Humidity

The humidity of gases is an important topic within anaesthesia and intensive care medicine. An appreciation of the underlying physics helps to ensure that we monitor and deliver optimally humidified gases to our patients, thus minimizing the pathophysiological consequences when normal humidification processes are bypassed. In this article the different techniques and equipment used to measure humidity are illustrated, as well as the methods of humidification used in clinical practice.     

The principles of anaesthetic vaporizers

Fluorinated hydrocarbons have transformed inhalational anaesthesia, and vaporizers are essential for safe and accurate delivery of these agents. The modern day vaporizers have evolved considerably since the ether inhaler invented by John Snow in 1847 and are robust, precise and efficient. For an anaesthetist to administer safe inhalational anaesthetic, it is important to understand the physical principles of the various inhalational anaesthetic agents along with the working principles of the vaporizers. Almost all modern vaporizers are located outside the circle system and the have multiple safety mechanisms in place.     

The principles of anaesthetic vaporizers

Fluorinated hydrocarbons have transformed inhalational anaesthesia, and vaporizers are essential for safe and accurate delivery of these agents. The modern day vaporizers have evolved considerably since the ether inhaler invented by John Snow in 1847 and are robust, precise and efficient. For an anaesthetist to administer safe inhalational anaesthetic, it is important to understand the physical principles of the various inhalational anaesthetic agents along with the working principles of the vaporizers. Almost all modern vaporizers are located outside the circle system and the have multiple safety mechanisms in place.     

Physiology of patient transfer by land and air

Patient transfer is an important part of many patients’ journeys through the healthcare system. In the UK, the majority of transfers are undertaken by land ambulance but some are by air utilizing helicopters or fixed wing aircraft. The transfer of patients is challenging often involving unstable critically ill patients, trainee staff, time pressure, out of hours work and unfamiliar transfer equipment. Patients are exposed to a number of physical factors including acceleration and deceleration, decreased barometric pressure, noise, vibration, reduced humidity and altered ambient temperatures. These factors have a significant effect on patient physiology and it is important that clinicians understand these effects and integrate them with planning and decision making. Other challenges include staff fatigue, communication difficulties, the effects of transfer on medical equipment and the hazards of caring for patients in confined spaces for prolonged periods of time.     

The enhanced Total Body Wrap—The new frontier in dressing care for burns

The management of extensive burns with their associated high fluid exudate following burn excision and skin grafting has always posed a challenge in burn wound care. The ideal dressing should protect the wound from physical damage and micro-organisms; be comfortable and durable; allow high humidity at the wound; and be able to allow maximal activity for wound healing without retarding or inhibiting any stage of the process.     

Humidity affects the performance of von Frey monofilaments

Background: Assessment of tactile and nociceptive thresholds of the skin with calibrated polyamide monofilaments is an established testing method both in animal and in human research. It is known that changes in relative humidity may affect the physical properties of the monofilaments. As this effect has only been studied in very small diameter monofilaments, used in neonatal research, we therefore studied complete sets of polyamide monofilaments. Methods: The effects were studied in a controlled climate chamber during six incremental changes in relative humidity from 20% to 79% (22–24 °C). Following 24 h of equilibration at each humidity level, calibration with a precision scale was performed. Results: A highly significant linear correlation between the natural logarithm (In) of the bending force and the von Frey number was observed at all humidity levels (相似文献   

Measurement of humidity

Humidity is a measure of the amount of water vapour present in a gas. It can be expressed in a number of ways. Absolute humidity is the mass of water vapour present in a given volume of gas, and is expressed as mg/ml or g/m³. Relative humidity is the ratio of the mass of water vapour present in a volume of gas to the maximum amount of water vapour the gas could hold at a specific temperature, and is expressed as a percentage. The dew point is the temperature at which the gas is fully saturated and condensation begins to occur. Hygrometers are instruments which measure humidity; they can measure absolute humidity, relative humidity or dew point. They range from simple mechanical hygrometers, through psychrometers, to more complex electrical and optical instruments. The importance of humidity for anaesthetists lies in the comfort of the theatre environment, safety with regard to static electricity, adverse effects of dry medical gas supplies and heat loss from the body. Other examples of when measurement and control of humidity are important in medicine include sterilization of equipment and neonatal incubators.     

