O. Prakash

Criteria for early extubation after intracardiac surgery in adults.

Of 142 adult patients undergoing open-heart surgery, 123 were extubated either in the operating room or within 3 hours after admission to the recovery room, to avoid the discomfort and risks of prolonged mechanical ventilation. The remaining 19 patients, who had impaired cardiac function, were mechanically ventilated for 1 to 7 days postoperatively. The most important criteria for cardiopulmonary malfunction indicating the need for continued mechanical ventilation were a low mixed venous O2 saturation (S−VO2.) of < 60% and a high left atrial pressure (>20 torr). Of the 123 patients, 118 had an uneventful postoperative recovery and 5 needed reintubation, 2 because of low S−VO2 and 3 because of complications unrelated to respiratory management.Most adult patients can spontaneously breathe adequately immediately after or within 3 hours of completed open-heart surgery, but a thorough physiologic and clinical evaluation should precede extubation, to identify those who need prolonged mechanical ventilation in the postoperative phase. Criteria for selection of patients for early extubation are presented.

Cardiorespiratory and metabolic effects of profound hypothermia.

At operation the body temperature of mechanically ventilated infants was initially decreased to 25--22 degrees C with surface cooling and further lowered to 16 degrees C by total body perfusion. During circulatory arrest, averaging 40 min, repair of complex intracardiac deformities was carried out. Rewarming to 36 degrees C was achieved by 35--65 min of total body perfusion. Of 29 infants, 23 under 10 kg survived their correction; normothermic ventilation without added CO2 was given throughout the cooling period. The following measurements were made: gas exchange, lung mechanics, heart rate, arterial pressure, right atrial pressure, cardiac output (Qt), ECG, core and nasopharyngeal temperature, as well as biochemical determinations. During surface cooling O2 consumption (VO2), CO2 production (VCO2), endtidal CO2 (PETCO2) and PaCO2 decreased proportionally and linearly with body temperature. Inspiratory resistance, total compliance, physiological dead space (VD/VT), and the single breath CO2 curve did not reveal disturbed lung function. Mean arterial pressure was 98, 90, and 70 mm Hg and heart rate was 141, 107, and 76 beat/min, at temperature 35, 30, and 25 degrees C, respectively. Cardiac index was 2.2 +/- 0.2 liter/min/m2 (mean +/- SEM, n = 25) 2 hours after surgery. Arterial lactate reached peak values of 4.1 +/- 0.3 mM/liter (n = 17), during rewarming but returned to normal. Respiratory alkalosis caused by hyperventilation during cooling caused no apparent harm. No neurological damage was observed. It is concluded that surface cooling performed with normothermic ventilation under guidance of core temperature, VO2, PETCO2, and VCO2, is a safe method.

A microcomputer based charting system for documentation of circulatory, respiratory and pharmacological data during anesthesia

SummaryA system for the on-line production of anaesthetic records with a microcomputer is described. The requirements of the system are a keyboard, a video display unit and a colour plotter. The system requires no programming expertise from anaesthetists and nurses. The records have improved information display, patient care and reduced time spent in administration effort. Disadvantages are the relatively high cost and requirement of preprocessing of haemodynamic and respiratory parameters.

Real-time respiratory monitoring workstation-software and hardware engineering aspects

We have applied advanced real-time techniques in softwave, that are intensively used in critical areas like space research and defence applications, to realise an Integrated Real-Time Respiratory Monitoring System at the Thorax Anesthesiology, Academic Hospital Rotterdam. The system is called the ‘SERVO WINDOW’ —a window to the servo ventilator. The heart of the system is a real-time kernel that uses preemptive scheduling to achieve multitasking on a IBMPC compatible hardware platform. To the clinician this means that he gets all relevant information from one source i.e. the Respiratory Workstation. The waveforms of the airway pressure, airway flow and the expired CO2 curve are displayed continuously on the screen. The Vector Loops like Pressure Volume, Flow Pressure and Flow Volume loops are also available in addition to the lung mechanics parameters like Expiratory and Inspiratory Resistances, Compliance, Peak Pressure, PEEP, etc. The Single Breath Diagram i.e. expired CO2 concentration versus volume and dead space ventilation is also calculated. The blood gas analysis data is plotted in convenient diagrams like the O2−CO2 diagram, Oxygen Chart, etc. The trend of all these parameters are available with a granularity of one minute. An industry standard laser printer is used for report generation to produce reports of the real-time waveforms, parameter values and the trends. User interface is through easy menus with the traditional keyboard, touchscreen including keyborad on screen for data entry and the mouse.

