INITIAL VENTILATION

Mode of ventilation

After deciding to start positive-pressure ventilation with a volume-cycled ventilator, the clinician must now select the safest initial mode of machine operation.

In most circumstances, the initial mode of ventilation should be the assist-control mode, in which a tidal volume and rate are preset and guaranteed. The patient can affect the frequency and timing of the breaths. If the patient makes an inspiratory effort, the ventilator senses a decrease in the circuit pressure and delivers the preset tidal volume. In this way, the patient can dictate a comfortable respiratory pattern and may trigger additional machine-assisted breaths above the set rate. If the patient does not initiate inspiration, the ventilator automatically delivers the preset rate and tidal volume, ensuring minimum minute ventilation. In the assist-control mode, the work of breathing is reduced to the amount of inspiration needed to trigger the inspiratory cycle of the machine. This trigger is adjusted by setting the sensitivity of the machine to the degree of pressure decrease desired in the circuit (see image below).

The pressure, volume, and flow to time waveforms for assist-control ventilation.

Assist-control differs from controlled ventilation because the patient can trigger the ventilator to deliver a breath and, thereby, adjust their minute ventilation. In controlled ventilation, the patient receives only breaths initiated by the ventilator at the preset rate (see image below).

The pressure, volume, and flow to time waveforms for controlled ventilation.

Although the work of breathing is not eliminated, this mode gives the respiratory muscles the greatest amount of rest because the patient needs only to create enough negative pressure to trigger the machine. An added advantage is that the patient can achieve the required minute ventilation by triggering additional breaths above the set back-up rate.

In most cases, a minute ventilation that provides a reasonable pH based on the respiratory rate is determined by the patient's chemoreceptors and stretch receptors. The respiratory center in the central nervous system receives input from the chemical receptors (arterial blood gas tensions) and neural pathways that sense the mechanical work of breathing (mechanoreceptors). The respiratory rate and respiratory pattern are the result of input from these chemoreceptors and mechanical receptors, which allow the respiratory center to regulate gas exchange. In the assist-control mode, this process is accomplished with the minimum work of breathing.

A second possible advantage of this mode of mechanical ventilation is that cycling the ventilator into the inspiratory phase maintains normal ventilatory activity and, therefore, prevents atrophy of the respiratory muscles.

A potential disadvantage of the assist-control mode is respiratory alkalosis in a small subset of patients whose respiratory drive supersedes the chemoreceptors and mechanical receptors. Patients with a potential for alveolar hyperventilation and hypocapnia in the assist-control mode include those with end-stage liver disease, those in the hyperventilatory stage of sepsis, and those with head trauma. These conditions are typically identified with the first arterial blood gas results, and the assist-control mode of ventilation can then be changed to an alternate mode.

Another possible disadvantage is the potential for serial preset positive-pressure breathes to retard venous return to the right side of heart and to affect global cardiac output. Nevertheless, the assist-control mode may be the safest initial choice for mechanical ventilation. It may be switched to another option if hypotension or hypocarbia are evident from the first arterial blood gas results.

Tidal volume and rate

For a patient without preexisting lung disease, the tidal volume and rate are traditionally selected by using the 12-12 rule. A tidal volume of 12 mL for each kilogram of lean body weight is programmed to be delivered 12 times a minute in the assist-control mode.

For patients with chronic obstructive pulmonary disease (COPD), the tidal volume and rate are slightly reduced to the 10-10 rule to prevent overinflation and hyperventilation. A tidal volume of 10 mL/kg lean body weight is delivered 10 times a minute in the assist-control mode.

In acute respiratory distress syndrome (ARDS), the lungs may function best and volutrauma (see Complications of Mechanical Ventilation) is minimized with low tidal volumes of 6-8 mL/kg. Tidal volumes are preset at 6-8 mL/kg of lean body weight in the assist-control mode. This ventilatory strategy is called lung-protective ventilation. These lowered volumes may lead to slight hypercarbia. An elevated PCO2 is typically recognized and accepted without correction, leading to the term permissive hypercapnia. However, the degree of respiratory acidosis allowable is a pH not less than 7.25. The respiratory rate of the ventilator may need to be adjusted upward to increase the minute ventilation lost by using smaller tidal volumes.

