Automating the recording and improving the presentation of the anesthesia record.

Although anesthesia records have been kept for over a hundred years, there is still discussion of their value and content. Two uses of the record are widely accepted: (1) review after the anesthetic event (as in medicolegal disputes), and (2) support of patient care during the delivery of an anesthetic. Although the anesthetic record is mandatory in much of the world, there is not a single standard for its format. Automating the generation and presentation of the record will enhance its value and help develop a consensus as to content. Merely automating the steps used to produce the manually generated record does not realize the full benefit of automation. For maximum benefit, the primary goal of automation should be to support the uses of the record. Specific techniques that are discussed include increasing time resolution, optimizing the type and location of input and display equipment, and tailoring the human interface. Particular attention is paid to the issue of how much detail is acceptable in the record, how to use visual cues to present detail properly, how to exclude extraneous detail, and how to avoid misleading presentations (erroneous interpretation of the data). Specific elements discussed include line width, the use of color, presentation of gradients, statistical summaries, contexts for reporting data, graphical techniques for increasing data content, and pictorial presentations. Current records are more often confusing because presented information is inconsistently displayed or irrelevant than because too much information is offered, and automation can ameliorate this problem.

The longitudinal distribution of pulmonary vascular resistance during unilateral hypoxia.

Pulmonary capillary hydrostatic pressure and the longitudinal distribution of pulmonary vascular resistance (arterial and venous components) can be determined by analysis of pressure decay curves following pulmonary artery occlusion. To validate this technique in intact animals, pulmonary artery occlusion pressure decay curves were obtained from both lungs in six anesthetized sheep during control conditions (100% O2) and during unilateral hypoxic ventilation (100% O2 versus 100% N2). Analysis of pulmonary artery occlusion pressure curves indicated the following: 1) in the hypoxic lung, unilateral hypoxia increased the precapillary portion of pulmonary vascular resistance from 72% of the total resistance to 89% of the total resistance in that lung; 2) in the nonhypoxic lung, unilateral hypoxia did not significantly affect the distribution of pulmonary vascular resistance; and 3) unilateral hypoxia produced no significant change in pulmonary capillary pressure in the hypoxic lung compared with control; however, pulmonary capillary pressure was significantly greater in the nonhypoxic lung. These results are consistent with other evidence that hypoxic pulmonary vasoconstriction acts locally and primarily affects resistance at the arteriolar level. Pulmonary artery occlusion pressure decay curve analysis appears to be a valid technique for the measurement of pulmonary capillary pressure and the longitudinal distribution of pulmonary vascular resistance in intact anesthetized animals. These measurements pertain only to the vasculature distal to the site of pulmonary artery occlusion with the catheter, and, thus, caution must be used when applying this technique in a setting of nonhomogenous lung injury.

Simultaneous measurements of cardiac output by thermodilution, esophageal Doppler, and electrical impedance in anesthetized patients.

Simultaneous intraoperative measurements of cardiac output were obtained in nine patients with transesophageal Doppler, transthoracic impedance, and pulmonary artery thermodilution techniques to evaluate the utility of the noninvasive methods. Pairs of noninvasive and thermodilution measurements were obtained 25 times with transesophageal Doppler and 58 times with transthoracic impedance. Correlation of the noninvasive measurements with thermodilution was poor, with r = 0.43 for transthoracic impedance and r = .68 for transesophageal Doppler. The average difference between the noninvasive and the thermodilution values was -0.4 +/- 1.4 L/min (mean +/- SD) and -0.1 +/- 1.6 L/min for impedance and Doppler, respectively. Changes in cardiac output at sequential time points as measured by thermodilution were predicted with 95% confidence only when a change of >4 L/min was observed by transesophageal Doppler or >8 L/min was observed by transthoracic impedance. Therefore, it is concluded that neither noninvasive technique reliably estimated cardiac output as determined by thermodilution, and neither tracked trends.

Isolated left ventricular assist as bridge to cardiac transplantation.

