Richard L. Keenan

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 (Fishers 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.

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 non-cardiac 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 (vw. 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.

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, Fishers 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.

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.

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.

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.

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.

How rebreathing anaesthetic systems control Paco2: Studies with a mechanical and a mathematical model

SummaryResults from a proposed equation for rebreathing systems,

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

Pa_{CO_2 } = \frac{{\dot V_{CO_2 } (P_B - P_{H_2 O} )}}{\begin{gathered} \dot V_E (1 - V_D /V_T ) \hfill \\ + \frac{{\dot V_{CO_2 } (P_B - P_{H_2 O} )}}{{\dot V_F }} \hfill \\ \times \frac{{\dot V_E - \dot V_F }}{{\dot V_E }} \hfill \\ \end{gathered} }