Intra-arterial and extra-arterial pH, PCO2 and PO2 monitors

In vitro blood gas analysers inherently limit the frequency of serial blood gas measurements because of blood loss and cost. In vivo blood gas monitors eliminate an inherent cost and blood loss associated with measurement. Optode microsensing is a technology that can be readily adapted to in vivo measurement of pH, PCO₂ and PO₂. Optode-based intra-arterial devices that display continuous values have been developed that are practical for routine use but consistent performance remains a problem; an extra-arterial device that provides intermittent values has been shown to be consistent but is not yet available for routine use. The transfer of blood gas measurements from laboratory analysers to the combination of point-of-care analysers and monitors should have as profound an impact on acute respiratory care as did the introduction of laboratory-based blood gas analysers over 30 years ago. However, we must be sure these devices are reliable, consistent and cost beneficial in order to avoid widespread adoption of yet another technology that provides more data, more cost, and questionable patient benefit.     

End-tidal CO2 monitoring

Two cases of malignant hyperthermia are described where the earliest sign was a rise in the end-tidal CO2 concentration. This led to nearly immediate detection and adequate treatment with sodium dantrolene. These cases demonstrate the efficacy of monitoring end-expired CO2 concentrations in patients at risk from malignant hyperthermia, as well as a means for following the adequacy of treatment.     

Acute Xenograft Rejection Mediated by Antibodies Produced Independently of TH1/TH2 Cytokine Profiles

There is substantial support for the hypothesis that T(H)1 cytokine responses are critical for the normal elaboration of allograft rejection. Recent studies by Wang et al. (1) underscore the importance of T(H)2 responses in xenograft rejection and revealed that T(H)1 cytokines, IL-12 and interferon-gamma (IFN-gamma), can negatively regulate the development of humoral responses necessary for xenograft rejection. Their exceptional studies prompted us to test whether the ability of allografts to elicit cellular rejection and xenografts to induce humoral rejection also result from the differential ability to induce T(H)1 and T(H)2 responses. We compared the kinetics of antibody and cytokine (IFN-gamma and IL-4) production in C57BL/6 mice following allograft transplantation with BALB/c hearts and in C57BL/6 and BALB/c mice following transplantation with Lewis rat hearts. We also compared the ability of BALB/c mice, deficient in the ability to produce IL-4 or IFN-gamma, to reject xenografts and produce xenoantibodies. We observed that T(H)1/T(H)2 cytokine production minimally affected the kinetics of graft rejection but regulated the magnitude of IgG subclass production. Anti-graft IgM played a critical role in initiating acute antibody-mediated xenograft rejection, and the production antigraft IgM was unaffected by IL-4 or IFN-gamma deficiency. In contrast to the report by Wang et al. (1), we conclude that antibody-mediated xenograft rejection in the concordant Lewis rat heart-to-C57BL/6 mouse xenotransplantation model is dependent on anti-IgM production but independent of T(H) cytokine profiles.     

Transcutaneous Pco2 in adults

Using a transcutaneous Pco₂ (PtcCO₂) electrode, arterial Pco₂ (Paco₂) was compared with PtcCO₂in eight adults (seven patients, one normal subject) over a wide range of values of PaCO₂(2.4 to 7.87 kPa). At an electrode temperature of 43°C, PtcCO₂=1.25 Paco₂kPa (95% confidence limits: 0.60 kPa). Change in PtcCO₂accurately reflected change in Paco₂.     

