Ulf Sjöstrand

Comparison of intramuscular and epidural morphine for postoperative analgesia in the grossly obese: influence on postoperative ambulation and pulmonary function

In a randomized double-blind study of thirty grossly obese patients undergoing gastroplasty for weight reduction, the effects of intramuscular and epidural morphine were compared as regards analgesia, ambulation, gastrointestinal motility, early and late pulmonary function, duration of hospitalization, and occurrence of deep vein thrombosis in the postoperative period. The patients were operated on under thoracic epidural block combined with light endotracheal anesthesia. A six-grade scale was devised to quantify postoperative mobilization. A radioactive isotope method using 99mTc-plasmin was employed to detect postoperative deep vein thrombosis. For 14 hr after the first analgesic injection, respiratory frequency was noted every 15 min and arterial blood gases were measured hourly. Peak expiratory flow was recorded daily until the patient was discharged from hospital. Spirometry was performed the day before and the day after surgery. Plasma concentrations of morphine were measured after both intramuscular and epidural administration. Both intramuscular and epidural morphine gave effective analgesia, but the average dose of intramuscular morphine was up to seven times greater than that required by the epidural route. A larger number of patients receiving epidural morphine postoperatively were able to sit, stand, or walk unassisted within 6, 12, and 24 hr, respectively. Being alert and more mobile as a result of superior postoperative analgesia from epidural morphine, patients in this group benefited more from vigorous physiotherapy routine, which resulted in fewer pulmonary complications. Furthermore, earlier postoperative recovery of peak expiratory flow and bowel function presumably contributed to a significantly shorter hospitalization in patients receiving epidural morphine. There was no evidence of prolonged respiratory depression in this high-risk category of patients. The 99mTc-plasmin tests revealed no significant difference between the two groups.

Review of the physiological rationale for and development of high-frequency positive-pressure ventilation--HFPPV.

In 1967, a method of artificial positive‐pressure ventilation without circulatory effects synchronous with respiration was required for experimental studies and for this purpose high‐frequency positive‐pressure ventilation (HFPPV) was developed. The original rationale for the HFPPV technique was (a) by means of endotracheal insufflation a reduction in dead space should make it possible, with smaller tidal volumes and higher ventilatory frequencies, to provide adequate alveolar ventilation at lower maximal and lower mean airway pressures than those required in conventional IPPV; (b) under insufflation with a high frequency and a short insufflation period the inertia characteristics of the lungs should be able to achieve critical suppression of the circulatory effects of the ventilatory pattern.

Influence of Naloxone Infusion on Analgesia and Respiratory Depression Following Epidural Morphine

The influence of two different concentrations of iv naloxone infusion on the analgesia and adverse effects of epidural morphine were compared in a double-blind, placebo-controlled study. Fortyfive patients undergoing gallbladder surgery were provided postoperative analgesia by 4 mg epidural morphine; they then received an iv infusion over a 12-h period consisting of either 5 μg · kg−1 · h−1 naloxone, 10 μg · kg−1 · h−1 naloxone, or saline. Pain relief was assessed by hourly visual analog scoring (VAS) and by direct questioning of the patient. Requirement of additional analgesia was noted. Respiratory frequency was monitored every 15 min and arterial blood gases were analyzed every 2 h for 24 h. Peak expiratory flow (PEF) was recorded 6 and 24 h postoperatively. Steady-state kinetics of naloxone were determined by a modified radioimmunoassay (RIA) method. All patients had good to excellent postoperative pain relief. Naloxone, 5 μg · kg−1 · h−1, did not appear to have any effect on epidural morphine analgesia. However, naloxone infusion at the rate of 10 μg.kg−1 h−1 reduced the duration of analgesia by about 25%, and more frequent injections of epidural morphine were required to give effective analgesia. Complete reversal of analgesia was not seen in any patient. A dose-related stimulatory effect on respiratory frequency was noted in the groups receiving naloxone. Paco2 values also were better in these groups as compared to values in the placebo group. The steady-state plasma concentration of naloxone was 2.8–3.7 ng/ml during infusion at the rate of 5μg.kg−1 h−1 and 4.3–5.1 ng/ml during 10 μg · kg−1 h−1 naloxone infusion. The plasma clearance of naloxone was 30.5 and 35.4 ml. min−1. kg−1 for the low and high dose groups, respectively, and showed a four-fold interindividual variation. The authors conclude that naloxone reverses epidural morphine analgesia in a dose-dependent manner. Low-dose naloxone infusion (5 μg.kg−1 h−1)prevents respiratory depression due to epidural morphine without affecting its analgesia.

Postoperative Pain Relief by Epidural Morphine

Postoperative pain relief was studied in 280 patients undergoing various kinds of surgery, e.g., thoracic, upper and lower abdominal, perineal, obstetric, and orthopedic. Morphine, 2 or 4 mg, was given after surgery through an indwelling epidural catheter. Excellent analgesia was noted in 87% of patients; only 3.5% of patients were dissatisfied. A single injection gave complete pain relief for the entire postoperative period in 30% of cases; in the remaining patients the mean duration of analgesia was 10.7 hours (SD ± 4.3). Plasma morphine concentrations recorded after 2-mg doses suggest a regional spinal action as the basis for the long duration of analgesia, although the initial effect after 4-mg doses might well include systemic responses due to rapid vascular uptake of morphine from the epidural space. Peak expiratory flow (PEF) measurements and arterial blood gas analyses showed no significant early postoperative respiratory depression. Absence of sedation, orthostatic hypotension, respiratory depression, and motor paralysis facilitated early ambulation with less risk for postoperative respiratory complications. It is concluded that 2-mg doses of epidural morphine give good analgesia of long duration despite low plasma levels. After upper abdominal and thoracic surgery higher doses (4 mg) may be necessary in healthy patients. Elderly and frail patients appear to be sensitive to epidural morphine and doses in excess of 2 mg should be avoided regardless of the type of surgery. With this dose schedule we have not encountered delayed respiratory depression.

