Henrik Zetterström

A new device for administration of nasal continuous positive airway pressure in the newborn: an experimental study.

During treatment with continuous positive airway pressure (CPAP), optimal re-expansion of lung units with minimal work of breathing is best accomplished when the airway pressure (Paw) is kept constant at the desired CPAP level throughout the entire breathing cycle. To achieve this, a new device was constructed in which CPAP was generated by a jet of fresh gas close to the nasal airway. The performance of the new device was investigated experimentally using a lung model which simulated the breathing pattern of a newborn. Paw, flow, and external work of breathing were measured at three CPAP levels, with and without controlled airway leakage. The new device was compared with a traditional continuous-flow CPAP system with standard nasal prongs. Despite a virtually constant pressure within the traditional system, Paw variations and external workload were considerably less with the new device, which was also less sensitive to airway leakage.

Albumin Treatment Following Major Surgery

The effect of a 20 % albumin solution on plasma oncotic pressure, renal function and peripheral oedema was investigated in 30 adult patients undergoing elective major abdominal surgery. Half of them received an average of 173 g of albumin between the end of the operation and the 5th postoperative day, in accordance with a standardized scheme. Otherwise the same schedules for fluid therapy and blood replacement were followed in all patients. Postoperatively, serum albumin and plasma oncotic pressure were fairly normal in the albumin group, but decreased by 28 % and 24 % in the control group. The difference between the groups was statistically significant during the first week, but disappeared during the second week. Arm and thigh circumferences increased postoperatively to a similar extent in both groups. There were no apparent differences in circulatory variables, alveolo‐arterial oxygen tension difference, incidence of wound infection or postoperative restoration of intestinal activity between the groups. Although renal and thromboembolic complications occurred only in the control group, the material is too small to permit any conclusions to be drawn from the possible difference in renal function and morbidity between the groups. The limited availability and high cost of albumin require strict indications for its use. Our results so far have failed to justify routine administration of concentrated albumin postoperatively.

A new nomogram facilitating adequate haemodilution

When using deliberate haemodilution to a certain haematocrit value (Hct), the appropriate preoperative blood volume of the patient must be determined and matched with the transfusion volume at a certain blood loss. In order to facilitate such calculations a nomogram was constructed, aiming for a final Hct of 33%. Preoperative Hct, height, weight and sex of the patient are input variables. After drawing three straight lines, the nomogram yields the normal blood volume and the acceptable pre‐transfusion blood loss (BL). This nomogram was used during surgery when the preoperative Hct exceeded 35%. Protocols from 100 patients bleeding more than 50% of their BL were studied. Blood loss was 1.1±0.6 I (mean±s.d.) ranging from 0.4 to 4.0 1. Fifty‐one of the patients received blood transfusion. This program resulted in a decrease of Hct (mean ± s.d.)from 41 ± 3% preoperatively to 33 ± 4% during the first 30 min postoperatively. Sixty‐three of the patients had a final Hct of 30–35%, 13 had 27–29% and one had 26%. The low values were most likely due to underestimation and consequent unsubstituted blood loss. In summary, the nomogram makes time‐consuming mathematical operations unnecessary. It was easy to use and the postoperative Hct was close to that desired in most patients.

Prehospital analgesia using nasal administration of S-ketamine – a case series

Pain is a problem that often has to be addressed in the prehospital setting. The delivery of analgesia may sometimes prove challenging due to problems establishing intravenous access or a harsh winter environment. To solve the problem of intravenous access, intranasal administration of drugs is used in some settings. In cases where vascular access was foreseen or proved hard to establish (one or two missed attempts) on the scene of the accident we use nasally administered S-Ketamine for prehospital analgesia. Here we describe the use of nasally administered S-Ketamine in 9 cases. The doses used were in the range of 0,45-1,25 mg/kg. 8 patients were treated in outdoor winter-conditions in Sweden. 1 patient was treated indoor. VAS-score decreased from a median of 10 (interquartile range 8-10) to 3 (interquartile range 2-4). Nasally administered S-Ketamine offers a possible last resource to be used in cases where establishing vascular access is difficult or impossible. Side-effects in these 9 cases were few and non serious. Nasally administered drugs offer a needleless approach that is advantageous for the patient as well as for health personnel in especially challenging selected cases. Nasal as opposed to intravenous analgesia may reduce the time spent on the scene of the accident and most likely reduces the need to expose the patient to the environment in especially challenging cases of prehospital analgesia. Nasal administration of S-ketamine is off label and as such we only use it as a last resource and propose that the effect and safety of the treatment should be further studied.

Influence of Plasma Oncotic Pressure on Lung Water Accumulation and Gas Exchange After Experimental Lung Injury in the Pig

In 18 anaesthetized and artificially ventilated pigs, oleic acid was infused intravenously in order to induce a lung injury characterized by increased lung water content, decreased compliance and a ventilation/perfusion disturbance. After a stabilizing period, half of the animals (group P) underwent repeated plasmapheresis, which halved their plasma oncotic pressure (POP). The rest of the animals were bled and re‐transfused with the shed blood, thus serving as a control group. In both groups, care was taken to keep the mean left atrial pressure as constant as possible. During plasmapheresis and “shamapheresis”, there was no significant increase in venous admixture (Fio2 0.21 and 0.6) in either of the groups. At the end of the study, end‐inspiratory pressure, dead space/tidal volume ratio and wet/dry lung weight ratio (WW/DW) were significantly higher in group P. Venous admixture and WW/DW correlated significantly with pulmonary arterial pressure and calculated pulmonary capillary pressure, but not with POP or POP minus pulmonary arterial occlusion pressure. It is concluded that reduction of plasma oncotic pressure may increase the lung water content in previously injured lungs, but this extra water accumulation does not necessarily impair oxygenation in the lungs.

