Patient Monitoring

Despite changes in the acoustic properties of compressed air, blood pressure may be measured without difficulty with a standard sphygmomanometer and stethoscope. It is recommended that aneroid pressure gauges be used rather than mercury columns because of the risk of spillage of mercury and contamination of the chamber. More detailed monitoring of the electrocardiogram (ECG) and intravascular pressure requires some planning and engineering. It is advisable to minimize the number of electronic devices inside the chamber. ECG and pressure transducer cables can be plumbed through the chamber wall to preamplifiers kept outside. Provision of appropriate cable connectors inside the chamber will minimize the delay needed to connect a patient to the monitors after being placed in the chamber. Two simultaneous displays should be available, one for viewing by an outside observer and one facing through a porthole for use by the inside attendant. Standard intensive care monitors can be used to provide simultaneous measurement of arterial and pulmonary artery (PA) pressure and intermittent measurement of cardiac output by thermodilution. Occasionally, the increase in ambient temperature induced by chamber compression may alter the zero offset of pressure transducers, with the older nondisposable type exhibiting greater drift than the newer, disposable ones, which have smaller diaphragms. We therefore suggest that transducers be rezeroed immediately after compression. Additionally, if pressure bags are used to drive continuous-flow systems for vascular monitoring, it is necessary to repressurize the bags during compression. Similarly, intermittent venting will be necessary as the chamber is decompressed. This minor inconvenience can be solved by using a spring-loaded system to compress the flush bag.

PA catheter balloon ports should be vented to chamber pressure (i.e., remove the balloon inflation syringe from the port and ensure that the gate valve is open) before compression and decompression to avoid forceful implosion and breakage during compression and hyperexpansion and rupture during decompression. Although general recommendations suggest that tracheal tube cuffs should be filled with water (see later) to avoid loss of seal with compression, PA catheter balloons should never be inflated with liquid, which may cause rupture of the balloon.

Because of increased fire hazard in a hyperbaric chamber and the possibility of electrical sparking during defibrillation, this procedure must be accomplished in an extremely careful manner and only in a multiplace chamber. Flammable materials, including tape that may have been used to secure the head tent to the torso, must be removed from the immediate area of the defibrillator paddles. An adequate conductive bridge must be obtained between the electrode paddle and the skin by using gel designed for the purpose. A low-resistance gel is recommended because of the evidence that high-resistance gels may pose a risk of fire as a result of the increased amount of heat generated at the paddle-skin interface during defibrillation. ^[169] An alternative, possibly safer approach from the point of view of sparking entails the use of preapplied conductive disposable pads.^[170] Control of the defibrillator by an outside person will reduce the risk that the device will be unintentionally fired. Despite the fear of causing fire during routine defibrillation, this procedure has been carried out in multiplace chambers numerous times without incident.^{[171] [172]}