Allen K. Ream

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

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

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

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

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.

THE LONGITUDINAL DISTRIBUTION OF PULMONARY VASCULAR RESISTANCE DURING UNILATERAL HYPOXIA

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.

Development of a totally implantable, electrically actuated left ventricular assist system

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.

Cutaneous monitoring of systemic PCO2 on patients in the respiratory intensive care unit being weaned from the ventilator.

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.

Epidural Measurement of Intracranial Pressure

Abstract A totally implantable left ventricular assist system has been under development at Stanford since 1972. The system fabricated for clinical use employs a highly efficient, electrically powered solenoid drive system coupled to a dual pusher-plate blood pump with xenograft inflow and outflow valves. The system is of suitable size for implantation either within the anterior abdominal wall or anterolateral within the peritoneal cavity, with pump inflow and outflow cannulas from the left ventricular apex and to the supraceliac aorta, respectively. Thus, the system is well suited for short-term cardiac support after cardiac surgical procedures, being easily explantable due to its superficial location. In addition, long-term support, with the possibility of subsequent cardiac transplantation, is feasible when intrinsic myocardial dysfunction is irreversible, in contrast to existing pneumatically powered systems which require percutaneous drive-lines and compressed air sources. Although the integrated clinical left ventricular assist system described has not been extensively tested in vivo, more than 6,500 hours of operation in calves has been accumulated with a related system; the maximum duration of continuous left ventricular assist using this system in vivo has been 129 days, the longest reported successful operation of such an electrically driven system. These experimental studies have demonstrated the capability of the device to provide total systemic circulatory support for a prolonged period in the context of a severely failing left ventricle.

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

A procedure for measuring the partial pressure of CO2 in equilibrium with the epidermis was developed at Hewlett‐Packard Laboratories. It consists of determining by infra‐red absorption techniques the concentration of CO2 inside a small (50 μl) chamber applied hermetically over and around an epidermal window (2.25 cm2) stripped of its stratum corneum or horny layer. We have applied the procedure to 25 patients in the Respiratory Intensive Care Unit at Stanford Hospital. Only patients scheduled for weaning from the ventilator were selected for the study. The epidermal windows were on the medial aspect of the forearm and were monitored for 3–6 h. Arterial blood samples were periodically withdrawn from the catheterized radial artery and were analysed by conventional means for subsequent comparison with the cutaneous measurements which were recorded in real time at the rate of one a minute. The range of arterial Pco2 values that were measured varied from 3.33 to 9.30 kPa (25 to 70 mmHg) and correlated well with the corresponding cutaneous Pco2 values that were typically higher than the arterial values by 0.7 kPa (5.2 mmHg) with a standard deviation of 0.2 kPa (1.5 mmHg). Some typical recordings of cutaneous Pco2 are shown and discussed.

Mean blood pressure algorithms

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.

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

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.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.