Double-checking the selected tidal volume

After a tidal volume is selected, the peak airway pressure necessary to deliver a single breath should be determined. As the tidal volume increases, so does the pressure required to force that volume into the lung. Persistent breath-to-breath peak pressures greater than 45 cm water are a risk factor for barotrauma (see Complications of Mechanical Ventilation). The tidal volume suggested by the above rules may need to be decreased in some patients to keep the peak airway pressure less than 45 cm water (see image below).

The components of mechanical ventilation inflation pressures. Paw is airway pressure, PIP is peak airway pressure, Pplat is plateau pressure.

Some researchers have suggested that plateau pressures should be monitored as a means to prevent barotrauma in the patient with ARDS. Plateau pressures are measured at the end of the inspiratory phase of a ventilator-cycled tidal volume. The ventilator is programmed not to allow expiratory airflow at the end of the inspiration for a set time, typically half a second. The pressure measured to maintain this lack of expiratory airflow is the plateau pressure. Barotrauma is minimized when the plateau pressure is maintained at less than 30-35 cm water (see image above). Monitoring the peak and plateau pressures allows physicians to make clinical judgments on the progress of their patient (see image below).

The effects of increased airway resistance (A) and decreased respiratory system compliance on the pressure-time waveform.

Sighs

Because a spontaneously breathing individual typically sighs 6-8 times each hour to prevent microatelectasis, some investigators once recommended that periodic machine breaths that were 1.5-2 times the preset tidal volume be given 6-8 times per hour. However, the peak pressure often needed to deliver such a volume was high enough to predispose the patient to barotrauma. At present, accounting for sighs is not recommended if the patient is receiving tidal volumes of 10-12 mL/kg or if the patient requires positive end-expiratory pressure (PEEP). When a low tidal volume is used, sighs are preset at 1.5-2 times the tidal volume and delivered 6-8 times an hour if the peak and plateau pressures are within acceptable limits.

Initial FIO2

The highest priority at the start of mechanical ventilation is providing effective oxygenation. For the patient's safety after intubation, the FIO2 should always be set at 100% until adequate arterial oxygenation is documented. A short period with an FIO2 of 100% is not dangerous to the patient receiving mechanical ventilation and offers the clinician several advantages. First, an FIO2 of 100% protects the patient against hypoxemia if unrecognized problems occur as a result of the intubation procedure. Second, using the PaO2 measured with an FIO2 of 100%, the clinician can easily calculate the next desired FIO2 and quickly estimate the shunt fraction.

The degree of shunt with 100% FIO2 can be estimated by applying this general rule: The measured PaO2 is subtracted from 700 mm Hg. For each difference of 100 mm Hg, the shunt is 5%. A shunt of 25% should prompt the clinician to consider the use of PEEP.

Inadequate oxygenation despite the administration of 100% oxygen should lead to a search for complications of endotracheal intubation (eg, mainstem intubation) or positive-pressure breathing (pneumothorax). If such complications are not present, PEEP is needed to treat the intrapulmonary shunt pathology. Because only a few disease processes can create an intrapulmonary shunt, a clinically significant estimated shunt should narrow the potential source of hypoxemia to the following conditions:

Alveolar collapse - Major atelectasis

Alveolar filling with something other than gas - Lobar pneumonia

Water and protein - ARDS

Water - Congestive heart failure

Blood - Hemorrhage

Positive end-expiratory pressure

PEEP is a mode of therapy used in conjunction with mechanical ventilation. At the end of mechanical or spontaneous exhalation, PEEP maintains the patient's airway pressure above the atmospheric level by exerting pressure that opposes passive emptying of the lung. This pressure is typically achieved by maintaining a positive pressure flow at the end of exhalation. This pressure is measured in centimeters of water.

