Physical Address

304 North Cardinal St.
Dorchester Center, MA 02124

Mechanical Ventilators


Case Synopsis

A 100-kg, 68-year-old man is anesthetized and intubated. Bilateral breath sounds are verified. The ventilator is turned on and set to a tidal volume of 600 mL, respiratory rate of 10, and inspiratory-expiratory ratio of 1:2. Two minutes later, the lowering tone of the pulse oximeter alerts the anesthesiologist, who notices an absence of chest wall movement. The ventilator appears to be cycling normally, so the anesthesiologist picks up a stethoscope and reaches to adjust the switch-over valve to manual, but it is already in the manual position.

Problem Analysis

Definition

Failure to change the ventilator-manual switch to the ventilator position after a period of manual ventilation is the source of many mechanical ventilator complications that can cause serious harm to patients. In the American Society of Anesthesiologists (ASA) closed claim analysis of adverse anesthetic outcomes, there were threefold more claims related to misuse of equipment or operator error compared with equipment failure.

Examples of ventilator misuse or operator error include the following:

  • Failure to turn the ventilator on after a period of manual ventilation

  • Inappropriate set rate or tidal volume for patient size

  • Maximum pressure limit set too high for patient size

  • Maximum pressure limit set too low, causing low tidal volume

  • Inappropriate inspiratory-expiratory ratio

  • High fresh gas flow causing increased tidal volume

  • Oxygen (O 2 ) flush during ventilator inspiration

  • Alarms for pressure, volume, or fraction of inspired oxygen (Fi o 2 ) inactivated by the operator, causing a delay in noticing other malfunctions

Equipment failure or incorrect assembly can include the following problems:

  • Hole in the bellows

  • Bellows mounted incorrectly, so no seal is formed between the bellows and the casing

  • Electrical or mechanical failure, stalling the mechanism

  • Failure of the alarms for pressure, apnea, or Fi o 2

Other causes of ventilator failure actually arise elsewhere on the anesthesia machine. These complications, covered in other chapters, include failure of driving gas pressure (see Chapter 116 ); circuit disconnection, sticking valves, and misconnections of the circuit hoses (see Chapter 105 ); and scavenger errors (see Chapter 120 ).

Recognition

The failure to recognize and promptly rectify problems with ventilators can have catastrophic consequences. In the ASA closed claim analysis, 12 cases were associated with ventilator problems; 7 resulted in death, and 5 resulted in brain injury. There is only a small window of opportunity to correct the malfunction of the ventilator before adverse physiologic events take place as a result of it.

Turning the Ventilator On

Failure to actually turn the ventilator on is common. This usually occurs soon after induction and may be unnoticed for many minutes. If the ventilator-manual switch has not been turned to the ventilator position, the signs are as follows:

  • Loss of the end-tidal carbon dioxide (ETCO 2 ) waveform

  • Activation of the ETCO 2 apnea alarm

  • Distention of the reservoir bag and rising airway pressure on the manometer if the pop-off valve is closed

If the ventilator has not been turned on but the ventilator-manual switch has been turned to the ventilator position, the signs are as follows:

  • Loss of the ETCO 2 waveform

  • No airway pressure perceived by the manometer

  • Activation of the apnea pressure and ETCO 2 apnea alarms

You're Reading a Preview

Become a Clinical Tree membership for Full access and enjoy Unlimited articles

Become membership

If you are a member. Log in here