Nature’s wrath—The effect of weather on pain following orthopaedic trauma

BackgroundDespite frequent complaints by orthopaedic trauma patients, to our knowledge there is no data regarding weather’s effect on pain and function following acute and chronic fracture. The aim of our study was to investigate the influence of daily weather conditions on patient reported pain and functional status.MethodsWe retrospectively examined prospectively collected data from 2369 separate outpatient visits of patients recovering from operative management of acute tibial plateau fractures, acute distal radius fractures, and chronic fracture nonunions. Pain and functional status were assessed using a visual analogue scale (VAS) and the DASH and SMFA functional indexes. For each visit date, the mean temperature, difference between mean temperature and expected temperature, dew point, mean humidity, amount of rain, amount of snow, and barometric pressure were recorded. Statistical analysis was run to search for associations between weather data and patient reported pain and function.ResultsLow barometric pressure was associated with increased pain across all patient visits (p = 0.007) and for patients at 1-year follow-up only (p = 0.005). At 1-year follow-up, high temperature (p = 0.021) and high humidity (p = 0.030) were also associated with increased pain. No significant association was noted between weather data and patient reported functional status at any follow-up interval.ConclusionsPatient complaints of weather influencing pain after orthopaedic trauma are valid. While pain in the immediate postoperative period is most likely dominated by incisional and soft tissue injuries, as time progresses barometric pressure, temperature, and humidity impact patient pain levels. Affirming and counseling that pain may vary based on changing weather conditions can help manage patient expectations and improve satisfaction.     

Are postoperative activity restrictions evidence-based?

BACKGROUND: Many surgeons restrict activities postoperatively. Intra-abdominal pressure during some activities is known; however, many everyday activities have not been studied. Our aim was to compare the intra-abdominal pressures created during unavoidable physical activities with activities that commonly are restricted after surgery. METHODS: Nine healthy subjects (2 men, 7 women; age, 28 +/- 7 y) performed 5 repetitions of various activities while their intravesicular pressures was measured. RESULTS: The resting intravesicular pressure was 17 +/- 5 mm Hg, increasing to a maximum of 112 +/- 35 mm Hg during forceful coughing. The intravesicular pressure increase was greatest with forceful coughing, followed by the Valsalva maneuver. CONCLUSIONS: The results suggest that the greatest increase in intra-abdominal pressure occurs during some unavoidable activities. Based on this study, postoperative restrictions may be unnecessary. Further experience based on a larger study is needed to answer this important clinical question.     

Orthopedic immobilization

The classical plaster bandage was devised in the mid 19th century. Until recently, osteoarticular trauma has been treated mostly by plaster cast immobilisation using plaster of Paris. Synthetic materials have been introduced on the market place in the seventies, but they have not superseded the traditional plaster of Paris. The more recent thermoplastic materials are used to make splints and orthoses, particularly at the wrist and hand. The present review of the literature confirms that synthetic materials present better physical and mechanical properties than the traditional plaster of Paris. In addition, they are lighter, they are more resistant to humidity, they are more radiotransparent and they generate less dust when removed. However, they are less malleable and cause higher pressure in case of limb edema. Plaster of Paris therefore remains indicated in the acute posttraumatic or postoperative period. This material is also cheaper, but the pecuniary benefit is limited for several reasons, particularly because plaster of Paris is associated with a higher rate of cast replacement.     

Rugby Injuries Sustained during Tournament Play

Rugby football is a fast growing physical contact sport that is known for its ruggedness and injuries. Tournament play tests the stamina of the individual players and may have a cumulative wear and tear effect that results in different types of injuries. This study was conducted to determine what body parts are injured in a rugby tournament and how serious those injuries are. Climatic conditions, mainly heat and humidity, were considered to be major factors. Heat-related injuries were the single most important cause for termination of play. This type of injury is very serious and may be reduced or prevented by following simple guidelines for play based on the temperature-humidity index. Most other injuries were strains, sprains, contusions, and several lacerations to the knee, thorax, head, and neck; none was catastrophic. The reputation that rugby football is brutal does not seem justified by the injuries sustained in this tournament. J Orthop Sports Phys Ther 1985;7(1):16-19.     