PEEP therapy can be effective when used in patients with a diffuse lung disease that results in an acute decrease in functional residual capacity (FRC), which is the volume of gas that remains in the lung at the end of a normal expiration. FRC is determined by primarily the elastic characteristics of the lung and chest wall. In many pulmonary diseases, FRC is reduced because of the collapse of the unstable alveoli. This reduction in lung volume decreases the surface area available for gas exchange and results in intrapulmonary shunting (unoxygenated blood returning to the left side of the heart). If FRC is not restored, a high concentration of inspired oxygen may be required to maintain the arterial oxygen content of the blood in an acceptable range.

Applying PEEP increases alveolar pressure and alveolar volume. The increased lung volume increases the surface area by reopening and stabilizing collapsed or unstable alveoli. This splinting, or propping open, of the alveoli with positive pressure improves the ventilation-perfusion match, reducing the shunt effect.

After a true shunt is modified to a ventilation-perfusion mismatch with PEEP, lowered concentrations of oxygen can be used to maintain an adequate PaO2. PEEP therapy may also be effective in improving lung compliance. When FRC and lung compliance are decreased, additional energy and volume are required to inflate the lung. By applying PEEP, the lung volume at the end of exhalation is increased. The already partially inflated lung requires less volume and energy than before for full inflation.

When used to treat patients with a diffuse lung disease, PEEP should improve compliance, decrease dead space, and decrease the intrapulmonary shunt effect. The most important benefit of the use of PEEP is that it enables the patient to maintain an adequate PaO2 at a low and safe concentration of oxygen (< 60%), reducing the risk of oxygen toxicity (see Complications of Mechanical Ventilation).

Because PEEP is not a benign mode of therapy and because it can lead to serious hemodynamic consequences, the ventilator operator should have a definite indication to use it. The addition of external PEEP is typically justified when a PaO2 of 60 mm Hg cannot be achieved with an FIO2 of 60% or if the estimated initial shunt fraction is greater than 25%. No evidence supports adding external PEEP during initial setup of the ventilator to satisfy misguided attempts to supply prophylactic PEEP or physiologic PEEP.

Many clinicians use the least-PEEP philosophy, which recommends using the lowest positive pressure that provides an adequate PaO2 with a safe FIO2. Another manner of selecting the optimal PEEP is based on identifying the low inflection point on the volume-pressure curve generated breath to breath by using modern mechanical ventilators. PEEP should be set 1-2 cm of water pressure above this measured low inflection point to obtain the optimal PEEP.

Because trials comparing higher versus lower levels of PEEP in adults with acute lung injury or acute respiratory distress syndrome (ARDS) have been underpowered to detect small but potentially important effects on mortality or to explore subgroup differences, Briel et al performed a systematic review and meta-analysis of data from 2299 patients in 3 trials. Treatment with higher versus lower levels of PEEP was not associated with improved hospital survival: 374 hospital deaths occurred in 1136 patients (32.9%) assigned to treatment with higher PEEP, and 409 hospital deaths occurred in 1163 patients (35.2%) assigned to lower PEEP (adjusted relative risk [RR], 0.94; 95% confidence interval [CI], 0.86-1.04; P = .25). However, in the subgroup of patients with ARDS, higher levels were associated with improved survival: 324 hospital deaths (34.1%) occurred in the higher PEEP group and 368 (39.1%) occurred in the lower PEEP group (adjusted RR, 0.90; 95% CI, 0.81-1.00; P = .049).[1]

Because PEEP basically resets the baseline of the pressure-volume curve, the peak and plateau pressures will be affected. The clinician should pay close attention to the status of these pressure measurements (see image below).

Determination of the lower inflection point to estimate the best (optimal) positive end-expiratory pressure (PEEP) from the pressure-volume hysteresis curve.