Sublingual buprenorphine as postoperative analgesic: a double-blind comparison with pethidine.

Buprenorphine and pethidine as postoperative analgesics were compared in 96 women having gynaecological operations by lower laparotomy. A fixed dose of the respective drug was given in a double‐blind and double‐dummy manner, initially intramuscularly and thereafter by sublingual buprenorphine (0.4 mg) or intramuscular pethidine (75 mg) at the request of the patient during the first 24 h postoperatively. Patients receiving buprenorphine had longer dose intervals and thus needed fewer doses. The analgesic effect, as assessed by a visual analog scale, was similar with both drugs. There were no significant differences between the groups regarding respiratory depression and nausea. It appears that sublingual buprenorphine is as effective and safe as intramuscular pethidine in the postoperative period.

Flow Pattern and Respiratory Characteristics during Halothane Anaesthesia

Using pneumotachography, the flow pattern was analysed in detail and tidal volume, respiratory rate, dead‐space to tidal volume ratio (VD/Vr) and carbon dioxide output were measured in adults (Group A, n= 12) and 3–8‐year‐old children (Group B, n= 10) during spontaneous breathing anaesthesia with halothane and surgery. The respiratory cycle was divided by equidistant points into 40 parts and the flow at each point related to peak inspiratory and expiratory flow. Thus a relative flow pattern was derived. This relative flow pattern was almost identical in both groups. Characteristically, the flow curve showed rapid turns from high expiratory to high inspiratory flow rates without any end‐expiratory flow pause (except in one adult). The minute ventilation was 6.6 ± 2.0 1 × min‐1 in Group A and 3.4 ± 0.6 1 × min‐1 in Group B, being correlated both to body weight and body surface area in Group A but not in Group B. The tidal volume was 210 ± 60 ml in Group A and 78 ± 13 ml in Group B, respiratory rate 31 ± 4 × min‐1 and 44 ± 10 × min‐1, respectively, and the VD/Vr ratio 0.40 ± 0.10 and 0.55 ± 0.12, respectively. Carbon dioxide output was 173 ml × min‐1 (STPD) in the adults and 82 ± 13 ml × min‐1 (STPD) in the children. It was correlated to both body weight and body surface area in the adults but not in the children.

Fresh gas flow in coaxial Mapleson A and D circuits during spontaneous breathing

In a lung model simulating spontaneously breathing halothane anaesthesia, the rebreathing characteristics of the coaxial Mapleson A (Lack circuit) and D (Bain circuit) systems were tested. Using decrrasing fresh gas flows (Vf), the end‐tidal carbon dioxide fraction (Faco2) was monitored and the point of rrbreathing (R.P.) detected. The effects of changes in minute volume (Ve), dead‐space to tidal volume ratio (Vd/Vt) and carbon dioxide elimination (Vco2) were studied. The effect of increased tidal volumes (Vt) on Faco2 was investigated for some different fresh gas flows (Vf). The Vf/Ve ratio for R.P. in the Bain circuit was approximately 2 and in the Lack circuit 0.88. In both circuits an increase in Ve and a decrease in the Vd/Vt ratio resulted in higher demands on Vf if rebreathing was to be avoided. The latter effect was much more pronounced in the Lack circuit. In neither system did any changes in Vco2 affect the rebreathing characteristics. The conclusion was drawn that the Lack system is a much better choice concerning the fresh gas flows for anaesthesia with spontaneous breathing than the Bain system. It was also concluded that the fresh gas flows recommended by Humphrey for the Lack system (it. 51 ml × min‐1 ± kg b.w.‐1) and by the manufacturers for the Bain system (i.e. 100 ml × min‐1 × kg b.w.‐1) are inadequate and should be increased if a considerable degree of rebreathing is to be avoided.

Preserved oxygenation in obese patients receiving protective ventilation during laparoscopic surgery: a randomized controlled study.

Venous admixture from atelectasis and airway closure impedes oxygenation during general anaesthesia. We tested the hypothesis that continuous positive airway pressure (CPAP) during pre‐oxygenation and reduced fraction of inspiratory oxygen (FIO2) during emergence from anaesthesia can improve oxygenation in patients with obesity undergoing laparoscopic surgery.

Simulated Spontaneous Breathing. A New Model for Testing Anaesthetic Circuits

A carbon‐dioxide‐producing lung model capable of simulating spontaneous breathing is presented. It consists of a piston in a cylinder, a mixing chamber and a dead space volume. The piston is driven by a direct‐current motor controlled by a micro‐processor and a servo unit. Respiratory waveform and rate, tidal volume, carbon dioxide production and dead space are easily adjustable within a wide range. The model is easy to handle and accurately mimics a given breathing pattern. It seems suitable for investigations of rebreathing and carbon dioxide elimination in different anaesthetic circuits.