Ralph T. Geer

Early extubation after coronary artery bypass graft surgery.

Data were collected on the postoperative respiratory courses of two groups of patients following cardiac surgery: one group of 31 patients under typical management for 1973, and a second group of 72 patients from 1975–1976 representing our current management regimen. The patients in the 1973 group were allowed to wake up passively before our seeking extubation criteria. Almost half of these were extubated in the period 15 to 20 hours after admission to the ICU, i.e., the morning after surgery, and 29% were discharged from the ICU within 48 hours of admission. The patients in the 1975–1976 series had pharmacological reversal of muscle relaxants and somnolence following admission to the ICU, when their condition was shown to be stable by clinical and laboratory assessment. Criteria for extubation were then sought. Within 5 hours of ICU admission, 62.5% of the patients were extubated and almost 50% of the patients were discharged from the ICU within 24 hours. No patient in either series required reintubation, and there were no complications due to the early extubation and ICU discharge of patients in the 1975–1976 series. We believe that early extubation of patients whose postoperative course is otherwise uncomplicated following cardiac surgery allows rapid mobilization and progress to the intermediate care areas without introducing undesirable sequelae.

Errors in Measurement of Oxygen Uptake due to Anesthetic Gases

Errors in measurement of exhaled gas volume, mixed expired oxygen and carbon dioxide concentrations, and inspired oxygen concentration and the presence of exhaled anesthetic agents cause errors in on-line calculated oxygen uptake that increase geometrically with increasing inspired oxygen concentration. No one has quantified the decrease in the magnitude of the error that might be realized if directly measured nitrogen concentration were included in the calculation. We used a computer model to evaluate this improvement, assuming an oxygen uptake of 200 ml/min and normal ventilatory parameters. Using a Monte Carlo technique, we generated 100 sets of data points, with random errors averaging 0.5% around the expected gas concentrations, and compared the accuracy of oxygen uptake calculated with and without inclusion of directly measured inspired and expired nitrogen concentrations. When the inspired oxygen fractions were 0.2, 0.5, and 0.8, the calculated oxygen uptakes +/- % standard deviation were 200 +/- 4.3, 200 +/- 12, and 196 +/- 21 when directly measured nitrogen was included versus 200 +/- 3.5, 196 +/- 16, and 205 +/- 71 when it was not. The procedure was repeated, assuming 50 ml/min of anesthetic excretion and the calculated oxygen uptakes were 200 +/- 4.6, 202 +/- 12, and 195 +/- 17 versus 212 +/- 3.8, 251 +/- 17, and 398 +/- 64. Including direct measurement of inhaled and exhaled concentrations of nitrogen or another insoluble inert tracer gas allows accurate measurement of oxygen uptake, even in the presence of exhaled anesthetic gases. It also decreases the error in oxygen uptake determination by a factor of nearly six when the inhaled oxygen fraction is 0.8.

Unreliability of Hemodynamic Indexes of Left Ventricular Size during Cardiac Surgery

Pulmonary artery diastolic (PADP) and wedge pressures (PAWP) and left ventricular end-diastolic pressure (LVEDP) are commonly used to estimate left ventricular (LV) preload. To assess the ability of hemodynamic indexes of preload to estimate anatomical preload, or LV volume, we studied 45 patients during a coronary (18 patients) or aortic valve (27 patients) procedure and compared epicardial two-dimensional echocardiographic LV cavity area with simultaneous measurements of PADP, PAWP, and high-fidelity LVEDP. Pulmonary artery diastolic pressure, PAWP, and their percent change after bypass did not correlate with absolute values (before or after bypass) or percent change in LVEDP. Percent change in LV area correlated weakly with percent change in PADP (r = .34, p less than .03) but not with changes in PAWP or LVEDP. Changes were opposite in direction in 45% (PADP), 50% (PAWP), and 67% (LVEDP) of patients. In conclusion, both PADP and PAWP were poor guides to LVEDP and neither reflected changes in LV size. Thus, hemodynamic indexes of preload should be used with caution during cardiac operations.

A Departmental Policy Addressing Chemical Substance Abuse

Substance abuse is a major socioeconomic problem. However, the ready availability of potent narcotic and sedative drugs probably constitutes a unique risk for anesthesiologists. Until recently, few anesthesia departments were prepared to recognize or safely manage afflicted colleagues. Because we felt it important to educate our staff and residents and to have a response mechanism established prior to the advent of a substance abuse problem, a departmental committee was formed to develop a Substance Abuse Policy. The policy has served to increase our general awareness and to direct our actions effectively when dealing with physician impairment. It is presented here in the belief that other departments might find it useful in tailoring their approach to this problem.

The Effect of Long-term Controlled Mechanical Ventilation with Positive End-expiratory Pressure on Renal Function in Dogs

