vacuum insulated evaporator

Oxygen is a non-metallic element existing as a colourless odourless diatomic gas (O2) in the lower atmosphere and as a triatomic oxygen (O3) and monatomic oxygen (O) in the upper atmosphere. Joseph Priestley is usually credited with the discovery of oxygen because he was the first to describe it in 1775 in his work entitled Experiments and Observations on Different Kinds of Air. However Scheele, a Swedish apothecary, first discovered oxygen in 1772. Manufacture of oxygen Oxygen is manufactured by the fractional distillation of air. Air is compressed to 5 atmospheres and cooled to -181oC using reverse heat exchangers. A two-stage distillation process yields 99.5% O2 (and 0.4% argon). It is stored at 137 bar in silver cylinders with green shoulders in the United States. Storage of Oxygen: The VIE Hospitals store large quantities of oxygen as a liquid in a vacuum insulated evaporator (VIE). The inner shell of the VIE is made of stainless steel. It is separated from the outer carbon steel shell by an insulated gap with a vacuum of 0.16-0.3KPa. The contents are at 1000KPa and a temperature of -150oC (critical temp -119oC). A gauge indicates the pressure within and a differential pressure gauge (compares top to bottom) indicates the oxygen contents by weight. Compensatory adjustments made by the VIE system If there is a period of low oxygen use or hot weather this will result in the temperature of the liquid oxygen increasing.. This leads to increased pressure in the VIE and at 1500KPa the blowoff valve opens allowing vaporisation into the environment, (the latent heat of vaporisation cools the liquid oxygen). If there is a period of high oxygen use by the hospital or very cold weather, there will be reflected by a decreased temperature of liquid oxygen and thus a decreased pressure in the VIE system. At 1000KPa the Pressure Raising Valve (PRV) opens, and allows liquid oxygen to shunt through a Pressure Raising Vapouriser (PRV). This allows environmental heat to enter the system. This mechanism ensures that the pressure and temperature of the VIE rises back to normal. All outgoing gases pass through a heat exchanger to warm them.

TEE

Absolute contraindications:
Esophageal spasm.
Esophageal stricture.
Esophageal laceration.
Esophageal perforation.
Esophageal diverticula (e.g. Zenker's diverticulum).

Relative contraindications:
Large diaphragmatic hernia may significantly hinder TEE imaging because of lack of transducer mucosal approximation.
Atlantoaxial disease and severe generalized cervical arthritis: TEE should never be performed if there is any question about stability of cervical spine.
Patients who received extensive radiation to the mediastinum: this can cause significant difficulty in probe manipulation within the esophagus and is a relative contraindication if the anatomy of the esophagus is not known.
Upper gastrointestinal bleeding, significant dysphagia and odynophagia are also relative contraindications

Indication:
cardiac output
valve
congenital heart disease
evaluation of LA and LA appendage before cardioversion

nitric oxide

-bronchodilator

-no tachyphylaxis

-synthesised in body from aspartate

-high affinity for Hb

-used therapeutically at 10-100bpm

Circle

Soda lime: 94% calcium hydroxide, 5% sodium hydroxide, small amount of potassium hydroxide.

pH13.5 moisture 14-19%

silica, dye

newer : zeolite

pink to white or

white to violet

colour changes when pH <10

1L absorb 120L of CO2

CO2 absorbed-->water and heat produced (exothermic)

adult CO2 production:250ml/min

compound A from sevo+sodalime

CIRCLE system

high FGF of several litres to denitrogenate circle and FRC (only if nitrous is used)

can later reduce to 0.5-1L/min

short period of high flows needed to prime patient and circle

desflurane Tec 6 vaporiser

http://www.equipmentexplained.com/physics/agent_delivery/vaporizer/vaporizers.html#desflurane

radial art cannulation

(May-2008 Q2) Why is the radial artery a common site for arterial cannulation? What complications may occur from radial artery cannulation and how may they be minimised?

The radial artery is a common site for cannulation because it is superficial and easy to assess, distal and therefore allows more proximal arteries to be left intact in case of failing to cannulate distally, the proximal brachial artery is still available as an alternative (although this is not ideal).

It is compressible and therefore in the case of a hematoma, expansion of the hematoma may be limited by direct pressure

Clean, correlates well with BP, collateral circulation, discrete from nerves

Complications:

1) hematoma

2) thrombosis/ vasospasm/air bubbles leading to distal ischaemia

- minimized if pre cannulation allen’s test is done to ensure presence of collateral circulation to the hands prior to radial art cannulation

3) infection- this may be minimized by using an aseptic technique, vigilance for infection/ cellulitis and prompt removal of the cannula, changing the site of the cannula every week (?evidence?) strict asepsis when obtaining blood samples from cannula

4) Invasive arterial cannulation only when indicated : >4 ABG /day, hemodynamic monitoring crucial

5) Drug injection- adequate labelling, staff training, prompt recognition if drug has been given to do corrective measures

virtual anaesthesia machine

http://vam.anest.ufl.edu/

laser

(May-2008 Q9) A 25 yo man is to have laser surgery for a vocal cord papilloma. What are the hazards associated with the use of laser in this situation and how can they be minimsed?

Laser defined as: Light Amplification by Stimulated Emission of Radiation
Hazards of use are mainly related to airway fire due to ignition by heat generated from the laser beam.

It can be minimized by surgical preparation and anaesthesia factors
Surgical preparation: use laser in short bursts

Sterile water for irrigation should always be available.
OT preparation
In the event of an airway fire, irrigation with saline or sterile water

Anaesthesia factors: use as low an FiO2 as possible (as low an oxygen concentration to maintain adequate oxygenation)
Vigilance
Use of ETT with ? wire/armoured tube


Laser may cause airway papillomas?

LASER officers, fire drill

types of laser: CO2, Yag, ?

TOW cell saver

http://ccforum.com/content/8/s2/s53