The electrically driven Novacor implantable left ventricular assist device has been implanted in six patients (four men and two women) since Sept. 7, 1984. In four of the six patients (67%) the device was a successful bridge to cardiac transplantation. One patient died of multiple organ failure and Candida sepsis after 16 days of support with the device. One patient died in the operating room of uncontrollable hemorrhage and biventricular failure caused by severe cardiac rejection. Three patients are alive with cardiac transplants 38, 17, and 10 months after transplantation. One patient died after cardiac transplantation of presumed sepsis. The Novacor left ventricular assist device performed in all cases without mechanical or electrical failure. Excluding the intraoperative death, assist duration ranged from 2 to 16 days. The cardiac index (synonymous with device output) ranged from 2.4 to 3.4 L/min/m2. No embolic events (cerebrovascular or systemic) occurred during assistance with the device. Minimal red cell hemolysis was documented during the period of support. The Novacor left ventricular assist device is a safe and effective bridge to cardiac transplantation in patients with refractory cardiogenic shock.

Anesthetic mishaps and the cost of monitoring: a proposed standard for monitoring equipment.

Review of insurance data indicates that approximately 1.5 claims are paid per 10,000 anesthetic procedures, a conservative estimate of the incidence of preventable serious injury associated with anesthesia. Insurance data permit estimation of the premium cost for the anesthesiologist and hospital, per operating room per year, of $69,429.00. We propose the use of an enhanced monitoring standard requiring a pulse oximeter, capnograph, spirometer, halometer, automatic sphygmomanometer, breathing circuit oxygen analyzer, stethoscope, electrocardiographic monitor, and temperature monitor. We suggest that this premium cost, together with the estimate that 50% of incidents would be avoided, predicts a resultant saving of over $27,000/operating room/year, a savings equal to the entire cost of the enhanced monitoring system in approximately 8 months, or a yearly savings of over five times the annualized expense of the monitoring system. Thus, in addition to the moral imperative to monitor a patient during anesthesia to avoid injury and death, there is an economic incentive to monitor effectively.

A quantitative evaluation of the Hewlett-Packard 78354A noninvasive blood pressure meter.

Oscillometrically determined brachial artery pressures were compared with simultaneous contralateral radial intraarterial pressures in 19 anesthetized adult cardiac surgical patients throughout their surgical procedures, interrupted only by nonpulsatile, low-pressure, low-flow cardiopulmonary bypass. Radial intraarterial pressure values ranged widely for systolic (55 to 207 torr), mean (43 to 141 torr), and diastolic (26 to 106 torr). Both error specification methods proposed by the Association for the Advancement of Medical Instrumentation were used and compared. As expected, error method 1 gave consistently lower mean errors, smaller error standard deviations, and higher correlation coefficients than did error method 2. The errors during time periods immediately before and after cardiopulmonary bypass were compared with those from more quiescent times. Higher mean errors, larger error standard deviations, and lower correlation and regression coefficients were found during those time periods surrounding cardiopulmonary bypass. In general, mean errors were lowest for systolic pressure, followed by mean and diastolic pressures in that order, whereas error standard deviations were smallest for mean pressure, followed by systolic and diastolic pressures. Correlation and regression coefficients were highest for systolic pressure, followed by mean and diastolic pressures. In summary, the oscillometric method provides convenient and reproducible estimates of radial intraarterial pressure during most clinical situations, typically with better accuracy than the auscultatory Korotkoff method. The accuracy and reproducibility are diminished during those periods immediately surrounding cardiopulmonary bypass, perhaps due to direct surgical manipulation of the heart with its attendant rapid changes in cardiac output and blood pressure.

Pressure control to accommodate patient breathing efforts during volume ventilation.

Intermittent positive-pressure ventilation is used to support patients whose unassisted breathing is inadequate. Mechanical ventilators deliver pressurized gas to the patient's lungs by using a pattern of volume and timing that is preset by the clinician. A weakness of existing control methods is their emphasis on maintaining adequate gas exchange while poorly accommodating the patient's efforts to reassume control of the delivery pattern. A method is proposed to control airway pressure within a breath by making it respond to measurements of volume. This method using pressure as a function of volume, or P(V) method, permits the patient to have transient control over flow rate and delivered volume. In addition, an adaptive controller is included that modifies the applied pressure during subsequent breaths; it assures an average flow rate and delivered volume at the levels prescribed by the clinician, when sustained changes occur in airway resistance, lung-thorax compliance, or breathing efforts. Analyses and computer simulations suggest that the P(V) method will be better than conventional volume ventilation in accommodating, within a breath, transient breathing efforts without long-term degradation of the prescribed delivery pattern. The P(V) method can restore the delivery pattern, using the adaptive controller, within a few breaths after changes occur in the patient's lung mechanics. We conclude that the P(V) method is feasible, that it may represent an improved method of patient ventilation, particularly during fighting or weaning from the ventilator, and that it warrants further investigation.