Summary of initial ventilator setup

Initial settings for ventilation may be summarized as follows:

Assist-control mode

Tidal volume set depending on lung status - Normal = 12 mL/kg ideal body weight; COPD = 10 mL/kg ideal body weight; ARDS = 6-8 mL/kg ideal body weight

Rate of 10-12 breaths per minute

FIO2 of 100%

Sighs rarely needed

PEEP only as indicated after first arterial blood gas determination, ie, shunt greater than 25%

Inability to oxygenate with an FIO2 less than 60%

Careers In Mechanical Engineering

For those looking for a career in mechanical engineering, we have good news! Jobs are in excess in today's job market. Overall, mechanical engineering is right behind civil engineering in terms of number of engineers in the workplace today, according to the Occupational Outlook Handbook. The Handbook adds that mechanical engineers are projected to have an average rate of employment growth through 2014. Although total employment in manufacturing industries is expected to decline, employment of mechanical engineers in manufacturing is expected to actually increase because the demand for improved machinery and machine tools will grow, and industrial machinery and processes will become increasingly complex. Also, emerging technologies in biotechnology, materials science and nanotechnology will create new job opportunities for mechanical engineers.

Opportunities Abound

The need for mechanical engineers by EPC companies is in high demand, says Charles Nash, vice president of engineering for Yoh, a talent and outsourcing firm in the engineering community. And mechanical engineers have many options to apply their skill sets to the real world, he adds.

"As an example, in the chemical plant environment, they may work with the design or application of equipment or the stress characteristics of a process piping system," Nash says.

"In the food industry, they may be involved with development and design of conveying systems, or packing and packaging systems. In research and development, they may be involved with systems related to jet propulsion, space-travel, land-travel and sea- and sub-sea systems."

In a sense, Nash says, a mechanical engineer is an inventor of mechanical components and systems involving the application of principles of physics for analysis, design and manufacturing, and maintenance of mechanical systems.

Build Your Backup

With all of these opportunities, the only way to get started in the industry is by getting the proper education. An undergraduate engineering program usually requires four to five years of study.

"The coursework includes a foundational course in mathematics and physics, which provides the necessary background to study mechanical engineering," says Margaret Bailey, associate professor of mechanical engineering at Rochester Institute of Technology (RIT). "Core mechanical engineering courses are numerous and vary significantly in content, ranging from statics and dynamics to engineering design, heat transfer and numerical methods."

Bailey adds that in addition to core courses, students further explore their interest areas within mechanical engineering at RIT through completion of technical elective courses and completion of a capstone design.

"For example, at RIT we have developed several option areas which are closely aligned with our students' technical interests, including aerospace, energy and the environment, bioengineering and automotive," she says. "Within each option there are numerous courses to help students develop a depth of understanding.

At some engineering colleges, including RIT, students are required to complete a series of co-op educational experiences, which complement and strengthen their mechanical engineering foundation," Bailey explains. At RIT, students work outside of the classroom as "engineers-in-training" at locations around the country and the world.

In the Real World

"Once in the workplace, mechanical engineers can take on a number of functions," says David Bonifacic, managing principal of WB, a Manhattan-based mechanical/electrical/plumbing firm. "Consulting mechanical engineers design, plan and supervise the construction of new buildings or the renovation of existing facilities," he says. "Mechanical consulting engineers work on the complete infrastructure in a facility, including any part that moves such as people, air and water."

In addition to design and construction, mechanical engineers often work on due diligence studies of facilities.

"This involves developing life cycle costs analysis to verify if a project is worth undertaking," says Bonifacic. "Mechanical engineers in one field often work closely with specialists in other building disciplines—for example electrical engineers, plumbing and fire protection engineers, architects, structural and civil engineers. A lot of our time is spent outside of the office or in the field. We conduct site surveys, attend meetings and during construction we regularly visit the project site in order to monitor or direct operations or solve onsite problems."

In order to be successful as a mechanical engineer, Bailey says that there are a number of personal characteristics you should have. Being able to work together in teams is just one of many of these characteristics.

"Engineers must be able to work effectively on teams which consist of engineers from other disciplines as well as non-engineers, such as scientists, researchers, architects, industrial designers and medical professionals," she says. "Therefore, an ideal personal characteristic for an engineer is someone who likes working with people who may be quite different from themselves as far as educational background."

