable xenon/CT method and the radiolabelled microsphere technique at a PaCO2 of 40 mm Hg. The xenon/CT method was implemented by fitting the arterial xenon uptake with a double exponential function, by measuring the oxygen and carbon dioxide concentrations continuously during each breath and by taking into account the lung-to-brain transit time of xenon. The time of xenon inhalation was extended to 30 minutes to obtain more reliable estimates of CBF in white matter regions. The results indicate an overall correlation coefficient of 0.92 between the two methods and good numeric agreement.

Prolonged isoflurane anesthesia in status asthmaticus.

We report a case of status asthmaticus that was unresponsive to the usual agents. The use of an inhalational anesthetic agent allowed us to ventilate the patient with lower inspiratory pressures; however, lasting improvement did not occur until she mobilized large quantities of secretions. To our knowledge, this is the first clinical report on the use of isoflurane anesthesia to treat severe asthma. Despite prolonged administration, there were no significant side-effects. This case demonstrates both the benefits and limitations of such therapy.

Cardiac arrest due to anesthesia. A study of incidence and causes.

Cardiac arrests due solely to anesthesia were studied in a large university hospital over a 15-year period. There were 27 cardiac arrests among 163,240 anesthetics given, for a 15-year incidence of 1.7 per 10,000 anesthetics. Fourteen of these patients (0.9 per 10,000) subsequently died. Detailed examination of the data from these 27 patients revealed that the pediatric age group had a threefold higher risk than adults, and that the risk for emergency patients was six times that for elective patients. Failure to provide adequate ventilation caused almost half of the anesthetic cardiac arrests, and one third resulted from absolute overdose of an inhalation agent. Hemodynamic instability in very ill patients was an association in 22%. Specific errors in anesthetic management could be identified in 75%. Progressive bradycardia preceding the arrest was observed in all but one case.

Bag-valve-mask ventilation; two rescuers are better than one: preliminary report.

This study suggests that the bag-valve-mask (BVM) used by a single rescuer with minimal training fails to deliver adequate tidal volumes for resuscitation. When two rescuers use the BVM, tidal volumes are more than recommended and are comparable to those seen with endotracheal intubation. Two-person BVM ventilation should be considered for initial resuscitation in cardiopulmonary arrest.

Regional cerebral blood flow measurements using stable xenon enhanced computed tomography: a theoretical and experimental evaluation.

Several theoretical and practical aspects of regional cerebral blood flow measurements using stable xenon gas and CT are discussed. It is shown that by comparing the enhancement at any time T1 with that at saturation or any other time T2, the need to use arbitrary means to bring the arterial concentration data and the CT enhancement data to the same system of measurement units can be eliminated. If CT is performed continuously during the washin phase, say at intervals of 1 min, least squares analysis of the enhancement data can be used to obtain the best possible estimates for the flow rate constant kappa and the saturation enhancement. However, if only a limited number of scans can be performed, as may be the case in human studies, it is also possible to get a good estimate of kappa from a knowledge of the ratio of the enhancement at any time T1 with that at any other time T2. Combinations of T1 = 2.0 min and T2 = 4.0 min, T1 = 1.0 min and T2 = 6.0 min, or T1 = 2.0 min and T2 = 5.0 min were found to be the most convenient. It is also shown that the end-tidal xenon concentration in the exhaled air can be accurately assessed indirectly by measuring the oxygen, CO2, and water vapor concentrations, thereby eliminating the need for more expensive methods involving the use of a mass spectrometer or a thermal conductivity gas analyzer.

Spontaneous breathing with a T-piece circuit: minimum fresh gas/minute volume ratio which prevents rebreathing.

Thirty adults undergoing elective superficial surgery under enflurane-nitrous oxide anesthesia which intubated and breathing spontaneously via a modified Mapleson D (Brain) T-piece circuit were studied with their consent. Total fresh gas flows which were initially high were adjusted downward until minimal rebreathing (inspired CO2 tension of 5 to 10 mmHg) was present. At this point both fresh gas flow (VF) and minute volume (VE) were recorded, and the ratio of the two (VF/VE) was calculated. The mean VF/VE ratio was found to be 1.89 +/- 0.27 (SD). Linear regression was used to plot VF against VE breathing frequency, tidal volume, age, weight, and end-tidal CO2 tension. Significant correlation was found only with VE (r2 = 0.48, P less than 0.001) and frequency (r2 = 0.44, P less than 0.001). When the ratio VF/VE was plotted against the same variables, no significant correlations was found. This study showed a wide variability in the minimum VF/VE ratio which prevents rebreathing. The respiratory waveform, which was not studied, probably played a role in determining the VF/VE. Nevertheless, 87 per cent of our patients required a VF/VE ratio of 2.0 or less to prevent rebreathing. If one is especially concerned about rebreathing, VE should be measured in the VF adjusted to about twice the measured.

Mouth-to-mask ventilation: a superior method of rescue breathing.

Tidal volumes achieved using endotracheal intubation with a self-inflating bag were compared to those achieved with the esophageal obturator airway, a bag-valve mask system, and mouth-to-mask ventilation in an experimental model employing 18 unskilled and 4 partially skilled rescuers. When compared to mean tidal volumes achieved with endotracheal intubation (1,193 ml with unskilled, 942 ml with semi-skilled rescuers), ventilation with the bag-valve-mask system was significantly less (509 and 495 ml tidal volumes) and was, in fact, well below the value of 800 ml recommended for rescue breathing. Mouth-to-mask ventilation produced tidal volumes (1,093 ml and 1,200 ml) not significantly different from those seen with endotracheal intubation. If clinical findings confirm these experimental results, mouth-to-mask ventilation should replace the bag-valve-mask system in the initial management of respiratory arrest.