Respiratory and Ventilatory Assessment
3.6 Noninvasive Ventilation Monitoring and Managementand Management
3.6.1 Helmet CPAP
come, prolong MV and hospital LOS, and increase mortality [24]. Moreover, several studies have shown a relationship between asynchronies and poor quality of sleep in ICU patients [25]. Recognizing PVA is an advanced competence for nurses.
3.6 Noninvasive Ventilation Monitoring
30 0 0 0 03090 -90 500
a cmH2O ηVml1/min Ineffective effort
Ineffective effort EdiVolume
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ABC Rise time during PSV Volume Double triggering during Pressure control ventilationDouble triggering. Continued subject effort duringthe second breath causes the airway pressure to drop below the trigger thershold, which initiates onadditional breath.
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-70 It/min 400 ml
time time time time
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Airway pressure Volume 50 µV-70 It/min 400 ml Fig. 3.11Patient-ventilator asynchronies
endotracheal intubation (invasive airway) or via facial mask/
helmet (noninvasive interface).
Literature promotes noninvasive CPAP in case of acute cardio- genic pulmonary edema, ARDS (adult respiratory distress syn- drome), posttraumatic acute respiratory failure, and postoperative hypoxemia. Moreover, it appears to be a useful respiratory sup- port as a bridge to complete weaning after extubation. Nowadays in immunocompromised patients, it represents the first-line choice in case of hypoxemic respiratory failure [27, 28].
During the 1980s, noninvasive CPAP therapy was only deliv- ered via facial mask. The limits were its timing: a short length of stay in situ (no more than 2 h), due to the high pressures generated onto facial skin, tissues, and bones structures, result- ing in an intermittent application of this support [29]. In order to deal with these limitations, during the early 1990s, a new NIV delivery interface was developed in Italy: the CPAP helmet. It’s a reusable, single patient interface, made of a clear plastic hood on a hard-plastic ring with a multi-sized silicon-polyvinyl chloride soft collar, to fit a wide range of necks’ dimensions. Its capability to provide a permanent pneumatic seal keeps a con- tinuous positive pressure throughout the whole respiratory cycle. Inlet for fresh gases and outlet for PEEP valve (mechani- cal or water) should be available. A correct management of the helmet is helpful to minimize claustrophobia, preserving full visual contact and communication with healthcare providers and patient’s significant others [30, 31].
Basic principles of helmet monitoring are related to gas flow regulation, circuit handling, patient surveillance, noise reduc- tion, helmet anchorage, and gas humidification [32, 33].
3.6.1.1 Gas-Flow Management
Despite the helmet’s size, the total amount of inlet gas flow shouldn’t be lower than 30 L/min. Literature has clearly proved
that under the aforementioned gas flow cutoff limit, carbon dioxide rebreathing occurs inside the helmet [29].
As far as the unplanned disconnection takes place, from the helmet inlet, after 240 s the CO2 level detected is ranging from 50 to 60 mmHg, depending on the size of CPAP helmet in use.
Due to these safety issues, several of CPAP helmets available on markets are equipped with anti-suffocation or safety valves.
These safety valves remain closed due to the pressure generated inside the helmet by the PEEP. When any accidental disconnec- tion occurs, the loss of pressure opens the valve, allowing the patient to breath ambient air. The PEEP cutoff limit for opening these valves is 3 cmH2O. These safety valves cannot prevent the hazardous of unplanned disconnections, but they contribute to reduce risks as demonstrated 240 s after disconnection: carbon dioxide value is around 20 mmHg [33].
The use of an ICU pulmonary ventilator to deliver CPAP through helmets is not recommended. Limitations are, even in case of high performance pneumatic pressure ventilators, related to the inability to deliver continuous flows over 30 L/
min, fatally leading to CO2 rebreathing [33].
3.6.1.2 Basic Monitoring on CPAP: Patient and Circuit The basic monitoring of patient on a CPAP helmet should con- sider as follows [31]:
• Oxygen saturation SpO2
• Heart rate
• Blood pressure
Checking the gastric residual volume represents a key point as well during CPAP. Airway pressurization can lead to gastric distention due to bloating of stomach. Even if potential inhala- tion hazard is far from happening due to free space available in the helmet, a nasogastric tube placement should be considered,
especially when CPAP therapy discontinuation is not allowed.
Nasogastric tube placement is mandatory only if the CPAP therapy via helmet is continued without time breaks allowed.
Otherwise, if discontinuity of therapy (also to orally feed the patient) is permitted, nasogastric tube positioning should be avoided.