Continuous Measurement of Arterial Po2, Pco2 and pH During Autotransplantation of Canine Hearts

Arterial PO2, PCO2 and pH were measured continuously with electrodes placed in a flow cuvette. Comparison between continuous readings and results of single sample analyses showed practically no discrepancy, and the drifts of the electrodes during time of measurements were negligible. During hypothermic perfusion with a Rygg-Kyvsg?rd bubble oxygenator, autotransplantation of canine hearts was performed. PO2, PCO2 and pH were measured continuously to check the performance of the heart-lung machine, and to evaluate the therapeutic and diagnostic significance of these blood gas values during cardiac surgery. At the start of perfusion, a steep fall in all three parameters was observed. The average fall in PO2 was 313 mmHg; PCO2 fell by 15 mmHg and pH BY 0.15. PCO2 rapidly returned to normal values, while pH and PO2 increased slowly during the perfusion period. PO2 reached its highest value at the lowest temperature and fell during rewarming. PCO was regulated by the carbon dioxide concentration in the heart-lung machine. pH did not return to normal levels within the time of perfusion. In the transistional period from perfusion, PCO2 increased and pH fell. Alterations in the distribution and direction of blood flow and a low systemic blood pressure are possible explanations of the initial fall in PO2 and the post-perfusion changes in PCO2 and pH. The variations in pH and PCO2 at the start of perfusion were caused by an acid priming fluid with low CO2 content. The post-perfusion changes indicated an unstable circulation, but imminent myocardial failure could not alone be diagnosed by continuous measurement.     

Measurement of FEV1 and FVC

The performance of a pocket spirometer was compared with that of the Vitalograph to assess the extent of agreement between the instruments and the repeatability of measurements with each instrument. Both instruments showed a similar level of accuracy when measurements were repeated and in the estimation of forced vital capacity, but there was a mean difference of 201 ml in measurements of forced expiratory volume in one second, for which the Vitalograph gave the larger reading.     

H2 antagonists and bupivacaine clearance

The effect of the H2 receptor antagonists cimetidine and ranitidine on bupivacaine clearance was assessed in women scheduled to undergo elective Caesarean section under epidural anaesthesia. Thirty-six women were randomly allocated to receive either no medication, cimetidine 400 mg or ranitidine 150 mg on the night prior to and on the morning of surgery. No significant difference was found between the peak bupivacaine levels: the mean (SD) values were 0.74 (0.17) microgram/ml, 0.81 (0.38) microgram/ml and 0.70 (0.24) microgram/ml in the control, cimetidine and ranitidine groups, respectively. Similarly, the H2 receptor antagonists did not alter the plasma bupivacaine against time curves, half-life or bupivacaine clearance in the three groups studied.     

Acquired C1 esterase inhibitor deficiency

A case of acquired C1 esterase inhibitor deficiency and its anaesthetic implications is presented. Prophylaxis against angioneurotic oedema using danazol and tranexamic acid is described and the resultant complication of mesenteric venous thrombosis reported.     

Dermabrasion Using CO2 Dry Ice

BACKGROUND: The cosmetic dermatologic surgeon can improve facial scars by using a variety of techniques. Chemical peels, lasers, and dermabrasion are among the most common modalities used. In recent years, laser resurfacing has enjoyed great popularity; however, there is still a role for the time-honored and effective technique of dermabrasion. The recent withdrawal of Freon from the market has made dermabrasion more difficult. OBJECTIVE: To introduce a novel technique of using solid carbon dioxide (CO2) to freeze the skin before dermabrasion. METHOD: Twenty-five consecutive patients with facial acne scars underwent a combination of procedures including chemical peeling and CO2 laser resurfacing, followed by freeze-dermabrasion. Compressed CO2 was then used to make a solid ball of dry ice. The ice was used to freeze the skin prior to dermabrasion. After the application of the dry ice ball to the skin for about 4 seconds, the scares were dermabraded with the large mushroom wheel. As the tissue defrosted, the operator started at the outer edge of the freeze and planed into the center. This procedure was repeated until the desired improvement was achieved. RESULTS: With dry ice, a good skin turgor was achieved. This provided a good foundation for the sanding of the acne scars. The patients were pleased with the results and complications were minimal. CONCLUSION: "Home-made" dry ice works as well as Freon in providing skin turgor for dermabrasion. CO2 dry ice has the added benefits of being inexpensive and environmentally friendly.