A 29-week, 1,250-g male, is now 24 h old. He has received three doses of surfactant. The current ventilator settings are synchronized intermittent mandatory ventilation (SIMV) with a rate of 30; peak inspiratory pressure (PIP) 26; positive end-expiratory pressure (PEEP) 4; inspiratory time (T_i) 0.35 s; and fraction of inspired oxygen (F_iO₂) 0.55. The spontaneous respiratory rate (RR) is 75. Arterial blood gas (ABG): pH 7.21; partial pressure of carbon dioxide (PCO₂) 62; and partial pressure of oxygen (PO₂) 50. The measured tidal volume (V_t) varies from 2 to 5 mL/kg. The graphics are shown in Fig. 7.1 (showing the two populations of breaths during SIMV, mechanical and spontaneous).

This infant is showing the effects of inadequate respiratory support. His supported breaths have adequate V_t, but his spontaneous breaths do not and are too small, thus resulting in tachypnea. His lung volume also is inadequately supported; the persistently high F_iO₂ after surfactant indicates inadequate mean airway pressure (Paw). The A/C mode provides support for all breaths, with the rate of 40 providing apnea protection and the pressure limit allowing the pressure to vary based on V_t. The higher PEEP will begin the recruitment process. Increasing the SIMV rate may address the problem but still has the potential for either too much or too little support. HFO is not needed here, and CPAP with PSV does not protect against apnea or allow volume targeting.

A 700-g female is now 10 days old and is receiving A/C at a control rate of 40 (spontaneous rate, 60); T_i 0.2 s; volume target, 4–6 mL/kg; inspiratory pressure limit set at 28; PEEP 6; F_iO₂ 0.35. The low-volume and high-pressure alarms are sounding. The most recent ABG: pH 7.21; PCO₂ 60; PO₂ 55; oxygen saturation in arterial blood (SaO₂) 93 %. The current graphic screen is shown in Fig. 7.2.

The problem here is inadequate V_t delivery, evidenced by tachypnea, low-V_t/high-pressure alarms, and respiratory acidosis. The likely culprit is a T_i that is too short. In flow-cycled A/C, T_i is a limit variable, that is, the longest allowed time. This baby’s time constants do not allow enough gas flow in the 0.2 s, so PIP increases in an to attempt to move gas (and, hence, volume) faster. The flow waveform will show this and also will show the immediate improvement with a longer T_i. Fig. 7.3 shows the impact of this change.

A 6-day-old female born at 26 weeks has been relatively stable receiving A/C with volume targeting. The nurse calls you to the bedside because the ventilator is alarming “high pressure.” V_t is 2.5 mL/kg even though the PIP is 30 cm H₂O, the maximum allowed. Previous pressure requirements had been in the 20–22 cm H₂O range.

The issue here is the low V_t in spite of high PIP. Either the lung is suddenly stiffer or there is a leak preventing all of the gas from reaching the alveoli. The graphics show higher inspiratory versus expiratory volumes—evidence of air leak (Fig. 7.4). A chest radiograph may be helpful, but is not the solution; additional surfactant will not help either. HFJV is probably not needed. Note that, in Fig. 7.5, neither the flow-volume (F-V) nor the pressure-volume (P-V) loop closes, which is indicative of a leak. Try to identify the source of the leak.

A 27-week preterm newborn is intubated shortly after birth and placed on mechanical ventilation. She is transferred to the NICU and placed on mechanical ventilation using pressure control in the A/C mode. The initial waveforms are shown in Fig. 7.6. A dose of surfactant is administered, resulting in the changes shown in Fig. 7.7. The ABG now shows pH 7.46; PCO₂ 28; and PO₂ 66.