High-frequency Positive-pressure Ventilation (hfppv): A Review Based upon Its Use during Bronchoscopy and for Laryngoscopy and Microlaryngeal Surgery under General Anesthesia

* Research Engineer (project 4252) of the Swedish Medical Research Council; t Senior Clinical Associate of Anesthesia, Department of Anesthesiology and Intensive Care, Regional Hospital of Orebro.

High frequency positive pressure ventilation during anaesthesia and routine surgery in man.

Associate Professor of Medical Physiology, University of Uppsala, Uppsala; Research Associate of the Swedish Medical Research Council; Deputy Head, Department of Anesthesiology and Intensive Care, Regional Hospital of Orebro. This work was supported by the Swedish Medical Research Council (project 4252). the Orebro County Council, and the Research Fund of the Orebro County Council. During this investigation Ulf Sjostrand was a full-time Research Associate (project 4937) of the Swedish Medical Research Council. Received from the Department of, Anesthesiology and Intensive Care, Regional Hospital, 5-701 85 Orebro, Sweden. Accepted for publication May 15, 1980. Reprint requests to Dr. Sjostrand, Department of Anesthesiology and Intensive Care.

High‐Frequency Positive‐Pressure Ventilation (HFPPV) During Transthoracic Resection of Tracheal Stenosis and During Peroperative Bronchoscopic Examination

The respiratory and circulatory conditions in high frequency positive pressure ventilation (HFPPV) in the dog have been investigated previously. By means of expiratory resistance a positive intratracheal pressure was maintained throughout the respiratory cycle. Adequate ventilation was achieved at low intratracheal and transpulmonary pressures.

Long-term treatment of two patients with respiratory insufficiency with IPPV/PEEP and HFPPV/PEEP.

Operation of a patient with intrathoracic tracheal stenosis using a new ventilation technique (HFPPV) is described. The technique permits tracheoscopy during ventilation and operation, thus enabling exact location of the stenosis to be obtained. Further, peroperative tracheoscopic checking of the anastomosis can be carried out. Resection and anastomosis can be performed without interference of a bulky endotracheal tube.

Peak airway pressure increase is a late warning sign of partial endotracheal tube obstruction whereas change in expiratory flow is an early warning sign.

The respiratory centre is a multi‐input system and positive‐pressure ventilation is known to interfere with respiratory control mechanisms. Further, in intermittent positive‐pressure ventilation (IPPV) the ventilatory pattern produced by the ventilator and the lung systems is known to influence pulmonary and cardiovascular functions. High‐frequency positive‐pressure ventilation (HFPPV) has been shown to eliminate respiration‐synchronous variations in blood pressure and blood flow, and at frequencies of 60 per min or more spontaneous breathing ceases almost instantaneously if adequate alveolar ventilation and arterial oxygenation are achieved. However, activation of other inputs to the respiratory centre, e.g. chemo‐receptor inputs, can induce spontaneous respiration during HFPPV. Consequently the balance between excitatory and inhibitory afferents is decisive for the patients spontaneous respiratory efforts (discoordination) during artificial ventilation.

Summary of Experimental and Clinical Features of High-Frequency Positive-Pressure Ventilation—HFPPV

If peak inspiratory airway pressure (Ppeak) is used to monitor airway patency, progressive obstruction of the endotracheal tube (ETT) resulting from secretions can go undetected for a prolonged period. The reason is that any increase in Ppeak depends not only on the degree of narrowing but also on the inspiratory flow (&OV0312;) rate. Although the impact of narrowing on low inspiratory &OV0312; is small, its decelerating effect on the high expiratory &OV0312; is pronounced and, hence, easily detectable. Dividing the volume-flow curve of a passive expiration into five consecutive segments (slices) and calculating the time constants (&tgr;&Egr;) of these slices allows for analyzing whether and how expiratory &OV0312; is impeded by a partial obstruction. In nine piglets, during volume-controlled ventilation, three grades of ETT obstruction were created with an external clamp. In all animals the &tgr;E increased with ETT obstruction (mean for the first slice: 550 ms with unobstructed ETT; grade 1: 661; grade 2: 877; and grade 3: 1563 ms, respectively) and this increase was significant with grade 2 and 3 obstruction. Ppeak, by contrast, did not increase significantly (base: 13, grade 1: 14, grade 2: 15 cm H2O) until the most severe (grade 3: 20 cm H2O) obstruction was created. We conclude that partial obstruction of the ETT can be reliably monitored with the expiratory &OV0312; signal and has the potential of monitoring ETT narrowing in ventilator-dependent patients independent of the inspiratory &OV0312; pattern applied.