Engineers also need to be able to creatively solve problems. "People who enjoy problem solving and who push themselves towards creative solutions should consider engineering," she adds. "The problems that engineers solve are usually focused on people and affect quality of life. Therefore, having an interest in improving the quality of life is also quite common among engineers."

Now's the Time

With the shortage of engineers entering the field, Nash says now is the time to become a mechanical engineer, if it appeals to you.

"We currently are in short supply of all disciplines of engineering personnel as related to the typical energy engineering industry needs," he says. "This is in part due to the fact that many of our graduating engineers have chosen to focus their training in a different line of business, such as the information technology industry." Depending on the specific industry chosen, many mechanical engineers will earn six-figure salaries within a few years.

Home ventilation’ system cuts energy bills and improves health

The new Ventis system, is a revolutionary home health product that can cut a family’s heating bills by approximately half, as well as making the home environment healthier, by removing damp and mould.

THIS new technology, never seen before in NSW, simply takes the warmer air out of the roof space of a house, pushes it through hospital grade filters, taking out dust, pollens and other allergens and pushes fresh, clean air through the home, drying it out and warming homes in the coolers months.

It also cools homes in the summer months by taking the cooler, evening air from outside the home and filtering it into the home, so that people can sleep easier in cool, ventilated rooms, without having to leave windows open.

Similar product philosophies have been extensively tested in Europe, the States and New Zealand and had staggering results not just on customers’ power bills, but also on family health, improving the health of family members suffering from respiratory illnesses, such as asthma, as well as other allergic conditions, such as eczema.

The solution is tailor-made by the Ventis consultants to suit each home and is easy and hassle free to install.

Dave Kennedy from Ventis said about the new company and product, “We’re passionate about offering new environmental solutions to energy issues and to help improve family health.

“Additionally, we know that Sydney homes can suffer from damp and mould issues, all of which not only slowly degrade the structural aspects of your home, but are also extremely bad for people’s health long term. Breathing in mould has been proven to cause respiratory illnesses and black mould has been proven to be a carcenogen.

“We have already had amazing feedback from a customer who suffered badly from allergies, in particular, hayfever. Following the installation of their Ventis system, she has woken up without itchy and puffy eyes and feels more energized. This is what we are excited about, being able to offer the people of the Northern Beachers a way to make their homes even more comfortable,” continued Mr Kennedy.

Ventilation for the Prevention of Airborne Contagion

Background

Tuberculosis (TB) is a major cause of ill health and death worldwide, with around one-third of the world's population infected with the bacterium that causes it (Mycobacterium tuberculosis). One person with active tuberculosis can go on to infect many others; the bacterium is passed in tiny liquid droplets that are produced when someone with active disease coughs, sneezes, spits, or speaks. The risk of tuberculosis being transmitted in hospital settings is particularly high, because people with tuberculosis are often in close contact with very many other people. Currently, most guidelines recommend that the risk of transmission be controlled in certain areas where TB is more likely by making sure that the air in rooms is changed with fresh air between six and 12 times an hour. Air changes can be achieved with simple measures such as opening windows and doors, or by installing mechanical equipment that forces air changes and also keeps the air pressure in an isolation room lower than that outside it. Such "negative pressure," mechanically ventilated systems are often used on tuberculosis wards to prevent air flowing from isolation rooms to other rooms outside, and so to prevent people on the tuberculosis ward from infecting others.

Why Was This Study Done?

In many parts of the world, hospitals do not have equipment even for simple air conditioning, let alone the special equipment needed for forcing high air changes in isolation rooms and wards. Instead they rely on opening windows and doors in order to reduce the transmission of TB, and this is called natural ventilation. However, it is not clear whether these sorts of measures are adequate for controlling TB transmission. It is important to find out what sorts of systems work best at controlling TB in the real world, so that hospitals and wards can be designed appropriately, within available resources.

What Did the Researchers Do and Find?