Breath detection algorithm in digital computers

SummaryAn algorithm for the detection and deliineation of breaths is described. The proposed algorithm takes into account the different, common modes of ventilation like the pressure controlled, volume controlled and patient triggered modes of ventilation. Airway flow curve is used as the basic delineator and the airway pressure and the Co2 concentration curves are used to confirm the delineation. A flow chart is also included to explain the algorithm. The detailed explanation and modifications, for additional confirmation and for the selections of constants, to check for the rise or fall of the pressure and Co2 curves, are also included.

A Microcomputer-Based Charting System for Documentation of Heamodynamic, Respiratory Parameters and Drug Administration During Cardiac Anaesthesia

The practice of documentation of respiratory and heamodynamic parameters during an anaesthetic procedure has proven to be of great value. Documentation of anaesthetic records can be achieved by either manual or automatic methods. Manual record keeping is done by entering into the chart, the relevant parameters every 15 minutes. Manual record keeping was found to be laborious and time consuming specially during an acute episode. During this period, important vital information was often missed and forgotten. In such situations conventional record keeping by hand has proved to be unsatisfactory and unreliable. If one is looking for precise documentation then automatic recording system is preferable.

Development of software for pulse oximeter and investigation of its realtime response in clinical environment

We developed a pulse oximeter software at Thorax Centre, Erasmus University as a joint project with an industry and evaluated it in the clinical environment of thorax anaesthesia using a computerized protocol for realtime data collection during routine clinical procedures. This paper gives an account of the results we obtained from the development project and the clinical study. The paper consists of two parts. First part describes different components of the software module and their influence on different aspects of the clinical behaviour of the oximeter. The second part describes the results of realtime response investigation. The investigation was carried out using a personal computer to collect the data continuously during anaesthesia, surgery and post-operative periods. Two other industry standard oximeters, Nellcor and Ohmeda were also included in our study. We collected data on more than fifty patients on an average of eight hours per patient over a period of four months with major emphasis on low-saturation occurrences. The interpretation of the data was focused more on the realtime response anomalies on random cases than on ensemble statistical data evaluation. We found, that there are few factors in clinical environment which often influences the measurement of a pulse oximeter very strongly. Most often the anomalies were found during low saturation measurement. The main objective of this paper is to make the results available to practising clinicians so that it may be useful to identify these occurrences during routine clinical usage.

Anesthesia support systems.

Rapid growth in computer technology in producing high-performance systems with superior ergonomic design has opened new avenues in various application areas in different segments of engineering which demand visual presentation and communication capabilities in addition to excellent number-crunching power. Incidentally, most of these applications are related to a category of monitoring, real-time model simulation, intelligent alarm annunciation, and maintaining a record of events. This new trend has very recently diversified into medical monitoring and computing. Cost is a major criterion from the point of widespread acceptance, and these systems were not economical until recently. Today, many high-end personal computer systems can provide an excellent platform for many concepts in medical monitoring to become a reality. The promises of such progress is phenomenal. With good cooperation among industries and between industries and users and with well-defined set of standards, computerized monitoring can certainly become, in a couple of years, the nucleus of support systems for anesthesia.

Lung mechanics in patients undergoing mitral valve replacement. The value of monitoring of compliance and resistance.

Measurements of compliance, resistance of the respiratory system, and left atrial pressure were made before, during, and after mitral valve replacement in 30 patients. Postoperatively left atrial pressures decreased, resistance decreased and compliance increased significantly. Monitoring and recordkeeping of lung mechanics were found to be useful in predicting the feasibility for extubation and as indicators of impending disasters, e.g., due to bleeding in the thoracic cavity.

Use of mass spectrometry and infrared CO2 analyzer for bedside measurement of cardiopulmonary function during anesthesia and intensive care

In response to the increasing abilities to provide continuous and detailed information on the cardiopulmonary status during and after open heart surgery, we measured hemodynamic and pulmonary functions including cardiac index, end-tidal CO2, minute volume, dead space, ventilation/perfusion ratio, O2 consumption, and other derived variables with a mass spectrometer. This was found useful, for example, in evaluating the need for artificial ventilation in postoperative cardiac patients.