Mean blood pressure algorithms.

Alternative methods of calculating average blood pressure are examined. It is suggested that the preferred method is calculation of the arithmetic mean if the average value itself is required. However, when blood pressure values are used to calculate other results, only the instantaneous value is appropriate in all situations. Arithmetic mean blood pressure values may be used with arithmetic mean flow values to calculate resistance, but only if resistance is constant over the interval (laminar flow). To calculate ventricular stroke work, the root mean square averages must be used because in this instance the arithmetic average yields large errors. Most monitors do not use these methods consistently to derive average blood pressure values, thus, the displayed values differ from those obtained from the appropriate calculation. Computational convenience, truncation error in averaging, or true errors in measurement or understanding of the associated physiologic state may account for observed differences. The interpretation of maximum systolic and minimum diastolic pressures with each beat requires additional considerations. Common monitoring algorithms obscure clinically important details, particularly by distorting the relationship between respiratory variation and pulse pressure.

Reappraisal of cardiopulmonary bypass with deep hypothermia and circulatory arrest for complex neurosurgical operations.

Although cardiopulmonary bypass (CPB) with hypothermia and circulatory arrest is routinely used for certain cardiovascular procedures, its advantages have infrequently been applied for other unusual surgical problems. Fourteen patients (six men and eight women, average age 48 years, range 29 to 74 years) underwent 15 operations over a 4-year period beginning in November 1978. Preoperative diagnosis included giant middle cerebral aneurysm (n = 8), internal carotid aneurysm (3), basilar artery aneurysm (2), and medullary hemangioblastoma (2). All patients had lesions that were considered inoperable by standard neurosurgical techniques. Operative technique consisted of peripheral cannulation with a long and short femoral vein cannula for venous return (24 to 28F) and a single femoral arterial cannula (18 to 24F). CPB flows ranged from 1 to 3.5 L/min, and the total CBP times averaged 146 minutes (range 66 to 282 minutes). Circulatory arrest times averaged 21 minutes (range 5 to 51 minutes), with two patients having no period of circulatory arrest. Lowest core temperature ranged from 16 degrees to 20 degrees C, with cooling and rewarming aided by Brown-Harrison heat exchangers placed in a countercurrent fashion within the venous return line. The heart spontaneously defibrillated in six patients, and external countershock was required in nine patients. No difficulty was encountered with cardiac distention. The intended operation was accomplished in all cases with 13 of 14 patients being discharged from hospital, having had a good neurosurgical result. One patient sustained a hemorrhagic infarction of the cerebellum and pons and is presently recovering. Our experience indicates that peripheral CPB with induced hypothermia and circulatory arrest is a safe technique for approaching otherwise inoperable neurosurgical lesions.

Operative treatment of a giant cerebral artery aneurysm with hypothermia and circulatory arrest: report of a case.

A patient with a giant left middle cerebral artery aneurysm is presented. Because of previous operations and dense adhesions of the dominant frontal and temporal lobes to the aneurysm sac, we elected to obliterate the aneurysm by endaneurysmorrhaphy with the patient under hypothermia and cardiac arrest. Elective cardiac arrest has become a relatively safe, controllable procedure and may be of significant value in the treatment of difficult neurosurgical problems.

Epidural measurement of intracranial pressure.

Although the measurement of intracranial pressure (ICP) is gaining widespread acceptance, the most desirable method of measurement is disputed. Subdural fluid-coupled techniques are associated with an increased risk of infection, and epidural techniques are associated with decreased accuracy. We investigated epidural measurement techniques and suggest that the necessary and sufficient criteria for accurate epidural measurement of ICP are adequate transducer size and stiffness, transducer-dura coplanarity, transducer-guard ring coplanarity, complete dural contact, and rigid fixation. An epidural transducer design was developed and prototypes were constructed using these principles. The transducer requires no percutaneous connections, fluid coupling, or batteries. Transducer accuracy was +/- 2.2 torr in bench stability studies lasting up to 198 days, +/- 3.0 torr in acute animal studies of less than 24 hours, and +/- 7.9 torr in chronic animal studies lasting up to 112 days. Error bounds are expressed such that 95% of individual measurements are expected to have error less than the bound; average error is one-third of the bound. Average transducer drift was 0.1 torr per day; our reported accuracy in chronic studies used drift correction from preimplantation data. We conclude that accurate measurement of ICP using an epidural transducer is feasible.