This study was based in Lima, Peru's capital city. The researchers studied a variety of rooms, including tuberculosis wards and respiratory isolation rooms, in the city's hospitals. Rooms which had only natural measures for encouraging airflow were compared with mechanically ventilated, negative pressure rooms, which were built much more recently. A comparison was also done between rooms in old hospitals that were naturally ventilated with rooms in newer hospitals that were also naturally ventilated. The researchers used a particular method to measure the number of air changes per hour within each room, and based on this they estimated the risk of a person with TB infecting others using a method called the Wells-Riley equation. The results showed that natural ventilation provided surprisingly high rates of air exchange, with an average of 28 air changes per hour. Hospitals over 50 years old, which generally had large windows and high ceilings, had the highest ventilation, with an average of 40 air changes per hour. This rate compared with 17 air changes per hour in naturally ventilated rooms in modern hospitals, which tended to have lower ceilings and smaller windows. The rooms with modern mechanical ventilation were supposed to have 12 air changes per hour but in reality this was not achieved, as the systems were not maintained properly. The Wells-Riley equation predicted that if an untreated person with tuberculosis was exposed to other people, within 24 hours this person would infect 39% of the people in the mechanically ventilated room, 33% of people in the naturally ventilated new hospital rooms, and only 11% of the people in the naturally ventilated old hospital rooms.

What Do These Findings Mean?

These findings suggest that natural methods of encouraging airflow (e.g., opening doors and windows) work well and in theory could reduce the likelihood of TB being carried from one person to another. Some aspects of the design of wards in old hospitals (such as large windows and high ceilings) are also likely to achieve better airflow and reduce the risk of infection. In poor countries, where mechanical ventilation systems might be too expensive to install and maintain properly, rooms that are designed to naturally achieve good airflow might be the best choice. Another advantage of natural ventilation is that it is not restricted by cost to just high-risk areas, and can therefore be used in many different parts of the hospital, including emergency departments, outpatient departments, and waiting rooms, and it is here that many infectious patients are to be found.

Minimum Quantity Of Outside Air For Mechanical Ventilation.

§  27-754  Minimum quantity of outside air for mechanical ventilation.
  The minimum quantity of outside air required for mechanical  ventilation
  in  any  occupiable  room,  where  not  otherwise  prescribed,  shall be
  determined according to table 12-2.
 
         Table 12-2 Required Minimum Outdoor Air Supply and Exhaust
                              (cfm per sq. ft.)
  ========================================================================
  Ventilated Rooms    Ventilated Rooms with Natural       without  Natural
  Index for           Ventilation        Ventilation       Air Conditioned
  Ventilation           Openings           Openings             Rooms
  ------------------------------------------------------------------------
  Supply  Exhaust     Supply  Exhaust    Supply Exhaust
  ------------------------------------------------------------------------
     0- 300...       2.5     2.0         2.5     2.0        1.5     1.5
   301- 520...       2.0     1.5         2.0     1.5        1.2     1.2
   521- 850...       1.5     1.25        1.5     1.25       0.9     0.9
   851-1250...        ..     1.0         1.0     1.0        0.6     0.6
  1251-1650...        ..     0.67        0.67    0.67       0.5     0.5
  over 1650...        ..      ..         0.33    0.33       0.4     0.4
  ========================================================================
 