Factors influencing the severity of medical device-related pressure injuries: Pressure injury staging comparison

Medical device-related pressure injuries are receiving increased attention because their social and economic costs are increasing. This study aimed to analyse the stages for each risk factor, and to assess which has a greater impact on severity. We performed a retrospective analysis of 237 patients. Severity was evaluated by pressure injury stages, and the following categories were considered as risk factors: perceptual functioning, malnutrition, reduced mobility, comorbidities, extrinsic factors, medical devices, anatomical areas, and hospital stay. The stages of pressure injury stages were more for vascular access devices than for respiratory devices. The following were related to severity: mental deterioration-related diseases, mental status, albumin level, haemoglobin level, total cholesterol level, intensive care unit care, days of hospitalisation, and time to develop pressure injuries after admission. Decreased mental status, anaemia, hypoalbuminemia, and low total cholesterol levels were particularly critical. However, factors such as anatomical areas, age, malignancy, diabetes mellitus, diseases related to malnutrition, abnormal body mass index, immobility-related diseases, physical restraints, and Braden scale scores were not. A different approach to the management of medical device-related pressure injuries is necessary because they have distinctive characteristics and causative factors than other pressure injury types.     

A paediatric canopy system for aerosol administration and minimized environmental pollution

Background: A canopy system for ribavirin aerosol administration to infants has been developed in order to improve the control of aerosol treatment, facilitate access to the infant and minimize environmental pollution. The system comprises a transparent canopy, fitted with four sealable apertures. An evacuation flow that is 3 1/min higher than the gas supply was anticipated to prevent aerosol leakage from the canopy.
Method: In a clinical evaluation , 10 infants with body weights of 1.8-7.1 kg were placed inside the canopy during 1 hour of simulated treatment. The temperature, relative humidity and carbon dioxide concentration within the canopy were measured repeatedly to study the stability of these variables and their dependence on body weight. Infant body temperature, skin temperature and the respiratory frequency were measured. In a laboratory evaluation , aerosol leakage was studied using an ambient air admixture procedure and smoke tests. The sound level inside the canopy was measured.
Results: All physical variables inside the canopy remained stable. The sound level was 52 dBA. The carbon dioxide concentration (1000–3900 PPM) correlated with infant body weight ( P <0.001), as did canopy temperature (25.1–29.6°C, P <0.05). The relative humidity was 52–88%. Infant body temperatures were not influenced. The respiratory frequency decreased by 13% ( P <0.01). No aerosol leakage was observed. Conclusion: The canopy system facilitates a controlled aerosol therapy with good infant surveillance and accessibility, a minimum of environmental pollution and a comfortable physical environment without apparent risks of carbon dioxide rebreathing or cooling stress at body weights of 1.8-7.1 kg.     

Compensating for the effect of inlet gas temperature on heated humidifier performance

The humidity output of heated humidifiers may be compromised by inlet gas temperatures exceeding approximately 26 degrees C, with humidity dropping below the recommended levels for intubated patients. A new version of the Fisher & Paykel MR850 humidifier claims to deal with this problem by offering a humidity compensation option. The present study tested this feature by measuring humidity output using the gravimetric method and a hygrometer at different inlet gas temperatures (16.6 degrees C to 40.0 degrees C) with compensation on and off. It was found that the compensation is effective in maintaining humidity levels despite high inlet gas temperatures.     

An integrative approach to intracranial hydraulic physiology. I. Basic concepts, pressure-volume relationships, and infusion studies

A computer simulation of the anatomy of the intradural fluid compartment is used to explore intracranial hydraulic physiology. It examines the mutual interactions of fluid flow rates, volumes, and pressures that control the physiology of the intracranial fluid. The mechanisms of change in intracranial pressure despite the fixed volume constraint are elucidated. The physical origins of the pressure-volume curve and data on the infusion of cerebrospinal fluid are examined. The dynamic behavior of this passive system closely simulates the observed physiologic response to bolus infusion, constant rate infusion, hypercapnia- hypocapnea , and hydrocephalus.     

The moisture-conserving performance of breathing system filters in use with simulated circle anaesthesia breathing systems

Breathing system filters can be used to humidify gases delivered to patients. Performance can be determined by measuring the net moisture loss (the difference between expired and inspired levels of humidity) from a patient model. The net moisture loss should be decreased by increasing the level of humidity in the breathing system by, for example, using a circle breathing system. The effect of four different filters, three different levels of humidity in the breathing system (7, 13 and 19 g.m-3) and two tidal volumes (0.5 l and 1.0 l) on the net moisture loss from a patient model was measured. The net moisture loss decreased as the humidity in the breathing system increased and was less for the lower tidal volume. Adequate levels of humidity (>/= 20 g.m-3) will be delivered to patients by most filters provided they are used in conjunction with circle breathing systems and low fresh gas flows.     