In healthy subjects, the esophageal valve occlusion is able to oppose against external pressure until 25–30 cmH2O [33], avoiding abdominal bloating and gastric distention, but those pressure levels are not within the CPAP range of pressure deliv- ering. Instead, nasogastric tube represents the real determinant factor for the lower esophageal sphincter failure.
3.6.1.3 Noise Reduction
The gas airflow moving through the restricted area of flexible CPAP tubing hose generates turbulence and, subsequently, noise levels. This phenomenon is more evident for Venturi-based devices. For those reasons the use of precautions is essential to reduce noise levels inside CPAP helmets, especially for long- term therapy [32, 34].
Several options are available:
• Hose tubing with inner smooth surface. The choice of smooth interior wall hoses rather than corrugated type allows to avoid flow turbulence and the consequent reduction of the gas flow noise.
• HME filter: its usual purpose as a gas humidifier is intention- ally avoided (absence of reverse flow direction). Basically, the inner membrane works like an engine exhaust muffler, resulting in a real noise reduction.
• Earplugs: blocking the noise wave transmission. It’s neces- sary to educate the patient about experiencing a sort of ear
pressurization feeling, similar to scuba diving, because it is not unusual and is related to the pressure generated inside the helmet.
3.6.1.4 Helmet Anchorage
From a physical point of view, the pressure inside the helmet results in a vertical thrust of itself. To manage this issue, several solutions are available [31]:
• Armpit strap
• Band fastened on bedsides
• Counterbalance system
Armpit straps represent the basics of all possible options.
Extremities of both straps are secured onto the rigid part of the helmet, while the midportion passes under the patient’s armpit.
Indications for this kind of system are 2 h at least CPAP deliver- ing and PEEP levels less than 10 cmH2O in order to avoid pres- sure ulcers, venous stasis, and clotting phenomena in the axillary region. PEEP levels between 5 and 10 cmH2O generate a traction force more than 2 kg against each armpit’s tissue, leading into an axillary discomfort experience.
Bed rails and bedsides can be used as anchorage structure for band fixing lines (usually with a cross-shaped layout). Despite its reliability, this choice results in a major limitation for patient’s freedom of movement. This leads to distress/frustra- tion and then less collaborative behavior.
The counterweight system requires the armpit straps above- mentioned but in a modified way of use. In this setting, the midportion of the strap passes over patient’s shoulders. For each strap, a 2 kg weight is attached as a counterbalance (e.g., skel- etal traction counterweight). This kind of anchorage does not constrain the patient’s freedom of movements (Fig. 3.12).
3.6.1.5 Airway Humidification
Invasive ventilation (tube or tracheostomy) completely bypasses the natural process of air filtering and humidification; in the noninvasive one, those physiological processes are fully active.
However, gases for medical purpose are not equivalent to natural fresh air: temperature and moisture of natural air are basically influenced by environment’s climate, while the medi- cal gases usually have a temperature range of 10–20 °C and a humidity level lower than 3% [35].
Fig. 3.12 Patient with helmet CPAP and counterweight system
According to the International Consensus Conferences in Intensive Care Medicine’s statement about noninvasive positive- pressure ventilation in acute respiratory failure [36], the mini- mal water content in 1 L of air, to prevent alterations of physiological humidification’s process, is 10 mg.
Early detection of patients at risk during NIV via helmet is necessary. Lately, it has been showed that helmet CPAP performed by high flow rate of gas delivery (>40 L/min) needs the use of an active humidifier, especially for a long-term CPAP therapy.
Technical issues are related to the employment of active humidifiers with high flow delivery: the conventional setup for invasive ventilation doesn’t fit for this option.
An optimal active humidification setup for a ventilated patient via ET tube requires a temperature of heater equal to 35 °C plus a relative humidity of 100% and 37 °C for gases on inspiratory inlet. Those parameters will result in a temperature of 37° and a relative humidity of 80%.
The air temperature inside the helmet space fueled by raw medical gas with no moisture and no temperature treatment is around 29–30 °C [37]. Gas delivery at 37 °C will lead to con- densation on the inner side of helmet, increasing patient’s dis- comfort. Due to this technical reason, the clinical goal about humidification setting for CPAP helmet is to keep a gas relative humidity of 100%, according to a comfortable temperature of helmet environment before mentioned (29–30 °C) [32].
Humidifier outlet chamber temperature setting could be titrated (if NIV option is available) to 28 °C with 100% of rela- tive humidity, while the distal inlet at the helmet is settled on 30 °C. Those settings provide a proportional amount of water fitted for the helmet inner temperature, due to a rising of tem- perature inside the hosing line and reducing the moisture buildup before the helmet inlet.
If HME filter as noise reduction system is in place, it will be connected between the medical gas source and the heater cham- ber inlet. Otherwise the filter itself would be a real block to moisture due to its technical nature.