    (a)  Window requirements. To be credited as ventilating openings under
  the provisions of this subchapter, windows or other openings shall  meet
  the  requirements  of  section 27-749 of article six of this subchapter,
  and where mechanical supply ventilation is not provided,  shall  have  a
  free  openable  area  of at least one square foot per one hundred square
  feet of floor area.
    (b) Air conditioning.
    (1) In air conditioned rooms, the windows and other openings shall not
  be credited  as  such  in  computing  the  index  for  ventilation.  Air
  conditioned rooms shall be considered as interior rooms.
    (2)  Air  that has been exhausted from an air conditioned space may be
  reconditioned  by  air  conditioning  apparatus  and   recirculated   as
  equivalent  outdoor  air,  provided  that the total of supply air is not
  less than required for air conditioned rooms by table 12-2 and that  the
  amount  of actual outdoor air is at least thirty-three and one-third per
  cent of the required total. The actual outdoor  air  supply  shall  not,
  under  any circumstances, be reduced to less than five cfm per occupant,
  except that these minimum requirements may be reduced by fifty per  cent
  as provided in section 27-755 of this article.
    (c)  Required exhaust. Required exhaust may be accomplished by raising
  the pressure within the space with consequent leakage through doors  and
  windows, or by drawing the vitiated air from air conditioned spaces into
  the  return  air  duct  of air conditioning apparatus or into an exhaust
  duct discharging directly to the outdoor air.
    (d) Make-up air. A sufficient quantity of  air  to  make  the  exhaust
  system  effective  shall be provided to the space being exhausted by one
  or by any combination of the following methods:
    (1) By supplying air to the space by means of a blower system.
    (2) By infiltration through louvres,  registers,  or  other  permanent
  openings  in  walls, doors, or partitions, adjoining spaces where air is
  supplied by one of these methods.
    (3) By infiltration through cracks around window sash and doors.
    (4) By other methods acceptable to the commissioner.
    (e) Prohibited use of recirculated air. Air  drawn  from  any  of  the
  following  spaces  may not be recirculated; mortuary rooms; bathrooms or
  toilet rooms; or any space where an objectionable quantity of  flammable


  vapors,  dust,  odors, or noxious gases is present. Air drawn from rooms
  that must be isolated to prevent the spread of infection  shall  not  be
  recirculated, except that air drawn from hospital operating rooms may be
  recirculated, if in compliance with the following requirements:
    (1)  There  shall  be  a  minimum of twenty-five total air changes per
  hour, of which five air changes per hour shall be outdoor air.
    (2) All fans serving exhaust systems shall be located at the discharge
  end of the system.
    (3) Outdoor air intakes shall be located  at  least  twenty-five  feet
  from   exhaust   outlets   of  ventilation  systems  and  other  exhaust
  discharges,  combustion  equipment  stacks,  medical   surgical   vacuum
  systems,  and  plumbing  vent  stacks,  from  areas  which  may  collect
  vehicular exhaust such as off-street loading bays, and from areas  which
  may  collect  other  noxious  fumes.  The  bottom of outdoor air intakes
  serving central systems if installed above a roof, shall be  located  at
  least three feet above roof level.
    (4) Positive air pressure shall be maintained at all times in relation
  to adjacent areas.
    (5)  All  ventilation  or  air conditioning systems serving such rooms
  shall be equipped with a filter bed of twenty-five per  cent  efficiency
  upstream  of  the  air conditioning equipment and a filter bed of ninety
  per cent efficiency downstream of  the  supply  fan,  any  recirculating
  spray  water  systems  and  water reservoir type humidifiers. All filter
  efficiencies shall be average atmospheric dust spot efficiencies  tested
  in accordance with ASHRAE standard 52-68.
    (6) A manometer shall be installed across each filter bed.
    (7) Duct linings shall not be used in ventilation and air conditioning
  systems  serving  such  rooms unless terminal filters of at least ninety
  per cent efficiency are installed downstream of linings.
    (8) Air supplied shall be delivered at or near the  ceilings  and  all
  exhaust air shall be removed near floor level, with at least two exhaust
  outlets not less than three inches above the floor.
    (f)  Outdoor  air  intakes.  For  high-rise  office  buildings erected
  pursuant to new building applications filed on or  after  the  effective
  date  of  this  section,  outdoor  air  intakes serving spaces above the
  second story and serving spaces greater than ten thousand square feet of
  floor area shall be located at least twenty feet above ground level,  at
  least  twenty feet from exhaust outlets of ventilation systems and other
  exhaust discharges, and at least twenty feet from areas that may collect
  vehicular exhaust such as off-street loading bays.