Cavernous haemangiomas in the oral cavity: Results of treatment with the 578 nm copper vapour laser

Three patients with symptomatic mucosal haemangiomas in the oral cavity were treated with 578 nm yellow light generated by a copper vapour laser. All have shown marked shrinkage after a single treatment utilizing an energy density of 20 J cm⁻². The patients have not required any further surgical or laser treatment. Conservative management of these haemangiomas using this laser is both useful and logical. The biological effects of the copper vapour laser are described as related to these haemangiomas resulting in highly satisfactory clinical responses.     

Copper vapour laser treatment of port wine stains: a patient questionnaire

A questionnaire was sent to 242 patients who had undergone treatment with yellow light (578 nm) from a copper vapour laser for a port wine stain (PWS), for facial telangiectasia (FT), or for a spider naevus (SN). The questionnaire covered the social implications of the lesion, the physical appearance of the lesion after treatment and the patient's judgement of how the treatment has affected them. Replies were received from 73% of the patients.The replies revealed that 83% PWS, 74% FT, and 81% SN patients felt there had been an improvement in their appearance compared with 2.5% PWS, 14% FT, and 7.5% SN patients who felt that their appearance had changed for the worse. The overall impression of the treatment was also very positive, especially with PWS patients, 91% would recommend the treatment to others, 84% would have the treatment again and 60% indicated their feelings regarding their overall treatment and the effect it had on their lives was very good.     

Variability of pressure provided by sustained compression

Compression therapy is the cornerstone of treatment for patients with venous leg ulcers (VLUs). Although it is generally accepted that the therapeutic outcomes are directly related to the quality of compression therapy, delivering precise and sustained compression therapy is an ongoing challenge for health care professionals. Several factors influence quality of compression therapy: physical structure and elastomeric properties of the compression system, size and shape of the leg, skill and technique of the bandager and physical activity undertaken by the patient. Graduated compression is achieved by applying a bandage at the same tension from ankle to knee, providing the shape of the leg is normal. Many patients with VLUs have distorted legs, challenging the delivery of a desired pressure gradient. Poor bandaging technique can result in little or no benefit or may deliver too high a pressure causing a detrimental effect to the wearer. If the wearer is unable to tolerate the compression, patient concordance and effectiveness are affected. Training has been shown to reduce variability of sub-bandage pressure. Sub-bandage pressure increases during standing and walking. These pressure changes are related to the elastomeric properties of the compression systems. Health care professionals need to understand the properties of the available compression systems and how their application technique must be adjusted.     

Exercise Training During Hemodialysis Reduces Blood Pressure and Increases Physical Functioning and Quality of Life

Hypertension and cardiovascular diseases are highly prevalent in hemodialysis patients and are associated with the reduction of physical functioning and quality of life. We evaluated the effects of supervised aerobic exercise training on physical functioning, blood pressure, quality of life, and laboratory data in hemodialysis patients. Fourteen patients were evaluated at the beginning and after 12 weeks of stretching exercises (control phase) and at the end of 12 weeks of aerobic exercise training performed during hemodialysis sessions (intervention phase). Patients underwent a 6‐min walking test (6MWT), 24‐h ambulatory blood pressure monitoring, a Medical Outcomes Study 36—Item Short‐Form Health Survey (SF‐36) quality of life questionnaire, and blood sample collections. After the intervention phase, the 6MWT distance increased from 508.7 ± 91.9 m to 554.9 ± 105.8 m (P = 0.001), systolic and diastolic blood pressure decreased respectively from 150.6 ± 18.4 mm Hg to 143.5 ± 14.7 mm Hg and from 94.6 ± 10.5 mm Hg to 91.4 ± 9.7 mm Hg (P < 0.05), while hemoglobin levels increased from 10.8 ± 1.2 g/dL to 11.6 ± 0.8 g/dL (P < 0.05). Moreover, there was a significant increase in the physical functioning, social functioning, and mental health dimensions of the SF‐36. Aerobic exercise training during hemodialysis increased physical functioning, reduced blood pressure levels, and improved the control of anemia and quality of life in patients with end‐stage renal disease.