The effects of 46 h of mechanical ventilation and PEEP on urinary output, sodium excretion, and renal and cardiovascular function were examined. Dogs sedated with sodium pentobarbital were ventilated using one of three modes: spontaneous ventilation (SV), controlled mechanical ventilation (CMV), or CMV with 10 cmH2O positive end-expiratory pressure (CMV with PEEP). Intravenous fluids were given at a constant rate throughout the study and measurements of renal and cardiovascular function were made over four periods. Dogs whose lungs were ventilated with PEEP displayed more than two times the amount of fluid retention seen in the other groups as assessed by mean weight gain. This was due to an initial depression of urine flow, sodium excretion, and free water clearance. Urinary flow rate approximated the rate of fluid infusion by 20 h in SV dogs and by 27 h during CMV, while the maximum during CMV with PEEP occurred at 46 h. There were no significant differences in glomerular filtration rate, renal corticomedullary blood flow distribution, or renal blood flow between groups. During the 46 h, cardiac index increased (SV, +16%; CMV, +19%; CMV with PEEP, +64%), while systemic vascular resistance (SV, –28%; CMV, –30%; CMV with PEEP, –57%), renal vascular resistance (SV, –12%; CMV, –20%; CMV with PEEP, –23%), and mean arterial pressure (SV, –16%; CMV, –15%; CMV with PEEP, –15%) decreased in all groups. This study has demonstrated that when a constant sodium and water load was provided, the SV and CMV groups were rapidly able to adjust the urinary excretion to meet input, while the return of renal function toward normal in the CMV with PEEP group was delayed until almost 46 h from the start of ventilation.

Influence of ventilation on response to fluid load in dogs: body water and albumin distribution.

Beagie dogs were sedated with intravenous pentobarbital ventilated for 46 h with either spontaneous ventilation (SV), controlled ventilation (CV), or controlled ventilation with 10 cmH2O end-expiratory pressure (CV + PEEP). Throughout the study period saline (0.45 per cent with added KCl) was infused at 120 ml/h. The influence of ventilatory mode on the accumulation and organ distribution of body water during continuous fluid loading was determined. Five animals were studied with each ventilatory mode. In all groups body weight increased, but with SV weight increase began only after 28 h and increased by 7.2 per cent of body weight by 46 h. With CV the weight increase was continuous and was 9.2 per cent of initial body weight at 46 h. With CV + PEEP the increase was earlier and greater reaching 22 per cent by 46 h. Radioisotopic analysis of total body water, extracellular water, and plasma and erythrocyte water demonstrated that the body weight increase was due to water retention principally in the extracellular compartment.Postmortem analysis of the major body organs for water and albumin distribution demonstrated increased water in the muscle and subcutaneous tissue of the CV + PEEP group that accounted for the total difference in water retention compared to the SV or CV animals. Organ extravascular albumin content varied relatively little between ventilatory modes.Ventilation with increased mean intrathoracic pressure was accompanied by marked and prolonged fluid retention. In these otherwise healthy dogs the water accumulation was confined to sites that appeared unlikely to interfere with organ function.

A comparison of ketorolac and fentanyl for controlling postoperative uterine cramping pain in ambulatory surgery patients

Abstract Non-steroidal anti-inflammatory drugs (NSAIDs) have been shown to reduce the pain of dysmenorrhea by inhibiting the synthesis of prostaglandins that cause the uterus to contract. Studies have not been undertaken previously to determine the effectiveness of NSAIDs in controlling uterine pain resulting from gynecological surgery. This study compares the NSAID ketorolac tromethamine to fentanyl, a commonly used opioid, in 100 women undergoing gynecological surgery in an ambulatory setting. Subjects were randomly assigned to receive either fentanyl or ketorolac IM at the end of the surgical procedure. Uterine cramp pain and non-uterine pain were rated on separate verbal analog scales in the recovery room. Incidence of nausea and vomiting and need for postoperative opioid analgesics were also compared between the two study groups. No significant differences were found between the two groups in the severity of uterine cramp pain, in the need for supplemental analgesia or in the incidence of nausea or vomiting. Both drugs appeared to provide reasonable patient comfort, but in the sub-group of patients who required postoperative opioid, the ketorolac group had lower non-uterine pain scores in the late postoperative period than did the fentanyl group. The absence of clear superiority of the NSAID may indicate that a biochemical pathway other than the prostaglandin mechanism is involved in the production of postoperative uterine cramping pain.

Esmolol as an anaesthetic adjunct in ambulatory surgery

Abstract The aim of this study was to compare the efficacy of esmolol and fentanyl as anaesthetic adjuncts. Forty healthy patients presenting for laparoscopic tubal fulguration were randomly assigned to either an esmolol or fentanyl protocol, as part of a nitrous oxide/muscle relaxant anaesthetic technique. Blood pressure and heart rates, measured pre- and post-induction and intubation, showed no significant differences nor did the times of return of cognitive function and extubation respectively. Patients from the esmolol group were both ambulatory and discharged significantly sooner than the fentanyl group. The incidence of nausea and urinary retention, combined as adverse recovery room events were significantly higher in the fentanyl group. Esmolol proved to be a satisfactory substitute for narcotics in a nitrous oxide/relaxant anaesthetic technique and was associated with shorter times to ambulation and discharge.

A portable, low cost ventilation system for transportation of patients with severe acute respiratory failure.

As part of the development of a life support stretcher for transportation of critically ill patients, a portable ventilation system was developed. This system was used successfully during transportation of 6 of 11 patients who required ventilatory assistance and who were being considered for extracorporeal membrane oxygenator support. Immediately after transportation, PaCO2 values were significantly lower (p less than 0.05) in patients ventilated with this system, when compared to PaCO2 values of the remaining 5 patients in whom ventilation was assisted with a 2-liter anesthesia bag (PaCO2 = 58.7 +/- 3.6). This system offers significant advantages over other presently manufactured systems, including low cost, portability, and efficiency in terms of oxygen utilization. (Manual ventilation is supplied so that no auxiliary electrical power supply is necessary.) Positive end-expiratory pressure (PEEP) can be varied by 2.5 cm H2O increments using a commercially available, weighted ball valve. In addition, it has been useful for transporting patients with acute respiratory failure within the hospital for therapeutic maneuvers or diagnostic studies.