Music May Ease Stress of Mechanical Ventilation

The sound of music played for patients on mechanical ventilation may help soothe their anxiety and distress, a Cochrane review showed.

In three studies, the state anxiety of patients on vents was reduced by 1.06 standard deviations (P=0.04) when researchers played prerecorded music, according to Joke Bradt, PhD, a music therapist at Drexel University in Philadelphia, and colleagues.

Listening to music also reduced patients' heart rates by an average of nearly 5 bpm across five studies and respiratory rates by more than 3 bpm across six studies (P≤0.001 for both), suggesting a relaxation effect.

There were no significant effects from hearing music on patients' blood pressures or oxygen saturation, and no information was available about quality of life, patient satisfaction, post-discharge outcomes, mortality, or cost-effectiveness related to the music interventions.

"Because of these results, and because music listening is an easy intervention to implement, it is recommended that music listening be offered as a stress-management intervention to these critically ill patients," Bradt and her colleagues wrote.

Because mechanical ventilation often causes major distress and anxiety in patients, analgesia and sedation are considered important treatment options. But both options may lead to prolonged hospitalization resulting from associated complications, such as weakened immune function and venous thrombosis and pressure damage from immobility.

Music interventions have been used to ease anxiety and distress in patients with various conditions, but studies looking specifically at patients on mechanical ventilation have been small.

To evaluate the evidence for music interventions in this patient population, the researchers searched for randomized and quasi-randomized controlled trials that compared standard care with standard care plus a music intervention. They identified eight trials involving 213 participants.

Only one of the eight studies used a trained music therapist and involved the selection of live music to match the respiratory rate of the patients. The rest used prerecorded music delivered through headphones.

The intervention in all of the studies was delivered in a single session.

As measured using the Spielberger State and Trait Anxiety Inventory-State Anxiety Short Form, mean state anxiety was lower with a music intervention than in the control group. However, results were not consistent across the three studies included in the anxiety analysis, and the quality of the evidence was rated as very low by the researchers.

In addition, Bradt and her colleagues noted that the results should be interpreted with caution because of the small sample size.

The findings concerning heart rate and respiratory rate were more consistent, but were still based on evidence rated as very low to low.

The researchers noted that the mean reduction in heart rate may not be clinically significant when the resting heart rate is within the normal range, but added that the reduction may be important when the rate is tachycardiac.

They called for more research on the effects of music interventions delivered by trained music therapists, rather than by other healthcare professionals, pointing to evidence that music therapists seem to be more effective for numerous outcomes.

"This difference might be attributed to the fact that music therapists individualize their interventions to meet patients' specific needs; more actively engage the patients in the music making; and employ a systematic therapeutic process, including assessment, treatment, and evaluation," Bradt and her colleagues wrote.

Mechanical Ventilation

Benefits of Mechanical Ventilation

Moisture, odors, and other pollutants can build up inside a home if it does not have mechanical ventilation to provide fresh air. Mechanical ventilation systems circulate fresh air using ducts and fans rather than relying on airflow through small holes or cracks in a home’s construction assemblies (e.g., walls, roofs, or windows). Homeowners can breathe easier knowing their home has good ventilation.

The benefits of proper home ventilation include the following:

1. Better Indoor Air Quality: Indoor air can be many times more polluted than outdoor air, yet the average American spends 90 percent of the day inside. Ventilation systems can significantly improve a home’s air quality by removing allergens, pollutants, and moisture that can cause mold problems. Mechanical ventilation allows for proper ventilation of your home resulting in your breathing cleaner air.
   
2. More Control: When homes rely on air flow through construction assemblies for ventilation, the air delivery rate is unpredictable; and there is no control over the source or amount of air. In fact, air leaking into the house may come from undesirable areas such as the garage, attic, or crawl space. Mechanical ventilation systems, however, provide proper fresh air flow along with appropriate locations for intake and exhaust.
   
3. Improved Comfort. Mechanical ventilation systems allow a constant flow of outside air into the home and can also provide filtration, dehumidification, and conditioning of the incoming outside air.